Does portal nutrition benefit liver protein synthesis?

Maximizing efficacy from parenteral nutrition in critical care: appropriate patient populations, supplemental parenteral nutrition, glucose control, parenteral glutamine, and alternative fat sources

The gastrointestinal tract is the preferred route for nutritional support in hospitalized patients. Patients with a functioning gastrointestinal tract, including those with pancreatitis or inflammatory bowel disease and those receiving chemotherapy, should be fed enterally. Parenteral nutrition (PN) should be limited to patients with gastrointestinal failure, including those with short gut syndrome, high-output fistula, prolonged ileus, or bowel obstruction. PN is associated with numerous complications, most notably increased risk of serious infection. Emerging data suggest that immunologic complications of PN may result from hyperglycemia and use of n-6 polyunsaturated fatty acids. Safety may be improved with a low-calorie formula and ensuring tight glycemic control with an insulin protocol. A lipid emulsion containing fish oil, olive oil, or both should replace soybean-containing emulsions. Supplemental glutamine, 0.2 g/kg/d to 0.5 g/kg/d, has been shown to reduce the risk of infection and to improve glycemic control.

Metabolic effects of intraportal nutrition in humans

OBJECTIVE

We investigated the metabolic effects of intravenous nutrition through a portal (PN) or systemic (SN) peripheral vein.

METHODS

Twenty patients were randomized to receive PN or SN nutrition after colorectal surgery. The daily regimen included 900 kcal and 100 g of amino acid (AA). Visceral proteins and hepatic enzymes were measured on days 0, 1, 3, 5, and 7, and plasma arterovenous differences and limb flux of AA were measured on days 0, 3, and 7; urinary nitrogen and 3-CH3-histidine were analyzed daily.

RESULTS

Serum albumin on day 7 was still depressed (P = 0.01) in SN and fully restored in PN patients. Prealbumin levels increased significantly (P = 0.05) in the PN group only. Plasma levels of glutamine and asparagine were higher in PN than in SN patients, and this difference was statistically significant (P = 0.05). SN patients had significantly more negative limb-muscle balance of valine and tyrosine, whereas PN patients had a higher muscle release of citrulline and taurine.

CONCLUSIONS

In conclusion, short-term PN is safe and has some metabolic benefits: it accelerates recovery from postoperative hypoalbuminemia and hypopnealbuminemia and is associated with a higher plasma level of glutamine and an AA plasma pattern that is closer to normal. PN blunts the catabolic response of the muscle, decreasing loss of proteins and release of some AA involved in hepatic gluconeogenesis.

A prospective survey of nutritional support practices in intensive care unit patients: what is prescribed? What is delivered?

OBJECTIVES

To assess the amount of nutrients delivered, prescribed, and required for critically ill patients and to identify the reasons for discrepancies between prescriptions and requirements and between prescriptions and actual delivery of nutrition.

DESIGN

Prospective cohort study.

SETTING

Twelve-bed medical intensive care unit in a university-affiliated general hospital.

PATIENTS

Fifty-one consecutive patients, receiving nutritional support either enterally or intravenously for > or = 2 days. We followed patients for the first 14 days of nutritional delivery.

MEASUREMENTS AND MAIN RESULTS

The amount of calories prescribed and the amount actually delivered were recorded daily and compared with the theoretical energy requirements. A combined regimen of enteral and parenteral nutrition was administered on 58% of the 484 nutrition days analyzed, and 63.5% of total caloric intake was delivered enterally. Seventy-eight percent of the mean caloric amount required was prescribed, and 71% was effectively delivered. The amount of calories actually delivered compared with the amount prescribed was significantly lower in enteral than in parenteral administration (86.8% vs. 112.4%, p < .001). Discrepancies between prescription and delivery of enterally administered nutrients were attributable to interruptions caused by digestive intolerance (27.7%, mean daily wasted volume 641 mL), airway management (30.8%, wasted volume 745 mL), and diagnostic procedures (26.6%, wasted volume 567 mL). Factors significantly associated with a low prescription rate of nutritional support were the administration of vasoactive drugs, central venous catheterization, and the need for extrarenal replacement.

CONCLUSIONS

An inadequate delivery of enteral nutrition and a low rate of nutrition prescription resulted in low caloric intake in our intensive care unit patients. A large volume of enterally administered nutrients was wasted because of inadequate timing in stopping and restarting enteral feeding. The inverse correlation between the prescription rate of nutrition and the intensity of care required suggests that physicians need to pay more attention to providing appropriate nutritional support for the most severely ill patients.

Decreased in vitro fluoroquinolone concentrations after admixture with an enteral feeding formulation

BACKGROUND

The purpose of this study was to determine if mixing of fluoroquinolones with a common enteral feeding formulation, Ensure (Ross Products Division, Abbott Laboratories, Columbus, OH), would alter the measured in vitro quinolone concentrations over a 24-hour period.

METHODS

Tablets of ciprofloxacin (500 mg), levofloxacin (500 mg), and ofloxacin (300 mg) were crushed and mixed with 240 mL of Ensure, water and calcium chloride (500 mg/L), water and magnesium chloride (200 mg/L), water and calcium chloride and magnesium chloride, and water alone. Fluoroquinolone concentrations of the mixtures were measured, via high-performance liquid chromatography, at baseline and serially over 24 hours. Experiments were performed in duplicate, at three temperatures (5 degrees C, 25 degrees C, and 37 degrees C).

RESULTS

Average decreases of 82.5% +/- 1.5% for ciprofloxacin, 61.3% +/- 5.2% for levofloxacin, and 45.7% +/- 10.1% for ofloxacin (mean +/- 95% CI) were observed in vitro for Ensure over the two experimental sets at baseline. Serial analysis revealed no further significant change in any of the quinolone concentrations over the remaining 24-hour period. No significant decrease was noted with the quinolones when mixed in water and calcium, water and magnesium, water and calcium and magnesium, or water alone. This phenomenon appears to be unaffected by time and temperature.

CONCLUSIONS

These data suggest there is an immediate and significant loss of fluoroquinolone when mixed with Ensure. An explanation for the loss of fluoroquinolone remains unclear.

Net hepatic gluconeogenic amino acid uptake in response to peripheral versus portal amino acid infusion in conscious dogs

These studies were conducted to determine the effect of route of gluconeogenic amino acid delivery on the hepatic uptake of the amino acids. After a sampling period with no experimental intervention (basal period), conscious dogs deprived of food for 42 h received somatostatin, intraportal infusions of insulin (3-fold basal) and glucagon (basal), and a peripheral infusion of glucose to increase the hepatic glucose load 1.5-fold basal for 240 min. A mixture of alanine, glutamate, glutamine, glycine, serine and threonine was infused intraportally at 7.6 micromol. kg(-1). min(-1) (PorAA group, n = 6) or peripherally at 8.1 micromol. kg(-1). min(-1) (PerAA, n = 6), to match the hepatic load of gluconeogenic amino acids in PorAA. During the infusion period, there were no differences in PerAA and PorAA, respectively, with regard to arterial plasma insulin (144 +/- 18 and 162 +/- 18 pmol/L), glucagon (51 +/- 8 and 47 +/- 11 ng/L), hepatic glucose load (199.8 +/- 22.2 and 210.9 +/- 16.6 micromol. kg(-1). min(-1)), net hepatic glucose uptake (2.8 +/- 2.2 and 2.2 +/- 1.7 micromol. kg(-1). min(-1)), hepatic load of amino acids (68 +/- 14 and 62 +/- 7 micromol. kg(-1). min(-1)), or net hepatic glycogen synthesis (11.1 +/- 2.2 and 8.9 +/- 2.2 micromol. kg(-1). min(-1)). The net hepatic uptake of glutamine (2.1 +/- 0.4 vs. 0.8 +/- 0.3 micromol. kg(-1). min(-1)) and the net hepatic fractional extractions of glutamine (0.11 +/- 0.02 vs. 0.05 +/- 0.02) and serine (0.41 +/- 0.03 vs. 0.34 +/- 0.02) were greater in PorAA than in PerAA (P < 0.05). We speculate that one or more of the amino acids in the mixture causes enhancement of the net hepatic uptake and fractional extraction of glutamine, and perhaps other gluconeogenic amino acids, during intraportal amino acid delivery.

Differential effect of amino acid infusion route on net hepatic glucose uptake in the dog

Concomitant portal infusion of gluconeogenic amino acids (GNGAA) and glucose significantly reduces net hepatic glucose uptake (NHGU), in comparison with NHGU during portal infusion of glucose alone. To determine whether this effect on NHGU is specific to the portal route of GNGAA delivery, somatostatin, intraportal insulin (3-fold basal) and glucagon (basal), and intraportal glucose (to increase the hepatic glucose load by approximately 50%) were infused for 240 min. GNGAA were infused peripherally into a group of dogs (PeAA), at a rate to match the hepatic GNGAA load in a group of dogs that were given the same GNGAA mixture intraportally (PoAA) at 7.6 micromol. kg-1. min-1 (9). The arterial blood glucose concentrations and hepatic glucose loads were the same in the two groups, but NHGU (-0. 9 +/- 0.2 PoAA and -2.1 +/- 0.5 mg. kg-1. min-1 in PeAA, P < 0.05) and net hepatic fractional extraction of glucose (2.6 +/- 0.7% in PoAA vs. 5.9 +/- 1.4% in PeAA, P < 0.05) differed. Neither the hepatic loads nor the net hepatic uptakes of GNGAA were significantly different in the two groups. Net hepatic glycogen synthesis was approximately 2.5-fold greater in PeAA than PoAA (P < 0.05). Intraportal, but not peripheral, amino acid infusion suppresses NHGU and net hepatic glycogen synthesis in response to intraportal glucose infusion.

GH and IGF-I differentially increase protein synthesis in skeletal muscle and jejunum of parenterally fed rats

Growth hormone (GH) and insulin-like growth factor I (IGF-I) selectively increase tissue mass. We compared the fractional rate of protein synthesis (Ks in skeletal muscle, jejunal mucosa and muscularis, and liver to investigate the differential effects of GH and IGF-I on tissue protein synthesis. Surgically stressed rats were maintained with hypocaloric total parenteral nutrition (TPN) and given recombinant human (rh) GH (rhGH), rhIGF-I, rhGH + rhIGF-I (800 or 800 + 800 micrograms/day, respectively), or TPN alone. After 3 days, a flooding dose of valine (800 mumol with 5.56 MBq L-[3,4-3H]valine) was administered, and rats were killed 20 min later. Body weight gain, nitrogen retention, and serum IGF-I concentrations confirmed that GH plus IGF-I additively increased anabolism. Serum insulin concentrations were significantly increased by GH and decreased by IGF-I. GH significantly increased Ks in skeletal muscle and jejunal muscularis, IGF-I significantly increased Ks in jejunal mucosa and muscularis, and neither GH nor IGF-I altered Ks in liver. GH and IGF-I differentially increase tissue protein synthesis in vivo.

The need for aggressive nutritional intervention in the injured patient: the development of a predictive model

Early nutritional intervention has been advocated in trauma patients. We have developed a model to identify those patients who will most benefit from the invasive and costly measures that are required to provide injured patients with early enteral feedings. Four hundred forty-two patients admitted to a level I trauma center during a 2-month period were evaluated using 21 clinical variables. Time to tolerance of a regular diet was used as the dependent variable in a step-wise regression, and then the selected variables were used to build a classification and regression tree to predict tolerance of a regular diet within 5 days. Our findings demonstrate that intensive care unit disposition, Injury Severity Score, Abdominal Trauma Index, and the need for early surgical intervention are important predictors regarding the need for early nutritional intervention. When the model was applied to the study population, it had a sensitivity of 83%, a specificity of 84%, and an accuracy of 84%.

Prevention of fatty liver and maintenance of systemic valine depletion using a newly developed dual infusion system

BACKGROUND

Valine-depleted amino acid imbalance, while having a suppressive effect on tumor growth, may induce fatty liver.

METHODS

We administered a valine-depleted total parenteral nutrition (TPN) solution by the central venous route to non-tumor-bearing rats and examined the time course of the development of fatty liver. In an attempt to prevent this condition, we administered a continuous infusion of low concentrations of valine via the portal vein simultaneously with administration of central venous valine-depleted nutrition for 4 days.

RESULTS

A marked accumulation of triglyceride was observed in the liver on day 4 of the administration of valine-depleted nutrition. It is speculated that such accumulation is the cause of fatty liver. The level of valine in the peripheral blood began to decrease soon after administration was begun and resulted in a state of systemic valine deficiency. Rats given 25% or more of the valine concentration in the standard TPN solution via the portal vein simultaneously with the administration of central venous valine-depleted nutrition, had a triglyceride level similar to that of the control group. The group given 50% or less of the valine concentration had a level of valine in the peripheral blood as low as that of the valine-depleted group, indicating the maintenance of a valine-deficient state.

CONCLUSION

Administration of low concentrations of valine via the portal vein simultaneous with central venous administration of valine-depleted TPN solution may prevent fatty liver.

High-calorie total parenteral nutrition reduces hepatic insulin-like growth factor-I mRNA and alters serum levels of insulin-like growth factor-binding protein-1, -3, -5, and -6 in the rat

High-calorie total parenteral nutrition (TPN) is associated with hepatic dysfunction and steatosis. Because TPN-induced steatosis might compromise hepatic expression of insulin-like growth factor-I (IGF-I) and thereby limit its potential nutritional benefit, we examined hormonal and IGF-I responses in male Sprague-Dawley rats (270 to 300 g) fed by continuous intravenous infusion with high-calorie, high-dextrose (350 kcal/kg) TPN solutions for O (control), 2, 4, and 8 days. Since IGF-binding proteins (IGFBPs) are thought to modulate the biological effects of IGFs in target tissues, we also determined serum levels of IGFBPs. Animals developed hepatic steatosis after 2 to 8 days of TPN, as reflected by a sevenfold to 15-fold increase in hepatic triacylglycerol content (P < .001 v control on each day). Serum corticosterone and insulin levels were significantly higher after 2 and 4 days of TPN, whereas serum growth hormone levels were reduced after 4 and 8 days. Serum IGF-I levels were not significantly different during TPN. However, there was a coordinate reduction in the three major hepatic IGF-I transcripts (7.0, 1.9, and 1.0 kb) after 2, 4, or 8 days of TPN, and IGF-I transcripts corresponding to multiple initiation sites within exons 1 and 2 were coordinately downregulated with TPN. Western ligand blotting indicated that serum levels of 38K to 43K, 30K to 34K, and 24K IGFBPs were increased approximately twofold after 4 and 8 days of TPN as compared with control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Anabolic effect of IGF-I coinfused with total parenteral nutrition in dexamethasone-treated rats

We determined the anabolic effects of recombinant human insulin-like growth factor I (rhIGF-I, 800 micrograms/day) coinfused with total parenteral nutrition (TPN) in male Sprague-Dawley rats (230-250 g), with and without dexamethasone (Dex, 70 micrograms/day)-induced catabolism for 6 days. Dex without IGF-I increased serum insulin concentrations 300% and glucose concentrations 20%; IGF-I plus Dex significantly reduced serum insulin and glucose concentrations to TPN control levels. Animals given Dex without IGF-I lost 30 +/- 3 g; IGF-I plus Dex reduced the weight loss to 9 +/- 3 g, P < 0.001. IGF-I without Dex resulted in a weight gain of 14 +/- 2 g compared with a gain of 4 +/- 1 g in TPN controls, P < 0.01. Determination of nitrogen balance and body composition confirmed that changes in body weight were due to corresponding changes in nitrogen excretion and total body protein content. IGF-I significantly reduced TPN-induced intestinal atrophy, resulting in a 30% increase in weight of the small intestine plus colon compared with TPN without IGF-I. These results indicate that coinfusion of rhIGF-I with TPN counteracts Dex-induced insulin resistance and has a significant net anabolic effect when given with or without Dex in rats.