There is growing evidence to support the idea that promoting food intake as early as possible after surgery is essential. This article will review the evidence base and benefits of early enteral nutrition, with a discussion on how to best provide nutritional support in the post-operative phase, including what should be fed. It will also cover considerations for optimising food intake in hospitalised patients.
The benefits of early nutritional support
In human medicine, it is now reasonably well accepted that early nutritional support can both decrease mortality rate and shorten the duration of hospitalisation (Serón-Arbeloa et al., 2011; Chambrier and Sztark, 2012). While research is more limited in the veterinary sphere, similar findings have been documented – for example, initiation of consistent caloric intake within 24 hours of surgery in dogs with septic peritonitis has been associated with a significantly shorter hospital stay (Liu et al., 2012).
While nutritional support can be delivered enterally or parenterally (via the intravenous route), the enteral route is preferred where possible. In humans, enteral nutrition is associated with shorter hospital stays, a lower infection rate and earlier gut function compared to parenteral nutrition (Seres et al., 2013). Enteral nutrition provides intraluminal agents. These can stimulate the gastrointestinal (GI) tract and support GI motility, thus helping to counteract post-operative ileus, a common complication after surgery. It can also help to protect against the risk of bacterial translocation (Chung et al., 2013), which cats and dogs may be at particular risk from if they have an underlying disease or have received medications that have the potential to damage the GI mucosal barrier.
While nutritional support can be delivered enterally or parenterally (via the intravenous route), the enteral route is preferred where possible
A lack of intraluminal nutrients can result in decreased GI cell turnover and mucus production, impairing the gut barrier function and increasing gut permeability. This, alongside lower GI blood flow due to reduced luminal contents, can increase the risk of infection. Enteral nutrition is also essential to help preserve a healthy gut epithelium and reduce the risk of GI villous atrophy, which, in a study in rats, was observed to begin to occur within three days when total parenteral nutrition alone was provided (Okuma, 2007). Thus, while there may be occasions where enteral feeding is contraindicated – for example, due to excessive vomiting – it should be attempted wherever possible.
The two phases of post-operative recovery
In human medicine, it is estimated to take an average of 14 days for optimal recovery after surgery, and two phases of post-surgical recovery are described. In the first 48 hours (phase 1), metabolic rate drops and GI blood perfusion is reduced. At this point, the priority should be maintenance of the circulation; energy is less of a concern. Initiation of voluntary intake as soon as the patient is fully recovered from anaesthesia should, therefore, be a key focus to supply nutrients to the intestinal tract and start the recovery process. Fluid intake is also an important consideration (Corbee and Van Kerkhoven, 2014).
After the first 48 hours and up to 14 days post-surgery, the need for increased calorie administration becomes greater (Corbee and Van Kerkhoven, 2014). A high level of protein is also required, as protein is used for wound healing and the synthesis of acute phase proteins and immunoglobulins, as well as being catabolised for energy. Diets should, therefore, have a high energy density and sufficient protein of high biological value. A highly digestible diet is also a priority, given the likelihood of appetite reduction.
Diets should […] have a high energy density and sufficient protein of high biological value. A highly digestible diet is also a priority
In addition, specific nutrients may potentially help shorten the recovery period. These include long-chain polyunsaturated omega-3 fatty acids, such as EPA and DHA, which have natural anti-inflammatory effects. Essential amino acids such as arginine, known to promote wound healing, and glutamine, which provides 50 percent of enteric cell nutrition when absorbed from the GI lumen, are also important. Glutamine also has a role in supporting immunity and is not fully synthesised by stressed animals (including stress induced by surgery), so provision of increased dietary levels can be helpful (O’Flaherty and Bouchier-Hayes, 1999).
Maximising support of the GI microbiome – particularly if it has been adversely impacted by stress, medication or underlying disease – can also be important. Prebiotics such as inulin and fructo-oligosaccharides can provide support for the GI microbiome during recovery. These are non-digestible carbohydrates fermented by colonic bacteria into short-chain fatty acids, providing essential nutrients for the enteric epithelium, as well as producing an environment more favourable for the growth of beneficial bacteria (Valdes, 2018). Probiotics may also be used to help support the microbiome.
Post-operative feeding plans in the clinic
In the veterinary clinic, the two most important influencers of effective post-operative nutritional support are the selection of an appropriate diet and ensuring the patient’s intake meets their calorie requirements. There may be a large number of causes of inappetence in hospitalised patients, some of which are detailed in Figure 1. Undernutrition is unfortunately common: in one study conducted, 84 percent of hospitalised dogs consumed less than 25 percent of their energy requirement, and only 3.4 percent of the dogs met their requirement (Molina et al., 2018). Furthermore, an association was found between inadequate energy intake and death (Molina et al., 2018), so focusing on meeting calorie needs is key. For most patients in the hospitalised setting, calculation of their resting energy requirement (RER = (body weight in kg)0.75 × 70) provides a useful starting point.
When considering diet type, it helps to identify the specific metabolic changes that occur in the recovery phase and consider how these relate to nutritional requirements. There are a number of commercial diets available on the market that incorporate many of the key nutritional factors important to optimise post-operative recovery. Importantly, these are also designed to be highly palatable to encourage pets to eat, especially as many patients show some reluctance to eat in the immediate post-operative period. Diets most appropriate for post-operative nutritional support can generally be split into two groups: gastrointestinal diets and convalescence diets.
A highly digestible gastrointestinal diet is likely to be an ideal choice for most healthy animals after routine surgery. Some of the key benefits of such diets are summarised in Box 1. Gastrointestinal diets tend to come in a range of formats and textures (including dry products, mousses and pouches), which can help to support voluntary intake.
|– Highly digestible, low residue|
– High carbohydrate digestibility (greater than 90 percent)
– Protein of a high biological value, from a limited number of sources
– Appropriate level of soluble and insoluble fibres
– Prebiotics incorporated
– Appropriate fat levels
– Energy dense (4 to 4.5kcal/g)
– Increased omega-3 fatty acids
Depending on the clinical situation, some pets may require a different specialised diet. Critical care or convalescence diets can be particularly useful if a patient is suffering from significant malnutrition or when tube feeding is required. These diets generally have a higher energy density than gastrointestinal diets and are very high in digestibility and protein to help aid recovery of tissues, and high in fat to maximise energy density. They may be helpful to reduce the volume a patient needs to eat, and in some cases can be diluted to make them appropriate for tube feeding. It is important, however, to bear in mind that the high fat content can delay gastric emptying and may also cause increased maldigestion and malabsorption in dogs with GI compromise as they generally struggle to digest fat efficiently in the presence of GI disease. Convalescence diets generally come in a mousse or liquid format, which can be helpful in some patients – particularly for patients that find lapping or eating very soft-textured food easier.
Maximising the likelihood of voluntary intake
As well as selecting an appropriate diet, it is crucial to ensure the patient consumes enough and to monitor their intake. The WSAVA Global Nutrition Toolkit provides some excellent monitoring tools and checklists which are free to download (Figure 2).
Anorexia and hyporexia are common, especially immediately after surgery, and nursing care plays a crucial role in encouraging these patients to eat. A diet history on admission can be helpful to guide appropriate care for each patient. There can be a tendency to offer wet food first in the clinic, but this is highly unlikely to encourage food intake if a pet strongly prefers dry food. So, documenting any favourite flavours or a preference for wet or dry food and catering to these preferences is crucial. Cats in particular may be very texture-sensitive. If a patient is more likely to eat when hand-fed, such information can be documented on admission and trialled on recovery.
Voluntary food intake can also be encouraged by a variety of other methods:
- Food should be offered fresh and left down for a maximum of 20 minutes at a time
- The gentle heating of wet food can help to release aromas
- Offering a “buffet” of several food options at a time should be avoided to reduce the risk of food aversions
- Administering oral medication in main meals should be avoided
- Palatability enhancers may be helpful
- Consideration of the environment is also essential: in some cases, patients may be more likely to eat if taken out of their kennel environment and into a quiet area
Pain scoring and provision of adequate pain relief can play an essential role in maximising the likelihood of a patient eating post-operatively. Other medications – particularly anti-emetics and, where relevant, appetite stimulants – should also be considered.
Pain scoring and provision of adequate pain relief can play an essential role in maximising the likelihood of a patient eating post-operativel
If sufficient voluntary food intake cannot be encouraged, assisted feeding may be required, with the technique dependent on the clinical situation. Where there is current or predicted reduced food intake after surgery, proactive placement of a feeding tube under anaesthesia is sensible. Prompt use of a feeding tube should also be instigated if there is not sufficient voluntary food intake after surgery.
Post-operative nutritional support must always be tailored to the individual patient’s needs. Consideration of what to feed, the amount needed to optimise recovery, when to institute this feeding and how to best promote voluntary intake are all key considerations for post-operative feeding in companion animals. Factoring the importance of early enteral nutrition into post-operative plans can make a significant difference to help improve patient outcomes.