practical recommendations on the measurement of indirect ......international society of feline...

International Society of Feline Medicine(www.icatcare.org/vets)supported by Ceva Animal Healthisfm

Practical recommendationson the measurement ofindirect blood pressure

in cats

isfm International Society of Feline Medicine


ContentsIntroduction

Procedures: Background, methods, patient andenvironment considerations

Blood pressure assessment with the Doppler techniqueBlood pressure assessment with the HDO technique

Blood pressure assessment forms

ISFM Panel of AuthorsDr Andrew Sparkes (Veterinary Director)

Caroline BlundellMartha Cannon

Nikki GautAndrea Harvey

Zuzanna JacmenikovaSam Taylor

Audra-Lynne Turner

Aga Zoltowska

ISFM would also like to thank Ceva Animal Health for their help makingthe development of these recommendations possible

isfm Recommendations


IntroductionHypertension is a common clinical problem in cats, most frequently diagnosed in older cats(above 7-10 years of age), but still often overlooked. In some studies, hypertension hasbeen diagnosed in more than 5% of apparently healthy older cats.

The majority of hypertensive cats have an underlying disease that predisposes to thecondition, and chronic kidney disease (CKD) is the single most common of these, withstudies suggesting between 20% and 35% of cats with CKD may have hypertension

A diagnosis of hypertension may be suspected when a cat has a predisposing underlyingdisease (such as CKD, hyperaldosteronism, hyperthyroidism) or on the basis of clinicalsigns associated with so-called target organ damage (signs present in organs that arerecognised as being susceptible to the effects of systemic hypertension) such as:

• Hyphaema• Sudden onset blindness (retinal detachment)• Hypertensive retinopathy• Left ventricular hypertrophy• Neurological signs

Ideally, hypertension should be diagnosed and managed before systemic effects occur, soblood pressure measurement of at-risk cats (including older cats and those withassociated diseases) is strongly recommended on a routine basis.

It is generally considered that if systolic blood pressure is less than 150-160 mmHg, thenthe risk of target organ damage is mild to minimal, whereas if systolic pressure isconsistently greater than 180 mmHg the risk becomes severe. However, interpretation ofblood pressure measurements should take into account the individual cat, risk factors forhypertension, and the circumstances under which blood pressure was measured. It isimportant to exclude so-called white-coat hypertension (temporary elevations in bloodpressure due to stress) to avoid treating cats unnecessarily, and this is a common andimportant issue in cats.

This booklet provides recommendations from the International Society of Feline Medicineon the practical measurement of blood pressure in conscious cats in order to make thesemeasurements as accurate and reproducible as possible. Four short videos are alsoavailable to accompany these recommendations and illustrate the techniques involved.



Procedures: Background, methods,patient and environment considerations



isfm Recommendations on proceduresfor blood presure assessment

BackgroundHypertension (both primary and secondary to other diseases such as chronic kidneydisease - CKD) is a common disorder, especially in older cats, but the evaluation of bloodpressure and the diagnosis andmonitoring of hypertension are complex.Indirect blood pressure measurement isthe only acceptable method of assessingblood pressure in conscious cats, butthis is as much an art as a science.The two commonly used techniques forindirect blood pressure assessment arethe Doppler and oscillometric methods.In general, the Doppler method has beenregarded as more accurate (more closelyrepresenting true or direct bloodpressure readings) in conscious cats, butnewer generation oscillometric equipment (especially newer high definition oscillometric -HDO - machines) also appear to have acceptable accuracy for measuring systolicpressures in conscious cats.

Whether Doppler or oscillometric equipment is used to assessblood pressure, measurement of systolic blood pressure (SBP)in cats is considered adequate for clinical assessment, asisolated diastolic hypertension appears to be rare. However,because blood pressure assessment can be affected by somany variables (including the operator, the conditions andenvironment theprocedure isperformed in, theequipment used, theposition of the cat,and the site ofmeasurement) it isimportant to use

standardised protocols to reduce externalvariables as much as possible, but oncemastered, blood pressure measurement can be arelatively quick procedure in many cats.


Recommended protocolsSystolic blood pressure is labile and will vary considerably both within and betweenindividuals. Using a standardised protocol (as recommended by the American College ofVeterinary Internal medicine (ACVIM) in their consensus guidelines - JVIM 2007;21:542–558) will help to reduce the effect of external influences on blood pressure and makemeasurements more clinically reproducible and reliable. These recommendations, adaptedfrom the ACVIM consensus guidelines, are recommended for use in cats:1. Environment: It is essential to assess blood

pressure in a calm, quiet environment. This shouldbe away from other animals, with minimalpersonnel, with no other procedures occurring atthe same time and with no interruptions. Thechoice of room will depend on clinical needs and

circumstances - itmay (for example)be in a consultationroom, in a procedures room, in a hospital ward or in thehome environment. In some situations it may bepossible to measure blood pressure in a hospitalisedcat while it remains calm andcomfortable in its cage in thehospitalisation ward. However in

general blood pressure should be assessed while the cat is awayfrom other animals, never in the same room as a dog, and awayfrom noise, lighting or smells that may contribute to stress. Try tohave the cat resting on bedding which it is used to and whichcontains its own scent. The use of Feliway® in the environment oron the bedding may be valuable.

2. Acclimatisation: A minimum of 5–10 minutes shouldbe allowed in the environment (room) for the cat toacclimatise before blood pressure is measured. Thecat should be free to explore the environment andinteract with people in the room if it chooses to, butshould not be forcibly removed from the carrier. Acarrier with a removable top can allow the cat to stayin the bottom of the carrier, where some may feelsafer.



3. Personnel: The people present in the room during the acclimatisation period shouldbe the same people that will be present during measurement of the blood pressure.Blood pressure should be measured by a trained individual, and using a veterinarynurse or technician who is empathetic with cats is often desirable. When measuringblood pressure in cats seen as outpatients, it is often preferable to have the ownerpresent to reassure the cat in a quiet, gentle way.

4. Restraint: It is vitally important that minimaland gentle restraint is used in order to keepthe cat in a settled, comfortable position. Ifthe cat becomes agitated during theprocedure, it is better to stop and take abreak to allow the cat to settle down ratherthan persist with more active restraint. Whereappropriate, owners may assist withreassurance and gentle restraint of the cat –having comfortable and familiar bedding forthe cat to rest on will be helpful.

5. Positioning the cat: Where possible the cat shouldbe allowed to relax in a comfortable posture – lateral orsternal recumbency, sitting or standing. The cat shouldnot be restrained in lateral recumbency but if he or shechooses to lie in this position that is fine. It is best toattempt to keep the cat in the same positionthroughout the procedure and to avoid measuringblood pressure while the cat is moving.

6. Choice and position of cuff: For cats, the correct cuff width is 30–40% of thecircumference of the site where it is being applied (forelimb, hindlimb or tail). Anincorrect size will lead to false elevation (if too small) or false lowering (if too large) of the

measured blood pressure. Blood pressure can bemeasured on any limb or on the tail - the forelimb may beeasier and more reliable for Doppler, and the tail may bepreferable for HDO. Care may also be needed inmanipulating limbs of older arthritic cats in particular. Wherepossible, the site of blood pressure measurement should beroughly on the same horizontal plane as the heart. Moreexpensive cuffs are generally better and easier to use thancheaper ones!



7. Measuring blood pressure: Before measuring blood pressure it may be advisable toinflate and deflate the cuff a few times to get the cat used to the sensation.

Always discard the first SBP measurement andthen record 5–7 consecutive and consistent(<20% variability between readings)measurements. If there is a consistentdownward (or upward) trend in the individualSBP readings, further measurements should beundertaken (possibly after giving the cat a break)until consistent readings are achieved. The meanof 5-7 consistent recordings can then becalculated to give the final SBP. If necessary, theprocedure should be repeated to achieveconsistent individual readings, keeping the catcalm and still, and changing position andplacement of the cuff if necessary. If less than5-7 readings are available but they all suggest aconsistent blood pressure well within the normalrange, additional measurements may not be

necessary (especially if the cat is becoming agitated). However, if there is any doubtabout the validity of the measured SBP, regardless of the number of measurements,the procedure should be repeated - eitherimmediately, after a further period of quietacclimatisation, or at a later time point.

8. Written records: Careful records should be kept ofall important aspects of the blood pressuremeasurement (see example) ... these should includedate, time, environment, people involved, position ofthe cat, size of the cuff, site of cuff placement,equipment used, individual SBP measurements, andcalculated mean SBP.

9. Consistency: Where repeat blood pressureassessments are being performed over time, for thepurposes of meaningful comparison, it is important totry to replicate the assessment using the sameequipment, personnel and procedures as far aspossible each time.



Blood pressure assessment with theDoppler technique



A variety of different Doppler machines are available to measure blood pressure in catsincluding the CAT+ Doppler (Thames Medical), Vet-Dop2 (Vmed Technology), and the 811-

B Doppler (Parks Medical). These are all used in a similar way andhave been shown to be reliable in measuring blood pressure inconscious cats.As always when measuring blood pressure, it is important tominimise stress, use a quiet room, keep the cat away from otheranimals and noise, and allow at least 5-10 minutes foracclimatisation to the environment (see previous section).In some situations and with a relaxed cat, it may be possible tomeasure blood pressure single-handed. However, in practice, it isoften preferable to have two people so that one can gently holdand reassure the cat.

Where to measure blood pressureBlood pressure measured with the Doppler technique isusually performed using the forelimb or tail, although ahindlimb can also be used. There is evidence that theforelimb is generally tolerated better and is easier andquicker in most cats.

On the forelimb,blood flow isdetected (with theDoppler probe) in thecommon digital arterybetween the carpaland metacarpal pads,the inflatable cuffbeing placed belowthe elbow. On the tail, blood flow is detected in thecoccygeal artery (on the ventrum of the tail) and the cuffis placed around the tail base.

Selecting cuff sizeThe circumference of the limb or the tail atthe site where the cuff is to be placedshould be measured. The ideal width ofthe inflatable cuff used should be 30-40%of the measured circumference. A cuffwidth of around 2.5cm is suitable for mostcats, but the tail/limb circumferenceshould be measured and recorded foreach cat.

isfm Recommendations on the use ofDoppler blood pressure monitors


Should you clip the hair?To detect blood flow in the artery, it is important there is excellent contact between theDoppler probe and the skin. This is achieved with the use of alcohol to dampen the hairand skin and the use of ultrasound coupling gel (see below). Clipping the hair at the sitewhere the probe is used is not necessary, but some prefer to do this as it can makedetection of blood flow easier. If done, use quiet, gentle, cat-friendly clippers, and allow thecat time to settle down after the hair has been clipped.

Placing the cuffThe cuff, with the inflatable side towardsthe skin, should be placed around theforelimb or tail and should fit snugly, but notbe too tight. If the cuff has only a shortinflatable section, make sure this part ispositioned over the artery to be occluded.The cuff is usually secured in place with aVelcro fastener - if needed a small piece ofadhesive tape may be used in addition, butthis should never be wrapped around thelimb. The tubing from the cuff is attached tothe sphygmomanometer. Before use,check the cuff for leaks (inflate it, and checkit does not spontaneously deflate).

Prepare the skin and Doppler probeTo ensure good contact between the Doppler probe and the skin,first dampen the hair and skin (at the site theprobe will be applied) with a cotton woolswab soaked in alcohol.A liberal quantity of ultrasound gel shouldthen be applied to the hair between thecarpal and metacarpal pads, or the ventrumof the tail, where the probe will be used. Thegel should be massaged in so that the hairand skin becomes completely saturated withgel. A small amount of gel should also beapplied to the Doppler probe.

Use headphones!Always use headphones - have these plugged in before turningthe unit on to avoid sounds from the Doppler unit disturbing thecat.



Measuring blood pressure withthe DopplerThe Doppler probe is positioned between the carpaland metacarpal pads or over the ventrum of the tail,and held with gentle pressure. Excessive pressure(that restricts blood flow) should be avoided, butgentle pressure is needed to ensure good contact anda good signal.The position of the probe is carefully adjusted untilpulsatile blood flow can be heard from the commondigital artery (forelimb) or coccygeal artery (tail). If asignal is difficult to detect, applying more ultrasoundgel may be helpful.

Measuring systolic blood pressure (SBP)Once pulsatile blood flow is detected, the Doppler probe should be gently held in place,avoiding any movement. The sphygmomanometer is then inflated by gently squeezing the

compressible bulb. Watch the pressure on the dial of thesphygmomanometer, and inflate to around 20-40 mmHgabove the point where blood flow is no longer heard.Air is then allowed to slowly bleed from the valve at the backof the sphygmomanometer (usually a trigger- or screw-valve).The air must be released slowly, and the systolic bloodpressure (SBP) is the reading when return of blood flow is firstdetected (first heard).The first SBP reading is usually discarded, as the cat needs tobecome accustomed to the procedure. SBP should bemeasured five to seven times subsequently (allowing the cuffto deflate completely between each and then repeating theprocedure as above).If the Doppler signal (blood flow) is lost, the probe may needrepositioning. If the cat becomes agitated, stop and allow thecat to relax before starting again. The aim is to get 5-7

readings that are all consistent (<20% variation) and the SBP is taken as the mean of thesereadings. Fewer (3-5) readings can be acceptable, but more readings increase theaccuracy of the data. Sometimes several initial readings may have to be discarded if thereis a consistent drop in SBP (eg. due to initial stress).All readings, patient and procedure information should be recorded.



Blood pressure assessment with theHDO technique



isfm Recommendations on the use ofHDO blood pressure monitors

High definition oscillometryWhile Doppler has been used for many years for theindirect measurement of blood pressure in cats, andhas been shown to have acceptable accuracy in anumber of studies, traditional oscillometric units wereregarded as generally unreliable in conscious catswith poor accuracy and sometimes being unable togenerate a valid reading.The more recent introduction of high definitionoscillometry (such as the VetHDO, S+B medVet) hasovercome many of the problems associated withtraditional oscillometry and in published studies hasbeen shown to provide an accurate assessment ofsystolic blood pressure in conscious cats.

Advantages and disadvantagesIn general the HDO equipment is a little easier to usethan the Doppler. HDO will also provide a measure ofdiastolic (DBP) and mean arterial pressure (MAP) in addition to systolic pressure (SBP) -while potentially helpful, DBP and MAP readings may in fact be much less accurate than

SBP with HDO, and isolated diastolichypertension is regarded as rare incats.Compared with Doppler, HDO is moreexpensive to purchase, and also it isstrongly recommended that the HDOmachine is always linked to a PC ortablet computer while measuring bloodpressure. Connecting the HDO to aPC allows visualisation of therecording, which is important asmovement or other artefacts can leadto false blood pressure readings.Using the HDO without a PC may givespurious results without the operatorbeing aware.Because patient movement can readilycause false readings, it isrecommended that the cuff be appliedto the tail when using HDO in cats,and to keep the cat as still as possible.However, the cuff can also be used onthe limbs if needed.



Patient preparationAs with any technique, when measuring bloodpressure it is important to minimise stress. Use aquiet room, keep the cat away from otheranimals and noise, and allow at least 5-10minutes for acclimatisation to the environment(see earlier section).In some situations, it may be possible tomeasure blood pressure single-handed.However, in practice, it is often preferable tohave two people so that one can gently hold andreassure the cat. The HDO machine should belinked to a PC or tablet (via a USB cable or viaBluetooth, depending on the unit).

Cuff positioningIn general the HDO equipment comes witha single size cuff for cats and so long as itis well tolerated, this should be used onthe tail, as this is easier and less likely toresult in false readings from movementartefact. If more than one cuff size isavailable, the circumference of the tail atthe point where the cuff is to be placedshould be measured, and a cuff widthselected that is 30-40% of thatcircumference.

The cuff should be positioned so that thearea where the inflation tube enters the cuffis placed ventrally on the tail (close to thecoccygeal artery) as this maximises thesensitivity of the HDO. As with Doppler, thecuff should be checked for leaks beforeuse.The cuff should be applied snugly aroundthe base of the tail and secured with theVelcro fastener - it should be tight enoughto stay in place but not so tight as to causeconstriction of the tail. In some cats, oncethe cuff has been placed, they may behappy to curl up or lie in a basket or bedwithout any further restraint or interference.



Measuring blood pressureOnce the cuff is in place and the cat is comfortable, the machine can be turned on andblood pressure recordings can begin. First check the settings on the machine are correct

though (for example, that the correct cuff sizehas been entered into the machine).The PC or tablet should also be connected,and the software loaded to enable computerrecording and display to take place.When a blood pressure reading is initiated (bypressing the ‘Start’ button on the HDOmachine), the cuff will automatically inflateand then deflate at a constant speed. Theblood pressure (SBP, MAP and DBP) willsubsequently be shown on the display alongwith the heart rate. This will also be shown onthe PC along with a visual trace.The first blood pressure reading should bediscarded as the cat acclimatises to theinflation and deflation of the cuff.Subsequently, 5-7 further blood pressurereadings should be taken. Additionalmeasurements should be made if these arenot consistent (<20% variation) or if there is a

trend for lower measurements over time (suggesting the cat was stressed).The mean of 5-7 consistent readings is taken for SBP (and for DBP and MAP). If the catbecomes restless, agitated or starts moving, take a break, allow the cat to settle, and thenstart again.In some cats, if they are veryrelaxed and not movingmuch, it may also be possibleto use a forelimb to measureblood pressure, placing thecuff below the elbow.With each blood pressurereading, it is important to takenotice of the PC reading andthe curves displayed toassess whether the readingmay have been affected bymovement or other artefact(see below).



Checking for artefacts with the PC or tabletWhen linked to a PC, witheach set of readings fromthe HDO monitor, alongwith storing the data, avisual display is shown ofthe deflation of the cuff(top line) and the pulsewaves detected (bottomcurve).The top line should bechecked to ensure itdisplays a steady constantdeflation of the cuff, andthe pulse waves shouldgenerate a pattern thatapproximates a bell-curve.

If the above criteriaare not met (mostcommonly the pulsewaves will showsignificant distortion)the reading shouldbe discarded asmovement or someother artefact mayhave affected theaccuracy of theblood pressuresrecorded.This step should notbe ignored, as themachine itself willoften not detecterrors associatedwith movement.

All readings should be recorded (along with other patient and procedure information).Note studies suggest that while the SBP is accurate, the DBP and MAP measured byHDO may be inaccurate in cats.


Blood pressure assessment form



isfm Blood Pressure Assessment Form

Date TimeCat's nameAgeSexWeightBody Condition Score

Owner details

Position of the cat

Other (specify):

Position of the cuff:

Equipment used Size of cuffLocation (room) Others presentPerformed by

Subjective assessment of stress:

Record of all SBP measurements (mmHg):1. 3. 5. 9.2. 4. 6. 10.

Strike through readings that are ignored and take mean of the remaining values

7.8.

Mean SBP (mmHg)

Sitting Sternal recumbency StandingLateral recumbency

Right forelimb

Left forelimb

Right hindlimb

Tail

Left hindlimb


isfm International Society of Feline Medicine

icatcare.org/vetsFor videos go to:www.youtube.com/icatcareand search for 'blood pressure'

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