I read with great interest the article by Dubois et al.1 evaluating the impact of deep neuromuscular blockade on surgical conditions during laparoscopy. It represents a welcome contribution to the field of the management of neuromuscular blockade during laparoscopic surgery. However, two important issues about the study deserve consideration.1
Firstly, after an intubating dose of rocuronium 0.6 mg kg−1, patients in the deep neuromuscular blockade group received a bolus dose of rocuronium 5 mg to deepen their neuromuscular blockade whenever a second twitch (T2) or more appeared on train-of-four stimulation.1 In doing so, the authors essentially included patients with moderate neuromuscular blockade in the deep neuromuscular blockade group,1 as moderate neuromuscular blockade is characterised by the appearance of T1-T2 on train-of-four stimulation.2
Secondly, the authors defined deep neuromuscular blockade as the absence of T1 on train-of-four stimulation;1 however, it is more appropriate to define deep neuromuscular blockade as the presence of no twitches on train-of-four stimulation and only one to five twitches observed as the posttetanic count during posttetanic stimulation.2,3 In a previous study evaluating recovery from deep to moderate neuromuscular blockade after rocuronium 0.6 mg kg−1, the posttetanic count was 8 when T1 first appeared on train-of-four stimulation.4 Thus, with a posttetanic count of 5 to 20 on electromyography, the probability of inadequate deep neuromuscular blockade is high, and a repeat dose of rocuronium is necessary to avoid moderate neuromuscular blockade.4,5 Indeed, it has been reported that when the posttetanic count is 1, T1 appears in approximately 10 min, whereas when the posttetanic count is more than 5, the appearance of T1 is imminent.4 The posttetanic count may not only predict the return of the reactivity of the adductor pollicis muscle during recovery from deep neuromuscular blockade,5 but, most importantly, it may also be a reliable indirect method of estimating diaphragm recovery.6 A posttetanic count of 5 or less signifies deep neuromuscular blockade of the diaphragm, whereas a posttetanic count more than 5 does not.5,7 Deep neuromuscular blockade of the diaphragm is crucial for providing superior surgical conditions during laparoscopic surgery.3,6 Furthermore, maintaining the posttetanic count less than 5 may prevent hiccups, bucking and coughing, all of which can occur during surgery despite total abolition of train-of-four responses at the adductor pollicis muscle.5,6
Both of the aforementioned issues likely led to at least some patients in the deep neuromuscular blockade group exhibiting only a moderate degree of neuromuscular blockade at least part of the time. The presence of moderate neuromuscular blockade may explain the surgical conditions being rated as ‘good but not optimal’ in 22% of patients in the deep neuromuscular blockade group and ‘poor but acceptable’ in another 10% of patients in the deep neuromuscular blockade group.1 Indeed, the authors noted that unfavourable surgical conditions only occurred when the train-of-four response was T1 or more.1 Moreover, it is quite possible that deep neuromuscular blockade at the diaphragm recovered in some instances despite the absence of a train-of-four response at the adductor pollicis, which may have also reduced the percentage of patients in the deep neuromuscular blockade group with ‘excellent’ surgical conditions.1 Martini et al.3 reported that good and optimal conditions were observed in almost all patients undergoing laparoscopic surgery when deep neuromuscular blockade was maintained with a posttetanic count in the range of 1 to 5.
Despite these methodological issues that may have reduced the observed effectiveness of deep neuromuscular blockade, the results of Dubois et al.1 support the view that adequate rocuronium-induced deep neuromuscular blockade allows to optimise surgical conditions during laparoscopy.
Acknowledgements relating to this article
Assistance with the letter: none.
Financial support and sponsorship: none.
Conflicts of interest: the author has received payments for lectures from Merck Sharp & Dohme (MSD), Italy.
1. Dubois PE, Putz L, Jamart J, et al. A deep neuromuscular block improves the surgical conditions during laparoscopic hysterectomy. A randomised controlled trial. Eur J Anaesthesiol
2. Abrishami A, Ho J, Wong J, et al. Sugammadex a selective reversal medication for preventing postoperative residual neuromuscular blockade. Cochrane Database Syst Rev
3. Martini CH, Boon M, Bevers RF, et al. Evaluation of surgical conditions during laparoscopic surgery in patients with moderate vs deep neuromuscular block. Br J Anaesth
4. Schultz P, Ibsen M, Østergaard D, Skovgaard LT. Onset and duration of action of rocuronium-from tracheal intubation, through intense block to complete recovery. Acta Anaesthesiol Scand
5. El-Orbany MI, Joseph NJ, Salem MR. The relationship of posttetanic count and train-of-four responses during recovery from intense cisatracurium-induced neuromuscular blockade. Anesth Analg
6. Dhonneur G, Kirov K, Motamed C, et al. Posttetanic count at adductor pollicis is a better indicator of early diaphragmatic recovery than train-of-four count at corrugator supercilii. Br J Anaesth
7. Viby-Mogensen J, Howardy-Hansen P, Chraemmer-Jørgensen B, et al. Posttetanic count (PTC): a new method of evaluating an intense nondepolarizing neuromuscular blockade. Anesthesiology