Aeromedical retrieval: invasive vs noninvasive blood pressure

The chaps from the Emergency Medical Retrieval Service in the UK compared invasive (IABP) and non-invasive blood pressure (NIBP) measurements on the ground and in the air. They concluded that NIBP was unreliable, although it was no worse in the aeromedical environment than in the hospital. Not surprisingly there was a better correlation between the mean IABP and NIBP than systolic or diastolic pressures (oscillometric NIBP devices measure the mean BP and derive systolic and diastolic using an algorithm specific to the device).

In their summary, they recommend:

  • IABP monitoring should be used in any unwell patient in whom accurate blood pressure measurement is desirable.
  • The aeromedical transport environment does not lead to less precise NIBP results than the non-transport environment.
  • Where NIBP measurement is the only option, the mean blood pressure should be used in preference to systolic measurements

Blood pressure measurement is an essential physiological measurement for all critically ill patients. Previous work has shown that non-invasive blood pressure is not an accurate reflection of invasive blood pressure measurement. In a transport environment, the effects of motion and vibration may make non-invasive blood pressure less accurate.

Consecutive critically ill patients transported by a dedicated aeromedical retrieval and critical care transfer service with simultaneous invasive and non-invasive blood pressure measurements were analysed. Two sets of measurements were recorded, first in a hospital environment before departure (pre-flight) and a second during aeromedical transport (in-flight).

A total of 56 complete sets of data were analysed. Bland-Altman plots showed limits of agreement (precision) for pre-flight systolic blood pressure were -37.3 mmHg to 30.0 mmHg, and for pre-flight mean arterial pressure -20.5 mmHg to 25.0 mmHg. The limits of agreement for in-flight systolic blood pressure were -40.6 mmHg to 33.1 mmHg, while those for in-flight mean blood pressure in-flight were -23.6 mmHg to 24.6 mmHg. The bias for the four conditions ranged from 0.5 to -3.8 mmHg. There were no significant differences in values between pre-flight and in-flight blood pressure measurements for all categories of blood pressure measurement.

Thus, our data show that non-invasive blood pressure is not a precise reflection of invasive intra-arterial blood pressure. Mean blood pressure measured non-invasively may be a better marker of invasive blood pressure than systolic blood pressure. Our data show no evidence of non-invasive blood pressures being less accurate in an aeromedical transport environment.

Comparison of non-invasive and invasive blood pressure in aeromedical care
Anaesthesia. 2012 Dec;67(12):1343-7