Michael E. Mahla

Mild Hypothermia as a Protective Therapy during Intracranial Aneurysm Surgery: A Randomized Prospective Pilot Trial

OBJECTIVE To conduct a pilot trial of mild intraoperative hypothermia during cerebral aneurysm surgery. METHODS One hundred fourteen patients undergoing cerebral aneurysm clipping with (n = 52) (World Federation of Neurological Surgeons score < or =III) and without (n = 62) acute aneurysmal subarachnoid hemorrhage (SAH) were randomized to normothermic (target esophageal temperature at clip application of 36.5 degrees C) and hypothermic (target temperature of 33.5 degrees C) groups. Neurological status was prospectively evaluated before surgery, 24 and 72 hours postoperatively (National Institutes of Health Stroke Scale), and 3 to 6 months after surgery (Glasgow Outcome Scale). Secondary outcomes included postoperative critical care requirements, respiratory and cardiovascular complications, duration of hospitalization, and discharge disposition. RESULTS Seven hypothermic patients (12%) could not be cooled to within 1 degrees C of target temperature; three of the seven were obese. Patients randomized to the hypothermic group more frequently required intubation and rewarming for the first 2 hours after surgery. Although not achieving statistical significance, patients with SAH randomized to the hypothermic group, when compared with patients in the normothermic group, had the following: 1) a lower frequency of neurological deterioration at 24 and 72 hours after surgery (21 versus 37-41%), 2) a greater frequency of discharge to home (75 versus 57%), and 3) a greater incidence of good long-term outcomes (71 versus 57%). For patients without acute SAH, there were no outcome differences between the temperature groups. There was no suggestion that hypothermia was associated with excess morbidity or mortality. CONCLUSION Mild hypothermia during cerebral aneurysm surgery is feasible in nonobese patients and is well tolerated. Our results indicate that a multicenter trial enrolling 300 to 900 patients with acute aneurysmal SAH will be required to demonstrate a statistically significant benefit with mild intraoperative hypothermia.

The effect of body inclination during prone positioning on intraocular pressure in awake volunteers: a comparison of two operating tables.

Visual loss is a rare, but catastrophic, complication of surgery in the prone position. The prone position increases intraocular pressure (IOP), which may lead to visual loss by decreasing perfusion of the anterior optic nerve. We tested whether the reverse Trendelenburg position ameliorates the increase in IOP caused by prone positioning. Furthermore, we compared two prone positioning setups. The IOP of 10 healthy awake volunteers was measured in the prone position at 3 different degrees of inclination (horizontal, 10° reverse Trendelenburg, and 10° Trendelenburg) and in the sitting and supine positions in a randomized crossover study comparing the Jackson table and the Wilson frame. In a given eye, all prone IOP values (median [25th–75th percentile] exceeded those of the sitting (15.0 mm Hg [12.8–16.3 mm Hg]) and supine (16.8mm Hg [14.0–18.3 mm Hg]) positions. IOPs in the reverse Trendelenburg, horizontal, and Trendelenburg positions were 20.3 mm Hg (16.3–22.5 mm Hg), 22.5 mm Hg (19.8–25.3 mm Hg),* and 23.8 mm Hg (21.5–26.3 mm Hg),*† respectively (*P < 0.001 versus reverse Trendelenburg; †P < 0.001 versus horizontal). The reverse Trendelenburg position ameliorated the increase in IOP caused by the prone position. Furthermore, the reverse Trendelenburg position decreased the number of grossly abnormal IOP values (>23 mm Hg) by 50% and 75% compared with the prone horizontal and Trendelenburg positions, respectively. The prone positioning setups did not differ in their effect on IOP. The increase in IOP caused by prone positioning was ameliorated by the reverse Trendelenburg position and was aggravated by the Trendelenburg position. The short time period between changes in position and changes in IOP suggests an important role for ocular venous pressures in determining IOP. Therefore, IOP can be beneficially manipulated by operating table inclination in the prone position.

Effects of Enflurane, Isoflurane, and Nitrous Oxide on Somatosensory Evoked Potentials during Fentanyl Anesthesia

The effects of nitrous oxide, enflurane, and isoflurane on cortical somatosensory evoked potentials (SEPs) were studied in 29 patients undergoing intracranial or spinal operations. Anesthesia was induced with fentanyl (25 μg/kg, iv) plus thiopental (0.5–1.0 mg/kg, iv). In one group of patients (n = 12), nitrous oxide (50%) was compared with enflurane (0.25–1.0%), and in another group (n = 12) nitrous oxide (50%) was compared with enflurane (0.25–1.0%). In all third group of patients (n = 5) with preexisting neurologic deficits, nitrous oxide (50%) was compared with enflurane (0.25–1.0%). In all three groups, one gas was administered for 30 min, and then the alternate gas was administered for 30 min; then the cycle was repeated for a total of two administrations of each of the two anesthetics. SEPs were determined before and after induction of anesthesia and at the end of each 30-min study period. The latencies and amplitudes of the early cortical components of the upper- and lower-extremity SEP were examined. Induction of anesthesia resulted in increases of latency in both upper- and lower-extremity SEPs-without any alteration of amplitude. Nitrous oxide, enflurane, and isoflurane each decreased the amplitude of the upper-extremity SEPs compared with the postinduction value. The amplitude of the upper-extremity SEPs was less during nitrous oxide than with either enflurane or isoflurane. Nitrous oxide decreased the amplitude of lower-extremity SEPs below postinduction value, while enflurane and isoflurane had no effect. Isoflurane and enflurane increased the latency of both upper- and lower-extremity SEPs slightly, while nitrous oxide had no effect. In patients with preexisting neurologic deficits, nitrous oxide decreased amplitude more than enflurane. The authors conclude that during fentanyl-based anesthesia either enflurane or isoflurane (0.25–1.0%) results in less alteration of cortical SEPs than does nitrous oxide (50%), and these concentrations of enflurane or isoflurane are compatible with the generation of waves that are adequate for evaluation.

Surgical excision of a cavernous hemangioma of the rostral brain stem: case report.

A 23-year-old pregnant woman presented with sudden diplopia, ataxia, hemiparesis, and headache secondary to a brain stem hemorrhage. Magnetic resonance imaging (MRI) revealed a hematoma associated with a probable cavernous hemangioma of the rostral brain stem. In this report, we discuss the MRI findings leading to the preoperative diagnosis, as well as the surgical techniques involved in the successful resection.

Noninvasive Monitoring of Cerebral Perfusion by Transcranial Doppler During Fulminant Hepatic Failure and Liver Transplantation

Survival in patients with fulminant hepatic failure (FHF) treated medically, rather than surgically, ranges from 12%-67% (mean 39%), depending on the cause of the disease (1). The major cause of mortality is increased intracranial pressure (ICI’) from brain edema (2). For patients with a poor prognosis (3), orthotopic liver transplantation may be the definitive treatment (41, even though, only a few years ago, some considered this treatment ineffective by the time patients reached Grade 4 encephalopathy (5). ICI’ monitoring allows physicians to use specific therapy to control intracranial hypertension. Continuous measurement of ICI’ perioperatively in the management of FHF has been associated with a survival rate of 54%74% in a series of six to 23 patients (6-9), which is generally higher than with medical means (l), and was as high as 92% for the selected group who had undergone liver transplantation (6). Such invasive monitoring, however, is especially risky in FHF patients with coagulopathy, in whom the incidence of bleeding from ICI’ monitoring ranges from 5%-22% (6,8) with a mortality rate of 60% (6). Although the use of ICI’ monitoring for FHF has become more routine (8), not all centers support the use of this invasive monitoring. We describe a patient with FHF and brain edema who underwent liver transplantation and whose cerebral perfusion was monitored noninvasively by transcranial Doppler (TCD) imaging, as well as invasively by ICI’. The noninvasive technique provided adequate information when cerebral perfusion was low, comparable with the invasive technique, and allowed intracranial hypertension to be diagnosed and treated effectively.

Delayed Respiratory Depression after Alfentanil

Delayed respiratory depression following narcotic administration has been reported by several authors.1,2 The new synthetic short-acting narcotic, alfentanil, was developed to facilitate rapid recovery of respiratory and psychomotor function following general anesthesia. We report two cases of delayed respiratory depression occuring following administration of alfentanil.

Problem-Based Learning in Residency Education: A Novel Implementation Using a Simulator

Background. We developed a problem-based learning exercise with a full-scale human patient simulator to teach residents the emergency management and differential diagnosis of acute intraoperative hypotension. Methods.We developed the exercise through the following steps: clear definition of learning objectives, preparation of an appropriate case stem, development of clinically realistic scenarios to illustrate objectives, and an interactive instructor to stimulate discussion. Results. The exercise focused on the differential diagnosis of intraoperative hypotension, and the acute treatment of hypovolemia, cardiac tamponade, tension pneumothorax, and anaphylaxis. Conclusions. Exercises on a full-scale patient simulator are a natural extension of problem-based learning. Recent research in learning theory provides the rationale for this teaching modalitys potential as a learning tool.

The Stealth Station Image Guidance System may interfere with pulse oximetry.

PurposeInterference on pulse oximetry can come from many sources. We found an additional source of interference from the Stealth Station. This article gives an overview of sources of pulse oximeter interference so that clinicians can better prevent them.Technical featuresThis article discusses the infrared disturbances caused by the Stealth Station. The Stealth Station is a frameless stereotactic positioning system that utilizes a three dimensional location system to measure the position of the patient and the surgical tools, and to relate those positions to previously recorded imaging. To understand the disturbance caused by the Stealth Station, we discuss its operation and that of pulse oximeter monitors. Pulse oximeter interference can come from volume artifacts, electrical and light noise, and can be caused by issues related to the patient. Because the passive Stealth Station contains a strong infrared light source, interference caused by light is a likely reason for the interference we noted. Pulse oximeters rely on the timevariant light signal modulated by arterial volume variations in the finger. Although relatively immune to static light sources, pulse oximeters are extremely sensitive to time-varying light sources. The light emitted by the passive Stealth Station is time-varying at 4 Hz and this is causing the pulse oximeter to provide invalid results. Shielding can generally be used to stop the light from the Stealth Station from being picked up by the pulse oximeter sensor.ConclusionInfrared light interference can be very common, but is easily dealt with if one is aware of it.ObjectifL’interférence sur la sphygmo-oxymétrie peut provenir de nombreuses sources, dont une nouvelle provenant de la Stealth Station. Nous présentons un aperçu des interférences avec le sphygmo-oxymètre, ce qui permettra aux cliniciens de la prévenir.Caractéristiques techniquesLa Stealth Station est un système de positionnement stéréotaxique sans cadre qui utilise un système de repérage en trois dimensions pour mesurer la position réelle du patient et des instruments chirurgicaux et pour relier cette position à des images virtuelles préalablement enregistrées.L’interférence avec le sphygmo-oxymètre peut provenir d’artéfacts volumique, des produits électriques et de légers bruits et elle peut être causée par des problèmes reliés au patient. Comme la Stealth Station passive contient une puissante source de lumière à infrarouges, c’est une raison probable de l’interférence notée. Les sphygmo-oxymètres dépendent du signal lumineux variable dans le temps qui est modulé par les variations du volume artériel dans le doigt. Bien que relativement soustraits aux sources de lumière statiques, les sphygmo-oxymètres sont extrêmement sensibles aux sources de lumière variables dans le temps. La lumière émise par la Stealth Station passive varie dans le temps à 4 Hz, ce qui invalide certains résultats au sphygmooxymètre. Une protection peut généralement être utilisée pour empêcher la lumière provenant de la Stealth Station d’être captée par le détecteur du sphygmo-oxymètre.ConclusionL’interférence de la lumière infrarouge peut se rencontrer souvent, mais on peut facilement la contourner pourvu qu’on en prenne conscience.

Somatosensory-Evoked Potentials During Aortic Coarctation Repair

OBJECTIVE To determine the incidence of somatosensory-evoked potential (SSEP) changes and the interventions based on these changes during aortic coarctation repair. DESIGN Retrospective review. SETTING Single-institution, university hospital. PARTICIPANTS Eighty-four children who had undergone surgical repair of aortic coarctation from January 1984 to May 1996. INTERVENTIONS SSEPs were monitored in all patients throughout the procedure. A persistent decrease in amplitude greater than 50% from baseline was considered significant. Duration of SSEP changes in relation to the time course of surgical repair and whether a surgical or anesthetic intervention resulted from a change in SSEPs were documented. MEASUREMENTS AND MAIN RESULTS Eighty-four patients underwent 87 surgical procedures. SSEP changes occurred in 40% of the procedures: 38.5% with repair and 15% with test clamp, with 9% occurring during both test clamp and repair. Interventions, which included repositioning the aortic cross-clamp, elevating blood pressure, and aborting surgery, occurred in 26.4% of all procedures based on SSEP changes. No patient sustained a neurologic deficit. CONCLUSION This is the largest series to date describing the use of SSEPs in aortic coarctation repair. These SSEP changes were often immediately amenable to changes in surgical and anesthetic management. SSEP changes and interventions based on these changes occurred with a considerable frequency.

Three balanced anesthetic techniques for neuroanesthesia: Infusion of thiopental sodium with sufentanil or fentanyl compared with inhalation of isoflurane☆

STUDY OBJECTIVE To compare emergence from anesthesia and the hemodynamic and respiratory depressant effects of thiopental sodium infusion plus sufentanil or fentanyl with those of isoflurane as the primary component of a balanced technique for neuroanesthesia. DESIGN Randomized, double-blind, prospective study. SETTING University hospital and its affiliated Veterans Affairs Medical Center. PATIENTS Thirty patients undergoing elective craniotomy for aneurysm or tumor. INTERVENTIONS Thiopental with infusion of sufentanil 0.1 microgram/kg/hr, thiopental with infusion of fentanyl 1 microgram/kg/hr, or inhalation of 0.25% to 2% isoflurane as the major component of a balanced anesthesia technique that included nitrous oxide (N2O) and vecuronium (potency ratio of sufentanil to fentanyl, 10:1). MEASUREMENTS AND MAIN RESULTS Intraoperative stress response (as indicated by intraoperative hypertension) was said to be the percentage of time the patient required administration of an antihypertensive drug, measuring from the first dose of thiopental to discontinuation of N2O at the end of the procedure, excluding any period of induced hypotension. Rapidity of emergence was measured by the number of minutes from discontinuation of N2O to first opening of the eyes on command. Adequacy of spontaneous ventilation was evaluated by determining partial pressure of arterial carbon dioxide 1, 2, and 3 hours after discontinuation of N2O. Extent of vasoactive drug administration for control of intraoperative hypertension (as determined by the clinicians caring for the patients) was described by minutes of vasodilator infusion and milligrams of propranolol or labetalol administered. The frequency of postoperative hypertension was defined as the number of patients in each group who required medication for postoperative hypertension. No significant differences in variables were found for thiopental/sufentanil, thiopental/fentanyl, or isoflurane when these drugs were used with N2O and vecuronium. CONCLUSIONS Any one of these balanced anesthetic techniques appears appropriate for craniotomy.