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Measuring Hypercapnia and Hypoventilation Using the TOSCA Monitor after Intrathecal Morphine Administration for Postoperative Analgesia following Cesarean Delivery
Abstract Number: S-33
Abstract Type: Original Research
INTRODUCTION: The true incidence of respiratory depression following administration of intrathecal (IT) opioid is unknown given its rare occurrence and lack of a standardized definition.1 Hypercapnia is a sensitive measure of respiratory depression.2 This is interim data measuring transcutaneous carbon dioxide (TcCO2) in women receiving IT morphine for cesarean delivery (CD) using the Topological Oscillation Search with Kinematical Analysis (TOSCA) CO2 monitor.
METHODS: This prospective observational study includes ASA PS 1-2 women ≥37 weeks gestation with body mass index (BMI)<40kg/m2 scheduled for CD under spinal anesthesia with IT morphine for postoperative analgesia. A sleep apnea STOP questionnaire was given and baseline TcCO2 was obtained. Subjects received spinal anesthetic (hyperbaric bupivacaine 12 mg+fentanyl 15 µcg); postoperative analgesic regimen (IT morphine 150 µcg+ketorolac 30 mg q 6h for 24h and 1-2 tablets of acetaminophen 325 mg/hydrocodone 10 mg q6h prn). TOSCA monitor was reapplied in recovery room and continued for 24 h. Routine orders for sedation and respiratory rate (RR) monitoring were applied. All episodes of RR <10, administration of narcan or need for continuous respiratory monitoring were noted. NRS scores, Richmond agitation-sedation scales, and sedative/opioid administration were recorded. 200 patients are needed to detect a difference in CO2 measurements with 81% power.
RESULTS: Interim analysis on 20 recruited women were analyzed. Mean age was 35 yr and mean BMI was 29 kg/m2. No women had a questionnaire suggesting sleep apnea. 20% required additional opioid analgesics in the PACU. Mean NRS scores were 1.5 and 1.7 at 4 and 10 hours post IT morphine injection respectively. No one had continuous pulse oximetry readings less than 97%. Mean hourly RR was 18, with no RR < 16. Mean peak TcCO2 was 43mmHg. 19 of 20 women did not have a reading of 45mmHg for greater than 1 min. (Top figure). One woman had TcCo2>45mmHg starting at 3 h and continuing for 14 h. (Bottom figure). Peak TcCO2 was 54mmHg at 11 h. Lowest SpO2 was 97% and lowest RR was 16. She received no additional sedatives or opiates.
DISCUSSION: One of 20 patients had prolonged hypercapnia as demonstrated by the TOSCA monitor. Further data is needed to assess predictability and frequency of hypercapnia after IT morphine for cesarean delivery and its implications on clinical care.
1. Can J Anesth 2003;50:679-88
2. Anesthesiology 2009;110:218-30