Transcutaneous carbon dioxide levels and oxygen saturation following caesarean section performed under spinal anaesthesia with intrathecal opioids.

BACKGROUND: Intrathecal opioids can be associated with respiratory depression which may have serious consequences. We describe the use of a non-invasive monitor (TOSCA) to measure transcutaneous carbon dioxide levels and percentage of haemoglobin oxygen saturation in post-caesarean section patients in two hospitals which used different intrathecal opioids.
METHODS: Eighty-nine women undergoing caesarean section were monitored postoperatively until 08.00h on the first postoperative day. In addition to hyperbaric bupivacaine, patients from Hospital 1 received intrathecal diamorphine 300μg: those from Hospital 2 received intrathecal fentanyl 15μg and postoperative intramuscular morphine 10mg and were given morphine patient-controlled analgesia. Data from TOSCA were analysed the following day. Respiratory depression was defined as oxygen saturations <90% or transcutaneous carbon dioxide levels >7kPa for >2min or the need for medical intervention for clinical respiratory depression.
RESULTS: Sustained hypercapnia was recorded in 8/45 (17.8%) patients from Hospital 1 and 3/44 (6.8%) from Hospital 2. Sustained oxygen saturations <90% were recorded in one patient from Hospital 2 and none from Hospital 1. The overall incidence of respiratory depression was 17.8% in Hospital 1 and 9.1% in Hospital 2. The median duration of hypercapnia was 9min [IQR 5.8-12.4] in Hospital 1 and 11.5min [IQR 7-32.8] in Hospital 2. No patient required medical intervention.
CONCLUSIONS: The incidence of opioid-induced respiratory depression detected by TOSCA is higher than previously reported by other monitoring methods. TOSCA may have a role in detecting subclinical respiratory depression in the obstetric population. Further studies with a control population are needed.