Researchers have found that pupillary light reflex (PLR) recovery from general anesthesia (GA) varies greatly among patients, regardless of the anesthesia drug used.
Thus while PLR has long been used in the neurologic assessment of an anesthetized patient, physicians should be cautious about using the technique to measure brain stem function in patients who have been under GA.
The study, conducted by researchers at the Université libre de Bruxelles in Belgium, was presented at the 2016 PostGraduate Assembly in Anesthesiology (poster P-9067).
“The main studies in the pupillary domain focus on pupillary dilation reflex, which assesses nociception,” said Stefano Corda, MD, the study’s lead author. “Very few studies focus on PLR, and the few we found focused only on the direct effect of GA on PLR. We all know that GA depresses PLR. We don’t know yet how PLR recovers after GA.”
Addressing a Lack of Data
Dr. Corda and his colleagues explored how patients recovered light reflex during emergence from GA.
All 80 patients were American Society of Anesthesiologists physical status I or II, between 18 and 75 years of age, and underwent surgery under GA.
The patients were randomly assigned to receive either propofol target-controlled infusion (TCI) or sevoflurane anesthesia. Both groups received remifentanil (Ultiva, Mylan) TCI to ensure intraoperative analgesia. PLR was tested via bilateral pupillometric measurement: first in the awake patient, and then serially between induction and emergence from GA. A final measurement was made in the PACU when the patient was awake and responsive. The study end point was the time necessary to recover a third (T1/3) or half (T1/2) of the pupillary relaxation velocity measured before the induction of GA.
Much to the investigators’ surprise, no correlation was found between the parameters at the end of GA (bispectral index, mean arterial pressure, heart rate, end-tidal carbon dioxide monitoring) and the recovery times of T1/3 and T1/2. Additionally, effect-site concentration of propofol and end-tidal sevoflurane were not correlated with the T1/3 and T1/2. The T1/3 and T1/2 weren’t influenced by age, duration of anesthesia, time to extubation, pupillary reaction velocity or PLR variation before GA. For patients in the sevoflurane group, a statistically significant correlation was found between effect-site concentration of remifentanil at the end of GA and the T1/2. However, recovery times were extremely variable regardless of the general anesthetic used.
“This was unexpected,” Dr. Corda admitted. “We expected elderly people to recover slower, for instance. But it wasn’t the case.”
Overall, Dr. Corda and his colleagues found the study to be an interesting initial look at this issue. “It is a good starting point,” Dr. Corda said. “But of course there is always room for perfecting and improvement.”