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UNLABELLED We enrolled nulliparous women in induced labor in a randomized study to determine whether increasing the concentration of the solution used in a patient-controlled epidural analgesia (PCEA) device was required as labor progressed. Patients were assigned to 6 groups (n = 25 in each group), receiving ropivacaine/fentanyl in concentrations of either 0.1%/0.5 microg/mL or 0.2%/1 microg/mL via a PCEA pump. Three groups received boluses of 12, 16, or 20 mL dilute solution in early labor (uterine contractions every 3 min and 4-cm cervical dilation) then 6, 8, and 10 mL concentrated solution in late labor. Three other groups received boluses of 12, 16, or 20 mL dilute solution during both periods. The lockout interval was 25 min. The primary outcome was time until the first request for staff-administered analgesia supplement. Hourly assessments included pain scores on a visual analog scale (VAS) graded from 0 to 10, satisfaction scores, arterial blood pressure, motor block intensity, and the upper sensory level of epidural anesthesia. Patients, midwives, and the observer were unaware of study solutions and PCEA settings. The maximum pain score was defined as the highest score experienced by each patient during each period. Duration of analgesia was defined as the time from the start of each period to the first injection of rescue analgesia and was compared using a survival analysis. There were no differences among the groups with regard to demographic and obstetric variables, arterial blood pressure, motor block intensity, upper sensory level, or satisfaction scores. At least 75% of the women rated their satisfaction as either good or excellent during each period. During late labor, the maximum pain score was lower in the group receiving 20 mL dilute solution compared with the group receiving 6 mL concentrated solution. Maximum pain score was not significantly different between 20 mL dilute solution and 10 mL concentrated solution (difference between VAS values = -0.4; 95% confidence limits, -1.599 and 0.799; P = 0.5055). During late labor, the duration of analgesia was longer in groups receiving 20 mL dilute solution (99 +/- 4 min) (mean +/- SD) than in those receiving 12 mL (77 +/- 30 min) and 16 mL (80 +/- 23 min). Duration of analgesia did not differ between groups receiving 20 mL and 10 mL (92 +/- 23 min) or between groups receiving 12 mL and 6 mL (78 +/- 30 min) of each respective solution. Duration of analgesia was longer in the groups receiving 8 mL concentrated solution (94 +/- 16 min) than in those receiving 16 mL dilute solution. We concluded that 0.1%/0.5 microg/mL ropivacaine/fentanyl was effective throughout labor when 20 mL was injected with each PCEA demand. With 16 mg ropivacaine and 8 microg fentanyl, the duration of analgesia was prolonged by doubling the concentration when labor became active. When 12 mg ropivacaine and 6 microg fentanyl were injected at each demand, analgesia was less satisfactory and doubling the concentration was not clinically effective. These results suggest that the effectiveness of PCEA is dependent on drug mass rather than the volume or concentration administered with each successful pump demand. IMPLICATIONS There is no clinical reason for increasing the concentration of the patient-controlled epidural analgesia (PCEA) solution when labor becomes active provided that an effective dose is already being administered with each demand. The quality of PCEA depends on the drug mass given with each demand rather than the concentration of the pump solution.

UNLABELLED To determine the minimal sufentanil concentration required to improve the quality of patient-controlled epidural analgesia during labor, we compared the efficacy of a combination of 0.125% bupivacaine with 1:800,000 epinephrine and different concentrations of sufentanil in a double-blinded randomized study. Concentrations were no sufentanil (n = 66), 0.078 microg/mL sufentanil (n = 65), 0.156 microg/mL sufentanil (n = 65), 0.312 microg/mL sufentanil (n = 65), and 0.468 microg/mL sufentanil (n = 67). The patient-controlled epidural analgesia setting was a 12-mL bolus dose and a 25-min lockout interval. Pain was scored at 5-6 cm, 7-8 cm, and full cervical dilation by using a 10-cm visual analog scale. At full cervical dilation, the pain scores were lower in the groups receiving a solution of at least 0.156 microg/mL sufentanil. Few differences were observed when using the larger concentrations, except for increased pruritus intensity. The duration of labor and the mode of delivery were similar in each group. Rescue analgesia, which consisted of 6 mL of 0.25% bupivacaine, was infrequent and comparable between groups. The use of the pump did not differ between groups. Adding a small concentration of sufentanil to 0.125% bupivacaine for patient-controlled epidural analgesia during labor improved the quality of analgesia but did not modify the bupivacaine requirement. Reducing the sufentanil concentrations to 0.156 microg/mL decreased the pruritus intensity without reducing analgesia. IMPLICATIONS Adding a small concentration of sufentanil to 0.125% bupivacaine for patient-controlled epidural analgesia during labor improved the quality of analgesia but did not modify the bupivacaine requirement. Reducing the sufentanil concentrations to 0.156 microg/mL decreased the pruritus intensity without reducing analgesia.

Most studies use a bolus size of

Clonidine is commonly given for premedication, and it impairs normal thermoregulatory responses to warm and cold stimuli while depressing sympathetic tone.We studied the effect of premedication by clonidine on redistribution hypothermia induced by the induction of anesthesia. Sixteen ASA physical status I or II patients were randomly assigned to receive either clonidine 150 [micro sign]g or a placebo. Anesthesia was induced 45 min later by thiopental, fentanyl, and vecuronium IV and was maintained by the administration of 0.6% isoflurane. We monitored central core (tympanic) temperature and skin surface temperatures at the forearm and the fingertip during the 2 h after the induction of anesthesia before surgery. We estimated skin blood flow at the level of the forearm by using laser Doppler during the same period. The core temperature decreased comparably in the two groups of patients, from 37.1 +/- 0.2[degree sign]C to 35.3 +/- 0.4[degree sign]C and from 37.1 +/- 0.2[degree sign]C to 35.5 +/- 0.3[degree sign]C in the clonidine and placebo groups, respectively. The forearm-fingertip surface temperature gradient decreased similarly in the two groups. There was no evidence of cutaneous vasoconstriction. The laser Doppler index at the fingertip increased similarly in the two groups, as did the forearm-fingertip temperature gradient. We conclude that premedication with clonidine does not significantly impair the profile of central hypothermia induced by heat redistribution after the induction of anesthesia. Implications: The induction of general anesthesia is associated with redistribution hypothermia. This study shows that premedication with oral clonidine does not worsen the decrease in core temperature resulting from general anesthesia. (Anesth Analg 1998;87:168-72)

The incorporation of local anesthetics into injectable polymer microspheres can be useful in providing prolonged regional effects.This randomized study was designed to compare the effects of bupivacaine and bupivacaine-loaded microspheres on the time course of motor block in rabbits injected epidurally. Bupivacaine-loaded microspheres and drug-free microspheres 1-10 micro meter in size were devised from poly-d,l-lactic acid by using a solvent evaporation/extraction method. The effects of bupivacaine and of similar amounts of bupivacaine-loaded microspheres were studied in 26 rabbits as follows: 0.9% sodium chloride, followed by drug-free microspheres, then 1.25 mg of bupivacaine and 1.25 mg of bupivacaine-loaded microspheres (Group I; n = 8); 2.5 mg of bupivacaine, then 2.5 mg of bupivacaine-loaded microspheres (Group II; n = 8); and 5 mg of bupivacaine and 5 mg of bupivacaine-loaded microspheres (Group III; n = 10). Motor block was evaluated blindly by observation of walking disturbances, using a scale from 0 (free movements) to 3 (total limb paralysis). A period of 3 days elapsed between each injection. No limitation on movements was observed after 0.9% sodium chloride and drug-free microsphere injection. With 5 mg, both bupivacaine solutions provided complete motor block which was significantly more prolonged (+244% +/- 129%, mean +/- SD) with bupivacaine-loaded microspheres than bupivacaine. With 2.5 and 1.25 mg, block intensity was less marked, and block duration was shorter after administration of bupivacaine-loaded microspheres than after bupivacaine. We concluded that blocks resulting from bupivacaine-loaded microspheres are highly influenced by the amount of drug initially released by the polymer. (Anesth Analg 1995;81:519-24)

Short-term infusion of nicardipine can be used to induce deliberate hypotension but may result in plasma drug accumulation. To assess long-term nicardipine administration for deliberate hypotension in 10 patients in a moderately hemodiluted state who were undergoing spinal surgery, hemodynamics and plasma nicardipine concentrations were concomitantly measured before and 20, 80, and 140 min after starting nicardipine, at drug discontinuation, and 20 and 80 min later. A dose of 6.2 +/- 0.9 mg (mean +/- SEM) of nicardipine was initially required to obtain mean arterial blood pressures at 55-60 mm Hg. Maintenance doses of nicardipine were 3-5 mg/h. The duration of nicardipine administration was 270 +/- 20 min (mean +/- SEM). Hypotension was associated with decreased systemic and pulmonary vascular resistances, increased cardiac index, and decreased arteriovenous difference in O2 contents. Only two patients required homologous blood transfusion. Plasma nicardipine concentrations peaked at 110 +/- 21 ng/mL (mean +/- SEM) and then decreased to 38 +/- 11 ng/mL (mean +/- SEM) without changes in arterial blood pressure. After vasodilator discontinuation, hypotension was observed during a mean time of 43 min (range 27-88 min) despite plasma concentrations less than 20 ng/mL. No relationship was found between plasma nicardipine concentrations and hemodynamics. These findings suggest that an increasing effect of nicardipine over time may occur during prolonged administration. Because the reasons for this hysteresis remain unclear, use of nicardipine infusion during major surgery and anesthesia requires particular caution.

Catecholamine and renin-angiotensin responses to enflurane- or isoflurane-hypotensive anesthesia were compared in a randomized study. Two groups of 10 patients undergoing total hip arthroplasty were premedicated with morphine hydrochloride (0.1 mg/kg). Anesthesia was induced with thiopental and the trachea intubated after pancuronium. Equal concentrations of each volatile agent (1.3 MAC) were administered until mean arterial blood pressure decreased to 50-60 mm Hg. Hemodynamic data and blood samples for measurements of plasma renin activity (PRA) and plasma epinephrine (E) and norepinephrine (NE) concentrations were collected 1) after induction and intubation but before the start of isoflurane or enflurane; 2) 15 min (T15) after the start of isoflurane or enflurane administration; and 3) 45 min (T45) after the start of isoflurane or enflurane administration. The desired level of hypotension was achieved at T15 with isoflurane and at T45 with both anesthetics. When hypotension was achieved, cardiac index and stroke index were significantly lower in the enflurane group while systemic vascular resistance index was lower in the isoflurane group. Increases in E and NE levels above baseline levels were significantly greater in the isoflurane group than in the enflurane group. Use of isoflurane to induce hypotension is associated with more rapid induction of hypotension, less depression of cardiac output, and better preservation of homeostatic responses than is use of enflurane.