Geoffrey A. Lane

The influence of induced hypotension and spine distraction on canine spinal cord blood flow

Deliberate hypotension is used in scoliosis surgery to reduce the need for blood transfusion and to improve operating conditions. There are concerns, however, that hypotension may decrease spinal cord blood flow (SCBF) and thereby predispose the spinal cord to ischemic injury, particularly when it is distracted during Harrington instrumentation. In a canine model, the mean arterial pressure (MAP) was reduced to 50% of the normotensive value with sodium nitroprusside and halothane to study its effects, with and without spinal distraction, on spinal cord blood flow measured by the hydrogen clearance technique. The induction of systemic hypotension resulted in a significant decrease in spinal cord blood flow from 15.7 ± 1.1 ml/min/100g (control) to 10.7 ± 4.7 ml/min/100g. This initial decrease in spinal cord blood flow returned to normotensive values by 35 minutes following the induction of hypotension, suggesting an autoregulatory effect. This indicates that the induction of deliberate hypotension to half its normotensive mean arterial pressure is associated with a significant decrease in spinal cord blood flow that returns to normotensive levels by 35 minutes. One and two centimeters of longitudinal distraction applied during systemic hypotension did not reduce spinal cord blood flow when it was applied at least 45 minutes after the hypotension was induced. Thus, when longitudinal stretch of a magnitude approximating that used clinically during Harrington instrumentation is applied in the presence of systemic hypotension, the normal SCBF is not reduced when the autoregulating system is functioning. Cautiously extrapolating these findings clinically suggests that nitroprusside-induced hypotension does decrease spinal cord blood flow, but this effect is not sustained, and spine distraction applied during hypotension induced to 50% of MAP does not reduce SCBF once it has returned to normotensive flows.

Urodynamic Studies in Anesthetized Children

Urodynamic study was done on 31 neurologically normal children with urinary infection and/or severe voiding disturbances. The evaluation was performed with the child under anesthesia because awake testing proved unsatisfactory. Detrusor contraction occurred in 29 children under anesthesia and sufficient data were obtained to identify accurately patterns of dysfunction and to initiate therapy. A method for anesthetic neurourologic study using enflurane is presented, which permits reliable and reproducible urodynamic observations to be made in patients in whom awake investigations are incomplete or unsatisfactory.

Hormonal and hemodynamic changes induced by pentolinium and propranolol during surgical correction of scoliosis.

Deliberate hypotension has had variable success in decreasing blood losses and facilitating extensive surgical procedures. In this study, hemodynamic variables, catecholamines, plasma renin activity, and angiotensin II levels were studied in 11 patients undergoing operative correction of idiopathic scoliosis. Deliberate hypotension with mean arterial blood pressures ranging from 55 to 42 torr was provided with the ganglionic blocking agent, pentolinium tartrate, supplemented by beta blockade with propranolol during morphine–nitrous oxide anesthesia. Stroke volume index, systemic vascular resistance, and left ventricular stroke work index decreased 16, 19, and 40 per cent, respectively, with blood pressure reduction. Following the return to normal blood pressure, stroke volume index increased to a value 28 per cent greater than control, while systemic vascular resistance remained decreased. At this time left ventricular stroke work index increased slightly, but the increase was not statistically significant compared with control. The epinephrine level had risen from 59 to 270 pg/ml an hour after hypotension, probably secondary to infiltration of the skin prior to the surgical procedure. It had decreased to control levels by the end of the procedure. Norepinephrine and dopamine concentrations and plasma renin activity were unchanged. The angiotensin II level was significantly decreased, from 60 to 40 pg/ml, during deliberate hypotension. Blood loss correlated with left ventricular stroke work index, while changes in systemic vascular resistance and heart rate correlated well with changes in angiotensin II and plasma renin activity, respectively. The ability of ganglionic blockade and propranolol to inhibit the increases in catecholamines and angiotensin II during morphine–nitrous oxide anesthesia, hypotension, and surgical intervention may be of considerable importance.

Carotid injury and cerebral infarction in a revascularization hand injury case

A case of internal carotid artery thrombosis with cerebral infarction occurring in a patient with a massive hand injury is presented. In this case it can be postulated that the mechanism of injury was that of traction of the carotid during the patients attempts at release of an immobilized extremity. Although the diagnosis of such an injury is difficult, the knowledge that such injuries occur and a suspicion of the examining physician at the time of the initial examination may help avoid such problems in the future.

Anesthetics as Teratogens: Nitrous Oxide Is Fetotoxic, Xenon Is Not

Exposure of pregnant rats to the anesthetic nitrous oxide on the ninth day of gestation causes fetal resorption, skeletal anomalies, and macroscopic lesions including encephalocele, anophthalmia, microphthalmia, and gastroschisis. The inert gas xenon, which has anesthetic properties similar to those of nitrous oxide, does not cause teratogenic effects under the same experimental conditions.