Anesthesia and analgesia
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Anesthesia and analgesia · Apr 1998
The influence of acute normovolemic hemodilution on the dose-response and time course of action of vecuronium.
To evaluate the influence of acute isovolemic hemodilution on the dose-response and time course of action of vecuronium, we studied 60 adult patients with and without hemodilution during surgery. The patients with hemodilution underwent major elective plastic surgery with an anticipated surgical loss of more than 600 mL. Anesthesia was induced with thiopental 4-6 mg/kg and fentanyl 2-4 microg/kg i.v. and was maintained with 60% nitrous oxide in oxygen. Further increments of thiopental 2 mg/kg or fentanyl 2 microg/kg were given as required. Acute isovolemic hemodilution in the hemodilution group was induced by drainage of venous blood and an i.v. infusion of lactated Ringer's solution and 6% dextran, during which hematocrit and hemoglobin decreased from 45.7% to 26.2% and from 148.5 g/L to 90.2 g/L, respectively. Neuromuscular function was assessed mechanomyographically with train-of-four stimulation at the wrist every 12 s, and the percent depression of T1 response was used as the study parameter. The dose-response relationships of vecuronium in the two groups were determined by using the cumulative dose-response technique. The results showed that during hemodilution, the dose-response curve of vecuronium was shifted to the left in a parallel fashion, and the potency of vecuronium was increased. There were significant differences in the 50%, 90%, and 95% effective doses between the two groups. After the i.v. administration of vecuronium 80 microg/kg, vecuronium-induced neuromuscular block was significantly longer in the patients with hemodilution than in the control patients. The duration of peak effect, clinical duration, recovery index, and total duration in the hemodilution patients were significantly different from those in the control patients. We conclude that hemodilution induces significant changes in the pharmacodynamics of vecuronium. ⋯ We found that patients with hemodilution were 20% more sensitive to vecuronium and had a longer duration of action after the administration of the same dose than the controls. This should be taken into account when vecuronium is used as a muscle relaxant during acute hemodilution.
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Anesthesia and analgesia · Apr 1998
Interrupted expiratory flow on automatically constructed flow-volume curves may determine the presence of intrinsic positive end-expiratory pressure during one-lung ventilation.
We studied patients undergoing elective pulmonary surgery to establish whether observing interrupted expiratory flow (IEF) on the flow-volume curves constructed by the Ultima SV respiratory monitor is a reliable way to identify patients with dynamic pulmonary hyperinflation and intrinsic positive end-expiratory pressure (PEEPi). Patients' tracheas were intubated with a double-lumen endotracheal tube and ventilated with a Siemens 900C constant flow ventilator. In 30 patients, PEEPi was determined by the end-expiratory occlusion (EEO) method during the periods of two-lung and one-lung ventilation in the lateral position. Sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of the IEF method were calculated. From the 122 measurement pairs, PEEPi was identified with the EEO method in 65 occasions. The mean level of PEEPi was 4.4 cm H2O. During one-lung ventilation, the level of PEEPi and the number of true-positive findings was significantly higher (PEEPi = 4.7 cm H2O and 32 episodes) than during two-lung ventilation (2.9 cm H2O and 19 episodes). When the level of PEEPi was higher than 5 cm H2O, the predictive value of IEF was 100%. The overall sensitivity of the IEF method was 0.78, its specificity was 0.91, and its predictive value was 0.92. In conclusion, examination of the flow-volume curves displayed on the respiratory monitor may identify patients with dynamic hyperinflation and PEEPi during anesthesia for thoracic surgery. ⋯ To identify patients with intrinsic positive end-expiratory pressure during anesthesia without the need to interrupt mechanical ventilation, the flow-volume curves of an online respiratory monitor may be examined. The presence of an interrupted expiratory flow may suggest the presence of intrinsic positive end-expiratory pressure with a reasonable accuracy.
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Anesthesia and analgesia · Apr 1998
Comment Letter Comparative StudyIs there a place for meperidine in intravenous regional anesthesia?
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Anesthesia and analgesia · Apr 1998
Comparative StudyThe effects of verapamil and nimodipine on bupivacaine-induced cardiotoxicity in rats: an in vivo and in vitro study.
The purpose of this in vivo and in vitro study was to compare the effects of verapamil or nimodipine pretreatment on bupivacaine-induced cardiotoxicity. In the in vivo study, the dose-response curve for the 50% lethal dose (LD50) of bupivacaine was determined for rats. Two separate groups of rats were pretreated with i.v. verapamil 150 microg/kg (n = 35) or i.v. nimodipine 200 microg/kg (n = 35). Each pretreatment group was then subdivided into four groups of at least four rats each. Three minutes after pretreatment, bupivacaine was administered to each of four groups in doses of 2.5, 3.0, 3.25, and 3.5 mg/kg, respectively. Both verapamil and nimodipine pretreatment increased the LD50 and 95% confidence intervals for bupivacaine and increased survival. In the in vitro study, the effects of verapamil or nimodipine perfusion on bupivacaine cardiotoxicity (negative chronotropic, negative inotropic, and arrhythmogenic effects) and coronary perfusion pressure (CPP) were investigated in isolated, perfused rat heart preparations. Depression of heart rate, contractile force, and CPP, and the incidence of arrhythmias caused by bupivacaine alone were similar to those caused by bupivacaine after verapamil pretreatment. In contrast, bupivacaine induced less negative chronotropic effects (P < 0.05, paired t-test) and arrhythmias (P < 0.05, chi2 analysis) after nimodipine pretreatment. The results of this study demonstrate that both verapamil and nimodipine pretreatment decrease bupivacaine-induced cardiotoxicity in vivo, whereas only nimodipine pretreatment decreased bupivacaine-induced cardiotoxicity and arrhythmias in vitro. ⋯ In this experimental study consisting of two stages (in vivo and in vitro), we compared the effects of two calcium channel-blocking drugs (verapamil and nimodipine) on bupivacaine toxicity. Bupivacaine is a local anesthetic frequently used in clinical practice, and cardiotoxicity is one of its severe side effects. Verapamil and nimodipine were both effective in decreasing bupivacaine cardiotoxicity in this rat model.