March 2023

In this VETgirl online veterinary continuing education blog, Dr. Amy Kaplan, CVMA, DACVECC, MRCVS highlights an uncommon condition that can arise from blunt force trauma in dogs and cats: pneumopericardium. Tune in to learn more!

By Dr. Amy Kaplan, CVMA, DACVECC, MRCVS
VETgirl Contributor/Webinar Moderator

Pneumopericardium in a Dog Post Trauma

In today’s VETgirl online continuing education blog we highlight an uncommon condition that can arise from blunt force trauma in dogs and cats… pneumopericardium and pneumo-everywhere!

As a perhaps “seasoned?” ECC doctor (those grey hairs and aches and pains are really setting in…) at Urgent Pet Care, I feel like I’ve seen one of just about everything in the ER. We see a lot of vehicular trauma patients and I’ve personally treated hit-by…-cars, -bikes, -motorbikes, -buses, -snowmobiles, -trains, and yes, even a hit-by-tractor here in the Midwest. The treatment and triage of vehicular trauma is now a bit more like a reflex: triage the patient’s initial shock, quickly wrap their bleeding wounds to address at later time, and first and foremost, assess the patient’s respiratory status and treat any life-threatening conditions. Even though blunt force trauma workup might be a bit routine at this time, every now and again I have the joy of seeing a “well THAT’S a first!” to keep me on my toes.

The case started out as so many other hit-by-car patients had before: A 7-year-old neutered male Labrador retriever transferred to our ER from a rural veterinarian for us to manage the aftermath of a suspected (but unwitnessed) hit-by-car event. The dog’s owners had found him at 6AM laying outside and conscious, breathing much faster than usual and they saw blood on his front paw. By 8AM, the dog was at their local veterinary office where he was sedated with dexmedetomidine for radiographs and to wrap the paw (Figure 1). Medical records reported radiographic evidence of bilateral pneumothorax and subcutaneous emphysema, but these images were not available for review at the time of presentation.

Left dog lesion Dr. Amanda Meyer photo

Figure 1. Injured leg. Photo courtesy of Dr. Amanda Meyer

As an FYI, as everything is easier with 20:20 hindsight, remember that non-life-threatening lacerations are low priority at triage and should instead be quickly wrapped and surgically addressed AFTER the patient has been stabilized. The criticalist’s general rule? Unless something life-threatening (e.g., intestines, etc.) is dangling out of the wound, it can wait (even eyeballs). As a criticalist, I often do use dexmedetomidine in the ER as it’s a great sedative; however, be aware of its vasoactive consequences. In general, I limit dexmedetomidine’s use in unstable and shocky patients until they are resuscitated and stable.

On to the ER visit. When the dog arrived to the ER, he was in a state of decompensated shock. His blood pressure was unmeasurable on Doppler, he had a respiratory rate of 90 bpm and absent dorsal lung sounds bilaterally, a heart rate of 180 bpm, and a prolonged CRT over 3 seconds. An IV catheter was placed, and a left-sided thoracocentesis was performed where 3 liters of air were removed. A 1 liter bolus of Normosol-R was administered IV over 10 minutes to improve perfusion followed by an IV injection of methadone for pain relief. After both the thoracocentesis and bolus were complete, recheck blood pressure via Doppler showed an systolic of 130 mm Hg.

Baseline bloodwork (e.g., CBC, chemistry) revealed a stress leukogram: mild neutrophilia of 12.35×10^3/uL (ref. 3.62-12.3×10^3/uL), mild lymphocytopenia of 0.66×10^3/uL (ref. 0.83-4.91×10^3/uL) and mild eosinopenia of 0.03 (ref. 0.04-1.62×10^3/uL). The chemistry showed a mild phosphorus elevation of 5.4 mg/dL (ref. 1.9-5.0mg/dL), elevated ALT of >1000 (ref 0-120 U/l), and mildly decreased total protein of 5.3 (ref. 5.5-7.7 g/dL) with all other values in the normal reference ranges. The biochemistry changes were assessed to be secondary to shock and poor organ perfusion. ECG monitoring revealed polymorphic ventricular premature contractions (VPCs) with a rate fluctuating between 100-160 bpm. Due to the polymorphic nature of the VPCs (and small but potential risk of it progressing to a fatal arrhythmia), the patient received a bolus of 2mg/kg lidocaine IV; the VPCs resolved shortly thereafter and immediately revealed a new arrhythmia…

While consulting on this case from home, I received the text, “Does that look like electrical alternans to you?” (See Figure 2).

ECG electrical alternans dog

Figure 2. Looks like electrical alternans to me… Photo courtesy of Dr. Amanda Meyer

I saw perhaps what could be mild electrical alternans with an occasional, isolated VPC, and I asked if the attending clinician saw any pericardial effusion. The text back? Figure 3 below!

Figure 3. Pneumo-everything. Photo Courtesy of Dr. Amanda Meyer

Later, the boarded radiologist would confirm our suspicions: bilateral pneumothorax, pneumomediastinum, pneumoretroperitoneum, subcutaneous emphysema, and air in the pericardial sac (AKA-pneumopericardium)!

So how on earth does AIR get into the pericardial sac? After all, even as a criticalist, I rarely ever see pneumopericardium in dogs!

Sorry everyone, but unfortunately, we still don’t exactly know the theory on why pneumopericardium develops in dogs and cats! Looking just at the blunt force traumatic causes of pneumopercardium, one theory is that a small tear forms in the pericardium, allowing air to communicate from a torn trachea, bronchi, or from air in the pleural space (pneumothorax).1 Another theory from human literature describes something called the “Macklin effect” where air from ruptured alveoli tracks along the outside of the blood vessels within the lung interstitium, traveling up the perivascular sheath where the blood vessels join the heart within the pericardium.2

So, the question was? Do we have to remove the pericardial air/pneumopericardium in this dog? Well, just like with pericardial effusion, the rate and volume of the air will determine whether we need to get it out of there. When accumulation of air or fluid in the pericardial space occurs quickly or in high volumes, the heart gets compressed and the patient can experience circulatory collapse (this is what cardiac tamponade is!). If the accumulation is slow and in low volume, the patient is unlikely to experience cardiovascular effects that would require intervention (e.g., Do no harm!). The air will resolve over time in these cases – whether the air leaks out of a pericardial tear or whether the air is resorbed is still not really known, and reports suggest it can take anywhere from 24 hours to a week to resolve.2,3

So, how did this dog do? Initially, this patient was monitored through the day on nasal oxygen insufflation. In the evening, his respiratory rate had increased; recheck radiographs worsening of his pulmonary contusions (which is to be expected) along with worsening of his pneumothorax. Bilateral chest tubes were place but for cost reasons, continuous evacuation was not performed, but was and is advised when air in the pleural space builds up to this degree in short period of time. Instead, the chest tubes were aseptically aspirated every hour, with decreasing frequency if production decreased at each aspiration. The left chest tube drained both air and roughly 30-40ml of serosanguinous discharge every 2-3 hours. Pain was controlled with methadone and a bupivacaine block in the thoracostomy tubes. As the dog’s perfusion parameters had improved, the IV fluid rate was decreased to 60-75 ml/kg/day to prevent fluid overload (which could worsen the pulmonary contusions). The patient was also started on ampicillin/sulbactam (22 mg/kg, IV q 8) due to the paw wound that hadn’t been addressed yet.

The following day, the left chest tube was still producing hemorrhagic fluid; recheck radiographs revealed that the chest tube had migrated dorsally and caudally, so it was removed. (Why don’t these chest tubes just stay in place. The right chest tube remained patent despite having also migrated caudally.

Oxygen therapy was discontinued after 24 hours, as the patient was oxygenating well (e.g., pulse oximetry readings of 96-97% on room air). On day 3, a local block was used around the left forepaw wound to facilitate closure of the wound under minimal sedation. On day 4, the right chest tube was removed, and the dog was observed overnight.

Figure 4. Day 4 recheck radiographs. Photo Courtesy of Dr. Amanda Meyer

Figure 4. Day 4 recheck radiographs. Photo Courtesy of Dr. Amanda Meyer

Finally, on day 5, the dog was discharged home successfully. At a 3-day recheck, the dog was still eating and doing great at home, although not loving his restricted activities to permit continued healing (and resolution of his pneumo-everything).

Figure 5. Cutest Labrador patient ever. Of course he was eating once he got home. Photo courtesy of Dr. Amanda Meyer

Although infrequently reported, cases of pneumopericardium in dogs appear to resolve without any drainage of the pericardial space required. In this particular case, radiographic resolution was achieved at 48 hours, despite continued pneumothorax and pneumomediastinum. Other veterinary literature has reported resolution anywhere between days 2 and 10.

Traumatic pneumopericardium is apparently not as uncommon in human blunt-force trauma as it seems to be in our veterinary literature. For dogs and cats, a quick google search revealed only a handful of case reports, so I hope that bringing this condition to light can help others when faced with this “well that’s a first!” scenario. And this is why I love emergency medicine, because even if you get a bit routine with the more commonly seen emergency cases, you never truly know if and when a curve ball is headed your way!

P.S. A huge thank you to Dr. Amanda Meyer and the amazing staff at Urgent Pet Care for making this a successful outcome!

References:
1. Leclerc A, Brisson BA, Dobson H. Pneumopericardium associated with a pulmonary-pericardial communication in a dog. J Am Vet Med Assoc 2004 Mar 1;224(5):710-2, 698. doi: 10.2460/javma.2004.224.710. PMID: 15002809.
2. Anand R, Brooks Md Facs SE, Puckett Y, Richmond RE, Ronaghan CA. Pneumopericardium Resulting From Blunt Thoracic Trauma. Cureus 2020 Nov 22;12(11):e11625. doi: 10.7759/cureus.11625. PMID: 33376639; PMCID: PMC7755601.
3. Agut A, Costa-Teixeira MA, Cardoso L, Zarelli M, Soler M. What is your diagnosis? Pneumopericardium. J Am Vet Med Assoc 2010 Aug 15;237(4):363-4. doi: 10.2460/javma.237.4.363. PMID: 20707744.

  1. Danea Allen says:

    What an amazing case for a very lucky pup! It’s nice to know that those pneumopericardium’s do resolve on their own for the most part if the air and fluid aren’t too overwhelming for the heart! Excellent read!

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