Abstract
Pupillometry is a technique for objective quantification of nociception that takes into account the central processing of noxious stimuli and its sympathetic response. This narrative review provides an overview of the physiology of the pupil, the principles of pupillometry, and its potential application in the perioperative environment, especially in nociception monitoring and quantifying responses to opioids. Relevant articles, including reports of original investigation, review articles, and meta-analyses were identified from searches of PubMed and Google Scholar databases. Articles that described pupillary physiology and pupillometry, along with original research reports of the application of pupillometry in perioperative and critical care environment were used to synthesize a narrative review. Pupillometry is emerging as an objective measure of nociception, especially in patients under general anesthesia, children, non-verbal patients, and critically ill patients who cannot effectively communicate ongoing pain. Portable automated pupillometers have made accurate quantification of pupillary reflexes, including light reflex and dilatation reflex, possible. This technique has been successfully studied in the perioperative setting for a number of applications, including quantification of nociception, response to analgesia, and assessing efficacy of regional blocks. Pupillary oscillations have shown promise in assessing central opioid effects. Pupillometers can also accurately quantify light reflexes during the neurologic evaluation of critically ill patients. Pupillometry is an easy to use non-invasive bedside technique to quantify nociception and monitor opioid effects. It has the potential to personalize pain management in perioperative and intensive care unit environments. Additional studies are needed to further understand the utility of pupillometry in this context.
Highlights
Pupillometry is a technique for objective quantification of nociception that takes into account the central processing of noxious stimuli and its sympathetic response
A review by Ledowski describes the nociception monitoring technologies that are currently commercially available.[3]. This present review focuses on pupillary evaluation for assessment of nociception and its effects on analgesic therapy
With respect to Pupillary light reflex (PLR), opioids do not alter pupillary light reflex amplitude (PLRA) or constriction velocity (CV) when the values are normalized to the resting size of the constricted pupil.[32,34]
Summary
Correlated different aspects of Percentage variation in pupil In patients unable to the PLR with established size ([ 19%) during dressing communicate verbally, strategies for pain assessment change predicted the presence pupillometry may potentially to evaluate the adequacy of of pain as determined by guide caregivers to adjust analgesia before surgical behavioural pain scale score analgesia before painful dressing changes [ 3 with 100% sensitivity procedures and 77% specificity. The authors were not able to show any association of PD with early postoperative pain or pain relief.[53] They postulated the residual effect of intraoperative opioids and the lower level of nociceptive stimulation in the PACU as the reasons for their findings Another cross-sectional study of 145 individuals reported no correlation between PACU pain scores and PD or PLRA.[54] The authors concluded that the lower intensity and continuous nature of postoperative pain (unlike the transient pain stimulus used to measure PRD), residual effects of anesthetic agents and concurrent use of medications including anticholinergics and anesthetics could have contributed to their results, insisting on the need for further research.[54] In an observational study of 345 patients who received GA, the authors recorded postoperative VAS along with pupillary parameters PD, PLR, and VCPD.[31] The ANI was recorded, which is derived from heart rate variability. In another study of deeply sedated and mechanically ventilated patients (n = 34), PRD in response to cutaneous tetanic stimulation was found to be predictive of insufficient analgesia for endotracheal suction.[56] pupillometry may be a non-invasive, rapid technique to assess nociception in critically ill patients for opioid titration. This could be very painful in awake patients, so can only be used in anesthetized, sedated patients and unconscious ICU patients
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