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Agreement of Nexfin® non-invasive cardiac output monitor with non-invasive blood pressure measurement in patients undergoing Cesarean delivery under spinal anesthesia: a pilot observational study
Abstract Number: O1-01
Abstract Type: Original Research
Hypotension occurs under spinal anesthesia in 55-90% of Cesarean deliveries (CD), causes feto-maternal morbidity, and can be managed with vasopressor infusions necessitating frequent blood pressure (BP) measurement(1). Non-invasive blood pressure (NIBP) measurement devices record BP once per minute at most, and measurement may fail due to patient movement or shivering(2). Frequent NIBP measurement is uncomfortable and may be associated with permanent injury(3).
The Nexfin® non-invasive cardiac output monitoring system uses a finger cuff to display continuous cardiac output data including BP. It is validated in the pregnant population(4) and has been studied in elective CD under spinal anesthesia(5).
We aimed to assess agreement between Nexfin® and NIBP, hypothesising acceptable agreement with lower measurement failure rates and higher patient comfort scores in the Nexfin® group.
Healthy term pregnant patients undergoing CD under spinal anesthesia gave written consent. In the operating room, standard monitors were applied. An appropriately-sized Nexfin® finger cuff was applied on the contralateral side to the NIBP cuff. Baseline NIBP data comprising systolic (SBP), diastolic (DBP) and mean arterial pressures (MAP) were calculated from the mean of three readings taken 1 minute apart. Nexfin blood pressures (also SBP, DBP and MAP) were recorded simultaneously with each NIBP. Failure of either device (including re-cycling of the NIBP) to display a measurement was recorded.
After the anesthesiologist administered spinal or CSE anesthesia, NIBP was recorded every minute until 5 minutes after delivery. NIBP frequency was then reduced to once per 2 or 2.5 minutes at the anesthesiologist’s discretion. Data collection terminated at the end of surgery. The patient was asked to rate each device's comfort by marking a 100 mm visual analog scale (VAS) from 0 mm = extremely uncomfortable to 100 mm = extremely comfortable.
307 measurement pairs were obtained. Correlation coefficients for Nexfin vs NIBP were 0.51, 0.59 and 0.42 for MAP, SBP and DBP respectively. Bland-Altman plots are shown. The mean bias (95% limits of agreement) of Nexfin® over NIBP was 12.93 (-11.0 to 36.8) mmHg for MAP, 13.43 (-22.2 to 49.1) mmHg for SBP and 12.34 (-8.86 to 33.5) mmHg for DBP.
Measurement failure occurred in 14 NIBP and 2 Nexfin® measurements. Patient-reported comfort scores on the 100mm VAS were 80.7 mm (Nexfin®) vs 60.9 mm (NIBP), p<0.05.
We compared agreement between Nexfin® and NIBP and found it to be clinically unacceptable. Correlation between Nexfin® and NIBP was better for SBP than for MAP or DBP. However measurement failure rates and patient comfort scores were better in the Nexfin® group.
1 Minerva Anestesiol 2013;79(1):62-73
2 SOAP 2013 Abstract S1
3 Indian J Anaesth 2012;56(4):428–430
4 Hypertens Pregnancy 2009;28(2):230-42
5 Anaesthesia 2015 Jun;70(6):691-8