Rocuronium for rapid sequence induction in morbidly obese patients

Rocuronium is considered as non-deporalising muscle relaxant that can be used instead of succinylcholine for rapid sequence induction (RSI). The dose (1.2 mg kg−1) provides neuromuscular blockade that allows for atraumatic intubation within 60–90 s. In morbidly obese patients, RSI or fast intubation is still considered the preferred method of induction to general anaesthesia, except for expected difficult airways in which fibre optic intubation is better.1 The pharmacology of rocuronium was studied in several trials to estimate the adequate dosing in morbidly obese patients: per kilogram of ideal body weight (IBW), corrected body weight (CBW) or total body mass. It is suggested that rocuronium can be dosed basing on IBW.2,3 However, these studies were testing the typical induction dose of rocuronium – 0.6 mg kg−1, but in the case of RSI, higher doses are used (1.2 mg kg−1). In this prospective, single-blinded study, intubation conditions at 60 s as well as onset and duration of action were evaluated after administration of rocuronium 1.2 mg kg−1 IBW. After obtaining Local University Ethics Committee approval (protocol number RNN/356/09/KB, Chair Person Professor Przedzislaw Polakowski, 12 May 2009), 173 morbidly obese patients (BMI > 40 kg m−2) scheduled for bariatric operations gave written informed consent to take part in the study. The exclusion criteria were expected difficult intubation, neuromuscular disease, known impaired hepatic or renal function, suspected allergy to study drug and medications known to interfere with neuromuscular function. The rocuronium was administered by the study investigator in a single, fast (<5 s) intravenous injection. IBW was counted as follows: IBW = 22 × H2 for both men and women, where H is patient height in meters.4 For induction of anaesthesia, propofol 2 mg kg−1 CBW [IBW+(total body weight − IBW) × 0.4] was administrated intravenously.5 For maintaining anaesthesia, the patient's lungs were ventilated with mixture of 50% oxygen/50% air and desflurane in volume percentage (Vol%) according to age (manufacturer recommendations). Neuromuscular monitoring followed good clinical research practice (GCRP) guidelines for pharmacodynamic neuromuscular studies.6 After careful cleaning of the skin, two electrodes were placed over the ulnar nerve near the wrist of the patient with a distance of 3–6 cm. The accelerometer was taped on the tip of the thumb. The arm was placed in a way not limiting thumb movement with the accelerometer. The inbuilt calibration mode was used. The TOF-Watch accelerometer (Organon Teknika, Boxtel, The Netherlands) was used for neuromuscular transmission monitoring. After loss of consciousness, autocalibration was performed by using supramaximal stimulation and neuromuscular monitoring was started using continuous single-twitch stimulation of 0.1 Hz (T1). The Sellick manoeuvre was not performed routinely in order to not interfere with evaluation of intubation conditions. Any additional manoeuvres to improve glottis view (e.g. pressure on thyroid cartilage) were recorded. The investigator measured onset time, that is, time to achieve 100% suppression of neuromuscular function. Endotracheal intubation was performed by an experienced anaesthesiologist, blinded to the TOF-Watch display, 60 s after injection of muscle relaxant and evaluated according to GCRP.6 After successful endotracheal intubation, neuromuscular stimulation was changed to train-of-four (TOF). Duration time (the time to achieve one response to TOF stimulation) was measured. Peripheral body temperature was controlled to maintain at least 36°C. Statistical analysis included the simple summary test. Microsoft Excel 2003 v.11.5612.5606 (Microsoft, Warsaw, Poland) was used. One hundred and seventy-three patients were analysed. The demographic data are provided in Table 1. The mean onset time and duration are presented in Table 2. According to GCRP evaluation of intubation conditions, 98.8% of patient had excellent or good intubation conditions – in two cases intubation conditions were considered as poor (Cormack–Lehane grade 3). There were no complications of rocuronium administration or intubation. Mean Vol% of desflurane was 6.45%. Our study has shown that in morbidly obese patients, rocuronium at a dose of 1.2 m kg−1 provides excellent or good intubation conditions within 60 s after administration. The dose can be based on IBW in the case of RSI for morbidly obese patients. The onset time was short, but the duration time was not as long as it would be in non-obese patients receiving the same dose (1.2 mg kg−1).7 Our observation confirms results of previous studies that duration of action of rocuronium is shorter in obese patients.8 The pharmacodynamics and pharmacokinetics of rocuronium in morbidly obese patients suggest that this muscle relaxant can be administrated according to IBW.2,3 However, previous studies were performed with a dose of 0.6 mg kg−1 which is not recommended for RSI. As times of onset and duration strongly depend on the dose of rocuronium, it is important to give the appropriate dose to achieve the effect – fast and atraumatic endotracheal intubation. Meyhoff et al.2 administered rocuronium at a dose of 0.6 mg kg−1 IBW or CBW. They observed an onset time of 85 s when rocuronium was administered according to IBW and 80–84 s according to CBW. Leykin et al.3 observed 87.5 s when rocuronium was administered on the basis of IBW and 77 s for dosing based on real body weight. The results of the study by Meyhoff et al.2 confirm that duration of action of rocuronium was 21 min (dosing based on IBW) and 28–31 min (dosing based on CBW). Leykin et al.3 made similar observations: 22 min (IBW) and 55.5 min for dosing based on real body weight. In our study, we observed a duration of 52.2 min. The intubation conditions in our study were excellent or good in almost every case (two cases of poor conditions: difficult laryngoscopy, Cornack–Lehane grade 3 due to anatomical factors), significantly more excellent conditions at 60 s (75.14%) than good. Meyhoff et al.2 reported 82 (IBW) and 64–82% (CBW) excellent intubation conditions at 90 s after injection of muscle relaxant. In conclusion, we claim that rocuronium administered at the dose of 1.2 mg kg−1 of IBW provides short onset of action and excellent or good intubation conditions at 60 s after administration in 98.8% of morbidly obese patients.