In studies of neurosurgical procedures utilizing the nasal passages and transsphenoid approaches, the TCR has occurred in 10% to 18% of patients. 16,24 The TCR has been consistently, although infrequently, noted by otolaryngologists in the management of epistaxis. 10,26 Even when performed properly, posterior nasal packing has been reported to cause apnea, hypoxemia, and dysrhythmia. 10 Although there has been debate about the importance of the TCR in humans, this response explains the sequence of events in and the death of this patient. 27
The mechanism of the TCR is not well understood. The available data suggest that the response of the TCR when triggered by peripheral stimulation is different from the response when the TCR is triggered by central stimulation. 18 There is additional anatomic evidence that different areas can be distinguished within the nasal mucosa with regard to stimulation site and stimulus properties. 25 Specifically, it has been demonstrated in animals that mechanoreceptors are not equally sensitive throughout the nasal mucosa. The most sensitive areas for mechanical stimuli are located in the posterior parts of the nasal passages. In many animals, including humans, pronounced respiratory and cardiovascular responses can be elicited by appropriate stimulation of the nasal mucosa. These responses have been studied by many researchers in various animals and may be evoked by mechanical, electrical, and chemical stimuli. 18,25
Risk Factors
Several risk factors for heightening the TCR have been described. 25 Risk factors known to enhance the expression of TCR include hypercapnia, hypoxemia, light general anesthesia, the nature of provoking stimulus, the strength and duration of the stimulus, and medications. The specific pharmaceutical agents known to increase the manifestation of the TCR are narcotics, such as sufentanil and alfentanil, beta blockers, and calcium channel blockers. 16,24 This patient was not on any of these medications. In addition, he had not been hypoxemic. He had no known risk for elevation of the TCR.
Evidence suggests that the intensity of the TCR corresponds with the intensity of the mechanical stimulation of the trigeminal pathway. 24 Abrupt and sustained traction is more likely to evoke the TCR than is smooth and gentle manipulation. Immediate cessation of the stimulus, such as removal of the nasal packing, may be helpful in the prevention of fatal complications. 16 Unfortunately, this was not accomplished in this patient. Other interventions, including the administration of atropine, local anesthetic infiltrations, or blockage of the nerve, may be helpful in preventing fatal complications.
The TCR may be elicited without prior hemodynamic changes. Nevertheless, it is important to anticipate hypoxemia and bradycardia as the first indication of a cardiopulmonary response. 26 Administration of the anticholinergic atropine may be required in some cases where bradycardia is severe or persists despite cessation of the stimulus.
However, premedication with intramuscular administration of an anticholinergic medication has not been effective in preventing this reflex. Moreover, the TCR may at times be refractory to the conventional methods of treatment, and use of vasopressors and immediate cardiac life support may be required. Thus, if mechanical stimulation to the trigeminal nerve is anticipated, continuous monitoring of hemodynamic parameters may allow the clinician to more readily identify the TCR and immediately interrupt the inciting stimulus. 24