Dose effect of sevoflurane and isoflurane anesthetics on cortical blood flow during controlled hypotension in the pig.

BACKGROUND: The ability of the brain to preserve adequate cerebral blood flow (CBF) during alterations in systemic perfusion pressure is of fundamental importance. At increasing concentrations, isoflurane and sevoflurane have been known to alter CBF, which may be disadvantageous for patients with increased intracranial pressure. The aim was to examine the effects of isoflurane and sevoflurane at increasing minimum alveolar concentrations (MAC) on CBF, during controlled hypotension. METHODS: We studied eight pigs during variations in perfusion pressure induced by caval block (100, 60, 50, and 40 mmHg) under normocapnia. CBF was measured locally in a defined area (4 x 5 measurement points covering 1 cm(2)) of the motor cortex using laser Doppler perfusion imaging. Physiological variables, assessed by analysis of arterial O(2) and CO(2), hemoglobin and hematocrit, were controlled. CBF was measured during propofol (10 mg x kg(-1)x h(-1)) and fentanyl (0.002 mg x kg(-1)x h(-1)) anesthesia, and then during anesthesia with either isoflurane or sevoflurane (given in random order) at increasing MAC (0.3-1.2). After a washout period, the measurements were repeated with the other gas. RESULTS: CBF was significantly higher in the cortex during normotensive (control) settings, MAP approximately 100 mmHg, compared with during hypotension (MAP 40-60 mmHg). Neither different anesthetic nor MAC or local measurement sites were found to influence CBF at any perfusion pressure. CONCLUSION: In this experimental model, the effect of hypotension on CBF was not altered by the anesthetics used [isoflurane, sevoflurane (MAC 0.3-1.2) or propofol (10 mg x kg(-1)x h(-1))]. In this aspect (cortical tissue perspective), these volatile agents appear as suitable as propofol for neurosurgical anesthesia for patients at risk.

Moderate hypothermia for 359 operations to clip cerebral aneurysms.

BACKGROUND: Experimental data have suggested that hypothermia (32-34 degrees C) may improve outcome after cerebral ischaemia, but its efficacy has not yet been established conclusively in humans. In this study we examined the feasibility and safety of deliberate moderate perioperative hypothermia during operations for subarachnoid aneurysms. METHODS: A total of 359 operations for intracranial cerebral aneurysms were included in this prospective study. By using cold intravenous infusions (4 degrees C) and convective cooling our aim was to reduce the patient's core temperature to more than 34 degrees C within 1 h before operation. The protocol assessed postoperative complications such as infections, prolonged mechanical ventilation, pulmonary complications and coagulopathies. RESULTS: During surgery, the body temperature was reduced to a mean of 32.5 (SD 0.4) degrees C. Cooling was accomplished at a rate of 4.0 (SD 0.4) degrees C h(-1). All patients were normothermic at 5 (sd 2) h postoperatively. Peri/postoperative complications included circulatory instability (n=36, 10%), arrhythmias (n=17, 5%) coagulation abnormalities and blood transfusion (n=169, 47%), infections (n=29, 8%) and pulmonary complications (infiltrate or oedema while on ventilatory support) (n=97, 27%). Eighteen patients died within 30 days (5%). There was no significant correlation between the extent of hypothermia and any of the complications. However, there was a strong correlation between the occurrence of complications and the severity of the underlying neurological disease as assessed by the Hunt and Hess score. CONCLUSION: Moderate hypothermia accomplished within 1 h of induction of anaesthesia and maintained during surgery for subarachnoid aneurysms appears to be a safe method as far as the risks of peri/postoperative complications such as circulatory instability, coagulation abnormalities and infections are concerned.

Cortical blood flow autoregulation revisited using laser Doppler perfusion imaging.

Methods of laser Doppler perfusion monitoring (LDPM) and imaging (LDPI) have been validated and found useful for measurements of brain blood flow in several studies. The present work was undertaken to examine the cortical blood flow autoregulatory phenomenon as it has lately been questioned and claimed to be method-dependent and related to sample volume. Spatial variations in cerebral cortical blood flow (CBF(cortex)) in the pressure range 20-140 mmHg (static cerebral autoregulation; caval block/angiotensin infusion) were studied in six mechanically ventilated (hypocapnic, normocapnic and hypercapnic) pigs anaesthetized with propofol and fentanyl. Although the cortical blood flow values sampled were highly heterogeneously distributed, they were strongly pressure-dependent as well as CO2-dependent (P < 0.001). A cumulative cerebral blood flow (CBF)-pressure (MAP) plot comprising all values obtained indicated a pressure range between 70 and 120 mmHg where CBF remained almost constant. However, at the local level in the cortex (mm2) the same type of 'classic' autoregulatory flow : pressure graphs (FPG) were found in only a few of the cases of the cortical areas examined (n = 96). Alterations in blood P(a)CO2 saturation did not affect the pressure : flow relationship at low perfusion pressures, whereas at normal or above normal values, and as anticipated, hypercapnia considerably increased CBF (P < 0.001). 'Classic' autoregulatory FPGs were found only when all values sampled were clustered together, whereas, as a new finding, data are presented indicating that autoregulatory capacity is lacking at the local level at some cortical surface areas.

High incidence of pruritus after large doses of hydroxyethyl starch (HES) infusions.

BACKGROUND: There are several studies indicating a correlation between treatment with hydroxyethyl starch (HES) and pruritus. In order to see whether there is a possible dose-response relationship between HES and pruritus, we retrospectively studied 50 patients who had received HES in varying doses (cumulative dose 500-19500 ml) as hemodilution therapy after subarachnoid hemorrhage. METHODS: Of 50 consecutive patients, 6 were excluded due to severe neurological sequelae. A questionnaire was sent to the remaining 44 patients at 6 months (5-12 months) median (range) after the end of HES treatment. RESULTS: We received answers from 37 patients, of whom 54% reported pruritus. On average pruritus lasted for 15 weeks. There was significantly more pruritus in patients who received more than 5000 ml of HES versus those who received less than 5000 ml (P=0.023). Pruritus had a delayed onset and appeared as pruritic crises lasting for 2-30 min. It had a patchy distribution in most patients and no predilected locations. In 4 patients (20%) the pruritus lasted longer than 21 weeks. CONCLUSION: Our study indicates that there is a dose-dependency for the incidence of HES-induced pruritus, and that in some cases the pruritus may be severe and long-lasting.

The effect of pacing-induced heart rate variation on longitudinal and circumferential regional myocardial function after acute beta-blockade--a cardiac ultrasound study.

AIMS: To evaluate the effect of acute beta-blockade in combination with differing heart rates on longitudinal and circumferential regional myocardial function using Doppler myocardial imaging and two-dimensional-echocardiography. METHODS AND RESULTS: In seven pigs the following echocardiographic indices were measured at baseline, after beta-blockade both without and with atrial pacing: wall thickening fraction, fractional shortening, myocardial peak systolic velocity, transmyocardial velocity gradient and systolic velocity time integral of the posterolateral wall in short-axis view; mitral valve plane excursion, myocardial peak systolic velocity and systolic velocity time integral of the posterolateral wall in an apical five-chamber view. Peak systolic velocities and velocity gradients decreased significantly following acute beta-blockade but no further decay occurred at high heart rate due to pacing. The velocity time integrals and mitral valve plane excursion showed a tendency to decrease following beta-blockade but only after pacing were they significantly reduced. The wall thickening fraction and fractional shortening showed a significant reduction after beta-blockade but no further decay after pacing. CONCLUSION: Changes in systolic velocities and velocity gradients were independent of heart rate reduction under high dosage beta-blockade, whereas wall thickening fraction, mitral valve plane excursion and velocity time integrals changed due to pacing.

Cerebral blood flow of the exposed brain surface measured by laser Doppler perfusion imaging.

A novel application of laser Doppler flowmetry (LDF) laser Doppler perfusion imaging (LDPI), was used to study cerebral cortical blood flow (CBFcortex). In contrast to the conventional laser Doppler perfusion monitor, LDPI creates two dimensional maps of the tissue perfusion in a well defined area of up to 120 x 120 mm comprising 4096 measurements points. Measurements of CBFcortex were made through an optically transparent polyester film applied to a cranial window preparation in ventilated anaesthetized pigs. Temporal and spatial heterogeneity in CBFcortex were visualized by LDPI during provocations which are known to alter CBF (varying arterial PCO2 or MABP, or infusion of adenosine at constant MABP (concomitant angiotensin administration) or by hyperoxemia). During hypercapnia the recorded CBFcortex increased homogeneously. The adenosine-mediated increase in recorded CBFcortex was concentrated on the lower flow interval, as was the hyperoxemia-caused decline. At decreasing MABP the autoregulatory threshold was found to vary locally within the cortex. The results suggest that LDPI, apart from detecting localized changes in CBFcortex' also visualizes flow changes within different vascular segments. Together with the practical advantages of the system, i.e. not necessitating direct contact with the tissues, this feature makes the technique suitable for studies of CBFcortex distributions.