P r o c e d u r e s P r o

Indirect Blood Pressure Measurement

aintenance of appropriate systemicarterial blood pressure is vital for sur-vival. Because many common situations

and conditions (eg, general anesthesia, renal orcardiovascular disease) place animals at risk fordangerously high or low blood pressure, bloodpressure monitoring is a fundamental necessity.

In clinical practice, blood pressure is usuallymeasured indirectly. The two most commonmethods of indirect blood pressure measurementare Doppler ultrasound using a sphygmomanome-

ter and oscillometry. Both techniques use aninflatable cuff placed around an extremity. High-definition oscillometry, a newer indirect tech-nique, is not used often in clinical practice.

DOPPLER ULTRASOUNDMEASUREMENTDoppler ultrasound measurement is likely themost common blood pressure measurementtechnique used in small animal practice. Theprocedure is straightforward, and the equipmentis relatively inexpensive and reliable.

C A R D I O L O G Y

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Peer Reviewed

WHAT YOU WILL NEED

For Doppler Ultrasound Blood PressureMeasurement

� Doppler ultrasound with attached Doppler probe

� Headphones, if desired

� Sphygmomanometer

� Tape measure with metric scale

� Cuff of appropriate size

� Clippers with clean blade

� Ultrasound transmission gel

For Standard Oscillometry Blood PressureMeasurement

� Oscillometer with pressure tubing attached

� Tape measure with metric scale

� Cuff of appropriate size

M

Jamie M. Burkitt Creedon, DVM, DACVECC

Red Bank Veterinary Hospital Network

Cherry Hill, New Jersey

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Doppler ultrasound reliably measures only sys-tolic blood pressure in dogs and cats; it cannot beused to measure mean or diastolic blood pressure.

STANDARD OSCILLOMETRYMEASUREMENTIn clinical practice, oscillometers are often builtinto multiparameter monitors and usually have astat feature that allows continual, repeated meas-urements. Thus oscillometers are commonly usedfor critically ill or anesthetized patients that mayrequire more intensive monitoring.

Oscillometers report systolic, diastolic, and meanblood pressures; however, they are unreliable inpatients with cardiac dysrhythmias because meas-urement relies on rhythmic arterial pulsations.

GENERAL TECHNIQUESWhile actual blood pressure measurement variesbetween the techniques described here, someimportant points apply to both.

Patient Acclimation & RestraintIdeally, blood pressure should be measured in aquiet, comfortable environment after the patienthas become acclimated (ie, without disturbance)for at least a few minutes, but acclimation israrely possible for acutely or critically ill patients.

The patient should remain still during measure-ments to optimize accuracy and, if necessary, canbe physically restrained gently. However, somepatients cannot be restrained in lateral recum-bency because of agitation, respiratory distress, orother reasons. Chemical restraint should beavoided, as it often alters results.

Cuff HeightTo acquire the most accurate blood pressure val-ues, cuff height should be as close to the level ofthe right atrium as possible (Step 1A, page 28).

The cuff can be placed on the antebrachium,distal pelvic limb, or tail.

If the vertical distance between the cuff site andthe right atrium exceeds 10 cm, a correction fac-tor must be integrated to interpret blood pressuremeasurement results (see Correcting for Cuff &Right Atrium Level Disparity, page 28). Whenthe cuff is much lower than the right atrium,pressure values are falsely high because of theweight of the blood column between the atriumand cuff site.

Multiple MeasurementsThe first blood pressure measurement should bediscarded. At least 3 additional measurementsshould be obtained for a minimum of 3 to 7 con-secutive, consistent measurements with less than20% variability. Once these measurements havebeen obtained, they should be averaged to yieldthe blood pressure measurement.

C O N T I N U E S

All photos of Beezus courtesy ofDr. Burkitt Creedon

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STEP-BY-STEP DOPPLER ULTRASOUND BLOOD PRESSURE MEASUREMENT

STEP 1

STEP 2

Clip the hair overlying the Doppler probe’s target artery.The target artery must lie distal to the cuff site. Whenusing the antebrachium for cuff placement, clip over thepalmar aspect of the metacarpals (shown). When using thedistal pelvic limb, clip from the dorsal or plantar surface ofthe metatarsals for access to the dorsal pedal artery orbranch of the saphenous artery, respectively. When placingthe cuff at the tail base, clip from the tail’s ventral midlinejust distal to the intended cuff site.

Gather supplies and selectappropriate cuff size. Thenumeric cuff size (ie, widthin centimeters) should be40% of the circumference ofthe cuff site in dogs and 30%to 40% of the circumferenceof the cuff site in cats.Measure the site using acentimeter-marked tape (A)or estimate using the cuffitself (B). A cuff that is toosmall or tight results infalsely elevated readings, anda cuff that is too large orloose results in falsely lowreadings.

A B

CORRECTING FOR CUFF & RIGHTATRIUM LEVEL DISPARITY

If the height differencebetween the cuff and theright atrium exceeds 10 cm,subtract 0.8 mm Hg forevery 1 cm the cuff sitsbelow the right atrium.In lateral recumbency, thesternum can generally beused as the reference. Insternal recumbency theright atrium level is at about40% the height of an imagi-nary line between the ster-

num and the dorsal spinous process at the caudaledge of the scapula.

Here, the midpoint of the cuff sits approximately 27cm below the right atrium. If the measured systolicpressure at this level were 142 mm Hg, correct themeasurement as follows to yield a more accuratereading:

27 cm × 0.8 mm Hg/cm = 21.6 mm Hg

142 mm Hg – 21.6 mm Hg = 120.4 mm Hg

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STEP 3

Apply the cuff securely and snuglyaround the appendage, and attachit to the sphygmomanometer. Thecuff should not be occlusivelytight, and there should be noroom to insert a finger betweenthe cuff and appendage. Thesphygmomanometer pressureshould read 0 mm Hg.

STEP 4

Apply copious acoustic gel to theconcave surface of the Dopplerprobe, and press the concave sur-face gently but firmly over the tar-get artery. Turn the Doppler uniton and listen for the pulsatilewhooshing sound of the artery.With the patient in lateral or ster-nal recumbency, it is usually possi-ble to hold the limb comfortably atapproximately the level of the rightatrium (see Step 5).

STEP 5

Use the sphygmomanometer to inflate the cuff to approximately 20 mm Hggreater than the expected systolic blood pressure. The cuff should occlude theartery at this pressure, and whooshing arterial pulsations should be inaudible.Slowly deflate the cuff and note the pressure at which arterial pulsation isagain audible; this marks the systolic arterial blood pressure.

Most com-mercial cuffs

have Velcro closures that can loosenduring inflation. Medical tape can beplaced to secure the cuff ’s closure, butbe certain not to further tighten the cuffwith the tape, which would invalidatethe measurement. This is true for bothtechniques.

AUTHOR INSIGHT

Consider using headphones to minimize ambientnoise and to avoid frightening the patient.

AUTHOR INSIGHT

Deflate the cuff only a few mm Hg/sec in order to hear thefirst pulse wave passing under the cuff, heralding systolic

pressure. Opening the valve too quickly results in falsely low readings because thetrue systolic pressure is missed.

AUTHOR INSIGHT

C O N T I N U E S

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STEP-BY-STEP STANDARD OSCILLOMETRY BLOOD PRESSURE MEASUREMENT

STEP 1

STEP 2

Place the cuff securely and snugly around theappendage. It should not be occlusively tight,but there should be no room to insert a fingerbetween the cuff and the appendage. Attachthe cuff to the oscillometer.

STEP 3

Turn on the oscillometer and depress the measurement buttonwhile holding the cuff at approximately the height of the rightatrium.

Support the dog’s limb fromunderneath while restraining the

dependent limb. Many dogs resent having their paws han-dled, and this technique minimizes patient movement andtension in the limb, which can adversely affect results.

AUTHOR INSIGHT

See Aids & Resources, back page, for references & suggested reading.

A B

Note: Same as Step 1 for Doppler Ultra-sound Blood Pressure Measurement.Gather supplies and select the appro-priate cuff size. The numeric cuff size(ie, width in centimeters) should be40% of the circumference of the cuffsite in dogs and 30% to 40% of thecircumference of the cuff site in cats.Measure the site using a centimeter-marked tape (A) or estimate usingthe cuff itself (B). A cuff that is toosmall or tight results in falsely ele-vated readings, and a cuff that is toolarge or loose results in falsely lowreadings.