Page 110 - Basic Monitoring in Canine and Feline Emergency Patients

was poor correlation between the A–a gradient and However, the presence of certain substances in the
P/F ratio with the actual degree of venous admix- blood can be incorrectly perceived by the electrodes
VetBooks.ir ture measured in anesthetized horses. Therefore, in as normal analytes (see Chapter 8). For example,
halogen ions such as bromide in patients receiving
veterinary medicine, trends within an individual
patient rather than exact values may be more reli-
ride by chloride-sensitive electrodes and give abnor-
able to assess progression of lung function. potassium bromide therapy will be detected as chlo-
mally high chloride readings. Severely high salicylate
levels (as in extreme toxicities) can do the same. If
anion gap calculations or non-traditional acid–base
5.5 Pitfalls of the Monitor analysis are being performed, incorrect electrolyte
values will skew these calculations.
Sample handling/acquisition
The majority of errors in blood gas analysis are pre-
analytical and result from improper sample han- 5.6 Case Studies
dling or acquisition. If arterial samples are obtained
by direct puncture rather than from a dedicated Case study 1: Traditional versus
arterial line, they may contain venous or mixed non-traditional acid–base analysis
venous–arterial blood and not accurately represent A 10-year-old castrated male Labrador Retriever col-
arterial values. In this case, comparison to values lapses during his first jog this spring. The owner ini-
taken from a known venous sample and correlation tially took him home after the collapse, but the dog
with severity of clinical signs may help determine if began to have bloody diarrhea and continued to have
the initial puncture was truly arterial. Venous values an increased respiratory rate and effort, so he is pre-
being used in lieu of arterial (e.g. PvCO , pH) may sented to the ER clinic 3 hours following the initial
2
be inaccurate in low-flow hemodynamic states such collapse event. On presentation, the dog is carried in by
as post-arrest, or if drawn from tissue beds that do the owner, is mentally dull, has poor pulse quality, pale
not represent appropriate blood flow in the patient to cyanotic mucous membranes with a capillary refill
as a whole (e.g. from the hind limb of a feline time of 3–4 seconds, a heart rate of 180 bpm, tempera-
thromboembolism patient). Similarly, if the sample ture of 103.5°F (39.7°C), and stridorous upper airway
introduced into the analyzer is not homogeneous, noise. Petechiae are present on his ventral abdomen. A
such as allowing sedimentation of red cells to occur diagnosis of heat stroke and upper airway obstruction
without re-mixing immediately prior to analysis, (presumed laryngeal paralysis) is made.
values such as Hb and hematocrit (Hct) may be Oxygen is provided by mask, an intravenous
skewed. (IV) catheter is placed, and the following venous
Samples contaminated with fluids or medica- blood gas and chemistry information is drawn
tions (such as those collected inappropriately from from the IV catheter and analyzed on your stat
central lines) can lead to false values. For example, bedside cartridge-based analyzer:
samples contaminated with significant amounts of
total parenteral nutrition or dextrose will have PCV/TP: 67%/9.2
erroneously high blood glucose values. Other com- Blood glucose: 29 mg/dL
mon pre-analytical errors and their expected
effects are outlined in Table 5.7. Parameter (unit) Patient value Normal value a
pH 7.4 7.4
Monitor output PvO (mmHg) 30 35
2
Appropriate quality control and maintenance is PvCO (mmHg) 55 45
2
−
important for all instruments, but especially for HCO (mmol/L) 32.9 22
3
noncartridge-based systems to ensure accuracy of BE (mmol/L) 10 0
results where multi-use electrodes must be appro- Na (mmol/L) 160 146
priately maintained and replaced. Analyzers will
give error readings rather than inappropriate results K (mmol/L) 5 4
in most cases if samples are improperly loaded (not Cl (mmol/L) 110 110
enough sample, air bubbles, fibrin clots, etc.). Continued

102 A.C. Brooks