Photoplethysmogram change by Trendelenburg position and insufflation of abdominal carbon dioxide

Abstract

To the Editor: Laparoscopic surgery has an inherent risk of complications because of increased abdominal pressure (IAP) and intra-abdominal carbon dioxide inflation [1]. We report a case where venous pulsation was detected in finger photoplethysmogram (PPG) during laparoscopic surgery in the head-down position (HDP). A 32-year-old woman (height 160 cm, weight 64 kg) was scheduled for laparoscopic right ovarian cystectomy. Preoperatively, she had no significant medical history except for a previous caesarian section. Before induction of anesthesia, the blood pressure was 125/74 mmHg and the heart rate was 90/min. The patient’s status was monitored by routine protocols. The PPG probe (DS 100A; Nellcor, Pleasanton, CA) was placed on the right index finger and connected to a patient monitor (Solar 8000M; GE Medical System, Milwaukee, WI). PPG data were stored via a 12-bit analog-digital converter (EZAD-512; ELBIO, Seoul, Korea) at a rate of 100 Hz. After induction of anesthesia, the patient was placed in the lithotomy position with the right arm abducted at 90 and the left arm attached to the side of body. Initial PPG was normal (Fig. 1a) and pulse oximetry values (SpO2) were 99 %. After carbon dioxide was insufflated at a pressure of 12 cmH2O, the operating table was tilted to 30 in the HDP. The SpO2 was 95 % and the waveform of PPG showed unexpected peaks and high amplitude (Fig. 1b). Arterial blood pressure changes were within 20 mmHg during the position change. When the PPG probe was moved to the patient’s other finger, the same SpO2 and PPG were observed. However, when the PPG probe was placed on a finger of one of the authors, normal PPG was obtained, thereby confirming that the PPG probe was functioning well. A tourniquet (tourniquet 4500; VBM, Sulz, Germany) was applied to the right upper arm at a pressure of 20, 30, 40, and 50 mmHg to confirm the venous origin of the abnormal waveform (Fig. 1c) [2], with subsequent increase in the SpO2 to 97 %. The amplitude of abnormal peaks in PPG was slightly reduced when abdominal CO2 was deflated in the HDP, but its waveform was still different from that of normal PPG (SpO2 96 %). Normal SpO2 (99 %) and PPG similar to that in Fig. 1a were displayed when the patient was placed in the supine position without tourniquet application. It is possible that the pressure of the tourniquet could block the venous effect resulted from mild tricuspid regurgitation (around 20 mmHg), HDP (around 20 mmHg), and IAP (12 mmHg). The implication of this case report is that venous pulsation in PPG could be induced by IAP and HDP. The possible mechanism is that mild tricuspid regurgitation aggravated by HDP may cause a high degree of variability in the PPG. In this case, HDP significantly contributed to the formation of venous pulsation in PPG; however, IAP J.-H. Bahk W. Ahn (&) Department of Anesthesiology and Pain Medicine, Seoul National University Dental Hospital, 103 Daehangno Jongno-gu, Seoul 110-768, Republic of Korea e-mail: aws@snu.ac.kr