Cerebral resuscitation: pathophysiology and therapy

Effects of esmolol continuous infusion on blood loss in patients undergoing posterior lumbar internal fixation surgery: A prospective randomized study

Objective

To determine the intravenous (i.v.) dose of esmolol needed to attenuate blood loss in patients undergoing posterior lumbar internal fixation (PLIF) surgery.

Methods

This study randomized patients to either the E5 or E10 group. Patients in the E5 group received a 0.25 mg/kg i.v. loading dose of esmolol before anaesthesia, followed by an infusion of 5 µg/kg/min throughout the operation. Patients in the E10 group received a 0.5 mg/kg i.v. loading dose of esmolol before anaesthesia, followed by an infusion of 10 µg/kg/min throughout the operation.

Results

The study analysed 33 patients: 16 in the E5 group and 17 in the E10 group. The mean ± SD blood loss at the end of surgery was significantly greater in the E5 than E10 group (586.3 ± 160.1 versus 347.7 ± 138.0 ml, respectively). The total amount of patient-controlled analgesia (PCA) used was significantly higher in the E5 than E10 group at 8 (26.1 ± 12.0 versus 17.5 ± 8.3 ml, respectively), 24 (58.4 ± 21.3 versus 44.1 ± 16.2 ml, respectively) and 48 h after surgery (90.0 ± 22.5 versus 69.3 ± 22.1 ml, respectively).

Conclusion

A continuous infusion of 10 µg/kg/min of esmolol can safely reduce blood loss during PLIF surgery. It was also shown to reduce postoperative PCA consumption.

Effects of milrinone on cerebral perfusion and postoperative cognitive function in spine surgery: Secondary analysis of a CONSORT-compliant randomized controlled trial

OBJECTIVE

To compare the effects of milrinone, sodium nitroprusside (SNP), and nitroglycerin (NTG) on induced hypotension, cerebral perfusion, and postoperative cognitive function in elderly patients undergoing spine surgery.

METHODS

Sixty patients >60 years scheduled for lumbar fusion surgery were assigned to receive milrinone (group M), SNP (group S), or NTG (group N). The administration of the study drug was initiated immediately after perivertebral muscle retraction and was stopped after completion of interbody fusion. Target blood pressure was a decrease of 30% in systolic blood pressure from baseline or mean blood pressure of 60 to 65 mm Hg. The regional cerebral venous oxygen saturation (rSVO2), as a measure of cerebral perfusion, and the change in perioperative Mini-Mental State Examination (MMSE) score, as a measure of postoperative cognitive function, were assessed.

RESULTS

During the administration of the study drug, the overall and lowest intraoperative rSVO2 values were significantly higher (P = .01 and P = .01, respectively), and the duration of rSVO2 <60% was shorter in group M than in the other groups (P = .03). In group M, intraoperative rSVO2 was not different from the basal value, whereas in groups S and N, rSVO2 was significantly lower than the basal value during the administration of the study drug, but then returned to the basal value after terminating the study drug. Basal MMSE scores were comparable among the 3 groups. The MMSE score on postoperative day 5 was higher in group M than the other groups.

CONCLUSIONS

Milrinone used to induce hypotension resulted in better intraoperative cerebral perfusion and postoperative cognitive function compared to SNP and nitroglycerin.

Comparison of the Effects of Milrinone, Sodium Nitroprusside, and Nitroglycerine for Induced Hypotension in Elderly Patients Undergoing Spine Surgery: A Randomized Controlled Trial

BACKGROUND

The use of induced hypotension is limited because of concerns about hypoperfusion to major organs in elderly patients. The aim of this study was to compare the effects of milrinone with those of other vasodilating hypotensive agents on induced hypotension in elderly patients undergoing spine surgery.

METHODS

In total, 60 patients older than 60 years who underwent lumbar fusion surgeries were randomized to groups M (milrinone), S (sodium nitroprusside), and N (nitroglycerine). The study drug was infused after perivertebral muscle retraction until complete interbody fusion occurred. The infusion dose was adjusted to achieve a fall of 30% in systolic blood pressure or mean blood pressure to 60 to 65 mm Hg. Intraoperative blood loss, grade of the surgical field, and urine output were recorded.

RESULTS

Intraoperative blood loss per fused spine level was 288.5±94.4 mL in group M, 399.8±60.3 mL in group S, and 367.0±122.5 mL in group N (P=0.002). The grade of the surgical field was similar among the 3 groups (P=0.439). Hourly urine output was 1.4±0.5 mL in group M, 0.7±0.3 mL in group S, and 0.9±0.4 mL in group N (P<0.001).

CONCLUSIONS

The use of milrinone for induced hypotension led to less intraoperative blood loss and higher urine output than the use of sodium nitroprusside or nitroglycerine in elderly patients undergoing spine surgery.

Screening for cerebroprotective agents using an in vivo model of cerebral reversible depolarization in awake rats

The need to screen cerebroprotective compounds without anesthetic interference prompted the development of a model using hypoxic rats. In this model two outcome measures were used: (1) the time to reach isoelectric electroencephalogram (iEEG), caused by nitrogen gas inhalation in the test chamber, and (2) the time for behavioral recovery measuring the latency of restoration of the head-withdrawal reflex upon vibrissae stimulation. We report here data of blood chemistry, cerebral tissue oxygen measurements, a definition of a proposed scoring system, and the pharmacological results of RGH-2202. The findings with RGH-2202 are used here to show the utility of the screening method. Events during hypoxia: Arterial and venous pO(2), pCO(2), and pH, and brain tissue pO(2)significantly declined. Significant correlations were established among the pO(2)of cerebral tissue, blood, and the test chamber. RGH-2202 significantly and dose-dependently shortened the iEEG time; the compound's Effective Dose(30)was 227.8 mg kg(-1). Events during recovery: Immediately after the iEEG, when the atmosphere in the chamber was replaced with room air, the arterial, venous and brain tissue pO(2)increased above the control level and subsequently recovered to baseline levels. Behavioral recovery occurred before blood chemistry was otherwise normalized. RGH-2202 significantly and dose-dependently shortened the recovery time; the Effective Dose(30)was 8.71 mg kg(-1). The available data define and support the physiological basis of this practicable rat-screening model.

Gas Embolism: Part II. Arterial Gas Embolism and Decompression Sickness

Gas emboli syndromes are known to occur in many different settings, and they may result in life-threatening emergencies. Venous gas embolization was discussed previously in Part I of this review. Gas emboli that gain access to the arterial circulation or that result from exposures to decreased ambient pressures in the environment are discussed in Part II. The prevalence of arterial gas emboli and decompression sickness are likely not as high as for venous gas emboli. Most cases are preventable, and prompt treatment is frequently effective. Once present, gas bubbles generally distribute themselves throughout the body based on the relative blood flow at the time, thus making the nervous system, heart, lung, and skin the primary organ systems involved. Both mechanical and biophysical effects lead to intravascular and extracellular alterations that result in tissue injury. The clinical manifestations of these disorders are varied, and a high index of suspicion in the appropriate settings will aid health care providers in prompt recognition of these problems and allow timely intervention with specific therapy. Management of arterial gas emboli and decompression sickness is similar, with a focus on hyberbaric chamber therapy and intermittent hyperoxygenation. Recompression schedules in current use have withstood the test of time. Research continues to refine our understanding of these diseases and to optimize the treatment regimens available.

Transmitter amino acid release from rat neocortex: complete versus incomplete ischemia models

Release of the excitotoxic amino acids, glutamate and aspartate, from the ischemic rat cerebral cortex was compared in two models; the seven vessel occlusion model (7VO) of complete cerebral ischemia and the four vessel occlusion model (4VO) of incomplete cerebral ischemia. Amino acid efflux into cortical superfusates was measured using cortical cups placed on both hemispheres. Whereas a 20 min period of ischemia causes a pronounced release of glutamate and aspartate from the 4VO model, efflux was significantly reduced in the 7VO model. Release of the inhibitory transmitter GABA, was similar in the two models. This result suggests that excitotoxic amino acid efflux into the extracellular spaces of the cerebral cortex may be enhanced by the residual blood flow in an incomplete ischemia.

Adenosine A3 receptor stimulation and cerebral ischemia

Chronic treatment with the selective adenosine A3 receptor agonist N6-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide (IB-MECA) administered prior to either 10 or 20 min forebrain ischemia in gerbils resulted in improved postischemic cerebral blood circulation, survival, and neuronal preservation. Opposite effects, i.e., impaired postischemic blood flow, enhanced mortality, and extensive neuronal destruction in the hippocampus were seen when IB-MECA was given acutely. Neither adenosine A1 nor A2 receptors are involved in these actions. The data indicate that stimulation of adenosine A3 receptors may play an important role in the development of ischemic damage, and that adenosine A3 receptors may offer a new target for therapeutic interventions.

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)

Possible cerebroprotective and in vivo NMDA antagonist activities of sigma agents

The recent finding that ifenprodil binds with high affinity to sigma sites suggests that other sigma agents may have ifenprodil-like cerebroprotectant and functional N-methyl-D-aspartate (NMDA) antagonist effects. The present study, compared the in vivo effects of ifenprodil and the sigma agents, BMY 14802, caramiphen and haloperidol, in three tests sensitive to NMDA antagonists and purported cerebroprotectant drugs. When administered at or below the rotorod TD50 dose, all four compounds significantly increased survival time in an hypoxic environment (4% O2 in nitrogen). Caramiphen and ifenprodil (ED50 = 52 and 61 mg/kg, respectively) also blocked maximal electroshock-induced seizures, whereas BMY 14802 and haloperidol were ineffective. Finally, caramiphen (ED50 = 95 mg/kg) antagonized seizures and lethality induced by administration of NMDA (250 mg/kg, IP). BMY 14802, haloperidol and ifenprodil only partially antagonized NMDA-induced seizures, but did enhance the anticonvulsant potency of the noncompetitive NMDA antagonist, MK-801. Together, these findings suggest that sigma agents may have cerebroprotective effects.

Experimental and clinical main forms of hypoxic-ischaemic brain damage and their monitoring

A short review of main pathogenetic forms of hypoxic-ischaemic brain damage and its consequences for causally orientated therapy and monitoring is given. Different pathogenetic components act in several combinations. In these processes disturbances of the cardio-vascular system, of the haemorheology mainly at the level of microvessels, and disturbances of the blood brain barrier are involved. Furthermore, there are relevant disturbances of the neuronal metabolism such as accumulation of cytosolic Ca++ or disturbances caused by the effect of radicals, lipid peroxidation and changes of protein synthesis. Nowadays, chances of a cause-related therapy are increased by improved evaluation of main pathogenetic components especially regarding secondary brain damage. To evaluate these components in detail, animal models must be more clinically related, especially regarding long-term studies. The increasing knowledge about critical thresholds of reversible and irreversible brain changes also favours effective cerebral function monitoring. The main conclusions from previous experimental as well as clinically related studies indicate the necessity of very early therapeutical interventions.

Neurological damage in a cardiopulmonary arrest model in the rat

In view of the interest in cerebral protection in the framework of cardiopulmonary arrest (CPA), we assessed the neurological damage in a CPA model in the rat. CPA was induced in anesthetized Wistar rats by discontinuation of the jet ventilation and intracardiac injection of KCl. The animals were resuscitated after a CPA of either 7 min, 10.5 min, or 14 min. Six rats were used as nonischemic controls. All nonischemic rats survived, whereas in the resuscitated rats the 7-day survival rate decreased with increasing CPA duration. In the resuscitated rats, the neurological score was worse than in the control rats, and the score after 10.5-min CPA was worse than after 7-min CPA. Seizures were observed in 68% of resuscitated rats. Histopathological evaluation revealed moderate but selective neuronal necrosis in the hippocampus of all ischemic rats, and no cortical necrosis. However, neither the occurrence of seizures nor the extent of neuronal necrosis was related to the CPA duration. We conclude that in this model survival rate, neurological score, occurrence of seizures, and histopathological assessment can be used to evaluate neurological damage, although the contribution of other organ failure to these effects cannot be excluded.

Long-term neurological assessment of the post-resuscitative effects of flunarizine, verapamil and nimodipine in a new model of global complete ischaemia

In anesthetized rats, global complete ischaemia lasting for 9 min was induced by controlled hydraulic compression of the chest. A neurological score, based on cranial and spinal reflexes, postural tone, gait, movement and limb placement, was determined at 2 hr and 1, 2, 3, 7, 14, 21 and 28 days after resuscitation. Three doses of three calcium antagonists, flunarizine, verapamil and nimodipine and their respective solvents, were given intravenously during the resuscitation. The total neurological score was significantly better than solvent with 0.16 and 0.63 mg/kg of flunarizine and 0.04 and 0.16 mg/kg of verapamil; it was significantly better with solvent (10% ethanol) than with 0.04 and 0.16 mg/kg of nimodipine. The deficiency in tactile placing reactions of the hindpaws was the most resistant to therapy. This non-invasive model of global ischaemia in rats seems useful for the evaluation of drugs, since it requires minimal anesthesia and allows assessment of neurological recovery over an extended period of time.

A modified four-vessel occlusion model for inducing incomplete forebrain ischemia in rats

The four-vessel occlusion (4VO) model of Pulsinelli and Brierley (Stroke 1979;10:267-272) has been modified for use in halothane-nitrous oxide-anesthetized, physiologically controlled rats that were ventilating spontaneously. Selection criteria for the classification of severity of ischemia were established by correlating changes in the electroencephalogram and the general physiological status with measurements of regional blood flow and regional energy metabolism. In 13% of animals, 4VO did not cause flattening of the electroencephalogram, and such animals were classified as undergoing only "oligemia." In 65% of rats, the electroencephalogram flattened and blood pressure sharply increased with 4VO, whereas spontaneous respiration continued. This group exhibited almost complete ischemia in autoradiographic blood-flow studies, severe acidosis, and depletion of adenosine 5'-triphosphate and glucose in the forebrain and, hence, was classified as the "ischemia" group. The remaining 22% stopped breathing after vascular occlusion and were rejected for further study. Survival experiments of ischemic animals revealed the typical postischemic sequelae, with primary metabolic recovery after 8 hours of recirculation in all brain structures followed after 8-24 hours by severe biochemical deterioration and neuronal death in the striatum and hippocampus. Postischemic seizure activity was rare. The main advantages of the present modification in comparison with the original method are 1) the application of anesthesia without loss of primary selection criteria, 2) the possibility of invasive physiological monitoring, and 3) the absence of postischemic seizures, which eliminates the necessity for secondary selection criteria.