Keywords
microsurgeon - tissue oximetry - near-infrared spectroscopy
Microsurgical techniques have allowed the performance of complex reconstructive endeavors
with a good rate of success. Compromise of the arterial or venous anastomosis is commonly
responsible for free flap failure. This most frequently occurs during the first 48
hours postoperatively.[1] The early detection of microvascular complications improves flap salvage rate.[2] Detecting the complication alone is insufficient if it is only detected after salvage
is no longer feasible. Therefore, ideal flap monitoring modalities should detect potentially
catastrophic events early, allowing a microsurgeon an opportunity to salvage the flap.
Conventional free flap monitoring includes assessing the color, turgor, temperature,
capillary refill, and arterial and venous Doppler signals with a handheld Doppler
probe. The potential drawback with conventional monitoring techniques is that they
may only detect the problem after it has progressed beyond the point of salvage. Qualities
of ideal flap monitoring modalities include being noninvasive, quantitative, sensitive,
generalizable, easy to interpret, providing real-time information, detecting early
changes flap perfusion, and having minimal risks to the patient and flap.[3]
[4] Near-infrared spectroscopy measures scattering and absorption of light at 700 to
100 nm wavelength.[5] Tissue oximetry technology makes use of spectroscopy and the chromophores in human
tissue to calculate tissue oxygen saturation as a measure of flap perfusion.
Herein, we present a unique case report of a pediatric patient who underwent a free
vertical rectus abdominis myocutaneous (VRAM) flap for a right Gustilo–Anderson IIIb
open tibial fracture sustained in an all-terrain vehicle (ATV) accident. The flap
was monitored postoperatively with handheld Doppler as well as continuously with a
ViOptix near-infrared spectroscopy device (ViOptix T.Ox Tissue Oximeter, ViOptix,
Freemont, CA). We highlight the utility in the ViOptix device detecting impending
microvascular compromise of the flap from a positional change in the extremity, which
resulted in external pedicle compression. The rapid detection of the problem prompted
urgent flap evaluation and repositioning of the extremity by the plastic and reconstructive
surgery resident, with subsequent recovery of tissue oximeter readings and avoidance
of free flap compromise.
Methods and Case Description
Methods and Case Description
Consent was obtained from the patient's father to document a description of the patient's
reconstructive surgery course including the use of photography.
The patient is a 16-year-old boy who sustained a Gustilo–Anderson IIIb open tibial
fracture to his right lower extremity from an ATV accident ([Fig. 1]). Fractures of his tibia and fibula with periosteal stripping and extensive soft
tissue loss resulted. He was initially treated with debridement and external fixator
placement. The Plastic and Reconstructive Surgery Service was consulted for soft tissue
coverage. The patient had anatomically small caliber anterior tibial vessels, which
were occluded in the zone of injury. The vascular surgeon assisted with exposure of
the posterior tibial vessels proximal to the zone of injury. The left VRAM free flap
was selected on the basis of a preoperative CT angiogram and the perforators were
marked with a handheld (9 MHz) Doppler ([Fig. 2]). The flap was elevated in routine fashion preserving the dominant perforators.
The ViOptix probe (ViOptix, Inc., Newark, CA) was placed on the flap skin paddle prior
to ligation of the deep inferior epigastric vessels. The orthopedic surgery team performed
the intramedullary nailing of the tibia while the flap perfused in situ with stable
ViOptix readings.
Fig. 1 Gustilo–Anderson IIIb injury with substantial soft tissue defect.
Fig. 2 Preoperative planning of the rectus abdominis myocutaneous free flap with the placement
of the ViOptix probe prior to deep inferior epigastric vessel ligation.
Following this, the flap was harvested and an end-to-side arterial anastomosis was
performed from the deep inferior epigastric artery to the posterior tibial artery.
There was immediate brisk bleeding sustained from the larger one of the venae comitantes.
This vessel was then anastomosed to the posterior tibial vein with a 3 mm coupler.
With flow restored to the flap, arterial and venous signals were detected in multiple
locations on the flap skin paddle as well as over the flap muscle. The flap was inset
over the defect with exposed portions of the muscle covered with allograft. The ViOptix
probe was placed on the distal aspect of the flap skin paddle ([Fig. 3]) and had a highest recorded value of 63% intraoperatively and maintained acceptable
values immediately postoperatively, and the patient was transferred to the intensive
care unit (ICU).
Fig. 3 Immediate postoperative placement of the ViOptix probe with the deep inferior epigastric
vessel anastomosis at the proximal leg into the posterior tibial vessels.
Results
The patient did well and was extubated immediately after surgery. He had no acute
complications in the immediate postoperative period.
On postoperative day 1, the resident evaluated the patient at 17:02 at which time
the ViOptix read 71%. Sometime thereafter, the ICU nurse performed a handheld Doppler
check then repositioned the extremity to offset pressure on the patient's heel. In
doing so, one of the pillows under the patient's distal extremity slid forward, compressing
the pedicle. By 18:25 the reading dropped to 51% ([Fig. 4]), meeting the preset parameters on account of which a call was made to the Plastic
Surgery team. The attending and resident assessed the ViOptix readings remotely on
their cellular devices and called to mobilize the operating room for a possible flap
exploration while heading into the hospital. The resident first assessed the patient
and he had hardly discernible arterial and venous Doppler signals. He noted the new
position of the pillow and repositioned the extremity with rapid improvement in the
ViOptix reading as well as in the quality and volume of the flap Doppler signals.
By 18:50 the flap's ViOptix was improving after repositioning, and by 19:00 the perfusion
had returned close to the baseline ([Figs. 5] and [6]).
Fig. 4 Acute drop in ViOptix more than 20% in less than 1 hour depicting time of nurse repositioning,
time of resident repositioning, and time of recovery with corresponding ViOptix readings.
Fig. 5 Sustained recovery as seen on ViOptix reading after repositioning the leg to relieve
pedicle compression.
Fig. 6 Position of leg without compression to the pedicle.
The patient had normal ViOptix readings the remainder of postoperative day 1 with
normal color, turgor, capillary refill, and Doppler signals. He went on to have an
uneventful subsequent postoperative course. On postoperative day 7, the ViOptix probe
was removed and extremity dangling commenced on postoperative day 9. He was discharged
on postoperative day 14. His extremity retained full sensation, plantar flexion, and
dorsiflexion. His only functional limitation was absence of extensor hallucis longus
function sustained during the initial injury. At follow-up, he continues to do well
and is working with physical therapy on active range of motion.
Discussion
Microvascular compromise most commonly results from kinking, twisting, compression,
or thrombosis of the pedicle. Other potential causes include a tight closure, positional
changes, prolonged vasospasm, and hematoma.[6] Anastomotic thrombosis is a devastating and at times unavoidable potential complication
of free flap microvascular surgery.[7] Earlier detection of problems with more timely intervention prevents the progression
to microvascular thrombosis.[8] The ViOptix tissue oximeter measures tissue oxygen saturation using the near-infrared
spectroscopy technology. The device measures the scatter and absorption of near-infrared
light by the principle chromophore in the skin, which is hemoglobin, with minor contributions
from cytochrome c oxidase.[5] The wavelength for near-infrared laser light is 700 to 100 nm.[7] Near-infrared light is scattered due to the heterogeneous nature of human tissue.[3] As hemoglobin selectively absorbs the near-infrared light, there is variation in
the reflected scatter intensity and this is detected by the device. These data are
a measure of the tissue oxygen saturation, which is an indirect indication of flap
perfusion and congestion. The device itself has a sensor connected to a console by
a fiberoptic cable. The external sensor is part of a 25 cm2 adhesive pad, while there is an intraoral sensor housed in a silicon block. The laser
light sources and photodetectors measure up to a depth of 10 mm.[9] The ViOptix device has a built-in alarm that is triggered by a drop in 20% points
within an hour or below an absolute value of 30% tissue oxygen saturation.[9] The tissue oximeter can be monitored remotely in real time via a webpage link accessible
on a personal computer or a mobile device.
Tissue oximetry provides critical information and warnings to a discerning microsurgeon
who can then make a quicker decision than conventional flap monitoring would allow.
Conventional flap monitoring, the current gold standard, is not without its own challenges.
Monitoring the flap's color, capillary refill, turgor, and Doppler signals is subjective,
relying on the individual's experience with flap monitoring. To make a clinical determination
of a flap's perfusion status, this person must be able to differentiate normal from
pathologic. Typical postoperative protocols involve flap monitoring every 30 minutes
or 1 hour during the first 24 to 48 hours followed by every 2 hours for the subsequent
24 hours, and so on. Flap salvage rates are directly related to the time that elapses
from complication to detection.[9] ViOptix tissue oximeters are able to detect vascular compromise before conventional
clinical symptoms are present, which may coincide with irreversible compromise of
the flap. Flap perfusion, and hence compromise, is detectable by noninvasive near-infrared
spectroscopy in real time. Even though a flap may be evaluated frequently by the nursing
staff using conventional means, the practical benefit of this technology goes further
by allowing real-time monitoring by all team members including the nurse at bedside
as well as remotely by the microsurgeon, fellow, resident, and other team members.
Other advancements in free flap monitoring include color duplex sonography, microdialysis,
and laser Doppler flowmetry.[10] The implantable Doppler is invasive, color duplex sonography requires a radiologist
along with a microsurgeon for interpretation, microdialysis requires time and laboratory
analysis, and laser Doppler flowmetry is operator dependent.
In the case presented, a pillow was inadvertently moved causing compression of the
vascular pedicle (most likely the venous limb). The ViOptix monitor alerted the nurse
to the change prior to clinical manifestations of flap compromise. This prompt identification
of a problem led to evaluation of the flap within minutes of onset resulting in the
urgent nonsurgical intervention of repositioning to relieve the pedicle compression.
This saved the flap without the morbidity of operative exploration, thus preventing
a potentially catastrophic complication. This is a unique instance of positional compromise
in a pediatric patient monitored in real time using the ViOptix technology.
Many studies have evaluated the efficacy of tissue oximetry in microsurgical procedure.
One case study describes using a saphenous vein stoma for mechanical leeching with
monitoring of congestion using the ViOptix device.[10] In a case series by Steele of 208 flaps in 145 patients undergoing autologous tissue
perforator free flap breast reconstruction, five patients exhibited complications
that were predicted using this device and no flap loss occurred.[9] Keller evaluated 614 consecutive microsurgical flaps, using conventional methods
to monitor the first 380 flaps and then included tissue oximetry for the subsequent
234 patients.[8] They had no statistically significant difference in rates of flap reexploration,
but the flap salvage rate increased from 57.7% without tissue oximetry to 93.75% with
the technology. Steele evaluated 128 free flaps in a 3-year period with a statistical
difference in the length of stay and flap survival in the tissue oximeter cohort.
Scheufler et al used tissue oximetry to detect changes in tissue hemoglobin content
and oxygenation in pedicled transverse rectus abdominis flaps.[11] In a second series, these authors evaluated continuous tissue oxygen tension with
near-infrared spectroscopy intraoperatively and postoperatively, noting that the measurements
correlated with iatrogenic surgical discontinuation of vascular inflow.[12] Repez et al found that near-infrared spectroscopy detected an abrupt decrease in
tissue oxygen saturation due to arterial thrombosis before clinical signs were evident
in 50 free flaps for autologous breast reconstruction.[13]
The learning curve for ViOptix tissue oximetry is not steep. Koolen et al studied
the learning curve of using this technology in flap monitoring and found that as the
curve improved, the rate of early detection increased and more flaps were salvaged.[3] In their study, they also reported common pitfalls for the novice user. Striae on
the skin are prone to insufficient signal strength, intense operating room lighting
may interfere with analysis, and placing the probe directly over a vessel does not
appropriately monitor perfusion of the flap tissue. This technology has been shown
to influence clinical decision making. Bellamy et al showed that surgeons were significantly
more likely to return to the operating room when tissue oximetry data were concerning,
more so than based on the standard 8 MHz Doppler.[14]
The biggest limitation of using tissue oximetry is the cost related to fiberoptic
probes and monitor.[8] The estimated cost of a tissue oximetry probe is $700 to $1200 with consoles costing
about $30,000.[15]
[16] Another limitation is the depth of penetration and need for placement of the adhesive
pad on the flap. The depth of penetration for the ViOptix tissue oximeter is 10 mm.
There are cases where the flap is buried and there is no location to place the pad.
Furthermore, experience is needed to learn the optimal placement of the sensor with
different flaps. These limitations are acceptable compared with those involving the
other technologies available including the invasive nature of implantable Doppler
systems and the reliance on expertise staff with color duplex sonography.
Conclusion
Tissue oximetry is a noninvasive yet sensitive, reliable, and easy to implement flap
monitoring modality.[7] Increased salvage rate of flaps monitored with tissue oximetry has been demonstrated
in the literature. We present a unique case of a pediatric trauma patient where real-time
remote monitoring and ViOptix alarming alerting the microsurgical team to the early
development of a potentially catastrophic complication. This technology is clearly
an essential tool in the armamentarium of the microsurgeon with practical benefits
to flap monitoring and indeed overall patient care.
