Equine & Livestock

13 Fall/Winter 2021 | Equine Solutions We feel that the measurement of blood pressure during equine anesthesia is the most important parameter to monitor. The inhalant anesthetics used during surgery often cause vasodilation, which commonly results in arterial hypotension for horses. This can cause serious problems during the recovery and post-operative phases where the heavy horse tries to stand up almost immediately after coming out of anesthesia. We therefore pay very close attention to the monitoring of blood pressure and put immediate interventions into place when problems occur to prevent further issues arising later. There are two methods for obtaining blood pressure: Non- invasive (NIBP) and Invasive (IBP). Both are important, as they indicate the status of the horse under anesthesia, but early placement is important to ensure access when blood pressure drops - IBP allows for an accurate measurement to be given during those critical moments. As well as measuring blood pressure, placing an IBP line can also provide reliable samples of oxygen, CO 2 , pH, electrolytes and haematocrit - making an arterial catheter one of the most vital tools available to the anesthesiologist. Since hypotension and other complications to anesthesia can cause difficulty obtaining an accurate SpO 2 reading, blood gas analysis provides a crucial indication of what may not be able to be obtained by oximetry. To measure invasive blood pressure in adult horses, we place an invasive blood pressure line into the arterial lumen of the patient. This is either done in the facial (most often), metatarsal, or tail artery depending on the location of the surgery being performed. This is simple to do in horses as their arteries are usually very easy to access. During foal surgeries, a non-invasive cuff can be placed on the leg or tail, as well as using the invasive method. TIP 1 When placing the invasive blood pressure line, start as low as possible on the artery and place the catheter in the direction of the heart. We tend to use a needle or small catheter, and in the case of long surgeries, a little bit of glue helps to hold the catheter in place. TIP 2 Don't forget to zero the IBP function on the monitor to record a correct reading. The sensor needs to be placed at the level of the right atrium and be opened to the air before zeroing on the monitor. TIP 3 The height of the pressure transducer should always be at the height of the heart. When the surgery table moves up or down, the height of the pressure transducer should be adapted accordingly for correct IBP measurement. This is an example of a normal blood pressure wave with consistent waves followed by a small peak after each one (wave shown in red). Normal readings: Systolic: 90 to 120 mmHg Diastolic: 40 to 70 mmHg MAP: 60 to 85 mmHg Hypotension: MAP: <60 mmHg TIP 4 If this pattern changes, flush the catheter and check the wave again, and ensure proper IV fluid therapy is being given. IBP line in facial artery IBP line in metatarsal artery Invasive Blood Pressure – IBP Equine anesthesia tips

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