Comparison of blood pressure measurements obtained using non-invasive and invasive techniques, in anaesthetised companion animals

Measurement of blood pressure is a critical tool in the monitoring of patients undergoing general anaesthesia and has become standard practice within medical fields. Adequate vital organ perfusion is reported to be achieved if a central mean arterial pressure (MAP) is greater than 60mmHg. In clinical practice, peripheral arterial blood pressure (ABP) is used as an estimate of central ABP. Measurement of peripheral ABP can be performed either invasively or non-invasively. While invasive blood pressure measurements (IBP) are considered to be more accurate than non-invasive blood pressure (NIBP) measurements, several studies comparing the two methods have demonstrated that measurements obtained non-invasively are still clinically useful. As the algorithms used for measuring blood pressure vary between different machines it is not possible to extrapolate results from one machine to another and thus each machine must be assessed separately to ensure interpretation of the measurements obtained in clinical patients is appropriate. The purpose of this thesis was to compare both NIBP and IBP measured using the multi-parameter Surgivet monitor (V9203) in anaesthetised dogs, horses, and sheep. Concurrent measurements of NIBP and IBP were obtained in each species at different pressure levels. These pressure levels were divided into the following categories: hypotension (< 60mmHg), low blood pressure (60-80 mmHg), normotension (80-100mm Hg), high blood pressure (100-120 mmHg), and hypertension (> 120 mmHg).For pooled data and data subdivided based on BP category the relationship between IBP and NIBP was determined using the Bland-Altman technique. The bias and precision for concurrently recorded IBP and NIBP measurements was calculated. In all species, NIBP measurements were generally lower than IBP. Overall for both the dog and the horse data, the mean arterial pressure showed the least bias i.e. the greatest agreement between the two methods. Systolic blood pressure tended to