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Tracheal Intubation with Rocuronium Using the "Timing Principle

1998, Anesthesia & Analgesia

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This study evaluates the intubating conditions after administering rocuronium using the timing principle and compares them with succinylcholine. Forty-five ASA physical status I or II patients were randomized into three groups: rocuronium (0.6 mg/kg) for 45 s, rocuronium for 60 s, and succinylcholine (1.5 mg/kg). Excellent to good intubating conditions were achieved with rocuronium at 45 and 60 s, similar to that of succinylcholine. The findings suggest the timing principle with rocuronium is an effective alternative to succinylcholine for intubation.

Tracheal Intubation with Rocuronium “Timing Principle” Thomas J. Sieber, MD*, Alex M. Zbinden, George D. Shorten, MDt MD*, Michele Using the Curatolo, MD*, *Department of Anesthesia and Intensive Care, University Hospital Bern, Bern, Switzerland; Anesthesia and Intensive Care, Beth Israel Hospital, Boston, Massachusetts We compared the endotracheal intubating conditions after rocuronium, using the “timing principle,” with those after succinylcholine. The timing principle entails administration of a single bolus dose of nondepolarizing muscle relaxant, followed by an induction drug at the onset of clinical weakness. Forty-five patients were randomly assigned to three groups. Patients allocated to Groups 1 and 2 received rocuronium 0.6 mg/kg. At the onset of clinical weakness (onset of ptosis), anesthesia was induced with thiopental4-6 mg/kg; intubation was accomplished after 45 s in Group 1 and after 60 s in Group 2. Patients in Group 3 received vecuronium (0.01 mg/kg) 3 min before the administration of thiopental and succinylcholine 1.5 mg/kg, and their tracheas were intubated 60 s later by a blind anesthesiologist. Intubating conditions were assessed according to a 0 of the ideal muscle relaxant is a rapid onset of action. Succinylcholine reliably produces muscle relaxation within 60 seconds of its administration, but it can produce serious side effects (l-5) and is contraindicated in certain patients (6). Different techniques that have been used to decrease the effective onset time of nondepolarizing muscle relaxants include priming (7) and the administration of large doses (8). Recently, a technique that uses the “timing principle” has been applied to rapidly produce good intubating conditions with vecuronium (9,lO) and atracurium (11). When this technique is used, a single bolus dose of a muscle relaxant is administered, and anesthesia is induced at the onset of clinical weakness. In this way, the time from the induction of anesthesia to complete muscle relaxation is reduced, and the peak effect of the muscle relaxant and IV induction drug may more closely coincide. ne characteristic Accepted for publication February 4, 1998. Address correspondence to Thomas J Sieber, MD, Department Anesthesia and Intensive Care, Inselspital, 3010 Bern, Switzerland. Address e-mail to [email protected]. 01998 by the International 0003-2999/98/$5.# Anesthesia Research of and and tDepartment of grading scale and were either good (5 patients in Groups 1 and 2,4 patients in Group 3) or excellent (10 patients in Groups 1 + 2,11 patients in Group 3) in all patients. Patients were interviewed postoperatively, and all were satisfied with the induction of anesthesia. We conclude that rocuronium 0.6 mg/kg provides good to excellent intubating conditions 45 and 60 s after the induction of anesthesia using the timing principle. Implications: We compared the ease with which a breathing tube could be placed in patients using three techniques. The standard technique (succinylcholine) was compared with two others in which a musclerelaxing drug (rocuronium) was administered just before the anesthetic drug (so-called timing principle). No difference among the techniques was observed. (Anesth Analg 1998;86:113740) Rocuronium is a steroidal nondepolarizing muscle relaxant with an onset time (after 3-4 x the 95% effective dose) not different from that of succinylcholine (12-16). In a prospective, randomized, double-blind clinical trial, we evaluated the intubating conditions 45 and 60 s after the induction of anesthesia using rocuronium with the timing principle, and compared them with those after the administration of succinylcholine 60 s after the induction of anesthesia. Methods With institutional ethical committee approval, and after having obtained written, informed consent from each, 45 ASA physical status I or II patients (18-70 yr) undergoing elective surgical procedures were studied. Exclusion criteria were: increased risk of pulmonary aspiration, neuromuscular disease, medications known to influence neuromuscular function, anticipated difficulty with airway management, and contraindications to succinylcholine. The usual monitoring was used. Neuromuscular function was measured using accelerography (TOFGuard@; Organon Teknika, Durham, NC). Patients Society Anesth Analg 1998;86:113740 1137 1138 SIEBER ET AL. ROCURONIUM AND THE “TIMING ANESTH ANALG 1998;86:113740 PRINCIPLE” were informed that they might feel weak before going to sleep. All patients received midazolam (l-3 mg) and fentanyl (1 pg/kg) IV on arrival in the operating room. Patients were randomly assigned to one of three groups: rocuronium 45s (Group l), rocuronium 60s (Group 2), and succinylcholine (Group 3). Cutaneous electrodes were placed for measurement of the trainof-four (TOF) response of the first dorsal interosseous muscle of the hand to stimulation of the ulnar nerve. Patients allocated to Groups 1 and 2 received rocuronium (0.6 mg/kg) administered over 5 s through a rapidly running infusion placed in the forearm. Patients were asked to keep their eyes widely open as long as possible and were closely observed for the first signs of weakness, specifically the onset of ptosis (i.e., furrowing of the forehead, which indicates that the occipitofrontalis muscle is being used to compensate for neuromuscular weakness of the levator palpebrae superioris muscle). At this time, thiopental (46 mg/kg) was administered IV. TOF monitoring was commenced on loss of the eyelid reflex. Supramaximal square wave stimuli were applied to the ulnar nerve at 2 Hz for 2 s (i.e., TOF stimulation). This was repeated at 10-s intervals until no response was detected. After the administration of thiopental (45 s in Group 1 or 60 s in Groups 2 and 3), the TOF count was recorded, and tracheal intubation was performed by an experienced anesthesiologist unaware of the group to which the patient belonged. This person was waiting outside the induction area and did not enter until the patient was ready for intubation. Intubating conditions were assessed according to a previously described grading scale (Table 2) (9). In addition, a second blind observer observed the abdomen for evidence of diaphragmatic response to endotracheal intubation. On capnographic confirmation of correct tube placement, controlled positive pressure ventilation was commenced using 70% nitrous oxide in oxygen (6 L/min fresh gas flow) and isoflurane (inspired concentration l%-1.5%). Patients in Group 3 (succinylcholine) were treated according to the protocol described for those in Groups 1 and 2 with the following exceptions. Three minutes after the administration of a defasciculating dose of vecuronium (0.01 mg/kg), thiopental (4-6 mg/kg) and succinylcholine (1.5 mg/kg) were administered in succession over 5 s. Sixty seconds after administration of thiopental, tracheal intubation was performed. TOF monitoring was not performed in Group 3. All patients were interviewed by the investigator (nonblinded) 4-24 h after the surgical procedure. Four questions were asked: 1. Did you feel weak immediately sleep for your operation? before going to 2. Did you feel short of breath immediately before going to sleep for your operation? 3. Do you have muscle pains now? 4. If you were to have an operation in the future, would you choose to be put to sleep in a different way? Age, body weight, sex, thiopental doses (all three groups), and time to clinical onset of neuromuscular blockade (Groups 1 and 2 only) were compared by using one-way analysis of variance when data were normally distributed; otherwise, the Kruskal-Wallis one-way analysis of variance on ranks was used. Normality of distribution of the data was checked by using the Kolmogorov-Smirnov test (17). A P value co.05 was considered statistically significant. The statistical package used was Sigma Stat, version 2.0 (Jande1 Corporation, San Rafael, CA). Results There were no significant demographic differences among groups with respect to age and weight, but there were significantly more female patients in Group 3 compared with Groups 1 and 2. There was no statistically significant difference in the thiopental doses of the three groups (Table 1). Tracheal intubation score results (all three groups) and TOF counts at the time of intubation (Groups 1 and 2 only) are summarized in Figure 1 and Table 3. Intubating conditions were either good or excellent in all patients. The mean (2 SD) onset time to clinical weakness was not different in the two rocuronium groups: 32 -+ 4.9 s in Group 1 and 32 f 5.3 s in Group 2. In the postoperative interview, none of the patients complained about weakness or shortness of breath before induction of anesthesia, and only one patient in Group 3 (succinylcholine) experienced postoperative muscle pain. All patients were satisfied with the manner in which anesthesia had been induced. Discussion Using the timing principle, the administration of rocuronium (0.6 “g/kg) resulted in adequate intubating conditions 45 seconds after the induction of anesthesia or approximately 77 s after the injection of the muscle relaxant. All patients found the manner in which anesthesia had been induced to be acceptable. Using the timing principle with rocuronium, it is possible to reduce the interval between induction of anesthesia and intubation of the trachea to <60 s. Such a technique is desirable because of the significant side effects associated with the use of succinylcholine (l-5). Alternative strategies to reduce the onset time of nondepolarizing muscle relaxants, such as ANESTH ANALG 1998;86:113740 ROCURONIUM priming (7) and administering large doses (8), have not been completely successful. The objective of the use of the timing principle is not to increase the speed of onset of the muscle relaxant, but to induce muscle relaxation and general anesthesia simultaneously rather than sequentially. When the timing principle is used, the initial signs of clinical weakness precede loss of consciousness. A potential risk, therefore, is that patients would experience an uncomfortable feeling during the induction sequence. In our study, no patient demonstrated restlessness at the time that ptosis was observed. This suggests that patient satisfaction with the manner in which they went to sleep (in response to the postoperative questionnaire) was not because of amnesic effects of anesthetics, but because the degree of muscle weakness present was not associated with discomfort. Debaene et al. (18) demonstrated that onset of neuromuscular blockade in the diaphragm was similar to that in orbicularis oculi but faster than that in adductor pollicis. Koh and Chen (11) also used ptosis (rather than handgrip strength) as the marker for the onset of clinical weakness, postulating that onset time for neuromuscular block at levator palpebrae superioris would be similar to that in orbicularis oculi and, therefore, that in the diaphragm. In Koh and Chen’s (11) study of the use of the timing principle with atracurium (0.5, 0.75, or 1.0 mg/kg), only one patient expressed dissatisfaction with the anesthetic technique used, and three felt discomfort. It is unlikely that the absence of such complaints in our study was due to a pharmacodynamic effect of rocuronium, because the times to onset of clinical weakness in our study (32 +- 4.9 and 32 + 5.3 s) were similar to those after atracurium (32 + 9.3, 29 + 1.0, and 28 t 11.7 s). Table 3 2 1 0 Table Intubating 12 Reference 1139 v) =.a, ii! ‘i; conditions I Gr 1 (Rot 45) 10 I Gr 3 (Succinylcholine) 8- 64- Definition ELxcellent (jaw relaxed,cordsabducted,no movement) Good (jaw relaxed,slightcough) Poor (jaw poorly relaxed,cordsmoving, or bucking) Unableto intubate See also SIEBER ET AL. PRINCIPLE” 2- (Intubation Score) Grade THE “TIMING It is more likely due to the administration of midazolam and fentanyl before the muscle relaxant. Because of the rapid speed of onset of neuromuscular block after rocuronium and the narrow range of standard deviation in the time to onset of clinical weakness (32 t 4.9 and 32 2 5.3 s), another approach of the timing principle might be not to wait for the onset of clinical weakness, but to induce anesthesia after a fixed interval, e.g., 20 s after the administration of rocuronium. Further studies are needed to address a safe time interval. There are several reports about pain on injection of rocuronium (19), even in subparalyzing doses. In our study, only 5 of 30 (16.7%) patients who received rocuronium withdrew their forearm during the injection of rocuronium. This withdrawal was interpreted as a reaction to a painful stimulus. Because the issue of pain on injection was not actually raised until the study was under way, we had not included any questions concerning this problem specifically in the postoperative interview. Nevertheless, none of the patients complained postoperatively about a uncomfortable event during the induction of anesthesia. A possible explanation is the prior administration of midazolam and fentanyl, which has been used to reduce pain on injection (20), plus the fact that the IV cannulas were z” 1. Grading of Intubating Conditions AND 9. 2 lntubation Figure 1. Intubating 1 0 score conditions. Intubation (jaw relaxed, cords abducted, no movement), slight cough), 1 = poor (jaw poorly relaxed, ing), 0 = unable to intubate. scores: 3 = excellent 2 = good (jaw relaxed, cords moving or buck- 2. Demographic Data and Thiopental Doses Age (~4 Weight (kg) Group 1 (rocuronium 45 s) Group 2 (rocuronium 60 s) Group 3 (succinylcholine) 46.9 -+ 15.8 70.9 -c 14.4 45.3 + 14.6 79.1 + 11.2 42.9 + 12.2 67.1 + 14.0 7 8 9 6 5.2 + 0.4 11* Sex Male Female Thiopental (mg/kg) Values are mean t SD. * P < 0.05 compared with 5.1 +- 0.4 Groups 1 and 2. 4* ---- 5.2 t 0.4 1140 SIEBER ET AL. ROCURONIUM Table 3. TOF Count Immediately AND THE “TIMING Before Endotracheal 2/4 l/4 movement TOF = train-of-four. * P < 0.05 compared with Groups Intubation Group 1 (rocuronium 45 s) 12 3 0 0 9% TOF count 4/4 3/4 Diaphragm ANESTH ANALG 1998;86:113740 PRINCIPLE” Group (rocuronium 7 6 0 0 4 2 60 s) Group 3 (succinylcholine) 3 2 and 3. placed in the forearm and not in the small veins of the back of the hand. Pulmonary aspiration of gastric contents has been associated with a priming dose of vecuronium (21,22). This may be attributable in part to the rapid speed of onset of the muscle relaxant at the adductor muscles of the larynx, compared with that at the adductor pollicis. A similar potential risk may exist when the timing principle technique is used. Indeed, anxiety associated with sensation of weakness or the application of cricoid pressure might result in vigorous inspiratory efforts when airway protective reflexes are compromised, further increasing the risk of pulmonary aspiration. 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