Page 242 - Small Animal Internal Medicine, 6th Edition

214 PART I Cardiovascular System Disorders

include mild LA enlargement and sometimes mild mitral or is monitored to detect the return of blood flow. A standard-
aortic regurgitation. Systolic BP could be estimated during ized protocol for noninvasive BP measurement in dogs and
VetBooks.ir an echocardiographic examination in animals with mitral cats has been described. The patient is gently restrained in
sternal or lateral recumbency, with the cuff’s vertical posi-
valve insufficiency by measuring the peak velocity of the
mitral regurgitation jet using continuous-wave Doppler
lateral recumbency, the nondependent limb is used for BP
imaging; the modified Bernoulli equation (see p. 30) then is tion close to the level of the RA during BP measurement. In
used to estimate the pressure gradient between the LV and measurements. A sitting position is not recommended due
LA. However, this method can underestimate BP and cor- to poor repeatability and systematic overestimation of BP.
relates only moderately with indirect BP measurements. Doppler ultrasonic flow detection and oscillometric
methods are used most often. Both techniques produce mea-
BLOOD PRESSURE MEASUREMENT surements that correlate somewhat well with direct BP mea-
Several methods can be used to measure systemic arterial BP surement but are not exactly predictive of it; falsely high or
in the clinic. High pressures should be confirmed by repeated low values occur. Calculating the average of several measure-
measurement sessions before a diagnosis of hypertension is ments (generally five to seven) in succession is recommended
made. Anxiety related to the clinical setting can falsely to increase accuracy. Often the first reading, or the highest
increase BP in some animals (i.e., the white-coat effect), and and lowest, is discarded. If there is more than 20% variability
BP measurements can decrease with acclimation. Using as in systolic pressure readings among successive measure-
little restraint as possible in a quiet environment and allow- ments, the cuff placement or limb may need to be changed
ing time (e.g., 5-15 minutes) for acclimatization is best for to obtain more consistent readings. If the accuracy of the BP
awake animals. It is often helpful to have the owner present. measurements is in doubt, the process should be repeated at
Use of consistent technique and cuff sizing (for indirect a later time, when the patient (hopefully) is better acclimated
methods) is important. The technical skill and experience of and more relaxed. Indirect methods are most reliable in nor-
the individual who obtains the BP measurements are also motensive and hypertensive animals. The BP device used
highly relevant to achieving consistent results. should be calibrated semiannually to maximize accuracy.
Other methods such as auscultation and arterial palpa-
Direct Blood Pressure Measurement tion are not recommended for estimating BP. The ausculta-
Arterial pressure can be measured directly by a needle or tory method (used to detect Korotkoff sounds in people) is
catheter placed into an artery and connected to a pressure technically impractical because of the limb conformation of
transducer. Direct arterial pressure measurement is consid- dogs and cats. Direct arterial palpation is not reliable for
ered the gold standard, but it requires greater technical skill; estimating BP because pulse strength depends on the pulse
moreover, in awake animals the physical restraint and dis- pressure (systolic minus diastolic arterial pressure), not the
comfort associated with arterial puncture may falsely absolute level of systolic or mean pressure. Pulse strength is
increase BP. Direct arterial pressure measurement is more also influenced by body conformation and other factors.
accurate than indirect methods in hypotensive animals. Cuff size and placement. A wide selection of cuff
For arterial pressure monitoring over a period of time, an sizes, including human pediatric- and infant-size cuffs, is
indwelling arterial catheter is often the best approach. The available for indirect BP measurement in dogs and cats. The
dorsal metatarsal artery is commonly used for this tech- cuff must be the correct size for the patient. The width of the
nique. An electronic pressure monitor provides continuous cuff should be about 40% of the circumference of the extrem-
measurement of systolic and diastolic pressures and calcu- ity it surrounds for dogs (30%-40% for cats). The length of
lated mean pressure. With fluid-filled systems, the pressure the inflatable balloon (bladder) within the cuff should cover
transducer must be placed at the level of the patient’s right at least 60% of this circumference. Cuffs that are too large
atrium (RA) to prevent a false increase or decrease of the can cause falsely low BP readings, whereas cuffs that are too
measured pressure related to the effects of gravity on the small can cause falsely high BP readings. Some of the cuff
fluid within the connecting tubing. inflation pressure goes toward tissue compression. Cuffs that
When occasional BP measurement is necessary, a small- are too narrow are more affected by this phenomenon and
gauge needle attached directly to a pressure transducer may produce falsely increased pressure readings; cuffs that are too
be used to puncture the dorsal metatarsal or femoral artery. wide may underestimate BP. Intra-individual differences in
To prevent hematoma formation, direct pressure should be BP between forelimb and hindlimb measurement sites have
applied to the arterial puncture site for several minutes after been reported. For these reasons, the cuff size and specific
removing the catheter or needle used for BP measurement. placement site used should be noted in the animal’s record
for consistency when repeating BP measurements over time.
Indirect Blood Pressure Measurement The cuff bladder should be centered over the target artery.
Several noninvasive methods are available to measure BP Common cuff locations are midway between the elbow and
indirectly. These techniques involve the use of an inflatable carpus, in the tibial region, or at the base of the tail; skeletal
cuff placed around a limb to occlude blood flow, usually over prominences are avoided. The cuff should encircle the limb
the brachial, radial, or saphenous artery, or the median snugly without being excessively tight. Tape (not just Velcro
caudal artery of the tail. Controlled release of cuff pressure on the cuff) can be used to secure the cuff in position.