Navigating excessive train-of-four ratios: If it is “beyond 1.0,” go “back to the basics”
Year: 2025
Type: article
Abstract: Sir, The latest evidence supports quantitative neuromuscular monitoring in the operating room.[1] With emerging techniques of neuromuscular monitoring, knowledge regarding calibration, normal range, outlier values, and interpretation of data obtained is vital to guide appropriate management. We report a supra-centennial train-of-four (TOF) ratio and discuss it in brief. A 25-year-old male patient with S1–S2 cord tethering was posted for detethering with intraoperative neurophysiological monitoring (IONM). The anesthetic plan included general anesthesia with neuromuscular transmission (NMT) and bispectral index (BIS) monitoring. BIS™ Quatro sensors (Medtronic Limited, United Kingdom) were placed. Standard induction with fentanyl, propofol, and atracurium (0.5 mg/kg) was done. NMT monitor (A7 workstation, Mindray Medical India Private Limited, India) was attached, with electrodes placed on the left forearm – one at the wrist crest and the other 3–6 cm proximal and the transducer taped to the thumb. The TOF was recorded using supramaximal stimulation (30 mA) to the ulnar nerve (frequency of two hertz for 2 s) at 20-s intervals and later at 10-min intervals. Propofol infusion started at 75–100 mcg/kg/h to maintain a BIS value of 40–50. IONM was successfully being performed. Intraoperatively, at 110 min of the initial NMBD dose, the TOF ratio exceeded 100 [Figure 1]. Throughout the last hour of the 5-h surgery, TOF ratios recorded at 10-min intervals were 122, 126, 126, 102, 104, and 105. Since the TOF ratio was >0.9 and a single NMBD dose was given at induction, spontaneous recovery from neuromuscular blockade was allowed without a reversal agent. Extubation was done once the clinical signs of recovery were present. Postoperatively, the patient showed no residual neuromuscular blockade.Figure 1: Intraoperative train-of-four values between the 3rd and 4th h (a and b); placement of electrodes and transducer on the volar aspect of the left forearm of the patient (c)Acceleromyography (AMG) monitoring reduces residual neuromuscular blockade and related complications. The AMG devices have been shown to show baseline TOF ratios >1.0, leading to discrepancies with mechanomyography (MMG) or electromyography (EMG).[2] Normalizing AMG TOF values to baseline measurements can reduce bias. For example, if the baseline TOF ratio is 1.20, a TOF of 0.9 in the PACU normalizes to 0.75 (0.9/1.20) which might indicate persistent neuromuscular blockade precluding extubation. Since AMG TOF values are about 10% higher than MMG values, a TOF of at least 1.0 is needed to rule out significant muscle weakness.[2] Additionally, AMG readings can be affected by the “staircase effect,” where muscle contraction strength increases with repeated stimulation.[3] In our case, due to some logical issues in applying the NMT monitor before administration of Atracurium, we did not have a baseline which is of importance with AMG monitors and not with the more commonly used EMG monitors. Having TOF ratios >1.0 is not common for us since we have EMG monitors with most of our anesthesia workstations and the workstation being used in this instance was a backup machine and not all were aware that it had an AMG monitor and were amazed to see TOF ratios >1.0 at first. Claudius et al. also noted that AMG monitoring’s “reverse fade” issue complicates neuromuscular recovery assessment, recommending a normalized TOF ratio >0.9 to minimize bias compared to MMG.[4] Despite standards recommending objective NMT monitoring, its use is still insufficient. Training is needed to raise clinicians’ awareness of the importance of objectifying the degree of neuromuscular blockade to ensure safe anesthesia and recovery.[5] Understanding the type of monitor, baseline TOF ratios, patient variability, and obtaining corrected TOF ratios by normalization is crucial for guiding neuromuscular recovery and preventing postextubation complications. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Source: The Indian Anaesthetists Forum
Institution: All India Institute of Medical Sciences Jodhpur
Language: English
Subfield: Anesthesiology and Pain Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4411852572