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

Drynan, Eleanor (2013) Comparison of blood pressure measurements obtained using non-invasive and invasive techniques, in anaesthetised companion animals. Masters by Research thesis, Murdoch University.

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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 show the least agreement between the methods and this was much more evident in the low blood pressure and normotensive blood pressure groups. Interestingly, from the sheep component of the study, the systolic blood pressure had the greatest agreement in each group.

To determine the clinical usefulness of the NIBP measurements the calculated bias and precision was assessed using the guidelines of the American Association for the Advancement of Medical Instrumentation and the American College of Veterinary Internal Medicine Hypertension Consensus Panel (AVCIMHCP). Using these guidelines, the agreement between NIBP and IBP measurements in greyhounds and horses, were found to be within the limits of agreement recommended by the ACVIMHCP for all pressures except systolic blood pressure. This suggests that the Surgivet NIBP can be used to provide a good estimate of IBP for mean and diastolic pressures in these species.

In conclusion, the results of this study demonstrated that non-invasive measurements of diastolic and mean ABP provide a clinically useful alternative to IBP measurements, particularly in the horses and greyhounds. However systolic BP measured using non-invasive techniques does not, and therefore needs to be interpreted cautiously. The results also demonstrate a tendency for NIBP measurements to underestimate IBP. This finding needs to be remembered when interpreting NIBP measurements obtained in clinical patients.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Raisis, Anthea and Glyde, Mark
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