Anesthesia and analgesia
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Anesthesia and analgesia · Aug 1997
Comparative StudyLaser Doppler skin blood flow and sympathetic nervous responses to surgical incision during halothane and isoflurane anesthesia.
The aim of the present study was to evaluate whether a sudden decrease in skin blood flow measured using a laser Doppler velocimeter reflects sympathetic nervous response to surgical skin incision during halothane (n = 17) and isoflurane (n = 16) anesthesia in 33 ASA physical status I or II patients scheduled for laparotomy. Plasma norepinephrine concentrations in the responding patients who showed a sudden decrease in the skin blood flow after surgical incision increased significantly and continued to increase 1-10 min after skin incision under halothane and isoflurane anesthesia. Although plasma norepinephrine concentrations in the nonresponders did not increase after surgical incision with halothane, the concentrations increased significantly at 1 min, but not at 3 and 10 min, after skin incision with isoflurane. ⋯ Plasma epinephrine concentration increased during skin incision, but the concentrations did not differ between the patients with and without a sudden decrease in skin blood flow. Increases in systolic blood pressure and rate-pressure product on skin incision were also significantly more in patients with skin blood flow response compared with those without the response. The magnitude of changes in plasma norepinephrine concentration and hemodynamic variables with skin incision was greater with isoflurane than with halothane at the same minimum alveolar anesthetic concentration level.
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Anesthesia and analgesia · Aug 1997
Comparative StudyRadial artery diameter decreases with increased femoral to radial arterial pressure gradient during cardiopulmonary bypass.
A clinically significant femoral to radial artery pressure gradient sometimes develops during cardiopulmonary bypass (CPB), but the mechanism responsible is not clear. We investigated when the pressure gradient developed and what mechanism could be responsible by comparing mean femoral to mean radial artery pressure and radial artery diameter in 75 male patients undergoing coronary artery bypass grafting. A pressure gradient > or =5 mm Hg (High-P) occurred in 38 patients, and the remaining 37 patients had pressure gradients <5 mm Hg (Low-P) at sternal closure. In High-P group, the pressure gradient was significantly greater (4.8 +/- 3.1 vs 1.0 +/- 3.1 mm Hg; P < 0.001) than in Low-P group, and the ratio of radial artery diameter to the diameter after induction of anesthesia was significantly decreased (0.79 +/- 0.12 vs 0.87 +/- 0.14; P = 0.006) at 5 min after aortic clamping. The pressure gradient and the arterial diameter changes persisted until sternal closure. There was a negative linear correlation between the pressure gradient (deltaP) and the radial artery diameter ratio (D) at sternal closure (D = -15.0deltaP + 16.6, r = 0.39, P < 0.001). In a subgroup of 11 High-P patients, palm temperature was significantly lower (P < 0.05) than that of 11 Low-P patients during and after CPB. We conclude that the femoral to radial artery pressure gradient develops by 5 min after aortic clamping during CPB and persists until sternal closure, and that radial artery constriction could be responsible for the pressure gradient. ⋯ A femoral to radial pressure gradient has been observed after cardiopulmonary bypass. Arterial vasodilation and vasoconstriction have been considered as causes for this gradient. We measured radial artery diameter using pulsed Doppler ultrasound and examined radial artery vasodilation versus vasoconstriction as possible mechanisms for the pressure gradient.
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Anesthesia and analgesia · Aug 1997
Does the platelet-activated clotting test (HemoSTATUS) predict blood loss and platelet dysfunction associated with cardiopulmonary bypass?
Platelet dysfunction is a major cause of bleeding after cardiopulmonary bypass (CPB). No timely, simple, point-of-care determinant of platelet function is available for clinical use. Adding platelet-activating factor to conventional activated clotting time methods (platelet-activated clotting test [PACT]) (HemoSTATUS; Medtronic, Inc., Parker, CO) produces rapid results (<3 min) and may yield a measure of platelet responsiveness and whole blood procoagulant activity. ⋯ The PACT had a sensitivity and specificity comparable to routine laboratory coagulation tests in predicting blood loss. The TEG maximum amplitude, however, was more predictive than both the PACT and routine coagulation tests in this respect. The PACT may be a useful indicator of platelet responsiveness or whole blood procoagulant activity, but we did not find it superior to other tests of coagulation function for predicting excessive blood loss after CPB.
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Anesthesia and analgesia · Aug 1997
Structure-affinity relationships and stereospecificity of several homologous series of local anesthetics for the beta2-adrenergic receptor.
Local anesthetics inhibit binding of ligands to beta2-adrenergic receptors (beta2ARs), and, as a consequence, inhibit intracellular cAMP production. We hypothesized that among homologous local anesthetics, their avidity at inhibiting binding of tritiated dihydroalprenolol (3H-DHA) to beta2ARs would increase with increasing length of alkyl substituents and would demonstrate stereospecificity. Specific binding of 3H-DHA to human beta2ARs was assayed in the presence of six different members of the 1-alkyl-2,6-pipecoloxylidide class of local anesthetics (including mepivacaine, ropivacaine, and bupivacaine), the R(+) and S(-) bupivacaine enantiomers, lidocaine, prilocaine, etidocaine, procaine, and tetracaine. Avidity of binding to beta2ARs increased with increasing length of the alkyl chain (pKi values = 2.4, 3.6, 4.3, 4.1, 4.1, 5.9 for the methyl [mepivacaine], ethyl, S(-)propyl [ropivacaine], butyl [bupivacaine], pentyl, and octyl derivatives, respectively). We found no evidence for bupivacaine stereospecificity (pKi values = 4.3 and 4.9 for the S(-) and R(+) isomers, respectively). Other amide and ester local anesthetics also showed increasing potency with increasing length of alkyl substituents (pKi values = 3.6, 3.8, and 4.3 for lidocaine, prilocaine, and etidocaine; 4.2 and 5.6 for procaine and tetracaine, respectively). The correlation between increased inhibition of beta2AR binding and alkyl chain length resembles the correlation between local anesthetic potency at nerve block and increased alkyl chain length. The lack of clear stereospecificity is consistent with the relatively low potency these agents demonstrate at inhibition of beta2AR binding. Finally, the relatively potent inhibition of beta2ARs by etidocaine, tetracaine, and bupivacaine suggests that their propensity for cardiovascular depression after accidental intravenous overdose could result from beta2AR or beta1AR blockade and inhibition of cAMP production. ⋯ Local anesthetics demonstrate a rank order of avidity for displacing ligands from beta2-adrenergic receptors such that larger molecules displace ligands at lower concentrations than smaller local anesthetic molecules. This relationship between molecular size and receptor avidity could explain the greater propensity for cardiovascular toxicity of relatively large local anesthetics such as bupivacaine.
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Detection of the intravascular placement of epidural catheters is an important but difficult task. In this study, we evaluated maternal and fetal hemodynamic responses to intravenous (i.v.) and epidural injection of isoproterenol (ISO), a proposed chronotropic test dose, in gravid ewes. Near-term, chronically instrumented, gravid ewes with single fetuses were studied at least 48 h after surgery. ⋯ However, ISO seems to be rapidly absorbed from the epidural space. Identifying the source of maternal tachycardia after epidural injection of a large dose of ISO could be difficult. If the absence of histopathological change is confirmed, ISO represents an alternative to EPI as a chronotropic test dose.