Application of control chart statistics to blood pressure measurement variability in the primary care setting

This study was undertaken as an interdisciplinary effort in response to a frequently frustrating clinical problem of interpreting variable blood pressure measurements under uncertain conditions of quality control. The method is an application of the Shewhart Control Chart analysis to blood pressure measurement in adults in an academic nursing center. The natural variability found in a series of blood pressure readings is measured and described after a pilot study to eliminate examiner, equipment, and time interval variability. Results revealed that there was a significant drop from the first systolic reading to subsequent readings. A three standard deviation limit will be met if the range between the second and third systolic reading does not exceed 13 and the range between the second and third diastolic readings does not exceed 11. Thus for recognition and management of measurement variability, three blood pressure measurements 1 minute apart should be taken as a routine, and the average of the second and third reading recorded. The positive impact on clients, providers, and interdisciplinary research colleagues in changing measurement technique to achieve greater quality in clinical practice is discussed. Limitations and recommendations are presented.