Page 115 - Basic Monitoring in Canine and Feline Emergency Patients

skin lesions showed pyogranulomatous inflamma- deficit in 24 hours were initiated. An arterial line
tion and broad-based budding organisms consistent was placed to allow for serial blood gas sampling. In
VetBooks.ir with Blastomyces dermatitidis. A diagnosis of dis- the chart below, serial arterial blood gasses are
shown along with degree of oxygen support. The
seminated blastomycosis was made. Treatment with
itraconazole 5 mg/kg PO q12h and IV fluid support
below:
at 120 mL/kg/day to correct an estimated 5% fluid bolded values are discussed further in the text

Value (unit)
normal range] Presentation 12 h 24 h 36 h 37 h

pH [7.35–7.45] 7.35 7.44 7.47 7.26 7.32
PaO (mmHg) 56 85 72 60 192
2
[4−5 × FiO ]
2
PaCO (mmHg) 22 27 25 40 35
2
[34−40]
−
HCO (mmol/L) 11.7 17.7 17.6 17.3 17.4
3
[19–25]
BE [0 ± 3] −12.5 −5.7 −5.4 −8.5 −7.6
FiO provided 21% (room air) 40% (bilateral 40% (bilateral 40% (bilateral 100% (intubated
2
nasal cannulas) nasal cannulas) nasal cannulas) and hand
ventilated with
anesthesia
machine bag)
P/F ratio 267 213 180 150 192
[400–500]

1. Assess the pH. At presentation, the patient is 3. Assess PaO . The initial blood gas at pres-
2
acidemic. The PaCO is low (hyperventilation) entation indicates severe hypoxemia (PaO =
2
2
−
which should not cause an acidosis. The HCO 56 mmHg) on room air. The low PaCO indicates
2
3
and BE are also low, consistent with a metabolic that the patient is hyperventilating, therefore the
−
acidosis. Using 22 as a normal HCO level, the low PaO cannot be attributed to hypoventilation.
3
2
−
HCO is 10.3 points below normal. Using the As a confirmation of this information, you per-
3
equations from Table 5.4, the PCO should form an A–a gradient (A–a = 66.5, significant lung
2
−
decrease by 0.7 for every 1 point the HCO is low pathology) or rule of 120 (56 + 28 = 78 which is
3
if compensation is appropriate. 10.3 × 0.7 = 7.21. <120) which again supports that the hypoxemia is
Therefore, the CO should be approximately separate from hypoventilation.
2
33 mmHg (40–7.21). The measured CO of Bilateral nasal cannulas were placed in this dog at
2
22 mmHg is lower than expected for compensa- a setting of 100 mL/kg/min. Oxygen supplementa-
tion alone. Therefore, this patient has a mixed tion with bilateral nasal cannulas at 100 mL/kg/
metabolic acidosis and respiratory alkalosis. min of O is presumed to generate a FiO of
2
2
Further information (electrolytes, lactate) would approximately 40%. The PaO in this dog improved
2
be needed for more in-depth assessment of the met- to an acceptable level of 85 mmHg at the 12-hour
abolic alkalosis using the non-traditional approach. mark on oxygen supplementation. All subsequent
For brevity, this remainder of this example focuses on assessments of oxygenation must take this change
the oxygenation/ventilation status of this patient in FiO into account.
2
rather than the acid–base component. 4. At 12 hours, lung function as represented by
2. Assess PaCO . The PaCO is low, consistent the P/F ratio declined slightly, but interpretation
2
2
with hyperventilation. Causes of hyperventilation is complicated by the fact that the PaCO also
2
are likely multifactorial in this patient (Table 5.1), slightly increased. The patient’s hyperventilation
including hypoxemia, pulmonary receptor activa- has been reduced because he is no longer hypox-
tion due to primary lung pathogen, and SIRS. emic. Because the P/F ratio does not take ventilation
Venous and Arterial Blood Gas Analysis 107