Anesthesiology
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The toxicity of mepivacaine in chronically instrumented nonpregnant and pregnant sheep was evaluated, and compared with data from previous studies of the toxicity of other local anesthetics. Thirteen preparations were studied, seven nonpregnant (NP) and six pregnant (P). Mepivacaine 2 mg.kg-1.min-1 was infused at a constant rate into the femoral vein until toxic manifestations occurred, in the following sequence: convulsions, hypotension, respiratory arrest, and circulatory collapse. ⋯ In contrast, the proportion of bound bupivacaine was 73% in NP and 51% in P, a significant difference. These protein binding data suggest that, although lethal concentrations of bupivacaine, determined in the previous study, were higher in NP than in P animals, concentrations of free drug were similar. Thus, the difference between the two drugs may be related to gestational increases in the availability of free drug in the case of bupivacaine.
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Randomized Controlled Trial Clinical Trial
Prolongation of succinylcholine block by metoclopramide.
Laboratory and clinical evidence of the inhibition of plasma cholinesterase by metoclopramide was demonstrated. When succinylcholine is used as the substrate and the product choline assayed by choline oxidase-peroxidase-quinone dye colorimetry, the rate of the choline production as optical density change was reduced to 50% by 19.5 X 10(-6) M metoclopramide at 20 degrees C. Prolongation of neuromuscular blockade produced by concurrent administration of succinylcholine and metoclopramide was studied in 22 patients aged between 18 and 40 years undergoing elective gynecological surgery. ⋯ Recovery times were again measured and found to be prolonged in patients receiving metoclopramide compared with those not receiving metoclopramide (P less than 0.05). Metoclopramide has no intrinsic neuromuscular blocking activity, but its ability to inhibit plasma cholinesterase probably is the mechanism by which it prolongs succinylcholine block. Reducing the dose of succinylcholine may be appropriate when metoclopramide is given concurrently.
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The frequency and severity of oxyhemoglobin desaturation was compared in 49 patients receiving epidural morphine, 5 mg (n = 21); patient-controlled analgesia (PCA) using meperidine (n = 20); or intramuscular (im) meperidine (n = 8) for postoperative analgesia following elective cesarean section performed with epidural anesthesia. Oxygen saturation (SpO2) was monitored for 24 h using a pulse oximeter; data were continuously collected and stored every 30 s via an interface connected to a computer. For analysis purposes, SpO2 was divided into five categories: 96-100%, 91-95%, 86-90%, 81-85%, and less than or equal to 80%. ⋯ PCA patients spent the longest cumulative time with SpO2 between 91 and 95%, 231 +/- 49 min (mean +/- SEM), compared with only 112 +/- 30 min and 152 +/- 42 min for the epidural and im groups, respectively (P less than 0.05 vs. epidural group). PCA patients also spent longest with SpO2 at 86-90% (19 +/- 10 min, vs. 6 +/- 3 and 0.5 +/- 0.3 min for the epidural and im groups, respectively), although this difference was not statistically significant. Severe desaturation episodes, defined as SpO2 less than or equal to 85% for more than 30 s, occurred in 71% of patients in the epidural group, 30% in the PCA group, and 63% in the im group (P less than 0.05 PCA vs. epidural and im).(ABSTRACT TRUNCATED AT 250 WORDS)
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Pharmacokinetics and blood concentrations of bupivacaine were studied after intercostal nerve blocks were performed intraoperatively using 1.5 mg.kg-1 in 11 neonates (age 0-28 days) and 11 infants between age 1 and 6 months. The study aimed to provide pharmacokinetic data that are limited in these age groups, and to identify any adverse effects of intercostal nerve block in infancy. Arterial blood samples were taken at 0, 5, 10, 15, 20, 30, 60, 120, 240, and 360 min. ⋯ Patients were further divided into those with acyanotic and cyanotic disease. Cyanotic infants were significantly heavier than acyanotic infants (P less than 0.05), but no other differences were demonstrated. No adverse effects resulting from the technique were identified.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Radial artery-to-aorta pressure difference after discontinuation of cardiopulmonary bypass.
To test whether the radial artery-to-aorta pressure gradient seen in some patients after cardiopulmonary bypass (CPB) is due to reduction in hand vascular resistance, the authors compared pressures in the ascending aorta with pressures in the radial artery before and after CPB in 12 patients. They increased hand vascular resistance by briefly occluding the radial and ulnar arteries at the wrist and recorded that effect on the radial artery-to-aorta pressure relationship. They also recorded the effect of wrist compression on radial artery pressures before and after CPB in 38 patients not having aortic pressure measurements. ⋯ After CPB, the radial artery and aortic SAPs were not statistically different (P greater than 0.05), but wrist compression restored the higher radial artery SAP. The mean arterial pressure (MAP) was equal in four patients and 1-3 mmHg higher or lower in eight patients before CPB, and wrist compression did not alter those relationships. After CPB, MAP was equal in four patients; radial MAP was 1-3 mmHg higher or lower in six patients, and 7 and 10 mmHg lower in the last two patients.(ABSTRACT TRUNCATED AT 250 WORDS)