[Diprivan and epilepsy]

Propofol can be used safely in patients with a history of epilepsy. In the known epileptic patient, propofol is not contra-indicated, provided that the anaesthetist ensures that the anti-epileptic treatment is correctly maintained.

Pharmacokinetics and pharmacodynamics of pipecuronium in patients with cirrhosis

To determine the effect of liver cirrhosis on the pharmacokinetics and pharmacodynamics of pipecuronium, the authors administered 100 micrograms/kg of pipecuronium intravenously to eight patients with liver cirrhosis and eight patients with normal liver and renal function undergoing elective abdominal surgery. All patients were anesthetized with thiopental (5-7 mg/kg), nitrous oxide (50-70% in oxygen), and fentanyl in repeated doses (2 micrograms/kg). Plasma concentrations of pipecuronium were determined by high-pressure liquid chromatography. A two-compartment open model was used for pharmacokinetic analysis. Thumb-elicited mechanical response to single-twitch ulnar nerve stimulation was also measured. Total plasma clearance did not differ between controls (2.96 +/- 1.05 mL.min-1.kg-1, mean +/- SD) and cirrhotics (2.61 +/- 1.16 mL.min-1.kg-1). Terminal elimination half-life was 111 +/- 46 min in controls and 143 +/- 25 min in cirrhotics. The total apparent volume of distribution at steady state did not differ between controls (350 +/- 81 mL/kg) and cirrhotics (452 +/- 222 mL/kg). The volume of the central compartment was not different between the two groups. The onset of neuromuscular blocking effect was longer in cirrhotics (233 +/- 112 s) (P < 0.05) than in controls (170 +/- 33 s). The clinical duration (injection until single twitch returned to 25%) was similar between the two groups: 167 +/- 41 min in controls and 165 +/- 48 min in cirrhotics. The authors conclude that hepatic insufficiency due to cirrhosis does not alter the pharmacokinetics and pharmacodynamics of pipecuronium (100 micrograms/kg).

Priming doses of atracurium and vecuronium depress swallowing in humans

The administration of low doses of muscle relaxant may cause peripheral muscular weakness including difficulty in swallowing. In the present study, the effect of priming doses of atracurium and vecuronium on swallowing was studied. Sixty patients undergoing elective surgery under general anesthesia were divided randomly into four groups of 15 patients and received as a priming dose either vecuronium (10 or 15 micrograms/kg) or atracurium (50 or 75 micrograms/kg). Swallowing muscle activity was measured by electromyography using submental surface electrodes. Swallowing was initiated by administration of 0.3 ml distilled water through an oral catheter. Swallowing reflex was determined by measuring the latency time (i.e., time from water administration to start of EMG activity of glossal muscles). Swallowing activity was determined by integration of the EMG of glossal muscles during swallowing. Peripheral muscle strength was determined by hand grip strength. Swallowing reflex activity and peripheral muscle strength were measured before and 3 and 6 min after administration of vecuronium or atracurium. Latency time remained unchanged after any of the priming doses. Integrated EMG decreased significantly (P < .001) 3 and 6 min after all priming doses tested (42-75% of baseline value). Only after atracurium 75 micrograms/kg was the hand grip strength significantly decreased (P < .01). These results suggest that owing to its effect on swallowing, the priming dose should be used with caution.

Oxygen consumption after flumazenil reversal

The effect of flumazenil reversal of midazolam-induced anesthesia on whole body oxygen uptake (VO2) was investigated in a double-blind trial in 48 patients (ASA, 1 or 2) undergoing elective surgery under general anesthesia. VO2 was measured in spontaneously breathing patients during recovery from anaesthesia induced with midazolam 0.25 mg.kg-1 and maintained with nitrous oxide 60% in oxygen and halothane. The level of sedation was evaluated by a subjective score. To reverse midazolam-induced anesthesia, patients were randomly allocated to receive placebo or flumazenil (6 micrograms.kg-1). No significant changes in VO2 (160 +/- 53 vs 150 +/- 39 ml.min-1.m-2 or sedation score (2.5 +/- 1.0 vs 2.1 +/- 0.9) were observed in the placebo group. After flumazenil administration, the sedation score significantly (P less than 0.05) improved (2.9 +/- 1.0 vs 1.3 +/- 0.8) whereas no significant change in VO2 was observed (158 +/- 67 vs 157 +/- 61 ml O2.min-1.m-2). These data show that reversal of benzodiazepine effects with flumazenil resulted in no significant change in oxygen uptake.

DOES A SUBPARALYSING DOSE OF VECURONIUM ENHANCE DIAPHRAGM FATIGUE?

We have examined, in six healthy volunteers, the effect of a subparalysing dose of vecuronium on the development of diaphragm fatigue. Vecuronium was given as a 0.5-mg bolus i.v. followed by 0.5 mg infused over 30 min; as a control, saline was given in random order. Diaphragm strength was assessed by measuring transdiaphragm pressure and by electromyography. Diaphragm fatigue was induced by breathing against an inspiratory resistance. The plasma concentration of vecuronium varied between 15 and 30 ng ml-1 15 min after administration of vecuronium was started. Peripheral neuromuscular block was not detected in any subject. Diaphragm fatigue developed within the same period in both groups: mean 334 (SD 166) s after saline and 345 (190) s after vecuronium. The electromyographic pattern of diaphragm fatigue and the time constant of relaxation of transdiaphragm pressure after fatigue were similar in both groups. We conclude that, at low plasma concentrations of vecuronium, similar to those present in the postoperative period, there was no predisposition to diaphragm fatigue.

Test of 20 similar intensive care ventilators in daily use conditions--evaluation of accuracy and performances

Infrequent control, aging of components, may compromise the accuracy of ICU ventilators. In order to assess the reliability of ventilators during their clinical use, we bench tested a group of 20 CPU1 ventilators (Ohmeda) sampled at random in several ICU units. We found major leaks in 5 ventilators, attributable to the disposable tubings used in these systems. Mean error in expired tidal volume and corresponding standard deviation (precision) were greater than 100 ml in two. Positive end expiratory pressure measurement comprised a mean error higher than 2 cm H2O in 40% of the ventilators tested. The valve opening pressure threshold was correlated to the inspiratory flow (r = 0.81) contrary to the valve opening delay (average 138 +/- 40 ms). These two parameters did not correlate with the age of the ventilator. Our study addresses the need for periodic control of ventilator performance in order to minimize the risks of errors and malfunctions.

Pressure support ventilation using a new tracheal gas injection tube

In order to explore new types of jet ventilation, we tested a tracheal gas injection tube (TGIT) which included six thin capillaries and provided high pressure injection. The driving pressure was chosen to yield a plateau of inspiratory tracheal pressure of 10 cm H2O. An original controller was built to monitor spirometry and trigger injection in order to deliver both pressure controlled ventilation (PCVTGIT) and a new mode of inspiratory pressure support jet ventilation (IPSTGIT). The PVCTGIT mode maintained the same end-tidal carbon dioxide concentration as conventional ventilation with the same tidal and minute ventilation. We studied 10 patients after abdominal surgery. During spontaneous breathing, the patients were allowed to breathe through the tube, successively with and without IPSTGIT. IPSTGIT, compared with spontaneous breathing increased minute ventilation (from 5.7 (SD 1.6) to 7.1 (1.7) litre min-1) (P less than 0.001). It reduced the total work of breathing (from 0.625 (0.223) to 0.263 (0.151) J litre-1, respectively) (P less than 0.01) and the occlusion pressure (from 2.62 (1.28) to 1.36 (0.74) cm H2O, respectively) (P less than 0.01). It is concluded that this TGIT used with a specific system for sensing and triggering ventilation allows inspiratory pressure support during low frequency jet ventilation.

Clonidine decreases postoperative oxygen consumption in patients recovering from general anaesthesia

Twenty ASA I patients, undergoing thyroid surgery were allocated randomly to receive at the end of surgery either an isotonic saline solution or clonidine 2 micrograms kg-1 i.v. administered over 20 min. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured during recovery in patients breathing spontaneously with a head canopy system. Clonidine was found to attenuate the increase in VO2 and VCO2 associated with recovery from anaesthesia. The effect of clonidine was associated with a reduction in shivering. Sedative and analgesic properties of clonidine may also contribute to the reduction in metabolic demand during recovery from anaesthesia.

Effect of upper abdominal surgery and cirrhosis upon the pharmacokinetics of methohexital

The pharmacokinetic profile of methohexital was studied in cirrhotic patients (n = 8), patients undergoing upper abdominal surgery (n = 8) and orthopaedic patients under general anaesthesia (n = 8). The total plasma clearance of methohexital was unchanged in cirrhotics: 54 +/- 22 l.h-1 (mean +/- s.d.) as well as in patients undergoing upper abdominal surgery: 60 +/- 14 l.h-1 in comparison to orthopaedic surgery: 70 +/- 24 l.h-1. The central volume and total volume of distribution and the distribution and elimination half-lives were similar between the three groups. Despite its hepatic dependent elimination, methohexital elimination kinetics were unchanged in patients undergoing upper abdominal surgery and in cirrhosis. Owing to the high hepatic extraction ratio of methohexital, its elimination should be influenced by the hepatic blood flow. The unchanged elimination kinetics presently observed in patients with cirrhosis or those undergoing upper abdominal surgery suggest that the hepatic blood flow is less diminished than expected in these patients.

[Anesthesia for thalamic stimulations: value of flumazenil]

Five cases are reported of peroperative awakening in order to obtain patient cooperation during stereotaxic procedures. General anaesthesia was induced with 0.25 mg.kg-1 midazolam, 1.5 to 2 micrograms.kg-1 fentanyl, and 0.1 mg.kg-1 vecuronium. Maintenance was obtained with isoflurane, nitrous oxide, and small doses of fentanyl. Isoflurane inhalation was discontinued 30 to 40 min before the time of awakening required by surgery. Once expiratory isoflurane concentration reached a level less than or equal to 0.1%, nitrous oxide administration was stopped, and 0.5 mg flumazenil administered. After surgical checking, on the fully awake patient of the efficiency of thalamic stimulation and the lack of any motor deficit, anaesthesia was deepened again, with either isoflurane or a non benzodiazepine intravenous agent. All five patients recovered rapidly and calmly.

[Current data on curarization]

The knowledge of the mechanism of action of neuromuscular blocking agents has improved together with the better understanding of the physiology of the neuromuscular junction at the molecular and cellular levels. The main action of competitive neuromuscular relaxants is the blockade of the acetylcholine binding site of the acetylcholine receptor when the latter is its inactive-closed conformation. Owing to the high margin of safety of the neuromuscular transmission, the blockade of an important fraction (75-90%) of acetylcholine receptors is necessary to cause a decrease in muscle strength. An other mechanism of action of competitive agents is the blockade of presynaptic secretion of acetylcholine during repetitive stimulations which may explain the phenomenon of train of four fade or of tetanic fade.

[Opening of a foramen ovale during liver transplantation. The value of transesophageal echocardiography]

A case is reported of a foramen ovale becoming patent during orthotopic liver transplantation (OLT). The patient had a hepatoma secondary to post-hepatitis cirrhosis. Monitoring included transesophageal echocardiography (TEE). A veno-venous shunt between the right femoral, portal and left axillary veins was used so as to maintain the venous return during portal and caval clamping. The patient's haemodynamic state remained quite stable throughout this period, and no vasoactive drug was required. Five min after graft reperfusion, pulmonary arterial pressure increased suddenly (mean PAP: 27 mmHg). TEE revealed paradoxical movements of the atrial septum. Colour coded Doppler ultrasound showed blood flowing from the right to the left atrium through a patent foramen ovale. Fifteen min later, mean PAP decreased (18 mmHg) and TEE no longer showed any flow between the two atria. Several studies have reported transient pulmonary hypertension after unclamping when the donor liver is reperfused. This could induce right ventricular failure, with transient inversion of the atrial pressure gradient, which, in turn, could result in a right-to-left shunt through a patent foramen ovale. TEE can monitor regional and overall left ventricular function as well as the atrial septum. This technique might therefore to be useful for cardiac monitoring during OLT.

Relative potency of vecuronium on the diaphragm and the adductor pollicis

To quantify the neuromuscular blocking effect of vecuronium on the diaphragm and the adductor pollicis, single twitch stimuli were applied to the phrenic nerves at the neck and the ulnar nerve at the wrist in anaesthetized patients. The evoked responses were measured simultaneously by recording the transdiaphragmatic pressure with a differential pressure transducer and the adductor pollicis strength with a force displacement transducer. Cumulative vecuronium dose-response curves were determined for both muscles in 11 ASA class I adult patients. The mean (SD) doses required to depress adductor pollicis and diaphragm responses to 50% (ED50) were 30 (9) micrograms kg-1 and 37 (12) micrograms kg-1, respectively. Corresponding values for 95% depression of the twitch response (ED95) were 48 (13) micrograms kg-1 and 67 (23) micrograms kg-1 (P less than 0.02), indicating that the diaphragm required approximately 40% more vecuronium for subtotal abolition of the single twitch response.

[Use of halothane in a semi-closed circuit]

Halothane was administered to 10 ASA or 11 patients undergoing elective peripheral surgery. The vaporizer was included in the delivery gas line of the semiclosed system. Löwe's square root of time model of uptake was used to calculate the required doses of halothane. In order to reach an alveolar concentration corresponding to 1.3 MAC, 0.5 vol % of halothane (1.3 MAC) combined with 60 vol % of nitrous oxide (0.6 MAC) were administered at a fresh of 20 ml.kg-1. The ventilation controlled in order to maintain end-tidal CO2 partial pressure at a 5 vol %. Inspiratory halothane concentration was measured during the inspiratory plateau. The alveolar fraction was defined as being the mean end expiratory concentration. The latter was well above the theoretical values during the first 9 min of anaesthesia (0.85% at the 4 th min). This concentration then decreased progressively, becoming less than the expected value after 15 min (0.4% at the 30 th min). Löwe's model would therefore seem to lead to a gross overestimation of the amount of anaesthetic vapour to be delivered to a patient at the beginning of anaesthesia, and an underestimation thereafter.

Sufentanil pharmacokinetics in patients with cirrhosis

The effects of cirrhosis on the elimination kinetics and plasma protein binding of sufentanil were evaluated in 12 anesthetized patients with uncomplicated cirrhosis and these findings were compared with data from age-matched control anesthetized patients with normal hepatic and renal function. Sufentanil 3 micrograms/kg was given intravenously as a bolus injection and venous plasma concentrations were measured at intervals up to 10 hrs. The average (+/- SD) elimination half life was 3.5 +/- 0.9 hrs in controls and did not differ in cirrhotics: 4.1 +/- 0.6 hrs. The plasma clearance did not differ between the two groups: 11.3 +/- 2.5 ml.min-1.kg-1 in controls and 10.8 +/- 4.6 ml.min-1.kg-1 in cirrhotic patients. The sufentanil free fraction was also similar in controls (8.3 +/- 1.5%) and in cirrhotic patients (9.6 +/- 1.8%). These data suggest that sufentanil in a single dose should have a similar duration of action in patients with uncomplicated cirrhosis and in normal patients.

Pharmacokinetics of midazolam in anaesthetized cirrhotic patients

The pharmacokinetics of midazolam were compared in cirrhotic patients (n = 10) and control patients (n = 9), during general anaesthesia. Total plasma clearance was 637 +/- 223 ml min-1 (mean +/- SD) in control patients and 402 +/- 170 ml min-1 in cirrhotic patients (P less than 0.05). The total volume of distribution was similar. Elimination half-life was 135 +/- 40 min in controls and 168 +/- 30 min in cirrhosis (P less than 0.05). Protein binding was evaluated by equilibrium dialysis in both groups at two concentrations of midazolam: 20 and 500 micrograms litre-1. No saturation occurred, but the free fraction was 4.9 +/- 1.7% in cirrhotic patients, compared with 1.9 +/- 0.6% in controls (P less than 0.01). Despite its mainly hepatic elimination, midazolam disposition appears to be only slightly impaired in cirrhotic patients.

Pharmacokinetics of alfentanil in children undergoing surgery

Alfentanil pharmacokinetics and protein binding were determined in 20 children aged 10 months-6.5 yr. The data were compared with those from 10 adult patients. Eighteen children received a single i.v. dose of alfentanil 20 micrograms kg-1. The apparent volume of distribution (V beta) did not differ between the two groups. The degree of plasma protein binding was also similar in children and adults with mean free fractions of 11.5 +/- 0.9% (+/- SD) and 11.8 +/- 3.9%, respectively. There were marked differences in the elimination half-life of alfentanil (63 +/- 24 min in children; 95 +/- 20 min in adults (P less than 0.001] and plasma clearance of alfentanil (11.1 +/- 3.9 ml min-1 kg-1 in children and 5.9 +/- 1.6 ml min-1 kg-1 in adults (P less than 0.001].