Page 341 - Small Animal Internal Medicine, 6th Edition

CHAPTER 20 Diagnostic Tests for the Lower Respiratory Tract 313

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A

B C

FIG 20.27
Bronchoscopic images of normal airways. The labels for the lobar bronchi are derived
from a useful nomenclature system for the major airways and their branches presented by
Amis et al. (1986). (A) Carina, the division between the right and left mainstem bronchi.
(B) Right mainstem bronchus. The carina is off the right side of the image. Openings to
the right cranial (RB1), right middle (RB2), accessory (RB3), and right caudal (RB4)
bronchi are visible. (C) Left mainstem bronchus. The carina is off the left side of the
image. The openings to the left cranial (LB1) and left caudal (LB2) bronchi are visible. The
left cranial lobe (LB1) divides immediately into cranial (Cr) and caudal (Ca) branches.
(From Amis TC et al.: Systematic identification of endobronchial anatomy during
bronchoscopy in the dog, Am J Vet Res 47:2649, 1986.)

BLOOD GAS ANALYSIS abnormalities to be measurable because the body has tre­
mendous compensatory mechanisms.
Indications
Measurement of partial pressures of oxygen (PaO 2 ) and TECHNIQUES
carbon dioxide (PaCO 2 ) in arterial blood specimens pro­ Arterial blood is collected in a heparinized syringe. Dilution
vides information about pulmonary function. Venous blood of specimens with liquid heparin can alter blood gas results.
analysis is less useful because venous blood oxygen pres­ Therefore commercially available syringes preloaded with
sures are greatly affected by cardiac function and peripheral lyophilized heparin are recommended. Alternatively, 0.5 mL
circulation. Arterial blood gas measurements are indicated of liquid sodium heparin is drawn into a 3­mL syringe with
to document pulmonary failure, to differentiate hypoventila­ a 25­gauge needle. The plunger is drawn back to the 3 mL
tion from other causes of hypoxemia, to help determine the mark. All air is then expelled from the syringe. This proce­
need for supportive therapy, and to monitor the response dure for expelling air and excess heparin is repeated three
to therapy. Respiratory compromise must be severe for times.