Journal of neurosurgical anesthesiology
-
J Neurosurg Anesthesiol · Jul 1994
Comparative StudyDoppler sensor placement during neurosurgical procedures for children in the prone position.
Precordial ultrasonic Doppler devices are effective monitors for detecting venous air emboli (VAE). However, placing an ultrasonic probe on the anterior part of the chest of a prone patient can lead to dislodgment or pressure sores and makes the probe inaccessible to the anesthesiologist. The purpose of this study was to compare placement of a Doppler probe on the patient's back with the traditional precordial site for the ability to detect VAE. ⋯ Positive tests were obtained from the posterior site in 23 of 24 (96%) children < 10 kilograms (group I), 28 of 39 (72%) children between 10 and 20 kg (group II), and 6 of 22 (27%) children > 20 kilograms (group III). This study demonstrates that a posterior Doppler probe can be effective for monitoring infants at risk of VAE. However, this method is not reliable in children weighting > 10 kg.
-
J Neurosurg Anesthesiol · Jul 1994
Ketamine directly dilates bovine cerebral arteries by acting as a calcium entry blocker.
This in vitro study was performed to determine the role of calcium in ketamine-induced cerebral vasodilation. Isolated bovine middle cerebral arteries were cut into rings to measure isometric tension development or into strips to measure radioactive 45Calcium (45Ca) uptake. Ketamine produced direct relaxation of arterial rings; the relaxation was attenuated in Ca(2+)-deficient media. ⋯ In Ca(2+)-deficient media containing potassium or the stable thromboxane A2 analogue, ketamine produced competitive inhibition of subsequent Ca(2+)-induced constriction. Ketamine blocked potassium- and thromboxane A2-stimulated 45Ca uptake in a dose-dependent manner, but had no effect on basal 45Ca uptake, the externally bound 45Ca content, or the volume of the 3H-sorbitol space. These results indicate that ketamine can directly dilate cerebral arteries by acting as a calcium channel antagonist; ketamine inhibits 45Ca uptake through both potential-operated (potassium) and receptor-operated (thromboxane A2) channels in cerebrovascular smooth muscle.
-
J Neurosurg Anesthesiol · Jul 1994
Case ReportsDetection of site of air entry in venous air embolism: role of Valsalva maneuver.
Venous air embolism in posterior fossa surgery is a well-documented complication. Various highly sensitive devices help in early detection of air embolism. In management of air embolism, sealing the site of air entry is an important step in preventing further episodes. Here we discuss the importance of inspiratory hold after lung inflation (Valsalva maneuver) in helping to localize the site of air entry and its role in the management of venous air embolism observed in two cases of posterior fossa mass, operated in sitting position.
-
J Neurosurg Anesthesiol · Jul 1994
Effects of THAM and sodium bicarbonate on intracranial pressure and mean arterial pressure in an animal model of focal cerebral injury.
Episodes of arterial hypotension are associated with an increased mortality in head injury patients. Rapid infusion of sodium bicarbonate in such patients may cause hypotension and elevate intracranial pressure. Therefore, we examined the effects of tromethamine (THAM) versus bicarbonate on intracranial pressure and blood pressure in a model of focal cerebral injury. ⋯ THAM infusion was associated with a significantly lower intracranial pressure and blood pressure than bicarbonate. The fall in blood pressure was great enough that cerebral perfusion pressure after THAM infusion was significantly lower than after bicarbonate infusion. In this model of cerebral injury, rapid infusion of THAM offered no therapeutic advantage over bicarbonate.