Pentobarbital changes compartmental contribution to cerebral blood flow

Local O2 Balance in Cerebral Ischemia-Reperfusion Improved during Pentobarbital Compared with Isoflurane Anesthesia

BACKGROUND

Most anesthetics affect cerebral blood flow and metabolism. We compared microregional O2 balance in cerebral ischemia-reperfusion during pentobarbital and isoflurane anesthesia.

METHODS

After 1 hour of middle cerebral artery occlusion and a 2-hour reperfusion under isoflurane (1.4%, n = 14) or pentobarbital (50 mg/kg, n = 14) anesthesia in rats, regional cerebral blood flow using (14)C-iodoantipyrine autoradiography, microregional arterial and venous O2 saturation (20-60 μm in diameter) using cryomicrospectrophotometry, and the size of cortical infarct were determined.

RESULTS

Ischemia-reperfusion decreased the average cortical venous O2 saturation in both pentobarbital and isoflurane groups (P < .0001), which was higher (P < .05) with pentobarbital despite a similar average regional cerebral blood flow and O2 consumption. The heterogeneity of venous O2 saturation reported as a coefficient of variation (100 × standard deviation/mean) was smaller (P < .005) with pentobarbital than that with isoflurane (7.5 versus 16.1). The number of veins with low venous O2 saturation (<50%) was smaller (P < .005) with pentobarbital (5 of 80 versus 24 of 80). The percentage of cortical infarct in total cortex was smaller with pentobarbital (5.2 ± 2.5% versus 12.3 ± 2.6%, P < .001).

CONCLUSIONS

In the cerebral ischemic-reperfused cortex, the average venous O2 saturation was higher, and its heterogeneity and the number of veins with low O2 saturation were smaller under pentobarbital than isoflurane anesthesia. This improvement in microregional O2 balance with pentobarbital was accompanied by the reduced cortical infarct. Our data suggest that the neurologic outcome could vary during cerebral ischemia-reperfusion depending on the anesthetics used.

Intracranial hypertension after resection of cerebral arteriovenous malformations. Predisposing factors and management strategy

BACKGROUND AND PURPOSE

Surgical excision of cerebral arteriovenous malformations (AVMs) may be complicated by postoperative breakthrough edema and hemorrhage and by intracranial hypertension. Embolization, staged resection, and meticulous surgical technique have decreased but not completely eliminated this complication. In this study we prospectively assess the prevalence of intracranial hypertension after excision of cerebral AVMs, examine factors predisposing to this complication, and document the outcome of aggressive monitoring and treatment of elevated intracranial pressure (ICP).

METHODS

During a 4-year period at a single institution, 32 consecutive patients with cerebral AVMs underwent surgical excision after staged embolization. All patients underwent postoperative monitoring of ICP and a uniform management protocol of intracranial hypertension.

RESULTS

Intractable intracranial hypertension was encountered after resection of 9 of 32 cerebral AVMs, including 3 of 20 (15%) AVMs 6 cm or less in maximum diameter and 6 of 12 (50%) AVMs greater than 6 cm in maximum diameter. This complication occurred in 5 of 10 (50%) lesions located in distal or border-zone locations, in 4 of 9 (44%) AVMs arising directly off proximal cerebral arteries, and in none of 13 AVMs in other locations. Preoperative single-photon emission-computed tomography perfusion scans were performed in 17 patients and demonstrated parenchymal hypoperfusion beyond the AVM nidus in 5 of 10 AVMs 6 cm or less in maximum diameter, none of which manifested postoperative intractable ICP. Hypoperfusion was observed on single-photon emission-computed tomography in 7 of 7 AVMs greater than 6 cm that were studied by this modality, and intractable ICP was observed postoperatively in 5 of these cases despite preoperative staged embolization in every case. Patients with symptomatic intractable ICP were treated with intravenous short-acting barbiturates under a strict critical care protocol. There was no instance of uncontrollable intracranial hypertension or break-through edema while on barbiturate therapy. There was no permanent morbidity related to this treatment and no mortality or new disability morbidity in this series.

CONCLUSIONS

We conclude that intractable intracranial hypertension remains a common complication after resection of a subgroup of cerebral AVMs despite preoperative embolization, modern neuroanesthesia and critical care management, and microsurgical technique. A proactive management protocol aimed at ICP control is safe and effective in the management of this complication.

Barbiturates in severe head injuries?

Possible mechanisms for the therapeutic effects of barbituric acid derivatives in severe head injuries have been discussed for half a century. In the following, a survey of the literature, and a discussion of three controlled clinical studies available until now is presented. A proven effect in terms of a beneficial long-term outcome for all injured patients has not been established. On the other hand there might be a subgroup of patients with an intact CO2 reactivity of the brain vessels who may profit from barbiturates administered after head trauma.

Interference of pentobarbital and verapamil with the reactivity of middle cerebral artery of cat exposed to experimental subarachnoid hemorrhage

1. Pentobarbital and verapamil produced concentration-dependent vasodilation in segments of middle cerebral artery of either control or exposed to experimental subarachnoid hemorrhage (SAH) cats precontracted with 5-hydroxytryptamine (5-HT, 10(-5) M) or K+ (75 mM), the potency to evoke relaxation being greater for verapamil than pentobarbital. 2. Pentobarbital (10(-4) M and 10(-3) M) or verapamil (10(-6) M) inhibited the contractions induced by 10(-5) M 5-HT or 75 mM K+ in both kinds of vessels. 3. Pentobarbital (10(-3) M) and verapamil (10(-6) M) reduced the concentration-dependent contractions induced by Ca2+ addition in control and SAH arteries previously exposed to Ca2+-free medium containing K+ or 5-HT. 4. All these vasodepressor effects of pentobarbital and verapamil were similar in control and SAH vessels, suggesting that the sensitivity of them to these agents is unaffected by SAH.

A model of embolic cerebral ischemia in the rat

Experimental studies of embolic cerebral ischemia using the rat are limited by variability in the location, size, and frequency of lesions produced. A technique is described herein which improves the reliability of an established model. Eight male Sprague-Dawley rats underwent injection of the cervical internal carotid artery with 0.1 ml of 1-h-old fragmented autologous blood clot through an external carotid artery cannula. The pterygopalatine artery was ligated prior to embolization. At killing 2 h after embolization, clot was observed in the proximal middle cerebral and posterior cerebral arteries in all animals. Areas of reduced blood flow at 2 h postembolization were assessed by digital image processing of iodo-[14C]antipyrine autoradiographic images. No-flow and low-flow areas were measured for each of approximately 25 serial brain sections with a computerized bit-pad. Volumes were calculated and lesions localized by anatomical reconstructions. No animal sustained a hemorrhagic lesion. One animal sustained only a very small area of ischemia in the internal capsule. Of the remaining seven, all had large regions of ischemia in the middle cerebral distribution involving cortex and basal ganglia. Posterior cerebral involvement was observed in six of the seven animals as well. The contralateral hemisphere was unaffected. Volume values could be calculated for primary vascular distributions. Most variability occurred in the pattern of posterior cerebral involvement. The technique described produces a relatively consistent region of ischemia in the middle and posterior cerebral artery distributions in the rat and is a useful model for the study of cerebral ischemia.

Induced hypertension for the treatment of cerebral ischemia after subarachnoid hemorrhage. Direct effect on cerebral blood flow

The best treatment for symptomatic cerebral ischemia from presumed vasospasm after aneurysmal subarachnoid hemorrhage remains a matter of controversy. A direct effect of any treatment modality on regional cerebral blood flow has never been documented. In a series of 43 patients operated on for ruptured anterior circulation aneurysms, five patients (11.6%) developed clinical signs of cerebral ischemia postoperatively. In four of those patients, the diagnosis of "vasospasm" was made with measurements of cerebral blood flow (133Xe inhalation or intravenous injection, 10-16 detectors, cerebral blood flow infinity). Treatment with induced arterial hypertension with phenylephrine was instituted. Hemodilution was instituted in one patient; the other three patients already had hematocrits in the range of 33. Within 1 hour, the cerebral blood flow measurement was repeated to document the effect of treatment. The average pretreatment hemispherical blood flow on the operated side was 18.8 mL/100 g per minute, on the contralateral side 21.0 mL/100 g per minute. With treatment these flows increased to 30.8 and 35.8 mL/100 g per minute, respectively. There was also an immediate and obvious positive clinical effect in all patients. The role of measurement of cerebral blood flow in the clinical management of vasospasm is discussed. We stress the theoretical and practical advances of measurements of cerebral blood flow over cerebral angiography, especially in comatose patients.

Pharmacologic inhibition of cerebral vasospasm in ischemia, hallucinogen ingestion, and hypomagnesemia: barbiturates, calcium antagonists, and magnesium

Experiments indicate that several different calcium antagonists have vasodilatory properties which may be expressed selectively on different organ vascular beds. Verapamil was most active as a vasodilator in muscular microvasculature. Cerebral venules are most sensitive to nimodipine. Nisoldipine is inactive in cerebral vascular dilation. We have also studied the vasodilatory effects of several barbiturates. Pentobarbital is the most active cerebrovasodilator in this class of anesthetics. This agent inhibits the vasospastic activity of potassium, serotonin, and prostaglandins, and appears to be a calcium entry antagonist in vasculature. The hallucinogens phencyclidine, mescaline, and LSD all induce cerebral vasospasm. This can be either blocked or reversed with calcium antagonists. Magnesium is a competitive calcium antagonist, and alterations in the extracellular content of this ion have profound effects on cerebral vascular resistance.