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.     

Dyspnea in aging rats due to disseminated intravascular coagulation (DIC)

During an 18-month oncogenicity study using rats, approximately 10% of the animals developed a form of respiratory distress very similar to that seen in the terminal stages of chronic respiratory disease, commonly associated with Mycoplasma pulmonis infection. Investigation of the lungs of the affected rats revealed not only that they did not have the consolidation usually associated with chronic respiratory disease, but they also appeared macroscopically normal. Further investigation of a number of cases revealed systemic intravascular thrombus formation of the type usually referred to as disseminated intravascular coagulation. Using an antiserum to fibrin we have demonstrated the presence of intravascular fibrin deposits in the lungs of the affected rats and have shown them to be the same as experimentally induced intravascular fibrin deposits induced in rat lungs by the administration of thrombin after blocking the fibrinolytic system. This is the first example of such a phenomenon being recorded in aging rats.     

Acute lung injury and acute respiratory distress syndromes in veterinary medicine: consensus definitions: The Dorothy Russell Havemeyer Working Group on ALI and ARDS in Veterinary Medicine

Background: As veterinary medicine has become more sophisticated, with greater numbers of veterinary patients receiving intensive care, more patients with an acute respiratory distress (ARDS)‐like syndrome have been recognized. Methods: A consensus definition meeting was held for the purpose of developing veterinary‐specific definitions for acute lung injury (ALI) and ARDS. Results/conclusions: Three clinically based definitions for acute lung injury and acute respiratory distress‐like syndromes occurring in veterinary patients were described. Neonatal equine respiratory distress syndrome (NERDS) was defined separately due to the specific requirement for primary developmental surfactant dysfunction and lack of an inflammatory component. Five diagnostic criteria categories were established for Veterinary ALI/ARDS (Vet ALI/ARDS) with 4 required and a fifth highly recommended criteria. A strong consensus was reached that onset of respiratory distress must have been acute and that known risk factors must be present. Additional criteria included evidence of pulmonary capillary leak with no evidence of increased pulmonary capillary pressure, evidence of inefficient gas exchange and, finally, evidence of inflammation. Some features of ALI/ARDS in the neonatal horse were recognized as unique, therefore, equine neonatal ALI/ARDS (EqNALI/EqNARDS) was similarly defined but with a graded gas exchange inefficiency table to allow for normal developmental changes in gas exchange. Use of these definitions in planning prospective studies of these problems in veterinary patients should allow for more direct comparisons of studies and clinical trials, with a larger goal of improving outcome in veterinary patients.     

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 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.     

Neonatal respiratory distress syndrome in the calf

Thirty-five calves were delivered by caesarean section near to term. During the operation amniotic fluid was collected for determination of the lecithin/sphingomyelin (L/S) ratio. Clinical examination of the calves and analysis of blood gas concentration (venous blood) were carried out within the first hour of life. Fifteen out of 35 calves under examination did not show clinical or blood gas disorders in the course of the first hour of life. In these calves, the L/S ratio, which represents a measure for the maturity of the surfactant system, averaged 2.6. The other 20 calves, however, developed a respiratory distress syndrome together with a progressive respiratory and metabolic acidosis within the first hour of life. The L/S ratio in the animals affected with respiratory distress syndrome reached an average value of 1.5 which was significantly below that of the calves not suffering from respiratory distress. Eleven of the 20 calves which developed respiratory distress syndrome died within the first 60 hours of life. The most striking findings in the post mortem examinations of these animals were intracranial haemorrhages and pulmonary lesions (hyaline membranes, interstitial and alveolar oedema). On the basis of the significantly lower L/S ratio and the post mortem findings, it is to be assumed that the respiratory distress syndrome in calves, equally with that in infants, is attributable to a surfactant deficiency.     

Chronic upper airway obstruction caused by laryngeal adenocarcinoma in a cat

An eight-year-old spayed female cat developed upper respiratory obstruction, abnormal vocalisation and anorexia over a period of a few months. Examination under general anaesthesia revealed unilateral laryngeal distortion by a soft tissue mass; there was no radiographic evidence of metastatic disease at this time. Over the next four months the upper respiratory obstruction became more severe as a result of progressive laryngeal stenosis and metastatic lung masses were observed radiographically four months after initial examination. Necropsy revealed an infiltrating laryngeal adenocarcinoma with metastases in the upper cervical lymph node and lungs. This case illustrates the value of early biopsy diagnosis to spare the patient the distress of progressive upper respiratory obstruction.     

Acute respiratory distress in cattle.

The term "fog fever" was originally used identify a disease of adult cattle grazing lush pastures in the autumn. Unfortunately, the name has subsequently been applied to other respiratory disorders which occurred under different epidemiological circumstances, so that the name "fog fever" has lost much of its original specificity and become almost synonymous with "acute respiratory distress". The pulmonary lesions in 151 cattle, of all ages, with acute respiratory distress are described in this report. While most of the animals were referred as examples of "fog fever", in only 43 of the 151 cases were the clinical signs, epidemiology and post mortem findings consistent with that disease. Twelve other pulmonary disturbances were encountered in the other animals and the pathology of these conditions has bee described.     

An overview of positive pressure ventilation

Objective: The purpose of this article is to give the reader a brief overview of the indications for positive pressure ventilation (PPV). Data sources: Current human and veterinary literature. Summary: There are numerous indications for PPV in veterinary medicine. These include both pulmonary parenchymal disease and diseases that affect ventilation. When choosing PPV, a clinician must have a comprehensive understanding of the different ventilation mode options available and the physiologic effects of ventilation on the patient. Conclusions: PPV is becoming more widely used in veterinary medicine and is improving the survival of animals with hypoxemic and hypercapnic respiratory failure.     

Conventional versus high-flow oxygen therapy in dogs with lower airway injury

Dogs with lower airway pathology that present in respiratory distress often receive oxygen therapy as the first line of treatment regardless of the underlying cause. Conventional “low-flow” systems deliver oxygen with a maximum flow rate of 15 L/minute. Traditionally, when an animal’s respiratory status does not improve with conventional oxygen therapy and treatments for underlying disease, options might be limited to either intubation and mechanical ventilation or humane euthanasia. High-flow oxygen therapy (HFOT) has been gaining popularity in veterinary medicine as an alternative route of oxygen supplementation for animals that require support beyond conventional therapy. High-flow oxygen therapy can supply a mixture of air and oxygen via a heated and humidified circuit. It is user friendly and can be used in an environment in which mechanical ventilation is unavailable.This review article is written for emergency doctors and general practitioners who lack access to mechanical ventilation. This article briefly reviews pertinent respiratory physiology, traditional oxygen supplementation techniques, the physiology of HFOT, and the limited evidence available in veterinary medicine regarding the use of HFOT, its applications, and limitations. Guidelines for the use of HFOT are suggested and HFOT is compared to conventional therapy.     

Immunisation of pigs with a major envelope protein sub-unit vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) results in enhanced clinical disease following experimental challenge

Disease exacerbation was observed in pigs challenged with virulent porcine reproductive and respiratory syndrome virus (PRRSV) following immunisation with a recombinant GP5 sub-unit PRRSV vaccine (rGP5) produced in E. coli. Eighteen animals were divided into three experimental groups: group A were immunised twice IM with rGP5, 21 days apart; group B acted as positive controls (challenged but not immunised); and group C were negative controls. Pigs in groups A and B were challenged 21 days after the second immunisation of the group A animals. Following challenge, three pigs given rGP5 exhibited more severe clinical signs than the positive controls, including respiratory distress and progressive weight-loss. Although not statistically significant, the more severe disease exhibited by group A animals may suggest previous immunisation as a contributory factor. The mechanisms of these findings remain unclear and no association could be established between the severity of disease, non-neutralising antibody concentrations and tissue viral loads.     

Evaluation of respiratory parameters at presentation as clinical indicators of the respiratory localization in dogs and cats with respiratory distress

Objective ? To describe clinical respiratory parameters in cats and dogs with respiratory distress and identify associations between respiratory signs at presentation and localization of the disease with particular evaluation between the synchrony of abdominal and chest wall movements as a clinical indicators for pleural space disease. Design ? Prospective observational clinical study. Setting ? Emergency service in a university veterinary teaching hospital. Animals ? Cats and dogs with respiratory distress presented to the emergency service between April 2008 and July 2009. Interventions ? None. Measurements and Main Results ? The following parameters were systematically determined at time of admission: respiratory rate, heart rate, temperature, type of breathing, movement of the thoracic and abdominal wall during inspiration, presence of stridor, presence and type of dyspnea, and results of thoracic auscultation. Abdominal and chest wall movement was categorized as synchronous, asynchronous, or inverse. Diagnostic test results, diagnosis, and outcome were subsequently recorded. Based on the final diagnoses, animals were assigned to 1 or more of the following groups regarding the anatomical localization of the respiratory distress: upper airways, lower airways, lung parenchyma, pleural space, thoracic wall, nonrespiratory causes, and normal animals. One hundred and seventy‐six animals (103 cats and 73 dogs) were evaluated. Inspiratory dyspnea was associated with upper airway disease in dogs and expiratory dyspnea with lower airway disease in cats. Respiratory noises were significantly associated and highly sensitive and specific for upper airway disease. An asynchronous or inverse breathing pattern and decreased lung auscultation results were significantly associated with pleural space disease in both dogs and cats (P<0.001). The combination is highly sensitive (99%) but not very specific (45%). Fast and shallow breathing was not associated with pleural space disease. Increased or moist pulmonary auscultation findings were associated with parenchymal lung disease. Conclusions ? Cats and dogs with pleural space disease can be identified by an asynchronous or inverse breathing pattern in combination with decreased lung sounds on auscultation.     

Reducing the oxygen concentration of gases delivered from anaesthetic machines unadapted for medical air

High fractional concentrations of inspired oxygen (FiO(2)) delivered over prolonged periods produce characteristic histological changes in the lungs and airway of exposed animals. Modern medical anaesthetic machines are adapted to deliver medical air (FiO(2)=0.21) for the purpose of reducing FiO(2); anaesthetic machines designed for the veterinary market have not been so adapted. Two inexpensive modifications that allow medical air to be added to the gas flow from veterinary anaesthetic machines are described. The advantages and disadvantages of each modification are discussed.     

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.     

Respiratory and cardiopulmonary arrest in dogs and cats: 265 cases (1986-1991).

Outcomes of cardiopulmonary arrest and resuscitation in clinically affected dogs and cats have not been adequately studied. We examined the records from 200 dogs and 65 cats that had received cardiopulmonary resuscitation for respiratory or cardiopulmonary arrest; none of the animals had been anesthetized or intubated at the time of arrest, and all had been hospitalized in a veterinary critical care facility. Cardiopulmonary arrest was found to be more common than respiratory arrest in dogs and cats. Hospital discharge rates for animals with cardiopulmonary arrest ranged from 4.1% for dogs to 9.6% for cats, and were consistent with those reported from studies of human beings with cardiopulmonary arrest. Hospital discharge rates for dogs and cats with respiratory arrest were 28% and 58.3%, respectively.     

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.     

Use of animation-enhanced video clips for teaching abnormal breathing patterns

The ability to characterize disease of the respiratory tract accurately based on breathing pattern is helpful for the development of differential diagnoses and an efficient diagnostic plan and critical for the stabilization of patients in respiratory distress. Veterinary students do not have sufficient clinical experience to observe personally all types of respiratory diseases and their resultant abnormal breathing patterns. We developed a teaching tool, the animated breathing pattern videotape (ABV), to fill this gap. The ABV is a collection of video clips of small animal patients with normal and abnormal breathing patterns on a conventional videotape of approximately 20 minutes duration. Each video clip is shown for 20 to 40 seconds, followed by the same clip with superimposed animation of rib and diaphragm motion, followed by the initial clip again, without overlying animation. The ABV has since been used in teaching third-year veterinary students, interns, residents, practicing veterinarians, and veterinary technicians. Student evaluations and responses to questionnaires by interns, residents, practicing veterinarians, veterinary technicians, and peer reviewers have been uniformly positive.     

动物专用大环内酯类新药——泰拉霉素

泰拉霉素是动物专用的新型大环内酯类抗生素,国内已批准用于猪呼吸系统疾病的防治。泰拉霉素的药动学特性优良,吸收快,达峰时间短,生物利用度高,在肺中可达到很高的组织浓度,消除半衰期长,药效持久。单次肌注或皮下给药即能提供全程的治疗,在兽医临床具有广阔的应用前景。本文综述了泰拉霉素的理化性质、作用机理、抗菌活性、药动学、药效学、不良反应及残留,为该药在兽医临床的应用提供参考资料。     

Spinal shock--comparative aspects and clinical relevance

Spinal shock is the loss of muscle tone and segmental spinal reflexes that develops caudal to a severe spinal cord injury. Although little recognized in the veterinary literature, spinal shock occurs in animals and is important in both accurate lesion localization and case management. In this review, we consider why spinal shock occurs and discuss the subsequent physiologic alterations, including the development of reflex hyperactivity. We also discuss differences in the expression of spinal shock between species and suggest why recovery of reflexes is relatively rapid in animals compared with humans. Finally, the implications for clinicians dealing with animals in the period immediately after severe spinal injury are considered.