Page 385 - Small Animal Internal Medicine, 6th Edition

CHAPTER 22 Disorders of the Pulmonary Parenchyma and Vasculature 357

more often patchy and unpredictable in their distribution.
BOX 22.4 Edema resulting from increased vascular permeability tends
VetBooks.ir Possible Causes of Pulmonary Edema to be most severe in the dorsocaudal lung regions.
Radiographs should be carefully examined for signs of
heart disease, venous congestion, PTE, pleural effusion, and
Decreased Plasma Oncotic Pressure
Hypoalbuminemia mass lesions. Echocardiography is helpful in identifying
Gastrointestinal loss primary cardiac disease if the clinical signs and radiographic
Glomerulopathy findings are ambiguous.
Liver disease Decreased oncotic pressure can be identified by the serum
Iatrogenic overhydration albumin concentration. Concentrations less than 1 g/dL are
Starvation usually required before decreased oncotic pressure is consid-
Vascular Overload ered to be the sole cause of the pulmonary edema. Pulmo-
Cardiogenic nary edema resulting purely from hypoalbuminemia is
Left-sided heart failure probably rare. In many animals volume overload or vasculi-
Left-to-right shunts tis is a contributing factor. Plasma protein quantitation using
Overhydration a refractometer can indirectly assess albumin concentration
in emergency situations.
Lymphatic Obstruction (Rare) Vascular permeability edema can result in the full range
Neoplasia of compromise, from minimal clinical signs that spontane-
ously resolve to the frequently fatal, fulminant process of
Increased Vascular Permeability ARDS. A consensus group has determined definitions for
Inhaled agents ALI/ARDS in veterinary patients (Wilkins et al., 2007). At
Smoke inhalation least four, and ideally five, of the following criteria must
Gastric acid aspiration be met: acute onset (<72 hours) of tachypnea and labored
Oxygen toxicity
Drugs or toxins breathing at rest; known risk factors; evidence of pulmonary
Snake venom capillary leak without increased pulmonary capillary pres-
Cisplatin in cats sure (e.g., bilateral diffuse pulmonary infiltrates on radiogra-
Paraquat phy or computed tomography, proteinaceous fluid retrieved
Electrocution from airways); evidence of insufficient gas exchange; and
Trauma evidence of diffuse pulmonary inflammation based on tra-
Pulmonary contusions cheal wash or BAL fluid analysis. One measure of insufficient
Multisystemic gas exchange is a low PaO 2 (partial pressure of oxygen in the
Sepsis or systemic inflammatory response (SIRS) blood)/FiO 2 (fraction of inspired oxygen) ratio without the
Pancreatitis mechanical ventilation technique of positive end-expiratory
Uremia pressure (PEEP) or continuous positive airway pressure
Disseminated intravascular coagulation
Inflammation (infectious or noninfectious) (CPAP). A ratio of < 300 mm Hg is consistent with ALI.
A ratio of < 200 mm Hg is consistent with the more severe
Miscellaneous Causes form, ARDS. Arterial blood gas analysis and pulse oxim-
Thromboembolism etry in dogs and cats with pulmonary edema of any origin
Upper airway obstruction are useful in selecting and monitoring therapy. Hypoxemia
Near-drowning is present, usually in conjunction with hypocapnia and a
Neurogenic edema widened A-a gradient.
Seizures
Head trauma Treatment
It is easier for the body to prevent edema fluid from forming
than it is to mobilize existing fluid. The initial management
Diagnosis of pulmonary edema should be aggressive. Once edema has
Pulmonary edema in most dogs and cats is based on typical resolved, the body’s own compensatory mechanisms become
radiographic changes in the lungs in conjunction with clini- more effective and the intensity of therapeutic interventions
cal evidence (from the history, physical examination, radi- can often be decreased.
ography, echocardiography, and serum biochemical analysis All animals with pulmonary edema are treated with cage
[particularly albumin concentration]) of a disease associated rest and minimal stress. Dogs and cats with significant
with pulmonary edema. hypoxemia should receive oxygen therapy (see Chapter 25).
Early pulmonary edema assumes an interstitial pattern on Positive-pressure ventilation is required in severe cases.
radiographs, which progresses to become an alveolar pattern. Methylxanthine bronchodilators (see Chapter 21) may also
In dogs edema caused by heart failure is generally more be beneficial in some patients. They are mild diuretics that
severe in the hilar region. In cats the increased opacities are also decrease bronchospasms and possibly respiratory