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Clinical Study
| Precision of Low-Dose Insulin Administration Using the Jet
Injector | Naomi D Neufeld, M.D.
Clinical Professor of
Pediatrics, UCLA School of Medicine, Attending Physician, Cedars-Sinai Medical
Center
Control of blood glucose in
young children with diabetes mellitus is often difficult. Multiple factors
contribute to the erratic control of glucose, including sporadic or
unpredictable activity and poor compliance with diet. Sometimes, the fear of
injections may further impair our attempts at diabetic control.
Children under the age of 5
yr. may require very low doses of insulin; adjustments of as little as
one-fourth of a unit are sometimes recommended and the response to a given dose
of insulin may vary. Previous studies have shown the limitations by caretakers
of children with diabetes of accurately and precisely measuring small amounts of
insulin using currently available low dose syringes. 2 Variations ranging from 5
to 33% were demonstrated when adult caretakers of juvenile diabetics attempted
to measure doses below 5 units; pediatric nurses and other medical personnel
fared only slightly better. These errors in measurement may therefore contribute
to the inconsistency of response to insulin dose adjustments in the very young
pediatric patient.
Many diabetics have
successfully been treated with needle-free jet injectors, which are effective in
enhancing compliance with therapy, particularly when multiple doses of insulin
are used. Some injectors are now on the market for the pediatric age group, the
only difference being in the strength of the spring-based injection system. The
purpose of this study was to compare the validity and precision of two different
techniques of insulin volume measurement used by both medical personnel and
caretakers of young diabetic children. I undertook this study to determine if
the needle-free jet injector could more precisely measure the small volumes of
insulin (ranging from 10-35 ul) in comparison to currently available low dose
syringes.
Materials and
Methods:
Low dose syringes, 0.5 ml,
were purchased from BectonDickinson (Franklin Lakes, N.J.) and Terumo Medical
Corp. (Elkton, MD). Individual participants used different syringes for this
study. For comparison, we utilized the AdvantaJet® & GentleJet® Advanced
Needle-Free Injection System. For
the purposes of this study a different AdvantaJet® injector, selected at random
from a pool of 22, was used for each participant. A single vial of regular human
insulin (Humulin®-R, Eli Lilly Corp, Indianapolis, IN) was used for all
determinations. A pre weighed polypropylene beaker was lined with absorbent
tissue, and weighed using a Mettler Analytic Balance, model AE 200 (Mettler
Instrument Company).
Participants:
Medical office staff,
parents of diabetic children less than 9 yr. as well as diabetic subjects older
than 10 yr. were recruited to participate in this study. There were a total of 28
participants. They were instructed to draw up three different doses of insulin,
1.0 U, 2.0 U and 3.5 U. After drawing up each dose in a syringe the amounts of
insulin were ejected into the beaker, weighed and the results
recorded.
Each participant was given a
brief demonstration with the Gentlejet® and shown how to draw up the tested
volumes after the injector had been attached to the vial adapter. Then they were
each asked to draw up 1.0 U, 2.0 U and 3.5 U of insulin; the doses were then
expressed into the pre weighed beaker, and the results recorded.
Data
analysis:
The mean and standard
deviation of the weight at each dose was calculated for the group; further
analysis of the data, using the Minitab statistics package were
performed.
For purposes of this
analysis, the weight of 1 ml of insulin was 1.004 gin = 100 units. Thus, 1 unit
weighed 0.01004 gm.
Results:
Table 1 shows the individual
data from each participant at each dose measurement. These data represent the
findings at each dose for different observers as well as for different
instruments. The comparative measurements between the GentleJet®
("Jet") and the Becton-Dickinson and Terumo low dose insulin syringes ("Needle")
are shown. Analysis of variance was used to test the type of device effect
(injector vs. syringe), and the volume effect at each of the volumes measured
(10, 20 and 35 ul).
At a dose of 1 U, the mean
was 1.43 ± 0.281, whereas for the syringe measurements, the mean was 1.06 ±
0.847. At this dose, the sample variance was 7.9% for the GentleJet®, whereas
it was 71.7% for the syringe group measurements.
At 2 units, the Jet measured
2.39 ± 0.259, whereas for the Needles, the mean was 2.14 ± 0.823. At this dose
the sample variance was 6.7% for the Jet, and 67.7% for the Needle. At 3.5
units, a reading which required interpolation between markings on the Needle,
the mean was 3.77 ± 0.426 U by the Jet as compared to 3.44 ± 0.722 U measured by
the Needles. The variation in reading at this dose was 18.1% for the
measurements from the Jet groups, whereas it was 52.1% for the measurements
obtained from the needles.
Graphic analysis of the data
are shown in Figure 1. The individual readings
obtained by the GentleJet® groups (represented by u ) are compared to those
obtained Using the low-dose syringes (represented by n ). From this graph it is
very apparent that the variation in measurements obtained using the GentleJet®
was far narrower than those obtained using conventional insulin
syringes.
At the higher volumes of
insulin employed (Figure 2 and
Figure 3) the variation was slightly greater for the
doses measured by syringe, as compared to the GentleJet®.
Conclusion:
The care of very young
children with diabetes mellitus is often problematic, due to multiple factors
which also influence the ability to regulate blood glucose. Clearly, erratic
diet and activity in toddlers are often factors making diabetic control
difficult. For some patients, fear of insulin injection and therefore lack of
compliance with insulin therapy may occur. These factors may contribute to the
lack of predictability of a given dose of insulin to work in a consistent way,
and thus may compromise diabetic control. In addition, recent studies suggest
that lack of precision in insulin dose delivery of low doses of insulin, by
medical personnel and parents using commercially available syringes may also
contribute to this problem.
Jet injectors have been
available for more than 30 years, and have been shown to be efficacious in
people with fear of needles; they are particularly useful in promoting
compliance for individuals requiring multiple injections. They permit the mixing
of varied proportions of insulin and can reliably deliver doses repeatedly with
great consistency. In the case of the GentleJet®, they consist of a calibrated
cylindrical stainless steel chamber which ends with a 0.006 in. diameter opening
(1/4 the diameter of a 29G needle). At the other end of the chamber is a
spring-driven piston device. Release of the spring forces the stream of insulin
through the opening under sufficient pressure to pierce the skin. Dead space in
the insulin chamber-orifice system is minimal, allowing the consistent delivery
of precise volumes of insulin. Recent adaptations in these devices, using
springs with lower pressure have made these injectors suitable for use in
pediatric patients.
One factor critical to
diabetes management, in young patients in particular, is the need to assure the
precision of repeated injections of small doses of insulin, the findings of the
present study are encouraging. At doses of insulin commonly used in the youngest
patients, we found that the GentleJet® injector was uniformly more consistent
in delivering a given dose of insulin than currently available low-dose
syringes. The variation in the latter was extremely high; review of our data
showed that delivery of a 1 unit dose by insulin syringes varied from 0.02 to
2.56 Units. Such variation in delivery clearly would contribute to the apparent
unpredictability of a given insulin dose.
At higher doses, variation
of the jet injector was more consistent than those measured using the
conventional low-dose syringe. We also observed a greater inter-observer
consistency of measurements using different GentleJet® injectors, than was seen
using different syringes. The consistent delivery of insulin by the GentleJet®
injector is a reflection of the precision engineering of this equipment, as
compared to that of disposable syringes. Thus, a physician can, with a greater
degree of confidence give a recommendation of dose change using this jet
injector as compared to the conventional low dose syringe.
The consistency of
measurement using the Gentlejet® Advanced Needle-Free Injection System
by multiple care givers, is further support for the precision of measurement of
insulin. In practice this would further support the role of the jet injector in
the care of small child with diabetes, who may have more than one caretaker
during the day. Fear of injection is sometimes seen in patients receiving
insulin, particularly those in pediatrics. The GentleJet® provides consistent
dosing, as well as a relatively painless injection, resulting overall in a
better and more predictable outcome for our youngest patients.
References
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