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Rebecca White
Pharmacy Team Manager
Surgical Specialities and Nutrition
Oxford Racdliffe Hospitals NHS Trust
Since the 1930s, it has been acknowledged that patients with poor nutritional status have an increased incidence of post-operative complications. This is in part due to reduced immune and muscle function leading to an increase in morbidity and mortality, and a longer length of stay compared to well nourished patients.
Cuthbertson first discovered the muscle catabolism and increased metabolic rate associated with injury, but despite evidence of catabolism in the immediate post-operative phase, there is no indication to provide excessive levels of nutrition. Indeed, the high incidence of complications in early studies of parenteral nutrition is attributed to the high calorie levels provided: often up to 45kcal/kg/day.
The provision of appropriate nutrition support can have beneficial effects on outcomes in the surgical patient population. In general, prolonged periods of starvation are now a thing of the past as pre-operative fasting and post-operative restriction are now rare in clinical practice. However,
the practicalities of delivering adequate nutrition, particularly in patients undergoing extensive or complicated gastrointestinal surgery, can be challenging.
This article aims to identify those patient groups who may benefit from nutritional intervention in the peri-operative period and how this is delivered in practice.
Who may benefit?
Many of the clinical trials investigating the benefits of nutrition support in the peri-operative period are flawed in design, either through poor patient selection or through use of inappropriate routes of delivery.
Specific groups who will benefit from timely nutrition support are those with pre-existing malnutrition in a pre-operative state, and those who cannot eat within seven to 10 days of surgery.
Screening
Pre-operative assessment for elective surgery is usually undertaken two to four weeks prior to surgery, and should include screening for nutritional risk or malnutrition and appropriate referral criteria to ensure that nutritional status can be optimised prior to surgery in the outpatient setting.
Parameters to assess nutritional history include height, weight, recent nutritional intake and history of unintentional weight loss; these are sufficient to identify the majority of patients who may benefit from nutrition intervention pre-operatively.
Delaying surgery
In the case of emergency admissions requiring surgical intervention, the decision to delay surgery to allow for pre-operative nutritional optimisation must be taken on a case-by-case basis. Although the evidence is not robust due to other influences on post-operative complications, it has been suggested that 7–10 days of adequate nutrition can reduce complication rates by 10%, and should be provided prior to surgery if practicable and safe.
Peri-operative delivery
To ensure enteral nutrition can be delivered early in the post-operative phase, surgical access to provide such nutritional support is increasingly being fitted during surgery. Surgical jejunostomies are routinely placed for oesophago-gastric and hepatobiliary procedures: such patients would have traditionally required parenteral nutrition in the post-operative phase until oral intake was deemed safe. Gastrostomy tubes are also routinely placed in head and neck surgery patients, thus ensuring safe enteral nutrition access. Early post-operative enteral nutrition has been shown to stimulate the splanchnic and hepatic circulation, improving intestinal mucosal blood flow and minimising the intramucosal changes and permeability alterations. Its use has been shown to be safe and effective in numerous clinical trials.
Post-operative ileus (POI) remains the primary cause of extended length of stay in gastrointestinal surgery patients and is the main obstacle to successful early enteral nutrition in the post-operative phase. The use of laparoscopic surgery, enhanced recovery protocols and reduced opioid use all help to minimise the incidence of POI. For patients who develop prolonged POI, the use of nasojejunal tubes with a gastric decompression port has allowed enteral feeding to be safely established.
Gut rest post-operatively is now no longer advocated, even in patients with complicated anastomosis. Oral or enteral nutrition are preferred feeding methods unless there are complications such as obstruction, anastomotic breakdown or if fistulae develop. However, there is no evidence to suggest that any of these complications are related to the passage of nutrition through the gut.
Despite the increasing use of early oral nutrition and aggressive enteral nutrition approaches, there will always be patients who develop complications that require parenteral nutrition. For these patients it is imperative that the potential complications of this therapy are minimised. It is accepted that there remain several indications for parenteral nutrition therapy.
Appropriate vascular access must be secured for the safe provision of parenteral nutrition. In the short-term, peripheral parenteral nutrition via a short cannula may be appropriate for a few days to provide nutrition until enteral or oral nutrition can be established. If prolonged parenteral nutrition is likely, as in the case of anastomotic leaks or fistulae, central access should be secured. A short-term device, such as a peripherally inserted central catheter or a non-tunnelled central catheter may be preferred until the infection risks associated with intra-abdominal sepsis have abated. Peripherally inserted central catheters can be used safely for prolonged periods of time.
Determining patients’ nutritional requirements is now more of a challenge. The changes in anaesthesiology, surgical techniques and analgesia have all contributed to a reduction in stress response to surgery, and this attenuates the catabolism. Unfortunately, the majority of clinical studies determining energy and amino acid requirements immediately after surgery pre-date the enhanced recovery programmes. Available studies indicate that energy expenditure in the post-operative phase was 10–50% above pre-operative expenditure.
Energy provision should be based on standard predictive equations with the addition of a moderate stress factor of 10–20%, and the patient should be monitored closely, with provision titrated to response. Amino acid provision should account for the catabolic response and a daily provision of 1.25–1.5g/kg (0.2–0.25gN/kg) is recommended to meet requirements. For patients with an open abdomen, an additional 12g amino acid/L of wound fluid (2gN/L) should be provided.
Currently, there is insufficient robust evidence to support the routine inclusion of glutamine; however, there is an increasing body of evidence to support the inclusion of lipid emulsion with n-3 PUFA, with a possible effect on length of stay. The inclusion of novel substrates and the newer lipid emulsions still require more rigorous studies.
Parenteral nutrition is best delivered as an all-in-one nutrient admixture with the inclusion of adequate electrolytes, vitamins and trace elements. There is evidence that overprovision of sodium and fluid in the post-operative phase contributes to the incidence of post-operative ileus; close monitoring of fluid balance is essential.
Enhanced recovery and the benefit of glucose loading
Enhanced recovery programmes involve a number of measures. These include: minimal opioid use, use of epidurals, minimal or no bowel preparation, laparoscopic techniques, no post-operative nasogastric tubes, intra- and post-operative fluid restrictions, no abdominal drains and early post-operative mobilisation. Nutritional factors are: minimal pre-operative fasting, oral pre-operative carbohydrate loading, and early reintroduction of an oral diet.
Pre-operative carbohydrate loading, using a solution containing 12% carbohydrate, serves to produce an insulin response which has been shown to reduce post-operative insulin resistance and influence outcomes such as improved nitrogen balance, muscle strength and decreased nausea, vomiting and length of stay.
The long-term effects of surgery on nutritional status
In the nutritional management of the surgical patient it is important to recognise not just the immediate nutritional needs and management issues, but also the long-term consequences of the surgical procedure.
With an understanding of sites of nutrient absorption, it is easy to determine effects of surgery and identify strategies to manage potential deficiencies.
The most profound effect of surgery on nutritional competence is extensive resection that leads to short bowel syndrome, thereby requiring the provision of long-term parenteral fluids, electrolytes and nutrition. Even a simple ileo-caecal resection will eventually lead to vitamin B12 depletion if routine replacement therapy is not performed; whereas, following a pancreatectomy the patient will be dependent on insulin therapy and exogenous pancreatic enzyme supplementation.
The use of bariatric surgery to induce weight loss continues to increase. Gastric banding tends to cause fewer nutrient deficiencies than gastric bypass; however, both of these interventions can induce altered eating patterns due to the size of the gastric pouch. Routine supplementation following surgery and regular micronutrient monitoring over the long term are both necessary, and nutritional progress should be monitored by a specialist dietitian.
Summary
It is acknowledged that nutrition and nutritional status can influence the outcome of surgical intervention and that surgery can impact on nutritional status. An understanding of the factors involved will ensure that pharmacists are able to optimise patients’ nutritional care. Until studies are undertaken to determine the post-operative nutritional requirements in the modern era of surgery, a conservative and closely monitored approach is appropriate
