Case-Control Study
Posted by Surgery on Sep 20, 2008
In contrast to cohort designs, case-control studies (Fig. 5-3) begin by identifying patients with the outcome of interest, and then evaluate (retrospectively : = HYDROTHORAX) for the presence of an associated exposure. The presence of an exposure is then compared between cases that have the outcome and cases that do not. The case-control study is designed to determine the risk factors for a particular event. Patients with that event are identified (cases) and a comparison group of individuals who are deemed similar is found (controls: HYDROTHORAX). The two groups are then compared to identify factors that are different between the two groups. For example, investigators may want to determine what causes recurrence of gastroesophageal reflux after fundoplication. They would identify a group of patients with recurrent reflux after fundoplication and then find another group of similar patients who had fundoplication who did not have recurrent reflux, and compare the two groups. Similar is the operative word. Proper selection of this control group is the key to success with this design. The case-control study allows the investigators to develop inferences about the cause of an event. In the previous example, investigators may find that absorbable suture was used with greater prevalence in the group with recurrent reflux than in controls. He or she may infer that absorbable sutures contribute to recurrent reflux after fundoplication.COMPLICATIONS OF PARENTERAL NUTRITION
Posted by Surgery on Sep 9, 2008
Despite over 30 years of experience with PN, complications continue to be a major obstacle in the care of pediatric patients. Complications of PN can be classified into metabolic, respiratory, technical hepatobiliary, and infectious categories.
Metabolic Complications
Hyperglycemia in patients receiving PN is primarily the result of excessive dextrose infusion. Factors that exacerbate glucose intolerance include sepsis, surgery, diabetes, pancreatitis, prematurity, and corticosteroid therapy. Elevated blood glucose levels may coincide with PN initiation, but endogenous insulin secretion usually adapts within 48 to 72 hours. Untreated hyperglycemia causes osmotic diuresis that can lead to hyperosmolar, hyperglycemic, nonketotic dehydration with electrolyte disturbances, impaired phagocytosis (42), and liver steatosis (43). The first effort in managing hyperglycemia is to decrease the dextrose load or reduce the infusion rate. However, this may compromise nutritional intake as dextrose is the major source of calories in PN. If reducing dextrose does not improve hyperglycemia, insulin therapy is then indicated. Because infants have variable responses to insulin therapy, adding insulin to the PN solution should be avoided. Instead, a regular insulin drip via alternative IV access should be initiated and titrated based on serial serum glucose checks.
Hypoglycemia with PN is usually the result of a sudden reduction of the PN infusion rate. In patients who receive PN over a portion of the day (“cycled”), hypoglycemia may be avoided by gradually reducing the rate over 1 to 2 hours prior to discontinuation. Premature infants are at higher risk for hypoglycemia due to their underdeveloped metabolic response and often do not tolerate cycling (44). If PN must be unavoidably discontinued, intravenous administration of dextrose 10% in water will prevent symptomatic hypoglycemia (3).
High concentrations of dextrose in the infusate is the primary cause of hypertriglyceridemia in PN patients. Excessive carbohydrate intake enhances hepatic and adipose tissue lipogenesis (45). Other factors that predispose to hypertriglyceridemia in pediatric patients receiving PN include prematurity, lipid overfeeding, critical illness, and sepsis (46).
Additives to Parenteral Nutrition
Posted by Surgery on Sep 9, 2008
Additives to Parenteral Nutrition
The addition of heparin to the PN solution at a concentration of 0.5 to 1 units per mL (36) maintains the patency of the venous catheter, reduces vein irritation, and enhances lipid clearance by improving lipoprotein lipase enzyme activity. 
Heparin should not be used in patients with bleeding or at risk for bleeding, or in patients with thrombocytopenia.
Heparin should not be used in patients with bleeding or at risk for bleeding, or in patients with thrombocytopenia.Histamine-2 Receptor Antagonists
Histamine-2 receptor antagonists such as ranitidine, famotidine, and cimetidine are compatible with PN and may be added to the PN solution for stress ulcer prophylaxis.
Regular insulin is compatible with the PN solution. However, insulin therapy is difficult to regulate in infants, and intravenous insulin should be administered as a separate intravenous infusion to allow safe titration of the insulin dose in this circumstance.
Iron deficiency anemia may occur in PN-dependent patients. Iron is not routinely added to PN. Iron dextran is the most common parenteral iron available for use when oral iron absorption is unreliable or results in gastrointestinal intolerance. Because iron can be used as a substrate for bacterial proliferation, iron dextran should be avoided in infected patients.
NUTRITIONAL REQUIREMENTS
Posted by Surgery on Sep 9, 2008
Water
The water content of infants is higher than that of adults (75% of body weight versus 65%). Fluids provide the principal source of water; however, some is provided via oxidation of food and body tissues. 
Water requirements are related to caloric consumption; therefore, infants must consume much larger amounts of water per unit of body weight than adults. In general, calorie requirements (kcal per kg per day) are matched to the amount of fluid needs (mL per kg per day). The daily consumption of fluid by healthy infants is equivalent to 10% to 15% of their body weight, in contrast to only 2% to 4% by adults. In addition, the natural food of infants and children is much higher in water content than that of adults; the fruits and vegetables consumed by infants and children contain about 90% water. Only 0.5% to 3% of total fluid intake is retained by infants and children. About 50% is excreted through the kidneys, 3% to 10% is lost through the gastrointestinal tract, and 40% to 50% is insensible loss.
Water requirements are related to caloric consumption; therefore, infants must consume much larger amounts of water per unit of body weight than adults. In general, calorie requirements (kcal per kg per day) are matched to the amount of fluid needs (mL per kg per day). The daily consumption of fluid by healthy infants is equivalent to 10% to 15% of their body weight, in contrast to only 2% to 4% by adults. In addition, the natural food of infants and children is much higher in water content than that of adults; the fruits and vegetables consumed by infants and children contain about 90% water. Only 0.5% to 3% of total fluid intake is retained by infants and children. About 50% is excreted through the kidneys, 3% to 10% is lost through the gastrointestinal tract, and 40% to 50% is insensible loss.Protein
The requirement for protein in infants is based on the combined needs of growth and maintenance (Table 7-1). Two percent of the infant’s body weight, compared with 3% of the adult’s body weight, consists of nitrogen. Most of the increase in body nitrogen occurs during the first year of life, which explains the major protein requirements of infancy. The nutritional value of protein is based not only on the amount of nitrogen available, but also on the amino acid composition of the protein (5). Protein provides 4 kcal per gram of energy, and should generally be included in estimates of caloric delivery. Twenty amino acids have been identified, of which nine are essential in infants (Table 7-2).
Other Cation Disorders
Posted by Surgery on Sep 9, 2008
Calcium is the major constituent of bone and is thus the most abundant mineral in the body. Almost 99% of the body’s calcium is in the bone and therefore unavailable for biochemical interactions. The other 1% remains in flux with the mineralized fraction and is estimated by serum calcium levels. The nonosseous extracellular calcium is either bound to albumin (40%), complexed to small molecules such as sulfates and phosphates (10%), or free and ionized (50%). It is the free ionized form that is physiologically active and thus serum measurements of ionized calcium are most reflective of calcium balance. Hyperproteinemia and alkalosis result in an increased proportion of protein-bound albumin and a decrease in ionized calcium. 
Chelators such as the citrate used in exchange transfusions or with massive blood resuscitation after trauma bind free calcium as well. Conversely, hypoalbuminemia decreases serum measurements of total calcium due to a decrease in protein-bound calcium, whereas the ionized fraction often remains constant.
Chelators such as the citrate used in exchange transfusions or with massive blood resuscitation after trauma bind free calcium as well. Conversely, hypoalbuminemia decreases serum measurements of total calcium due to a decrease in protein-bound calcium, whereas the ionized fraction often remains constant.The gastrointestinal tract is responsible for the intake of calcium and is regulated directly by the activated form of vitamin D and indirectly by the parathyroid glands. When calcium stores are low, the parathyroids are stimulated to secrete parathyroid hormone (PTH). PTH increases hydroxylase activity in the kidney, which in turn converts the inactive form of vitamin D to the active form. PTH also stimulates osteoclasts in the bone to reabsorb calcium. Both vitamin D and PTH induce renal resorption of calcium in the proximal convoluted tubule (85%) coupled with sodium resorption, and in the distal tubule (15%), which is independent of sodium. Increased calcium absorption may be found in conditions associated with increased activated vitamin D levels, such as sarcoid, leukemia, and multiple myeloma. Calcium loss is mainly via the urine, and is increased by diuretic administration, growth hormone, thyroid hormone, and glucagon. As with most other electrolytes, high-output stomas or fistulae may result in a large calcium deficit.
Tags: Hypocalcemia, Lipitor, NEWS SURGERY, pathophysiology, pharmacologic
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