Barbiturates in neurosurgery

Barbiturate infusion for intractable intracranial hypertension and its effect on brain oxygenation

OBJECTIVE

Barbiturate-induced coma can be used in patients to treat intractable intracranial hypertension when other therapies, such as osmotic therapy and sedation, have failed. Despite control of intracranial pressure, cerebral infarction may still occur in some patients, and the effect of barbiturates on outcome remains uncertain. In this study, we examined the relationship between barbiturate infusion and brain tissue oxygen (PbtO2).

METHODS

Ten volume-resuscitated brain-injured patients who were treated with pentobarbital infusion for intracranial hypertension and underwent PbtO2 monitoring were studied in a neurosurgical intensive care unit at a university-based Level I trauma center. PbtO2, intracranial pressure (ICP), mean arterial pressure, cerebral perfusion pressure (CPP), and brain temperature were continuously monitored and compared in settings in which barbiturates were or were not administered.

RESULTS

Data were available from 1595 hours of PbtO2 monitoring. When pentobarbital administration began, the mean ICP, CPP, and PbtO2 were 18 +/- 10, 72 +/- 18, and 28 +/- 12 mm Hg, respectively. During the 3 hours before barbiturate infusion, the maximum ICP was 24 +/- 13 mm Hg and the minimum CPP was 65 +/- 20 mm Hg. In the majority of patients (70%), we observed an increase in PbtO2 associated with pentobarbital infusion. Within this group, logistic regression analysis demonstrated that a higher likelihood of compromised brain oxygen (PbtO2 < 20 mm Hg) was associated with a decrease in pentobarbital dose after controlling for ICP and other physiological parameters (P < 0.001). In the remaining 3 patients, pentobarbital was associated with lower PbtO2 levels. These patients had higher ICP, lower CPP, and later initiation of barbiturates compared with patients whose PbtO2 increased.

CONCLUSION

Our preliminary findings suggest that pentobarbital administered for intractable intracranial hypertension is associated with a significant and independent increase in PbtO2 in the majority of patients. However, in some patients with more compromised brain physiology, pentobarbital may have a negative effect on PbtO2, particularly if administered late. Larger studies are needed to examine the relationship between barbiturates and cerebral oxygenation in brain-injured patients with refractory intracranial hypertension and to determine whether PbtO2 responses can help guide therapy.

An assessment of the cerebral protective effects of etomidate in a model of incomplete forebrain ischemia in the rat

The cerebral protective effects of etomidate were evaluated in a model of incomplete forebrain ischemia. Fourteen Wistar-Kyoto rats were anesthetized with halothane. After preparation, the rats were alloted to either the control group (halothane anesthesia, n = 7) or the etomidate group (n = 7). In the etomidate group, immediately before and during the period of ischemia, the animals received etomidate in sufficient concentration to achieve electroencephalogram burst suppression (loading dose, 7.5 mg/kg; infusion, 0.3-0.5 mg/kg/min). Both groups were subjected to a 10-minute ischemic insult accomplished by bilateral carotid artery occlusion and simultaneous hypotension (mean arterial pressure, 35 mm Hg). Histological evaluation of the brain was performed after a 4-day recovery period. Injury was evaluated in coronal brain sections in five structures: neocortex, striatum, reticular nucleus of the thalamus, and the CA1 and CA3 areas of the hippocampus. The location of the sections in the rostral-caudal axis was chosen to encompass anterior areas within the core of the ischemic territory as well as more posterior regions within the anticipated "watershed" zone between the occluded anterior and the intact posterior circulations. In the animals that received etomidate, statistically significant (P less than 0.05) reduction in the severity of the ischemic injury was observed in the CA3 area and in the ventral portion of the CA1 area of the hippocampus in the more posterior sections. There was an apparent trend toward protection in other structures in both rostral and caudal sections, but these changes were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral protection

Cerebral protection from an ischemic/hypoxic insult implies that tissue injury can be controlled or even prevented by certain therapeutic maneuvers. For example, physiological thresholds may be altered so that tissue vulnerability to the insult is reduced, or the intensity of an insult may be blunted by enhancing brain homeostasis. Such a therapeutic maneuver is carotid endarterectomy to improve blood flow in the disordered hemisphere. Alternatively, drugs with protective properties can be used before or even after the insult to "stabilize" injured tissue and prevent the harmful secondary effects that often follow. Various past and present approaches to cerebral protection employing physiological, pharmacological, and surgical intervention are reviewed. The mechanisms by which each allegedly protects the brain from ischemia and hypoxia are discussed briefly. Promising, but not always successful, approaches used in the past have pointed the way for new and more rational therapies. Truly effective protection of the brain from ischemia and hypoxia depends directly upon our capability to explore basic mechanisms of injury and our willingness to measure accurately and objectively the outcome of newly developed protective measures.