Hyperalimentation (Total Parenteral or Enteral Nutrition)
(also see Chapter
77
)
Hyperalimentation (i.e., total parenteral nutrition (TPN]) consists
of concentrating hypertonic glucose calories in the normal daily fluid requirements.
The solutions contain protein hydrolysates, soybean emulsions (i.e., Intralipid),
or synthetic amino acids. The major benefits
of TPN or enteral nutrition have been fewer complications postoperatively and shorter
hospital stays for patients scheduled to have no oral feeding for 7 days or who were
malnourished preoperatively.[160]
[161]
Starker and colleagues[162]
found that the response
to TPN, as monitored by serum albumin levels, predicted the postoperative outcome.
[163]
The group demonstrating a rise in serum albumin
with TPN had diuresis, weight loss, and fewer complications (1 of 15 patients) than
did the group that gained weight and had a decrease in serum albumin (8 of 16 patients
had 15 complications) ( Fig. 27-6
).
These data are echoed by those in the Veterans Administration (VA) studies, which
reported that the serum albumin level was one of the most powerful predictors of
perioperative outcome.[160]
[161]
The major complications of hyperalimentation are sepsis and metabolic
abnormalities. The central lines used for TPN require application with an absolutely
aseptic technique and should not be used routinely as an intravenous route for drug
administration. Major metabolic complications of TPN relate to deficiencies and
the development of hyperosmolar states. Complications of hypertonic dextrose can
develop if the patient has insufficient insulin (diabetes mellitus) to metabolize
the sugar or if insulin resistance occurs (e.g., because of uremia, burns, or sepsis).
[160]
A gradual decrease in the infusion rate of TPN prevents the hypoglycemia
that can occur on abrupt discontinuance. Thus, the infusion rate of TPN should be
decreased the night before anesthesia and surgery or be continued throughout the
operation at its current rate. The main reason for slowing or discontinuing TPN
before anesthesia is to avoid intraoperative hyperosmolarity secondary to accidental
rapid infusion of the solution or hypoglycemia
Figure 27-6
A-C, The response to hyperalimentation
(repletion), as measured by variation in serum albumin levels, predicted the outcome
of surgery. Patients who responded (B) to nutritional
support with increased albumin levels had a significantly better outcome than did
those whose albumin level did not increase (C). See
the text for a more complete explanation. (Adapted from Starker PM, Group
FE, Askanazi J, et al: Serum albumin levels as an index of nutritional support.
Surgery 91:194, 1982.)
if the infusion is discontinued because of the high levels of endogenous insulin
and lower levels of glucose present in the usual crystalloid solutions.[160]
Hypophosphatemia is a particularly serious complication that results from the administration
of phosphate-free or phosphate-depleted solutions for hyperalimentation. The low
serum phosphate level causes a shift of the oxygen dissociation curve to the left.
The resulting low 2,3-diphosphoglycerate and adenosine triphosphatase levels mean
that cardiac output must increase for oxygen delivery to remain the same. Hypophosphatemia
of less than 1.0 mg/dL of blood may cause hemolytic anemia, cardiac failure, tachypnea,
neurologic symptoms, seizures, and death. In addition, long-term TPN is associated
with deficiencies in trace metals such as copper (refractory anemia), zinc (impaired
wound healing), and magnesium.
For these reasons, we have adopted the following practices.[160]
Infusion of TPN or enteral nutrition is reduced beginning the night before surgery,
and a 5% or 10% dextrose solution is substituted preoperatively. If serum glucose
phosphate and potassium concentrations (measured preoperatively) are abnormal, they
are restored to within normal limits. Strict asepsis is maintained. Conversely,
we often continue infusing the TPN solution by using a pump system or enteral nutrition,
strictly maintaining its normal rate and asepsis, administering all fluids through
a different intravenous site, and performing a rapid-sequence induction of anesthesia
(for those who received enteral nutrition).
