Alan J. Hunter, MD, FACP

One of the most common causes of hospitalization in the elderly is aspiration pneumonia related to dysphagia due to numerous underlying diseases.1 Thus, it is clinically important to identify prognostic factors associated with increased mortality in elderly patients with aspiration pneumonia. Hyponatremia is the most common electrolyte abnormality in hospitalized patients occurring in up to 11% of elderly patients in hospital.2 Previous studies have suggested that the presence and degree of hyponatremia is associated with the severity of pneumonia in adults and children, although the results have differed among studies.37

Hyponatremia is caused by various factors, including volume depletion, use of diuretics, hypothyroidism, adrenal insufficiency, heart failure, renal failure, and cirrhosis. Additionally, the syndrome of inappropriate antidiuresis (SIAD) is a frequent and heterogeneous disorder characterized by hyponatremia and impaired urinary dilution in the absence of any recognized stimulation of antidiuretic hormone secretion.8 Because not all patients with SIAD have elevated circulating levels of arginine vasopressin (AVP), the term SIAD is preferred to the term syndrome of inappropriate secretion of antidiuretic hormone (SIADH).9 One study has shown an association between the severity of pneumonia in children and the development of hyponatremia due to SIAD.10 To our knowledge, there have been no studies evaluating the impact of different causes of hyponatremia on mortality in elderly patients with aspiration pneumonia.

We therefore sought to investigate whether hyponatremia of all etiologies (all‐cause hyponatremia) was associated with mortality in elderly patients with aspiration pneumonia. Additionally, we compared the impact of hyponatremia due to SIAD, with hyponatremia of other etiologies, on mortality in this population

METHODS

RESULTS

The baseline characteristics of the study population are listed in Table 2. There were 221 elderly patients identified as having aspiration pneumonia. Of those, 65 (29%) had hyponatremia; 3 (5%) with non‐hypotonic and 62 (95%) with hypotonic hyponatremia. In the latter group, patients were characterized has having hypovolemic (39 [63%]), hypervolemic (3 [5%]), and euvolemic (20 [32%]) hyponatremia. Among the euvolemic patients, SIAD occurred in 14 (70%) of patients. Non‐SIAD euvolemic hyponatremia occurred in 6 (30%) patients and was associated with hypothyroidism (1 patient), adrenal insufficiency (1 patient), and was unclassifiable due to lack of available clinical data in 4 patients. The kappa value was 0.87 for inter‐rater agreement of the classification of hypotonic hyponatremia.

The following variables were included in multivariate logistic analyses: congestive heart failure, cirrhosis, chronic renal failure, disorientation, body temperature <35C or >40C, anemia, and serum albumin <3 g/dL (see Supporting Information, Appendix, in the online version of this article).

In the multivariate logistic analyses, all‐cause hyponatremia was not associated with increased 30‐day mortality (odds ratio [OR] 1.85, 95% confidence interval [CI] 0.635.48; P = 0.262), but was associated with a trend toward increased risk of in‐hospital mortality (OR 2.10, 95% CI 1.004.42; P = 0.050) (Table 3). Moderate and severe hyponatremia were both significantly associated with increased in‐hospital mortality (OR 6.05, 95% CI 1.4625.0; P = 0.013 and OR 5.65, 95% CI 1.1428.1; P = 0.034, respectively). The same trends were observed for 30‐day mortality, although the results were not statistically significant. No such trend was observed for mild hyponatremia.

In the multivariate logistic regression analyses, hypotonic hyponatremia due to SIAD was significantly associated with both increased risk of 30‐day mortality (OR 7.40, 95% CI 1.7331.7; P = 0.007) and increased risk of in‐hospital mortality (OR 22.3, 95% CI 4.26117; P < 0.001) (Table 4). In contrast, hypovolemic or non‐SIAD euvolemic hyponatremia was associated with neither increased risk of 30‐day mortality nor increased risk of in‐hospital mortality. There were too few hypervolemic hyponatremia patients for us to perform effective logistic analyses. The P values of the HosmerLemeshow tests were 0.45 for the multivariate logistic regression model (hypovolemic, SIAD, and non‐SIAD euvolemic vs normonatremia) with 30‐day mortality, and 0.30 for the model with in‐hospital mortality.

Six patients with SIAD were classified as having an A‐DROP severity class of mild, 4 as moderate, and 4 as severe (P = 0.908, Wilcoxon‐type test for trend). There was no association between the occurrence of SIAD and the severity of pneumonia.

DISCUSSION

We demonstrated that mortality in elderly patients with aspiration pneumonia was significantly associated with SIAD, but not with all‐cause hyponatremia. Unlike SIAD, other etiologies of hyponatremia were not associated with mortality in elderly patients with aspiration pneumonia. A recent study by Waikar and colleagues concluded that hyponatremia subgrouped by severity was not significantly associated with in‐hospital mortality in pneumonia patients, although a trend between severe hyponatremia and mortality was observed.16 Likewise, a study by Zilberberg and colleagues reported no significant increased risk of death with hyponatremia compared with normonatremia.4 These results are similar to our results for all‐cause hyponatremia and for hyponatremia subgrouped by severity. In contrast, a study by Nair and colleagues reported some increased risk of death with hyponatremia.5 Our results suggest that the heterogeneity of these previous results was probably due to the fact that SIAD was not identified in these other studies.

While the rationale for increased mortality in patients with pneumonia associated with SIAD is not known, it may be that there is a direct deleterious effect of elevated AVP. AVP has 3 distinct receptor subtypes, V1A, V1B, and V2. Stimulation of the V1A receptor in vascular smooth muscle promotes an increase in systemic vascular resistance, and stimulation of the same receptor in cardiac myocytes promotes myocyte hypertrophy. Stimulation of the V1B receptor in the anterior pituitary promotes adrenocorticotropic hormone release, and stimulation of the V2 receptor in the renal collecting ducts promotes an increase in water retention, which plays the main role in SIAD.1719 Our hypothesis in elderly SIAD patients with aspiration pneumonia is that increased AVP levels may lead not only to water retention and hyponatremia, but also to other effects such as vasoconstriction and myocyte hypertrophy, which may adversely influence the cardiovascular systems of elderly patients (Figure 1).

Figure 1

In our study, SIAD in elderly patients with aspiration pneumonia was more strongly associated with in‐hospital mortality than with 30‐day mortality. The average length of stay (LOS) of all patients dying in hospital (42 days) was significantly longer than the average LOS of those dying within 30 days of admission (15 days; P < 0.001, MannWhitney Test; Table 2). These findings suggest that SIAD was associated more strongly with longer‐term mortality than with acute‐stage mortality. The reason for the association between SIAD and longer‐term mortality remains unclear, although there may be some association between longer‐term mortality and the pathophysiologic mechanisms of AVP.

Our study has some limitations. First, because of the retrospective observational design, there is a potential for bias. We used multivariate analyses adjusted for confounding factors, however, other residual confounding factors may have remained. In addition, since the diagnosis of pneumonia was based on chart review, there may have been imprecision in the accuracy of diagnosing aspiration pneumonia. Aspiration pneumonia sometimes occurs without apparent episodes of aspiration, and this would have led to underdiagnosis. In contrast, aspiration pneumonitis can be mistaken for aspiration pneumonia; this would have led to overdiagnosis.

Second, volume status is difficult to evaluate prospectively, and thus by nature of our design, appropriate assignment of volume status was difficult. Several studies have used test infusions of isotonic saline to discriminate between these alternatives, but because our study was retrospective, we were unable to use this test.11, 20 Some studies have reported that, in patients in a state of volume depletion, volume repletion removes the stimulus for antidiuretic hormone release, allowing excess water to be excreted in a dilute urine and the serum sodium concentration to return toward normal.21, 22 According to this theory, instead of using an isotonic test infusion, we added in our study a criterion of volume depletion in which patients with a sustained increase in serum sodium concentration of 5 mEq/L and a sustained decrease in blood urea nitrogen, even with administration of hypotonic solution, were classified as volume depleted.

Third, all patients were analyzed according to status on admission, although some patients with hypovolemic hyponatremia at admission were found to have hyponatremia due to SIAD after admission.

Fourth, because the sample size of this study was small with our results revealing wide confidence intervals, an effect between other causes of hyponatremia and mortality might not have been identified. However, for 80% power, the calculated sample size was 100 non‐SIAD patients with aspiration pneumonia versus 10 SIAD patients, given that the mortality rate of elderly patients with aspiration pneumonia was, at a moderate estimate, 15% according to the studies of both Stukenborg and colleagues and Oliver and colleagues, and the mortality rate of SIAD patients was increased by 400% compared with that of non‐SIAD patients according to the study of Song and colleagues, with an alpha error of 0.05.7, 23, 24 Our sample size was therefore greater than the required size.

Fifth, because the APD dataset was compiled in 2007 for another study, it was not concurrent, and this may have led to other limitations in interpreting the data.

Finally, in Japan, the average length of hospital stay was 36.3 days in 2004 and 34.1 days in 2007much longer than other developed countries.25 Because of this situation, in‐hospital mortality, and not 30‐day mortality, represented long‐term mortality. Therefore, our results may not be easily applicable to the situation in other developed countries.

In conclusion, our results suggest that the presence of SIAD on admission in elderly patients with aspiration pneumonia is associated with increased mortality. This novel finding should be re‐evaluated, but it does raise the question of a direct, negative impact of AVP on patients' clinical outcomes. In the future, a larger prospective cohort study should be conducted to confirm the findings of this study, given the small sample size and the retrospective nature of the study. Additionally, a different population of pneumonia patients, such as those with community‐acquired pneumonia, should be examined to further evaluate the etiologies of hyponatremia in pneumonia and the association between hyponatremia of these different etiologies and mortality.

One of the most common causes of hospitalization in the elderly is aspiration pneumonia related to dysphagia due to numerous underlying diseases.1 Thus, it is clinically important to identify prognostic factors associated with increased mortality in elderly patients with aspiration pneumonia. Hyponatremia is the most common electrolyte abnormality in hospitalized patients occurring in up to 11% of elderly patients in hospital.2 Previous studies have suggested that the presence and degree of hyponatremia is associated with the severity of pneumonia in adults and children, although the results have differed among studies.37

Hyponatremia is caused by various factors, including volume depletion, use of diuretics, hypothyroidism, adrenal insufficiency, heart failure, renal failure, and cirrhosis. Additionally, the syndrome of inappropriate antidiuresis (SIAD) is a frequent and heterogeneous disorder characterized by hyponatremia and impaired urinary dilution in the absence of any recognized stimulation of antidiuretic hormone secretion.8 Because not all patients with SIAD have elevated circulating levels of arginine vasopressin (AVP), the term SIAD is preferred to the term syndrome of inappropriate secretion of antidiuretic hormone (SIADH).9 One study has shown an association between the severity of pneumonia in children and the development of hyponatremia due to SIAD.10 To our knowledge, there have been no studies evaluating the impact of different causes of hyponatremia on mortality in elderly patients with aspiration pneumonia.

We therefore sought to investigate whether hyponatremia of all etiologies (all‐cause hyponatremia) was associated with mortality in elderly patients with aspiration pneumonia. Additionally, we compared the impact of hyponatremia due to SIAD, with hyponatremia of other etiologies, on mortality in this population

METHODS

RESULTS

The baseline characteristics of the study population are listed in Table 2. There were 221 elderly patients identified as having aspiration pneumonia. Of those, 65 (29%) had hyponatremia; 3 (5%) with non‐hypotonic and 62 (95%) with hypotonic hyponatremia. In the latter group, patients were characterized has having hypovolemic (39 [63%]), hypervolemic (3 [5%]), and euvolemic (20 [32%]) hyponatremia. Among the euvolemic patients, SIAD occurred in 14 (70%) of patients. Non‐SIAD euvolemic hyponatremia occurred in 6 (30%) patients and was associated with hypothyroidism (1 patient), adrenal insufficiency (1 patient), and was unclassifiable due to lack of available clinical data in 4 patients. The kappa value was 0.87 for inter‐rater agreement of the classification of hypotonic hyponatremia.

The following variables were included in multivariate logistic analyses: congestive heart failure, cirrhosis, chronic renal failure, disorientation, body temperature <35C or >40C, anemia, and serum albumin <3 g/dL (see Supporting Information, Appendix, in the online version of this article).

In the multivariate logistic analyses, all‐cause hyponatremia was not associated with increased 30‐day mortality (odds ratio [OR] 1.85, 95% confidence interval [CI] 0.635.48; P = 0.262), but was associated with a trend toward increased risk of in‐hospital mortality (OR 2.10, 95% CI 1.004.42; P = 0.050) (Table 3). Moderate and severe hyponatremia were both significantly associated with increased in‐hospital mortality (OR 6.05, 95% CI 1.4625.0; P = 0.013 and OR 5.65, 95% CI 1.1428.1; P = 0.034, respectively). The same trends were observed for 30‐day mortality, although the results were not statistically significant. No such trend was observed for mild hyponatremia.

In the multivariate logistic regression analyses, hypotonic hyponatremia due to SIAD was significantly associated with both increased risk of 30‐day mortality (OR 7.40, 95% CI 1.7331.7; P = 0.007) and increased risk of in‐hospital mortality (OR 22.3, 95% CI 4.26117; P < 0.001) (Table 4). In contrast, hypovolemic or non‐SIAD euvolemic hyponatremia was associated with neither increased risk of 30‐day mortality nor increased risk of in‐hospital mortality. There were too few hypervolemic hyponatremia patients for us to perform effective logistic analyses. The P values of the HosmerLemeshow tests were 0.45 for the multivariate logistic regression model (hypovolemic, SIAD, and non‐SIAD euvolemic vs normonatremia) with 30‐day mortality, and 0.30 for the model with in‐hospital mortality.

Six patients with SIAD were classified as having an A‐DROP severity class of mild, 4 as moderate, and 4 as severe (P = 0.908, Wilcoxon‐type test for trend). There was no association between the occurrence of SIAD and the severity of pneumonia.

DISCUSSION

We demonstrated that mortality in elderly patients with aspiration pneumonia was significantly associated with SIAD, but not with all‐cause hyponatremia. Unlike SIAD, other etiologies of hyponatremia were not associated with mortality in elderly patients with aspiration pneumonia. A recent study by Waikar and colleagues concluded that hyponatremia subgrouped by severity was not significantly associated with in‐hospital mortality in pneumonia patients, although a trend between severe hyponatremia and mortality was observed.16 Likewise, a study by Zilberberg and colleagues reported no significant increased risk of death with hyponatremia compared with normonatremia.4 These results are similar to our results for all‐cause hyponatremia and for hyponatremia subgrouped by severity. In contrast, a study by Nair and colleagues reported some increased risk of death with hyponatremia.5 Our results suggest that the heterogeneity of these previous results was probably due to the fact that SIAD was not identified in these other studies.

While the rationale for increased mortality in patients with pneumonia associated with SIAD is not known, it may be that there is a direct deleterious effect of elevated AVP. AVP has 3 distinct receptor subtypes, V1A, V1B, and V2. Stimulation of the V1A receptor in vascular smooth muscle promotes an increase in systemic vascular resistance, and stimulation of the same receptor in cardiac myocytes promotes myocyte hypertrophy. Stimulation of the V1B receptor in the anterior pituitary promotes adrenocorticotropic hormone release, and stimulation of the V2 receptor in the renal collecting ducts promotes an increase in water retention, which plays the main role in SIAD.1719 Our hypothesis in elderly SIAD patients with aspiration pneumonia is that increased AVP levels may lead not only to water retention and hyponatremia, but also to other effects such as vasoconstriction and myocyte hypertrophy, which may adversely influence the cardiovascular systems of elderly patients (Figure 1).

Figure 1

In our study, SIAD in elderly patients with aspiration pneumonia was more strongly associated with in‐hospital mortality than with 30‐day mortality. The average length of stay (LOS) of all patients dying in hospital (42 days) was significantly longer than the average LOS of those dying within 30 days of admission (15 days; P < 0.001, MannWhitney Test; Table 2). These findings suggest that SIAD was associated more strongly with longer‐term mortality than with acute‐stage mortality. The reason for the association between SIAD and longer‐term mortality remains unclear, although there may be some association between longer‐term mortality and the pathophysiologic mechanisms of AVP.

Our study has some limitations. First, because of the retrospective observational design, there is a potential for bias. We used multivariate analyses adjusted for confounding factors, however, other residual confounding factors may have remained. In addition, since the diagnosis of pneumonia was based on chart review, there may have been imprecision in the accuracy of diagnosing aspiration pneumonia. Aspiration pneumonia sometimes occurs without apparent episodes of aspiration, and this would have led to underdiagnosis. In contrast, aspiration pneumonitis can be mistaken for aspiration pneumonia; this would have led to overdiagnosis.

Second, volume status is difficult to evaluate prospectively, and thus by nature of our design, appropriate assignment of volume status was difficult. Several studies have used test infusions of isotonic saline to discriminate between these alternatives, but because our study was retrospective, we were unable to use this test.11, 20 Some studies have reported that, in patients in a state of volume depletion, volume repletion removes the stimulus for antidiuretic hormone release, allowing excess water to be excreted in a dilute urine and the serum sodium concentration to return toward normal.21, 22 According to this theory, instead of using an isotonic test infusion, we added in our study a criterion of volume depletion in which patients with a sustained increase in serum sodium concentration of 5 mEq/L and a sustained decrease in blood urea nitrogen, even with administration of hypotonic solution, were classified as volume depleted.

Third, all patients were analyzed according to status on admission, although some patients with hypovolemic hyponatremia at admission were found to have hyponatremia due to SIAD after admission.

Fourth, because the sample size of this study was small with our results revealing wide confidence intervals, an effect between other causes of hyponatremia and mortality might not have been identified. However, for 80% power, the calculated sample size was 100 non‐SIAD patients with aspiration pneumonia versus 10 SIAD patients, given that the mortality rate of elderly patients with aspiration pneumonia was, at a moderate estimate, 15% according to the studies of both Stukenborg and colleagues and Oliver and colleagues, and the mortality rate of SIAD patients was increased by 400% compared with that of non‐SIAD patients according to the study of Song and colleagues, with an alpha error of 0.05.7, 23, 24 Our sample size was therefore greater than the required size.

Fifth, because the APD dataset was compiled in 2007 for another study, it was not concurrent, and this may have led to other limitations in interpreting the data.

Finally, in Japan, the average length of hospital stay was 36.3 days in 2004 and 34.1 days in 2007much longer than other developed countries.25 Because of this situation, in‐hospital mortality, and not 30‐day mortality, represented long‐term mortality. Therefore, our results may not be easily applicable to the situation in other developed countries.

In conclusion, our results suggest that the presence of SIAD on admission in elderly patients with aspiration pneumonia is associated with increased mortality. This novel finding should be re‐evaluated, but it does raise the question of a direct, negative impact of AVP on patients' clinical outcomes. In the future, a larger prospective cohort study should be conducted to confirm the findings of this study, given the small sample size and the retrospective nature of the study. Additionally, a different population of pneumonia patients, such as those with community‐acquired pneumonia, should be examined to further evaluate the etiologies of hyponatremia in pneumonia and the association between hyponatremia of these different etiologies and mortality.

One of the most common causes of hospitalization in the elderly is aspiration pneumonia related to dysphagia due to numerous underlying diseases.1 Thus, it is clinically important to identify prognostic factors associated with increased mortality in elderly patients with aspiration pneumonia. Hyponatremia is the most common electrolyte abnormality in hospitalized patients occurring in up to 11% of elderly patients in hospital.2 Previous studies have suggested that the presence and degree of hyponatremia is associated with the severity of pneumonia in adults and children, although the results have differed among studies.37

Hyponatremia is caused by various factors, including volume depletion, use of diuretics, hypothyroidism, adrenal insufficiency, heart failure, renal failure, and cirrhosis. Additionally, the syndrome of inappropriate antidiuresis (SIAD) is a frequent and heterogeneous disorder characterized by hyponatremia and impaired urinary dilution in the absence of any recognized stimulation of antidiuretic hormone secretion.8 Because not all patients with SIAD have elevated circulating levels of arginine vasopressin (AVP), the term SIAD is preferred to the term syndrome of inappropriate secretion of antidiuretic hormone (SIADH).9 One study has shown an association between the severity of pneumonia in children and the development of hyponatremia due to SIAD.10 To our knowledge, there have been no studies evaluating the impact of different causes of hyponatremia on mortality in elderly patients with aspiration pneumonia.

We therefore sought to investigate whether hyponatremia of all etiologies (all‐cause hyponatremia) was associated with mortality in elderly patients with aspiration pneumonia. Additionally, we compared the impact of hyponatremia due to SIAD, with hyponatremia of other etiologies, on mortality in this population

METHODS

RESULTS

The baseline characteristics of the study population are listed in Table 2. There were 221 elderly patients identified as having aspiration pneumonia. Of those, 65 (29%) had hyponatremia; 3 (5%) with non‐hypotonic and 62 (95%) with hypotonic hyponatremia. In the latter group, patients were characterized has having hypovolemic (39 [63%]), hypervolemic (3 [5%]), and euvolemic (20 [32%]) hyponatremia. Among the euvolemic patients, SIAD occurred in 14 (70%) of patients. Non‐SIAD euvolemic hyponatremia occurred in 6 (30%) patients and was associated with hypothyroidism (1 patient), adrenal insufficiency (1 patient), and was unclassifiable due to lack of available clinical data in 4 patients. The kappa value was 0.87 for inter‐rater agreement of the classification of hypotonic hyponatremia.

The following variables were included in multivariate logistic analyses: congestive heart failure, cirrhosis, chronic renal failure, disorientation, body temperature <35C or >40C, anemia, and serum albumin <3 g/dL (see Supporting Information, Appendix, in the online version of this article).

In the multivariate logistic analyses, all‐cause hyponatremia was not associated with increased 30‐day mortality (odds ratio [OR] 1.85, 95% confidence interval [CI] 0.635.48; P = 0.262), but was associated with a trend toward increased risk of in‐hospital mortality (OR 2.10, 95% CI 1.004.42; P = 0.050) (Table 3). Moderate and severe hyponatremia were both significantly associated with increased in‐hospital mortality (OR 6.05, 95% CI 1.4625.0; P = 0.013 and OR 5.65, 95% CI 1.1428.1; P = 0.034, respectively). The same trends were observed for 30‐day mortality, although the results were not statistically significant. No such trend was observed for mild hyponatremia.

In the multivariate logistic regression analyses, hypotonic hyponatremia due to SIAD was significantly associated with both increased risk of 30‐day mortality (OR 7.40, 95% CI 1.7331.7; P = 0.007) and increased risk of in‐hospital mortality (OR 22.3, 95% CI 4.26117; P < 0.001) (Table 4). In contrast, hypovolemic or non‐SIAD euvolemic hyponatremia was associated with neither increased risk of 30‐day mortality nor increased risk of in‐hospital mortality. There were too few hypervolemic hyponatremia patients for us to perform effective logistic analyses. The P values of the HosmerLemeshow tests were 0.45 for the multivariate logistic regression model (hypovolemic, SIAD, and non‐SIAD euvolemic vs normonatremia) with 30‐day mortality, and 0.30 for the model with in‐hospital mortality.

Six patients with SIAD were classified as having an A‐DROP severity class of mild, 4 as moderate, and 4 as severe (P = 0.908, Wilcoxon‐type test for trend). There was no association between the occurrence of SIAD and the severity of pneumonia.

DISCUSSION

We demonstrated that mortality in elderly patients with aspiration pneumonia was significantly associated with SIAD, but not with all‐cause hyponatremia. Unlike SIAD, other etiologies of hyponatremia were not associated with mortality in elderly patients with aspiration pneumonia. A recent study by Waikar and colleagues concluded that hyponatremia subgrouped by severity was not significantly associated with in‐hospital mortality in pneumonia patients, although a trend between severe hyponatremia and mortality was observed.16 Likewise, a study by Zilberberg and colleagues reported no significant increased risk of death with hyponatremia compared with normonatremia.4 These results are similar to our results for all‐cause hyponatremia and for hyponatremia subgrouped by severity. In contrast, a study by Nair and colleagues reported some increased risk of death with hyponatremia.5 Our results suggest that the heterogeneity of these previous results was probably due to the fact that SIAD was not identified in these other studies.

While the rationale for increased mortality in patients with pneumonia associated with SIAD is not known, it may be that there is a direct deleterious effect of elevated AVP. AVP has 3 distinct receptor subtypes, V1A, V1B, and V2. Stimulation of the V1A receptor in vascular smooth muscle promotes an increase in systemic vascular resistance, and stimulation of the same receptor in cardiac myocytes promotes myocyte hypertrophy. Stimulation of the V1B receptor in the anterior pituitary promotes adrenocorticotropic hormone release, and stimulation of the V2 receptor in the renal collecting ducts promotes an increase in water retention, which plays the main role in SIAD.1719 Our hypothesis in elderly SIAD patients with aspiration pneumonia is that increased AVP levels may lead not only to water retention and hyponatremia, but also to other effects such as vasoconstriction and myocyte hypertrophy, which may adversely influence the cardiovascular systems of elderly patients (Figure 1).

Figure 1

In our study, SIAD in elderly patients with aspiration pneumonia was more strongly associated with in‐hospital mortality than with 30‐day mortality. The average length of stay (LOS) of all patients dying in hospital (42 days) was significantly longer than the average LOS of those dying within 30 days of admission (15 days; P < 0.001, MannWhitney Test; Table 2). These findings suggest that SIAD was associated more strongly with longer‐term mortality than with acute‐stage mortality. The reason for the association between SIAD and longer‐term mortality remains unclear, although there may be some association between longer‐term mortality and the pathophysiologic mechanisms of AVP.

Our study has some limitations. First, because of the retrospective observational design, there is a potential for bias. We used multivariate analyses adjusted for confounding factors, however, other residual confounding factors may have remained. In addition, since the diagnosis of pneumonia was based on chart review, there may have been imprecision in the accuracy of diagnosing aspiration pneumonia. Aspiration pneumonia sometimes occurs without apparent episodes of aspiration, and this would have led to underdiagnosis. In contrast, aspiration pneumonitis can be mistaken for aspiration pneumonia; this would have led to overdiagnosis.

Second, volume status is difficult to evaluate prospectively, and thus by nature of our design, appropriate assignment of volume status was difficult. Several studies have used test infusions of isotonic saline to discriminate between these alternatives, but because our study was retrospective, we were unable to use this test.11, 20 Some studies have reported that, in patients in a state of volume depletion, volume repletion removes the stimulus for antidiuretic hormone release, allowing excess water to be excreted in a dilute urine and the serum sodium concentration to return toward normal.21, 22 According to this theory, instead of using an isotonic test infusion, we added in our study a criterion of volume depletion in which patients with a sustained increase in serum sodium concentration of 5 mEq/L and a sustained decrease in blood urea nitrogen, even with administration of hypotonic solution, were classified as volume depleted.

Third, all patients were analyzed according to status on admission, although some patients with hypovolemic hyponatremia at admission were found to have hyponatremia due to SIAD after admission.

Fourth, because the sample size of this study was small with our results revealing wide confidence intervals, an effect between other causes of hyponatremia and mortality might not have been identified. However, for 80% power, the calculated sample size was 100 non‐SIAD patients with aspiration pneumonia versus 10 SIAD patients, given that the mortality rate of elderly patients with aspiration pneumonia was, at a moderate estimate, 15% according to the studies of both Stukenborg and colleagues and Oliver and colleagues, and the mortality rate of SIAD patients was increased by 400% compared with that of non‐SIAD patients according to the study of Song and colleagues, with an alpha error of 0.05.7, 23, 24 Our sample size was therefore greater than the required size.

Fifth, because the APD dataset was compiled in 2007 for another study, it was not concurrent, and this may have led to other limitations in interpreting the data.

Finally, in Japan, the average length of hospital stay was 36.3 days in 2004 and 34.1 days in 2007much longer than other developed countries.25 Because of this situation, in‐hospital mortality, and not 30‐day mortality, represented long‐term mortality. Therefore, our results may not be easily applicable to the situation in other developed countries.

In conclusion, our results suggest that the presence of SIAD on admission in elderly patients with aspiration pneumonia is associated with increased mortality. This novel finding should be re‐evaluated, but it does raise the question of a direct, negative impact of AVP on patients' clinical outcomes. In the future, a larger prospective cohort study should be conducted to confirm the findings of this study, given the small sample size and the retrospective nature of the study. Additionally, a different population of pneumonia patients, such as those with community‐acquired pneumonia, should be examined to further evaluate the etiologies of hyponatremia in pneumonia and the association between hyponatremia of these different etiologies and mortality.

Hospitalists are hospital‐based physicians whose primary professional focus is patient care, education, research, and administrative activities related to hospital medicine.1 Initially, community‐based hospitals were far more likely to employ hospitalists than academic centers. However, today most academic centers employ hospitalist models and it is now a fully recognized entity in academic settings.2

While much has been written about the structure, business operations, and potential benefits of nonteaching (clinical) hospitalist programs,3, 4 there is little known about the current state of academic hospitalist programs or their challenges. For example, who are the leaders of academic hospitalist medicine groups? Given the youth of the field, are academic hospitalists receiving adequate mentorship and are they advancing academically? What are future directions and goals for academic hospitalist groups?

To better understand academic hospitalist programs, we surveyed division chiefs and academic hospitalist leaders to explore existing business models and operations, the status of mentorship, and key issues in growth and retention.

Methods

Results

Discussion

Our survey provides a unique snapshot of academic hospitalist groups, highlighting a perceived lack of support and respect for their programs, a need to increase education and scholarly activities, and a desire to better prepare faculty for academic promotion.

Academic hospitalist groups and leaders reflected what one would expect from a field that is just over a decade old. Program leaders were relatively new to their position, as were their division group members. As a result, it is not surprising that most of the academic hospitalist leaders identified mentorship as a major issue. We were encouraged to see that most programs were offering annual reviews. However, the majority of these annual reviews were performed by the group leaders, many of whom are relatively junior (40% Assistant Professors) and may not be experienced in mentoring and performing annual reviews. Importantly, the absence of a mentor (or a high‐quality, experienced one) among physicians, and specifically hospitalists, may result in fewer peer‐reviewed first author and non‐peer‐reviewed publications, and less experience leading a teaching session at a national meeting.6 Research suggests that effective mentoring may help faculty increase career satisfaction and productivity and reduce their risk for burn‐out.7 Hospitalist groups might benefit nationally from focusing specifically on finding adequate mentorship either within or outside their groups. In addition, national organizations such as the SHM and the SGIM could potentially help these groups and individual hospitalists in creating mentorship networks and a mentoring infrastructure.

Academic hospitalist leaders were concerned about the ability of their faculty to develop sustainable nonclinical activities and scholarship. Notably, more than 40% of surveyed leaders agreed or strongly agreed that their faculty were not developing sustainable nonclinical activities. For individual faculty, the inability to develop scholarly activities and engage in academic pursuits may create challenges in getting promoted by traditional academic pathways. Some have recognized this issue and tried to develop practical solutions.2 In addition, academic hospitalists often engage in nonclinical activities such as quality improvement or patient safety which do not fit in the traditional tripartite mission of academics (clinical care, education, and research). In this survey, more than 90% of groups were engaged in quality improvement projects and over half in peer review exercises (Table 1). As many of these scholarly activities require innovation, sophisticated data analysis, and can have far‐reaching and substantial impacts on healthcare, some have argued these should be considered as part of the promotion process.8 Notably, the SGIM Academic Hospitalist Taskforce has created the Quality Portfolio, a structured adjunct to promotions packets to organize and document work in quality improvement and patient safety.9

While there were few CI in the divisions surveyed, building CI programs was a major priority of programs. In programs reporting the presence of CI's, they report limited access to research support. This highlights the potential role and benefit of post residency training in designing and conducting clinical research whether in a traditional general internal medicine fellowship or in 1 of the many growing hospital medicine fellowships.10 There also appears to be a need for funding to support the research careers of junior hospitalists. While access to effective mentorship is integrally linked to achieving increased academic accomplishments, there is certainly an ample call for research in the areas of quality improvement, patient safety; systems‐based practice, hospital efficiency, transitions of care,11 perioperative medicine,12 and education.2, 13, 14 While providing lower costs per admission and lower lengths of stay, hospitalists seem well‐positioned to spearhead active research in cost‐effectiveness in the hospital.14 Additionally, a quality portfolio, documenting such quality improvement projects, has been suggested as an effective means to provide a record of this work for academic promotion.9

The diverse activities of today's hospitalists are transforming the traditional view of academic work and are critical to the growth of hospitals, patient care, and development of the field of hospital medicine itself. Until these areas are fully embraced as legitimate areas of academic productivity and scholarship, the academic advancement of hospitalists will be slow.

It is unclear from our survey if academic hospitalist programs are truly getting the support they need to succeed. On one hand, there was general agreement that the Departments of Medicine and Divisions of General and Hospital Medicine were invested in the development of the academic accomplishments. Yet, the majority of program directors believed that they are viewed by the Department or Division as a clinical rather than an academic program. Moreover, over half of program directors report that their hospital was not supportive and therefore have limited the expansion of their hospitalist groups' educational and research activities. Lastly, for a large majority of programs, unavailable funding also acted to limit growth and expansion of academic functions. In a mere 2 decades, Emergency Medicine has become one of the largest US specialties and yet research and funding in the field have been lagging and are limiting academic expansion. Junior faculty seeking research careers struggled to find support and mentorship within their emergency medicine divisions.15 Challenges faced by academic emergency medicine provide important historical perspective for the even more rapidly growing field of academic hospital medicine. Learning from the Academic Emergency Medicine experience, academic hospitalists should proactively identify scholarship and research opportunities unique to hospitalist and fitting the needs of academic institutions. Involvement in national medical organizations, such as SGIM‐SHM‐ACGIM Academic Hospitalist Academy, or the SGIM Academic Hospitalist Task Force, where skill and career development is the focus, will undoubtedly promote the success of academic hospitalist. Expanding valuable niches of expertise, such as quality control, perioperative medicine and care transitions, create an indispensible component of hospital care. Lastly mentoring programs for academic hospitalist within SHM and SGIM are also essential for networking and career development. There are several limitations to our study. Our response rate of 40% was relatively low, and our results may not be representative of all academic hospitalist division chiefs and their programs, may be overstating the perceived difficulties of the survey sample, or conversely missing a large portion too overwhelmed by current duties who lacked the time to complete the survey. Having said this, our survey methodology targeted sites where we could identify potentialnot confirmedhospitalist groups and hospitalist group leaders. For this reason, our response rate could be higher (if some of our contacts were in error). Our results are a cross‐sectional survey based on self report and are subject to recall bias. In addition, our study was carried out in 2007, and while issues such as mentorship may remain important, our results regarding financial arrangements may not be applicable to the current economic climate. Finally, while improving mentorship was identified as a principle objective for program leaders, we did not explore the existing quality of mentorship, nor perceived shortfalls. This should be the subject of future exploration.

The vast majority of academic hospital medicine programs continue to view inadequate support, expanding research, mentorship, and academic promotion as critical issues for the future. Thus, further understanding of these features, and interventions to allow for success, are of crucial importance in the continued development of academic hospitalists. Our study supports the need for mentoring and career development programs, targeting academic hospitalists and their leaders. In addition, attention should be paid to activities that support career fit, creating sustainable and viable job descriptions for academic hospitalists, and preventing burnout.16 At the same time we must expand the traditional view of scholarship and training and advocate for promotion criteria that value the unique contributions of hospitalists to become in line with the broad areas that hospitalists work.

Hospitalists are hospital‐based physicians whose primary professional focus is patient care, education, research, and administrative activities related to hospital medicine.1 Initially, community‐based hospitals were far more likely to employ hospitalists than academic centers. However, today most academic centers employ hospitalist models and it is now a fully recognized entity in academic settings.2

While much has been written about the structure, business operations, and potential benefits of nonteaching (clinical) hospitalist programs,3, 4 there is little known about the current state of academic hospitalist programs or their challenges. For example, who are the leaders of academic hospitalist medicine groups? Given the youth of the field, are academic hospitalists receiving adequate mentorship and are they advancing academically? What are future directions and goals for academic hospitalist groups?

To better understand academic hospitalist programs, we surveyed division chiefs and academic hospitalist leaders to explore existing business models and operations, the status of mentorship, and key issues in growth and retention.

Methods

Results

Discussion

Our survey provides a unique snapshot of academic hospitalist groups, highlighting a perceived lack of support and respect for their programs, a need to increase education and scholarly activities, and a desire to better prepare faculty for academic promotion.

Academic hospitalist groups and leaders reflected what one would expect from a field that is just over a decade old. Program leaders were relatively new to their position, as were their division group members. As a result, it is not surprising that most of the academic hospitalist leaders identified mentorship as a major issue. We were encouraged to see that most programs were offering annual reviews. However, the majority of these annual reviews were performed by the group leaders, many of whom are relatively junior (40% Assistant Professors) and may not be experienced in mentoring and performing annual reviews. Importantly, the absence of a mentor (or a high‐quality, experienced one) among physicians, and specifically hospitalists, may result in fewer peer‐reviewed first author and non‐peer‐reviewed publications, and less experience leading a teaching session at a national meeting.6 Research suggests that effective mentoring may help faculty increase career satisfaction and productivity and reduce their risk for burn‐out.7 Hospitalist groups might benefit nationally from focusing specifically on finding adequate mentorship either within or outside their groups. In addition, national organizations such as the SHM and the SGIM could potentially help these groups and individual hospitalists in creating mentorship networks and a mentoring infrastructure.

Academic hospitalist leaders were concerned about the ability of their faculty to develop sustainable nonclinical activities and scholarship. Notably, more than 40% of surveyed leaders agreed or strongly agreed that their faculty were not developing sustainable nonclinical activities. For individual faculty, the inability to develop scholarly activities and engage in academic pursuits may create challenges in getting promoted by traditional academic pathways. Some have recognized this issue and tried to develop practical solutions.2 In addition, academic hospitalists often engage in nonclinical activities such as quality improvement or patient safety which do not fit in the traditional tripartite mission of academics (clinical care, education, and research). In this survey, more than 90% of groups were engaged in quality improvement projects and over half in peer review exercises (Table 1). As many of these scholarly activities require innovation, sophisticated data analysis, and can have far‐reaching and substantial impacts on healthcare, some have argued these should be considered as part of the promotion process.8 Notably, the SGIM Academic Hospitalist Taskforce has created the Quality Portfolio, a structured adjunct to promotions packets to organize and document work in quality improvement and patient safety.9

While there were few CI in the divisions surveyed, building CI programs was a major priority of programs. In programs reporting the presence of CI's, they report limited access to research support. This highlights the potential role and benefit of post residency training in designing and conducting clinical research whether in a traditional general internal medicine fellowship or in 1 of the many growing hospital medicine fellowships.10 There also appears to be a need for funding to support the research careers of junior hospitalists. While access to effective mentorship is integrally linked to achieving increased academic accomplishments, there is certainly an ample call for research in the areas of quality improvement, patient safety; systems‐based practice, hospital efficiency, transitions of care,11 perioperative medicine,12 and education.2, 13, 14 While providing lower costs per admission and lower lengths of stay, hospitalists seem well‐positioned to spearhead active research in cost‐effectiveness in the hospital.14 Additionally, a quality portfolio, documenting such quality improvement projects, has been suggested as an effective means to provide a record of this work for academic promotion.9

The diverse activities of today's hospitalists are transforming the traditional view of academic work and are critical to the growth of hospitals, patient care, and development of the field of hospital medicine itself. Until these areas are fully embraced as legitimate areas of academic productivity and scholarship, the academic advancement of hospitalists will be slow.

It is unclear from our survey if academic hospitalist programs are truly getting the support they need to succeed. On one hand, there was general agreement that the Departments of Medicine and Divisions of General and Hospital Medicine were invested in the development of the academic accomplishments. Yet, the majority of program directors believed that they are viewed by the Department or Division as a clinical rather than an academic program. Moreover, over half of program directors report that their hospital was not supportive and therefore have limited the expansion of their hospitalist groups' educational and research activities. Lastly, for a large majority of programs, unavailable funding also acted to limit growth and expansion of academic functions. In a mere 2 decades, Emergency Medicine has become one of the largest US specialties and yet research and funding in the field have been lagging and are limiting academic expansion. Junior faculty seeking research careers struggled to find support and mentorship within their emergency medicine divisions.15 Challenges faced by academic emergency medicine provide important historical perspective for the even more rapidly growing field of academic hospital medicine. Learning from the Academic Emergency Medicine experience, academic hospitalists should proactively identify scholarship and research opportunities unique to hospitalist and fitting the needs of academic institutions. Involvement in national medical organizations, such as SGIM‐SHM‐ACGIM Academic Hospitalist Academy, or the SGIM Academic Hospitalist Task Force, where skill and career development is the focus, will undoubtedly promote the success of academic hospitalist. Expanding valuable niches of expertise, such as quality control, perioperative medicine and care transitions, create an indispensible component of hospital care. Lastly mentoring programs for academic hospitalist within SHM and SGIM are also essential for networking and career development. There are several limitations to our study. Our response rate of 40% was relatively low, and our results may not be representative of all academic hospitalist division chiefs and their programs, may be overstating the perceived difficulties of the survey sample, or conversely missing a large portion too overwhelmed by current duties who lacked the time to complete the survey. Having said this, our survey methodology targeted sites where we could identify potentialnot confirmedhospitalist groups and hospitalist group leaders. For this reason, our response rate could be higher (if some of our contacts were in error). Our results are a cross‐sectional survey based on self report and are subject to recall bias. In addition, our study was carried out in 2007, and while issues such as mentorship may remain important, our results regarding financial arrangements may not be applicable to the current economic climate. Finally, while improving mentorship was identified as a principle objective for program leaders, we did not explore the existing quality of mentorship, nor perceived shortfalls. This should be the subject of future exploration.

The vast majority of academic hospital medicine programs continue to view inadequate support, expanding research, mentorship, and academic promotion as critical issues for the future. Thus, further understanding of these features, and interventions to allow for success, are of crucial importance in the continued development of academic hospitalists. Our study supports the need for mentoring and career development programs, targeting academic hospitalists and their leaders. In addition, attention should be paid to activities that support career fit, creating sustainable and viable job descriptions for academic hospitalists, and preventing burnout.16 At the same time we must expand the traditional view of scholarship and training and advocate for promotion criteria that value the unique contributions of hospitalists to become in line with the broad areas that hospitalists work.

Hospitalists are hospital‐based physicians whose primary professional focus is patient care, education, research, and administrative activities related to hospital medicine.1 Initially, community‐based hospitals were far more likely to employ hospitalists than academic centers. However, today most academic centers employ hospitalist models and it is now a fully recognized entity in academic settings.2

While much has been written about the structure, business operations, and potential benefits of nonteaching (clinical) hospitalist programs,3, 4 there is little known about the current state of academic hospitalist programs or their challenges. For example, who are the leaders of academic hospitalist medicine groups? Given the youth of the field, are academic hospitalists receiving adequate mentorship and are they advancing academically? What are future directions and goals for academic hospitalist groups?

To better understand academic hospitalist programs, we surveyed division chiefs and academic hospitalist leaders to explore existing business models and operations, the status of mentorship, and key issues in growth and retention.

Methods

Results

Discussion

Our survey provides a unique snapshot of academic hospitalist groups, highlighting a perceived lack of support and respect for their programs, a need to increase education and scholarly activities, and a desire to better prepare faculty for academic promotion.

Academic hospitalist groups and leaders reflected what one would expect from a field that is just over a decade old. Program leaders were relatively new to their position, as were their division group members. As a result, it is not surprising that most of the academic hospitalist leaders identified mentorship as a major issue. We were encouraged to see that most programs were offering annual reviews. However, the majority of these annual reviews were performed by the group leaders, many of whom are relatively junior (40% Assistant Professors) and may not be experienced in mentoring and performing annual reviews. Importantly, the absence of a mentor (or a high‐quality, experienced one) among physicians, and specifically hospitalists, may result in fewer peer‐reviewed first author and non‐peer‐reviewed publications, and less experience leading a teaching session at a national meeting.6 Research suggests that effective mentoring may help faculty increase career satisfaction and productivity and reduce their risk for burn‐out.7 Hospitalist groups might benefit nationally from focusing specifically on finding adequate mentorship either within or outside their groups. In addition, national organizations such as the SHM and the SGIM could potentially help these groups and individual hospitalists in creating mentorship networks and a mentoring infrastructure.

Academic hospitalist leaders were concerned about the ability of their faculty to develop sustainable nonclinical activities and scholarship. Notably, more than 40% of surveyed leaders agreed or strongly agreed that their faculty were not developing sustainable nonclinical activities. For individual faculty, the inability to develop scholarly activities and engage in academic pursuits may create challenges in getting promoted by traditional academic pathways. Some have recognized this issue and tried to develop practical solutions.2 In addition, academic hospitalists often engage in nonclinical activities such as quality improvement or patient safety which do not fit in the traditional tripartite mission of academics (clinical care, education, and research). In this survey, more than 90% of groups were engaged in quality improvement projects and over half in peer review exercises (Table 1). As many of these scholarly activities require innovation, sophisticated data analysis, and can have far‐reaching and substantial impacts on healthcare, some have argued these should be considered as part of the promotion process.8 Notably, the SGIM Academic Hospitalist Taskforce has created the Quality Portfolio, a structured adjunct to promotions packets to organize and document work in quality improvement and patient safety.9

While there were few CI in the divisions surveyed, building CI programs was a major priority of programs. In programs reporting the presence of CI's, they report limited access to research support. This highlights the potential role and benefit of post residency training in designing and conducting clinical research whether in a traditional general internal medicine fellowship or in 1 of the many growing hospital medicine fellowships.10 There also appears to be a need for funding to support the research careers of junior hospitalists. While access to effective mentorship is integrally linked to achieving increased academic accomplishments, there is certainly an ample call for research in the areas of quality improvement, patient safety; systems‐based practice, hospital efficiency, transitions of care,11 perioperative medicine,12 and education.2, 13, 14 While providing lower costs per admission and lower lengths of stay, hospitalists seem well‐positioned to spearhead active research in cost‐effectiveness in the hospital.14 Additionally, a quality portfolio, documenting such quality improvement projects, has been suggested as an effective means to provide a record of this work for academic promotion.9

The diverse activities of today's hospitalists are transforming the traditional view of academic work and are critical to the growth of hospitals, patient care, and development of the field of hospital medicine itself. Until these areas are fully embraced as legitimate areas of academic productivity and scholarship, the academic advancement of hospitalists will be slow.

It is unclear from our survey if academic hospitalist programs are truly getting the support they need to succeed. On one hand, there was general agreement that the Departments of Medicine and Divisions of General and Hospital Medicine were invested in the development of the academic accomplishments. Yet, the majority of program directors believed that they are viewed by the Department or Division as a clinical rather than an academic program. Moreover, over half of program directors report that their hospital was not supportive and therefore have limited the expansion of their hospitalist groups' educational and research activities. Lastly, for a large majority of programs, unavailable funding also acted to limit growth and expansion of academic functions. In a mere 2 decades, Emergency Medicine has become one of the largest US specialties and yet research and funding in the field have been lagging and are limiting academic expansion. Junior faculty seeking research careers struggled to find support and mentorship within their emergency medicine divisions.15 Challenges faced by academic emergency medicine provide important historical perspective for the even more rapidly growing field of academic hospital medicine. Learning from the Academic Emergency Medicine experience, academic hospitalists should proactively identify scholarship and research opportunities unique to hospitalist and fitting the needs of academic institutions. Involvement in national medical organizations, such as SGIM‐SHM‐ACGIM Academic Hospitalist Academy, or the SGIM Academic Hospitalist Task Force, where skill and career development is the focus, will undoubtedly promote the success of academic hospitalist. Expanding valuable niches of expertise, such as quality control, perioperative medicine and care transitions, create an indispensible component of hospital care. Lastly mentoring programs for academic hospitalist within SHM and SGIM are also essential for networking and career development. There are several limitations to our study. Our response rate of 40% was relatively low, and our results may not be representative of all academic hospitalist division chiefs and their programs, may be overstating the perceived difficulties of the survey sample, or conversely missing a large portion too overwhelmed by current duties who lacked the time to complete the survey. Having said this, our survey methodology targeted sites where we could identify potentialnot confirmedhospitalist groups and hospitalist group leaders. For this reason, our response rate could be higher (if some of our contacts were in error). Our results are a cross‐sectional survey based on self report and are subject to recall bias. In addition, our study was carried out in 2007, and while issues such as mentorship may remain important, our results regarding financial arrangements may not be applicable to the current economic climate. Finally, while improving mentorship was identified as a principle objective for program leaders, we did not explore the existing quality of mentorship, nor perceived shortfalls. This should be the subject of future exploration.

The vast majority of academic hospital medicine programs continue to view inadequate support, expanding research, mentorship, and academic promotion as critical issues for the future. Thus, further understanding of these features, and interventions to allow for success, are of crucial importance in the continued development of academic hospitalists. Our study supports the need for mentoring and career development programs, targeting academic hospitalists and their leaders. In addition, attention should be paid to activities that support career fit, creating sustainable and viable job descriptions for academic hospitalists, and preventing burnout.16 At the same time we must expand the traditional view of scholarship and training and advocate for promotion criteria that value the unique contributions of hospitalists to become in line with the broad areas that hospitalists work.