Effects of mechanical ventilation on Cushing's triad

Introduction

Cushing's triad of bradycardia, hypertension and abnormal breathing due to critically raised intracranial pressure was described in 1903 [1] and is generally accepted clinically. We recognised that our patients undergoing uncal herniation and brain stem compression (whilst intubated and ventilated) did not appear to exhibit this classic response.

Methods

We identified suitable patients from the Scottish Intensive Care Society Wardwatcher audit database for our ICU admissions from August 1999 to February 2007. We used the search terms subarachnoid haemorrhage and traumatic brain injury both linked to brain stem death testing. From the resultant 175 patients, a consecutive sample of 50 patients was chosen for chart review. There were 30 males, mean age 40.5 years, and 20 females, mean age 50 years. Diagnoses were subarachnoid haemorrhage n = 27, stroke n = 6, traumatic brain injury n = 5, subdural haematoma n = 3, intracerebral haemorrhage n = 6, other n = 3. The time of coning was identified by the development of fixed dilated pupils and loss of cough reflex. Haemodynamics were recorded 1 hour before coning occurred, at the time of coning and 1 hour later. In 43 ventilated patients a hypertensive surge was documented. One other patient underwent the blood pressure surge breathing spontaneously and was not intubated. In six patients the haemodynamic surge had not been documented by the bedside nurse. It was evident from chart review that coning had occurred in the hour between haemodynamic recordings.

Results

In 44 patients there was a significant rise in blood pressure at the time of confirmation of uncal herniation with a subsequent fall. This was accompanied by a major tachycardia in 38 patients and a normal heart rate in five patients. Only one patient exhibited a bradycardia and had been extubated as part of withdrawal of therapy.

Conclusion

We have demonstrated that the haemodynamic response to critically raised intracranial pressure in a ventilated patient is not a bradycardia. We have used an approach akin to that of Cushing but all of the six patients in Cushing's original paper were breathing spontaneously. All but one of our patients was ventilated. We suggest that by avoiding hypoxaemia and hypercapnic acidosis the cardiac response is altered. It is important for clinicians to be aware of this to aid recognition of coning for diagnostic and prognostic reasons.