Many anaesthetics contain neuromuscular blockage drugs (NBDs). While anesthesia is necessary for various operational procedures, residual NBDs can lead to prolonged neuromuscular blockage in the patient. Although it is known that monitoring and early reversal improves patient outcomes, quantitative monitoring is often not in place due to limitations in resources. In line with the list of identified risks of the 5th National Audit (NAP5)1, quantitatively monitoring neuromuscular function in patients with anaesthetics should be enforced, especially for patients receiving non-depolarising neuromuscular blockers2,3.
Acknowledging the resource limitation and the importance in quantitative neuromuscular monitoring, Kang et al tested the ability of iPhone’s built-in accelerometer to monitor the train of four (TOF) ratio and a peripheral nerve stimulator.
Train of four monitoring is used to objectively determine how well a patient’s muscles are able to function — and is used during recovery from anesthesia.
Typically, patients should recover to >0.9 TOF two hours after the application of anesthesia. Simulating electrodes were placed on the ulnar nerve of a healthy volunteer to quantify the adductor pollicis movement to calculate the TOF ratio. However, the weight and shifting of the iPhone on the subject’s hand made the results inconsistent and unreliable.
While the iPhone’s built-in accelerometer has been used successfully for many medical apps, such as detecting the Parkinson’s disease tremor, balance problems, and lumbar lordosis, it was not sufficient for TOF because “the iPhone applied a “high pass filter” to the data before it was displayed, confounding the accelerometer data, which could never be read as raw.”3 While this was a short proof of concept test, it tries to address an important issue on the lack of quantitative monitors. More research could be done to see if an algorithm could be created to reverse the processed data, and if smaller mobile devices like the Apple watch could be used to overcome the weight and shifting issues.
To see how The iPhone’s accelerometer is currently being used in several clinical trials check out our list of the current Apple ResearchKit studies. For a list of key anesthesia medical apps refer to our Anesthesiology app page.