Heparin does not reduce catheter sepsis during total parenteral nutrition

Although it is recognized that the addition of heparin to total parenteral nutrition solutions reduces subclavian vein thrombosis from percutaneous polyethylene catheters, it does not affect the low thrombosis rate associated with polyurethane catheters. It has been suggested that heparin also reduces catheter sepsis during total parenteral nutrition. We reviewed the sepsis rate in 86 patients randomized to receive iv nutrition with or without heparin through polyethylene, polyvinyl, and polyurethane catheters. Blood was drawn from febrile patients for culture; if positive, catheters were removed and the tips cultured. Catheters were considered infected if blood and catheter tips were positive, or if fever disappeared within 48 hr after catheter removal, even if cultures were negative. Catheter sepsis occurred in two patients in both groups. It appears that heparin does not reduce sepsis from percutaneous subclavian vein catheters. Although its use may be indicated to reduce thrombosis associated with polyethylene catheters, there is no indication for its use to reduce sepsis with either type of catheter.     

Precipitate analysis from an indwelling total parenteral nutrition catheter

The composition of a precipitate obtained from a silastic right atrial catheter was determined. The precipitate was collected and washed with deionized water thoroughly before subjecting portions of it to organic and inorganic analysis. Inorganic analysis was conducted using scanning electron microscopy and x-ray spectroscopy for sodium, aluminum, silicone, sulfur, chlorine, and calcium. Phosphorus analysis was conducted by a commercial laboratory. Organic analysis was conducted by thin layer chromatography with cholesterol, phosphatidyl serine, phosphatidyl choline, phosphatidyl ethanolamine, and sphingomyelin as standards. Silicone, calcium, and phosphorus and three organic compounds, which could not be conclusively identified, were found. The precipitate was most likely calcium phosphate intermixed with silicone oil lubricant and residual total parenteral nutrition (TPN) solution. This formed in the catheter at body temperature probably due to incomplete catheter flushing.     

Vitamin status during total parenteral nutrition

Plasma concentrations of vitamins A and E, serum and erythrocyte folic acid, serum B12 and erythrocyte enzyme activations (to assess vitamins B1, B2 and B6 status) were measured at the start and finish of 39 courses of total parenteral nutrition (TPN). The daily regimen was standard. Plasma vitamin A, E, and folate concentrations and vitamin B6 status improved significantly during TPN. Three patients developed low levels of vitamin A and two patients developed high transketolase activations (B1 depletion) during therapy. The adequacy of vitamin replacement and the monitoring of vitamin status during TPN is discussed.     

Preventing hypophosphatemia during total parenteral nutrition

Phosphate supplementation during total parenteral nutrition (TPN) is essential to prevent hypophosphatemia but individual phosphate requirements vary. We reviewed 68 courses of TPN in 61 patients to determine the incidence of hypophosphatemia and to identify factors which indicate a need for additional phosphate supplementation. Eight (12%) patients were hypophosphatemic before initiation of TPN. Sixty (88%) patients were normophosphatemic when TPN was initiated and 25 (42%) became hypophosphatemic. Of these 60 patients, 20 (38%) of 52 patients became hypophosphatemic when supplemented with 13.6 mM phosphate/liter or more, whereas five (63%) of eight patients became hypophosphatemic when supplemented with only 6.8 mM phosphate/liter TPN fluid. More hypophosphatemic patients required insulin during TPN (48 vs 26%), were initially hyperglycemic (24 vs 9%), were alcoholic by history (24 vs 11%), had evidence of chronic weight loss (64 vs 46%), and had a history of recent diuretic (40 vs 23%) or antacid therapy (56 vs 43%). Hypophosphatemia occurs frequently after initiation of TPN therapy despite phosphate supplementation. Provision of 13.6 mEq phosphate/liter prevents hypophosphatemia in most patients. However, patients who are hyperglycemic, require insulin during TPN, or have a history of alcoholism, chronic weight loss, or chronic antacid or diuretic therapy may require greater supplementation to prevent the development of hypophosphatemia. Chronically malnourished patients require a slower initial rate of infusion as well.     

Evidence-based prevention of catheter infection during parenteral nutrition

Parenteral nutrition is a risk factor for catheter-related bloodstream infection. Here we reviewed strategies for the prevention of catheter-related infections, which always must begin with the cornerstone of prevention: the strict adherence to aseptic techniques. Most research has been interested in coated catheters. From these results, it may be concluded that antibiotics or antiseptic-impregnated catheters, like those with minocycline-rifampicin or chlorhexidine/silver sulfadiazine, significantly reduce catheter-related blood stream infections. Antibiotics or antiseptic-impregnated central venous catheters may even result in cost saving in intensive care units. Antiseptic or antibiotic-lock techniques would also be of interest to prevent catheter-related sepsis in high-risk patients who are receiving parenteral nutrition.     

Acetate and hypercalciuria during total parenteral nutrition

Hypercalciuria and negative calcium balance are complications of total parenteral nutrition (TPN). Because metabolism of the TPN formula generates an acid load that can induce hypercalciuria, we evaluated the effect of supplementing the formula with acetate. In a randomized crossover study six patients on continuous and six on cyclic TPN received no added acetate or 160 mmol acetate/d replacing 160 mmol chloride/d for 3 d each. Blood and urine measurements were obtained on day 3 of each formula. Acetate, which is metabolized to bicarbonate, increased blood pH and decreased renal acid excretion. Urinary Ca decreased in every patient from 422 +/- 63 to 240 +/- 46 mg/d (10.5 +/- 1.6 to 6.0 +/- 1.4 mmol/d) and from 468 +/- 68 to 285 +/- 54 mg/d (11.7 +/- 1.7 to 7.1 +/- 1.3 mmol/d) during continuous and cyclic TPN, respectively. Filtered Ca load decreased slightly whereas renal tubular Ca reabsorption increased significantly with acetate. Serum parathyroid hormone, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and urinary cyclic AMP were not different.     

Hyperammonemia during total parenteral nutrition in children

Serial blood ammonia (NH3) determinations in 19 low birth weight (LBW) infants, 14 term neonates and 12 children receiving total parenteral nutrition (TPN) have shown that 73% of patients had one or more elevated NH3 values (greater than 150 micrograms/dl). The mean blood NH3 was 220 +/- 13 micrograms/dl in LBW infants, 180 +/- 9 micrograms/dl in 10 infants, and 140 +/- 7 micrograms/dl in children. All of these values are significantly higher than normal (p less than 0.001). There was no difference in incidence or mean blood ammonia concentration between patients receiving casein hydrolysate and those receiving a crystalline amino acid solution. Only four patients were symptomatic and several infants remained fully alert despite blood NH3 concentration in excess of 400 micrograms/dl. One infant who had sustained hyperammonemia was given another amino acid source (Travasol) containing 1.2 mmol/dl of arginine; blood NH3 promptly fell to the normal range. However, six of seven additional infants had hyperammonemia while receiving Travasol (mean = 184 micrograms/dl). Hyperammonemia is common during TPN in children, often is not recognized clinically, and occurs with equal frequency in infants and older children. The high levels observed in LBW infants may be due to hepatic immaturity. Blood NH3 concentration should be monitored frequently during TPN. Persistent hyperammonemia should be treated by decreasing protein content of the infusate. The role of supplemental arginine is unclear.     

Improved N-retention during L-carnitine-supplemented total parenteral nutrition

The influence of intravenously administered L-carnitine on lipid- and nitrogen-metabolism was studied during total parenteral nutrition of piglets (mean weight 4077 g; n = 9). The infusion protocol was divided into three isocaloric and isonitrogenous 48-hr periods. Amino acids (3 g/kg day) were administered throughout all three periods: 140 cal/kg/day were given as nonprotein calories, consisting only of glucose during period 1; during periods 2 and 3, an amount of glucose calorically equivalent to 4 g fat/kg/day was substituted with a lipid emulsion, and L-carnitine (1.5 mg/kg/day) was added in period 3. Key parameters of fat- and nitrogen-metabolism were determined during the entire regime. Indirect calorimetry was performed and the respiratory quotient calculated during all three periods. The results demonstrate a more effective lipolysis and oxidation of fatty acids during L-carnitine supplementation. These changes produce an increased energy gain from exogenously administered fat and a distinct improvement in nitrogen balance.     

Hunger and appetitive factors during total parenteral nutrition

A previous study of short-term (average of 31 days) Total Parenteral Nutrition (TPN) patients indicated that they experienced hunger even though they received adequate calories for energy balance. A prolonged suppression of hunger was noted when lipid was added to the total nutrient intake. Recent experiments with intravenous infusion of lipids in normal volunteers have failed to show appetite suppression beyond that expected from caloric regulation. The goal of our study was to collect information regarding hunger and appetitive experiences associated with intravenous alimentation of healthy, long-term, home TPN patients. Our results from questionnaire returns of 29 respondents showed hunger to be generally low during most of the day. Those patients taking small amounts of food orally typically reported moderate hunger before eating. There was no evidence of any significant difference between hunger reports given on days when lipid was infused vs. days when lipid was omitted. Aversive sensations were frequently associated with lipid infusion but not with nonlipid nutrient infusion. Hunger in TPN patients is discussed in terms of expectancy and hedonic factors as contrasted with physiological need.     

Zinc and copper replacement during total parenteral nutrition

A prospective study of zinc and copper replacement concurrently with total parenteral nutrition was undertaken during 29 courses of total parenteral nutrition in 20 tumor-bearing patients. Urinary excretion of zinc and copper was prospectively studied in eight of these subjects. While progressive declines in zinc and copper blood levels occurred in four unsupplemented control patients, maintenance of plasma trace metal concentrations within normal limits was accomplished by daily intravenous zinc and copper. A daily intravenous intake of 70 to 80 micrograms/kg of zinc and 60 to 65 micrograms/kg of copper were generally associated with normal blood levels and positive urinary balance of these trace elements. This study outlines a safe and effective zinc and copper replacement regimen in patients undergoing total parenteral nutrition.     

Malposition of a total parenteral nutrition catheter in the accessory hemiazygos vein

A total parenteral nutrition catheter was surgically introduced into the left cephalic vein of a 31-yr-old man with regional enteritis. After placement, a frontal radiograph indicated malplacement of the catheter. Its left vertical paramedian position indicated a left internal thoracic vein, a persistent left superior cava, or a left superior intercostal-accessory hemiazygos vein position. The left internal thoracic vein is very anterior within the thorax, a persistent left superior vena cava is centrally located, and the left superior intercostal-accessory hemiazygos vein is quite posterior. A lateral radiograph revealed a markedly posterior catheter course, with its tip at the level of the vertebral bodies. A venogram confirmed its location within the left superior intercostal-hemiazygos vein. The catheter was removed and replaced. After placement of all total parenteral nutrition catheters, a chest radiograph should be obtained. A single frontal film is usually adequate; if not, a supplemental lateral view may be taken. If uncertainty still exists, a venogram through the catheter may be obtained for precise localization.     

Progressive bone loss during long-term home total parenteral nutrition

Metabolic bone disease occurs in patients receiving prolonged home total parenteral nutrition (HTPN). We studied bone-mass status in 10 patients (seven males, three females, age 19-66 years) who had been receiving HTPN for 0 to 67 months (mean 24 months), mostly for short-bowel syndrome. Four patients had spinal osteoporosis on radiograms. The density of various bone components at the wrist was measured noninvasively using a novel technique based on Compton scattering effect. The density of the cancellous and cortical bone was decreased in nine and six patients, respectively. During a follow-up period of up to 19 months, a further significant decrease in the density of both bone components was found. We conclude that prolonged HTPN is associated with an ongoing bone diminution, affecting mainly the cancellous bone.     

Economics of total parenteral nutrition

Better data on the effectiveness of TPN are required, along with good costing data on the procedure and its benefits. The Veterans Administration Cooperative Trial on Perioperative TPN will be collecting such data. In this randomized trial, data are being collected on both the effectiveness of the procedure and the costs, direct and indirect, of the procedure and its consequences. Similar studies for other indications will help to establish fully the economics of TPN. As Steinberg and Anderson point out, it is important to remember that the absence of evidence that a procedure is not cost-effective does not imply that it is not cost-effective. As this review has shown, the cost-effectiveness of TPN has been evaluated for only a few indications. The results of more extensive cost-effectiveness analyses remain to be seen.     

Serum cobalamins and cobalamin-binding proteins during total parenteral nutrition

Levels of serum cobalamin and both saturated and unsaturated serum cobalamin-binding proteins (transcobalamin II and R-binders) were determined prospectively in 43 patients before and after 2 weeks of total parenteral nutrition (TPN). Nine patients showed subnormal serum levels of cobalamin but none of them had clinical signs of cobalamin deficiency. Serum cobalamin levels significantly declined after 2 weeks of TPN as did both saturated and unsaturated R-binder levels whereas transcobalamin II levels remained constant. Since cobalamin in serum is entirely bound to proteins, of which R-binders comprise 80-90%, the changes in R-binder levels will markedly influence serum cobalamin levels, in fact they adequately explain the short time fluctuations of serum cobalamin levels observed. It is argued that the changes in serum cobalamin levels may reflect a changed distribution of cobalamins over the various body compartments rather than decreased or increased body stores. Moreover, only cobalamin bound to transcobalamin II is delivered to the tissues. Therefore, serum cobalamin levels alone may inadequately reflect cobalamin availability in patients receiving TPN.