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Prediction of blood pressure based on peripheral pulse palpation in cats | VETgirl Veterinary Continuing Education Podcasts

How do you assess your feline patients for shock at the time of triage?

Most of us check mucous membrane color as well as capillary refill time (CRT). We auscultate the heart rate which – in shocky cats – can be fast or slow. We check rectal temperatures, and we check peripheral pulse quality. However, until now, the correlation between palpation of pulse pressure and actual blood pressure has been debatable. Just because you can’t feel the femoral pulses… does that mean that the systolic blood pressure is < 60 or 90 mm Hg?

Sphygmomanometers and Dopplers are mainstay tools commonly used in the animal ICU for measuring systolic blood pressure in cats and dogs. These units can be a bit clumsy on the table top and the ability to locate the artery with the piezoelectric crystal takes a bit of finesse from trained technicians and doctors. Obtaining a blood pressure measurement in this fashion can take up to a few minutes or may not be possible at all. When the patient is critically ill and life-saving decisions need to be made on the fly, you may not have time to wait for a blood pressure measurement before acting on behalf of the patient. It is for these times that the ability to use pulse palpation as a rough estimate of the patient’s blood pressure would come in handy. But how accurate is it?

So, Reinke et al out of University of Pennsylvania, wanted to see how accurate it was in a study called “Prediction of systolic blood pressure using peripheral pulse palpation in cats.” This article is the first known study to investigate the correlation between palpable pulse pressures in cats with the corresponding systolic blood pressures.

First, the ability to digitally feel a pulse pressure in superficial peripheral arteries relies on the existence of a physiologic difference between the animal’s (higher) systolic blood pressure and (lower) diastolic blood pressure. The pulse pressure intensity that you feel will be influenced by how much volume the heart is able to push forth with each beat (stroke volume) and the vascular tone of the artery walls. In a severely hypovolemic patient, where there may not be adequate blood volume, the heart has less volume to push “forward” with each beat. This translates into a lower systolic blood pressure that approaches your diastolic blood pressure. When the two pressures approach one another in measurement, the pulse pressure – or the difference between the two – will be softer and softer until it is no longer palpable. But clinically, can we really call our two fingers “poor man’s Dinamap? (A common quote by Justine Lee/VETgirl).

In this prospective observational study, the clinician was asked to assess the pulse palpation over the cat’s femoral artery and dorsal metatarsal artery and describe them as either strong, moderate, poor, or absent. The technicians would then obtain a systolic blood pressure measurement by way of Doppler flow detector using standard technique. The locations used by technicians for Doppler flow detection included the radial artery or the dorsal metatarsal artery. In the study, cats were classified as being hypotensive if their systolic blood pressure measurements were averaged to be < 90 mm Hg. Exclusion criteria included cats with known thromboembolic diseases in the back legs (due to the clot’s interference with pulse pressure palpation and systolic blood pressure measurements). In this study, a total of 102 cats were included; however, 3 cats failed to have femoral pulse palpation assessment recorded and 14 cats failed to have dorsal metatarsal pulse palpation assessment recorded. What did they find in this study? The median systolic blood pressure for all cats was 92.5 mm Hg (with a range of 30 to 240 mm Hg). The authors found that cats with no palpable metatarsal and femoral pulses had a median measured SBP of 30 mm Hg (range: 30-105 mm Hg), which makes sense. If you can’t feel either pulse, your cat is likely very hypotensive. Likewise, they found that cats that had strong metatarsal pulses on palpation had a median SBP of 135 mm Hg (range, 58-210 mm Hg).

Overall, this study showed good correlation between a clinician’s assessment of the femoral pulse palpation as absent, poor, moderate, or strong and a significant correlating change in the actual systolic blood pressure as measured by Doppler flow. When evaluating the metatarsal pulse palpation, they only found there to be a significant difference in the corresponding SBP when comparing the patients with a pulse palpation described as either “absent” or “strong” but no areas in between. The authors also found that the absence of palpation of metatarsal pulses did correctly identify cats with a blood pressure of 75 mm Hg or less 84% of the time.

So, what can we take away from this VETgirl podcast?

When assessing the dorsal metatarsal pulse palpation, an absent pulse palpation correlated well with an SBP of <75 mm Hg. Pretty hypotensive. If both the metatarsal and the femoral pulses were absent, or if the metatarsal pulse was absent and femoral pulse was poor, these findings correlated well with severe hypotension (no specific value ascribed). Really hypotensive. Since many cats that had absent dorsal metatarsal pulse palpation still had palpable femoral pulse palpation, the authors advise that if the clinician is trying to assess for cardiopulmonary arrest that the femoral pulse should be attempted and not the dorsal metatarsal. Most importantly? Palpation of the dorsal metatarsal and femoral artery pulse pressures correspond well to trends in actual systolic blood pressure, but the femoral pulse pressure is perhaps more sensitive and will only be palpably absent in the face of severe hypotension.

Some pros and cons of the study? It would have been nice if this study emphasized a bit more that the dorsal metatarsal artery palpation is not as sensitive an indicator of systolic blood pressure as the femoral artery, so perhaps we should be defaulting to femoral pulse palpation in felines. In other words, for real – these dorsal metatarsals are hard to feel, man! Also, to improve the accuracy of this study, it would have been nice to compare physical examination palpation of arteries with direct arterial blood pressure monitoring under general anesthesia, which is the most accurate way – or considered the gold standard – for measuring SBP.

It should also be stressed that the femoral artery pulse pressure palpation being described as our standard “absent”, “poor”, “moderate”, and “strong” correlated well with the systolic blood pressure measurements, whereas the dorsal metatarsal pulse palpation only showed significance when described as “absent” or “strong”, and that an absent pulse palpation in this location could only correlate with an systolic blood pressure cutoff of somewhere below 75 mm Hg.

So, femoral pulse pressure palpation should be incorporated as a standard triage assessment for all feline patients for quick assessment of hypotension. If dorsal metatarsal palpation is utilized, an absent palpation should warrant assessment of the femoral pulse palpation for comparison before assessing the patient to have either hypotension or severe hypotension. Pulse pressure palpations over the metatarsal and femoral arteries in felines correlates well with systolic blood pressure measurements and can be used as a subjective crude assessment of blood pressure at time of triage. When in doubt, trust your gut instinct. If you can’t feel arterial pulses, your patient is likely very hypotensive, as this study found that peripheral pulse quality assessment did correlate well with SBP. Remember, if you can’t feel the femoral pulses, your patient is likely very hypotensive. It doesn’t matter how many toys or whistles you have, your physical examination is your #1 tool in the veterinary patient!

References:
1. Reineke EL, Rees C, Drobatz KJ. Prediction of systolic blood pressure using peripheral pulse palpation in cats. J Vet Emerg Crit Care 2016;26(1):52-57.

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