The clinical evaluation of the Datex Ohmeda GE S/5 Monitor’s Non Invasive Blood pressure (E-PRESTN) module and the optimal placement of measurement cuff on the anaesthetized dog.

Abstract

Objective 1: To evaluate the Datex Ohmeda GE S/5 Non Invasive Blood Pressure module in comparison to the standard invasive arterial blood pressure (IABP) technique in anaesthetized dogs. Objective 2: To determine optimal cuff position and site for the noninvasive system on the patient. Objective 3: To assess the effect of different anesthetic protocols (methadone-isoflurane, dexmedetomidine-propofol and dexmedetomidine-alfaxalone) on the performance of the Datex Ohmeda GE S/5.

Study design: A prospective study.

Animals: Thirty-two client owned dogs undergoing a variety of surgical procedures.

Methods: Three different anesthetic protocols were used. Invasive blood pressure was measured using either the femoral or dorsal pedal artery. For oscillometric noninvasive blood pressure (O-NIBP) measurement, the cuff was placed at the contra lateral limb during the surgical procedure when possible, otherwise the tail base was used. Recordings were made pre-, per- and post operative. The tail base and front limb O-NIBP measurements were continued post operatively. Statistical analysis of the Invasive Arterial Blood Pressure (IABP) and O-NIBP data was performed using a (modified, percentual) Bland Altman analysis. An ANOVA was used to compare the different protocols.

Result 1: The Datex Ohmeda GE S/5 O-NIBP produced highly variable results for all blood pressure measurements. The least variable results came from the Mean Arterial Pressure (MAP) for all measurement-sites. Result 2: The most reliable site for O-NIBP measurements is the tail base followed by the hind limb. The front limb is less accurate. Result 3: The number of failures in order to obtain a direct reading in the Datex O-NIBP were higher in the dexmedetomidine protocols. Bias itself did not differ between the protocols.

Conclusion 1 & 2: The most accurate data produced by the Datex O-NIBP was the MAP. The optimal site for cuff placement was the tail base. However, due to the high variability of all values it is difficult to determine whether the machine is producing accurate (e.g. unbiased) results. It should be noted that trend information (multiple consecutive measurements) gathered with the Datex O-NIBP can be useful. However sudden drops or increases of O-NIBP do not necessarily indicate that the anesthesia is insufficient, as it could also be accounted for by the variability of the O-NIBP. Conclusion 3: Anesthetic protocols do influences the number of failures to provide direct measurement. This is most likely related to the use of dexmedetomidine (a2-agonist) which causes vasoconstriction. This vasoconstriction is the likely culprit for the increased failure to provide direct measurements with the Datex O-NIBP.

Clinical relevance: The Datex Ohmeda GE S/5 can not be used on patients that need accurate blood pressure monitoring because of high anesthetic risks (ASA-III or up). In cases where placement of the arterial catheter-system for the IABP fails and patients in ASA-I and ASA-II (where protocols usually don’t include measurement of the arterial blood pressure (ABP)) it can be used to get information on the arterial blood pressure trend. In these before mentioned situations, the MAP is shown to be the most reliable.