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Biomedical subjects

R S Weller

Publications and source records attributed to R S Weller.

6 recordsLinked to original sources
PubMed1995

Activation of the Bezold-Jarisch reflex in the sitting position for shoulder arthroscopy using interscalene block.

A retrospective analysis of 116 patients who underwent shoulder arthroscopy in the sitting position with interscalene block (ISB) revealed 20 patients who experienced potentially dangerous vasovagal events characterized by sudden severe hypotension and bradycardia (Group 1). The event occurred 61 +/- 18 min after the block placement. Ninety-six patients (Group 2) did not experience a vasovagal event. Of the patients in Group 2, 18 received beta-adrenergic blockers for increasing heart rate and/or arterial blood pressure (Group 2B) while 78 did not (Group 2A). The number receiving beta-adrenergic blockers was significantly greater than in Group 1 (18/96 vs 0/20, P < 0.05). There were no significant demographic or baseline hemodynamic differences between groups, but the beta-adrenergic blocker and vagal groups showed significantly greater intraoperative peak heart rates (P < 0.05). All patients received epinephrine in their local anesthetic for ISB, incision sites, and articular irrigating solution. Total and weight-corrected epinephrine doses differed significantly between groups (lowest in Group 2A, P < 0.01). Activation of the Bezold-Jarisch reflex, induced by increased circulating epinephrine levels and the sitting position, is the postulated mechanism.

Adult↗
PubMed1993

Nerve stimulator polarity and brachial plexus block.

To determine whether needle polarity significantly affects nerve stimulation during peripheral nerve block, we performed a randomized double-blinded study of 10 patients undergoing axillary block for upper extremity surgery. Using an insulated needle, we determined the minimum current necessary to elicit muscle contraction with positive and negative needle polarity at two needle placements: (A) where stimulation was first observed and (B) where stimulation was maximal. At Position A, stimulation required significantly more current when the needle was positive (2.32 +/- 0.45 mA, mean +/- SEM) than when it was negative (1.05 +/- 0.23 mA, P < 0.001). Similarly, at Position B, stimulation required more current when the needle was positive (1.49 +/- 0.49 mA) than when it was negative (0.47 +/- 0.15 mA, P < 0.001). The mean ratio of positive to negative threshold stimulation current at Position B (3.11 +/- 0.20) was significantly greater than that at Position A (2.37 +/- 0.19, P < 0.05). Our results emphasize the importance of attaching the negative terminal of the nerve stimulator to the stimulating electrode. Use of the positive terminal could lead to abandoning a block if stimulation were not obtained at a low enough current; alternatively, motor contraction might not be observed before neural contact or vascular puncture.

Adult↗
PubMed1991

Flumazenil antagonism of midazolam-induced ventilatory depression.

Flumazenil, a benzodiazepine antagonist, reliably reverses midazolam-induced sedation; however, its effect on respiratory depression has not been established completely. Twelve healthy volunteers received sufficient midazolam (0.13 +/- 0.01 mg.kg-1 mean +/- SE) to render them unresponsive to verbal command; they then received flumazenil 1.0 mg or placebo (flumazenil vehicle) in a randomized, double-blind fashion. Ventilatory drive was measured before and after administration of midazolam, as well as 3, 30, 60, and 120 min after administration of flumazenil or placebo. Seven to 30 days later, the study was repeated, with subjects receiving placebo or flumazenil (whichever they had not received during their first trial). Midazolam caused significant decreases in the slope of the CO2 response (-29 +/- 5%; P less than 0.005); minute ventilation (VE) at end-tidal CO2 tension (PETCO2) = 46 mmHg (-28 +/- 4%; P less than 0.001), and tidal volume at PETCO2 = 46 mmHg (-44 +/- 4%; P less than 0.005). Three minutes after intravenous administration of flumazenil 1.0 mg, VE46 and tidal volume increased to 108 +/- 6% and 105 +/- 6%, respectively, of their premidazolam values; at the same time after administration of placebo, VE46 and tidal volume remained significantly depressed (between groups, P less than 0.005 for each variable). Thirty minutes later, these variables did not differ between groups, probably because the effects of flumazenil and midazolam were diminishing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Ibuprofen provides longer lasting analgesia than fentanyl after laparoscopic surgery.

The authors compared the analgesic efficacy of one dose of oral ibuprofen with that of intravenously administered fentanyl for relief of pain after outpatient laparoscopic surgery. Thirty healthy female patients received either 800 mg of oral ibuprofen preoperatively or 75 micrograms of intravenous fentanyl intraoperatively plus respective intravenous or oral placebos in a randomized, double-blind manner. Patients recorded their degree of pain and nausea in the recovery room, in the same-day surgery stepdown unit, during the ride home, and upon arrival at home. The postanesthesia care nurse recorded the amount of fentanyl and droperidol needed to treat pain and nausea in the recovery room. Patients who received ibuprofen were more comfortable in the stepdown unit (P less than 0.05) and after arrival home (P less than 0.05) than those in the fentanyl group. Additionally, patients who received ibuprofen had lower nausea scores in the step-down unit (P less than 0.05); this may have been related to the lower total fentanyl dose in these patients. The authors conclude that ibuprofen may be a useful alternative to fentanyl for providing postoperative analgesia for outpatient surgery.

Administration, Oral↗
PubMed1988

A response algorithm for the low-pressure alarm condition.

A response algorithm consists of a logical sequence of maneuvers to be performed in response to a specific condition. With the advent of alarm-equipped monitors that alert anesthesiologists to the presence of potentially hazardous clinical conditions, a need has arisen to develop the corresponding alarm-oriented responses expected from anesthesiologists; this problem, however, has not been satisfactorily addressed in the literature. An algorithm is proposed that guides the anesthesiologist through the three limbs of the ventilation system--gas supply system, breathing circuit, and mechanical ventilator--in response to a low-pressure alarm condition during automatic mechanical ventilation. The three-limbed algorithm rapidly and efficiently localizes the likely cause of the low-pressure condition without compromising patient safety; in the event that the search for a cause is fruitless, a default mode of ventilation is employed. A discussion is provided of common causes (e.g., disconnections), alarm-defeating circumstances (false negatives), and potential algorithm-defeating situations (multiple faults).

Algorithms↗