Objective: Non-invasive blood pressure recordings may be inaccurate in the critically ill patient and measurement difficulties are intensified in the prehospital setting. This may adversely impact upon outcomes for many critically ill patients, particularly those with traumatic brain injury and/or lengthy prehospital times. This study aimed to validate a non-invasive, oscillometric, ambulatory blood pressure measuring device, the Oscar 2, Model 222 (SunTech Medical, Morrisville, USA) during the ambulance transport of critically ill patients.
Methods: We have previously shown that mean arterial blood pressures observed by Intensive Care Unit nurses from a patient monitor can be considered interchangeable with reference intra-arterial integrated mean pressures. In the current study, we compared non-invasive device mean pressures to intra-arterial pressures observed by retrieval nurses from the patient monitor, during the ambulance transportation of critically ill patients. Device performance was required to fulfil the Association for the Advancement of Medical Instrumentation (AAMI) protocol requirements. Additionally, linear mixed effects analyses and Bland-Altman comparisons were undertaken.
Results: For 157 measurements recorded from 23 patients, when the Oscar 2 did not indicate a measurement was associated with a fault, the device fulfilled the AAMI protocol requirements, with a mean error of -1.1 mmHg (standard deviation 7.8 mmHg), 95% confidence intervals (linear mixed effects analysis) -2.9, 0.8; P = 0.26. Bland-Altman plots indicated uniform agreement across a wide range of blood pressures. Sixteen percent of recordings were associated with a patient, environment, or device generated fault.
Conclusions: When the Oscar 2 does not indicate a fault has occurred, clinicians may be confident the mean pressure, within acceptable limits, is accurate, even during ambulance motion, administration of high doses of vasopressors and mechanical ventilation. The Oscar 2 appears to be an accurate and rugged out-of-hospital device.