Anesthesia and analgesia
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Anesthesia and analgesia · Jan 2003
Randomized Controlled Trial Comparative Study Clinical TrialTarget-controlled infusion for remifentanil in vascular patients improves hemodynamics and decreases remifentanil requirement.
Remifentanil is a potent ultra-short-acting opioid, which permits rapid emergence. However, remifentanil is expensive and may have detrimental effects on hemodynamics in case of overdose. Target-controlled infusion (TCI) permits adapting infusion to pharmacokinetic models. In this prospective randomized study, we compared intra- and postoperative hemodynamics, remifentanil requirement during anesthesia, and postoperative morphine requirement in patients scheduled for carotid surgery, and receiving either continuous IV weight-adjusted infusion of remifentanil (RIVA) or TCI for remifentanil (TCIR). Forty-six patients were enrolled in this study: all were anesthetized by using TCI for propofol. Twenty-three received RIVA (0.5 micro g. kg(-1) x min(-1)) for the induction of anesthesia and endotracheal intubation, with the infusion rate decreased to 0.25 micro g x kg(-1) x min(-1) after intubation, then adapted by step of 0.05 micro g x kg(-1) x min(-1) according to hemodynamics. Twenty-three patients received TCIR (Minto model, Rugloop), with an effect-site concentration at 4 ng/mL during induction, then adapted by step of 1 ng/mL according to hemodynamics. All patients received atracurium and a 50% mixture of N(2)O/O(2). Hemodynamic variables were recorded each minute. The number and duration of hemodynamic events were collected, and total doses of anesthetics (remifentanil and propofol) and vasoactive drugs were noted in both groups of patients. Data were analyzed by using unpaired t-tests. RIVA was significantly associated with more frequent episodes of intraoperative hypotension (16 versus 6, P < 0.001) and more frequent episodes of postoperative hypertension and/or tachycardia requiring more frequent administration of beta-adrenergic blockers (16 vs 10, P < 0.04) in comparison with TCIR. The need for morphine titration was not significantly different between groups. TCIR led to a significantly smaller requirement of remifentanil (700 +/- 290 versus 1390 +/- 555 micro g, P < 0.001) without difference in propofol requirement. This prospective randomized study demonstrated that, during carotid endarterectomy, in comparison with patients receiving remifentanil using continuous RIVA, TCI results in less hypotensive episodes during the induction of anesthesia, in fewer episodes of tachycardia and/or hypertension and a smaller beta-adrenergic blocker requirement during recovery, and a decrease in remifentanil requirement. Recommendations to prefer TCI for remifentanil administration during carotid endarterectomy may be justified. ⋯ Remifentanil for intraoperative analgesia in carotid artery surgery is associated with a better stability in perioperative hemodynamics when administered in target-controlled infusion compared with continuous weight-adjusted infusion. This may be related to a smaller requirement of this drug when using target-controlled infusion, as well as a smooth mode of administration.
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Anesthesia and analgesia · Jan 2003
Case ReportsAn unusual complication of total intravenous anesthesia: mutism.
We report a case of mutism secondary to total IV anesthesia with propofol, as an unusual complication that we have not found in the literature.
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Anesthesia and analgesia · Jan 2003
Volatile anesthetics reduce agonist affinity at nicotinic acetylcholine receptors in the brain.
In previous studies we and others have demonstrated that the activation of nicotinic acetylcholine receptors (nAChRs) is inhibited by subanesthetic concentrations of volatile anesthetics. The mechanism by which activation is inhibited is unknown. Studies of the evolutionarily related nAChRs from the electric fish Torpedo have suggested that volatile anesthetics alter the affinity of the agonist for the receptor. We studied the effect of two volatile anesthetics, isoflurane and sevoflurane, on equilibrium binding of the high-affinity nicotinic agonist epibatidine to nicotinic receptors from mouse brain. We studied binding to male and female brain separately, because sex differences in nicotine responses have been reported. Male and female brains have equal epibatidine binding without anesthetic. Isoflurane and sevoflurane reduce the binding of [(3)H]epibatidine to male and female nicotinic receptors, but only at concentrations at and above those required for anesthesia. The 50% inhibitory concentration for isoflurane inhibition of [(3)H]epibatidine binding to male brain was 0.58 +/- 0.07 mM and to female brain was 1.62 +/- 0.30 mM. The 50% inhibitory concentration for sevoflurane inhibition of [(3)H]epibatidine binding to male brain was 0.77 +/- 0.05 mM and to female brain was 0.77 +/- 0.04 mM. There was no statistically significant difference in the effect of either drug between sexes (P > 0.05). Although there is a slight decrease in agonist affinity at anesthetic concentrations, the marked reductions in nAChR function at subanesthetic concentrations cannot be attributed to changes in agonist affinity. ⋯ Volatile anesthetics reduce the activation of nicotinic acetylcholine receptors by an unknown mechanism. We have demonstrated that although isoflurane and sevoflurane inhibit agonist affinity, the concentrations required are too large to be responsible for the dynamic changes observed.
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Anesthesia and analgesia · Jan 2003
One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure is injurious in the isolated rabbit lung model.
We tested the hypothesis that one-lung ventilation (OLV) with high tidal volumes (VT) and zero positive end-expiratory pressure (PEEP) may lead to ventilator-induced lung injury. In an isolated, perfused rabbit lung model, VT and PEEP were set to avoid lung collapse and overdistension in both lungs, resulting in a straight pressure-time (P-vs-t) curve during constant flow. Animals were randomized to (a) nonprotective OLV (left lung) (n = 6), with VT values as high as before randomization and zero PEEP; (b) protective OLV (left lung) (n = 6), with 50% reduction of VT and maintenance of PEEP as before randomization; and (c) control group (n = 6), with ventilation of two lungs as before randomization. The nonprotective OLV was associated with significantly smaller degrees of collapse and overdistension in the ventilated lung (P < 0.001). Peak inspiratory pressure values were higher in the nonprotective OLV group (P < 0.001) and increased progressively throughout the observation period (P < 0.01). The mean pulmonary artery pressure and lung weight gain values, as well as the concentration of thromboxane B(2), were comparatively higher in the nonprotective OLV group (P < 0.05). A ventilatory strategy with VT values as high as those used in the clinical setting and zero PEEP leads to ventilator-induced lung injury in this model of OLV, but this can be minimized with VT and PEEP values set to avoid lung overdistension and collapse. ⋯ One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure (PEEP) is injurious in the isolated rabbit lung model. A ventilatory strategy with tidal volumes and PEEP set to avoid lung overdistension and collapse minimizes lung injury during one-lung ventilation in this model.
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Anesthesia and analgesia · Jan 2003
Hemodilution does not alter arterial baroreflex control of heart rate in anesthetized dogs.
The cardiovascular effects of acute normovolemic hemodilution (ANH) are characterized by increased cardiac output and decreased systemic vascular resistance. However, whether arterial baroreflex function is altered by ANH remains undetermined. We assigned 23 anesthetized, mechanically ventilated dogs to mild ANH (hemoglobin, 7-8 g/dL; n = 11) or profound ANH (hemoglobin, 4-5 g/dL; n = 12) achieved by phlebotomy and simultaneous exchange with lactated Ringer's solution at 1:3 ratio to maintain constant central venous pressure and pulmonary artery occluded pressure. Baroreflex sensitivity was assessed by measurements of RR intervals of the electrocardiogram and mean arterial blood pressure (MAP) through a femoral artery catheter. Baroreflex responses were triggered by bolus IV injections of phenylephrine (25-75 micro g) and nitroprusside (50-100 micro g). The linear portion of the baroreflex curves relating RR intervals and MAP were used to determine baroreflex sensitivities. Compared with the predilution period, both ANH groups had significant increases in cardiac output and decreases in systemic vascular resistance (P < 0.01), whereas MAP and heart rate (HR) remained unchanged. However, no significant difference was detected between pre-ANH and post-ANH baroreflex sensitivities in either group. Our results indicate that arterial baroreflex control of HR is preserved during ANH to a hemoglobin concentration of 4-5 g/dL in anesthetized dogs. ⋯ Acute normovolemic hemodilution may be preoperatively used to minimize the requirement of allogeneic blood products during major surgery. We found that baroreflex function is preserved during mild (hemoglobin concentration, 7-8 g/dL) and profound hemodilution (hemoglobin concentration, 4-5 g/dL) in pentobarbital-anesthetized dogs.