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We conducted this prospective randomized study to compare the success rate and the onset time between 3 intensities of stimulation threshold (0.5, 0.5-0.64, and 0.65-0.8 mA) when using a peripheral nerve stimulation at the midhumeral level.Sixty-nine adult patients undergoing elective hand surgery were studied. Blocks were performed using conventional nerve stimulation technique. Needle advance began at 2 mA (1 Hz, 0.1 millisecond). When motor response (MR) occurred at less than 0.5 mA, needle position was fixed for "group0.5 mA." For "group 0.5-0.64 mA," the needle was withdrawn until MR occurred at greater than 0.5 mA and disappeared at less than 0.5 mA. For "group0.65 mA," the needle was withdrawn until MR occurred at greater than 0.65 mA and disappeared at less than 0.65 mA. For each group, patients received 8 mL of ropivacaine 7.5 mg/mL on the 4 nerves (radial, median, ulnar, and musculocutaneous). Primary end point was the number of failed radial nerve sensory blocks at 30 mins.The time to perform the block was not different between the 3 groups (17 mins [SD, 7 mins] vs 13 mins [SD, 8 mins] and 13 mins [SD, 4 mins], respectively). The time required to obtain a complete sensory block was shorter for the 4 nerves in group0.5 mA, with a statistical significance for radial and musculocutaneous nerves in group0.5 mA versus group 0.5-0.64 mA and group0.65 mA. Patients in group0.5 mA had a greater success rate for complete sensory radial nerve compared with those of group 0.5-0.64 mA and group0.65 mA at any interval times between 5 and 30 mins (P = 0.0001). Supplemental local anesthesia was provided for the 3 groups more frequently for the median nerve, with no difference between groups. Group0.65 mA required 5 general anesthesias (20%) as compared with 1 (4%) in group0.5 mA (P0.05). No adverse event (dysesthesia) occurred after 48 hrs and 45 days.We conclude that intensity of stimulation influenced onset time and success rate.

Study objective: Carbicarb, sodium bicarbonate, and 5% dextrose were compared for effects on resuscitability in a canine model of electromechanical dissociation after ventricular fibrillation. Design/Interventions: 21 healthy mongrel dogs were anesthetized with pentobarbital, intubated, and mechanically supported. They were instrumented to measure heart rate, arterial pressure, pulmonary artery pressure, right atrial pressure, cardiac output, and arterial and mixed venous blood gases. The dogs were then subjected to a protocol that consisted of three successive CPR episodes. During each episode they were treated with repeated injections of one of the three substances, randomly chosen. After two minutes of ventricular fibrillation and four minutes of electromechanical dissociation, CPR was started with a thumper (rate, 60; duty cycle, 50%). If recovery was not obtained after five minutes of CPR, 1 mEq/kg carbicarb or sodium bicarbonate or 5 mL D5W was injected in the right atrium. Half the dose of the same substance was injected every five minutes thereafter; 1 mg epinephrine was also injected every five minutes until recovery. Hemodynamic and gasometric evaluations were performed five and 20 minutes after recovery. This later evaluation served as baseline for the next CPR episode. Measurements and main results: The duration and success rates of CPR are similar in the three CPR groups. Hemodynamic parameters were also similar during recovery. Bicarbicarb and sodium bicarbonate increased bicarbonate levels and corrected pH in the arterial and mixed venous blood. There was no difference in the blood gas values after carbicarb and sodium bicarbonate. Conclusion: In this model of cardiac arrest, carbicarb was not superior to sodium bicarbonate in the correction of metabolic acidosis during CPR.

While calcium administration has been recommended in CPR, its beneficial effects have been challenged. The effectiveness of calcium chloride was evaluated and compared with epinephrine during successive episodes of electromechanical dissociation (EMD) after ventricular fibrillation in closed-chest dogs. Each of three successive episodes of CPR was randomly and blindly treated by repeated (every 2 min) injections of 5 ml H2O plus either 500 mg of calcium chloride (CaCl2), 1 mg of epinephrine (Epi), or 5% dextrose (D5W). Of 42 CPR attempts performed on 16 dogs, 16 were reversed by only chest compression and artificial ventilation. For the 26 CPR with pharmacologic intervention, recovery was obtained after one injection in 5 of 6 Epi but only in 4 of 11 CaCl2 and 4 of 9 D5W. Only four CPR attempts were ultimately unsuccessful, all in CaCl2 group. During recovery, the Epi group showed significantly higher arterial pressures and heart rates but less severe acidemia. In this model, calcium chloride alone is ineffective during EMD.