Effect of isoflurane plus nitrous oxide versus propofol on intraoperative motor evoked potentials after high frequency repetitive electrical stimulation during neurosurgical procedures

The goal of this study was to test the influence of two widespread techniques of general anaesthesia on motor evoked potentials [MEP] in response to transcranial and cortical high frequency repetitive electrical stimulation. Total intravenous anaesthesia [TIVA] based on propofol and alfentanil was studied in 17 patients [Group A] and balanced anaesthesia [BA] based on nitrous oxide, isoflurane and alfentanil was studied in 13 patients [Group B]. Distinct motor responses were available in 15 of 17 patients [88%]] of [Group A] and in one of 13 patients [8%] of [Group B]. Amplitudes increased significantly with increasing stimulus intensity and number of pulses under conditions of TIVA. At the same time, latencies decreased significantly with increasing stimulus intensity and decreasing inter-stimulus intensity interval, but not with increasing number of pulses. It is hypothesized that propofol suppresses corticospinal I-waves at the cortical level resulting in a conduction block at the level of the alpha-motor neuron; this effect may be overcome by high frequency repetitive stimulation. In contrast, nitrous oxide and isoflurane seem to have an additional suppressive effect on corticospinal D-waves which may be overcome by higher stimulation intensity. It was concluded that transcranial high frequency repetitive stimulation and TIVA provide a feasible setting for intraoperative MEP monitoring, while higher doses of nitrous oxide and isoflurane are not compatible with recording of muscular activity elicited by the stimulation technique as described

Effect of remifentanil infusion on haemodynamics and stress response to pre-bypass phase of paediatric cardiac surgery

Fifty-two infants and children under 5 years old were randomized to receive one of four remifentanil infusion rates [0.25, 1.0, 2.5, or 5.0 mug.kg-1 min-1]. Blood samples were obtained at induction, pre-surgery, 5 min after opening the chest and immediately pre-bypass. Whole blood glucose was measured at all time points, while cortisol and neuropeptide Y [NPY] were measured in the first and last samples. Heart rate and arterial pressure were also recorded. There was a significant increase in whole blood glucose 5 min after opening the chest and pre-bypass in patients receiving remifentanil 0.25 mug.kg-1 min-1, but not in those receiving higher doses. Increased remifentanil dosage was associated with reduced plasma cortisol during surgery. Baseline NPY showed considerable variation and there was no association between pre-bypass NPY and remifentanil dose. There was a significantly higher heart rate at the pre-bypass stage of surgery in the remifentanil 0.25 mug.kg-1 min-1 group compared with higher doses. Four out of five neonates with complex cardiac conditions showed severe bradycardia associated with remifentanil. From these data, it was concluded that in infants and children under 5 years, remifentanil infusions of 1 mug.kg-1 min-1 and greater can suppress the glucose increase and tachycardia associated with the pre-bypass phase of cardiac surgery; while 0.25 mug.kg-1 min-1 did not. Remifentanil should be used with caution in neonates with complex congenital heart disease

Intraoperative visual evoked potential monitoring in suprasellar tumors in children

In this study, visual evoked potentials [VEPs] were studied in 15 children undergoing surgery for parasellar tumors [12 craniopharyngiomas and 3 chiasmal gliomas]. The preoperative visual function was assessed by a standard ophthalmological work up. VEP was performed at different time intervals during surgery and postoperatively. Anesthesia was induced with fentanyl 2 mu kg-1, followed by diprivan 2 mg kg-1 i.v. and tracium 0.5 mg kg-1 i.v. to facilitate intubation. Anesthesia was maintained using diprivan 0.1 mg kg-1 min-1 using a syringe pump and was adjusted to give the patient 0.1 g kg-1 hr-1 together with 1% sevoflurane and O2. The patients were chemically ventilated to maintain normocapnia PaCO2 [30-35 mmHg]. The hemodynamics [B1 Pr and HR], O2 saturation and body temperature were maintained constant throughout the operation. The equipment used in measuring VEP was LED goggles LS-101J [Nihon Koden]. Averages were obtained after stimulation of both eyes separately and the side of stimulation was changed after two averages. Visual acuity was improved postoperatively in eight cases. A significant VEP change occurred if latency prolongation of more than 50% was seen. The changes of VEPs were so profound [complete potential loss occurred in ten cases]

EEG bispectral index monitor and end-tidal sevoflurane concentrations: comparison between children and adults

This prospective study was designed to evaluate the correlation between the electroencephalographic bispectral index [BIS] and the hypnotic component of anesthesia [CA] induced by sevoflurane in 27 children and 27 adult patients. BIS and CA were compared at loss of consciousness [LOC] and on recovery of consciousness [ROC]. Mean +/- SD, BIS decreased significantly at LOC in children and adults from 94.2 +/- 2.6 to 87.3 +/- 4.1 and from 95.8 +/- 2.3 to 86.5 +/- 4.3, respectively, without any difference between groups. Correlation coefficients [p] between BIS and CA at LOC were -0.761 in children and -0.911 in adults. BIS increased significantly at ROC in children and adults from 73.9 +/- 4.3 to 87.2 +/- 1.9 and from 80.1 +/- 5.2 to 91.3 +/- 3, respectively, without any difference between groups. Correlation coefficients between BIS and CA in ROC were -0.876 in children and -0.837 in adults. BIS values at ROC were not different from those at LOC in either group. These data demonstrated that BIS correlates with the hypnotic component of anesthesia induced by sevoflurane in children as well as in adults

Effect of a new hydroxyethy1 starch HES 130/0.4 [voluven] compared with HES 200/0.5 on coagulation in major orthopedic surgery

Hydroxyethyl starch [HES] solutions are effective plasma volume expanders. Impairment of coagulation occurs with large HES volumes infused perioperatively. Therefore, a lower substituted novel HES [Voluven, Fresenius Kabi, Bad Homburg, Germany] was developed to minimize hemostatic interactions and was compared with HAES-steril [Fresenius Kabi] [pentastarch] regarding safety and efficacy. A prospective randomized double-blinded study was performed on 100 major orthopedic surgery patients. Because of the 95% confidence interval [-330 ml, + 284 ml] for the treatment contrast Voluven-HAES- steril was entirely included in the predefined equivalence range [ +/- 500 ml], comparable efficacy was established. Voluven interfered significantly less than HAES-steril with coagulation factor VIII levels and partial thromboplastin time postoperatively. Total amounts of red blood cells transfusion were comparable between the Voluven and HAES-steril groups, but a significantly reduced need for homologous red blood cells was observed in the Voluven group. It was concluded that in large-blood-loss surgery, Voluven has a comparable efficacy with HAES-steril and may reduce coagulation impairment possibly leading to a similar number of allogenic blood transfusion

Effect of clonidine on plasma lidocaine concentrations during continuous thoracic epidural anaesthesia in chidren

This study was performed to assess the concentrations of plasma lidocaine and its major metabolite [monoethylglycinexylidide [MEGX]] in children receiving continuous thoracic epidural anesthesia after oral clonidine premedication. Ten pediatric patients, aged 1-9 years, were randomly allocated to the control or clonidine 4 mug/kg group [n = 5 each]. Anesthesia was induced and maintained with sevoflurane in oxygen and air [F1O2 40%] epidural puncture and tubing was carefully performed at the thoracic 11-12 intervertebral space. An initial dose of 1% lidocaine [5 mg/kg] was injected through a catheter in the epidural space, followed by 2.5 mg/kg/hr. The plasma concentrations of lidocaine and MEGX were measured at 15 minutes, 30 minutes and every 60 minutes for 4 hours after the initiation of continuous epidural injection. The concentrations of lidocaine and MEGX were measured using high-pressure liquid chromatography with ultraviolet detection. The hemodynamic variables were similar between the control and clonidine groups during anesthesia. The clonidine group showed significantly smaller lidocaine concentrations and the concentration of MEGX tended to be smaller in the plasma of the clonidine group for the initial four hours after the initiation of epidural infusion. In conclusion, oral clonidine pre-anesthetic medication at a dose of 4 mug/kg decreases plasma lidocaine concentration in children

Cardiorespiratory effects and systemic stress response of abdominal laparoscopic procedures in children: comparison with conventional laparotomy

In this study, 30 children aged 1.5-14 years were assigned to undergo laparoscopy or laparotomy with a standard anesthetic technique. Heart rate and mean arterial pressure were monitored at different time intervals. An intra-arterial cannula was inserted. From blood gases, arterial partial pressure of CO2[PaCO2], O2 saturation [SaO2] and pH were measured at five min. after induction [T0], 15 min. into surgery [T15], 30 min. into surgery [T30], at end of surgery prior to extubation [T end] and following extubation [T ext]. Blood prolactin, cortisol, glucose, insulin and interleukin-6 levels were determined at five min. after induction of anesthesia [T0], 30 min. into surgery [T30] and at the end of surgery [T end]. It was concluded that the surgical stress and trauma imposed by laparoscopy seems to be similar to that caused by laparotomy in children undergoing elective abdominal surgery