Page 50 - Basic Monitoring in Canine and Feline Emergency Patients

pressure measurements on the tail or hindlimb very or hypertensive prior to anesthesia but are at risk
difficult to obtain. The presence of peripheral for developing marked blood pressure changes dur-
VetBooks.ir edema necessitates a greater pressure in the cuff to ing the surgical/anesthetic procedure (e.g. adrenal
gland surgery, biliary surgery, thoracic/pleural space
occlude arterial flow and subsequently will tend to
overestimate systolic blood pressure.
should ideally be monitored via direct blood pres-
Any condition causing peripheral vasoconstric- surgery, septic abdomen surgery). These patients
tion can compromise blood pressure readings. sure measurements throughout anesthesia and for
Detectable pulsatile flow is a prerequisite for indi- 24 hours post-anesthesia to allow for more rapid
rect blood pressure monitoring. The foundation of reaction to changes in blood pressure.
the Doppler blood pressure reading is the reflection
of ultrasonic sound waves off moving red blood
cells. Without this detectable motion, the ‘whoosh’ 2.6 Case Studies
associated with the unit cannot be obtained and the
reading is not possible. The oscillometric unit also Case study 1: Hypertension
requires arterial pulsatile flow to generate the arte- A 9-year old neutered male Labrador retriever is
rial wall oscillations; if these oscillations are absent presented for acute onset of blindness. Vital signs
or below the limits of detection, this measurement are normal and the physical examination is unre-
is also not possible. Patients with advanced shock markable aside from a bilaterally absent menace
are likely to have significant peripheral vasocon- response. The fundic evaluation reveals bilaterally
striction as blood flow is directed to more critical detached retinas. Following that finding, blood
organs. Hypothermic patients (e.g. secondary to pressure readings are obtained and the result of the
shock, secondary to anesthesia, environmental Doppler unit measurement is 200 mmHg averaged
exposure) will also experience peripheral vasocon- over five readings. The readings are consistent with
striction in an effort to minimize further heat loss. minimal variation and the patient is calm at the
Some drugs (e.g. α-2 agonists) induce peripheral time of the measurements. The blood pressure is
vasoconstriction and may cause inconsistent indi- double-checked with an oscillometric unit and the
rect blood pressure readings. reading is a systolic pressure of 205 mmHg, a MAP
In some situations, indirect blood pressure meas- of 155 mmHg, and a diastolic pressure of
urement is simply not the ideal option for the 130 mmHg. The dog is diagnosed with severe sys-
patient. As mentioned above, no indirect device has temic hypertension with evidence of TOD (the
met the human standards of validation for blood blindness).
pressure measurement in dogs or cats and no indi- Severe hypertension is unlikely to be effectively
rect device continuously displays blood pressures. controlled with ACEi or ARBs alone, but dogs
Patients at risk or suffering from either marked should not receive a CCB (e.g. amlodipine) without
hypertension or hypotension or with rapidly chang- some measure of efferent arteriole dilation.
ing blood pressures are more likely to benefit from Therefore, multimodal therapy is indicated in this
direct blood pressure monitoring. patient. Options for starting medical therapy
There are several examples of situations where include ACEi (either benazepril or enalapril) at a
patients should ideally have direct blood pressure 0.5 mg/kg dose likely administered twice daily com-
monitoring. One example are those suffering from bined with a CCB (likely amlodipine) at a 0.1–0.2 mg/
a hypertensive crisis and undergoing therapy, who kg dose administered once daily. An ACEi may be
may require accurate, minute-to-minute monitoring administered once or twice daily, but given the
to evaluate both the degree of hypertension and the degree of hypertension, twice daily therapy would
response to therapy. Also, as discussed previously, appear more appropriate in this dog. Another ini-
many patients with moderate-to-marked hypoten- tial option would be the use of an ARB (e.g. tel-
sion are also likely to suffer from peripheral vaso- misartan) at a 1 mg/kg dose administered once
constriction, further complicating accurate indirect daily combined with amlodipine.
blood pressure monitoring. Direct blood pressure A common recommendation for blood pressure
monitoring enables more accurate initial assessment monitoring is to re-check the patient’s blood pres-
and evaluation of the patient’s response to fluid and sure 7 days after institution or adjustment of ther-
vasopressor therapy. A final example are animals apy. Given this dog’s severe hypertension and TOD,
which may be normotensive or only mildly hypotensive a blood pressure re-check is indicated within 1–2

42 D.S. Foy