Parenteral Nutrition

What are indications for parenteral nutrition?

-Inability to feed enterally
-Inability to maintain nutritional goals enterally
-Newborns with GI anomalies
-Short bowel syndrome
-Malabsorption syndromes
-High-output enterocutaneous fistulas (>500ml/day)
-Enteroenteric, enterocolic, enterovesical fistulas
-Postoperative ileus over 7-10days
-Hypermetabolic critically-ill patients
-Functional GI disorders (i.e. post-CVA)
-Malnutrition/cachexia from malignancy

What are lengths of intact remaining small bowel from massive resection that usually necessitate chronic TPN?

Less than 100cm without colon or ileocecal valve
Less than 50cm with the colon and an intact ileocecal valve

What are contraindications to hyperalimentation?

-Enteral nutrition is possible
-Good nutritional status
-Hemodynamic instability
-Severe metabolic derangements (i.e. hyperglycemia, hyperosmolarity, electrolytes)

What is PPN?

Peripheral parenteral nutrition
Administered through a peripheral catheter
Often used for short term, sometimes while waiting for central venous access
Dextrose: 5-10% (D5 or D10)
Protein: 3%

What is TPN?

Total parenteral nutrition
Requires central venous access due to high osmolarity
Dextrose: 15-25%
Crystalline amino acids: 3-5%
With or without Lipids: 10-15% of calories, limited to 1 g/kg/d

What are classic signs of fatty acid deficiency?

Dry, Scaly Dermatitis
Alopecia

What are recommended caloric requirements?

Normal to Mild Stress 25-30 kcal/kg/day
Moderate stress 30 kcal/kg/day
Severe stress 30-35 kcal/kg/day

What are recommended protein requirements?

Normal 1.0 g/kg/day
Mild stress 1.2 g/kg/day
Moderate stress 1.5 g/kg/day
Severe stress 2.0 g/kg/day

What are calorie equivalents for carbohydrate, protein, and lipid?

carbohydrate = 4 kcal/g
IV dextrose = 3.4 kcal/g
protein = 4 kcal/g
lipid = 9 kcal/g

What are common supplements and additives for TPN infusions?

Multivitamins
Vitamin K (not in multivitamin preparations)
Trace minerals (Zn, Cu, Mn, Cr, Se)
Insulin
Heparin
H2 Blockers

What are signs of Zinc deficiency?

Excematoid Dermatitis (intertriginous zones)
Impaired wound healing

What is a sign of Copper deficiency?

Microcytic anemia

What is a sign of Chromium deficiency?

Impaired glucose tolerance

What does Selenium deficiency cause?

Cardiomyopathy

What are recommendations for electrolytes in TPN?

Sodium 60-150 mEq/d
Potassium 70-150 mEq/d
Phosphorus 20-30 mmol/d
Magnesium 15-20 mEq/d
Calcium 10-20 mmol/d

What is the role of administering chloride or acetate salts in TPN?

Maintenance of acid-base status
Maintenance of electrolyte balance
Sodium and potassium can be administered in either form

What are issues with administering too much calcium and phosphorus in TPN?

They can precipitate in solution

Can glutamine be administered in TPN?

It is typically unstable in solution
Glutamine dipeptide is available in Europe and can be given parenterally.

What are considerations when starting TPN?

1. Electrolyte status
2. Volume status
3. Acid-Base status
4. Risk for Septic complications

What is often monitored when administering TPN?

Daily weights
Electrolytes, starting daily then every 2-3days when stable
CBC, BUN, LFTs, Phos, Mg at least weekly
Glucose every 6 hours

What are methods of short-term central venous access for TPN?

16G percutaneous catheters via subclavian vein or internal jugular vein

What are methods of long-term central venous access?

PICC line (via basilic or cephalic vein)
Port-a-Caths
Tunneled catheters (Hickman, Broviac, Groshong)
Hohn catheters

Where should the catheter tip be placed?

In the superior vena cava adjacent to the right atrium

What are catheter-related complications?

Cardiac arrhythmias
Septicemia
Pneumothorax
Hemothorax
Subclavian artery injury
Thoracic duct injury
Air embolism
Catheter or guidewire embolism
Cardiac perforation

What are metabolic complications of TPN?

1. Hyperglycemia - administer insulin and correct electrolytes
2. Overfeeding - can cause ventilator dependence and hepatic steatosis
3. Cholestasis - monitor transaminases, alkaline phosphatase, and bilirubin

What is the risk of catheter-related infection?

For catheters present over 7 days, infection risks of 5-10% have been reported.
Among catheter tips that reach microbiology labs, only 15-25% are culture positive.
Catheter-related septicemia carries mortality rates of 12-25%.

What clinical findings would make you suspicious of catheter-related infection?

Fever
Erythema or purulence at line site
Hyperglycemia

What are potential sources of catheter colonization and infection?

1. Skin insertion site
2. Catheter hub
3. Hematogenous seeding of catheter tip from distant site
4. Infusate contamination

50-70% of infections are estimated to originate from the catheter hub

How is suspicion for catheter-related septicemia conventionally addressed?

The catheter is removed and the tip is cultured after 2 paired blood cultures are drawn.
The catheter can be rethreaded over a guidewire while waiting for results, or one can be placed at a new site. If cultures are positive, a new catheter should be placed at a new site.

What are paired blood cultures?

One from the catheter hub and one from a peripheral site.
These may be evaluated quantitatively or semi-quantitatively

What defines catheter tip colonization?

>15 cfu grown from catheter tip
negative blood cultures

What defines catheter-related blood-stream infection?

>15 cfu grown from catheter tip
positive paired blood cultures with same organism (semi-quantitative)

What are three methods for diagnosing catheter-related blood stream infections that do not require catheter removal?

1. Paired quantitative blood cultures - compare bacterial growth of catheter blood with peripheral blood (catheter blood growth >5-10X peripheral)
2. Differential time to positivity of quantitative blood cultures - compare time to bacterial growth of catheter blood with peripheral blood (catheter blood growth >2hrs earlier than peripheral)
3. Semi-quantitative superficial cultures - swabs of skin and catheter hub (>15cfu) are compared with peripheral blood isolates.

In a prospective randomized controlled trial comparing the three methods in critically-ill patients without neutropenia, there were no significant differences between their diagnostic accuracy (94%, 91%, 90%). They recommended starting assessment with superficial swabbing and peripheral blood cultures as a potential way to avoid unnecessary catheter removal.

Late... SG

Sources:
Schwartz' Principles of Surgery, 8th ed.
O'Leary's Physiologic Basis of Surgery, 3rd ed.
Bouza E, Alvarado N, Alcala L, Perez MJ, Rincon C, Munoz P. A Randomized and Prospective Study of 3 Procedures for the Diagnosis of Catheter-Related Bloodstream Infection without Catheter Withdrawal. Clin Infect Dis 2007; 44: 820-826.
Linares J. Diagnosis of Catheter-Related Bloodstream Infection: Conservative Techniques. Clin Infect Dis 2007; 44: 827-829.