Perfusion index may help assess analgesia during laparoscopic surgeries under general anaesthesia

Perfusion index may help assess analgesia during laparoscopic surgeries under general anaesthesia, according to a new study published in Indian Journal of Anaesthesia.

Anaesthesia is a combination of analgesia, unconsciousness, and paralysis of muscles. Because quantifying nociception under anaesthesia is difficult, the response to nociception is utilised to monitor it by increasing sympathetic activity or decreasing parasympathetic stimulation (i.e., increased heart rate (HR)).

The perfusion index (PI) is a continuous and non-invasive measure of peripheral perfusion. Sympathetic tone variations impact smooth muscle tone and may alter perfusion, although they are unaffected by saturation or HR variability.

A recent research looked at the changes in perfusion index (PI) in response to unpleasant stimuli when under general anaesthetic.

Twenty patients between the ages of 20 and 45, with informed consent, who were undergoing an elective laparoscopic procedure and were classified as physical status class I by the American Society of Anesthesiologists (ASA), were connected to standard monitors and SEDLINE, pulse oximetry (Root, Masimo Corporation®, Irvine, CA, USA) to monitor PI and Pleth-Variability Index (PVi). Anaesthesia was given to the patient. Pre-induction, during induction, before and after intubation, at the time of pneumoperitoneum (P0), and at the time of first laparoscopic port insertion, PI, PVi, heart rate (HR), and non-invasive blood pressure were all monitored (P1). After that, a 0.5 mcg/kg intravenous injection of fentanyl was given, and values were taken at the second (P2) and third (P3) port insertions. For up to 30 minutes, the aforementioned characteristics were recorded. Paired t tests were used to corroborate the findings statistically.

PI values after fentanyl enhanced from 5.33 ± 2.67 (P1) to 5.99 ± 2.8 (P2) (P < 0.001), and to 6.3 ± 2.88 (P3) (P < 0.001). This rise associated with a decline in HR, from 101.42 ± 12.53 (P1) to 87.93 ± 10.98 (P2) (P < 0.001), and to 83 ± 10.82 (P3) (P < 0.001).

The ratio of pulsatile to non-pulsatile blood flow in a person's peripheral tissue, such as their fingertip or earlobes, is known as PI. The finger photoplethysmographic waveform is based on two components of red and infrared light absorption. The steady quantity of light absorbed by the skin, bone, tissue, pigment, and non-pulsatile blood is the first component. A fluctuating quantity of light is said to be the second component. Pulsatile arterial blood flow is used to measure it. The infrared pulsatile signal is indexed against the non-pulsatile infrared signal and represented as a percentage for PI calculations. It varies from 0.02 percent (extremely weak pulse intensity) to 20%. (very strong pulse strength).

Pain causes sympathetic activation, which causes vasoconstriction and a drop in PI. Because of the clear link between pain and sympathetic nerve activation, it's possible that PI may be utilised to measure pain.

The rise in PI and reduction in HR after analgesic delivery were significant in this research (P 0.001). After excluding confounding factors, it was discovered that the change in PI could be used as a surrogate monitoring tool to determine nociception intraoperatively in relatively fit (ASA physical status class I and II) surgical patients.

Reference –

Surekha, C; Eadara, Venkata S.,; Satish Kumar, M N Evaluation of perfusion index as an objective tool to assess analgesia during laparoscopic surgeries under general anaesthesia, Indian Journal of Anaesthesia: April 2022 - Volume 66 - Issue 4 - p 260-265. doi: 10.4103/ija.ija_658_21