Pretreatment with small-dose ketamine reduces predicted effect-site concentration of propofol required for loss of consciousness and Laryngeal Mask Airway insertion in women.

STUDY OBJECTIVE: To investigate the effect of small-dose ketamine on the predicted effect-site concentration of propofol required for loss of consciousness (LOC) and Laryngeal Mask Airway (LMA) insertion. DESIGN: Randomized, double-blinded study. SETTINGS: Operating room. PATIENTS: 50 ASA physical status 1 and 2 women scheduled for elective breast or gynecological surgery. INTERVENTIONS: Patients were randomly allocated to a ketamine group or a control group. Thirty seconds before propofol injection, ketamine group patients received ketamine 0.2 mg/kg, while control group patients received saline. Propofol was given in a target-controlled infusion and target blood concentration was gradually increased until LOC. The effect-site concentrations for attempting LMA insertion was predetermined by modifying Dixon's up and down method. LMA insertion was attempted without muscular blocking agents. MEASUREMENTS: Pain scores on propofol injection, effect-site concentrations at LOC, hemodynamic variables, and patient movement or side effects on LMA insertion were recorded. MAIN RESULTS: The effect-site concentration of propofol required for LOC was 2.14 µg/mL for the control group and 1.66 for the ketamine group (P = 0.0082). The predicted effect-site concentration of propofol alone at which 50% of patients did not move with LMA insertion (EC(50)LMI) was 3.59 µg/mL (95% CI: 3.18 ∼ 4.19 µg/mL). Pretreatment with ketamine 0.2 mg/kg decreased EC(50)LMI from 3.59 (3.18 ∼ 4.19) to 2.39 (1.22 ∼ 2.99). CONCLUSIONS: Pretreatment with ketamine 0.2 mg/kg reduced the propofol concentration required for both LOC (22%) and LMA insertion (33%) in women.

Xenon and nitrous oxide do not depress cardiac function in an isolated rat heart model.

PURPOSE: To examine the inotropic and chronotropic effects of xenon (Xe) and nitrous oxide (N2O) compared with nitrogen (N2) on isolated rat hearts. The differences between Xe and N2O were also compared. METHODS: The effects of Xe, N2O and N2 on coronary perfusion pressure (CPP), heart rate, left ventricular developed pressure (LVDP) and double product (DP) were examined in isolated rat hearts perfused at constant flow (10 mL x min(-1)). Following stabilization and baseline measurement with 95% O2 (plus 5% CO2), the heart was exposed to buffer equilibrated with one of three test gases; 50% N2 with 45% O2 (Group N2: n=9), 50% Xe with 45% O2 (Group Xe: n=9), or 50% N2O with 45% O2 (Group N2O: n=9) for 30 min. Measurements were performed in the last minute of exposure to the test gases. RESULTS: Gas exposure in all three groups decreased O2 delivery (-50%), CPP (-11%), LVDP (-30%) and DP (-44%) compared with baseline values (P <0.001). However, there were no differences among the groups. CONCLUSION: Our data suggest that cardiac contractility was decreased by the effects of reduced O2 delivery, but both Xe and N2O did not cause further cardiac depressant effects compared to N2 in this experimental model.

Intrathecal phentolamine increases blood flow and skin temperature in the hind limbs of dogs.

Spinal anesthesia with local anesthetics increases blood flow and skin temperature in the lower extremities. Although the effect of α2 adrenoceptor agonists on the spinal cord has been confirmed, there has been no such report of the effects of α-adrenoceptor antagonists. We studied the effects of intrathecal administration of phentolamine on the blood flow in the femoral artery and skin temperature in the hind limbs of seven dogs. One ml of 3% lidocaine (L group) or 1 ml of 0.1% phentolamine (P group) was injected into the intrathecal space. Blood flow significantly increased at 3 min in both groups, and no significant difference was observed between the groups at any phase. Pad skin temperature in the hind limbs increased significantly at 5 min in the L group and at 3 min in the P group (P<0.05). The only significant difference was observed at 30 min. High pad skin temperature continued for 60 min in the L group and for 90 min in the P group. With phentolamine i.v. (1 mg), there were no changes in blood flow in the femoral artery or pad skin temperature; there was only a decrease in blood pressure. In conclusion, the intrathecal α-adrenoceptor antagonist, phentolamine, increases blood flow in the femoral artery and pad skin temperature in hind limbs in dogs similar to lidocaine.