Anesthesia and analgesia
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Recent advances in acute pain mechanisms and management have implicated the N-methyl D-aspartate receptor-ion channel complex in the development of postoperative hyperalgesia and acute opioid tolerance. N-methyl D-aspartate receptor antagonists such as ketamine have been used increasingly in clinical studies in an effort to minimize acute postoperative pain and reduce opioid requirements. A mixture of ketamine and an opioid administered in the same solution and syringe would be a practical and useful technique for postoperative epidural analgesia, continuous IV infusion, or patient-controlled IV analgesia. We investigated the stability of a morphine sulfate and racemic ketamine solution in saline at pH 5.5-7.5 over a period of 4 days. Our study demonstrates that the ketamine-morphine mixture at a clinically relevant concentration seems to be stable at room temperature, at a wide range of pH values, for at least 4 days. ⋯ Small-dose ketamine is used with increasing frequency in the acute postoperative setting as an adjunct to traditional opioid analgesics. We show that a racemic ketamine and morphine solution at a clinically relevant concentration seems to be stable at room temperature at a wide range of pH values for at least 4 days.
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Anesthesia and analgesia · Apr 2002
How to schedule elective surgical cases into specific operating rooms to maximize the efficiency of use of operating room time.
We considered elective case scheduling at hospitals and surgical centers at which surgeons and patients choose the day of surgery, cases are not turned away, and anesthesia and nursing staffing are adjusted to maximize the efficiency of use of operating room (OR) time. We investigated scheduling a new case into an OR by using two patient-scheduling rules: Earliest Start Time or Latest Start Time. By using several scenarios, we showed that the use of Earliest Start Time is rational economically at such facilities. Specifically, it maximizes OR efficiency when a service has nearly filled its regularly scheduled hours of OR time. However, Latest Start Time will perform better at balancing workload among services' OR time. We then used historical case duration data from two facilities in computer simulations to investigate the effect of errors in predicting case durations on the performance of these two heuristics. The achievable incremental reduction in overtime by having perfect information on case duration versus using historical case durations was only a few minutes per OR. The differences between Earliest Start Time and Latest Start Time were also only a few minutes per OR. We conclude that for facilities at which the goals are, in order of importance, safety, patient and surgeon access to OR time, and then efficiency, few restrictions need to be placed on patient scheduling to achieve an efficient use of OR time. ⋯ We showed how elective cases should be scheduled to maximize the efficiency of use of operating room time. The analysis applies to surgical suites at which surgeons and patients have access to operating room time every workday.
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Anesthesia and analgesia · Apr 2002
Neuromuscular pharmacology of TAAC3, a new nondepolarizing muscle relaxant with rapid onset and ultrashort duration of action.
We selected bis [N-(3,4-diacetoxybenzyl) tropanium-3alpha-yl] glutarate dibromide (TAAC3) from many new tropinyl diester derivatives to evaluate its neuromuscular blocking (NMB) and autonomic side effects on anesthetized rats, rabbits, guinea pigs, cats, pigs, dogs, and monkeys. NMB potency, onset, recovery index, and duration of action were determined. Comparisons of these pharmacologic variables were made between TAAC3 and rocuronium. In the cat, the degrees of train-of-four and tetanic fade, posttetanic potentiation, and pharmacologic antagonism were evaluated. For determination of the NMB maintenance dose, TAAC3 was also given to rabbits and pigs in the initial dose/maintenance infusion mode. Cardiac vagal block was evaluated in the rat, pig, cat, and guinea pig on the basis of the inhibition of the bradycardia to stimulation of the vagus nerve. Sympathetic ganglion block was studied on the superior cervical ganglion-nictitating membrane preparation of the cat. TAAC3 produced nondepolarizing NMB. Its NMB 90% effective doses ranged from 90 to 425 microg/kg, depending on the species. TAAC3 had a faster onset (0.8-1.0 min), shorter recovery index (0.6-1.1 min), and shorter duration of action (1.8-3.5 min) than rocuronium. It produced a slight cumulative effect on infusion, but not on repeated single-dose administration. Cardiac vagal block was present at doses exceeding the NMB 90% effective dose. In the cat and pig at equipotent NMB doses, the degree of cardiac vagal block was similar to that of rocuronium. There was no demonstrable sympathetic ganglion block in the cat. In view of its favorable NMB characteristics, TAAC3 is now undergoing detailed preclinical studies. ⋯ We developed a new nondepolarizing muscle relaxant, TAAC3, and investigated it in several animal models. TAAC3 has shown a very rapid onset and an ultrashort duration of neuromuscular blocking action. A minor degree of cardiac vagal block was observed. TAAC3 is promising for further studies.
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Anesthesia and analgesia · Apr 2002
Motor-evoked potential facilitation during progressive cortical suppression by propofol.
We characterized the effects of various stimulation patterns on motor-evoked potentials (MEPs) elicited by repetitive transcranial magnetoelectric stimulation at different levels of cortical suppression by propofol. In 20 patients undergoing lumbar disk surgery, propofol target plasma concentrations (PTPCs) were increased incrementally by target plasma-level controlled infusion during the induction of anesthesia. MEPs were recorded from the muscles of the upper extremities after single, double, and quadruple magnetoelectric stimulation at 500, 200, and 100 Hz. The mean PTPC during loss of responsiveness to verbal instructions (CP50) was 3 microg/mL (CP(95), 5 microg/mL). At PTPCs <3 microg/mL, maximal MEP amplitudes were elicited by quadruple stimulation at 100 Hz. At PTPCs > or =3 microg/mL, four pulses at 200 Hz yielded peak MEP amplitudes. Therefore, quadruple magnetoelectric stimulation at 100 Hz yields peak myogenic responses in awake patients. With progressive cortical suppression resulting from PTPCs beyond 3 microg/mL, the most effective stimulation frequency shifts to 200 Hz. This may be explained by a differential dose-dependent action of propofol on GABAergic cortical interneurons, corresponding to the clinically observed state of vigilance. Recording of spinal cord evoked potentials will aid in further elucidation of the modulatory effects of general anesthesia on intracortical facilitation. ⋯ We investigated the effect of different transcranial magnetoelectric stimulation paradigms on motor-evoked potentials during different levels of cortical suppression by propofol. The most effective stimulation frequency seems to change from 100 to 200 Hz during progressive propofol dose escalation, possibly because of specific interaction with cortical interneurons.
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Anesthesia and analgesia · Apr 2002
Randomized Controlled Trial Multicenter Study Clinical TrialPreserved gastric tonometric variables in cardiac surgical patients administered intravenous perflubron emulsion.
Low gastric intramucosal pH (pHi) and an increased gastric-arterial PCO2 difference (CO2 gap) are markers of tissue hypoperfusion. Perfluorocarbons (PFCs) have a large oxygen-carrying capacity and release oxygen when encountering low tissue oxygen tension. Nine cardiac surgical patients instrumented for gastric tonometry were enrolled as part of a multicenter, randomized, single-blinded study of a PFC emulsion (perflubron emulsion [Oxygent]). Patients were randomized to receive PFC (n = 4) or placebo (n = 5) after intraoperative autologous blood harvesting by acute normovolemic hemodilution. At baseline there were no intergroup differences in tonometric-, hemodynamic-, or oxygen delivery-derived variables, e.g., Control group (pHi, 7.37 +/- 0.06; CO2 gap, 6.4 +/- 1.3 mm Hg) versus PFC group (pHi, 7.38 +/- 0.06; CO2 gap, 6.7 +/- 1.5 mm Hg). After acute normovolemic hemodilution, pHi was significantly lower (P < 0.01) in the Control group (7.22 +/- 0.25) than in the PFC group (7.44 +/- 0.25), and CO2 gap was significantly higher (P < 0.001) in the Control group (23.4 +/- 5.1 mm Hg) than in the PFC group (1.8 +/- 0.8 mm Hg). These differences in tonometric variables persisted during surgery. The PFC group showed a significantly (P < 0.007) shorter time to first bowel movement postoperatively (2.0 +/- 0.8 vs 5.4 +/- 1.6 days). Time to consumption of solid food was also shorter in the PFC group and almost achieved statistical significance (P = 0.056). ⋯ This study suggests that the administration of perflubron emulsion prevents gastrointestinal tract ischemia in cardiac surgical patients and may preserve postoperative gastrointestinal tract function.