Lactate measurement is widely used in emergency departments (EDs) and intensive care units (ICUs) to facilitate the early diagnosis and management of sepsis, severe trauma, ischemic bowel, and necrotizing fasciitis. Measuring lactate levels is much less commonly utilized in the practice of obstetrics and gynecology; increasing measurement in our practices may improve our early recognition and treatment of women with severe sepsis and other serious diseases.
Lactate physiology
The metabolism of glucose in the Embden-Meyerhof pathway results in the production of pyruvate and the high-energy compounds ATP and NADH. Pyruvate can enter 3 alternative metabolic pathways: 1) the mitochondrial Krebs cycle, 2) conversion to lactate in the cell cytosol, or 3) conversion back to glucose in the process of gluconeogenesis.
Under aerobic conditions, most pyruvate enters the Krebs cycle and little is converted to lactate. Molecular oxygen is an absolute requirement for Krebs cycle activity. Under anaerobic conditions, pyruvate cannot enter the Krebs cycle and is preferentially converted to lactate.1
An elevated lactate level is a sensitive marker for tissue hypoxia caused by a variety of diseases, including sepsis, trauma, ischemic bowel, and necrotizing fasciitis. With sepsis, additional mechanisms also contribute to the increase in lactate, including increased glycolysis, impaired lactate clearance, and activation of inflammatory cells that shift cellular metabolism toward lactate production.2,3
The normal range for venous plasma lactate in adults is 0.5 to 2.2 mM, although the normal range may vary because of differences in local laboratory methods. Arterial, capillary, and venous lactate are all highly positively correlated.4 Venous lactate concentrations between 2.3 and 3.9 mM are suggestive of mild physiologic dysfunction, and values ≥4.0 mM are consistent with severe physiologic dysfunction. In hospitalized patients, sepsis is one of the most common causes of a lactate level ≥4 mM.5
In many patients with an elevated lactate concentration the anion gap is also increased—but this is not always the case. In fact, in one large observational study, among patients with sepsis and a lactate concentration ≥4 mM, approximately 25% had a normal bicarbonate level and normal anion gap.6
Elevated lactate levels applied in obstetric and gynecologic practice
CASE 1. Obstetric practice: Hernia identified during labor
A 30-year-old woman (G1P0) presents in early labor at 37 weeks’ gestation. Two years prior to the pregnancy she had a Roux-en-Y gastric bypass and lost more than 100 lb. In addition to reporting lower abdominal pain occurring during contractions, she reports the new onset of mid-epigastric pain. A surgical consult is requested. The initial white blood cell count is 6,290 per uL, and the lactate level is 1.0 mM.
The surgeon consulted orders a computed tomography (CT) scan with oral contrast, but the patient has difficulty retaining the oral contrast due to her nausea, delaying the performance of the CT scan. Three hours following admission a follow-up lactate measurement is 3.3 mM, and an emergency CT scan is performed.
The CT scan shows an internal hernia with swirling of the mesenteric vessels and twisting of the small bowel mesentery. An urgent cesarean delivery and repair of the internal hernia is performed.
The patient and her newborn do well postoperatively. The postoperative lactate level is 0.8 mM.
In pregnant women with a past history of a Roux-en-Y gastric bypass and abdominal discomfort who are in labor it is challenging to rapidly diagnose internal hernias and other bowel problems.7−9 In this case, the increased lactate level from 1.0 mM to 3.3 mM raised concern for ischemic bowel and triggered the emergency CT and urgent exploratory laparotomy and cesarean delivery.
Up to 14% of maternal deaths in the United States are due to infection.10 In many of these cases, there is a delay in sepsis recognition because previously healthy pregnant women with sepsis may not manifest classic signs such as fever, hypotension, or mental status changes until late in the disease course. Measurement of lactate can facilitate the early recognition of severe sepsis in pregnant women, thereby accelerating and focusing their treatment.11
To reduce mortality due to sepsis, aggressive intervention needs to occur within the first 6 hours following the onset of the infection.