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Transcutaneous Carbon Dioxide Measurements with the Topological Oscillation Search with Kinematical Analysis (TOSCA) Monitor in Women Receiving Intrathecal Morphine for Post-cesarean Delivery Analgesia
Abstract Number: BP-03
Abstract Type: Original Research
INTRODUCTION: No standard definition of respiratory depression exists, so the true incidence of respiratory depression following intrathecal (IT) morphine for cesarean delivery (CD) is unknown.1 Respiratory depression is low (0.07-0.9%) when using respiratory rates (RR), oxygen saturation and sedation monitoring, but is much higher (17.8%) when defined by hypercapnia (>50mmHg).2,3 This is the first study evaluating hypercapnia using transcutaneous CO2 (TcCO2) levels in women receiving IT morphine for CD.
METHOD: This is a prospective observational study. Inclusion: ASA PS 2 women ≥37 wk, BMI <40kg/m2, scheduled for CD with spinal anesthesia and IT morphine. Baseline sleep apnea risk was assessed. TcCO2 levels were monitored for 24 h with the TOSCA monitor, which approximates PaCO2 (median difference 2-7 mmHg).4,5 Protocol: spinal anesthesia (hyperbaric bupivacaine + fentanyl + morphine 150 µg); postoperative analgesia (ketorolac 30 mg q 6h 24h, acetaminophen 325 mg/hydrocodone 10mg, 1-2 q6h prn). Routine orders for sedation and RR monitoring applied. Adverse respiratory events were recorded.
RESULTS: 120 women were recruited; 108 completed the study. Median monitoring duration was 22 (16 to 23) hr. TcCO2 values increased from the baseline in 107 women. Median (IQR) baseline and maximal TcCO2 values following IT morphine were 30 (30 to 40) mmHg and 47 (42 to 53) mmHg, respectively. Median increase from baseline was 13 (9 to 17) mmHg. Forty women (37%) had ≥ 1 TcCO2 recording >50mmHg. Median number of TcCO2 events >50mmHg was 113 (26 to 760) events/subject and a median duration of 21 (7 to 146) min. Median time from IT morphine to first TcCO2 >50 mmHg was 400 (120 to 652) min. Binary logistic regression identified higher baseline TcCO2 and supplemental opioids as independent predictors of hypercarbia (Fig1). Predictive accuracy was 0.84 (95% CI 0.76 to 0.93). No respiratory depression (RR<10) or profound sedation events were recorded.
DISCUSSION: This study confirms that hypercapnia occurs frequently in women receiving intrathecal opioids for CD. The perception that respiratory depression in this patient population is low may reflect sparse monitoring and the stimulating postpartum environment. Women with higher baseline TcCO2 may need to be more closely monitored postpartum.
1. Can J Anesth 2003;50:679-88
2. Anesth Analg 2013;117:1368–70
3. Int J Obstet Anesth 2013;22:217–222
4. Br J Anaesth 2010;104:774-8
5. Can J Anaesth 1992;39:31-6