Monitoring neuromuscular block in infants and children

ABSTRACT

Neuromuscular blocking agents (NMBAs) have become a key component of anesthetic care as a means of facilitating endotracheal intubation, providing surgical relaxation of the skeletal musculature, and ensuring an immobile patient during surgical procedures. Although generally safe and effective, dosing of NMBAs and their reversal with acetylcholinesterase inhibitors (such as neostigmine) or encapsulating agents (such as sugammadex) require monitoring, including a means to quantify the degree of neuromuscular (NM) block and residual NM function. Although clinical evaluations (head lift, hip flexion, and grip strength) or respiratory parameters (tidal volume and vital capacity) have historically be used to assess return of muscle strength, these parameters have been shown to be insensitive means of detecting residual NM block and weakness. Furthermore, these subjective evaluations are not feasible during intraoperative anesthetic care and therefore cannot be used to guide initial and ongoing dosing of NMBAs, nor the adequacy of reversal. Assessing NM function using a peripheral nerve stimulator (PNS) and visual observation of the train-of-four (TOF) response was previously accepted as the standard monitor when administering NMBAs. However, subjective visual or tactile assessment is an indirect and insensitive measure of NM function, and measurement of the TOF ratio (T4/T1) is not feasible. It is generally accepted that a quantitatively determined TOF ratio ≥0.90 is the optimal method to document return of baseline NM function, avoid residual paralysis, and confirm the safe timing of tracheal extubation. The following educational review discusses the normal function of the NM junction, outlines clinical concerns of inadequate reversal of NM block, and reviews quantitative TOF monitoring with an emphasis on its use in the pediatric patient.