Page 48 - Basic Monitoring in Canine and Feline Emergency Patients

look for additional abnormalities that caused or represent the true blood pressure. Currently, no
contributed to the hypotension (or that might result indirect monitoring blood pressure device has met
VetBooks.ir from the hypotension). For example, electrolyte the human standards of validation in conscious
dogs or cats. Therefore, results must always be
derangements (e.g. hypokalemia, hyponatremia) or
hypoglycemia may also contribute to hypotension;
and no blood pressure measurement should be
a patient may not demonstrate an appropriate critically evaluated and interpreted with caution
response to fluid therapy until those abnormalities accepted without also assessing the patient.
are corrected. Marked hypokalemia (<3.0 mEq/L) Additional factors including the patient’s presenta-
leads to neuromuscular weakness and decreased tion or condition, examination findings (e.g. capil-
smooth muscle function. Hyponatremia (≥5.0 mEq/L lary refill time, heart rate, pulse quality), and
below the lower limit of the reference range) can be perfusion indices (e.g. lactate – see Chapter 1)
associated either with volume depletion with con- should be considered as a component of indirect
current sodium loss or water retention associated blood pressure monitoring assessment.
with ADH release (diluting the sodium concentra-
tion). Therefore, in the former setting, hyponatremia
may result in a decreased circulatory volume, contrib- Machine/operator factors
uting to hypotension. Hypoglycemia will interfere Steps must also be taken to improve the reliability
with appropriate smooth muscle function and poten- of the acquired measurements; the more trustwor-
tially cause peripheral arterial vasodilation and a thy the monitoring, the more useful the readings
subsequent drop in blood pressure. Tachyarrhythmias may be for clinical decision making. For example,
or bradyarrhythmias found during an examination it is important to reduce the effect of situational
can both lead to hypotension that will not easily hypertension on the measured blood pressure.
respond to intravenous fluid infusion (see Chapter Situational hypertension occurs when a dog or cat
3). Also, profoundly hypothermic or hypoxemic is especially anxious or excited, leading to falsely
dogs or cats will likely only show minimal blood elevated blood pressure measurements. To attempt
pressure response to fluid support. Decreased car- to reduce situational hypertension, patients should
diovascular function may begin to occur as the core be allowed to acclimate to a quiet area for at least
o
body temperature drops to <97 F (36.1°C); vaso- 5–10 minutes prior to taking any blood pressure
motor tone similarly cannot be maintained at low measurements. All readings should be obtained
body temperatures. with the owner present and ideally involved in
Some patients remain hypotensive despite appro- restraint of the animal. The first blood pressure
priate resuscitative fluid therapy and correction of measurement should be discarded and the average
laboratory abnormalities. In these cases, additional of the subsequent five to seven readings should be
sympathetic support is recommended to improve calculated to represent the patient’s blood pressure.
cardiac inotropy and peripheral vasoconstriction. When collecting the representative measurements,
Norepinephrine and vasopressin are often the ini- readings should only be accepted if they are reason-
tial medications utilized to improve vascular tone ably consistent; readings with substantial variation
and may be titrated to effect as a constant rate (>10%) should also be discarded. If the readings
infusion. Some patients may have a greater need for continue to decrease, measurements should be
positive inotropy and, in those cases, a dobutamine repeated until a plateau is reached and then five to
constant rate infusion should be considered. Please seven measurements should be obtained.
see the Further Reading section for more informa- Patient movement can also affect the results (or
tion on the use of positive inotropes and vasopres- ability to obtain an accurate measurement) in both
sive drugs in dogs and cats. Doppler and oscillometric units. Movement during
Doppler blood pressure measurement can alter the
probe placement over the peripheral artery leading
to either a loss of signal or artifactual noise; this
2.5 Pitfalls of the Monitor makes proper assessment of the ‘whoosh’ noise dif-
ficult to impossible. Motion during oscillometric
One of the greatest challenges with blood pressure readings can cause artifactual signals, making accu-
monitoring in companion animals is obtaining rate detection of the arterial wall vibration difficult
measurements that the reader can be confident or inconsistent.

40 D.S. Foy