Pupillary dilation reflex and pain measurement in the anesthesiated patient: literature review

Abstract

Introduction. The validation of the presence of pain in patients under general anesthesia remains a challenge. The correct measurement of sedoanalgesia can provide the use of minimum doses of anesthetics drugs to be achieved, avoiding underdoses or overdoses.  Recent studies have also correlated pupillometry with the level of pain in non-common patients. Objectives. Through a literature review, we sought to correlate pupillometry and pupillary dilation reflex in analgesia monitoring, in sedated and non-communicative patients, under the use of opioids and hypnotics, as well as to compare pupillometry with the use of vital parameters such as heart rate, use of analgesia and nociception index and BI. Method. A literature review was carried out based on articles found on the “PubMedociation, in English, Spanish and Portuguese, between the period 1996 to 2020. The search in the databases resulted in 38 articles. Results It was found that pupillometry presented more reliable data in the assessment of nociception when compared to heart rate and blood pressure, but there are still some difficulties in standardizing its application. Pupillometry measures several components: maximum amplitude, latency, speed of dilation and contraction, and maximum and minimum size. When evaluating vital signs such as heart rate and blood pressure, pupillometry has been shown to be a better predictor of analgesia, becoming a better indicator when remifentanil or propofol was used. Conclusions. The assessment of the pupillary dilation reflex allows the anesthesiologist to measure the reactivity of the autonomic nervous system to the pain stimulus being able to provide individualized treatment and with greater security.