Page 114 - Basic Monitoring in Canine and Feline Emergency Patients

Despite the elevated respiratory rate, it is impor- The HCO of 23.7 mmHg is within 3
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tant to remember that tachypnea ≠ hyperventila- points of this expected value, therefore com-
VetBooks.ir tion. Ventilation is a product of BOTH rate and pensation is adequate. There is also no sig-
tidal volume, and this patient’s cervical spinal cord
nificant deflection of the BE to imply a con-
disease is likely causing weakness of the diaphragm
as well as generalized weakness of the limbs. current metabolic component, therefore
more advanced assessment of the metabolic
Therefore, despite his tachypnea, this patient may side of this patient is not needed.
be hypoventilating if he cannot generate an appro- 3. Assess the FiO . The blood gas was obtained on
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priate tidal volume with each breath. To assess the room air, so FiO = 21%.
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ventilation status, we must assess PCO levels. 4. Assess the PaO . The PaO is low at 65.
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While PvCO would likely be enough to help us # # Of the five causes of hypoxemia, hypoventi-
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assess ventilation alone, this patient was also lation is already known to be present. Is
hypoxemic on presentation, requiring oxygen sup- there another cause of hypoxemia not
plementation. The next question is whether the explained by hypoventilation alone?
hypoxemia is secondary to hypoventilation alone, # # Perform the A–a gradient (see Box 5.5) for a
or, is there another underlying lung issue (e.g. aspir- patient breathing room air at sea level:
ation pneumonia secondary to syringe feeding or A = 150 – (PaCO /R)
silent regurgitation) that is also contributing to hyp- A = 150 – (56/0.8) = 80.
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oxemia? An arterial blood gas analysis would be Therefore, the A–a gradient = P O – PaO =
preferred for assessing both questions in this dog. (80 – 65) = 15 A 2 2
The following arterial blood gas is obtained at This is within acceptable limits and there-
sea level on room air: fore all of this patient’s current hypoxemia
can be explained by hypoventilation.
Value (unit) Patient value Normal range
Another approach using the ‘rule of 120’ shows that 65
pH 7.25 7.35–7.45 + 56 = 121, therefore this patient was unlikely to have
PaO (mmHg) 65 80–107 hypoxemia not explained by the hypoventilation.
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(FiO 21%) Thoracic radiographs were normal and did not
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PaCO (mmHg) 56 34–40 support any undiagnosed lung pathology. The patient
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HCO (mmol/L) 23.7 19–25 was mechanically ventilated prior to and shortly
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BE (mmol/L) -2.7 0 ± 3
after a ventral slot procedure for cervical IVDD. The
dog was weaned from mechanical ventilation within
1. Assess the pH. The pH is acidemic. 48 hours and was discharged home after an addi-
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2. Assess the PaCO and HCO to determine tional week of hospitalization. Following rehabilita-
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which is causing the acidosis. tion, the dog regained good ambulation with only
# # PaCO is high which would cause a respira- minor residual conscious proprioception deficits.
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tory acidosis. This indicates hypoventilation.
After assessing likely differentials for Case study 4: Assessment of lung function
hypoventilation (Table 5.1), the most likely in the hypoxemic patient
cause is a cervical spinal cord lesion.
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# # HCO is normal; this should not cause an A 7-year-old castrated male mixed breed dog pre-
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acidosis. Therefore, this is a primary respira- sents for a 1-week history of ocular discharge, skin
tory acidosis. lesions, and cough beginning in the last 48 hours.
# # Is compensation adequate? The history Temperature: 104.0°F (40°C); heart rate: 150 bpm;
implies this is likely an acute (last 24 hours) respiratory rate: 70 breathes per minute with
change. Using the equations from Table 5.4, harsh lung sounds diffusely.
for every 1 mmHg that the PaCO is elevated Thoracic radiographs show a mixed nodular and
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above normal, the HCO would be expected diffuse interstitial pattern with enlarged tracheo-
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to rise by 0.15. Using 37 as a mid-range normal bronchial lymph nodes. A complete blood count
PaCO , 56 − 37 = 19 points above normal × showed a mild non-regenerative anemia, an inflam-
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0.15 = 2.85. Therefore, if a mid-range normal matory leukogram with a left shift, and mild
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HCO is 22, then 22 + 2.85 = 24.85 mmHg. thrombocytopenia. Cytology of one of the draining
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106 A.C. Brooks