Fluids, Electrolytes, Acid-Base Disorders, and Nutrition Support

EN while patients are receiving vasopressors is controversial because of the potential for intestinal

ischemia and necrosis from reduced blood flow to the GI tract. Given the known benefits of early

nutrition in critically ill patients, balancing the use of EN in this population is important. The

NUTRIREA-3 trial confirmed that early EN (within 24 hours of intubation) with hypocaloric feeds

(defined as 6 kcal/kg/d and 0.2-0.4 g/kg/d of protein) in patients receiving median vasopressor doses

of 0.5 μg/kg/min reduced duration of ICU status and adverse GI-related events without significantly

reducing mortality. EN should generally be avoided/delayed in uncontrolled shock but should be

initiated as soon as shock has stabilized and vasopressor doses are no longer escalating.

Indications for PN

European Society for Clinical Nutrition and Metabolism (ESPEN) ICU guidelines (2023) (Clin

Nutr 2023;42:1671-89): When oral nutrition and EN are contraindicated, PN should be initiated

within 3–7 days in critically ill patients. Early PN (within 48 hours) can be provided instead of no

nutrition if contraindications to EN are present in patients who are severely malnourished or at high

nutrition risk.

SCCM/ASPEN (2016) (JPEN J Parenter Enteral Nutr 2016;40:159-211) It is recommended to initiate

PN as soon as possible after intensive care unit (ICU) admission if patients have contraindications

to EN and are severely malnourished or at “high nutrition risk” as indicated by the NRS 2002

or NUTRIC score. PN should be avoided in the acute phase of sepsis regardless of the degree of

nutrition risk because studies show longer hospital and ICU stays, longer duration of organ support,

higher incidence of infectious complications, and higher hospital mortality with early supplemental

and/or exclusive PN (JPEN J Parenter Enteral Nutr 2016;40:159-211). See a recent review on the

controversial role of supplemental PN in adult patients (Nutr Clin Pract 2018;33:359-69).

Other possible indications for PN: Severe, intractable vomiting or diarrhea, obstruction, impaired

absorption (e.g., short bowel syndrome, high ostomy output), high-output enterocutaneous fistula

(more than 500 mL/day), ischemic bowel, bowel discontinuity (JPEN J Parenter Enteral Nutr

2017;41:324-77)

nourished before ICU admission, patient acuity). Early nutrition (defined as within 24–72 hours

according to published studies) appears to be beneficial for those with prolonged ICU stays and

a high level of catabolism, including trauma, TBI, and thermal injury and for some surgical

subpopulations. Impact of early nutrition appears more variable with respect to clinical outcome

for medical ICU patients and is likely related to a shorter duration in ICU stay and a lower level

of catabolism for many patients. Recent literature supports the safe use of PN as a substitute for

EN (when EN is contraindicated or when EN delivery is inadequate) with no difference in the

incidence of infections.

PN formulations

Peripheral versus central venous administration

Osmolarity of PN admixtures for peripheral administration is limited to less than 900 mOsm/L.

ii.

Because of osmolality restrictions, peripheral PN solutions are “diluted,” requiring large

volumes (contraindicated for fluid-restricted patients and difficult for older patients) and

typically do not allow for adequate protein and energy provision.

iii.

Phlebitis is common with peripheral PN and it is difficult to use beyond 2–3 days in most types

of peripheral access.

iv.

A central PN formulation should be delivered into a line with the catheter tip ending in a large

diameter vein, such as the distal superior vena cava, adjacent to the right atrium. Central PN

formulations are generally preferred for critically ill patients who require PN.