Evaluation of noninvasive oscillometric blood pressure monitoring in anesthetized boid snakes

Abstract

Objective: To determine the accuracy of a noninvasive oscillometric monitor in the measurement of arterial blood pressure in anesthetized boid snakes.

Design: Evaluation study.

Animals: 4 boa constrictors (Boa constrictor), 2 carpet pythons (Morelia spilota), and 2 reticulated pythons (Python reticulatus).

Procedures: After induction of anesthesia with isoflurane, each snake was instrumented with an arterial catheter connected to a pressure transducer and oscilloscope to obtain invasive measurements of systolic (SAP), diastolic (DAP), and mean (MAP) arterial blood pressure as well as a pressure waveform. A cuff connected to an oscillometric device was placed on the tail immediately distal to the vent for noninvasive measurements. Heart rate, respiratory rate, and invasive and noninvasive measurements of SAP, DAP, and MAP were obtained every 5 minutes for 45 minutes. Delivered isoflurane concentration was increased in 15-minute increments to induce hypotension. Repeatability of each device and fixed and proportional biases between devices were calculated.

Results: Throughout most of the measured ranges of blood pressures, the oscillometric unit overestimated the SAP and underestimated the DAP and MAP, compared with respective direct measurements. When the invasively determined SAP was > 100 mm Hg, the oscillometric unit underestimated all 3 variables. Fixed bias was significant for SAP and DAP, and proportional bias was significant for SAP and MAP.

Conclusions and clinical relevance: When using an oscillometric blood pressure monitor on anesthetized boid snakes, veterinarians can potentially monitor changes in blood pressure, although the displayed readings may underestimate DAP and MAP and overestimate SAP. Indirect measurements of blood pressure made with the oscillometric device cannot substitute for direct measurements.