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KEY CONCEPTS
The fit, previously well-nourished patient undergoing elective surgery could be fasted for up to a week postoperatively without apparent adverse effect on outcomes, provided that fluid and electrolyte needs are met. On the other hand, it is well established in multiple studies that malnourished patients benefit from nutritional repletion via either enteral or parenteral routes prior to surgery.
The indications for total parenteral nutrition (TPN) are narrow, including those patients who cannot absorb enteral solutions (small bowel obstruction, short gut syndrome, etc); partial parenteral nutrition may be indicated to supplement enteral nutrition (EN) when EN cannot fully provide for nutritional needs.
TPN will generally require a venous access line with its catheter tip in the superior vena cava. The line or port through which the TPN solution will be infused should be dedicated to this purpose, if at all possible, and strict aseptic techniques should be employed for insertion and care of the catheter.
In the patient with critical illness, discontinuing an EN infusion may require multiple potentially dangerous adjustments in insulin infusions and maintenance of intravenous fluid rates. Meanwhile, the evidence is sparse that EN infusions delivered through an appropriately sited gastrointestinal feeding tube increases the risk of aspiration pneumonitis.
Regardless of whether the TPN infusion is continued, reduced, replaced with 10% dextrose, or stopped, blood glucose monitoring will be needed during all but short, minor surgical procedures.
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Issues related to nutrition tend to be far removed from the usual concerns of the surgical anesthesiologist, other than those related to whether patient listed for elective surgery has fasted for whatever interval one’s institution or colleagues insist upon (this highly controversial issue is also considered in Chapter 19). On the other hand, appropriate nutritional support has been recognized to be of key importance for favorable outcomes in patients with critical illness, a large fraction of whom will require procedural services. Severe malnutrition causes widespread organ dysfunction and increases the risk of perioperative morbidity and mortality. Nutritional repletion may improve wound healing, restore immune competence, and reduce morbidity and mortality rates in critically ill patients. Nutritional support is a key element of an enhanced recovery program (these issues are dealt with in Chapter 48).
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This chapter does not provide a complete review of nutrition in the patient undergoing surgery or with critical illness, but rather offers the framework for providing basic nutritional support in such patients. We consider, for example, whether enteral nutrition (EN) or parenteral nutrition (PN) will best meet the needs of an individual patient. This chapter also briefly reviews the conditions under which the ongoing nutritional needs of patients may come into conflict with anesthetic preferences and dogmas, such as the duration that patients must not receive EN before undergoing general anesthesia.
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BASIC NUTRITIONAL NEEDS
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Maintenance of normal body mass, composition, structure, and function requires intake of water, energy substrates, and specific ...