Canine parvovirus (CPV) infections cause severe gastroenteritis, lead to dehydration, shock, disseminated intravascular coagulation, bacterial translocation and sepsis when left untreated. With aggressive treatment, the mortality rate can be reduced to between 0% and 30% from 90%. Therapeutic options in addition to fluid and pharmacologic therapy speeding gastrointestinal recovery are desirable to reduce patient mortality and morbidity, as well as financial strain to the clients for prolonged aggressive treatment. Use of elaborate treatment options such as oseltamivir (Tamiflu), interferon omega, recombinant bactericidal proteins, equine lipopolysaccharide antitoxin, human recombinant factors, and antibody rich plasma have not shown promising results. One simple to implement, therapeutic option that makes a significant difference in survival chance is enteral feeding started within hours of admission, even when vomiting.
Feeding When Vomiting
Feeding a patient when they are vomiting goes against most traditional approaches to nutrition in a patient suffering from gastrointestinal ailments. A typical approach in such a case is to withhold food, designating an NPO (nil per os, or no food or water from the oral route) to prevent nausea from introduction of food and distension of the stomach. A small amount of easily digestible food is introduced, being increased to a normal amount gradually.
There are several reasons why withholding of food is thought to be beneficial. These include the idea of resting the bowel, as it is irritated and has a reduced ability to absorb the nutrients. Vomiting is also thought to be reduced in frequency when the stomach is empty, giving decreased chances of vomiting and potential aspiration in a critically ill animal. In addition, food contains fat and fibers that are difficult to digest potentially increasing the chances of vomiting even further. In a patient with dysfunctional gastrointestinal systems, food will pass into the intestines undigested, leading to bacterial proliferation and osmotic diarrhoea by pulling water into the intestinal lumen. All of these reasons combined, it may seem reasonable to withhold food in a patient with gastrointestinal issues. However, many of these beliefs actually might not be true.
One argument for feeding early, is that the guts are actually not able to rest when being fasted. Fasting causes a phenomenon called “hunger pains,” which arises from intense peristaltic contractions migrating down from the pylorus to the ileum. The peristaltic activity is decreased when nutrients are present in the intestinal lumen, allowing for better rest of the guts, and nutritional absorption. If fasting leads to less rest and pain to the patient, feeding is the better option.
Does feeding actually lead to more vomiting? A study evaluating this with patients with haemorrhagic gastroenteritis indeed did observe an increased frequency of vomiting upon feeding when compared to fasting. However, they also saw that the frequency of vomiting decreased below the fasted dogs by day 2. Feeding creates a prokinetic effect, and reduces emesis, leading to an overall shortening of the time before the patient stops vomiting. The presence of food in the gastrointestinal lumen also decreases insult to the mucosa from toxins, reducing vomiting. The concept behind food minimizing chances of vomiting when certain medication is given along with it applies here as well. Feeding causes more vomiting initially, but leads to a quicker subsiding of vomiting.
Food high in fat and soluble fibers and large volume feedings can indeed increase chances of vomiting. Maldigestion and gastrointestinal distention stimulates vomiting. Small, frequent feedings are recommended to reduce gastric acid release, leading to reduced vomiting. In many cases, employment of antiemetic drugs help in preventing vomiting, allowing earlier enteral nutrition. Adequate antiemesis is especially important for inappetent patients requiring placement of NE or NG tubes.
Undigested food being present in the intestinal lumen does increase nutritional resources for microorganisms leading to bacterial proliferation. However, feeding increases levels of volatile fatty acids such as butyrate and propionate, reducing the population of bacteria sensitive to acidic environments (Campylobacter and Clostridium spp.). The presence of food helps maintain enteric barriers, preventing bacterial translocation (movement of bacteria from the guts into the blood stream) and subsequent sepsis. Diarrhoea in dogs is attributed to unabsorbed nutrients and endogenously derived osmotic elements instead of osmotic pressure created by undigested food. Insult to the intestinal mucosa preventing absorption of water and increased effusion through leaky blood vessels (increased vascular permeability) is alleviated with enteral nutrition, which helps reduce diarrhoea when compared to a fasted state.
Fasting causes a plethora of negative effects that outweigh the small benefits it may have. Fasting causes reduced expression of digestive enzymes, impairing digestive function when food is reintroduced. Presence of nutrients reduces inflammation by inhibiting expression of adhesion molecules, preventing activation of neutrophils which contribute to mucosal damage and impair immune response. Malnutrition leads to protein, essential fatty acid, mineral and vitamin deficiencies preventing healthy turnover of gastrointestinal mucosa. Feeding leads to faster intestinal recovery, even when compared to parenteral nutrition, indicating benefits of passive luminal nutrition. Feed those guts!
Specifically for parvoviral enteritis, early enteral nutrition reduced the time for patient to have normal attitude, appetite, ceasing of vomiting and diarrhoea, increased body weight, and improved mucosal permeability when compared with fasting.
Nutritional Tubes
Nutritional interventions are a vital part of successful treatment of critical care patients, but often overlooked. An animal who is anorexic for as short as 3 days can develop nutritional deficiency related detrimental effects (metabolic derangements, depressed immune system, catabolic wasting, and deteriorating GI system, to name a few), and should receive nutritional support at latest by 5 days into anorexia. While enticing voluntary eating is most comfortable and beneficial for patients, this is not always sufficient to meet nutritional and caloric needs. When a patient is anorexic, there are several methods by which nutritional supplementation can be performed, divided into enteral and parenteral routes.
The least invasive of tubes utilized in nutrition are nasoenteral tubes. Nasoenteral tubes are inserted through the nares and down into the GI tract. Tubes terminating in the oesophagus are called nasooesophageal (NE) tubes, while nasogastric (NG) tubes terminate in the stomach. Nasoenteral tubes are used for short term feeding and are able to be used immediately after placement and typically no longer than 10 days. The tubes are typically too narrow to feed blended canned foods, and require a liquid diet to be infused. When a nasogastric tube is in use the gastric content may be evacuated and measured to determine the degree of functional gastric motility. The placement is typically well tolerated with none to minimal sedation. Contraindications include patients with intractable vomiting, poor mentation, respiratory distress, facial trauma, or nasal diseases. One of the most important aspects of nasoenteral tube placement lies in prevention of tracheal placement. Food infused into the trachea can very easily turn into life-threatening respiratory compromise. Radiographic confirmation of appropriate placement should always be performed to prevent this. Other complications include epistaxis, rhinitis, and vomiting. If vomiting occurs, the placement of the tube should be rechecked make certain the tube did not come up the oesophagus and inhaled into the trachea. The tube can also clog due to its narrowness, and requires constant infusions or flushing after bolus feedings.
Oesophagostomy tubes may be opted to be placed through the side of the neck in a surgical procedure for patients requiring longer term nutritional intervention. Oesophagostomy tubes can be used immediately upon placement and for up to 20 weeks when cared for properly. The larger diameter when compared to nasoenteral tubes allows for feeding of blended canned foods, providing the ability to meet nutritional needs more easily. It is also useful in patients with facial trauma or nasal diseases as it bypasses the muzzle into the GI tract. The procedure does require anaesthesia to perform. Another significant advantage is the ability for an owner to take a patient home with an oesophagostomy tube for long term care and relieving the need for hospitalization for nutritional management. The tube should be flushed with 5-10 ml of water after feeding to prevent the tube from being clogged. Main complications include blocked tubes, displacement of the tube by vomiting or intentional removal by the patient, and stoma site infections. The stoma site (insertion site) of the tube requires regular monitoring for redness, swelling, and signs of infections.
Gastrostomy tubes (G tubes) are another surgically placed enteral feeding tube. G tubes extend from the skin on the side of the abdomen and into the stomach. G tubes are used for long term enteral feeding, capable of providing nutrition for years after placement. Polyurethane or silicone based G tubes are required for long term use as they are resistant to loss of integrity from digestive enzymes. Fibrin sealing of the stoma site will occur within 12–24 hours after placement, and feeding should not be started until this seal is formed to avoid contamination and infection of the site. This option may be taken when the patient has oesophageal disorders, facial or oral trauma. There is a higher cost associated with the procedure, which may make it cost prohibitive. As this is a more invasive surgical procedure, there is a higher anaesthetic risk involved, and should be avoided with patients with healing impairments. Patients vomiting consistently should be held off for the procedure until vomiting is under control. G tubes require similar attention to the stoma site as oesophagostomy tubes. Complications include vomiting, aspiration pneumonia, peritonitis, accidental tube removal, pressure necrosis, and stoma site infection.
Jejunostomy tubes are more rarely placed, bypassing the stomach and into the jejunum. The tube may be used from weeks to months, and is used when resting of the upper GI tract is necessary. These include patients with pancreatitis, uncontrolled vomiting, gastroparesis, and recent gastric surgery. Feeding can commence 12–24 hours after placement. Liquid diets are necessary since the tube diameter is narrow. Constant infusions alleviate the risks of cramping and diarrhoea. Patients with jejunostomy tubes require close monitoring and will need to be hospitalized. Complications include osmotic diarrhoea and vomiting. Obstruction of the tube is a common complication, and can be best avoided through periodic flushing (every 4 hours). If there is leakage of GI tract content, a peritonitis can develop and is a serious complication. When the GI tract is dysfunctional all together, parenteral nutrition should be used, and can be provided through a dedicated sterile port through a central line.
Enteral nutrition is very important in maintaining a healthy GI tract and mucosa. Many of the traditional thoughts of benefits to withholding food do not hold up to be as detrimental when compared to the benefits of early enteral feeding. Because of this, knowledge of use and maintenance of enteral feeding tubes will allow one to help influence a positive patient outcome. In the case of parvovirus gastroenteritis, anything more invasive than nasoenteral tubes is rarely used.
Nutritional Plan
When the decision is made to feed the patient, there are a few key points to consider. What will we feed? How much of it will be fed and how fast?
Current recommendations include oral rehydration over 3–4 hours, and then introducing food. It is unreasonable to attempt feeding their full maintenance energy requirement for patients suffering from acute diarrhoea or frequent vomiting. The amount that can reasonably be fed initially should be targeted for 1/4 resting energy requirement (RER), as a highly digestible, low-fat diet in order to ensure healthy gut recovery and minimal stimulation of vomiting and diarrhoea.
An animal’s RER can be calculated by the formula: RER=70x(BW in kg)0.75 kcal per day. As an example, a patient that is 15 kg would have a RER of 70x150.75, or 533.5 kcal per day. ¼ of this will be 133.4 kcal, leading to a feeding rate of 5.6 kcal per hour. Depending on the energy density of the diet being fed, the volume will differ.
The type of food fed in these cases ideally should be highly digestible. There are many commercial diets available which are highly digestible (gastrointestinal diets). The diet should also be low in fat content, with less than 20% of metabolizable energy coming from fat. Excessive fibre content should be avoided since it can cause delayed gastric emptying, diarrhoea, flatulence, and abdominal pain. The recommended level is no more than 8% dietary fibre.
In critical care, especially for feeding through a nasoenteral tube, liquid diets are employed. Products such as CliniCare have been commonly used due to the simple calculation of the volume required to fulfill RER through its caloric density of 1 kcal/ml. The product also comes readily made as a liquid in a can, making preparation simpler. There are newer products on the market such as Emeraid Critical Care HDN specifically formulated for dogs and cats and being highly digestible. This product is formulated for critical care patients at a higher default caloric density of 1.5–2.4 kcal/ml (concentration is adjustable as it is mixed with water on preparation), allowing for lower volume feeding. The choice of liquid diet may vary depending on clinician preference.
Regardless of what product is used, early implementation of nutrition is the key element to encouraging swift recovery of patients with parvoviral enteritis, providing passive nutrition for the enterocytes which prevents mucosal breakdown and bacterial translocation. Technicians play a large role in advocating for patients and their proper nutrition to influence patient outcomes.
Outpatient vs. Inpatient Strategies for Parvoviral Enteritis
When a patient presents with parvoviral enteritis and the client is given the choice of hospitalized care for their pet, the cost of hospitalization commonly become a point of concern, especially when multiple animals in a litter is considered. In these situations, the question of whether parvoviral enteritis can be managed through an outpatient protocol can provide a significant chance of survival.
A study comparing outpatient protocol and inpatient protocol for treatment of canine parvoviral enteritis which utilized IV crystalloids, replacement of ongoing loss, KCl supplementation, IV antibiotics and IV antiemetics for the inpatient protocol and subcutaneous fluids ignoring ongoing loss, no potassium supplementation, long duration subcutaneous antibiotics, and subcutaneous antiemetics saw that there was no significant difference in survival chance and hospitalization time between patients in the two groups.
The one common intervention both groups received was the providing of a canine convalescence diet via syringe until the appetite regained, which likely highlights the importance of early enteral nutrition in survival chance. The authors commented that early enteral nutrition leads to earlier clinical improvement and syringe feeding is realistic for an outpatient protocol.
Oral Recuperation Fluids as a Supplement
An additional tool that has been added to our toolbox are oral recuperation fluids (ORFs). Oral recuperation fluids typically contain prebiotics, omega-3 and -6 fatty acids, and amino acids such as glutamine, arginine, and taurine and are provided to assist animals to recovery from illness. The intended effect of the fluid is to improve immune function and aid in regaining of normal mucosal morphology and permeability, as well as encouraging early regaining of voluntary appetite. The data associated with studies on ORFs shows significant decrease in time to regaining voluntary appetite and an increase in percent of RER consumed the first 24 hours after return of appetite. The ORF can be provided in place of, or alongside a bowl of water, fed via syringe, or through feeding tubes.
With the clear evidence of better patient outcome with institution of early enteral nutrition we should do everything we can to advocate for it to improve patient outcome in the GI patients.
References
1. Harris JP, Parnell NK, Griffith EH, et al. Retrospective evaluation of the impact of early enteral nutrition on clinical outcomes in dogs with pancreatitis: 34 cases (2010–2013). J Vet Emerg Crit Care. 2017;24:425–433.
2. Liu DT, Brown DC, Silverstein DC. Early nutritional support is associated with decreased length of hospitalization in dogs with septic peritonitis: a retrospective study of 45 cases (2000–2009). J Vet Emerg Crit Care. 2012;22:453–459.
3. Mohr AJ, Leisewitz AL, Jacobson LS, et al. Effect of early enteral nutrition on intestinal permeability, intestinal protein loss, and outcome in dogs with severe parvoviral enteritis. J Vet Intern Med. 2003;17:791–798.
4. Tenne R, Sullivan LA, Contreras ET, et al. Palatability and clinical effects of an oral recuperation fluid during the recovery of dogs with suspected parvoviral enteritis. Top Companion Anim Med. 2016;31:68–72.
5. Venn EC, Preisner K, Boscan PL, et al. Evaluation of an outpatient protocol in the treatment of canine parvoviral enteritis. J Vet Emerg Crit Care. 2017;27:52–65.
6. Will K, Nolte I, Zentek J. Early enteral nutrition in young dogs suffering from haemorrhagic gastroenteritis. J Vet Med. 2005;52:371–376.
7. Yu MK, Freeman LM, Heinze CR, et al. Comparison of compilation rates in dogs with nasoesophageal versus nasogastric feeding tubes. J Vet Emerg Crit Care. 2013;23:300–304.