Cycling PN

PN should be administered over 24 hours in most hospitalized patients to minimize glucose, fluid, and electrolyte abnormalities. However, administering PN via a cyclic infusion over less than 24 hours, or cycling PN, may be advantageous in certain patients and situations. Cycling PN typically involves administering the same PN volume to a goal infusion time usually over 12 hours rather than over 24 hours. Taper PN to the goal cycle over 2 to 4 days (e.g., 24 hours, then 18 hours the next day, then

14 hours the next day, and then 12 hours the next day). Titrate the PN infusion rate up over 1 to 2 hours to goal rate to avoid hyperglycemia, and taper down over 1 to 2 hours at the end of the cycle to avoid reactive hypoglycemia. Most home infusion pumps can be programmed to cycle a given PN volume automatically over a given time. However, the pharmacist may have to develop an appropriate PN cycle if the infusion pump cannot be programmed.

Cyclic PN has the following advantages:

• It may help alleviate PN-associated liver cholestasis by avoiding continuous com-

pulsive nutrient overload on the liver.

• It improves the quality of life of patients receiving home PN by allowing the patient time off from PN to engage in normal daily activities. If nocturnal cyclic PN infusion interferes with patient's sleep pattern by causing overdiuresis, the PN cycle can be extended over a longer infusion time or PN can be infused during other times of the day that are most convenient to the patient.

Concerns with cycling PN include hyperglycemia with high infusion rates, reactive hypoglycemia, and fluid and electrolyte abnormalities. Depending on potassium amounts in the daily PN admixture, cyclic PN infusion should also take into consideration the potassium infusion rate that should not exceed 10 mEq/h. Reactive hypogly-cemia can be minimized by tapering down PN over 1 to 2 hours before disconnecting. Typically, the nadir will occur around 30 to 60 minutes or even a little over an hour after the PN is stopped. Random capillary blood glucose concentrations should be checked 4 hours into the PN cycle (approximately 2 hours after reaching goal rate),

15 to 60 minutes after PN stops, and intermittently during the PN cycle as needed for glycemic control.

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