Development of a new analgesic index using nasal photoplethysmography

Abstract

Although surrogate measures to quantify pain intensity have been commercialised, there is a need to develop a new index with improved accuracy. The aim of this study was to develop a new analgesic index using nasal photoplethysmography data. The specially designed sensor was placed between the columella and the nasal septum to acquire nasal photoplethysmography in surgical patients. Nasal photoplethysmography and Surgical Pleth Index (GE Healthcare) data were obtained for 14 min both in the absence (pre-operatively) or presence (postoperatively) of pain in a group of surgical patients, each patient acting as their own control. Various dynamic photoplethysmography variables were extracted to quantify pain intensity; the most accurate index was selected using logistic regression as a classifier. The area under the curve of the receiver-operating characteristic curve was measured to evaluate the accuracy of final model predictions. In total, 12,012 heart beats from 89 patients were used to develop a new Nasal Photoplethysmography Index for analgesic depth quantification. The two-variable model (a combination of diastolic peak point variation and heart beat interval variation) was most accurate in discriminating between the presence and absence of pain (numerical rating scale (NRS) ≥ 3). The accuracy and area under the curve of the receiver-operating characteristic curve for the Nasal Photoplethysmography Index were 75.3% and 0.8018, respectively, and 64.8% and 0.7034, respectively, for the Surgical Pleth Index. The Nasal Photoplethysmography Index clearly distinguished pain (NRS ≥ 3) in awake surgical patients with postoperative pain. The Nasal Photoplethysmography Index performed better than the Surgical Pleth Index. Further validation studies are needed to evaluate its feasibility to quantify pain intensity during general anaesthesia.

Performance of the nasal photoplethysmographic index as an analgesic index during surgery under general anaesthesia

“…According to a previous study on the performance of the SPI in awake patients 8 , the threshold of the SPI for detecting pain was 43.7 in the awake state and 35.5 in the general anesthesia state. The cut-off value of SPI presented in this study was lower than the manufacturer's recommendation.…”

“…In the operating theatre, the patients were monitored for their heart activity by using electrocardiography, end-tidal carbon dioxide partial pressure, and non-invasive blood pressure. A specially designed sensor was placed between the columella and nasal septum to acquire nasal photoplethysmography 8 . NPI score was calculated by retrospectively analyzing the nasal photoplethysmography wave data.…”

“…General anaesthesia was performed by administering propofol and remifentanil by a target effect-site concentration-controlled infusion using the Schnider and Minto models 9,10 . Target effect-site concentrations (Ces) of propofol were titrated to maintain bispectral index (BIS, Covidien, Boulder, CO, USA) values of less than 60 during induction and maintenance of anaesthesia 8 . Target Ces of remifentanil were adjusted to maintain stable haemodynamics (i.e., systolic blood pressure >80 mmHg; heart rate >45 beats/min) 8 .…”

“…Target effect-site concentrations (Ces) of propofol were titrated to maintain bispectral index (BIS, Covidien, Boulder, CO, USA) values of less than 60 during induction and maintenance of anaesthesia 8 . Target Ces of remifentanil were adjusted to maintain stable haemodynamics (i.e., systolic blood pressure >80 mmHg; heart rate >45 beats/min) 8 . Tracheal intubation was facilitated by administration of rocuronium at 0.6 mg/kg.…”

“…We developed the nasal photoplethysmographic index (NPI), which is calculated from diastolic peak point variation (Dia var ) and heart beat interval variation (HBI var ); the NPI is the first dynamic index to objectively evaluate pain, and is superior to SPI in distinguishing pain above NRS 3 8 . However, because NPI was developed using photoplethysmographic data obtained from conscious patients with pain (numerical rating scale ≥ 3), the performance of the NPI during general anaesthesia needs to be assessed.…”