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Parenteral nutrition (PN) came of age in 1964 with the demonstration that beagle puppies could be nourished successfully from 12 weeks of age to maturity by providing all nutrients intravenously (1). The first total parenteral nutrition of an infant with extreme short bowel syndrome followed in 1967 (1). Since them many lessons have been learned as a result of complications of PN. These have included nutrient deficiencies and excesses, infections, complications of inadequate or excessive energy and protein intake, liver disease, and toxicities from product contamination. Our patients have paid the price for these lessons, but fortunately improved survival has also resulted. These incidents have reinforced to us the physicians the axiom that “good judgment comes from experience . . . and experience comes from bad judgment.” (2). Along the way we have learned much about nutrition, infection, liver pathophysiology, and child development (e.g., yes, infants really can “unlearn” how to suck and swallow). Have we learned so much that administration of PN can now be placed on autopilot?The question posed to the authors when this review was solicited was whether the art and science of PN had reached the stage where administration could be treated as a routine clinical algorithm such as diarrhea or croup. Do we only need to check the weight, calculate the administration rate and check the box next to “Standard Child Solution” on the PN pharmacy order sheet? Is there really anything new in PN?Our immediate reaction was to take offense, feel hurt, and shake our heads in disbelief that anyone could be so foolish as to think such things. However, as we thought about it, we realized that the question is pertinent and perceptive. Like the clinical pathways set out for common illnesses such as diarrhea and croup, the question is not so much how to follow the roadmap but rather, when not to follow it. Thus, our review will focus on two areas: 1) Common misconceptions surrounding the use of PN; and 2) When should “standard PN” (i.e., checking the weight and the box on the order sheet) not be used. These questions have lead us to review recent developments in PN (in the past 5–7 years). Whenever possible we will take an evidenced-based approach to the data. Unless specified, the studies we will discuss were carried out in pediatric patients. The risk of any review is that it is old hat to some and very new to others. We have done our best to strike a middle ground. Because it could be a subject unto itself, we will not review PN-associated cholestasis, although when pertinent, some comments will be made.Estimating the appropriate energy intake is a fundamental step in prescribing PN. Although we have long acknowledged the risks of underfeeding our patients, more recently we have come to reevaluate energy requirements in particular clinical scenarios and to appreciate the problems associated with excessive energy intake.A few terms must be defined in order to discuss energy expenditure (3). Basal metabolic rate is the energy expenditure of a recumbent child or adult in a thermoneutral environment after a 12- to 18-hour fast just when the individual has awakened but before daily activities have commenced. Basal metabolic rate is a reflection of the energy expenditure required for vital processes. Resting energy expenditure refers to the energy expenditure of a person at rest in a thermoneutral environment. Basal metabolic rate and resting energy expenditure usually do not differ by more than 10% (3).