ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundShivering can be characterized by its threshold (triggering core temperature), gain (incremental intensity increase), and maximum intensity. The gain of shivering might be preserved during epidural or spinal anesthesia if control mechanisms compensate for lower‐body paralysis by augmenting the activity of upper‐body muscles. Conversely, gain will be reduced approximately by half if the thermoregulatory system fails to compensate. Similarly, appropriate regulatory feedback might maintain maximum shivering intensity during regional anesthesia. Accordingly, the gain and maximum intensity of shivering during epidural anesthesia were determined.MethodsSeven volunteers participated on two randomly ordered study days. On one day (control), no anesthesia was administered; on the other, epidural anesthesia was maintained at a T8 sensory level. Shivering, at a mean skin temperature near 33 [degree sign] Celsius, was provoked by central‐venous infusion of cold fluid; core cooling continued until shivering intensity no longer increased. Shivering was evaluated by systemic oxygen consumption and electromyography of two upper‐body and two lower‐body muscles. The core temperature triggering an increase in oxygen consumption identified the shivering threshold. The slopes of the oxygen consumption versus core temperature and electromyographic intensity versus core temperature regressions identified systemic and regional shivering gains, respectively.ResultsThe shivering threshold was reduced by epidural anesthesia by [nearly =] 0.4 [degree sign] Celsius, from 36.7 +/‐ 0.6 to 36.3 +/‐ 0.5 [degree sign] Celsius (means +/‐ SD; P < 0.05). Systemic gain, as determined by oxygen consumption, was reduced from ‐581 +/‐ 186 to ‐215 +/‐ 154 ml [center dot] min sup ‐1 [center dot] [degree sign] Celsius sup ‐1 (P < 0.01). Lower‐body gain, as determined electromyographically, was essentially obliterated by paralysis during epidural anesthesia, decreasing from ‐0.73 +/‐ 0.85 to ‐0.04 +/‐ 0.06 intensity units/[degree sign] Celsius (P < 0.01). However, upper‐body gain had no compensatory increase: ‐1.3 +/‐ 1.1 units/[degree sign] Celsius control versus ‐2.0 +/‐ 2.1 units/[degree sign] Celsius epidural. Maximum oxygen consumption was decreased by one third during epidural anesthesia: 607 +/‐ 82 versus 412 +/‐ 50 ml/min (P < 0.05).ConclusionsThese results confirm that regional anesthesia reduces the shivering threshold. Epidural anesthesia reduced the gain of shivering by 63% because upper‐body muscles failed to compensate for lower‐body paralysis. The thermoregulatory system thus fails to recognize that regional anesthesia reduces metabolic heat production, instead responding as if lower‐body muscular activity remained intact.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundThermoregulatory shivering can be characterized by its threshold (triggering core temperature), gain (incremental intensity increase with further core temperature deviation), and maximum intensity. Meperidine (a combined micro‐ and kappa‐agonist) treats shivering better than equianalgesic doses of pure micro‐opioid agonists. Meperidine's special antishivering action is mediated, at least in part, by a disproportionate decrease in the shivering threshold. That is, meperidine decreases the shivering threshold twice as much as the vasoconstriction threshold, whereas alfentanil (a pure micro‐agonist) decreases the vasoconstriction and shivering thresholds comparably. However, reductions in the gain or maximum shivering intensity might also contribute to the clinical efficacy of meperidine. Accordingly, we tested the hypothesis that meperidine reduces the gain and maximum intensity of shivering much more than alfentanil does.MethodsTen volunteers were each studied on three separate days: (1) control (no drug); (2) a target total plasma meperidine concentration of 1.2 micro gram/ml; and (3) a target plasma alfentanil concentration of 0.2 micro gram/ml. Skin temperatures were maintained near 31 [degree sign] Celsius, and core temperatures were decreased by central‐venous infusion of cold lactated Ringer's solution until maximum shivering intensity was observed. Shivering was evaluated using oxygen consumption and electromyography. A sustained increase in oxygen consumption identified the shivering threshold. The gain of shivering was calculated as the slope of the oxygen consumption versus core temperature regression, and as the slope of electromyographic intensity versus core temperature regression.ResultsMeperidine and alfentanil administration significantly decreased the shivering thresholds. However, neither meperidine nor alfentanil reduced the gain of shivering, as determined by either oxygen consumption or electromyography. Opioid administration also failed to significantly decrease the maximum intensity of shivering.ConclusionsThe authors could not confirm the hypothesis that meperidine reduces the gain or maximum intensity of shivering more than alfentanil does. These results suggest that meperidine's special antishivering effect is primarily mediated by a disproportionate reduction in the shivering threshold.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundShivering can be characterized by its threshold (triggering core temperature), gain (incremental intensity increase with further core hypothermia), and maximum response intensity. Isoflurane produces a clonic muscular activity that is not a component of normal shivering. To the extent that clonic activity is superimposed on normal thermoregulatory shivering, the gain of shivering might be increased during isoflurane anesthesia. Conversely, volatile anesthetics decrease systemic oxygen consumption and peripherally inhibit skeletal muscle strength, which might limit maximum intensity despite central activation. The purpose of the present study was, therefore, to evaluate the effect of isoflurane shivering patterns and the gain and maximum intensity of shivering.MethodsTen volunteers were each studied in two separate protocols: (1) control (no drug) and (2) 0.7% end‐tidal isoflurane. On each day, the mean skin temperature was maintained at 31 [degree sign] Celsius. Core temperature was then reduced by infusion of cold fluid until shivering intensity no longer increased. The core temperature triggering the initial increase in oxygen consumption defined the shivering threshold. The gain of shivering was defined by the slope of the core temperature versus oxygen consumption regression. Pectoralis and quadriceps electromyography was used to evaluate anesthetic‐induced facilitation of clonic (5–7 Hz) muscular activity.ResultsIsoflurane significantly decreased the shivering threshold from 36.4 +/‐ 0.3 to 34.2 +/‐ 0.8 [degree sign] Celsius. The increase in oxygen consumption was linear on the control day and was followed by sustained high‐intensity activity. During isoflurane administration, shivering was characterized by bursts of intense shivering separated by quiescent periods. Isoflurane significantly increased the gain of shivering (as calculated from the initial increase), from ‐684 +/‐ 266 to ‐1483 +/‐ 752 ml [center dot] min sup ‐1 [center dot] [degree sign] Celsius sup ‐1. However, isoflurane significantly decreased the maximum intensity of shivering, from 706 +/‐ 144 to 489 +/‐ 80 ml/min. Relative electromyographic power in frequencies associated with clonus increased significantly when the volunteers were given isoflurane.ConclusionsThese data indicate that isoflurane anesthesia markedly changes the overall pattern of shivering during progressive hypothermia from a linear increase to an unusual saw‐tooth pattern. They further suggest that clonic muscular activity combines with shivering to increase the initial gain of shivering during isoflurane anesthesia, but that isoflurane peripherally inhibits the maximum expression of shivering.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundMethods of the kinetic analysis of vecuronium based on effect only were developed but have been limited by the short time period of the studies. Using a multicompartment model and sequential dosing, the authors studied the ability of tests to determine most pharmacokinetic and pharmacodynamic parameters of vecuronium without measuring plasma concentrations.MethodsThe time course of neuromuscular blockade by successive bolus doses of vecuronium was recorded using electromyography. Inhibition of neuromuscular transmission by vecuronium was modeled by a biexponential decline in the concentrations in the central compartment and first‐order transfer between the central and the effect compartments responsible for the inhibition of the first (T1) and fourth (T4) responses to train‐of‐four stimulation.ResultsThe time course of the effect of vecuronium was described well by the model. The mean half‐lives of equilibration between plasma and the effect compartments to inhibit T1 and T4 were 2.5 and 3.2 min, respectively. The mean half‐lives of distribution and elimination from the central compartment were 7.7 and 78 min, respectively. From the kinetic and dynamic parameters calculated after two and three doses, the time taken to recover to 50% of the maximal block of T1 was predicted for the succeeding dose. The mean prediction errors (100 x [absolute difference between actual and predicted times]/actual) were 13.6% (range, 0–40%) and 15% (range, 0–25%) after three and four doses, respectively.ConclusionsAfter sequential doses, measurement of the time course of the effect of vecuronium yields pharmacokinetic and pharmacodynamic parameters with clinically acceptable accuracy in individual patients.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundMood states during epidural opioids are not known. The authors studied the change in mood during the 48‐h period of epidural morphine and epidural fentanyl in 47 patients after elective hip or knee joint arthroplasty.MethodsAn epidural catheter was inserted at the L2‐L3 or L3‐L4 interspace. Anesthesia was induced with thiopenthal and maintained with isoflurane and nitrous oxide. One hour before the conclusion of the operation, patients received an epidural bolus injection of 2 mg morphine (n = 23) or 100 micro gram fentanyl (n = 24), followed by the same opiate (125 micro gram/ml morphine or 25 micro gram/ml fentanyl) epidurally delivered by a patient‐controlled analgesia (PCA) pump in the postoperative period for 48 h. Mood was assessed using the bipolar form of the Profile of Mood States before operation and 24 h, 48 h, and 72 h after operation.ResultsThere was no significant difference in pain intensity between the groups during epidural PCA. Mood states became more positive over time in the patients who received morphine (P < 0.01 at 48 h) and negative in those who were given fentanyl (P < 0.01 at 24 and 48 h, respectively) compared with those before the operation, and they were more positive in the morphine than in the fentanyl group at 24 h, 48 h (P < 0.05), and 72 h (P < 0.01). Patients in the morphine group were more composed, agreeable, elated, confident, energetic, and clearheaded than were those in the fentanyl group (P < 0.05). There was no correlation between mood scores and pain scores in either group. There was an inverse correlation at 48 h between mood scores and plasma fentanyl concentrations (r = ‐0.58, P < 0.05).ConclusionMood states are significantly more positive during epidural morphine PCA than they are during epidural fentanyl PCA.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundCarotid endarterectomy necessitates temporary unilateral carotid artery occlusion. Critical regional cerebral blood flow (rCBF) has been defined as the rCBF below which electroencephalographic (EEG) changes of ischemia occur. This study determined the rCBF50, the rCBF value at which 50% of patients will not demonstrate EEG evidence of cerebral ischemia with carotid cross‐clamping.MethodsFifty‐two patients undergoing elective carotid end‐arterectomy were administered 0.6–1.2% (0.3–0.6 minimum alveolar concentration) sevoflurane in 50% nitrous oxide (N2O). A 16‐channel EEG was used for monitoring. The washout curves from intracarotid133Xenon injections were used to calculate rCBF before and at the time of carotid occlusion by the half‐time (t1/2) technique. The quality of the EEG with respect to ischemia detection was assessed by an experienced electroencephalographer.ResultsIschemic EEG changes developed in 5 of 52 patients within 3 min of carotid occlusion at rCBFs of 7, 8, 11, 11, and 13 ml [center dot] 100 g sup ‐1 [center dot] min sup ‐1. Logistic regression analysis was used to calculate an rCBF50of 11.5 +/‐ 1.4 ml [center dot] 100 g sup ‐1 [center dot] min sup ‐1 for sevoflurane. The EEG signal demonstrated the necessary amplitude, frequency, and stability for the accurate detection of cerebral ischemia in all patients within the range of 0.6–1.2% sevoflurane in 50% N2O.ConclusionsThe rCBF50of 0.6–1.2% sevoflurane in 50% N2O, as determined using logistic regression analysis, is 11.5 +/‐ 1.4 ml [center dot] 100 g sup ‐1 [center dot] min sup ‐1. Further, in patients anesthetized in this manner, ischemic EEG changes due to carotid occlusion were accurately and rapidly detected.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundThe negative‐pressure test using a self‐inflating bulb (SIB) during emergency intubation was studied to determine its reliability and predictive value in this setting.MethodsThe endotracheal tube (ETT) position was tested in 300 consecutive patients undergoing in‐hospital emergency endotracheal intubation. Immediately after intubation and before ETT cuff inflation, the following protocol was strictly followed: (1) an SIB was compressed, connected to the ETT, and released. A 10‐s period was allowed for the bulb to inflate. (2) The ETT cuff was inflated, and the ETT position was confirmed using colorimetric or infrared carbon dioxide detection, or both, combined with clinical evaluation.ResultsThere were 19 esophageal intubations (6% incidence). The SIB correctly identified all patients with esophageal intubation (sensitivity, 100%) and correctly identified all but three ETTs placed in the trachea (specificity, 99%). The three tracheally placed tubes that were misidentified by the bulb syringe occurred during one case each of chronic obstructive pulmonary disease, copious secretions, and obesity; of note were three tracheally placed tubes that were misidentified by the carbon dioxide analyzers during cardiopulmonary resuscitation.ConclusionsThe SIB proved to be a sensitive and specific test for esophageal intubation in the emergency setting when used according to the protocol described, and it is complementary to carbon dioxide detection. The predictive value of the bulb syringe appears to be improved when a prolonged period for reinflation is allowed. It holds particular promise because of its low cost and portability.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundOpiate agonists have different analgesic effects in male and female patients. The authors describe the influence of sex on the respiratory pharmacology of the micro‐receptor agonist morphine.MethodsThe study was placebo‐controlled, double‐blind, and randomized. Steady‐state ventilatory responses to carbon dioxide and responses to a step into hypoxia (duration, 3 min; oxygen saturation, [approximately] 82%; end‐tidal carbon dioxide tension, 45 mmHg) were obtained before and during intravenous morphine or placebo administration (bolus dose of 100 micro gram/kg, followed by a continuous infusion of 30 micro gram [center dot] kg sup ‐1 [center dot] h sup ‐1) in 12 men and 12 women.ResultsIn women, morphine reduced the slope of the ventilatory response to carbon dioxide from 1.8 +/‐ 0.9 to 1.3 +/‐ 0.7 l [center dot] min sup ‐1 [center dot] mmHg sup ‐1 (mean +/‐ SD; P < 0.05), whereas in men there was no significant effect (control = 2.0 +/‐ 0.4 vs. morphine = 1.8 +/‐ 0.4 l [center dot] min sup ‐1 [center dot] mmHg sup ‐1). Morphine had no effect on the apneic threshold in women (control = 33.8 +/‐ 3.8 vs. morphine = 35.3 +/‐ 5.3 mmHg), but caused an increase in men from 34.5 +/‐ 2.3 to 38.3 +/‐ 3 mmHg, P < 0.05). Morphine decreased hypoxic sensitivity in women from 1.0 +/‐ 0.5 l [center dot] min sup ‐1 [center dot] % sup ‐1 to 0.5 +/‐ 0.4 l [center dot] min sup ‐1 [center dot] % sup ‐1 (P < 0.05) but did not cause a decrease in men (control = 1.0 +/‐ 0.5 l [center dot] min sup ‐1 [center dot] % sup ‐1 vs. morphine = 0.9 +/‐ 0.5 l [center dot] min sup ‐1 [center dot] % sup ‐1). Weight, lean body mass, body surface area, and calculated fat mass differed between the sexes, but their inclusion in the analysis as a covariate revealed no influence on the differences between men and women in morphine‐induced changes.ConclusionsIn both sexes, morphine affects ventilatory control. However, we observed quantitative and qualitative differences between men and women in the way morphine affected the ventilatory responses to carbon dioxide and oxygen. Possible mechanisms for the observed sex differences in the respiratory pharmacology of morphine are discussed.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BackgroundIn an attempt to combine the advantage of the lower solubilities of new inhaled anesthetics with the lesser cost of older anesthetics, some clinicians substitute the former for the latter toward the end of anesthesia. The authors tried to determine whether substituting desflurane for isoflurane in the last 30 min of a 120‐min anesthetic would accelerate recovery.MethodsFive volunteers were anesthetized three times for 2 h using a fresh gas inflow of 2 l/min: 1.25 minimum alveolar concentration (MAC) desflurane, 1.25 MAC isoflurane, and 1.25 MAC isoflurane for 90 min followed by 30 min of desflurane concentrations sufficient to achieve a total of 1.25 MAC equivalent ("crossover"). Recovery from anesthesia was assessed by the time to respond to commands, by orientation, and by tests of cognitive function.ResultsCompared with isoflurane, the crossover technique did not accelerate early or late recovery (P > 0.05). Recovery from isoflurane or the crossover anesthetic was significantly longer than after desflurane (P < 0.05). Times to response to commands for isoflurane, the crossover anesthetic, and desflurane were 23 +/‐ 5 min (mean +/‐ SD), 21 +/‐ 5 min, and 11 +/‐ 1 min, respectively, and to orientation the times were 27 +/‐ 7 min, 25 +/‐ 5 min, and 13 +/‐ 2 min, respectively. Cognitive test performance returned to reference values 15–30 min sooner after desflurane than after isoflurane or the crossover anesthetic. Isoflurane cognitive test performance did not differ from that with the crossover anesthetic at any time.ConclusionsSubstituting desflurane for isoflurane during the latter part of anesthesia does not improve recovery, in part because partial rebreathing through a semiclosed circuit limits elimination of isoflurane during the crossover period. Although higher fresh gas flow during the crossover period would speed isoflurane elimination, the amount of desflurane used and, therefore, the cost would increase.

ISSN:0003-3022    

出版商:OVID    

年代:1998

数据来源: OVID