In Response (2020)

We thank esteemed colleagues Drs Brull and Kopman,1 both well-known experts in the field of neuromuscular monitoring and blockade for their interest in our article and their comments. We would like to start by reiterating that our review2 was aimed at presenting technologies and techniques for coronavirus disease 2019 (COVID-19) patients who needed the use of neuromuscular blocking agents (NMBA) outside the operating theater. In particular, the editorial focused on severe COVID-19 patients with acute respiratory distress syndrome (ARDS). NMBA were needed for either intubation in the intensive care unit (ICU) or emergency room (ER) or during prolonged invasive mechanical ventilation.2 The creation of dedicated anesthesia intubation teams during the COVID-19 crisis as well as the increasing engagement of anesthesiologists in the ICU setting led us to believe that presenting basic principles of neuromuscular monitoring could be of interest for all readers.2 We purposely adopted the terminology widely used in the setting of intensive care medicine3 when we wrote about the train-of-four (TOF) monitoring. As a matter of fact, we deliberately referred to the way electric impulses are applied to a motor nerve. The TOF stimulation consists of applying 4 electric stimuli each separated by 0.5 s. Depending on the method of monitoring available, either qualitative—tactile or visual counting—or quantitative monitoring—using a specific monitoring device—is possible. In the former, the TOF count can be determined (1–4 twitches), or a definite ratio of T4/T1 ratio. The TOF ratio is the comparison of T4 (fourth twitch of the TOF) to T1 amplitude, expressed in percentage.4 We left the choice of using either qualitative or quantitative monitoring to the discretion of the physicians working in the ICU.2 In the operating room, quantitative monitoring devices are recommended as they give a more detailed and precise estimate of neuromuscular blockade (NMB). NMB monitoring is not standard of care in the ICU, despite the use of NMBAs for patients with severe ARDS or during proning maneuvers. The best compromise between practicability, usefulness, and validity of monitoring seems to be the use of qualitative, handheld monitoring devices.2 Handheld monitoring devices can be easily carried in the physician’s pocket, and properly disinfected.2 Monitoring is more frequently used during continuous infusion of NMBAs: it can be done in seconds using facial or eye muscles, adductor pollicis muscle, or others. The qualitative result can then be recorded in the patients’ chart. The frequency and the site of placement of such monitoring is chosen by the treating physician or the ICU guidelines. The COVID-19 pandemic has significantly increased the workload in most ICUs and the frequency of TOF monitoring has been compromised at times. Quantitative monitoring in the ICU is difficult because of the lack of standardization. Frequently asked questions are: shall one leave stimulating electrodes in the same place? How long could these stay on the skin without causing pressure damages? What position shall be used of the hand when monitoring is performed? In that respect, facial muscles are easier to monitor but they do not reflect NMB or neuromuscular transmission at the adductor pollicis muscle. We do not recommend the corrugator supercilii as the monitoring site of choice but wanted to point out that it best reflects NMB or neuromuscular transmission at the diaphragm or larynx, anatomic areas of particular interest for ICU physicians. Drs Brull and Kopman1 questioned the recommended target value of NMB in the ICU setting. The discussion of whether NMB is at all necessary for mechanical ventilation in the ICU is beyond the scope of our article. However, in a recent study,3 a positive relationship was found between the depth and duration of NMB and ICU-acquired weakness. The article entitled “Battle of the RSI Paralytics”5 describes the long-standing discussion around the use of succinylcholine versus rocuronium for rapid sequence induction (RSI) from the perspective of emergency medical services. In terms of onset time and intubation conditions, rocuronium in a dose of more than 1 mg/kg and succinylcholine in a dose of 1 mg/kg are equally efficient.6 COVID-19 patients who need intubation are predominantly suffering from multiple comorbidities.7 This leaves us with the eternal question which muscle relaxant is better for the “can’t intubate can’t ventilate situation.” Despite best efforts of preoxygenation, COVID-19 patients desaturate very quickly during the intubation process to alarming values of 70% or 60% or less within seconds. It is therefore important that intubation is provided by a dedicated team and mostly by the very experienced physicians, predominantly using videolaryngoscopy.2 The procedure can be particularly challenging in COVID-19 patients. Naguib et al8 found a significantly longer objectively measured duration of NMB after 1 mg/kg succinylcholine with 10 minutes versus 2 minutes after 1.2 mg/kg rocuronium followed 3 minutes later by 16 mg/kg sugammadex. As to the comments by Brull and Kopman1 concerning the time it takes to get this amount of sugammadex ready, one can easily imagine the fractionated injection of sugammadex by the anesthesiologist, while a second person prepares further doses. We argue that the time it takes to get sugammadex ready is not really an issue. Even when one looks at clinical parameters, such as a return to spontaneous ventilation, defined as respiratory rate of more than 8/min at a tidal volume of at least 3 mL/kg for 30 s, the combination of rocuronium/sugammadex is able to achieve this in half the time than succinylcholine.9,10 We finally would like to thank Drs Brull and Kopman1 to allow us to elaborate a bit more on neuromuscular monitoring and NMB in critical care in the time of COVID-19 pandemic. ACKNOWLEDGMENTS The authors thank Umesh Patel for editing the content. Francesca Rubulotta, MD, PhD, MBA, FRCA, FICMDepartment of Anaesthesia and Intensive Care MedicineImperial College LondonLondon, United Kingdom[email protected] Hatem Soliman-Aboumarie, MD, FEACVI, FASE, FHEADepartment of Anaesthetics and Critical CareHarefield HospitalRoyal Brompton and Harefield National Health System (NHS) Foundation TrustLondon, United Kingdom Kevin Filbey, MDGoetz Geldner, MD, PhDDepartment of Anesthesia, Intensive Care Medicine, Chronic Pain and Emergency MedicineLudwigsburg HospitalLudwigsburg, Germany Kai Kuck, PhDDepartment of Anesthesiology and BioengineeringUniversity of UtahSalt Lake City, Utah Mario Ganau, MD, PhD, FEBNS, FACSDepartment of NeurosurgeryJohn Radcliffe HospitalOxford University Hospitals NHS Foundation TrustOxford, United Kingdom Thomas M. Hemmerling, MSc, MD, DEAADepartment of AnesthesiaMcGill UniversityMontreal, Quebec, Canada