Organ dysfunction and mortality risk factors in severe canine bite wound trauma | VETgirl Veterinary Continuing Education Podcasts
In today’s VETgirl online veterinary continuing education podcast, we review organ dysfunction and mortality risk factors in dogs with severe bite wounds. How frequently do you see dogs with severe bite wounds requiring intensive care in your practice? While many of us see “routine” bite wounds that can be managed with wound care on an out-patient basis pretty frequently, there is another population of canine patients with bite wounds that are much more severely affected. These patients may have much more extensive wounds, and can develop complications such as SIRS, DIC, MODS and sepsis. Unfortunately, little evidence exists on which patients may develop these complications. So, Ateca et al from the University of Pennsylvania School of Veterinary Medicine set out to retrospectively evaluate dogs with bite wounds requiring hospitalization in the ICU, to characterize their treatments, complications and outcomes, and to identify any risk factors for mortality.
Before we reveal the results of this bite wound study, we should clarify what the authors used as definitions of organ dysfunction:
- Cardiovascular dysfunction: A systolic blood pressure of < 90 mmHg or MAP < 60 mmHg or the use of vasopressors
- Respiratory dysfunction: administration of oxygen supplementation or implementation of mechanical ventilation -Renal dysfunction: A creatinine > 3.4 mg/dl after initial fluid resuscitation
- Neurologic dysfunction: Seizure activity or objective evidence of intracranial disease such as abnormal central nervous system function or altered state of consciousness
- Hepatic dysfunction: A bilirubin > 0.5 mg/dl in the absence of anemia and increased activity of at least 1 liver enzyme
- Pancreatic dysfunction: Vomiting, abdominal pain and ultrasound evidence of pancreatitis
- Coagulation dysfunction: Prolonged PT or aPTT and platelets < 100×109/L
- DIC: Coagulation dysfunction as above and increased concentration of FDPs or D-dimers
- SIRS: Two or more of the following on the same day during postoperative hospitalization in the ICU: T < 100F or > 103 F; HR > 140/min; RR > 20/min; total WBC count < 6 or > 16×109/L; bands > 3%.)
So, back to this study. In this retrospective study, 94 dogs were included in the study; approximately ½ were male and female – 46 were male (18 intact) and 48 were female (11 intact). Mixed breed dogs (n=19), Yorkshire Terriers (13) and American Pit Bull Terriers (8) were the most common breeds represented in this study (it’s a West Philly study, after all), and 28 breeds were represented all together. The median age was 4.4 years and median body weight was 6.7 kg. Body weight wasn’t associated with outcome, but larger dogs did have a longer duration of hospital stay (p=0.03). The majority of dogs were ≤ 10 kg (65/94 dogs, 69%). Most dogs were attacked by a single dog (77/94); the remainder were attacked by two or more dogs. The most common breeds reported to have attacked patients in this study were American Pit Bull Terriers (23 dogs), Rottweilers (5), German Shepherds (4) and Great Danes (3). (Again, a West Philly study)
In this study, bite wounds were most commonly located on the thorax in 57 dogs (with 31 of which were penetrating thoracic wounds and 16 of which had rib fractures), followed by the extremities (33), abdomen (28 dogs, with 14 of these penetrating into the abdomen), the neck (20) and the head (16).
34 dogs were treated at another veterinary facility prior to presentation, and while the median time from attack to presentation was 3 hours, 1 dog was presented 1 day after attack, and 14 dogs were presented more than 1 day after attack. Time to presentation was not associated with duration of ICU or hospital stay, or with mortality (That said, when in doubt, refer them earlier than later, in VETgirl’s opinion!).
In this study, dogs received a variety of fluid treatments prior to surgery, including crystalloids in 77 dogs, synthetic colloids in 10 dogs, fresh frozen plasma in 8 dogs, and packed red blood cells in 5 dogs. The majority of dogs (98%) 92/94 dogs were treated surgically with debridement, lavage and closure; the other 2 dogs were treated at other veterinary hospitals prior to transfer. The median time to surgery was 6.08 hours after presentation, and dogs that had longer times in between presentation and surgery had longer post-op ICU stays (p=0.0099) but not higher mortality or overall hospital stays.
Once these canine bite wound patients were in surgery, median anesthesia duration was 3.8 hours, and 49/92 (53%) dogs had at least one instance of severe hypotension under anesthesia. Longer time under anesthesia was statistically associated with mortality (p=0.0044), DIC (p=0.043) and MODS (p=0.013), and hypotension under anesthesia was associated with mortality (p=0.0082). Some dogs underwent multiple episodes of anesthesia and surgery for wound management (3 dogs had 3 episodes, and 13 dogs had 2 episodes), and the number of surgeries was associated with increased duration of hospitalization and ICU stay (p=0.0004, p=0.0062 respectively) but not with mortality.
In this study, 72 dogs had cultures performed at the time of surgery, and about half (40/76 total cultures, 53%) didn’t grow anything. The remainder grew a number of different organisms, with Clostridium species (7 dogs, 9.2%) and Enterococcus species (6 dogs, 7.9%) being most common. All 94 dogs received antibiotics (most commonly ampicillin, in 74 dogs, and enrofloxacin, in 73 dogs, with some dogs receiving both antibiotics). 4 dogs had culture results which revealed an organism resistant to empirical therapy; 2 of those dogs had their antibiotics changed based on the results, and the other 2 died or were euthanized before results were available. Positive cultures were more common in dogs that had a longer time between attack and presentation (p=0.0066). Again, refer or cut them sooner than later!
There were a number of significant changes in blood work parameters. When evaluating the change in WBC counts over time (presentation compared to post-operative values in ICU), survivors had an increase in total WBC count, and non-survivors had a decrease in total WBC count (p=0.02). Mature neutrophils decreased significantly in all 94 dogs and band neutrophils increased significantly when comparing presentation values to post-op values (pwa=0.0166, p=0.0479 respectively). Lower post-operative albumin concentrations and colloid osmotic pressure (COP) measurements were associated with longer ICU stays (p=0.0024, p=0.0411 respectively) but not with mortality or duration of overall hospital stay. In the post-operative period, patients in the ICU received a variety of fluids, including crystalloids, synthetic colloids, fresh frozen plasma and packed red blood cells. Patients who received FFP were 5.2 times more likely to die than patients who did not (p=0.0057;CI 1.3-24), and dogs who received pRBCs were 3.1 times more likely to die than those that did not, although this wasn’t significant (p=0.0632;CI 0.7-13). It’s likely because this patient population was more critically ill.
About half of the dogs in the study developed SIRS (51/94, 54.3%), which was associated with mortality (p=0.01). Other organ system dysfunction that was diagnosed included respiratory (35 dogs, 37%), pancreatic (10 dogs, 11%), cardiovascular (8 dogs, 8.5%), coagulation (6 dogs, 6.4%), hepatic (3 dogs, 3%), DIC (3 dogs, 3%) and neurologic (2 dogs, 2%). No patients developed renal dysfunction (You should check out our podcast on the use of Hetastarch and acute kidney injury, just for fun). Dysfunction of the respiratory system, pancreas, cardiovascular system, coagulation system and development of DIC were associated with mortality (p<0.001-0.0232). Dysfunction of the cardiovascular system was most predictive of mortality, and these patients were 29 times more likely to die (CI 5-170). When evaluating multiple organ dysfunction, higher numbers of affected organ systems were associated with higher mortality (p<0.001) and longer ICU stay (p=0.0018). Mortality rates increased as the number of organs affected increased: 4/43 (9%) in dogs with one organ system affected, 3/15 (20%) in those with two, 3/5 (60%) in those with three systems affected, and 4/6 (67%) in those with 4 or more. Overall mortality rate for all dogs in the study was 15%. 80 dogs survived to discharge, 9 were euthanized, and 5 died during hospitalization.
So, what can we take away from this VETgirl podcast? The authors of this study found that patients with bite wounds requiring intensive care are at risk for complications such as SIRS and MODS, with the respiratory system most frequently affected. Longer anesthesia times and a longer period between presentation and anesthesia were also associated with mortality. As with previous studies, most of the dogs here were smaller breeds attacked by larger breeds, with an overall mortality rate of 15%. The authors suggest that because of their size, smaller dogs may suffer more severe injuries and be more likely to need ICU care. Interestingly, dogs with a longer time between attack and hospital presentation were more likely to have positive bacterial cultures, which is similar to findings in human medicine. This highlights the importance of early antimicrobial therapy in these patients, especially those at risk of developing sepsis. While ampicillin and enrofloxacin were the most common empirical antibiotics used in this study, susceptibility results that were available didn’t reveal a “best” antibiotic to use in cases of bite wounds. The authors stress that empirical choices should be broad spectrum and target gram-positive and gram-negative aerobes.
This study also demonstrated that longer anesthesia times were associated with increased risk of mortality as well as the development of MODS and DIC. The authors hypothesize that because exposure to anesthetic drugs can impair alveolar macrophage function, a diminished immune response might result and increase the risk of complications. Many patients also had periods of severe hypotension under anesthesia, which can impair oxygen delivery to the tissues, impeded healing and increase the risk of MODS. While respiratory dysfunction was the most common organ dysfunction in this study, the authors do conceded that they used a very broad definition of respiratory dysfunction, and that not all of the patients administered oxygen in the ICU may have needed it. Cardiovascular dysfunction was the strongest predictor of mortality in this study, followed by coagulation dysfunction, pancreatic dysfunction, SIRS, respiratory dysfunction and hepatic dysfunction, so make sure you are monitoring these critically ill bite wounds carefully!
Overall, this was a great study (VETgirl admits, we’re biased towards Penn, where we trained). This study does a nice job of highlighting how bite wounds can go bad! As an initial retrospective study, it brings up some important points to move forward with prospective studies in the future (for example, effects of anesthesia time, antimicrobial choices, monitoring for MODS). Because the study was retrospective, there are some limitations. The big ones were the authors criteria to diagnose respiratory dysfunction based on provision of supplemental oxygen – ideally a more objective measurement would be used, and a failure to differentiate between SIRS and sepsis, as some would argue that because bite wounds are inherently a source of infection, many patients with bite wounds and SIRS could be considered septic. That said, this study highlights the importance of monitoring patients with severe bite wounds for complications such as SIRS, organ dysfunction and sepsis. Taking measures to employ early antimicrobial therapy and limit anesthesia time may be important in achieving improved outcomes. In conclusion, this retrospective study highlights the importance of careful monitoring in dogs with severe bite wounds! These patients should be watched carefully for development of SIRS or organ dysfunction, which may be associated with worse outcomes. Trying to limit time under anesthesia and periods of hypotension might be important in getting these guys through surgery and out of the hospital.
Abbreviations:
DIC: disseminated intravascular coagulation
FFP: fresh frozen plasma
MODS: multiple organ dysfunction syndrome
pRBCs: packed red blood cells
SIRS: systemic inflammatory response syndrome
WBC: white blood cell
References:
1. Ateca LB, Drobatz KJ, King LG. Organ dysfunction and mortality risk factors in severe canine bite wound trauma. J Vet Emerg Crit Care 2014; 24(6): 705-714.
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