Anesthesia and analgesia
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Anesthesia and analgesia · Sep 2000
Comparative StudyTolerability of large-dose intravenous levobupivacaine in sheep.
In preclinical pharmacological studies of levobupivacaine (S-bupivacaine), we determined its tolerability, cardiovascular actions, and pharmacokinetics, and we estimated its margin of safety compared with bupivacaine in conscious sheep. Levobupivacaine HCl. H(2)O was infused IV for 3 min into 10 previously instrumented ewes (approximately 50 kg). On subsequent days, the doses were increased by 50 mg from 200 or 250 mg until fatality occurred. All doses produced convulsions, QRS widening, and cardiac arrhythmias. With incremental doses, 4 of 4 animals survived 200 mg, 7 of 10 survived 250 mg, 3 of 7 survived 300 mg, but 0 of 3 survived 350 mg. Death resulted from sudden onset ventricular fibrillation (n = 3, within 2-3 min), electromechanical dissociation-pump failure (n = 5, within 4-5 min), or ventricular tachycardia-induced cardiac insufficiency (n = 2, >10 min). The estimated fatal dose (mean +/- SD) was 277 +/- 51 mg for levobupivacaine (compared with 156 +/- 31 mg found previously for bupivacaine). Pharmacokinetic analysis indicated initial and total distribution volumes = 4.5 (+/-1.6) and 97 (+/-22) L, total clearance = 1.7 (+/-0.4) L/min, and slow half life = 70 (+/-29) min; these values did not differ from those found previously with smaller doses. Heart and brain tissue levobupivacaine concentrations were approximately 3 times those in arterial blood. The doses of levobupivacaine survived were larger than found previously for bupivacaine, indicating its greater margin of safety. ⋯ Levobupivacaine produced fatal cardiac toxicity at doses significantly greater than those found in previous studies with bupivacaine. As the two drugs have similar potency for producing clinical nerve blocks, the data imply that levobupivacaine should provide a safer alternative to bupivacaine in practice.
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Anesthesia and analgesia · Sep 2000
Clinical TrialThe hemodynamic and metabolic effects of tourniquet application during knee surgery.
We evaluated the effects of tourniquet application on the cardiovascular system and metabolism in 10 young men undergoing knee surgery with general anesthesia. The duration of inflation was from 75 to 108 min. Heart rate, mean arterial pressure, cardiac index (CI) by pulse contour method, and systemic vascular resistance were measured before, during, and after tourniquet inflation. pH, PaO(2), PaCO(2), and lactate blood concentrations were also measured. VO(2) and VCO(2) were assessed every minute from tracheal intubation up to 15 min after tourniquet deflation and VO(2) in excess of the basal value over the 15 min after deflation (VO(2)exc) was calculated. Mean arterial pressure increased 26% (P: < 0.05) during inflation and returned to basal values after deflation. CI did not change immediately after inflation; although, thereafter, it increased 18% (P: < 0.05). Five minutes after deflation, CI further increased to a value 40% higher than the basal value. Therefore, systemic vascular resistance increased 20% suddenly after inflation (P: < 0.05) and decreased 18% after deflation (P: < 0.05). VO(2) and VCO(2) remained stable during inflation and increased (P: < 0.05) after deflation. VO(2)exc depended on duration of tourniquet inflation time (Tisch) (P: < 0.05). After deflation, PaCO(2) and lactate increased (P: < 0.05) while Tisch increased. We conclude that tourniquet application induces modifications of the cardiovascular system and metabolism, which depend on tourniquet phase and on Tisch. Whether these modifications could be relevant in patients with poor physical conditions is not known. ⋯ The clinical effects of tourniquet application were evaluated in 10 young men undergoing knee surgery. Our data indicate that tourniquet application causes hemodynamic and metabolic changes which may become clinically relevant after a long period of tourniquet inflation, particularly in patients with concomitant cardiovascular diseases.
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Anesthesia and analgesia · Sep 2000
The safety of one, or repeated, vital capacity maneuvers during general anesthesia.
A vital capacity maneuver (VCM) (inflating the lungs to 40 cm H(2)O for 15 s) is effective in relieving atelectasis during general anesthesia or after cardiopulmonary bypass (CPB). The study was undertaken to investigate the safety of one or repeated VCM. Five groups of six pigs were studied. Two groups had general anesthesia for 6 h and one group received a VCM every hour. Three other groups received CPB. VCM was performed after CPB in two of these groups. VCM was then repeated every hour in one of the groups. Lung damage was evaluated by extravascular lung water (EVLW) measurement, light microscopy, and the half-time (T(1/2)) of disappearance from the lung of a nebulized aerosol containing (99m)Tc-DTPA. No changes were noted in extravascular lung water. The pigs subjected to VCM decreased their T(1/2). In the groups exposed to repeated VCM, T(1/2) remained lowered (CPB pigs) or decreased over time (non-CPB pigs). No lung damage could be seen on the morphology study. These results suggest that one VCM is a safe procedure. The increase in lung clearance of (99m)Tc-DTPA not associated with an increase in lung water when VCM is repeated may have been caused by an increase in lung volume. Therefore, repeated VCM also appears to be safe. ⋯ This study demonstrates in an animal model that inflating the lung once or repeatedly to the vital capacity is a safe procedure. This maneuver, also called the vital capacity maneuver, can be used to relieve lung collapse which occurs in all patients during general anesthesia.
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Anesthesia and analgesia · Sep 2000
Case ReportsGeneral anesthesia in a patient on long-term amphetamine therapy: is there cause for concern?
Amphetamines are powerful, sympathomimetic amines that, when used chronically, can profoundly effect a patient's cardiovascular stability during anesthesia and surgery. Amphetamines are the third most widely abused class of drugs in the United States. They also have legitimate medical use for attention deficit disorder with hyperactivity, exogenous obesity, and narcolepsy. We report a case of a patient with a 40-yr history of chronic amphetamine use having undergone two general anesthesias without complication.