Neostigmine but not edrophonium prolongs the action of mivacurium.

PURPOSE: To examine the influence of anticholinesterase drugs neostigmine and edrophonium (which have different effects on plasma cholinesterase activity) administered for antagonism of neuromuscular block on the duration of action of mivacurium (a neuromuscular blocking drug metabolised by plasma cholinesterase). METHODS: This was a randomized study where mivacurium 0.15 mg.kg-1 was administered to a control group or after administration of neostigmine 40 micrograms.kg-1 or edrophonium 1 mg.kg-1 (n = 10 for each group) administered 10 min earlier for antagonism of atracurium-induced neuromuscular block. Neuromuscular block was measured by stimulation of the ulnar nerve in a train-of-four mode (TOF) and measuring the force of contraction of the adductor pollicis muscle. Baseline plasma cholinesterase activity was estimated before drug administration in all the groups and following anticholinesterase administration. RESULTS: The times to recovery of T1 (first response in the TOF) to 25 and 90% of control and of the TOF ratio to 0.7 after 0.15 mg.kg-1 of mivacurium were 47, 65 and 70 min in the neostigmine group; 25, 36 and 36 min in the edrophonium group and 17, 29 and 27 min respectively in the control group (P < 0.01). The plasma cholinesterase activity (PCHE) after neostigmine decreased from 6596 to 1959 U.L-1 (P < 0.001) but there was no change after edrophonium (6140 to 6396 U.L-1). CONCLUSIONS: The duration of action of mivacurium is prolonged by previous administration of neostigmine and this is most likely to be due to inhibition of PCHE activity.

Potency and time course of action of rocuronium during desflurane and isoflurane anaesthesia.

We have studied the potency and onset and duration of action of rocuronium in patients anaesthetized with 1 MAC of desflurane or isoflurane (in 66% nitrous oxide). Potency was estimated using the single bolus dose technique. Neuromuscular block was measured by stimulation of the ulnar nerve and recording the force of contraction of the adductor pollicis muscle. The ED50 and ED95 of rocuronium were estimated as 138 (95% confidence limits 117-162) micrograms kg-1 and 281 (241-328) micrograms kg-1, and 126 (105-151) micrograms kg-1 and 283 (236-339) micrograms kg-1 during desflurane and isoflurane anaesthesia, respectively. The mean times to onset of maximum block after rocuronium 0.6 mg kg-1 were 1.0 (SD 0.10) min and 1.1 (0.15) min, respectively, during anaesthesia with desflurane and isoflurane. The respective times to recovery of T1 (the first response in the train-of-four (TOF) stimulation) to 25% and 90% were 36 (8.3) min and 54 (15.4) min during desflurane anaesthesia and 31 (8.2) min and 45 (12.7) min during isoflurane anaesthesia. The times to recovery of the TOF ratio to 0.7 were 66 (13.4) min and 52 (16.3) min and the 25-75% recovery indices 14 (5.3) min and 10 (3.2) min, respectively, in the desflurane and isoflurane groups. There were no differences in the estimated potency or onset of action of rocuronium during desflurane and isoflurane anaesthesia. However, duration of action tended to be longer curing desflurane anaesthesia although only the differences in times to TOF ratio of 0.7 and the recovery indices were close to being significantly different (P = 0.0503 and 0.0560).

Duration of stabilization of control responses affects the onset and duration of action of rocuronium but not suxamethonium.

The effect of the duration of stabilization of control responses on the onset and duration of clinical relaxation of suxamethonium 1 mg kg-1 and rocuronium 0.6 mg kg-1 were investigated in 90 patients. The control responses were allowed to stabilize for 1, 5, 10, 15 or 20 min prior to administration of rocuronium and for 1, 5, 10 or 15 min prior to suxamethonium. The mean onset time for rocuronium decreased from 150 to 46 s as the duration of stabilization increased from 1 to 20 min (P < 0.001) although the maximal effect was observed within the first 5 min. The average duration of clinical relaxation also increased from 25 to 40 min (P < 0.001). No effect was observed for either variable in the case of suxamethonium.

A comparison of the effects of isoflurane and desflurane on the neuromuscular effects of mivacurium.

The effects of 1 MAC of desflurane and isoflurane (in 66% nitrous oxide) on the potency and duration of action of mivacurium were studied in 80 patients. The ED95 of mivacurium was 86 micrograms.kg-1 (74-100) and 88 micrograms.kg-1 (76-103) (mean and 95% confidence intervals) during anaesthesia with desflurane and isoflurane respectively. The onset and duration of recovery to 25, 75 and 90% of T1 (first response in the TOF) of 200 micrograms.kg-1 of mivacurium were 1.4 (0.3) and 1.5 (0.3) min (mean and SD), 22 (4.9) and 19 (4.0), 29 (6.6) and 26 (5.8), and 32 (7.3) and 29 (6.6) min respectively. There was no significant difference in any of the variables between desflurane and isoflurane. It is concluded that the neuromuscular effects of mivacurium are similar during anaesthesia with 1 MAC of desflurane and isoflurane.

Antagonism of mivacurium block with edrophonium from various degrees of spontaneous recovery.

Seventy adult patients received mivacurium 0.15 mg kg-1 during anaesthesia with thiopentone, nitrous oxide and 0.5% halothane. Neuromuscular block was monitored using mechanomyography and train-of-four stimulation. Edrophonium 0.75 mg kg-1 was administered 5 or 10 min after mivacurium, or when the first response in the TOF (T1) had recovered to 5, 10, 25 or 50% of control in groups of 10 patients each. A control group was allowed to recover spontaneously. The mean time taken from administration of mivacurium to attaining a TOF ratio of 0.7 was between 19.3 and 24.9 min in the groups given edrophonium, regardless of the time of administration, compared with 26.7 min in the spontaneous recovery group. The differences, however, were not significant among the groups showing little advantage in antagonizing mivacurium block.

Demography, ranging patterns, and activity budgets of black spider monkeys (Ateles paniscus chamek) in the Manu National Park, Peru.

Results of a long-term field study on the ecology and social organization of two groups of black spider monkeys (Ateles paniscus chamek) in Peru are reported. Demography, ranging patterns, and activity budgets provide insight into some of the proximate determinants of fission-fusion social organization in this species and illustrate the different strategies used by males and females to gain access to critical resources. Longitudinal data on known individuals provide evidence for male natal philopatry and female emigration at sexual maturity in this population. Interbirth intervals are long (mean = 34.5 months) in comparison with most other primate species, and 5 of 15 infants seen within a few days of birth died or disappeared before they were a year old. Home ranges are large (150-250 ha) and fairly discrete; overlap with neighboring groups is on the order of 10-15%. Males and females differed substantially in their ranging patterns; females, particularly those with infants, restricted much of their ranging to a "core area" 20-33% the size of the total group range, whereas males ranged more evenly over the entire area occupied by the group. Daily path length varied over almost an order of magnitude from 465 m to 4,070 m, with a mean of 1977 m. Males spent more time traveling and less time feeding than most females. These results are compared with those obtained in previous studies of Ateles and with similar data from other primate species to assess their implications for the evolution of fission-fusion sociality in spider monkeys. The ecological factors responsible for the evolution of very similar social organizations in spider monkeys and chimpanzees are discussed.