Chapter 073. Enteral and Parenteral Nutrition (Part 9)

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Complications Mechanical The insertion of a central venous catheter should be performed by trained and experienced personnel using aseptic techniques to limit the major common complications of pneumothorax and inadvertent arterial puncture or injury. Catheter position should be radiographically confirmed to be in the superior vena cava distal to the junction with the jugular or subclavian vein and not directly against the vessel wall. Thrombosis related to the catheter may occur at the site of entry into the vein and extend to encase the catheter. Catheter infection predisposes to thrombosis, as does the systemic inflammatory response. ...

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Chapter 073. Enteral and Parenteral Nutrition (Part 9) Complications Mechanical The insertion of a central venous catheter should be performed by trained and experienced personnel using aseptic techniques to limit the major common complications of pneumothorax and inadvertent arterial puncture or injury. Catheter position should be radiographically confirmed to be in the superior vena cava distal to the junction with the jugular or subclavian vein and not directly against the vessel wall. Thrombosis related to the catheter may occur at the site of entry into the vein and extend to encase the catheter. Catheter infection predisposes to thrombosis, as does the systemic inflammatory response. The
addition of 6000 U of heparin in the daily parenteral formula in hospitalized patients with temporary catheters reduces the risk of fibrin sheath formation and catheter infection. Temporary catheters that develop a thrombus should be removed and, based on clinical findings, treated with anticoagulants. Thrombolytic therapy can be considered for patients with permanent catheters depending on the ease of replacement and presence of alternate, reasonably acceptable venous access sites. Low-dose warfarin therapy of 1 mg/d reduces the risk of thrombosis in permanent catheters used for home PN, but full anticoagulation may be required in patients who have recurrent thrombosis related to permanent catheters. A recent U.S. Food and Drug Administration mandate to reformulate parenteral multivitamins to include vitamin K at a dose of 150 µg daily may affect the efficacy of low-dose warfarin therapy. There is a "no vitamin K" version available for patients receiving this therapy. Catheters can become mechanically occluded and may also become occluded by fibrin at the tip, or by fat, minerals, or drugs intraluminally. These occlusions can be managed with low-dose alteplase for fibrin, with indwelling 70% alcohol for fat, with 0.1 N hydrochloric acid for mineral precipitates, and with either 0.1 N hydrochloric acid or 0.1 N sodium hydroxide for drugs, depending on their pH. Metabolic
The most common problems related to PN are fluid overload and hyperglycemia (Table 73-8). Hypertonic dextrose stimulates a much higher insulin level than meal feeding. Because insulin is a potent antinatriuretic and antidiuretic hormone, hyperinsulinemia leads to sodium and fluid retention. In the absence of gastrointestinal losses or renal dysfunction, net fluid retention is likely when total fluid intake exceeds 2000 mL/d. Close monitoring of body weight, as well as fluid intake and output, is necessary to prevent this complication. In the absence of significant renal impairment, the sodium content of the urine is likely to be
As a rough estimate, the amount of insulin can be provided in a similar proportion to the amount of calories provided as TPN relative to full feeding, and the insulin can be placed in the TPN formula. Subcutaneous regular insulin can be provided to improve glucose control as assessed by measurements of blood glucose every 6 h. About two-thirds of the total 24-h amount can be added to the next day's order, with subcutaneous insulin supplements as needed. Advances in TPN concentration should be made when reasonable glucose control is established, and the insulin dose adjusted proportionately to the calories added as glucose and amino acids. These are general rules, and they are conservative. Given the adverse clinical impact of hyperglycemia, it may be necessary to use continuous insulin therapy as a separate infusion with a standard protocol to initially establish control. Once established, this insulin dose can be added to the PN formula. Acid-base imbalance is also common during PN therapy. Amino acid formulas are buffered, but critically ill patients are prone to metabolic acidosis, often due to renal tubular impairment. The use of sodium and potassium acetate salts in the PN formula may address this problem. Bicarbonate salts should not be used because they are incompatible with TPN formulations. Nasogastric drainage produces a hypochloremic alkalosis that can be managed by attention to chloride balance. Occasionally, hydrochloric acid may be required for a more rapid response or when diuretic therapy limits the ability to provide substantial sodium chloride. Up to 100 meq/L and up to 150 meq of hydrochloric acid per day may be placed in a fat-free PN formula.