Monitoring of Neuromuscular Blockade in the Intensive Care Unit: a Reliability Study

Muscle relaxation in the intensive care unit is a commonly used therapeutic approach, but one that remains controversial due to a debated benefit-risk ratio depending on the clinical context. First, neuromuscular blockade is a common technique in the operating room to facilitate orotracheal intubation or to improve surgical comfort during the procedure.

The French Society of Anesthesia and Intensive Care (SFAR) recommends intraoperative monitoring of neuromuscular blockade and recovery from neuromuscular blockade for patients under general anesthesia who have received neuromuscular blocking agents. It is recommended to use ulnar nerve stimulation at the wrist with visual or tactile assessment of thumb adductor contraction, given the ease of access as well as the potential to quantify the muscular response of this muscle. When deep neuromuscular blockade of the body's most resistant muscles (diaphragm, abdominal wall muscles) is indicated, it is recommended to wait until the four responses to the four-pulse train to the thumb adductor have disappeared and to monitor using Post-Tetanic Count (PTC) stimulation. In this case, the presence of one to five responses to the thumb adductor indicates complete paralysis of the abdominal muscles. Stimulation of the facial nerve in four-pulse trains and visual assessment of the response in the corrugator supercilii muscle is an alternative to the ulnar nerve test. The neuromuscular blockade profile of the corrugator supercilii muscle is comparable to that of the body's most resistant muscles, such as the laryngeal adductors or the diaphragm.

In the intensive care unit, neuromuscular blockade is primarily used for emergency orotracheal intubation and in cases of severe acute respiratory distress syndrome (ARDS). In moderate-to-severe cases, some patients require deep, continuous sedation during the initial phase, sometimes in combination with neuromuscular blockade. Early and continuous infusion of cisatracurium during the initial phase of severe ARDS (P/F < 150) has demonstrated a clear clinical benefit in terms of 90-day mortality through several pathophysiological mechanisms. However, prolonged use of neuromuscular blockade is also associated with neuromuscular weakness and requires deep sedation, which can itself have negative consequences. Despite the lack of robust evidence, monitoring of neuromuscular blockade is recommended in patients in the intensive care unit. Monitoring the depth of neuromuscular blockade would help ensure that neuromuscular blockade goals are met while using the lowest possible doses of neuromuscular blocking agents.

Clinical assessment based on observation of respiratory effort or detection of patient-ventilator asynchrony should be combined with a quantitative method for evaluating neuromuscular blockade: "Train-of-four" (TOF) or "post-tetanic count" (PTC) . However, no study has examined the feasibility of this technique in our intensive care patients across different clinical contexts. The data have been extrapolated from the operating room, even though the use of neuromuscular blockers in the ICU differs and certain clinical situations may make interpretation of the monitoring results potentially difficult: ICU-acquired neuromyopathy, therapeutic hypothermia, and interstitial edema.

These clinical situations may alter the muscle response to electrical stimulation and thus skew the results of "TOF" or "PTC" monitoring.