Mercury versus Dinamap blood pressure measurement: a randomised crossover trial

A routine aspect of nursing practice is obtaining accurate and reliable assessments of patients' blood pressure. Traditionally, blood pressures have been measured using a manual mercury sphygmomanometer. In recent years the trend has been to use automated blood pressure machines. However, many nurses question the accuracy and reliability of these machines when used in the clinical setting. A review of studies that have evaluated the use of automated blood pressure machines provide conflicting results across a variety of patient populations and clinical settings. Of note is that no studies have been reported that test the use of automated blood pressure machines with adult hospital patients presenting with a range of common illnesses and health concerns. The purpose of this study was to determine the accuracy and reliability of a commonly used automated blood pressure machine (Dinamap 81 00) relative to the manual mercury sphygmomanometer. A randomized crossover design was used to test the hypothesis that there would be no significant difference in systolic and diastolic blood pressure readings between the two devices. Blood pressure measurements were obtained from a sample of 63 adult in-patients recruited from medical, surgical, orthopaedic and critical care wards of a large hospital in regional Victoria, Australia. Blood pressure measurements for each patient were taken concurrently by two registered nurses using a manual and an automated device, with type of device and the arm from which the measures were obtained randomly determined. Each nurse was blind to the readings obtained by the other nurse. To control for potential threats to the internal validity of the study, the technique for taking blood pressure readings was standardized as was cuff sizes. A data collection form was designed to record systolic and diastolic blood pressure readings, type of device, cuff size, time and date of measurement, and patient details such as age, gender and diagnosis. To test the hypothesis of 'no difference' between blood pressures taken with the Dinamap machine and those taken using a manual sphygmomanometer, level of agreement for systolic and diastolic readings were examined using four sets of criteria: intercorrelations between automated and manual readings, the Association for the Advancement of Medical Instrumentation (AAMI) criteria, the British Hypertensive Society (BHS) grading system, and Bland-Altman plots. Separate analyses were conducted for the two assessors: Nurse A with extensive nursing experience and Nurse B with less experience. Results of analyses for Nurse A supported the research hypothesis on all four criteria for both systolic and diastolic blood pressure readings. For Nurse B only partial support was provided, with agreement between the two devices on systolic but not diastolic readings. Thus the recommendation from this study is that nurses can use the Dinamap with confidence to assess blood pressures in a general population of adult hospital in-patients, but with the proviso the nurse taking the measures has sufficient experience. Comparison of mean differences in automated and manual measures found the Dinamap machine consistently under-read both systolic and diastolic blood pressures. With the exception of one diastolic comparison, these differences were not considered to be clinically significant. Findings from the study are discussed in relation to the research literature and implications for clinical practice. Also considered are methodological issues and directions for further investigation.