Mr Christopher Marlow1,2, Dr Alexander Jones1, Dr Benjamin Meadley2, Dr Alexander Olaussen2
1SA Ambulance Service, Adelaide, Australia, 2Monash University, Melbourne, Australia
Abstract:
Introduction: HEMS patients require accurate and precise monitoring. Non-invasive blood pressure (NIBP) provides an easy and low-harm means of monitoring BP. Invasive arterial blood pressure (IABP) remains the “gold standard” for accurate, beat-to-beat monitoring but is associated with risks. The effects of motion and vibration may make NIBP less accurate. This study aimed to compare IABP and NIBP monitoring during helicopter transport. We hypothesised that the mean difference between systolic NIBP and IABP measurements would be greater than a clinically significant 5mmHg both on the ground and in the air. We also hypothesised that the mean difference between NIBP and IABP MAPs would be smaller than 5mmHg both on the ground and in the air.
Methods: A prospective, observational study was conducted. It compared radial IABP and mid-humeral NIBP readings (Zoll X series) of adult patients transported via helicopter. (Bell 412EP).
Results: 2312 data points from 54 patients were collected. Bland Altman plots showed limits of agreement (precision) for in-flight systolic BP were -42.99mmHg to 23.72mmHg (P<0.0001): in-flight MAP were -20.35mmHg to 20.14mmHg (P=0.87); ground systolic BP were -38.09mmHg to 25.27mmHg (P<0.0001), and ground MAP were -23.68mmHg to 21.61mmHg. (P=0.12). The mean difference (bias) for systolic readings on the ground was -6.41, whereas in flight: -9.63. The mean difference for MAP readings on the ground was -1.04, whereas, in flight: -0.11. (See Figure 1).
Conclusion: NIBP measurements appear imprecise and inaccurate compared to IABP. There were no significant differences between measurements in flight and on the ground. NIBP appears to overread at low IABPs and underread at high IABPs. Systolic NIBP measurements were biased to a clinically significant degree, as well as being imprecise. MAP measurements showed an acceptable degree of average bias but were still imprecise. This data strengthens the argument for instituting IABP monitoring when accuracy is required.
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