Neuromuscular end-point predictive capability of published rocuronium pharmacokinetic/pharmacodynamic models: An observational trial

BACKGROUND

Objective neuromuscular monitoring remains the single most reliable method to ensure optimal perioperative neuromuscular management. Nevertheless, the prediction of clinical neuromuscular endpoints by means of Pharmacokinetic (PK) and Pharmacodynamic (PD) modelling has the potential to complement monitoring and improve perioperative neuromuscular management.s STUDY OBJECTIVE: The present study aims to assess the performance of published Rocuronium PK/PD models in predicting intraoperative Train-of-four (TOF) ratios when benchmarked against electromyographic TOF measurements.

DESIGN

Observational trial.

SETTING

Tertiary Belgian hospital, from August 2020 up to September 2021.

PATIENTS AND INTERVENTIONS

Seventy-four patients undergoing general anaesthesia for elective surgery requiring the administration of rocuronium and subject to continuous EMG neuromuscular monitoring were included. PK/PD-simulated TOF ratios were plotted and synchronised with their measured electromyographic counterparts and their differences analysed by means of Predictive Error derivatives (Varvel criteria).

MAIN RESULTS

Published rocuronium PK/PD models overestimated clinically registered TOF ratios. The models of Wierda, Szenohradszky, Cooper, Alvarez-Gomez and McCoy showed significant predictive consistency between themselves, displaying Median Absolute Performance Errors between 38% and 41%, and intra-individual differences (Wobble) between 14 and 15%. The Kleijn model outperformed the former with a lower Median Absolute Performance Error (16%, 95%CI [0.01; 57]) and Wobble (11%, 95%CI [0.01; 34]). All models displayed considerably wide 95% confidence intervals for all performance metrics, suggesting a significantly variable performance.

CONCLUSIONS

Simulated TOF ratios based on published PK/PD models do not accurately predict real intraoperative TOF ratio dynamics.

TRIAL REGISTRATION

NCT04518761 (clinicaltrials.gov), registered on 19 August 2020.

Intraoperative Monitoring of Neuromuscular Blockade

There is a global trend of new guidelines highly recommending quantitative neuromuscular monitoring in the operating room. In fact, it is almost certain that quantitatively monitoring the depth of intraoperative muscle paralysis may permit the rational use of muscle relaxants and avoid some of the major related complications, namely postoperative pulmonary complications. A specific culture related to this issue is necessary to integrate quantitative monitoring of muscle relaxants as part of a major monitoring entity in anesthetized patients. For this purpose, it is necessary to fully understand the physiology, pharmacology and concept of monitoring as well as the choice of pharmacological reversal, including the introduction of sugammadex a decade ago.

Neuromuscular Blockade Monitoring

Neuromuscular monitoring is essential for optimal management of neuromuscular blocking drugs. Postoperative residual neuromuscular blockade continues to occur with an unacceptably high incidence and is associated with adverse patient outcomes. Use of a peripheral nerve stimulator and subjective tactile or visual assessment is useful for intraoperative management of neuromuscular blockade, especially when the patient's hand is accessible. Quantitative monitoring is necessary for confirmation of adequate reversal and for identification of patients who have recovered spontaneously and therefore should not receive pharmacologic reversal agents. Guidelines, as well as more user-friendly monitoring equipment, have created momentum toward improving routine perioperative neuromuscular monitoring.

Train-of-four monitoring with the twitchview monitor electctromyograph compared to the GE NMT electromyograph and manual palpation

The purpose of this study was to compare train-of-four count and ratio measurements with the GE electromyograph to the TwitchView electromyograph, that was previously validated against mechanomography, and to palpation of train-of-four count. Electrodes for both monitors were applied to the same arm of patients undergoing an unrestricted general anesthetic. Train-of-four measurements were performed with both monitors approximately every 5 min. In a subset of patients, thumb twitch was palpated by one of the investigators. Eleven patients contributed 807 pairs of train-of-four counts or ratios. A subset of 5 patients also contributed palpated train-of-four counts. Bland-Altman analysis of the train-of-four ratio found a bias of 0.24 in the direction of a larger ratio with the GE monitor. For 72% of data pairs, the GE monitor train-of-four ratios were larger. For 59% of data pairs, the GE monitor train-of-four counts were larger (p < 0.0001). For 11% of data pairs, the GE monitor train-of-four count was 4 when the Twitchview monitor count was zero. When manual palpation of train-of-four count was compared to train-of-four count determined by the monitors, 70% of data pairs were identical between palpation and TwitchView train-of-four count, while 30% of data pairs were identical between palpation and GE train-of-four count. For 7% of data pairs, the GE monitor train-of-four count was 4 when the palpation count was 0. The GE electromyograph may overestimate the train-of-four count and ratio. The GE electromyograph frequently reported 4 twitches when none were actually present due to misinterpretation of artifacts.

Advances in Anesthesia Monitoring

During surgery, one of the primary functions of the anesthesiologist is to monitor the patient and ensure safe and effective conduct of anesthesia to provide the optimum operating conditions. Standard guidelines for perioperative monitoring have been firmly established by the American Society of Anesthesiologists. However, in recent years, new advances in technology has led to the development of many new monitoring modalities, especially involving the neurologic and cardiovascular systems. This article presents a targeted review to discuss the functions and limitations of these new monitors and how they are applied in the modern operating room setting.

The effect of preload on electromyographic train-of-four ratio at the first dorsal interosseous muscle during spontaneous recovery from neuromuscular blockade

Accurate and reliable quantitative neuromuscular function monitoring is desirable for the optimal management of neuromuscular blockade, selection of the most appropriate reversal agent and dosage, and assessing the completeness of reversal to exclude residual neuromuscular blockade. Applying preload to the thumb may affect the precision of electromyography. This study compared the precision and agreement of electromyography with and without preload during recovery from non-depolarising neuromuscular blockade. After induction of anaesthesia and before neuromuscular blockade, the supramaximal current required at the first dorsal interosseous muscle with and without preload was determined. During recovery, train-of-four ratios were recorded using electromyography every 20 seconds. Alternating pairs of measurements (with and without preload) were obtained until spontaneous recovery was achieved. The preload device applied a resting tension of 75-150 g to the thumb. Bland-Altman analysis for repeated measurements was used to assess precision and agreement of electromyography responses with and without muscle preload. Two hundred and seventy-five sets of repeated measurements were collected from 35 participants. The repeatability coefficient for train-of-four ratios recorded by electromyography with a preload was 0.030 (95% confidence intervals, CI, 0.028 to 0.031) versus 0.068 (95% CI 0.064 to 0.072) without. Train-of-four ratios with preload demonstrated a bias of +0.038 (95% CI 0.037 to 0.042) compared to electromyography without, with 95% limits of agreement of 0.035-0.111. Preload significantly improved the precision of electromyographic train-of-four ratios, with 95% of consecutive measurements differing by less than 3%. Furthermore, electromyography with preload demonstrated a positive bias of 0.04 compared with electromyography alone, the clinical significance of which requires further research.

The Impact of Residual Neuromuscular Blockade, Oversedation, and Hypothermia on Adverse Respiratory Events in a Postanesthetic Care Unit: A Prospective Study of Prevalence, Predictors, and Outcomes

BACKGROUND

Residual neuromuscular blockade (RNMB) has been linked to adverse respiratory events (AREs) in the postanesthetic care unit (PACU). However, these events are often not attributed to RNMB by anesthesiologists because they may also be precipitated by other factors including obstructive sleep apnea, opioids, or hypnotic agents. Many anesthesiologists believe RNMB occurs infrequently and is rarely associated with adverse outcomes. This study evaluated the prevalence and predictors of RNMB and AREs.

METHODS

This prospective cohort study included 599 adult patients undergoing general anesthesia who received neuromuscular blocking agents. Baseline demographic, surgical, and anesthetic variables were collected. RNMB was defined as a train-of-four ratio below 0.90 measured by electromyography on admission to the PACU. AREs were defined based on the modified Murphy's criteria.

RESULTS

RNMB was present in 186 patients (31% [95% confidence interval (CI), 27%-35%]) on admission to the PACU. One or more AREs were experienced by 97 patients (16% [95% CI 13-19]). AREs were more frequent in patients with RNMB (21% vs 14%, P = .033). RNMB was significantly associated with age (adjusted relative risk [RR], 1.17 [95% CI, 1.06-1.29] per 10-year increase), type of operation (adjusted RR, 0.59 [95% CI, 0.34-0.99] for laparoscopic surgery compared with open abdominal surgery), and duration of operation (adjusted RR, 0.59 [95% CI, 0.39-0.86] for ≥90 minutes compared with <90 minutes). Using multivariate logistic regression, AREs were found to be independently associated with decreased level of consciousness (adjusted RR, 4.76 [95% CI, 1.49-6.76] for unrousable/unconscious compared with alert/awake) and lower core temperature (adjusted RR, 1.43 [95% CI, 1.04-1.92] per 1°C decrease). Although univariate analysis found a significant association between AREs and RNMB, the significance became borderline after adjusting for other covariates (adjusted RR, 1.46 [95% CI, 0.99-2.08]).

CONCLUSIONS

The prevalence of RNMB in the PACU was >30%. Older age, open abdominal surgery, and duration of operation <90 minutes were associated with increased risk of RNMB in our patients. Our RR estimate for AREs was highest for depressed level of consciousness. When AREs occur in the PACU, potentially preventable causes including RNMB, hypothermia, and reduced level of consciousness should be readily identified and treated appropriately. Delaying extubation until the patient is awake and responsive may reduce AREs.

Current Status of Neuromuscular Reversal and Monitoring

Postoperative residual neuromuscular block has been recognized as a potential problem for decades, and it remains so today. Traditional pharmacologic antagonists (anticholinesterases) are ineffective in reversing profound and deep levels of neuromuscular block; at the opposite end of the recovery curve close to full recovery, anticholinesterases may induce paradoxical muscle weakness. The new selective relaxant-binding agent sugammadex can reverse any depth of block from aminosteroid (but not benzylisoquinolinium) relaxants; however, the effective dose to be administered should be chosen based on objective monitoring of the depth of neuromuscular block.

To guide appropriate perioperative management, neuromuscular function assessment with a peripheral nerve stimulator is mandatory. Although in many settings, subjective (visual and tactile) evaluation of muscle responses is used, such evaluation has had limited success in preventing the occurrence of residual paralysis. Clinical evaluations of return of muscle strength (head lift and grip strength) or respiratory parameters (tidal volume and vital capacity) are equally insensitive at detecting neuromuscular weakness. Objective measurement (a train-of-four ratio greater than 0.90) is the only method to determine appropriate timing of tracheal extubation and ensure normal muscle function and patient safety.

Comparison of Kinemyography and Electromyography during Spontaneous Recovery from Non-Depolarising Neuromuscular Blockade

This study compared two commercially available quantitative neuromuscular function monitoring techniques, kinemyography (KMG) and electromyography (EMG), to assess whether KMG could be used interchangeably with EMG to exclude residual neuromuscular blockade (RNMB). Train-of-four (TOF) ratios were recorded every 20 seconds using KMG at the adductor pollicis and EMG at the first dorsal interosseous of the same hand during spontaneous recovery from shallow neuromuscular blockade. TOF ratios were compared using Bland–Altman analysis for repeated measurements. The precision of each device was assessed by the repeatability coefficient. Agreement between devices was assessed by the bias and limits of agreement. Clinically acceptable agreement was defined as a bias <0.025 within limits of agreement ±0.05. We recorded 629 sets of TOF ratios from 23 patients. The repeatability coefficient for KMG was 0.05 (95% confidence interval [CI] 0.05 to 0.06) and for EMG 0.10 (95% CI 0.10 to 0.11). Overall, the bias of KMG TOF ratios against EMG TOF ratios was 0.11 (95% CI 0.10 to 0.12), with limits of agreement −0.11 to 0.32. In the 0.80 to 0.99 TOF range, the bias was 0.08 (95% CI 0.06 to 0.09) and the limits of agreement were-0.12 to 0.27. Overall, TOF ratios measured by KMG were on average 0.11 higher than EMG. In the 0.80 to 0.99 TOF range, KMG TOF ratios were 0.08 higher. EMG and KMG are not interchangeable because the bias is large and the limits of agreement are wide. Thus a maximum TOF ratio of 1.0 on KMG may not exclude RNMB.

Current recommendations for monitoring depth of neuromuscular blockade

PURPOSE OF REVIEW

Residual neuromuscular block is a relatively frequent occurrence and is associated with postoperative pulmonary complications, including aspiration, pneumonia and hypoxia, impaired hypoxic ventilatory drive and decreased patient satisfaction. Although adequate recovery of neuromuscular function has been defined as a train-of-four ratio of at least 0.9, monitoring with a qualitative peripheral nerve stimulator makes it impossible to determine the actual train-of-four ratio.

RECENT FINDINGS

Peripheral nerve stimulators are not routinely used in clinical practice. Without their use, dosing of neuromuscular blocking agents and anticholinesterases is often inappropriate and adequacy of recovery of neuromuscular function upon tracheal extubation cannot be guaranteed.

SUMMARY

Use of peripheral nerve stimulators allows clinicians to administer neuromuscular blocking and reversal agents in a rational manner. Routine use of quantitative monitors of depth of neuromuscular blockade is the best guarantee of the adequacy of recovery of postoperative muscle strength.