Anesthesia and analgesia
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Anesthesia and analgesia · Jan 2001
Randomized Controlled Trial Comparative Study Clinical TrialMinimum local anesthetic volume blocking the femoral nerve in 50% of cases: a double-blinded comparison between 0.5% ropivacaine and 0.5% bupivacaine.
Recent studies demonstrated that ropivacaine was nearly 40% less potent than bupivacaine in the first stage of labor, but contrasting results have been reported. We, therefore, conducted a prospective, randomized, double-blinded study to determine the effects of the ropivacaine/bupivacaine potency ratio on the minimum volume of local anesthetic required to produce effective block of the femoral nerve in 50% of patients. Fifty adults premedicated with IV midazolam, 0.05 mg/kg, undergoing elective knee arthroscopy received femoral nerve blocks with a multiple-injection technique with a nerve stimulator (contractions of vastus medialis, vastus intermedius, and vastus lateralis were elicited with a 0.5-mA stimulating current). Patients randomly received either 0.5% ropivacaine (n = 25) or 0.5% bupivacaine (n = 25). The anesthetic volume was decided according to Dixon's up-and-down method, starting from 12 mL and being equally divided among the three elicited twitches. Successful nerve block was loss of pinprick sensation in the femoral nerve distribution with concomitant block of the quadriceps muscle within 20 min after injection, as assessed by a blinded observer. Positive or negative responses determined a 3-mL decrease or increase for the next patient, respectively. According to the up-and-down sequences, the minimum local anesthetic volume providing successful nerve block in 50% of cases was 14 +/- 2 mL in the ropivacaine group (95% CI: 12-16 mL) and 15 +/- 2 mL (95% CI: 13-17 mL) in the bupivacaine group (P: = 0.155). We conclude that the volume of 0.5% ropivacaine required to produce effective block of the femoral nerve in 50% of patients is similar to that required when using 0.5% bupivacaine. ⋯ Considering the risk for drug-related systemic toxicity, the equipotency ratio between ropivacaine and bupivacaine is crucial for daily practice. Despite the 40% reduction in the analgesic potency of ropivacaine reported during epidural analgesia for labor pain, results of this prospective, randomized, double-blinded study demonstrated that the same volume of 0.5% ropivacaine or 0.5% bupivacaine is required to produce an effective block of the femoral nerve in 50% of cases.
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Anesthesia and analgesia · Jan 2001
Randomized Controlled Trial Comparative Study Clinical TrialS(+)-ketamine for rectal premedication in children.
Our purpose for this prospective, randomized, and double-blinded study was to evaluate the anesthetic efficacy of S(+)-ketamine, an enantiomer of racemic ketamine, compared with a combination of S(+)-ketamine and midazolam, and plain midazolam for rectal premedication in pediatric anesthesia. Sixty-two children, ASA physical status I and II, scheduled for minor surgery, were randomly assigned to be given rectally one of the following: 1.5 mg/kg preservative-free S(+)-ketamine, a combination of 0.75 mg/kg preservative-free S(+)-ketamine and 0.75 mg/kg midazolam, or 0.75 mg/kg midazolam. Preoperative anesthetic efficacy was graded during a period of 20 min by using a five-point scale from 1 = awake to 5 = asleep. ⋯ Whereas the mask acceptance score was comparable in the three study groups, a 25% rate of complications during anesthesia induction via face was observed in the S(+)-ketamine study group (P < 0.05 versus other study groups). Our conclusions are that S(+)-ketamine for rectal premedication in the dose we chose shows a poor anesthetic effect and a frequent incidence of side effects during induction of anesthesia via face mask compared with the combination of midazolam/S(+)-ketamine and plain midazolam. Dose-response studies of S(+)-ketamine for rectal premedication in pediatric anesthesia may be warranted.
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Anesthesia and analgesia · Jan 2001
Randomized Controlled Trial Comparative Study Clinical TrialOndansetron is no more effective than supplemental intraoperative oxygen for prevention of postoperative nausea and vomiting.
Supplemental oxygen maintained during and for 2 h after colon resection halves the incidence of nausea and vomiting. Whether supplemental oxygen restricted to the intraoperative period is sufficient remains unknown. Similarly, the relative efficacy of supplemental oxygen and ondansetron is unknown. We tested the hypothesis that intraoperative supplemental oxygen reduces the incidence of postoperative nausea and vomiting. Patients (n = 240) undergoing gynecological laparoscopy were given a standardized isoflurane anesthetic. After induction, they were randomly assigned to the following three groups: routine oxygen administration with 30% oxygen, balance nitrogen (30% Oxygen group), supplemental oxygen administration with 80% oxygen, balance nitrogen (80% Oxygen group), and Ondansetron 8 mg (immediately after induction), combined with 30% oxygen, balance nitrogen (Ondansetron group). The overall incidence of nausea and/or vomiting during the initial 24 postoperative h was 44% in the patients assigned to 30% oxygen and 30% in the Ondansetron group, but only 22% in those given 80% oxygen. The incidence was thus halved by supplemental oxygen and was significantly less than with 30% oxygen. There were, however, no significant differences between the 30% oxygen and ondansetron groups, or between the ondansetron and 80% oxygen groups. We conclude that supplemental oxygen effectively prevents postoperative nausea and vomiting after gynecological laparoscopic surgery; furthermore, ondansetron is no more effective than supplemental oxygen. ⋯ Supplemental oxygen reduces the risk of postoperative nausea and vomiting (PONV) as well or better than 8 mg of ondansetron. Because oxygen is inexpensive and essentially risk-free, supplemental oxygen is a preferable method of reducing PONV.
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Anesthesia and analgesia · Jan 2001
Randomized Controlled Trial Comparative Study Clinical TrialNegative pressure rewarming vs. forced air warming in hypothermic postanesthetic volunteers.
We compared changes in core temperature and systemic heat balance with a new negative pressure/warming device (Vital Heat(R) ) that uses negative pressure combined with heat to facilitate warming in vasoconstricted postoperative patients to those resulting from passive insulation or forced air. Seven healthy volunteers were anesthetized and cooled to a tympanic membrane temperature near 34 degrees C. Anesthesia was discontinued and shivering was prevented by using meperidine. ⋯ Core temperature increased no faster with Vital Heat warming (1.3 +/- 0.4 degrees C) than with a cotton blanket (1.2 +/- 0.4 degrees C). In contrast, core temperature increased more rapidly with forced air warming (2.6 +/- 0.6 degrees C). In this study we show that calories from a negative pressure rewarming device are largely constrained to the forearm and that heat does not flow to the core thermal compartment.
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Anesthesia and analgesia · Jan 2001
Randomized Controlled Trial Comparative Study Clinical TrialShould the angiotensin II antagonists be discontinued before surgery?
Angiotensin II antagonists (AIIA) are part of a new rational treatment of hypertension. Because adverse circulatory effects during anesthesia can occur in patients chronically treated with angiotensin-converting enzyme inhibitors, some clinicians discontinue them at least 24 h before operation. No data are available concerning AIIA administration in patients scheduled for vascular surgery performed under general anesthesia. The aim of this prospective randomized study was to compare hemodynamics during induction of anesthesia in patients chronically treated with AIIA and those of patients not receiving this drug on the morning before operation. Thirty-seven patients chronically treated with AIIA for hypertension were randomly assigned to two groups: Group I: AIIA discontinued on the day before surgery (n = 18); Group II: AIIA given 1 h before anesthesia (n = 19). Patients received sufentanil 0.4 microg/kg, propofol 1.5 mg/kg, and atracurium 0.5 mg/kg. During the procedure, the anesthesiologist was required to maintain systolic blood pressure and heart rate within 30% of baseline values using intravascular fluid administration and vasoconstric- tors (e.g. , ephedrine, phenylephrine, or terlipressin). Hemodynamic variables were recorded each 1 min. Hemodynamic study ended at incision. The number and duration of hemodynamic events were collected, and total doses of vasoactive drugs were noted in each group. Systolic arterial pressure was significantly decreased in Group II at 5, 15 and 23 min after induction of anesthesia (*P < 0.05). In this group, the decrease in systolic arterial pressure was associated with more frequent episodes of hypotension (AIIA withdrawn: 1 +/- 1; AIIA given: 2 +/- 1; P < 0.01), with a larger number of patients developing at least 1 episode of hypotension (AIIA withdrawn: 12; AIIA given: 19; P < 0.01), and a longer duration of an episode of hypotension (AIIA withdrawn: 3 +/- 4 min; AIIA given: 8 +/- 7 min; P < 0.01), and an increased need for vasoactive drugs. In conclusion, blockade of the renin-angiotensin system increases the potential hypotensive effect of anesthetic induction. A severe hypotensive episode, requiring vasoconstrictor treatment, occurs after induction of general anesthesia in patients chronically treated with AIIA. Recommendations to discontinue AIIA drugs on the day before the surgery may be justified. ⋯ This prospective randomized study demonstrated that more severe hypotensive episodes, requiring vasoconstrictor treatment, occur after induction of general anesthesia in patients chronically treated with AIIA and receiving this drug on the morning before operation, in comparison with those in whom AIIA were discontinued on the day before operation. Recommendations to discontinue these drugs on the day before the surgery may be justified.