Noncardiogenic pulmonary edema in small animals

OBJECTIVE

To review various types of noncardiogenic pulmonary edema (NCPE) in cats and dogs.

ETIOLOGY

NCPE is an abnormal fluid accumulation in the lung interstitium or alveoli that is not caused by cardiogenic causes or fluid overload. It can be due to changes in vascular permeability, hydrostatic pressure in the pulmonary vasculature, or a combination thereof. Possible causes include inflammatory states within the lung or in remote tissues (acute respiratory distress syndrome [ARDS]), airway obstruction (post-obstructive pulmonary edema), neurologic disease such as head trauma or seizures (neurogenic pulmonary edema), electrocution, after re-expansion of a collapsed lung or after drowning.

DIAGNOSIS

Diagnosis of NCPE is generally based on history, physical examination, and diagnostic imaging. Radiographic findings suggestive of NCPE are interstitial to alveolar pulmonary opacities in the absence of signs of left-sided congestive heart failure or fluid overload such as cardiomegaly or congested pulmonary veins. Computed tomography and edema fluid analysis may aid in the diagnosis, while some forms of NCPE require additional findings to reach a diagnosis.

THERAPY

The goal of therapy for all types of NCPE is to preserve tissue oxygenation and reduce the work of breathing. This may be achieved by removing the inciting cause (eg, airway obstruction) and cage rest in mild cases and supplemental oxygen in moderate cases and may require mechanical ventilation in severe cases.

PROGNOSIS

Prognosis is generally good for most causes of veterinary NCPE except for ARDS, although data are scarce for some etiologies of NCPE.

Management of refractory hypoxemia using recruitment maneuvers and rescue therapies: A comprehensive review

Refractory hypoxemia in patients with acute respiratory distress syndrome treated with mechanical ventilation is one of the most challenging conditions in human and veterinary intensive care units. When a conventional lung protective approach fails to restore adequate oxygenation to the patient, the use of recruitment maneuvers and positive end-expiratory pressure to maximize alveolar recruitment, improve gas exchange and respiratory mechanics, while reducing the risk of ventilator-induced lung injury has been suggested in people as the open lung approach. Although the proposed physiological rationale of opening and keeping open previously collapsed or obstructed airways is sound, the technique for doing so, as well as the potential benefits regarding patient outcome are highly controversial in light of recent randomized controlled trials. Moreover, a variety of alternative therapies that provide even less robust evidence have been investigated, including prone positioning, neuromuscular blockade, inhaled pulmonary vasodilators, extracorporeal membrane oxygenation, and unconventional ventilatory modes such as airway pressure release ventilation. With the exception of prone positioning, these modalities are limited by their own balance of risks and benefits, which can be significantly influenced by the practitioner's experience. This review explores the rationale, evidence, advantages and disadvantages of each of these therapies as well as available methods to identify suitable candidates for recruitment maneuvers, with a summary on their application in veterinary medicine. Undoubtedly, the heterogeneous and evolving nature of acute respiratory distress syndrome and individual lung phenotypes call for a personalized approach using new non-invasive bedside assessment tools, such as electrical impedance tomography, lung ultrasound, and the recruitment-to-inflation ratio to assess lung recruitability. Data available in human medicine provide valuable insights that could, and should, be used to improve the management of veterinary patients with severe respiratory failure with respect to their intrinsic anatomy and physiology.

Inclusion of airway pressure release ventilation in the management of respiratory failure and refractory hypercapnia in a dog

OBJECTIVE

To describe the use of airway pressure release ventilation (APRV) to relieve hypercapnia in a dog undergoing mechanical ventilation.

CASE SUMMARY

A 3-month-old male Shar-Pei mix presented to the emergency department with suspected noncardiogenic pulmonary edema. Due to severe hypercapnia, mechanical ventilation was initiated. The hypercapnia failed to improve with conventional pressure control mechanical ventilation, bronchodilator administration, suctioning, or endotracheal tube replacement. The dog was transitioned to APRV and maintained in this mode for 36 hours. A modified APRV protocol in which inverse inspiratory to expiratory ratios ranged from 4.3:1 to 6.0:1 was utilized, resulting in a drastic improvement in the patient's hypercapnia. The patient eventually was transitioned off the ventilator, and no respiratory abnormalities have been noted at subsequent recheck examinations.

NEW OR UNIQUE INFORMATION PROVIDED

This case documents the first use of APRV to relieve refractory hypercapnia in a dog undergoing mechanical ventilation and is one of the only recorded cases of using APRV for this purpose in the medical literature at large. APRV may be considered in cases of hypercapnia when traditional therapies fail, although caution is warranted as this mode of ventilation can also worsen hypercapnia.

Short-term surgical outcomes and histomorphological evaluation of thermal injury following palatoplasty performed with diode laser or air plasma device in dogs with brachycephalic airway obstructive syndrome

Brachycephalic obstructive airway syndrome (BOAS) is a common disorder presenting enlarged soft palate, stenotic nares and abnormal turbinate growth. Surgical correction of BOAS abnormalities with caudal palatoplasty is an elective therapy. This prospective study aimed to compare the effect of an air plasma device and diode laser in dogs undergoing palatoplasty. Outcome measures were as follows: (1) intra-operative and immediate post-operative complications; (2) evaluation of thermal injury in histological tissue sections of the excised soft palate. Twenty dogs with enlarged soft palates underwent palatoplasty, using an air plasma device (n=10) and diode laser (n=10). Soft palate specimens underwent masked histopathological analysis to assess post-operative thermal injury. In this pilot study, no differences were observed in surgical times; all dogs were discharged 24h after surgery and had stable respiration. In the air plasma group, post-operative bleeding occurred in two cases and revision surgery was performed. No difference in thermal injury was observed using the two devices (P>0.05). The air-plasma device was a viable surgical option for palatoplasty in dogs with BOAS.

Risk factors, characteristics, and outcomes of acute respiratory distress syndrome in dogs and cats: 54 cases

OBJECTIVE

To characterize the clinical features of the acute respiratory distress syndrome (ARDS), risk factors, and outcome in dogs and cats. The study also aimed to evaluate the current veterinary criteria for the diagnosis of ARDS by comparison of clinical diagnostic criteria with necropsy findings.

DESIGN

Retrospective study.

ANIMALS

Fifty-four client-owned animals, 46 dogs and 8 cats.

INTERVENTIONS

Medical records were reviewed for patients with the diagnosis of ARDS based on previously published clinical criteria or necropsy diagnosis. Signalment, clinical findings, and outcome were recorded.

MEASUREMENTS AND MAIN RESULTS

Animals were grouped according to a clinical or necropsy diagnosis: 43/54 (80%) were diagnosed with ARDS based on clinical criteria (group 1) and 11/54 (20%) were diagnosed with ARDS based on necropsy only (group 2). In group 1, 22/43 (51%) had a necropsy, which confirmed ARDS in 12/22 (54%). Direct (pulmonary) causes of ARDS were more common than indirect causes in dogs, while cats had a similar occurrence of direct and indirect causes. The most common risk factors identified in dogs were aspiration pneumonia (42%), systemic inflammatory response syndrome (SIRS) (29%), and shock (29%). All cats diagnosed clinically with ARDS had SIRS with or without sepsis. Of the animals with a clinical diagnosis of ARDS, 49% received mechanical ventilation and 58% received treatment (with or without mechanical ventilation) for 24 hours or longer. The overall case fatality rate was 84% in dogs and 100% in cats.

CONCLUSIONS AND CLINICAL RELEVANCE

As described in human literature, pneumonia was the most common risk factor in dogs with ARDS, whereas it was SIRS for the cat population. The high mortality rate and discrepancy between the clinical diagnosis and necropsy findings may highlight limitations in the clinical criteria for the diagnosis of ARDS and treatment in dogs and cats.

Successful treatment of canine acute respiratory distress syndrome secondary to inhalant toxin exposure

OBJECTIVE

To describe the successful management of a dog with acute respiratory distress syndrome secondary to inhalant toxin exposure.

CASE SUMMARY

An 8-year-old male neutered Greyhound was referred with severe respiratory distress 56 hours after exposure to an aerosol toxicant. The patient developed respiratory difficulties requiring veterinary attention within 12 hours of initial exposure. Treatment at the referral hospital included mechanical ventilation and supportive care. The patient was discharged 5 days after admission to the referral hospital.

NEW OR UNIQUE INFORMATION

This is the first report, to the authors' knowledge, of canine acute respiratory distress syndrome secondary to inhalant toxin exposure not associated with smoke inhalation. The report summarizes the provided care and subsequent successful outcome.

Retrospective evaluation of the prevalence, risk factors, management, outcome, and necropsy findings of acute lung injury and acute respiratory distress syndrome in dogs and cats: 29 cases (2011-2013)

OBJECTIVE

To determine the prevalence and risk factors for veterinary acute lung injury (VetALI) and veterinary acute respiratory distress syndrome (VetARDS), assess mechanical ventilation settings and patient outcomes, and to evaluate the relationship of clinical diagnoses with necropsy findings.

DESIGN

Retrospective study.

SETTING

University teaching hospital.

ANIMALS

Twenty-four dogs and 5 cats with a clinical diagnosis of VetALI or VetARDS. Control population includes 24 dogs and 5 cats with a clinical diagnosis of respiratory disease other than VetALI or VetARDS.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

VetALI and VetARDS were diagnosed in 3.2% of dogs and 1.3% of cats presenting to the ICU. Systemic inflammatory response syndrome was the most common inciting condition (16/24 dogs, 2/5 cats), followed by vomiting and subsequent aspiration of gastric contents (9/24 dogs), sepsis (5/24 dogs, 3/5 cats), multiple transfusions (4/24 dogs), trauma (3/24 dogs), and adverse drug reactions (1/24 dogs, 1/5 cats).  None of these conditions were found to be significantly associated with a risk of development of VetALI or VetARDS when compared to controls. Twelve dogs (50%) and 4 cats (80%) underwent mechanical ventilation for a median duration of 18 hours in dogs (range: 6-174 h) and 15.5 hours in cats (range: 6-91 h). Overall, 3/29 patients survived to discharge including 2/24 dogs and 1/5 cats. Necropsy results were available for 8/22 dogs and 3/4 cats. A total of 6/8 dogs (75%) dogs and 3/3 (100%) cats met the histopathologic criteria for diagnosis of VetALI or VetARDS.

CONCLUSIONS

VetALI and VetARDS can cause life-threatening respiratory distress in dogs and cats necessitating mechanical ventilation in 50% of dogs and 80% of cats in this study. These diseases are associated with a poor clinical outcome and a high rate of humane euthanasia.