Neuromuscular blockade: Recovery
Basic, Clinical Sciences: Anesthesia Procedures, Methods, and Techniques
Return to baseline function after neuromuscular blockade for different muscle groups is not uniform and appears to occur in relation to the muscle’s regional blood flow. Higher regional blood flow leads to faster onset and recovery of NMB. As such, the diaphragm, masseter, orbicularis oculi and laryngeal muscles, which receive relatively greater blood flow, recover more quickly, while the adductor pollicis, which receives relatively lower blood flow, recovers more slowly. Because of this delay relative to the laryngeal muscles, peripheral nerve monitoring of the adductor pollicis may be more sensitive in detecting adequate recovery from NMB.
Train of four (TOF) ratio monitoring after non-depolarizing neuromuscular blockade is a useful tool in determining recovery of function. Once the TOF ratio at the adductor pollicis has recovered to 0.70, tests of mechanical respiratory reserve (such as VC and peak expiratory flow rate), have usually recovered to near-baseline values. At TOF 0.70, however, there is decreased response in the ventilatory response to hypoxia and disorganization of the swallowing mechanism. This is due to the fact that at this TOF ratio, between 75-80% of ACh receptors remain blocked. Research has shown that there is an increased risk for aspiration with TOF ratio <0.90 and pharyngeal function is not returned to baseline until the TOF ratio is >0.90. As such, the current standard for adequate NMB recovery is TOF 0.90 or greater.