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Prospective observational investigation of postoperative respiratory monitoring in women undergoing cesarean delivery with intrathecal morphine administration
Abstract Number: BP-06
Abstract Type: Original Research
Background: Intrathecal morphine (ITM) for cesarean delivery (CD) provides effective analgesia, however oxygen desaturation and bradypnea have been reported.(1) We used capnography, Capnostream™20 (Medtronic Boulder,CO,USA), to assess respiratory variables and apnea alert events (AAEs) after CD.
Methods: A prospective, observational IRB-approved study. All CDs received ITM 150 mcg. Recruited subjects were requested to use capnography/pulse oximetry up to 24h after CD. Nasal CO2 sampling measured end-tidal CO2 (EtCO2, mmHg) and respiratory rate (RR, bpm); and pulse oximeter measured SpO2, %. Variables alerted when: EtCO2<10, RR<8 or SpO2<94. Capnography data was defined as valid when EtCO2>10, RR>5, SpO2>70; or “no breath” for 30-120 secs. AAE was defined as “no breath”, 30-120s. The number of AAEs and variable alerts prior to, during and after AAE, and nurse RR assessments (hourly and blinded to monitors) are reported.
Results: We recruited 80 subjects, aged 34.5±5.1yrs, 47% had >90kg/BMI>30, 11% had suspected obstructive sleep apnea. Duration of valid capnography and SpO2 data was 8:28(7:51)[0:00-22:32]h:min and 15:08(6:42)[1:31-23:07]h:min respectively; 6 subjects did not use the device. There were 198 AAEs (duration 57±27s) experienced by 39/74(53%) subjects; 35/74(47%) had no AAEs, Fig. 1. The number of variable alerts/min, 5 min prior to, during, 5 min after the AAEs were: EtCO2 1.7(2.2), 4.6(1.8), 4.6(5.5); RR 2.1(2.2), 5.7(0.6), 6.2(5.5); SpO2 0.9(1.7), 0.9(1.8), 2.1(4.1). The hourly means for RR and SpO2 are presented in Fig. 2. Nursing RR observation was RR ≥14 bpm at all time-points, the Pearson Correlation Coefficient is r=0.051 (p =0.246) between capnography and nursing RR. Two subjects (had 0 and 7 AAEs) received oxygen. 81% of subjects complained of itchy nose/feeling sick/visitors/baby/other inconvenience with capnography.
Conclusion: We report 198 AAEs detected by capnography after CD with ITM, however nursing observations did not reveal any clinical respiratory depression. Absence of observer verification precludes distinction between real, albeit non-clinically significant alerts with capnography, versus false AAEs.(2) Continuous respiratory measurements by capnography might alert for apneas that intermittent hourly nursing observations may miss. However subject-expressed device discomfort, and frequent alerts may impact capnography application after CD.
References: 1) Pan. J Clin Anesth 1994;6:124 2) Bauchaut. Anesth Analg 2017prepub