Page 41 - Basic Monitoring in Canine and Feline Emergency Patients

termed the Doppler effect or Doppler shift; the Doppler blood pressure readings are typically
difference in sound wave frequencies are converted obtained over the distal aspect of the limbs at the
VetBooks.ir to equivalent electrical impulses by the receiving level of either the tarsus or carpus, or from the tail.
Rather than a preference for one site over another,
piezoelectric crystal and are appreciated as a char-
acteristic ‘whoosh’ noise with the pulsatile arterial
ments and use the same site at each measurement
flow. It is essential that the transmitter is placed it is more important to be consistent in measure-
over a blood vessel as movement (such as red blood period. In the forelimb, the medial palmar artery is
cells) within the vessels is necessary to detect the appreciated just proximal to the metacarpal pad.
Doppler shift. In this way, the change in frequency The cuff should ideally be placed halfway along the
is amplified and audible to the person obtaining the antebrachium between the elbow and carpus (Fig.
pressure. 2.8A). If using the hindlimb, the dorsal pedal artery
A cuff connected to a sphygmomanometer is can be detected just distal to the tarsus on the dor-
required to obtain a Doppler blood pressure read- somedial aspect of the metatarsus and the medial
ing (Fig. 2.7). The circumference of the limb should plantar superficial artery proximal to the metatar-
be measured at the intended cuff placement site sal pad. Dependent on the artery used, the cuff on
with a soft measuring tape and width of the selected a hindlimb may be placed between the stifle and
cuff should be 30–40% of the limb circumference. hock (Fig. 2.8B) or just distal to the tarsus when
The cuff is placed proximally relative to the periph- monitoring the dorsal pedal artery or the medial
eral artery where the Doppler probe will be located. plantar superficial artery, respectively. When meas-
When the cuff is subsequently inflated to a pressure uring blood pressure from the coccygeal artery on
greater than that within the artery, blood flow will the tail, the cuff is placed at the tail base and the
be prevented. This effect will be clinically appreci- artery is identified along the ventral midline of the
ated through a loss of the ‘whoosh’ sound. tail just distal to the cuff site.

(A) (C) (D)

(B)

Fig. 2.7. The components (excluding the piezoelectric quartz crystals) used in obtaining a Doppler blood pressure.
(A) The Doppler ultrasonic unit which processes the signal received from the piezoelectric quartz and emits sound.
(B) A sphygmomanometer which is attached to the cuffs. The sphygmomanometer is utilized to inflate the cuff
and the needle reflects the pressure (in mmHg) within the cuff. (C) An array of different sizes of cuffs used in both
indirect blood pressure monitoring techniques. (D) The ultrasound gel which must be placed on the probe to permit
transmission and reception of the ultrasound waves.

Blood Pressure Monitoring 33