Analysis of the effect of perioperative magnesium sulphate on minimal alveolar concentration of desflurane using bispectral index monitoring.

BACKGROUND: In this study we aimed to analyze the effect of perioperative magnesium sulphate (MgSO(4)) on minimal alveolar concentration (MAC) of desflurane using bispectral index (BIS) monitoring. PATIENTS AND METHODS: Sixty patients undergoing abdominal surgery under general anesthesia were randomized into two groups: Mg - receiving perioperative MgSO(4) supplementation and C - control. Anesthesia was titrated to maintain the BIS value between 45-55. RESULTS: MAC values, tachycardia and hypertension during intubation was found to be lower in group Mg compared to group C (p<0.001). Time to extubation, verbal cooperation and eye opening was longer in patients receiving infusion of MgSO(4) (p<0.001). CONCLUSION: We concluded that perioperative MgSO(4) infusion may be used as an adjunct as it decreases MAC of desflurane and suppresses the hemodynamic response to intubation.

[The relationship between end-tidal isoflurane concentration and electroencephalographic bispectral index during isoflurane/epidural anesthesia].

We studied the effects of increases in isoflurane concentration on the bispectral index (BIS) in 16 patients undergoing lower abdominal surgery during isoflurane/epidural anesthesia. In 8 patients, the lungs were ventilated with an air/oxygen mixture (inspired oxygen fraction 0.33) [N(-) group], and in another 8 patients, the lungs were ventilated with 66% nitrous oxide in oxygen [N(+) group]. During surgery, patients received 1.0 MAC (1.15%) end-tidal isoflurane and the BIS was recorded after 10 min of unchanged end-tidal concentration. After this, we increased the end-tidal concentration of isoflurane by 0.2 MAC to 1.8 MAC. At each concentration step, the BIS was recorded again after 10 min of unchanged end-tidal concentration. At isoflurane concentration < 1.4 MAC, the BIS did not change with increasing isoflurane concentration in both groups (BIS values = about 40). In N (-) group, the BIS decreased in all patients at isoflurane concentration > 1.6 MAC. The mean BIS values were 22 (SD 18) at 1.6 MAC and 2(4) at 1.8 MAC, respectively. In N (+) group, the BIS decreased in four patients at isoflurane concentration > 1.6 MAC, and the BIS did not decrease at 1.8 MAC in another four patients. The mean BIS values were 27 (17) at 1.6 MAC and 21(21) at 1.8 MAC. The present data suggest that BIS may not correlate with anesthetic effect of isoflurane at isoflurane concentration > 1.0 MAC.

[Occupational exposure in the hospital to laughing gas and the new inhalation anesthetics desflurane and sevoflurane]. / Arbeitsplatzbelastung im Krankenhaus mit Lachgas und den neuen Inhalationsanästhetika Desfluran und Sevofluran.

BACKGROUND AND OBJECTIVE: There have been few studies of the occupational exposure of the new volatile anaesthetic agents desflurane and sevoflurane. Because a health risk through long-term exposure to these inhalants cannot as yet be definitely excluded, we undertook to measure the concentrations of these three anaesthetics in different parts of the Frankfurt University Medical Centre. Considering the results the relevance of exposure for surgical and anaesthesia personnel, possible consequences due to laws and possibilities of improvement were shown. METHODS: The concentration of the three anaesthetics was measured during and after 345 procedures under general anaesthesia, using photoacoustic infra-red-spectrometry every 90 sec in the breathing zone of the same operating room personnel or in the recovery room and the intensive care unit. RESULTS: Exposure of personnel in the air-conditioned operating rooms was very low, but in those rooms that were not or inadequately air conditioned was a times very high. The level of the concentrations was also significantly related to the anaesthesia system and the distance of the exposed person to the patient. The concentration of nitrous oxide was below the maximal working-place concentration (MWC) of 100 ppm, but it exceeded the threshold concentration of 0.1 MAC, as laid down in the "Maternal Protection Law" in the surgical intensive care unit and the recovery room. There are no limiting concentrations for desflurane and sevoflurane yet but their concentrations were clearly below the MWC laid down for isoflurane and enflurane. CONCLUSION: In principle the use of inhalation anaesthetics can be considered to be without occupational health risk under the present legally defined standards of air-conditioning and the requirements of a modern occupational protection law. Because of the increased concentrations in the recovery room and intensive care unit pregnant and breast-feeding women should not work in these areas.

Continuous infusions of atracurium and vecuronium, compared with intermittent boluses of pancuronium: dose requirements and reversal.

This study was designed to determine the effect of prolonged infusion on the ease of reversal of atracurium and vecuronium, and whether factors which potentiate the block delayed reversal. In phase one, 40 patients were randomized (double blind) to determine the steady state conditions for atracurium and vecuronium. Fourteen atracurium patients and 17 vecuronium patients were evaluable. The unblinded second phase involved the steady state conditions using halothane or isoflurane and atracurium infusions. The infusion required for 95% twitch depression (TD95) for atracurium was 7.6 +/- 1.1 micrograms.kg-1 x min-1. The requirement for vecuronium changes with time: TD95 at 30 min was 1.01 +/- 0.16, at 60 min 0.89 +/- 0.12 and after 90 min 0.85 +/- 0.17 micrograms.kg-1 x min-1 (P < 0.05). The mean TD95 was 0.94 +/- 0.23 micrograms.kg-1 x min-1. Multivariate regression analysis of the infusion data revealed a vecuronium model predicting TD95 by the duration of infusion (P < 0.05) and weight (P = 0.05). Atracurium TD95 was predicted by age (P = 0.05). The addition of an inhalation agent to atracurium reduced the infusion rate by 2.01 +/- 0.28 micrograms.kg-1 x min-1 (P = 0.0001) for each increase in MAC. The mean reversal times for atracurium with three different anaesthetics and for vecuronium were not different. Reversal of pancuronium blockade, from less profound twitch depression (86.4 vs 95%) took twice as long as for atracurium and vecuronium for which the following predictors were identified: age, weight, duration of infusion, level of blockade, and type of anaesthetic, using a stepwise regression model.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetic and hemodynamic effects of dexmedetomidine during isoflurane anesthesia in a canine model.

Dexmedetomidine, an alpha 2-adrenergic agonist, was administered during isoflurane anesthesia to investigate its anesthetic sparing and hemodynamic effects in the canine model. Eleven healthy dogs were anesthetized with isoflurane, intubated, and allowed to breathe spontaneously. The animals were instrumented in order to measure or calculate mean arterial blood pressure (MABP), heart rate (HR), left ventricular end diastolic pressure (LVEDP), cardiac output (CO), and systemic vascular resistance (SVR). Isoflurane minimum alveolar concentration (MAC), baseline hemodynamic measurements, and plasma catecholamine levels were determined. A 20 micrograms/kg bolus of dexmedetomidine was injected intravenously (IV) and MAC and hemodynamic values were redetermined. When isoflurane requirements were 33% of baseline, isoflurane was returned to 90% MAC and the alpha 2-antagonist, atipamezole, was administered. All dogs were treated with 40 micrograms/kg glycopyrrolate throughout the experiment to prevent any bradycardic response. Dexmedetomidine reduced isoflurane MAC by 86%. SVR, MABP, and LVEDP were significantly increased while CO and catechloamine levels were reduced. Atipamezole fully reversed the reduction in anesthetic requirements. MABP and catecholamine levels returned to baseline. SVR and LVEDP increased while CO decreased. The dogs exhibited a profound reduction in anesthetic requirement, reduced catecholamine levels, and changes in hemodynamic parameters with dexmedetomidine administration. The anesthetic sparing effect appears to be mediated by the alpha 2-receptor, since atipamezole reversed the reduction in MAC. Hemodynamic changes may be species or dose related, or due to differences in existing sympathetic tone. The role of dexmedetomidine warrants further study as an adjunct anesthetic agent.