Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Pediatric Anesthesia
Introduction Either cisatracurium (CIS) or rocuronium (ROC) may be used to facilitate intubation. The choice between these two blockers (NMBs) could be made on the basis of ease of intubation at a fixed time after administration or on the expected duration of block. We were interested in comparing block and intubation conditions after equipotent doses of CIS (0.1 mg/kg)  and ROC. (0.75 mg/kg)  and twice as much CIS (0.2 mg/kg) in children anesthetized with halothane.
Methods: Thirty children (23-69 mo) were studied after consent was obtained. All received midazolam 0.2-0.3 mg/kg IN (5-20 min) or 0.5-0.7 mg/kg PO (30-45 min) prior to inhalation of 70% N20-O2 and halothane up to 3%. After an intravenous catheter was inserted halothane was reduced to 2%.
The adductor pollicis (AP) electromyogram (EMG) was recorded by the Datex NMT monitor. During onset of block, the ulnar nerve was stimulated with a single supramaximal stimulus q10 sec by surface electrodes at the wrist. During recovery from block the stimulus frequency was 2 Hz for 2 sec q10 sec.
Patients whose anticipated duration of surgery exceeded one hour received 0.2 mg/kg of CIS. Age matched patients, whose surgery was expected to be less than one hour were randomly assigned to receive 0.1 mg/kg CIS or 0.75 mg/kg ROC. NMB was injected at the T-connector of the IV, 5.0 +/- 0.2 (4.0-5.8) min after beginning N2O/halothane. Ventilation was controlled with 1% halothane in N2O-O2 for 90 sec after injection of NMB. Then tracheal intubation was performed by one endoscopist. Intubation conditions were scored by the endoscopist, blind to the dose of NMB given and the level of block present. The incidence of excellent conditions, ie no movement, open glottis, was compared between groups with chi-square analysis. After intubation, anesthesia was maintained with 70% N2O, fentanyl as needed and 0.8% endtidal halothane.
The time from injection of NMB to 90% depression of EMG (B90), complete block (B100), and to recovery of the first response (T1) to 25% (T25) of initial baseline were recorded. These were compared with ANOVA and t-test with Bonferroni correction. Mean, SEM, and range are presented.
Results B90 and B100 were significantly shorter after ROC 0.75 than CIS 0.1. But there were no significant difference in B90 or B100 between ROC 0.75 and CIS 0.2. Neither was there a significant difference between the three groups in incidence of excellent intubation score (9 after CIS 0.2 and ROC, 8 after CIS 0.1). There was no significant difference between ROC and CIS 0.1 in T25. T25 after CIS 0.2 was significantly later than after CIS 0.1 by an average of 17.7 min.
Discussion Increasing the number of molecules of NMB delivered will result in a more rapid onset of block. Therefore block should occur faster after twice as much drug is given, or when an equipotent dose of a NMB of lesser potency is given. However, intubation conditions can be excellent when the AP is not blocked. During halothane anesthesia equipotent doses of CIS and ROC have the same duration. Doubling the dose of CIS increased duration by slightly more than its half-life. This is to be expected due to the linear plasma decay of CIS and potentiation by halothane. (Table 1)