BJA Advance Access originally published online on July 25, 2007
British Journal of Anaesthesia 2007 99(4):567-571; doi:10.1093/bja/aem206
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Observational study of perioperative PtcCO2 and SpO2 in non-ventilated patients receiving epidural infusion or patient-controlled analgesia using a single earlobe monitor (TOSCA)
1 Department of Anaesthesia, Greater Glasgow University Hospitals, Southern General Hospital, Glasgow, UK
2 Department of Anaesthesia, Greater Glasgow University Hospitals, Gartnavel General Hospital, Glasgow, UK
* Corresponding author: Department of Anaesthesia, Greater Glasgow University Hospitals, Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF, UK. E-mail: a.kopka{at}doctors.org.uk
Background: TOSCA, a non-invasive monitor with a single earlobe probe incorporating a Stow–Severinghaus electrode and optical sensor (Linde Medical Sensors AG, Basel, Switzerland), has previously been used with ventilated patients and in sleep laboratories. We recorded transcutaneous carbon dioxide pressures (PtcCO2) and oxygen saturations (SpO2) in non-ventilated patients to investigate opioid-induced respiratory depression.
Methods: This observational cohort study included 28 ASA I and II patients, monitored between 10 p.m. and 6 a.m., before and after elective major laparotomy. After operation, patients were kept on oxygen, 4 litre min–1, and received either bupivacaine (0.1%) containing fentanyl (2 µg ml–1) via epidural catheter (epidural analgesia group, EPI; n = 14) or morphine via patient-controlled analgesia infusion pump (PCA-morphine group, PCA; n = 14).
Results: The preoperative median (lower/upper quartile) PtcCO2 was similar in both groups at around 5.5 kPa, but significantly higher after operation in PCA with 6.9 kPa (5.6/7.3) (P = 0.02), accompanied by a longer hypercarbia time >6 kPa of 6.6 h (0.1/8.0) (P = 0.04), and lower respiratory rates of 13.9 breaths min–1 (13.3/15.4) (P = 0.04). In EPI, the corresponding results were 5.8 kPa (5.5/6.0), 1.2 h (0.1/4.3), and 16.2 breaths min–1 (14.8/16.7). The perioperative median SpO2 in both groups was comparable within the normal range, although generally higher when on supplemental oxygen (P = 0.26). The SpO2 time <94% was similar in both groups (P = 0.33) as were pain scores (P = 0.25).
Conclusions: PtcCO2 recording in patients on PCA-morphine and supplemental oxygen revealed hypercapnia in the presence of normal respiratory rates and SpO2 values. This is recommended as an easy and sensitive monitor of respiratory depression and may have a role in the safe administration of opioid-analgesia.
Keywords: capnometry; carbon dioxide, hypercapnia; carbon dioxide, hypercarbia; oxygenation, tissue, cutaneous; oxygenation, tissue, subcutaneous
Part of this work was presented at the 2005 annual meeting of the European Society of Anaesthesiology in Vienna, Austria, and published in the European Journal of Anaesthesiology 2005; 22 (Suppl 34): 16.