Acute lung injury/acute respiratory distress syndrome in 15 foals

REASONS FOR PERFORMING STUDY: Few reports exist in the veterinary medical literature describing clinical and pathological findings resembling conditions described as (ALI) and acute respiratory distress syndrome (ARDS) in man. OBJECTIVES: To document history, clinical, laboratory and diagnostic findings, treatment and outcome of foals age 1-12 months diagnosed with ALI/ARDS at a referral hospital. METHODS: Medical records, including radiographic, cytological, microbiological, serological and post mortem findings, were reviewed in a retrospective manner to identify foals with acute onset of respiratory distress, a partial pressure of arterial oxygen (PaO2) to fraction of oxygen in inspired gases (FiO2) ratio of < or = 300 mmHg, pulmonary infiltrates on thoracic radiographs or post mortem findings consistent with ALI/ARDS. RESULTS: Fifteen foals age 1.5-8 months were included in the study. Seven foals had previously been treated for respiratory disease, and all foals developed acute respiratory distress <48 h prior to presentation. Findings on presentation included tachycardia and tachypnoea in all foals, with fever recorded in 8 cases. Eight cases met the criteria for ALI and 7 for ARDS. Radiographic findings demonstrated diffuse bronchointerstitial pattern with focal to coalescing alveolar radiopacities. An aetiological agent was identified in foals ante mortem (n = 6) and post mortem (n = 4). All foals were treated with intranasal oxygen and antimicrobial drugs; 13 received corticosteroids. Nine patients survived, 4 died due to respiratory failure and 2 were subjected to euthanasia in a moribund state. Follow-up was available for 7 foals; all performed as well as age mates or siblings, and one was racing successfully. CONCLUSIONS: A condition closely meeting the human criteria for ALI/ARDS exists in foals age 1-12 months and may be identical to previously described acute bronchointerstitial pneumonia in young horses. POTENTIAL RELEVANCE: ALI/ARDS should be suspected in foals with acute severe respiratory distress and hypoxaemia that is minimally responsive to intranasal oxygen therapy. Treatment with systemic corticosteroids, intranasal oxygen and antimicrobials may be beneficial in foals with clinical signs compatible with ALI/ARDS.     

Acute respiratory distress syndrome.

Several combination therapies have been described throughout this article: in all likelihood, it is combination therapy that will allow improved survival of ARDS patients. As medicine moves into the future, clinical trials evaluating the efficacy of therapies for ARDS will be performed. In human critical care medicine, a large forward step was taken when ALI and ARDS were clearly defined. Unfortunately. as good as the definition is, ALI and ARDS occur secondary to many different underlying pathologic processes,perhaps obscuring the benefits of certain therapies for ARDS based on the underlying condition, for example, trauma versus sepsis. Selection of patients entering any ARDS trial is crucial: not only must those patients meet the strict definition of ARDS but the underlying disease process should be clearly identified. Identification of patients suffering from different disease processes before the onset of ARDS will allow for stratification of outcomes according to the intervention and the underlying pathology--comparing apples to apples and not to oranges. We are in a unique position in veterinary medicine. Although frequently financially limited by our clients, we have the opportunity to achieve several goals. First, we need to clearly define what constitutes ALI and ARDS in veterinary medicine. Do we want to rely on the human definitions? Probably not; however, as a group, we need to determine what we will accept as definitions. For example, we may not be able perform right heart catheterizations on all our patients to meet the wedge pressure requirement of human beings of less than 18 mm Hg. Do we agree that a PAOP of less than 18 mmHg is appropriate for animals, and is it appropriate for all animals? Will we accept another measure, for example, pulmonary artery diameter increases with echocardiographic evidence of acceptable left heart function? What is acceptable left heart function? As veterinarians, what do we consider to be hypoxemia? Is it the same in all species that we work with? What do we define as acute onset? Most human ARDS cases occur while patients are in hospital being treated for other problems, whereas many of our patients present already in respiratory distress. If we are unable to ventilate patients for economic or practical reasons, what do we use as the equivalent of the Pao2/Flo, ratio'? Reliance on the pathologist is not reasonable, because many disease processes can look similar to ARDS under the microscope. If anything, ALI and ARDS are clinical diagnoses. It is time for veterinarians to reach a consensus on the definition for ALI and ARDS in our patients.Only when we have a consensus of definition can rational prospective clinical trials of therapies be designed.     

Suggested Strategies for Ventilatory Management of Veterinary Patients with Acute Respiratory Distress Syndrome

Objective: To review the current recommendations and guidelines for mechanical ventilation in humans and in animals with acute respiratory distress syndrome.
Human data synthesis: Acute respiratory distress syndrome (ARDS) in humans in defined as an acute onset of bilateral, diffuse infiltrates on thoracic radiographs that are not the result of heart disease and a significant oxygenation impairment. These patients require mechanical ventilation. Research has shown that further pulmonary damage can occur as a result of mechanical ventilation. Various alveolar recruitment maneuvers and a low tidal volume with increased positive end expiratory pressure (PEEP) have been associated with an increased survival.
Veterinary dat synthesis: Two veterinary reports have characterized ARDS in dogs using human criteria. There are no prospective veterinary studies using recruitment that ventilator-induced lung injury (VILI) occurs in dogs, sheep, and rats.
Conclusion: Recruitment maneuvers in conjunction with low tidal volumes and PEEP keep the alveoli open for gas exchange and decrease VILI. Prospective veterinary research in needed to determine if these maneuvers and recommendation can be applied to veterinary patients.     

Acute respiratory distress syndrome in dogs and cats: a review of clinical findings and pathophysiology

Objective: To review the clinical and pathophysiologic aspects of acute respiratory distress syndrome (ARDS) in dogs and cats. Data sources: Data from human and veterinary literature were reviewed through Medline and CAB as well as manual search of references listed in articles pertaining to acute lung injury (ALI)/ARDS. Human data synthesis: Since the term ARDS was first coined in 1967, there has been a abundance of literature pertaining to this devastating syndrome in human medicine. More complete understanding of the complex interactions between inflammatory cells, soluble mediators (e.g., tumor necrosis factor, interleukin (IL)‐6, IL‐8, platelet activating factor) and the clinical patient has provided for timely recognition and mechanistically based protective strategies decreasing morbidity and mortality in human patients with ARDS. Veterinary data synthesis: Although little is known, ARDS is becoming a more commonly recognized sequela in small animals. Initial case reports and retrospective studies have provided basic clinical characterization of ARDS in dogs and cats. Additionally, information from experimental models has expanded our understanding of the inflammatory mechanisms involved. It appears that the inflammatory processes and pathologic changes associated with ARDS are similar in dogs, cats, and humans. Conclusions: Unfortunately, current mortality rates for ARDS in small animals are close to 100%. As our capability to treat patients with advanced life‐threatening disease increases, it is vital that we develop a familiarity with the pathogenesis of ARDS. Understanding the complex inflammatory interactions is essential for determining effective preventative and management strategies as well as designing novel therapies for veterinary patients.     

Thoracic trauma and post operative lung injury in a neonatal foal

A 24‐hour‐old Standardbred filly was referred with an acute history of weakness, respiratory distress and subcutaneous emphysema. Radiographic evaluation revealed left sided rib fractures, unilateral pneumothorax and pneumomediastinum. Serial arterial blood gas measurements pre‐ and post rib repair showed pulmonary dysfunction. Post operative radiographs revealed the presence of air bronchograms and a bronchointerstitial pattern, suggestive of alveolar parenchymal pathology consistent with pulmonary contusion, pulmonary oedema or ALI/ARDS. The filly was treated with intranasal oxygen and an active chest draining unit and recovered uneventfully.     

IMAGING DIAGNOSIS: ACUTE LUNG INJURY FOLLOWING MASSIVE BEE ENVENOMATION IN A DOG

A 5-year-old neutered male mixed breed dog presented for increased respiratory effort after being stung by over 100 bees and developing anaphylactic shock. Given the history, clinical signs and thoracic radiographic findings of a mild bilateral interstitial pattern, acute lung injury/acute respiratory distress syndrome (ALI/ARDS) was suspected. Further testing was performed to support this diagnosis. On computed tomographic images, there was a diffuse bilateral opacification of the lungs, with preservation of bronchial and vascular margins. Pulmonary function testing indicated decreased pulmonary compliance, decreased diffusion capacity and decreased functional residual capacity. These results supported the diagnosis of ALI/ARDS secondary to bee sting envenomation and development of anaphylactic shock. After 8 days of treatment with oxygen, steroids, antibiotics, and bronchodilators the dog improved. This case demonstrates the usefulness of computed tomography and pulmonary function testing in the diagnosis of ALI/ARDS.     

Successful treatment of acute respiratory distress syndrome in 2 dogs

Acute respiratory distress syndrome (ARDS) was diagnosed in 2 dogs with acute dyspnea. Short-term positive pressure ventilation and intense critical and nursing care were provided. Both dogs improved and were discharged. Few reports describe successful recovery from ARDS. Due to advances in positive pressure ventilation and improvement in the supportive care of critically ill veterinary patients, the prognosis for ARDS may improve.     

Application of Airway Pressure Therapy in Veterinary Critical Care: Part I: Respiratory Mechanics and Hypoxemia

Over the past several decades, recognition of acute respiratory failure as the cause of death in patients suffering from various clinical conditions has prompted aggressiv investigation into the area of respiratory physiology and supportive respiratory care. With the evolution of emergency medicine and critical care services in both human and veterinary medicine, many patients previously considered unsalvageable due to the severity of their underlying disease are now being resuscitated and successfully supported, creating a new population of critically ill patients. Where only a decade ago these patients would have succumbed to their underlying disease, they now survive long enough to manifest the complications of shock and tissue injury in the form of acute respiratory failure. Investigation into the pathophysiology and treatment of this acute respiratory distress syndrom (ARDS) has facilitated increased clinical application of respiratory theerapy and machanical ventilation.¹ The purpose of this paper is to provide a basic review of respiratory mechanics and the pathophysiology of hypoxemia as they relate to airway pressure therapy in veterinary patients and to review the use of airway pressure therapy in veterinary patients This paper is divided into two parts; part I reviews respiratory mechanics and hypoxemia as they apply to respiratory therapy, while part II deals specifically with airway pressure therapy andits use in clinical cases.     

Respiratory Distress Resulting from Acute Lung Injury in the Veterinary Patient

Because of improved management of animals in intensive care facilities, veterinarians are often confronted with patients at risk of developing adult respiratory distress syndrome (ARDS). The four objectives of this review are: 1) to describe the clinical conditions which place animals at risk for development of ARDS, 2) to give the reader a comprehensive understanding of the pathophysiology of endotoxin-induced lung injury, 3) to address the interspecies variability in susceptibility to endotoxin-induced lung injury, and 4) to outline areas where veterinarians should be concentrating their diagnostic and therapeutic efforts with regards to this syndrome. Because there is little written in the veterinary literature on ARDS, this review will rely heavily on the human ARDS literature as well as on research in animal models of acute lung injury.     

Neonatal respiratory distress and sepsis in the premature foal: Challenges with diagnosis and management

The presentation of a premature, neonatal foal affected with respiratory distress and seizures represents a difficult diagnostic and therapeutic challenge often best addressed by the provision of appropriate emergency care followed by prompt referral to a well‐equipped critical care facility. Veterinary management of the premature foal described in the accompanying report was complicated by the development of sepsis and pulmonary failure. The development of pulmonary emphysematous bullae was identified during the course of the foal's treatment and probably contributed to its clinical deterioration. Diagnostic imaging modalities that may be used for the diagnosis of respiratory distress in neonatal foals include thoracic radiography, ultrasonography, computed tomography (CT) and magnetic resonance imaging (MRI). Both CT and MRI require general anaesthesia. The likelihood of a successful outcome for the foal in this report might have been improved by the provision of urgent veterinary care and referral to the critical care facility earlier in the course of its management. Important early indicators of the need for urgent veterinary care in this case included the foal's prematurity, inability to stand, and the need to provide manual support to facilitate nursing from the mare's udder. Foals affected in this manner should warrant treatment with broad‐spectrum antimicrobials, circulating volume maintenance, immunoglobulin support, and the use of a nasogastric tube to facilitate nutritional support.     

Helium‐oxygen gas‐carrier mixture (heliox): a review of physics and potential applications in veterinary medicine

Background – To review the physics of helium with regard to airway physiology, as well as known human and potential veterinary applications of administration of inhaled helium‐oxygen gas‐carrier mixture (heliox). Data Sources – Human and veterinary studies. Human Data Synthesis – Helium‐oxygen mixtures have been used in human medicine for over 70 years as an adjunct therapy in various upper and lower respiratory disorders. Helium's low density promotes laminar flow through partially obstructed airways, resulting in a decreased work of breathing. Veterinary Data Synthesis – Little to no evidence‐based medicine exists to support or oppose the use of heliox in veterinary species. However, domestic animal species and humans share several common pathophysiologic aspects of various obstructive airway disorders. Thus, veterinary patients may also ultimately and significantly benefit from this novel therapy. Conclusion – Prospective studies are needed in veterinary medicine to determine the utility of heliox in clinical scenarios.     

Role of Lung Surfactant in Respiratory Disease: Current Knowledge in Large Animal Medicine

Lung surfactant is produced by type II alveolar cells as a mixture of phospholipids, surfactant proteins, and neutral lipids. Surfactant lowers alveolar surface tension and is crucial for the prevention of alveolar collapse. In addition, surfactant contributes to smaller airway patency and improves mucociliary clearance. Surfactant-specific proteins are part of the innate immune defense mechanisms of the lung. Lung surfactant alterations have been described in a number of respiratory diseases. Surfactant deficiency (quantitative deficit of surfactant) in premature animals causes neonatal respiratory distress syndrome. Surfactant dysfunction (qualitative changes in surfactant) has been implicated in the pathophysiology of acute respiratory distress syndrome and asthma. Analysis of surfactant from amniotic fluid allows assessment of fetal lung maturity (FLM) in the human fetus and exogenous surfactant replacement therapy is part of the standard care in premature human infants. In contrast to human medicine, use and success of FLM testing or surfactant replacement therapy remain limited in veterinary medicine. Lung surfactant has been studied in large animal models of human disease. However, only a few reports exist on lung surfactant alterations in naturally occurring respiratory disease in large animals. This article gives a general review on the role of lung surfactant in respiratory disease followed by an overview of our current knowledge on surfactant in large animal veterinary medicine.     

Application of Airway Pressure Therapy in Veterinary Critical Care: Part II: Airway Pressure Therapy

As the specialties of emergency medicine and critical care have grown and evolved in both human and veterinary medicine, so has the need for more advanced care of patients with primary lung disease. Treatment of acute respiratory failure has been the focus of several articles in the human medical literature of the past few years.^1,8 This paper deals with airway pressure therapy and its application in cases of acute respiratory failure in veterinary medicine. The reader is referred to part I of this paper for a reveiw of respiratory mechanics and hypoxemia as they apply to respiratory therapy.     

Histologic margins and the residual tumour classification scheme: Is it time to use a validated scheme in human oncology to standardise margin assessment in veterinary oncology?

There is no consensus on the definition of a complete histologic excision in veterinary oncology; many definitions have been used in various studies, but these have been arbitrarily selected with no apparent justification. The residual tumour classification scheme, where a complete histologic excision is defined as a histologic tumour‐free margin >0 mm, has been used for >40 years in human oncology by all of the major clinical staging organizations and is considered highly prognostic for the vast majority of malignant tumours in people. Because of the widespread use of the residual tumour classification scheme both clinically and in research studies, this standardized approach permits better communication between clinicians, an evidence‐based decision‐making process for adjuvant treatment options following surgical resection, minimizes exposing patients to unnecessary adjuvant treatments and a better ability to compare local tumour control for specific tumours between different studies. The adoption of the residual tumour classification scheme in veterinary oncology would likely achieve similar outcomes and minimize the prevalent confusion within the veterinary community, amongst both general practitioners and specialists, regarding the definition of what constitutes a complete histologic excision.     

Adult respiratory distress syndrome (ARDS). Incidence, clinical findings, pathomorphology and pathogenesis. A review

Acute and progressive respiratory distress ("shock lung") is a well known and feared complication in human patients with a variety of underlying disorders, even though the lungs are not involved primarily. In spite of the fact that dogs, and other animals, very often have been used in experimental models studying this syndrome, "shock lungs" have not received much attention in veterinary medicine. With the improved and more intensive treatment of severely diseased animals during the last years, especially pet animals, it is reasonable to assume that the lungs will be more important as an end organ also in veterinary practice. Animals in shock, particularly if complicated with sepsis, are prone to develop progressive respiratory distress. This paper reviews the current knowledge about the clinical picture, pathology and pathogenesis of acute respiratory disease, with main emphasize on the pathogenetic mechanism.     

Tools for the diagnosis of equine respiratory disorders.

Respiratory disorders are among the most common problems leading horse owners to seek veterinary attention. Accurate diagnosis of these conditions allows for proper treatment to be instituted, much to the benefit of the patient and satisfaction of the client. As an introduction to this issue on equine respiratory disorders, we review some of the tools that are available to equine veterinarians for the diagnosis of respiratory disorders. Physical and endoscopic examination, radiology, diagnostic ultrasound, techniques for sampling the respiratory tract, hematology, blood gas analysis, respiratory mechanics, and some modern diagnostic tools are briefly covered.     

Cardiovascular disease in the equine neonate

Cardiac disease in the equine neonate occurs infrequently. Murmurs are often heard in foals and are not considered significant unless they persist beyond 4 days of age. Congenital cardiac defects are the most common form of primary cardiac disease in the foal, with ventricular septal defects occurring most frequently. Other neonatal foal diseases such as ruptured bladders, white muscle disease, neonatal respiratory distress syndrome, and septicemia have secondary cardiac involvement.     

Assessment of a point‐of‐care cardiac troponin I test to differentiate cardiac from noncardiac causes of respiratory distress in dogs

Objectives – To (1) determine a reference interval for cardiac troponin I (cTnI) using a point‐of‐care device in normal dogs and compare the results with those published by the manufacturer and (2) determine if cTnI differs among dogs with cardiogenic and noncardiogenic respiratory distress. Design – Prospective observational study. Setting – Emergency and referral veterinary hospital. Animals – Twenty‐six clinically normal dogs and 67 dogs in respiratory distress. Interventions – All dogs underwent whole blood sampling for cTnI concentrations. Measurements and Results – Normal dogs had a median cTnI concentration of 0.03 ng/mL (range 0–0.11 ng/mL). Thirty‐six dogs were diagnosed with noncardiogenic respiratory distress with a median cTnI concentration of 0.14 ng/mL (range 0.01–4.31 ng/mL). Thirty‐one dogs were diagnosed with cardiogenic respiratory distress with a median cTnI concentration of 1.74 ng/mL (range 0.05–17.1 ng/mL). A significant difference between cTnI concentrations in normal dogs and dogs with noncardiogenic respiratory distress was not detected. Significant differences in cTnI concentrations were found between normals versus cardiogenic and cardiogenic versus noncardiogenic respiratory distress groups. Significant differences in cTnI concentrations were identified in >10 when compared with the <5 and the 5–10 years of age groups. Receiver operating curve analysis identified cTnI concentrations >1.5 ng/mL as the optimal “cut‐off point” having a sensitivity of 78% and specificity of 51.5%. The area under the receiver operating curve was 0.72. Overall test accuracy was 65%. Conclusions – cTnI concentrations were significantly increased in dogs with cardiogenic respiratory distress versus dogs with noncardiogenic respiratory distress and normal dogs. A significant difference between normal dogs and dogs with noncardiogenic causes of respiratory distress was detected. Although highly sensitive when cTnI concentrations exceed 1.5 ng/mL, the test has low specificity. Assessment of cTnI by the methodology used cannot be recommended as the sole diagnostic modality for evaluating the cause of respiratory distress in dogs.     

Controlled mechanical ventilation in equine anaesthesia: Physiological background and basic considerations (Part 1)

Controlled mechanical ventilation (CMV) is routinely used in equine anaesthesia, with many different options available to mechanically deliver breaths. The complexity of respiratory pathophysiology in anaesthetised horses and the wide range of devices available is described in this scoping review. The first part of the review outlines basic equine respiratory physiology and pathophysiology during anaesthesia to illustrate what makes horses prone to inefficient gas exchange and ventilation when they are recumbent. The difference between spontaneous ventilation and CMV is reviewed and basic considerations of CMV are explored in more detail.