Keywords
anorectal malformation - posterior sagittal anorectoplasty - muscle stimulator - resource-poor
Introduction
Repair of anorectal malformations (ARM) using either posterior sagittal anorectoplasty
(PSARP) or Georgeson's laparoscopic technique are optimally performed using a muscle
stimulator to clearly delineate the anal and pelvic muscle complexes for precise anatomic
placement of the rectal pull-through segment.[1]
[2]
[3] Unfortunately, purchase of commercially available muscle stimulators for ARM surgery
can be prohibitive[4] for many regions of the globe due to their high cost which may exceed US$10,000.
Not surprisingly, this cost barrier limits the use of this critically important tool
by surgeons in communities with limited resources to purchase this device.
Multiple authors have published an array of cleverly improvised devices to circumvent
this problem,[5]
[6] however no study has compared such devices to what might be considered a “gold standard”
muscle stimulator device. Our goal was to compare a low-cost, improvised device with
the PS2 Peña Muscle Stimulator on intraoperative functionality, energy delivery, and
cost.
Methods
A consecutive series of patients (five boys, one girl) with weight 5.9 to 11 kg underwent
PSARP for four prostatic fistulae, one bulbar fistula, and one vestibular fistula,
respectively. Following approval from the research ethics committee, we compared use
of the MicroStim (MS) peripheral nerve stimulator (Neurotechology, Houston, TX, USA),
commonly used in anesthesiology, and the Peña Muscle Stimulator (PS2, Integra NeuroSciences)
to identify muscle groups in a head-to-head comparison with video documentation during
surgery ([Fig. 1]). The sterile MS alligator clips were attached to two, 22-gauge hypodermic needles
and the anesthesiologist away from the operative field controlled the device settings.
A short-acting neuromuscular blocking agent was administered only during induction
of anesthesia, and its effects were no longer present at the start of the operations.
Before muscle stimulation, the tissue was moistened with warm saline in all cases,
and the MS device was used in tetanic mode. The surgical team identified each muscle
complex, and subjectively assessed stimulation response and ease of probe handling
and recorded their impressions at the time of each operation. The video footage of
each operation was subsequently reviewed retrospectively. ([Fig. 1])
Figure 1 Stimulator devices used in this study. (A) The improvised MicroStim peripheral nerve
stimulator was modified by attaching 22-gauge hypodermic needles to the alligator
clips. The needles were used to contact the tissue and delineate muscle complexes
during PSARP. (B) Peña muscle stimulator (PS2) and probe used for repair of anorectal
malformations.
Electrical potential, current, and energy delivery of each device were studied using
a 1000 ohm (1kΏ) resistor on a digital oscilloscope. The generated waveform, frequency,
current, potential, and duty cycle were measured and recorded; the energy delivery
was calculated. The MS device was tested at settings #3 through #10 in tetanic mode;
the PS2 was tested at currents of 60 to 140 mA (mA) as documented on the device. Device
costs in USD were obtained from United State vendors.
Results
All members of the surgical team (P.F., S.Z., S.S.) uniformly felt that both devices
demonstrated equivalent utility in clearly identifying all pelvic and anal muscle
groups necessary to perform PSARP operations safely and effectively ([Fig. 2]). However, the team found that the improvised MS tissue contact probe was less convenient
to use. There were no intraoperative complications, including tissue burns with either
device, and no early or late postoperative complications. Follow-up at 5 months after
PSARP, and 2 to 3 months after colostomy closure, finds that all of the children are
stooling daily with a bowel management regimen of daily oral senna-based laxative.
([Fig. 2])
Figure 2 Application of improvised MS stimulator device. (A) Prior to repair of anorectal
malformation. (B) Intraoperative delineation of muscle complex.
The properties and energy delivery of each device were compared over a range of settings
in [Table 1]. Both devices delivered a square wave of 200 μs duration with frequencies of 100 Hertz
(Hz) and 50 Hz for the MS and PS2, respectively. On the basis of our patients' size,
we found the optimal settings of #9 for MS and 120 mA for the PS2. Not surprisingly,
at these settings energy delivery of the devices was similar, 23.5 milliwatts (mW)
and 25.3 mW for the MS and PS2, respectively. Costs provided by United States vendors
were US$162 for MS and US$12,371 for PS2 ([Table 1]).
Table 1
Comparison of MicroStim and Peña muscle stimulator electrical properties. Both devices
delivered a square wave of 200 μsec duration with frequencies of 100 and 50 Hz for
the MS and PS2, respectively. Optimal settings for patients in this study are noted
in the shading
|
MicroStim
|
Peña stimulator (PS2)
|
|
Dial setting
|
Potential (V)
|
Current (mA)
|
Energy/pulse (mJ/μsec)
|
Power (mW)
|
Potential (V)
|
Current (mA)
|
Energy/pulse (mJ/μsec)
|
Power (mW)
|
|
10
|
10
|
129
|
0.258
|
23.5
|
22
|
140
|
0.616
|
32.0
|
|
9
|
10
|
129
|
0.258
|
23.5
|
20
|
120
|
0.48
|
25.3
|
|
8
|
8
|
103
|
0.165
|
15.0
|
16
|
100
|
0.32
|
16.8
|
|
7
|
6
|
77
|
0.092
|
8.4
|
14
|
80
|
0.22
|
11.7
|
|
6
|
5
|
64
|
0.064
|
5.8
|
10
|
60
|
0.12
|
6
|
|
5
|
4
|
52
|
0.042
|
3.8
|
|
|
|
|
|
4
|
3.3
|
42
|
0.027
|
2.5
|
|
|
|
|
|
3
|
2.3
|
29
|
0.013
|
1.2
|
|
|
|
|
Abbreviations: V, volt; mA, milliampere; mJ, millijoule; μsec, microsecond; mW, milliwatt.
Discussion
This study is the first to directly compare clinical use and energy delivery of an
improvised stimulator device to the Peña muscle stimulator for repair of ARMs in children.
The most striking finding of the study was a 75-fold lower cost of the MS compared
with the PS2 with equivalent clinical effectiveness. While we found that the improvised
MS “probe” was less convenient to use than the PS2, the team adjusted quickly to using
it.
We found that advantages of the PS2 were that the tissue contact probe was easy to
use and energy delivery was available over a wide range, thus enabling use from infants
to older children. However, the primary disadvantage was high cost, with a less obvious
drawback being the need for the probe to be gas sterilized, a process that may not
be readily available in resource-limited environments. On the other hand, the primary
advantage of the improvised MS device was low cost, making it considerably more accessible
either through purchase or donation. One drawback of the MS stimulator we found was
that the optimal setting of energy output was near the upper limit of energy delivery
for the device. Therefore, one potential concern is that the MS device may not be
practical for older (larger) children where increased energy delivery would be required.
Experienced surgeons have pointed out the difficulties of obtaining critical equipment
needed for treatment of ARM's in resource-limited areas of the world.[6] Not surprisingly, lack of financial resources represents a key bottleneck to obtaining
such instrumentation. Further highlighting the cost issue is the fact that the price
of the PS2 in our study is ∼2.8 times the mean annual Chinese salary,[7] and more than 30 times the annual per capita income of Africa's poorest nations.[8]
To provide the highest quality care for their patients, pediatric surgeons in these
challenging conditions are often forced to modify available equipment. One study references
surgeons utilizing the electrocautery as a method to identify the muscle complex for
repair of ARMs,[4] however this approach risks damaging the sensitive muscular complex and associated
morbidity. In an effort to maintain safety and excellence in care, other authors have
modified stimulators to recapitulate the action of the Peña stimulator.[6] Poenaru et al described the use of an anesthesia nerve stimulator as well as a home-made
version of the “Peña” stimulator with use of Bic pen for identification of the muscle
complexes while performing PSARP operations in Africa.[5] While these authors created ingenious methods to delineate critical surgical anatomy,
they had no means of assessing how similar (or different) their improvised devices
were compared with a Peña stimulator.
Our study demonstrates that this low-cost improvised MS stimulator is safe and effective,
and provided tissue energy delivery equivalent to a much more expensive stimulator.
Nonetheless, our study was limited by the small sample size and the subjective assessment
of outcome by the surgical team. Additionally, other improvised nerve/muscle stimulators
may not be as safe or efficacious as the device tested here.
Conclusion
The improvised MS stimulator tested in this study is a safe and effective, low-cost
tool for PSARP operation. The results of this study highlight the enormous unmet need
for a quality, affordable stimulator device to facilitate excellent treatment of children
with ARMs.
