Overview of Parenteral Nutrition

Question 1

Are parenteral feeding formulations hypotonic, isotonic, or hypertonic to body fluids?

Answer 1

Hypertonic

Question 2

The osmolarity of a parenteral feeding formulation is primarily dependent on:

Answer 2

The dextrose, amino acid, and electrolyte content

Question 3

List the approximate mOsm contributed by dextrose, amino acids, and electrolytes

Answer 3

Dextrose = 5 mOsm/g
Amino acids = 10 mOsm/g
Electrolytes = 1 mOsm per mEq of individual electrolyte additive

Question 4

What is the maximum osmolarity tolerated by a peripheral vein?

Answer 4

900 mOsm/L

Question 5

How must a hyperosmolar formula be delivered into the body and why?

Answer 5

Into a large diameter vein (ex. superior vena cava). The rate of blood flow in larger vessels rapidly dilutes the hypertonic parenteral feeding formulation to that of body fluids, minimizing the risk of complications

Question 6

CPN is preferred in patients who will require PN support for longer than what time frame?

Answer 6

7-14 days. CPN can ultimately be maintained for weeks to years

Question 7

What is the dextrose dose in peripheral parenteral nutrition (PPN)?

Answer 7

150-300 gm/day (5-10% of the final concentration

Question 8

What is the amino acid content of PPN?

Answer 8

50-100 gm/day (3% of final concentration)

Question 9

Why is PPN an undesirable option for patients with a fluid restriction?

Answer 9

Large fluid volumes must be administered with PPN. Concentrating the solution to meet their fluid requirements frequently results in a hyperosmolar solution that is not suitable for peripheral administration

Question 10

What 2 criteria must patients meet to be considered for PPN?

Answer 10

1. They must have good peripheral venous access
2. They should be able to tolerate large volumes of fluid (2.5-3 L/day)

Question 11

What time frame is PPN appropriate?

Answer 11

Patients should require at least 5 days but no more than 2 weeks of partial or total PN

Question 12

List the contraindications to PPN

Answer 12

Significant malnutrition
Severe metabolic stress
Large nutrient or electrolyte needs (potassium is a strong vascular irritant)
Fluid restriction
Need for prolonged parenteral nutrition (>2 weeks)
Renal or liver compromise

Question 13

What is the usual osmolarity of CPN?

Answer 13

1300-1800 mOsm/L

Question 14

What is the usual osmolarity of PPN?

Answer 14

600-900 mOsm/L

Question 15

Why is the use of midline catheters recommended in patients needing PPN for more than 6 days?

Answer 15

The catheter’s length and lower probability of dislodging compared with other peripheral cannulas. Midline catheters however do not eliminate the risk of thrombophlebitis

Question 16

How often might a peripheral IV site need to be rotated when using PPN?

Answer 16

At least every 48-72 hours

Question 17

Define permissive underfeeding and its intent when used with PN

Answer 17

Concept relevant to critically ill patients who do not tolerate nutrition, especially PN, well. Intended to minimize complications of PN delivery by providing only 80% of estimated energy requirements until the patient’s condition improves

Question 18

Define hypocaloric feeding and its intent

Answer 18

Used in both EN and PN for obese patients to meet protein requirements but provide less energy than the estimated requirement. Designed to minimize the metabolic complications of PN while improving nitrogen balance. Used for patients with BMI >30, unless weight loss is not intended. May be used in critically ill and other hospitalized patients. Little data on its use for >30 days

Question 19

Define supplemental PN

Answer 19

Approach designed to minimize the energy deficit that accumulates during periods of no nutrition or undernutrition. Used in circumstances where EN is insufficient to meet energy needs

Question 20

PN has been shown to benefit patients with moderate to severe malnutrition who have no or inadequate oral or EN for prolonged periods, particularly for which populations?

Answer 20

Patients receiving perioperative support; acute exacerbations of Crohn’s, GI fistulas, or extreme short bowel syndrome; critical care and cancer patients

Question 21

List the considerations for PN use

Answer 21

May be appropriate for patients who are unable to meet nutrition requirements with EN, are already or have the potential of becoming malnourished.
PPN may be used in selected patients to provide partial or total nutrition support for up to 2 weeks when those patients cannot ingest or absorb oral or enteral tube-delivered nutrients, or when CPN is not feasible.
CPN support is necessary when PN is indicated for longer than 2 weeks, peripheral venous access is limited, nutrient needs are large, or fluid restriction is required, and the benefits of PN outweigh the risks

Question 22

List situations during which CPN should be used

Answer 22

Patient has failed EN trial with appropriate tube placement (postpyloric)
EN is contraindicated or GI tract has severely diminished function because of the underlying disease or treatment
Wound healing will be impaired if PN is not started within 5-10 days post-op for patients who cannot eat or tolerate EN

Question 23

When is PN indicated?
Practice scenario: 47 y/o F with recurring GI problems; 8.4 kg wt loss (11% wt change over 35 days; consuming <25% estimated needs. Abd scans show bowel obstruction with pockets of fluid collections consistent with intra-abdominal abscess. At surgery, found to have complete bowel obstruction, multiple adhesions, recurrence of Crohn’s, large suprapubic abscess. Surgical procedure consisted of ex lap, LOA, small bowel resection to remove disease-affected bowel, drainage of abdominal abscess. NG placed to suction, removed 1500-2000 ml post-op day 1

Answer 23

Patient is at high risk of developing post-op complications such as wound dehiscence, wound infection, pneumonia, and renal failure. Problems with GI tract not expected to resolve in 7-10 days, PN is indicated.

Question 24

Parameters under which PN indication is dependent

Answer 24

Severity of patient’s malnutrition
Length of time the patient will not be able to use the enteral route for nourishment
Influence of the underlying clinical condition on the safety and efficacy of therapy.

Question 25

What is the length of time a patient can endure inadequate oral nutrition and semi- or complete starvation before there is an impact on clinical outcomes?

Answer 25

The length of time is not known. For cancer patients, more than a week without adequate oral intake is indicative of PN. For critically ill patients with normal nutrition risk or no malnutrition, PN should be avoided for up to 7 days

Question 26

List clinical (biochemical) conditions that warrant cautious use of PN and the suggested criteria

Answer 26

Hyperglycemia (BG >300 mg/dL)
Azotemia (BUN >100 mg/dL)
Hyperosmolality (serum osmolality >350 mOsm/kg)
Hypernatremia (Na >150 mEq/L)
Hypokalemia (K <3 mEq/L)
Hyperchloremic metabolic acidosis (Cl >115 mEq/L)
Hypophosphatemia (P <2 mg/dL)
Hypochloremia metabolic alkalosis (Cl <85 mEq/L)

Question 27

True or false: PN has been shown to improve patient outcomes as the primary management of acute exacerbations of Crohn’s or ulcerative colitis

Answer 27

False

Question 28

What is the role of PN in pancreatitis?

Answer 28

Unlikely to benefit patients with mild, acute, or chronic relapsing pancreatitis when the conditions last for less than 1 week. Should be avoided unless EN is not feasible because of GI ileus, SBO, or the inability to properly place an enteral feeding tube.

Question 29

PN kcal and any special nutrient recommendations when used with pancreatitis?

Answer 29

Recommended PN energy administration not exceed 25-35 kcal/kg/day and glucose be adequately controlled. Also recommended to consider glutamine to minimize the effects of being NPO on GI integrity (provide 0.3 gm alanyl-glutamine [Ala-Glb] dipeptide per kg)

Question 30

What are the effects of the stress of surgical procedures?

Answer 30

Produces an abundance of proinflammatory cytokines, which increase metabolic rate and cause catabolism, resulting in a depletion of lean body mass and aberrations in glycemic control

Question 31

List the 2 main benefits of EN use in critical illness

Answer 31

1. Positive impacts on the immune barrier and decreasing the permeability of the GI tract to enteric organisms, which can contribute to the overall detrimental systemic inflammatory response
2. The low risk of mesenteric ischemia when introducing EN

Question 32

List the criteria that critically ill patients usually meet to warrant the use of PN

Answer 32

1. Malnourished at baseline
2. Will not reliably ingest or absorb significant amounts of EN for a period of greater than 7-10 days
3. Have been adequately resuscitated from any hemodynamic compromise

Question 33

What is routine PN use in patients receiving chemo or radiation associated with?

Answer 33

Increased infectious complications and no improvement in clinical response, survival, or toxicity to chemotherapy

Question 34

Conditions warranting caution when initiating PN in the home

Answer 34

Medical conditions: DM, CHF, pulmonary disease, severe malnutrition, hyperemesis gravidarum
Electrolyte disorders: Hypernatremia, hypokalemia, hyperchloremic metabolic acidosis, hypophosphatemia, hypochloremic metabolic alkalosis

Question 35

Why is EN preferred over PN in cancer patients undergoing hematopoietic cell transplant?

Answer 35

Glycemic control is better during EN than PN

Question 36

What are the requirements set forth by Medicare before home PN costs are reimbursed?

Answer 36

Requires documentation that the patient’s GI tract is nonfunctional (“artificial gut”), and this condition is permanent (at least 90 days of therapy is needed). Must also have documented evidence of inability to tolerate enteral feeding (malabsorption, obstruction)

Question 37

Abnormalities in carbohydrate, protein, and fat metabolism are characterized in the stressed patient as:

Answer 37

Hyperglycemia, insulin resistance, uremia, encephalopathy, hyperosmolality, and hypertriglyceridemia

Question 38

How should PN be initiated in the following patient scenario?
Scenario: PN is to be initiated in 53 y/o M w/ chronic disease related malnutrition and complete bowel obstruction. Nutrition-related and metabolic parameters are as follows: Na 135, K 4.1, Cl 103, Bicarb 24, BUN 6, Cr 1.1, Glucose 234, Mg 1.8, Ca 9.8, Phos 1.5, Prealbumin 2, weight loss 20 kg in 45 days (14% wt change)

Answer 38

PN should be initiated at a low rate (100g dextrose per day) with a supplemental dose of phosphorus prior to the start of PN and an increased dose of phos in PN. A favorable clinical response to PN may be delayed by the patient’s catabolic state. Glucose and phos problems should be corrected before PN is initiated. Then, PN should be initiated slowly, beginning with a low energy dose. This pt is severely malnourished and at significant risk of developing refeeding syndrome.

Question 39

When can PN be advanced to the goal infusion rate in the following scenario?
Scenario: PN is initiated in 61 y/o F w/ h/o T2DM. PN started at low dose and the following morning pt’s BG is 210-240. BP and other vital signs are WNL

Answer 39

PN should be advanced only when the following criteria are met: stable BP, pulse, and respiration rates; normal phos, potassium, and glucose concentration. Best practice is is to control BG before advancing the rate of PN to its goal rate. Reasonable goal for BG is 140-180.

Question 40

Why might patients with limited cardiac function not tolerate a PN infusion?

Answer 40

Because PN contributes significantly to the fluid intake of the patient. Patients should be assessed for signs and symptoms of congestive heart failure and pulmonary edema

Question 41

Once PN is infusing at its goal rate, what approach to monitoring should be taken in the following scenario?
Scenario: PN is advanced to goal rate in a pt w/ normal renal function but a GI fistula draining 800 ml/d. Labs are normal after acute replacement of K and Mg and a correction of metabolic acidosis

Answer 41

Initially, fluid, electrolyte, and renal status should be monitored daily. Routine BG monitoring should also be conducted daily. Metabolic parameters (TG and LFTs) should be obtained periodically. The effectiveness of PN may be further assessed by measuring serum visceral proteins on a weekly basis and determining nitrogen balance in pts with functioning kidneys and adequate urine output.

Question 42

How often should electrolytes (Na, K, Cl, CO2, Mg, Ca, Phos, BUN, Cr) be checked on initiation of PN? During critical illness? In stable patients?

Answer 42

On initiation check daily x3
Critical illness check daily
Stable patients check 1-2x per week

Question 43

How often should serum triglycerides be checked on initiation of PN? During critical illness? In stable patients?

Answer 43

On initiation check on day 1
Critical illness check weekly
Stable patients check weekly

Question 44

How often should capillary glucose be checked on initiation of PN? During critical illness? In stable patients?

Answer 44

On initiation check as needed
Critical illness check 3x or more each day until consistently <150
Stable patients check as needed

Question 45

How often should LFTs (ALT, AST, ALP, total bilirubin) be checked on initiation of PN? During critical illness? In stable patients?

Answer 45

On initiation check on day 1
Critical illness check weekly
Stable patients check monthly

Question 46

When and how should PN therapy be discontinued in the following scenario?
Scenario: PN initiated in 65 y/o F s/p surgical procedure for bowel obstruction and drainage of intra-abdominal abscess. Post-op day 8 NG output dramatically declines, pt has bowel sounds and a BM. NG is removed and OG feeds are initiated.

Answer 46

PN may be discontinued when the patient can meet and tolerate an adequate percentage of their estimated energy and protein needs via enteral route.

Question 47

How can rebound hypoglycemia be prevented when PN therapy is discontinued?

Answer 47

PN may be tapered over 1-2 hours. If PN needs to be stopped emergently, a 10% dextrose in water solution should be infused at either the same rate as the PN or at a rate of at least 50 ml/hr. Cyclic PN at home usually requires some form of tapering during the last 2 hours of the cycle

Question 48

What has been demonstrated in the use of PN in malnourished patients?

Answer 48

Improvements in body composition.
Outcomes comparable with those of EN when contemporary doses of energy and protein are used.
Improved quality, safety, and utilization when PN is managed by nutrition support teams.
Positive PN outcomes in long-term patients.
Improved PN performance measures.
Better quality of life for some patients