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Techniques and Procedures
A Practical Guideline for Calculating Parenteral Nutrition Cycles
Chris Longhurst, MD, MS*; Louie Naumovski, MD, PhD†; Manuel Garcia-Careaga, MD‡; and
John Kerner, MD‡
*Department of Pediatrics, †Division of Hematology-Oncology, Department of Pediatrics, and ‡Division of
Gastroenterology and Nutrition, Department of Pediatrics, Stanford University, Stanford, California
ABSTRACT: Background: Both physiologic and psycho-
logical reasons for cycling total parenteral nutrition (TPN)
have been well established. Despite widespread accep-
tance of this practice, the only previously published
method for calculating TPN cycle rates is inherently
flawed. Methods: A mathematical formula was derived to
facilitate reliable calculation of cyclic TPN flow rates as a
function of total volume and cycle time. A publicly acces-
sible website was subsequently developed to expedite
rapid determination of TPN cycles. Results: A fail-safe
method of calculating TPN cycle flow rates can be
expressed as F ⫽ V/(4T-10), where F is equal to the basal
flow rate (mL/h), T is equal to the desired cycle time
(hours), and V is equal to the total volume of TPN (mL) to
be delivered in 24 hours. The basal flow rate and twice the
basal flow rate are used for the first and last 2 hours of the
TPN cycle, and the remainder of the cycle runs at 4 times
the basal flow rate. TPN cycles may be easily calculated
online using this formula at http://peds.stanford.edu/
tpn.html. Conclusions: We have developed a fail-safe
method of calculating TPN cycle flow rates that will
consistently deliver the desired volume and have made an
online implementation of this formula publicly available.
Cycling total parenteral nutrition (TPN) refers to
the technique of infusing a daily solution in a ⬍24-
hour period of time. Theoretical advantages of cyclic
TPN include prevention or treatment of TPN-induced
fatty infiltration of the liver, prevention or treatment
of essential fatty acid deficiency, more rapid restora-
tion of albumin levels, prevention of the hyperinsulin-
ism of continuous TPN, and prevention of lipogenesis
(which can increase the respiratory quotient).
1
In
1994, Collier and colleagues
2
published a study in
which they observed stabilization or improvement in
direct bilirubin concentrations of 8 of 10 infants ⬍6
months of age after initiating cyclic TPN. Several
years later, Meehan and Georgeson
3
published the
promising results of a retrospective analysis using
cyclic TPN as part of a comprehensive protocol to
prevent liver failure in parenteral nutrition–depen-
dent children with short bowel syndrome. Even more
recently, Hwang and colleagues
4
published a prospec-
tive, controlled trial in which they concluded that early
TPN cycling prevented further deterioration of liver
function in jaundiced patients who required prolonged
parenteral nutrition support.
Although the initial impetus behind cyclic TPN as
first described by Maini and coworkers
5
was to
confer a physiologic advantage over continuous infu-
sion, it is now well accepted that the psychological
benefits are equally tangible for many patients.
Freedom from the infusion apparatus allows for
greater social activity and interaction, and children,
in particular, may benefit from increased school
attendance and the opportunity to participate in
sports programs. Indeed, one of the earliest prospec-
tive studies of nocturnal TPN in hospitalized adults
suggested that “a main satisfaction of the present
technique was the appreciable comfort of the hospi-
talized patients” with subsequent improvement in
morale and acceptance of treatment.
6
The most important practical aspect of cycling
TPN is calculating tapered flow rates so that glucose
infusions are started and stopped slowly to prevent
potentially harmful fluctuations in blood glucose. It
is well known that hyperglycemia can be induced by
the rapid initiation of TPN
7
and clinical experience
with pediatric patients has shown that rebound
hypoglycemia can occur with acute discontinuation,
although the evidence in adult patients differs.
8,9
Given the substantial body of research supporting
the use of cyclic TPN in appropriately selected
patients, it is somewhat surprising that so few
guidelines for calculating these TPN cycles exist.
The Old Method
To our knowledge, Faubion et al have published
the only guideline for calculating TPN cycle flow
rates,
10
and their method is referenced in several
Correspondence: John Kerner, MD, Pediatric Gastroenterology,
Lucile Salter Packard Children’s Hospital, 750 Welch Road #116,
Palo Alto, CA 94304. Electronic mail may be sent to
john.kerner@stanford.edu.
0884-5336/03/1806-0517$03.00/0
Nutrition in Clinical Practice 18:517–520, December 2003
Copyright © 2003 American Society for Parenteral and Enteral Nutrition
517
textbooks.
1,11,12
Unfortunately, this formula is
inherently flawed and can cause patients to inadver-
tently receive an incorrect volume of nutrition sup-
port and therefore an incorrect amount of caloric
support. The problem with the method they
described is that flow rates are not calculated to
deliver 100% of the desired TPN volume. Rather, the
authors recommended calculating a peak infusion
rate by dividing 90% of the total volume by the
desired cycle time minus 4 hours, and the ramping
rates are simply one-half and one-quarter of this
peak flow rate. Therefore, whereas 90% of the TPN
will always be delivered during the time of peak
flow, either too much or too little volume may be
administered during the remainder of the infusion.
When the Faubion method is mathematically
deconstructed (data not shown), it becomes clear
that the percent of introduced error varies inversely
with the cycle time and independently of the desired
cycle volume (Fig. 1). In fact, flow rates calculated
using this method will deliver the correct volume
only at a cycle time of exactly 17
1
⁄
2
hours. If the
calculated flow rates are precisely administered,
TPN cycles longer than 17
1
⁄
2
hours will always
deliver too little TPN (2.5% less in a 22-hour cycle),
and shorter cycles will always result in a greater
volume administered than desired (6.9% more at 12
hours and 23.8% more at 8 hours). For example, a
5-kg infant receiving 120 mL/kg/day of TPN cycled
over 12 hours would receive 641 mL of TPN per day
rather than the desired 600 mL. It is conceivable
that such an error could become clinically significant
over several days, depending on the patient’s under-
lying condition and the length of therapy.
A New Method
We have developed a more reliable method of
calculating cyclic TPN flow rates for the patients of
Lucile Packard Children’s Hospital at Stanford Uni-
versity. An abstract TPN cycle was conceived such
that the total desired volume is delivered at a basal
rate during the first and last hour of the cycle, twice
that rate during the second and penultimate hour,
and 4 times the basal rate during the remainder of
the cycle. Because the product of the basal flow rate
(F) and the time spent flowing at that rate yields the
volume delivered in that time, given any total cycle
time (T), we can express the total TPN volume (V)of
that cycle as:
V ⫽ 1F ⫹ 2F ⫹ 4F(T ⫺ 4) ⫹ 2F ⫹ 1F
Solving for the basal flow rate, our equation
becomes:
6F ⫹ 4F(T ⫺ 4) ⫽ V
6F ⫹ 4FT ⫺ 16F ⫽ V
4FT ⫺ 10F ⫽ V
F(4T ⫺ 10) ⫽ V
F ⫽ V/(4T ⫺ 10)
Thus the basal flow rate of any TPN cycle can be
calculated by dividing the total volume to be deliv-
ered by the sum of 4 times the total cycle time minus
10 (Fig. 2).
Suppose a patient requires TPN with a total
volume of 1400 mL per day. Although this amount
would typically be delivered at 58.3 mL/h continu-
ously, if the same volume is to be cycled over 20
hours, our equation yields a basal flow rate of 20
mL/h. Therefore, the TPN should flow at 20 mL/h
during the first and last hour, 40 mL/h during the
second and penultimate hour, and 80 mL/h during
the remaining 16 hours. Similarly, the same volume
administered over a 12-hour cycle will flow at rates
Figure 1. The previously published guideline for cycling TPN can deliver significantly different volumes of TPN than
desired.
518 Vol. 18, No. 6LONGHURST ET AL
of 36.8 mL/h, 73.7 mL/h, and 147.4 mL/h during the
times indicated above.
The Online Implementation
This formula has been widely used to calculate
TPN cycles at our institution for ⬎10 years.
Although a spreadsheet was previously used to
facilitate calculations, a web-based version was
more recently developed for easier accessibility (Fig.
3). We welcome the reader to use this free tool
located online at http://peds.stanford.edu/tpn.html.
By entering the TPN volume and the number of
Figure 2. A mathematical overview of the method used to cycle TPN at Lucile Packard Children’s Hospital using a
22-hour cycle for illustration purposes.
Figure 3. The TPN cycle calculator available online at http://peds.stanford.edu/tpn.html.
December 2003 519CALCULATING PARENTERAL NUTRITION CYCLES
hours over which it should be cycled, users can
instantly calculate flow rates that, when adminis-
tered correctly, will always deliver the desired vol-
ume. A link with an example of a typical order for
cycling TPN can also be found on the same website.
Of note, the importance of using a similar online tool
to prevent medical errors was recently established
in a paper that also convincingly demonstrated that
such a tool rapidly gained enthusiastic support from
users.
13
Discussion and Future Directions
In conclusion, we have developed a rapid and
reliable method for calculating TPN cycle flow rates,
given the total volume of TPN and total cycle time. It
is important to note, however, that the division of
increasing and decreasing the rate by 1-hour time
blocks is arbitrary. Using the same mathematical
concepts, the TPN cycle flow rates could easily be
increased and decreased over any amount of time.
We did not investigate the physiologic effects of such
cycling. Additionally, our tool does not calculate
glucose infusion rates, a particular concern in the
neonatal intensive care unit. Further studies are
necessary to determine the optimal time over which
TPN rates can be increased and decreased and to
better elucidate the physiologic benefits and draw-
backs of such cycles. We encourage future research-
ers to use a mathematically accurate method for
calculating cycle flow rates in order to maintain
consistent and accurate delivery of desired TPN
volumes.
Acknowledgments
We thank Dr Stuart Turner, DVM, MS, for devel-
oping a Palm威 handheld-based version of the TPN
cycling program, also available at http://peds.stan-
ford.edu/tpn.html. We thank Dr Monte Klaudt for
reviewing this manuscript. The work was supported
in part by the Carl and Patricia Dierkes Endowed
Fund for Nutrition and Home Care.
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