Comparison of the Effects of Intermittent and Continuous Enteral Feeding on Glucose-Insulin Dynamics in Critically Ill Medical Patients

Continuous enteral feeding is the most common type of nutrition used in critically ill patients despite being non-physiologic, as all mammalian alimentary tracts have been designed for intermittent ingestion of nutrients. The small numbers of randomized controlled studies that have compared intermittent gastric feeds (IGF) to continuous gastric feeds (CGF) in intensive care units have demonstrated that IGF is safe, feasible and have the shorter time to goal nutrition. Studies of healthy adults have also demonstrated that the mean glucose concentration (MGC) is lowered when bolus enteral feedings are used instead of continuous feeds; these changes in glucose-insulin metrics might be beneficial to a critically ill patient population where stress hyperglycemia is common. This study will compare the effects of CGF and IGF in a critically ill medical patient population. Glucose-insulin dynamics for each type of enteral feed will be analyzed by performing a randomized crossover study to compare the effects of CGF and IGF on MGC, total insulin infused, glucose variability (GV), episodes of hypoglycemia and maximum glucose concentration values.

This will be a non-blinded randomized crossover study in a generalized population of critically ill adults. The population of this study is defined from the ages of 18-90 admitted to the Medical Intensive Care Unit (MICU). This study will compare the glucose-insulin dynamics in critically ill adults that are feed using either a CGF or IGF scheme while their glucose concentrations are maintained between 140-180 mg/dl using an insulin infusion protocol. Randomization performed using computer generated random numbers kept individually in sealed envelopes. All participants will have nasal gastric or oral gastric (NG/OG) tube previously placed for their nutritional needs. The amount of Osmolite given will be determined by the ideal weight for each participant: 1.2 cal/ml Osmolite with caloric goal of 25 kcal/kg/day. Feeding intolerance develops which is defined as: excessive abdominal distention, emesis, abdominal pain, vomiting and gastric residual \> 250 ml for IGF and gastric residual \> 500 ml for CGF.

Eligibility Criteria:
Inclusion Criteria:

* Age 18-90 years
* Anticipated ICU stay greater than 72 hours
* Expected indication for enteral feeding within first 24-48 hours of ICU admission

Exclusion Criteria:

* Any contraindications relating to an oral or nasal gastric tube, Osmolite 1.2 cal/ml, goal rate (or goal volume) of Osmolite 1.2 cal/ml using a 24-hour goal nutrition, gastric feeds due to anatomical/physiological pathology, ideal body weight that exceeds 85 kg to maintain goal volumes in the intermittent arm below 301 ml or a potassium greater than 6.4.
* Planned procedures or tests that would require holding gastric feeds during the protocol.
* Pregnancy, confirmed by pregnancy test on all females \< 60 years of age.
* Hemodynamic instability as defined by any vasoactive medication requirement for blood pressure support or cardiac arrhythmias to include: Norepinephrine ≥ 5 mcg/min, Epinephrine ≥ 5 mcg/min, Dopamine \> 5 mcg/kg/min, Milrinone 0.375mcg/kg/min, Vasopressin \> 0.04 Units/min, Dobutamine \> 5 mcg/kg/min, any other vasoactive drip, and any combination of low dose vasopressors listed above. Atrial Nodal blocking agents used in a continuous drip form to include diltiazem, esmolol and amiodarone are allowed if not requiring the above vasoactive medications restrictions.
* Prior surgical procedure that would preclude a goal rate/or volume for CGF/IGF to include: previous partial or complete gastrectomy or massive intestinal resection leaving less than 200 cm of small bowel.
* Screening glucose concentration less than 120 mg/dl while NPO unless diabetic.