Indications and outcomes for puppies undergoing mechanical ventilation: 59 cases (2006 to 2020)

Abstract

The medical records of 59 puppies from 6 hospitals undergoing mechanical ventilation (MV) between 2006 and 2020 were reviewed to describe the signalment, underlying disease, duration of ventilation, and outcome. The most common underlying diseases were pneumonia (n = 18), non-cardiogenic pulmonary edema (n = 16), and trauma (n = 8). Twenty-six (44%) puppies were weaned from the ventilator. The overall survival rate was 39% (23/59) including 19 non-brachycephalic dogs and 4 brachycephalics. Median duration of mechanical ventilation was 27 hours (range: 4 to 144 hours). Brachycephalic dogs were less likely to survive than nonbrachycephalic dogs (P = 0.032). English bulldogs were over-represented with pneumonia. No association between age and survival to discharge (P = 0.716) or outcome (P = 0.579) was detected. The survival rate, and underlying disease process and severity for mechanically ventilated puppies was similar to previous studies in adult dogs.

Introduction

Mechanical ventilation (MV) has been used with increasing frequency in veterinary medicine over the past 25 y (1–8). Provision of MV requires a knowledgeable and dedicated team with proper equipment and intensive nursing care abilities. In addition to a significant financial commitment by the client, the decision to pursue MV also has a considerable emotional burden (9). It is important to properly inform the client to establish realistic expectations, including duration of MV and prognosis. Puppies are often very new to the household and so the decision to make a considerable emotional and financial investment with an uncertain prognosis can be even more challenging. The success of ventilator support, defined either as weaning from MV or discharge home, varies with the underlying disease. Previously reported overall survival to discharge of dogs undergoing MV ranged from 21 to 71% (2–8). Previous studies have suggested that younger dogs are more likely to survive (2,3). One study with dogs ranging from 10 wk to 16 y of age identified a 10% decrease in the odds of survival with every 1 y increase in age, although the number of puppies was not reported (2). Puppies have never been studied specifically. The objectives of the present study, therefore, were to describe the indications for mechanical ventilation, duration of ventilation, and outcome in dogs less than 12 mo of age.

Materials and methods

The medical records of 5 university teaching hospitals and 1 private multispecialty referral hospital were reviewed to identify puppies (defined as dogs less than 12 mo of age), which underwent MV between August 2006 and February 2020. A standardized spreadsheet from a commercial software program (Microsoft Excel Version 16.36; Microsoft, Redmond, Washington, USA) was used to record signalment, body weight, indications for MV, underlying disease, duration of MV, and outcome for each puppy. Brachycephalic breeds were noted as such (10). Outcome was classified as death during MV, euthanasia during MV, survival to extubation but death before discharge, or survival to discharge. When present in the medical record, the primary reason for euthanasia (prognosis or financial) was recorded. Cases were excluded if the medical records were incomplete or if puppies were ventilated only long enough to contact the owners or to permit a visit after a clinical decline.

Statistical analysis

Statistical analyses were performed using a commercial software package (SPSS Statistics 27.0; IBM, Armonk, New York, USA). The distribution pattern of quantitative data was assessed by the Shapiro-Wilk test. Normally distributed data are reported as mean ± standard deviation (SD) values, and nonparametric data are reported as medians and ranges. Quantitative variables were compared between 2 groups (e.g., survivors versus non-survivors) using Student’s t-test or Mann-Whitney U-test, depending on data distribution patterns. Associations between categorical variables were compared by Chi-square or Fisher’s exact tests. The association between 2 quantitative variables was analyzed using Pearson’s or Spearman’s rank correlation tests, depending on data distribution pattern. Post-hoc analyses between the different groups were carried out using Tukey’s multiple comparison test. P-values ≤ 0.05 were considered significant in all cases.

Results

Population description

Sixty-nine puppies were supported with mechanical ventilation during the study period. Ten dogs were excluded because of incomplete records, leaving 59 puppies for evaluation. The mean age was 5.4 ± 2.9 mo. The youngest puppy was 1 mo old and the oldest 11 mo.

There were 26 intact females, 19 intact males, 9 spayed females, and 5 neutered males. There were 11 English bulldogs, 7 mixed breed dogs, 5 Labrador retrievers, 4 German shepherds, 4 golden retrievers, 3 French bulldogs, 2 boxers, 2 English springer spaniels, 2 mastiffs, 2 miniature pinschers, and 1 of each of the following breeds: Akita, Australian shepherd, basset hound, bichon frise, border terrier, Boston terrier, Brittany spaniel, Chihuahua, dachshund, Doberman pinscher, Gordon setter, Great Dane, Maltese, miniature poodle, shar pei, treeing Walker coonhound, and Yorkshire terrier. The median body weight was 9.9 kg (range: 0.5 to 74.5 kg). Eighteen dogs were categorized as brachycephalics.

Indications for mechanical ventilation

The most frequent underlying disease was pneumonia in 18/59 (31%) dogs, followed by non-cardiogenic pulmonary edema (NCPE) in 16/59 (27%) dogs, and trauma in 8/59 (14%) dogs (Table 1). Other conditions identified included recovery from cardiopulmonary arrest (7/59), cardiogenic pulmonary edema (2/59) and other diseases (8/59).

Table 1.

The most frequent underlying etiologies, successful weaning rate, and survival rate in puppies undergoing mechanical ventilation, in alphabetical order.

Underlying etiology	Successful weaning from MV (number/%)	Survival to discharge, number of dogs (number/%)
Cardiogenic pulmonary edema due to patent ductus arteriosus	2/2 (100%)	2/2 (100%)
Head trauma	1/3 (33%)	1/3 (33%)
Non-cardiogenic pulmonary edema	7/16 (44%)	6/16 (38%)
Other	4/8 (50%)	4/8 (50%)
Pneumonia	6/18 (33%)	5/18 (28%)
Recovery after CPR	2/7 (29%)	1/7 (14%)
Thoracic trauma	4/5 (80%)	4/5 (80%)

CPR — Cardiopulmonary resuscitation.

Duration of MV ranged from 4 to 144 h (median 27 h). Twenty-six (44%) dogs were successfully weaned. Twenty-three of these 26 dogs (88%) survived to discharge with an overall discharge rate of 39% including 19/41 non-brachycephalics dogs (46%) and 4/18 brachycephalic dogs (22%). Seven out of 10 dogs that were ventilated for more than 72 h survived to discharge. Of the 3 dogs that were weaned but not discharged, 2 were euthanized due to progressive respiratory failure that would have required re-initiation of MV, and 1 died from an unobserved cardiac arrest. Seven dogs died, 22 dogs were euthanized with prognosis as the main owner concern, and 4 dogs were euthanized with cost of care as the limiting factor. The mortality rate was 72% during the first 24 h of ventilation, with 21 dogs out of 29 dying/being euthanized during that specific period.

There was no association between age and survival to discharge (P = 0.716) or survival to weaning (P = 0.579), nor between weight and survival to discharge (P = 0.744) or survival to weaning (P = 0.842). There was no correlation between age and weight (r = 0.53), likely due to the wide variety of breeds represented. Duration of mechanical ventilation was significantly associated with survival to discharge (P = 0.012) and outcome (P = 0.005). Dogs that were ventilated longer than 72 h were more likely to survive (P = 0.027). Brachycephalic dogs were less likely to survive to discharge than non-brachycephalic dogs when all groups were combined (P = 0.032).

Sub-categories

Pneumonia

Pneumonia was identified in 18 puppies; 28% (5/18) of puppies with pneumonia survived. Brachycephalic breeds heavily contributed to the pneumonia group (10/18) with 6 puppies being English bulldogs. The median age for puppies with pneumonia was 5.5 mo (range: 2 to 11 mo). Puppies with pneumonia were ventilated for a median of 38.75 h (range: 4 to 131 h).

Non-cardiogenic pulmonary edema

Non-cardiogenic pulmonary edema was the second most frequent underlying disease, with 16 puppies being affected. The underlying cause was not always known but included history of drowning in 4 dogs, choking in 3 dogs, seizures in 2 dogs, and following restraint for a nail trim in 1 dog. The median age for puppies with non-cardiogenic pulmonary edema was 3 mo (range: of 3 to 8 mo). Dogs were ventilated for a median of 38.5 h (range: 5 to 96 h). Survival to discharge in these dogs was 37.5% (6/16).

Trauma

Trauma, the third most frequent underlying cause, was identified in 8 dogs; 5 with primarily thoracic trauma and 3 with primarily head trauma. The median age in this category was 4 mo (range: 2 to 11 mo). Dogs were ventilated for a median of 24 h (range: 12 to 144 h). Overall, patients with trauma had a survival rate of 62.5% (5/8) with an 80% survival rate in thoracic trauma cases (4/5) and a 33% survival rate in head trauma cases (1/3).

Miscellaneous

Dogs with underlying diseases included 7 puppies which had had successful cardiopulmonary resuscitation (CPR), 2 puppies with congestive heart failure from patent ductus arteriosus, 2 puppies with intoxications (unknown toxin), and 2 puppies with anaphylaxis. Dogs ventilated following return of spontaneous circulation suffered from trauma in 3 cases, anesthetic complications in 2, heatstroke in 1, and intoxication in 1. Single cases each of coral snake envenomation, congenital lobar emphysema, and diaphragmatic agenesis, were recorded. Two cases had unidentified pulmonary disease.

Discussion

This study describes the outcome in 59 puppies that were supported with mechanical ventilation and identified survival rates that were similar to those of adult dogs ventilated for various underlying disease. Puppies, as a unique group, had not been previously evaluated. Due to the financial, technical, and emotional implications of MV, it is important that owners are well-prepared for the potential benefits for a specific therapy. Despite only an overall moderate survival to discharge, without MV, it is unlikely any puppies would have survived. In addition, as puppies, there is tremendous potential for long-term benefit, with each surviving dog expected to survive at least 10 to 12 y.

Other recent veterinary studies focusing on dogs mechanically ventilated for congestive heart failure, lower motor neuron disease, pulmonary contusions, and cervical spinal disorders have reported survival rates of 62.5%, 21%, 30%, and 71%, respectively (4,5,8,11). Unfortunately, the underlying causes were very heterogeneous, which prevented clear-cut predication of the dogs with the highest chance of survival. The survival rate for thoracic trauma, including pulmonary contusions and pneumothorax, was greater at 80% than other veterinary studies have reported, although there was a relatively small number of dogs (2–4,12).

In this study, brachycephalic dogs were less likely to survive than non-brachycephalic dogs (P = 0.032). A previous retrospective study of brachycephalic dogs undergoing MV (6) did not identify this disadvantage and reported a discharge rate of 27%, which was similar to the 22% (4/18) reported in this study. Brachycephalic dogs, especially English bulldogs, were diagnosed more frequently with pneumonia of all causes than any other breed, which is consistent with findings of a previous study on brachycephalic dogs requiring MV (6). This could be due to the greater risk of aspiration pneumonia in brachycephalic dogs and the likely reduced ability to resolve pneumonia due to hypoplastic trachea and upper airway obstruction.

Median duration of ventilation was significantly longer for dogs that survived than for dogs that died or were euthanized. It could be hypothesized that puppies that were cardiovascularly stable survived longer and, therefore, had a greater chance of recovering adequate pulmonary or ventilatory function and being weaned off the ventilator. This has also been reported in a retrospective study of cats undergoing MV (13) but to the authors’ knowledge, this is the first time it has been reported in dogs. Similar to previous studies, the mortality rate in this study was highest within the first 24 h (6,7). This could be due to a more severe disease process leading to an early patient death (cardiovascular instability, multiple organ dysfunction), or that failure to show improvement over 24 h was associated with a higher risk of euthanasia.

The are several limitations to this study. A small number of puppies in each group could have led to both type-1 and type-2 errors. Additionally, data on ventilator settings was not included due to absence of standardization of recording protocols between institutions and individual clinicians. Inherent to the retrospective nature of the study, there was no standardized approach to initiation, maintenance, or monitoring of MV, with considerable variation in ventilator technique and weaning strategies. Clinicians at every institution treated each case individually based on their clinical judgment which contributed to variability in case management including anesthesia and monitoring techniques. Since the study period was over 10 y, it is possible that some management changes such as anesthetic agents and ventilation techniques could have introduced variabilities; for example, high flow oxygen therapy has been recently introduced in dogs (14,15). The decision to institute mechanical ventilation is complex and could not be accurately reported in this study due to its retrospective nature. The number of puppies that were critically ill but not ventilated during the study period due to financial or other reasons was unknown. CVJ