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Acid-base and electrolyte abnormalities seen in dogs with GI foreign bodies | VETgirl Veterinary CE Podcasts

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In today’s VETgirl podcast, we review the importance of performing a venous blood gas in the vomiting patient. Why? Because when we see a hypochloremic, hypokalemic metabolic alkalosis, we should be ruling out an obstructive gastrointestinal (GI) foreign body. Previously, the presence of a metabolic alkalosis has been associated with a upper GI (e.g., pyloric) foreign body. Why? Because of protracted vomiting and loss of chloride, which deletes the body of an anion. In order to maintain electroneutrality, when a sodium (Na+) moves, a negatively charged anion must exchange with it. While this is typically chloride, if the body is chloride deplete, it absorbs bicarbonate (HCO3-) instead, resulting in the classic metabolic alkalosis.

Normally, dogs reabsorb 98% of their gastrointestinal secretions per day. Once a GI obstruction is present for more than 24 hours, resorption in the bowel proximal to an obstruction results in increased secretion of Na+, K+, and water into the lumen. Historically, proximal GI obstructions have been said to lead to hypochloremic, hypokalemic metabolic alkalosis due to the reasons mentioned before (e.g., hypochloremia). Distal obstructions were thought to lead more to metabolic acidosis instead of alkalosis.

So Boag et al (originally out of Royal Veterinary College), wanted to identify the most common types of GI obstructions and to identify the metabolic derangements found in patients with various GI obstructions. This was published in JVIM (Now open access and free!) as Acid-base and electrolyte abnormalities in dogs with gastrointestinal foreign bodies. In this study, Boag et al retrospectively looked at 138 dogs, with a mean age of 3.8 years (range 0-14 years) who had presented for vomiting. They assessed several factors in this study including:EnterotVGBLG

  • Signalment
  • Initial acid-base status and electrolytes
  • Surgical findings
  • Location of foreign body
  • Historical information
  • Diagnostic imaging modalities used
  • Complications seen (e.g., intra- or postoperative)
  • Overall survival and cost of hospitalization

The mean duration of vomiting in these cases was 48 hours. Of these dogs, a foreign body was found in the stomach 50% of the time, in the proximal duodenum 3.6%, distal duodenum 2.9%, jejunum 27.5%, ileum 2.9%, and colon 3.6% of the time (Boo. Try not to cut those colon foreign body cases!). Of all these cases, 36.2% of the time, the cases had a linear foreign body; of these, 6% of the linear foreign bodies were anchored in the mouth (Again, reiterating the importance of a thorough oral examination!). Linear foreign bodies were more likely to be associated with  the presence of hyponatremia (OR 0.85).

In 28% of the cases (38/138), a resection and anastamoses (R&A) needed to be performed. Of these cases requiring an R&A, 55% (21/38) cases were due to linear foreign bodies, while the remaining were discrete foreign bodies. Overall, the prognosis for foreign body was excellent, with almost all (137/138) surviving to discharge.

So what about the electrolytes and acid-base status? The most common electrolyte disturbances found in all these cases included hypochloremia (51.2%), metabolic alkalosis (45.2%), hyperlactemia (40.5%), and hypokalemia (25%). 12% of dogs with proximal GI obstructions and 13.7% of dogs with distal obstructions had a hypochloremic, hypokalemic metabolic alkalosis. 40.5% of dogs were hyperlactatemic (which was defined as a lactate >2.3 mmol/L). No other biochemical abnormalities were significantly associated with the exact location of the foreign body.

Some limitations of this study?

First, it was retrospective, so it has limitations from data collection. Also, the variable duration of clinical signs in different patients may have affected the results and severity of acid-base and electrolytes changes. Another limitation? While this study had a very high reported survival rate, this may have been due to the short duration of clinical signs (with a mean of 2 days) in these patients. Keep in mind that 40% of United Kingdom pet owners have pet insurance, so maybe they are bringing in their dogs sooner to seek veterinary attention as compared to us in North America. As this study excluded septic peritonitis patients, their prognosis was likely artificially higher!

That said, what can we take away from this VETgirl podcast?

Remember to do a venous blood gas in those vomiting dogs. A patient presenting with an obstructive GI foreign body can develop a hypochloremic, hypokalemic metabolic alkalosis, regardless of the level of obstruction.

Another reminder? Let’s be aggressive with our fluid resuscitation in these patients! 40% of dogs are hyperlactetemic in this study, likely due to fluid loss into the GI lumen and systemic hypoperfusion. Crystalloids, crystalloids, crystalloids!

Remember, metabolic alkalosis is RARELY seen in veterinary medicine; however, it is the most common acid-base abnormality in patients with GI foreign bodies. Yes, we can still see a metabolic acidosis in those patients that are dehydrated or have an elevated lactate, but the majority of the time, it’s a metabolic alkalosis!

Finally, remember that patients with a linear foreign body are at a higher risk for hyponatremia and potential for the need for a resection and anastomosis.

Most importantly, keep in mind that these cases are savable – they have an excellent prognosis and survival to discharge, so don’t give up on these guys. Just recognize and identify the problem quickly, and let your venous blood gas guide you.

References:

1. Boag A, Coe R, Martinzed T, Hughes D. Acid-base and electrolyte abnormalities in dogs with gastrointestinal foreign bodies. J Vet Int Med  2005;19:816-821.

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