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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_885_Библиотеки_им_академика_М_И_Перельмана.pdf
298 M. A. Maccini and E. E. Moore
• Determination of nutritional requirements
{ Indirect calorimetry is the gold standard for determination of metabolic
energy expenditure. It is most useful in stable patients with an inspired
FiO2 of 50% or less and requires specialized equipment and personnel not
universally available. It is very resource-intensive, however, and rarely
used except for research. Thus, equations have been developed for estimating patients’ caloric needs and are widely used (Harris-Benedict, etc.).
Reasonable estimates of daily caloric requirements in surgical patients
are as follows:
Normal and underweight patients: 25 kcal/kg
Obese patients: 20–25 kcal/kg
Ö For obese patients, use adjusted feeding weight (AW):
AW = Ideal weight + [(actual weight – ideal weight) x 0.25]
— Ideal weight (male) ≈ 50 kg + (2.3 x height in inches − 60)
— Ideal weight (female) ≈ 45.5 kg + (2.3 x height in inches − 60)
{ Protein requirements vary with the degree of catabolism in hypermeta-
bolic critically ill patients. The goal is to provide enough protein to match
protein catabolism.
Estimates of protein needs are as follows:
Ö Normal adult: 0.8 g/kg
Ö Mild stress: 1.2–1.4 g/kg
Ö Moderate stress: 1.5–1.7 g/kg
Ö Severe stress: 1.8–2.5 g/kg
Most surgical ICU patients require at least 2 g/kg of protein daily.
A more accurate determination of protein requirements can be
obtained by calculating the patient’s nitrogen balance, but is rarely
helpful:
NB = (Protein (g/24h)/6.25) – (24h urine urea nitrogen (g/24h) + 4)
Ö
Goal is to maintain a 4–6 g positive nitrogen balance
Ö
In patients with hepatic encephalopathy, protein intake should be
limited to 0.6–0.8 g/kg. Other causes of encephalopathy should be
ruled out first, however, because patients with liver dysfunction who
are not encephalopathic can tolerate more normal protein intake and
needlessly withholding protein may be detrimental.
Patients with renal failure (especially those on dialysis) require
increased protein intake (typically 2–2.5 g/kg daily) to maintain a
Nutrition in the Critically Ill 299
positive nitrogen balance, due to loss of serum proteins in urine and in
dialysis.
{ Non-protein calories (NPC) should be provided to prevent protein catabo-
lism. If inadequate overall calories are provided, a portion of the protein
in the diet will be consumed for energy, leading to a negative nitrogen
balance.
{ It is also important to avoid overfeeding, as this has been associated with
hypercapnea and resulting prolonged weaning from mechanical ventilator
support, hyperglycemia, hyperlipidemia, liver dysfunction, and increased
risk of infections.
• Enteral Nutrition
{ Enteral nutrition should be initiated as soon as possible once it has been
determined that the patient will not be able to meet their caloric needs by
mouth. We generally aim to initiate enteral nutrition within 24 hours of
hospitalization.
Contraindications for enteral feeding include prolonged shock,
major GI bleed, ileus, mechanical bowel obstruction, or bowel in discontinuity. Recent GI tract surgery with an anastomosis is not a
contraindication.
Absence of bowel sounds and absence of flatus or bowel movements
are not contraindications to starting enteral nutrition.
Enteral nutrition is superior to total parenteral nutrition, reducing
infectious complications and reducing costs of care.
{ Options for enteral access include nasogastric or nasoduodenal tubes, or
percutaneous gastrostomy or jejunostomy tubes which can be placed at
bedside, in the operating room, or in interventional radiology.
Prokinetic agents (erythromycin and metoclopramide) improve feed-
ing tolerance rates in patients with elevated gastric residual volumes
but have not demonstrated associated decreases in pneumonia, duration of ICU stay, or mortality [Chapter 8-(ii)].
Post-pyloric feeding may also be better tolerated and allow adminis-
tration of more calories than gastric feeding in the acute post-surgical
or post-injury setting when there is delayed gastric emptying.
{ Choice of enteral formula is determined by the patient’s medical history
and clinical status. The general classes of formulas include polymeric,
(e.g. Jevity, Osmolite) which are standard formulas appropriate for the
majority of patients; concentrated (e.g. Two-Cal), which deliver higher
300 M. A. Maccini and E. E. Moore
caloric density per unit volume for patients on fluid restrictions; and
elemental (e.g. Vivonex), which are composed of partially digested
proteins and simple carbohydrates and are appropriate for patients with
short gut or other malabsorptive conditions.
Reduced carbohydrate formulas are not necessary in patients with a
history of diabetes unless unable to maintain good glycemic control.
{ Calculation of goal tube feed rates should start with estimation of non-
protein calorie requirements (see above). Using the total NPC requirement
in conjunction with NPC per unit volume of the selected enteral formula
allows determination of the total daily volume of formula needed, which
can then be divided over the time period of feeding administration
(typically 24 hours in ICU patients). Protein supplementation may be
required depending on the patient’s daily protein requirements.
Example: 75 kg male with goal 25 NPCs/kg and goal 2 g/kg protein
75 25 1875
kg NPC
NPC
1875
NPC
0.98
NPC
×=
kg
day
mL
1913 80 /
=≈
day
mL
mL hr
Protein content of tube feed regimen:
1.913 55.5
Lg
×
g
kg g g g
×= ≈2 75 150 – 106 44
kg
protein
106
g
=
L
protein
protein
Thus, the patient would have a goal rate of 80 mL/hr with 44 g of supplemental protein added to meet his nutritional needs.
{ Gastric residual volumes should be monitored while providing NG or
PEG tube feeds. If residual volumes are greater than 200 mL, consider
starting prokinetic medications; if volumes are greater than 500 mL, hold
feeds for at least 4 hours and then re-assess and restart at a lower infusion
rate. In patients with repeated high residual volumes, consider obtaining
small bowel enteral access.
Nutrition in the Critically Ill 301
{ In mechanically ventilated patients receiving enteral nutrition, there is no
need to discontinue enteral feeding perioperatively unless bowel surgery
is planned.
• Parenteral nutrition
{ If a patient is unable to tolerate enteral nutrition due to GI dysfunction
(i.e. ileus, obstruction, short gut, shock), they require nutritional support
via parenteral route. Parenteral nutrition should be initiated on hospital
day seven if the patient cannot receive enteral nutrition, or earlier if the
patient has preadmission malnutrition.
{ Parenteral nutrition solutions require central access due to their high
osmolarity. Ideally, a dedicated lumen should be used and sterile technique observed when administering TPN.
{ Although approximately 30% of calories are provided by fats in enteral
nutrition, parenteral lipid emulsions carry increased risk of infection and
are prone to oxidation, which can result in oxidative cell injury and exacerbate the already pro-inflammatory post-surgical/post-injury state. Thus,
the minimum of 3–4% of daily calories from lipids required to prevent
essential fatty acid deficiency should generally be sufficient and lipid
emulsions should actually be avoided in the initial/acute setting. The role
of omega-3 versus omega-6 remains controversial.
{ Monitoring of patients on TPN should include daily basic metabolic
profile with particular attention to calcium, magnesium, and phosphorus
levels, and glucose. The TPN formula should be adjusted based on these electrolyte levels and normoglycemia maintained with supplemental insulin.
{ Complications associated with TPN administration include risk of central
line infection, electrolyte abnormalities, impaired glucose metabolism,
liver dysfunction, hypercapnea (seen with overfeeding), and gut atrophy
(due to absence of nutrients in the bowel lumen).
• Hyperglycemia
{ Critically ill patients are at increased risk of developing hyperglycemia
due to stress-induced abnormalities of glucose metabolism. Patients
receiving total parenteral nutritional support are at further increased risk
due to the inherent changes in glucose metabolism seen with TPN.
{ Blood glucose should be monitored and a goal blood glucose of less than
180 maintained with intravenous insulin infusion if required, with transition to sliding scale insulin once insulin requirements have stabilized.
More stringent control with lower blood glucose goals does not appear to
be beneficial and may be harmful.
302 M. A. Maccini and E. E. Moore
• Glutamine
{ Glutamine is an important nutrient for bowel mucosa, and is included
in many enteral formulas. However, glutamine is usually not provided
in TPN because it must be delivered as a dipeptide. Production of glutamine
decreases in the acute high physiologic stress state, however, so including
supplemental glutamine in critically ill patients (enteral or parenteral) may
help preserve the small bowel mucosa and reduce bacterial translocation.
Practical Algorithm(s)/Diagrams
Basic NutriƟon Algorithm
Severe Injury/
CriƟcal Illness
IniƟate EN once
resuscitaƟon
completed
To le ra t ed
Target regimen:
25 NPC/kg/day
2g/kg protein/day
Start TPN at NPO
day 3
Not tolerated
Pre-exisƟng
malnutriƟon
present?
Yes No
Start TPN at NPO
day 7
Fig. 1. Basic algorithm for nutritional support in the critically ill, with caloric and protein
goals and timing of TPN initiation.
Review of Current Literature with References
History
• Benefit of Early Enteral Feeding: A prospective, randomized trial in 1986
demonstrated that patients receiving immediate enteral nutrition following emergent exploratory laparotomy for abdominal trauma had a lower
Nutrition in the Critically Ill 303
incidence of sepsis [Moore E, Jones T. “Benefits of immediate jejunostomy feeding after major abdominal trauma — a prospective, randomized
trial” J Trauma 26: 10 (1986): 874–881].
• Enteral vs Parenteral Nutrition: A 1989 prospective, randomized trial dem-
onstrated that patients receiving enteral nutrition had a lower rate of
infections and lower rate of septic morbidity. Multiple subsequent randomized trials have duplicated this result. [Moore F et al. “TEN vs TPN
following major abdominal trauma — reduced septic morbidity” J Trauma
29: 7 (1989): 916–922].
• Early Parenteral Nutrition: Early initiation of parenteral nutrition does not
improve mortality rates or hospital length of stay [Doig et al. “Early parenteral nutrition in critically ill patients with short-term relative contraindications
to early enteral nutrition” JAMA 309: 20 (2013): 2130–2138].
Controversial issues
• Glutamine supplementation in TPN: A 2010 meta-analysis demonstrated that
adding glutamine to parenteral nutrition regimens shortened hospital lengthof-stay and reduced morbidity from infection [Wang Y et al. “The impact of
glutamine dipeptide-supplemented parenteral nutrition on outcomes of surgical patients: a meta-analysis of randomized clinical trials” J Parenteral and
Enteral Nutrition 34: 5 (2010): 521–529].
• Gastric Residual Volume: A 2013 randomized controlled trial demonstrated
that not monitoring gastric residual volumes in mechanically ventilated
patients and only holding tube feeds in the presence of regurgitation/vomiting
did not result in an increase in ventilator-associated pneumonia. The intervention group had a higher proportion of patients receiving 100% caloric goal
[Reignier J et al. “Effect of not monitoring residual gastric volume on risk of
ventilator-associated pneumonia in adults receiving mechanical ventilation
and early enteral feeding: a randomized controlled trial” JAMA 309: 3 (2013):
249–256].
• Anti-Inflammatory Enteral Formulas: A randomized, double-blind, placebo-
controlled trial demonstrated no improvement in ventilator-free days or other
outcomes in ventilated patients who received omega-3 fatty acid, γ-linoleic
acid, and antioxidant supplementation. This is in contrast to three prior
studies demonstrating reduction in ventilator days, organ dysfunction, and
mortality. The intervention group did suffer more diarrhea [Rice et al.
“Enteral omega-3 fatty acid, γ-linoleic acid, and antioxidant supplementation
in acute lung injury” JAMA 306: 14 (2011): 1574–1581].
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Chapter 8-(ii)
Tube Feed Intolerance
Anna Kristina Melvin, PA-C* Janis Sandlin,
†
PA-C
and Walter L. Biffl, MD
* Physician Assistant, Boulder Community Hospital
†
Physician Assistant, Boulder Community Hospital
‡
Professor of Surgery, University of Colorado School of Medicine,
Associate Director of Surgery, Denver Health Medical Center
Take Home Points
• Diarrhea, emesis, or high gastric residual volumes (GRV) (>200 mL/4 hours)
are examples of tube feed intolerance.
• Once tube feed intolerance has been recognized, it is important to consider
organic causes such as intraabdominal infectious processes, or inadequate
tube placement.
• Tube feeds that have been stopped may be resumed after symptoms improve
or when GRVs are <200 mL/4 hours.
• Erythromycin and metoclopramide are first-line prokinetic agents.
• If gastric ileus is recalcitrant to prokinetic agents, consider post-pyloric tube
placement or gastrostomy.
‡
Contact information: (Anna Kristina Melvin and Janis Sandlin) Boulder Community
Hospital, 1100 Balsam Ave, Boulder, CO 80304; (Walter L. Biff) Department of Surgery,
Denver Health Medical Center, 777 Bannock St., MC 0206, Denver, CO 80204; Tel.: 303-6021861, email: walter.biffl @dhha.org; Anna.Kristina@bch.org; Janis.Sandlin@bch.org
305
306 A. K. Melvin, J. Sandlin and W. L. Biffl
Background
• Feeding intolerance in critically ill patients in the ICU can lead to prolonged
hospital stays, increased hospital costs, and a higher rate of morbidity. Early
recognition is imperative.
• Etiologies of tube feed intolerance can include opioid use, recent abdominal
surgery, increased age, preexisting comorbidities, prolonged ventilation,
fluid/electrolyte imbalance, or poor underlying nutritional status.
• Diagnosis is subjective and can include the presence of:
{ High GRVs (>200 mL/4 hour)
Although the importance of measuring GRVs has been questioned
recently, we still feel this is a safe approach particularly in high-risk
patients.
{ Abdominal pain
{ Abdominal distension
{ Diarrhea
{ Emesis
Main Body
Nutritional support is an essential component of critical care. The most critically
ill, who need support the most, are often unable to take nutrition by mouth
(i.e., eat). Consequently, the critical care provider must provide support. Enteral
nutrition is preferred over parenteral; various routes include:
• Eating
• Nasogastric tube
• Nasojejunal tube
• Gastrostomy tube
An awake, verbal patient can communicate lack of appetite, or nausea; however, critically ill patients are also often unable to tell the provider that they are
not tolerating nutritional support. Thus, we must rely on signs and symptoms of
intolerance. These may reflect either hyper- or hypomotility and include:
{ High GRVs ( >200 mL/4 hour)
Although the importance of measuring GRVs has been questioned
recently, we still feel this is a safe approach particularly in high-risk
patients.
Tube Feed Intolerance 307
{ Abdominal pain
{ Abdominal distension
{ Diarrhea
{ Emesis
If signs or symptoms of feeding intolerance are observed, it is important to
stop feeding due to the high risk of patient aspiration. It is important to exclude
mechanical obstruction as well as to consider organic causes such as intraabdominal infectious processes or suboptimal tube placement prior to initiating
promotility agents. Tube feeds that have been stopped may be resumed after
symptoms improve or when GRV’s are < 200 mL/4 hours.
Hypermotility may be treated by altering the dietary formula or rate of
administration. Prokinetic agents such as metoclopramide and erythromycin
should be initiated in patients who have high GR volumes and who are not
actively having diarrhea or emesis.
The two most common prokinetic agents used in the U.S. are metoclopramide and erythromycin. Metoclopramide is a dopamine D2 receptor antagonist
which enhances gastric antral contractions and decreasing postprandial fundus
relaxation. It carries potential side effects including anxiety, restlessness, and
QT interval prolongation, and extrapyramidal side effects (dystonia and tardive
dyskinesia) which have led to a FDA black box warning. Erythromycin is a
macrolide antibiotic and motilin agonist which induces high amplitude gastric
propulsive contractions and stimulates contractility of the fundus. Side effects of
erythromycin include emergence of resistant bacteria, as well as ototoxicity, QT
prolongation, and sudden death. In critically ill patients, erythromycin may be
more efficacious, but both agents lose effectiveness over time and are sometimes
used in combination.
If patient has recalcitrant gastric ileus, consider post-pyloric tube placement.
This may be an effective way to introduce nutrients to the GI tract and potentially
avoid some of the symptoms associated with gastric feeding tubes as mentioned
above. In the authors’ ICU, endoscopic positioning of postpyloric (nasojejunal)
tubes allows the added benefit of ruling out proximal obstruction and diagnosing
gastric pathology (e.g., gastritis, ulcers). Percutaneous endoscopic gastrostomy is
employed for long-term care, allowing feeding as well as decompression.