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28 Acute Respiratory Distress Syndrome

• Pneumonia (p. 795), especially if by aspira- TREATMENT Recommended Monitoring
tion (p. 793), affects cranioventral lung Treatment Overview Affected patients need intensive nursing care.
VetBooks.ir • PTE produces variable radiographic findings Intubation and ventilation should be imple- • Oxygen saturation (and ideally, arterial blood
regions most severely.
• Ventilation parameters, including airway
pressures
mented if respiratory distress lasts for > 1 hour
and is suspected (over noncardiogenic pul-
gas analysis)
monary edema or ARDS) when respiratory
mental oxygen (p. 1146), or in the presence
distress is disproportionately severe compared or is worsening, if SpO 2 < 89% despite supple- • Blood pressure (direct arterial is ideal)
to radiographic lung appearance (p. 842). of hypoventilation that may indicate respiratory • Continuous electrocardiographic monitoring
• Pleural space disease is usually easily dif- fatigue (e.g., PCO 2 > 65 mm Hg). • Urine output
ferentiated from noncardiogenic pulmonary Specific goals:
edema or ARDS on radiographs (lung • Treatment of the underlying disorder and, PROGNOSIS & OUTCOME
retraction). if necessary, positive-pressure ventilation are
• Any of these disorders may, if severe, produce the cornerstones of management of ARDS. Guarded to grave. Survival after ARDS is
pulmonary markings that are indistinguish- • No specific therapy for ARDS; limited tidal possible but rare. Multiple organ failure,
able from noncardiogenic pulmonary edema volumes during mechanical ventilation may progressive hypoxemia, circulatory collapse, and
or ARDS. mitigate ventilator-associated pulmonary ongoing costs associated with intensive care
Arterial blood gas analysis: the stress accom- injury and barotrauma. limit survival of affected dogs.
panying collection of an arterial blood sample • Provide support for the damaged lung
may outweigh the benefits with severe dyspnea parenchyma to permit healing. PEARLS & CONSIDERATIONS
(p. 1058). If a reliable pulse oximeter measure
is available, it may be used to estimate PaO 2 . Acute General Treatment Comments
• Calculation of the PaO 2 /FIO 2 ratio can • Optimize oxygenation; mechanical ventila- Accuracy in diagnosis: identify and treat causes
characterize the stage of ARDS. PaO 2 is tion with positive end-expiratory pressure of hospital-acquired respiratory distress that are
measured on an arterial blood gas sample; (p. 1185); may require referral. more commonly responsive (better prognosis):
FIO 2 is the fraction of inspired oxygen (room • Low tidal volumes (5-10 mL/kg) with • Pneumonia
air = 0.21; 40% oxygen = 0.4; 100% oxygen an attempt to limit barotrauma are • PTE
= 1). recommended. • Volume overload/congestive heart failure
○ Normal ratio > 475 • May result in increased PaCO 2 (permissive
○ ARDS < 300 hypercarbia) Prevention
○ Example: dog receiving 40% O 2 with • Other supportive measures: Early identification of patients at risk (i.e., those
measured PaO 2 of 60 mm Hg = 60/0.4 ○ Antibiotics (e.g., ampicillin 22 mg/kg IV with severe systemic inflammation from any
= 150 q 8h, with or without enrofloxacin 10 mg/ cause) and implementation of intensive sup-
If available, the protein content of expectorated kg IV diluted in sterile saline and given portive care:
pulmonary edema fluid/foam may be evaluated slowly IV q 24h [5 mg/kg q 24h in cats]) • Prevent sepsis from progressing to septic
on a refractometer. ○ Surgery, if indicated, for primary disease shock.
• Pulmonary edema from noncardiac sources • Diuretics are not directly indicated, although • Aggressive treatment for severely injured
such as ARDS has a protein content at least every effort should be made to prevent patients
75% that of serum, whereas cardiogenic volume overload.
pulmonary edema has a protein content ○ If it is unclear whether volume overload Technician Tips
≈30% that of serum. is present, 2 mg/kg furosemide IV may ARDS is one of the disorders that requires the
Other tests as indicated by primary disease be administered q 6h. If respiratory greatest degree of monitoring and supportive
process (e.g., coagulation profile if possibility character improves in < 24 hours and care (see Recommended Monitoring above).
of pulmonary hemorrhage) radiographic markings improve in < 48
hours after diuretic treatment, cardiogenic Client Education
Advanced or Confirmatory Testing pulmonary edema was more likely than ARDS is a severe disease associated with critical
• CT of lungs: superior resolution compared ARDS. illness. Successful treatment requires committed
with radiographs but limited availability and • Colloids are not indicated for acute lung clients with adequate emotional and financial
requires sedation or anesthesia. If patient is injury or ARDS. The altered permeability resources (e.g., pet insurance).
anesthetized for mechanical ventilation, CT of the capillary-alveolar membrane may allow
scanning is preferred. The level of PEEP is synthetic colloids to cross into the pulmonary SUGGESTED READING
important (usually 5-10 cm H 2O), and parenchyma and worsen gas exchange. Wilkins P, et al: Acute lung injury and acute respira-
motion (tachypnea) should be prevented. tory distress syndromes in veterinary medicine:
CT angiography may provide evidence to Chronic Treatment consensus definitions: The Dorothy Russell
support the presence of PTE. Empiric glucocorticoid use (prednisone Havemeyer Working Group on ALI and ARDS
• Echocardiography (p. 1094) to exclude 0.5-1 mg/kg PO q 24h) during recovery phase in Veterinary Medicine. J Vet Emerg Crit Care
cardiac dysfunction or PTE (by evaluating to delay/prevent pulmonary fibrosis; this 17:333-339, 2007.
for right-sided heart enlargement and tricus- therapy is unsupported by objective evidence AUTHOR: Elizabeth Rozanski, DVM, DACVIM,
pid regurgitant flow indicating pulmonary DACVECC
hypertension) Possible Complications EDITOR: Benjamin M. Brainard, VMD, DACVAA,
• Transtracheal wash or bronchoalveolar lavage • Failure of other organ systems DACVECC
(pp. 1073 and 1074) with cytologic evalu- • Chronic pulmonary insufficiency
ation and culture to exclude infection or • Death from respiratory failure
neoplasia

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