mivacurium and Body-Weight

Burned patients are usually resistant to the neuromuscular effects of nondepolarizing relaxants, mostly because of receptor changes. The magnitude of the resistance is related to burn size and time after burn. Mivacurium is a muscle relaxant, degraded by plasma cholinesterase, whose enzyme activity is decreased in burns. The present study tested the hypothesis that burn-induced depressed plasma cholinesterase activity counteracts the receptor-mediated resistance, resulting in a lack of resistance to mivacurium.. Burned patients (n = 23), aged 2-12 yr, subclassified into burns of 10-30% or > 30% of body surface, were studied at < or = 6 days and again at 1-12 weeks after burn if possible. Thirteen additional patients served as controls. Neuromuscular variables monitored included onset and recovery following bolus dose, continuous infusion rates required to maintain 95 +/- 4% paralysis, and recovery rates following infusion.. The onset times of maximal twitch suppression were not different between burns and controls, but recovery to 25% of baseline twitch height was prolonged in patients with > 30% burn irrespective of time after injury. The continuous infusion rates to maintain twitch suppression at 95 +/- 4% were not different between groups. The recovery indices, including train-of-four to > 75%, 25-75%, or 5-95% in burned patients, were similar or prolonged compared with controls. The prolonged recovery in burned patients was inversely related to plasma cholinesterase activity (R2 = 0.86, r = -0.93, P < 0.001), and the decreased plasma cholinesterase activity was related to burn size and time after burn.. A normal mivacurium dosage (0.2 mg/kg) effects good relaxation conditions in burned patients, with an onset time similar to that in controls. This finding contrasts with the response seen with other nondepolarizing drugs, higher doses of which are required to effect paralysis. The decreased metabolism of mivacurium, resulting from depressed plasma cholinesterase activity, probably counteracts the receptor-mediated potential for resistance. Because succinylcholine is contraindicated in burned patients, larger doses of nondepolarizing agents are advocated to effect rapid onset of paralysis. This generalization does not hold for mivacurium. diatrics; plasma cholinesterase; relaxant resistance; succinylcholine, alternative to.)

Topics: Body Weight; Burns; Child; Child, Preschool; Cholinesterases; Electric Stimulation; Female; Humans; Infusions, Intravenous; Isoquinolines; Male; Mivacurium; Muscle Relaxation; Neuromuscular Nondepolarizing Agents; Ulnar Nerve

Preoperatively administered midazolam may contribute to postoperative sedation and delayed recovery from brief outpatient general anesthesia, particularly in patients who receive significant postoperative opioid analgesics. We evaluated the effects of midazolam premedication (0.04 mg/kg) on postoperative sedation and recovery times after laparoscopic tubal sterilization (Falope rings) in 30 healthy women in a randomized, double-blind, placebo-controlled study. Patients received midazolam or saline-placebo intravenously 10 min before anesthesia. General anesthesia was induced with fentanyl, propofol, and mivacurium and was maintained with N2O and isoflurane. Sedation was quantified before and after premedication and 15, 30, and 60 min after emergence from anesthesia, using the digit-symbol substitution (DSST) and Trieger dot (TDT) tests. Management of postoperative pain and nausea and discharge criteria were standardized. Groups were similar with respect to age, weight, and duration of surgery and anesthesia. Midazolam was associated with impairment of performance on the TDT and DSST after premedication administration and 15 (TDT and DSST) and 30 (DSST) min after postanesthesia care unit (PACU) arrival. There were no differences in PACU time and time to discharge-readiness. In conclusion, midazolam premedication augments postoperative sedation in this population but does not prolong recovery times.

Topics: Adult; Age Factors; Ambulatory Surgical Procedures; Analgesics, Opioid; Anesthesia Recovery Period; Anesthesia, Inhalation; Anesthesia, Intravenous; Anesthetics, Inhalation; Antiemetics; Body Weight; Double-Blind Method; Female; Fentanyl; Humans; Hypnotics and Sedatives; Injections, Intravenous; Isoflurane; Isoquinolines; Laparoscopy; Midazolam; Mivacurium; Nausea; Neuromuscular Nondepolarizing Agents; Nitrous Oxide; Pain, Postoperative; Patient Discharge; Placebos; Preanesthetic Medication; Propofol; Prospective Studies; Psychomotor Performance; Sterilization, Tubal; Time Factors

To compare the clinical effect of mivacurium in morbidly obese and normal-weight patients.. Ten morbidly obese patients (body mass index >40) and 10 normal-weight patients (body mass index, 21-24) with normal plasma cholinesterase levels. Anesthesia was provided with propofol and remifentanil in continuous infusion and a mixture of oxygen and nitrous oxide. Mivacurium was administered at a dose based on the patient's weight (0.15 mg x kg(-1)). The neuromuscular block was monitored by train-of-four (TOF) acceleromyography after stimulation of the cubital nerve at the forearm. We measured the onset time (time from administration of the muscle relaxant to 95% twitch depression), duration of block (times from dosing to 5% recovery after the first twitch [T1] of a TOF stimulus and to a TOF ratio of 80%), and the recovery indices (time between 25% and 75% recovery after T1 and between recovery of TOF ratios of 25% and 80%). Groups were compared with the Student t test.. Mean (SD) onset time was similar in the 2 groups (normal weight 2.73 [1] minutes vs morbidly obese 1.91 [0.6] minutes). Other measures of duration and recovery were also similar in the 2 groups, respectively: duration of dose-T1 5%, 12.23 (2.1) vs 11.45 (3) minutes; dose-TOF ratio 80%, 24.71 (4.6) vs 24.81 (5) minutes); recovery index T1 25%-75%, 6.45 (2) vs 5.56 (1) minutes; recovery of TOF ratio T1 25%-80%, 9 (2) vs 10.11 (2) minutes.. We found no differences in the clinical effect of mivacurium between morbidly obese and normal-weight patients when doses were based on real weight.

Topics: Adult; Body Weight; Female; Humans; Isoquinolines; Male; Mivacurium; Neuromuscular Nondepolarizing Agents; Obesity, Morbid; Time Factors

In vitro protein binding of several neuromuscular blocking agents (NMBAs) was measured by ultrafiltration in plasma from patients susceptible to demonstrate changes in their protein constituents. First, the relationship between the free fraction of atracurium and plasma lipoproteins levels in young volunteers (22-32 yr old, n = 6) and hyperlipidemic patients (44-68 yr old, n = 13) was studied, and second, the free fraction of atracurium, mivacurium, doxacurium, and vecuronium was determined in plasma of healthy young (27-47 yr old, n = 10), elderly (72-89 yr old, n = 11) and obese (21-57 yr old, n = 9, 200%-360% ideal body weight) patients scheduled for elective surgery. In hyperlipidemic patients, atracurium free fraction was significantly less than in young volunteers (40% +/- 5% vs 50% +/- 5%, mean +/- SD), and decreased as total cholesterol, low-density lipoprotein cholesterol and triglycerides increased (P < 0.05). In young individuals, NMBA free fraction was 25% +/- 5% for vecuronium, 58% +/- 8% for doxacurium, 52% +/- 6% for atracurium, and 72% +/- 3%, 70% +/- 3%, 70% +/- 4% for mivacurium trans-trans, cis-trans, and cis-cis isomers, respectively. Higher triglyceride concentrations in obese patients and lower high-density-lipoprotein cholesterol concentrations in both obese and elderly patients were observed when compared with young subjects. However, there was no significant difference in protein binding of NMBAs among these three groups. We conclude that, in otherwise healthy patients, age and weight are not likely to alter the free fraction of NMBAs.

Topics: Adult; Age Factors; Aged; Atracurium; Blood Proteins; Body Weight; Cholesterol; Female; Humans; Hyperlipidemias; Isoquinolines; Male; Middle Aged; Mivacurium; Neuromuscular Nondepolarizing Agents; Protein Binding; Triglycerides; Vecuronium Bromide