Anesthesia and analgesia
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Anesthesia and analgesia · Jul 2003
Clinical TrialImplicit memory varies as a function of hypnotic electroencephalogram stage in surgical patients.
Previous studies have observed a correlation of implicit memory with certain electroencephalogram (EEG) measures during anesthesia. Here, we tested the relationship between hypnotic depth determined by computer system (Narcotrend(TM)) and implicit memory in anesthetized patients, assessed by a postoperative reading speed test. Thirty-two patients undergoing laparoscopic herniotomy and 30 age-matched volunteer controls were included the study. All patients received IV midazolam 2-3 mg followed by an induction dose of propofol and remifentanil. The anesthesia was maintained with propofol and remifentanil infusions and cisatracurium. Each patient was exposed to 2 of 4 stories, repeated 6 times. The first story was presented during light to moderate hypnotic EEG stages, and the second story was presented during deep hypnosis. Presentation of stories was balanced between patients and hypnotic stages. The controls listened to the two stories without receiving anesthesia. The reading speed for the previously presented stories and two new stories was measured approximately 7 h later with a computer program. No signs of inadequate anesthesia were observed, and no explicit memories of intraoperative events were revealed by a structured interview. No change of reading speed was observed for words presented during deep hypnotic stages. In contrast, an increased reading speed of 20 ms per word was found for content words (i.e., nouns, verbs, and adjectives), but not for function words (conjunctions, prepositions, and so on), presented during light to moderate hypnotic stages. Increased reading speed for semantically rich content words indicates that anesthetized patients are able to process acoustic information during light and moderate, but not deep, hypnosis. ⋯ In this study, implicit memory was observed during general anesthesia at light to moderate, but not deep, hypnotic stages. Hypnotic stages were determined by a commercial electroencephalogram device, and implicit memory was measured by using a postoperative reading speed task. During lighter phases of anesthesia, patients should be protected against acoustic information that could negatively influence their postoperative outcome.
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Anesthesia and analgesia · Jul 2003
Clinical TrialThe effects of tidal volume and respiratory rate on oxygenation and respiratory mechanics during laparoscopy in morbidly obese patients.
Morbidly obese (MO) patients undergoing laparoscopy have lower PaO(2) compared with normal-weight (NW) patients. We hypothesized that increases in tidal volume (V(T)) or respiratory rate (RR) would improve oxygenation. All measurements were performed at: 1) baseline: V(T) 600-700 mL and 10 breaths/min, 2) double V(T): V(T) 1200-1400 mL and 10 breaths/min, and 3) double rate: V(T) 600-700 mL and 20 breaths/min. We calculated static respiratory system compliance (Cst,rs) and inspiratory resistance (RI,rs). End-tidal CO(2) was measured with a mass spectrometer, and PaO(2) and PaCO(2) with a continuous blood gas monitor. Supine anesthetized MO patients had 29% lower Cst,rs than the NW patients (P < 0.05). Positioning patients head-up or head-down before pneumoperitoneum did not significantly affect Cst,rs in either group (P = 0.8). Doubling the V(T), but not RR, increased Cst,rs in both groups. Pneumoperitoneum caused large decreases in Cst,rs in both groups (both P < 0.001). During pneumoperitoneum, changing the body position, V(T), or RR did not further affect Cst,rs in either group (P > 0.7). Before pneumoperitoneum, RI,rs was higher in the MO patients compared with the NW patients regardless of body position (P = 0.01). Doubling either RR or V(T) before pneumoperitoneum did not change RI,rs in either group. After pneumoperitoneum, RI,rs increased in both the head-down and head-up positions (P < 0.05), but not in the supine position. Regardless of the conditions studied, alveolar-arterial difference in oxygen tension was always significantly higher in MO patients (P < 0.05). The alveolar-arterial difference in oxygen tension was not affected by body position, pneumoperitoneum, or the mode of ventilation. Arterial oxygenation during laparoscopy was affected only by body weight and could not be improved by increasing either the V(T) or RR. ⋯ Morbid obesity decreases arterial oxygenation and respiratory system compliance. During laparoscopy, arterial oxygenation is affected only by the patient's body weight. Increases in tidal volume or respiratory rate do not improve arterial oxygenation.
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Anesthesia and analgesia · Jul 2003
Comparative StudyThe relative toxicity of amitriptyline, bupivacaine, and levobupivacaine administered as rapid infusions in rats.
Intravascular injection of local anesthetics carries the risk of cardiovascular (CV) and central nervous system (CNS) toxicity. Amitriptyline, a tricyclic antidepressant, has local anesthetic potency that is more than that of bupivacaine. In this study, we compared the CV and CNS toxicity of the local anesthetics bupivacaine and levobupivacaine with that of amitriptyline. Twenty-nine Sprague-Dawley rats had their right external jugular vein and carotid artery cannulated under general anesthesia. On Day 2, rats were sedated with midazolam (0.375 mg/kg intraperitoneally) and received rapid infusions of either 1) bupivacaine, levobupivacaine, or amitriptyline at 2 mg x kg(-1) x min(-1) (5 mg/mL concentration) or 2) normal saline (400 micro L x kg(-1) x min(-1)) through an external jugular vein cannula. Electrocardiogram and arterial blood pressure were measured until the dose to cause impending death was reached (heart rate 50 bpm/asystole or apnea for >30 s). The mean dose required to cause apnea and impending death was significantly larger for amitriptyline (74.0 +/- 21 mg/kg and 74.5 +/- 21 mg/kg, respectively) than for levobupivacaine (32.2 +/- 20 mg/kg and 33.9 +/- 22 mg/kg, respectively) or bupivacaine (21.5 +/- 7 mg/kg and 22.7 +/- 7 mg/kg, respectively) (P < 0.05). A significantly larger dose of amitriptyline, given by rapid infusion, is required to cause CV and CNS toxicity in rats, when compared with bupivacaine and levobupivacaine. ⋯ Amitriptyline, a tricyclic antidepressant, has local anesthetic properties and is more potent than bupivacaine. Significantly larger doses of amitriptyline, given by rapid infusion, are required to cause cardiovascular and central nervous system toxicity in rats, when compared with bupivacaine and levobupivacaine.
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Anesthesia and analgesia · Jul 2003
Clinical TrialChronic treatment with antidepressants decreases intraoperative core hypothermia.
We investigated temperature regulation during anesthesia and postoperative shivering in chronically depressed patients given antidepressant drugs. We studied 35 depressed patients and 35 control patients who underwent orthopedic surgery. Tympanic membrane temperatures 60, 75, and 90 min after induction in the depression group were significantly (P < 0.05) higher than those of the control group. There were no significant differences in mean skin temperature between the depression and the control groups. Eight of 35 patients in the depression group and 2 of 35 patients in the control group developed postanesthetic shivering. The incidence of shivering in the depression group was significantly more frequent than that in the control group (P = 0.04). The tympanic membrane temperature of the patients treated with clomipramine tended to be higher than that of the patients treated with maprotiline. In conclusion, intraoperative core hypothermia in chronically depressed patients was decreased. However, the incidence of shivering in depressed patients was significantly more frequent. ⋯ Thermoregulation in chronically depressed patients is often altered. The alteration of body temperature is affected by depression itself and by antidepressants. General anesthesia has an influence on thermoregulatory control. However, temperature regulation during anesthesia in chronically depressed patients remains unclear.
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Anesthesia and analgesia · Jul 2003
Anesthetic sensitivities to propofol and halothane in mice lacking the R-type (Cav2.3) Ca2+ channel.
Because inhibition of voltage-dependent Ca(2+) channels can be a mechanism underlying general anesthesia, we examined sensitivities to propofol and halothane in mice lacking the R-type (Ca(v)2.3) channel widely expressed in neurons. Sleep time after propofol injection (26 mg/kg IV) and halothane MAC(RR) and MAC (50% effective concentrations for the loss of the righting reflex and for the tail pinch/withdrawal response, respectively) were determined. Significantly shorter propofol-induced sleep time (291.6 +/- 16.8 s versus 344.4 +/- 12.1 s) and larger halothane MAC(RR) (1.11% +/- 0.04% versus 0.98% +/- 0.03%) were observed in Ca(v)2.3 channel knockouts (Ca(v)2.3(-/-)) than in wild-type (Ca(v)2.3(+/+)) litter mates. To investigate the basis of the decreased anesthetic sensitivities in vivo, field excitatory postsynaptic potentials and population spikes (PSs) were recorded from Schaffer collateral CA1 synapses in hippocampal slices. Propofol (10-30 micro M) inhibited PSs by potentiating gamma-aminobutyric acid-ergic inhibition, and this potentiation was markedly smaller at 30 micro M in Ca(v)2.3(-/-) mice, possibly accounting for the decreased propofol sensitivity in vivo. Halothane (1.4%-2.2%) inhibited field excitatory postsynaptic potentials similarly in both genotypes, whereas 1%-2% halothane depressed PSs more in Ca(v)2.3(-/-) mice, suggesting the postsynaptic role of the R-type channel in the propagation of excitation and other mechanisms underlying the increased halothane MAC(RR) in Ca(v)2.3(-/-) mice. ⋯ Because inhibition of neuronal Ca(2+) currents can be a mechanism underlying general anesthesia, we examined anesthetic sensitivities in mice lacking the R-type (Ca(v)2.3) Ca(2+) channels both in vivo and in hippocampal slices. Decreased sensitivities in mutant mice imply a possibility that agents blocking this channel may increase the requirements of anesthetics/hypnotics.