SensiLase Studycast System: A Platform for Critical Limb Diagnostics and Electronic Referral Program

Abstract

Problem

Peripheral arterial disease (PAD) and critical limb ischemia (CLI) impede lower extremity wound healing. The highest-risk patient populations have foot ulcers, ischemic disease, diabetes mellitus, and/or compromised kidney function. Optimal wound healing protocols require evaluation of both tissue and arterial perfusion. The most widely known test, ankle brachial index (ABI), has general but limited utility in foot ulcer patients. False negatives secondary to medial artery calcification are common and ABI alone is not considered predictive of wound healing. As many high-risk patients consider their medical home to be their primary care physician (PCP) not a limb preservation center (LPC), high-risk patients can be underserved secondary to inadequate awareness of the disease, limited diagnostics, and inefficient referral.

Solution

Access to clinically appropriate, tissue-diagnostic tools for high-risk populations coupled with health information transfer (HIT) between PCP and LPCs provides the opportunity to bring PAD/CLI expertise to a patient's medical home. Coordinated data management coupled with PAD/CLI protocols can promote timely and appropriate referral and subsequent intervention.

New Technology

SensiLase^® Studycast^® System provides a noninvasive diagnostic and data management system specifically designed for high-risk patients. Studycast software automates and simplifies HIT between the PC and critical limb care experts at the LPC. Data can be integrated with existing electronic medical record systems.

Indications for Use

SensiLase Studycast is indicated for perfusion assessment in patients at high risk for peripheral ischemia.

Caution

Results of SensiLase System testing should be used in conjunction with other diagnostic information in formulating therapeutic plans.

Thomas Serena, M.D., FACS

Unmet Need

Peripheral arterial disease (PAD) and critical limb ischemia (CLI) are epidemic yet underserved in high-risk populations (elderly, diabetic, smoking history, kidney disease, and foot ulcers). PAD patients with diabetes are at extreme risk for polyvascular disease (PVD)—occlusion in other arteries—leading to heart attack and stroke. As the peripheral arterial bed is the ideal site for overall PVD detection,¹ tests that reliably and easily identify PAD are critical. The most widely known test ankle brachial index (ABI) can be falsely normalized in this patient group and is not particularly useful for foot ulcer evaluation. Therefore, tissue perfusion assessment coupled with HIT services that streamline communication, distribute results electronically and enhance workflow is critical.

Product Technology

The SensiLase^® Studycast^® System generates two noninvasive vascular tests: skin perfusion pressure (SPP) and pulse volume recording (PVR) (Fig. 1). SPP, a quantitative evaluation of microcirculatory perfusion in the skin, is measured using a laser Doppler sensor and an occlusive pressure cuff to evaluate reactive hyperemia. The system produces laser light, which is emitted into the skin at 785 nm. The laser light penetrates the skin up to 1.5 mm and is scattered. Light that hits moving red blood cells is “Doppler shifted,” but light returning from tissue is not shifted. Returned light enters the instrument, where an algorithm extracts flow information and provides a value at which capillary flow returns. A graph displays pressure and perfusion during cuff deflation and indicates the pressure at which skin perfusion is found to return. Other information observable from the graph includes percentage perfusion increase above baseline, total response time, perfusion reappearance time, and perfusion contour. PVR uses air plethysmography to evaluate variations in the volume of blood passing through a limb during each cardiac cycle. In combination, these tests help determine the severity and level of disease in the extremities.

Figure 1.

Skin perfusion pressure testing and pulse volume recording.

Studycast software and services provide web-accessible SensiLase data. SensiLase System studies are uploaded in 2 min or less and feature two-way physician notification services. Studycast permits consolidation of studies from multiple locations in one place. All data fields are independently searchable.

Product Innovation

The SensiLase Studycast service, as a web-based data management system and picture archiving and communication system (PACS), provides transmission of tests for interpretation from any internet-connected device. Coordinated use of SensiLase Studycast at a primary care site with oversight from limb preservation experts provides streamlined HIT and referral process. Tests performed by primary care are routed for vascular interpretation. The complete report (vascular history, findings, and recommendations) is automatically routed to the primary care physician (PCP) and administration. Interpretation templates are data driven to provide thorough reports. The turnaround time for generating reports required for utilization, billing, and documentation are substantially reduced when using digital structure reporting.² Studycast service meets Health Insurance Portability and Accountability Act (HIPAA) compliance, allows for customizable reports, and permits multiple users access to the data from any internet-connected device.

The system provides a customizable clinical and technology platform for collaborating departments and/or community clinics to direct patient care both short and long term. High-risk patients may require advanced diagnostic assessments, vascular intervention, and ancillary care to heal their wounds. Combining tissue perfusion data with other vascular and wound information into a critical limb care database optimizes care and demonstrates accountability of service. These attributes minimize operator error and offer utility to primary care and limb preservation experts in their varied care roles for the patient.

Peer-Reviewed Data

SPP has demonstrated utility in PAD/CLI detection, wound healing prediction, and optimizing limb salvage.

• Castronuovo et al.³—53 patients (61 limbs), prospective study (100% ulcers/gangrene). SPP reliably predicted wound healing and accurately identified CLI.

• Kondo et al.⁴—24 patients (44 limbs), prospective study (100% diabetes mellitus [DM]/hemodialysis). SPP was more sensitive to quantify ischemia compared with ABI; validation metric was digital subtraction angiography.

• Okamoto et al.⁵—140 patients (266 limbs), prospective study (100% hemodialysis patients). SPP was more effective in identifying PAD than transcutaneous partial pressure oxygen or transcutaneous oxygen tension (TcPO₂), ABI, or toe-brachial index or toe-brachial indices (TBI); validation metric was multidetector-row computed tomography angiogram.

• Yamada et al.⁶—211 patients (403 limbs), retrospective study. SPP was a more accurate, objective measurement for assessing severity of PAD and predicting wound healing compared with ABI, TBI, or TcPO₂.

• Lo et al.⁷—100 patients (100% chronic wounds), prospective study. SPP was more accurate in predicting wound healing potential (92%) than TcPO₂ (67%). All patients were followed up to 12 months or healing.

• Tsuji et al.⁸—47 patients (69 limbs), prospective study (100% ischemic wounds). SPP was shown to predict wound healing in patients undergoing vascular surgery for CLI. SPP accurately predicted wound healing and was useful in planning optimal amputation level.

Electronic referral programs clearly represent an improvement over traditional referral practices:

• O'Malley and Reschovsky⁹—4,720 PCPs and specialists survey of traditional referral and consult communication showed conflict over receipt of quality reports regarding patients with chronic conditions and support for monitoring patients with chronic conditions.

Non–Peer-Review Observation

Bailey and Schechter¹⁰—100-patient prospective study compared paired noninvasive vascular test (TcPO₂/ABI and SPP/PVR) for PAD detection, wound healing prediction, and time-to-test (100% lower extremity wounds) (Table 1). SPP/PVR demonstrated to be superior to other vascular tests for the following uses:

• PAD detection: 96.2% (50/52) for SPP/PVR and 61.5% (32/52) for TcPO₂/ABI. Arterial disease was confirmed in 52/100 patients; however, an ABI was unable to be obtained in 32.7% (17/52). Of these 17 patients, 47.1% (8/17) had DM.

• Wound healing prediction: 93.2% (82/88) for SPP/PVR compared with 75% (66/88) for the TcPO₂/ABI.

• Time to test: 6.72 min (±standard deviation [SD]: 2.41) compared with TcPO₂/ABI testing time of 35.54 (±SD: 8.86) for assessing wound healing with a single site. Good clinical practice dictates a multisite (×3) testing with a cumulative mean of 18.43 min for SPP and PVR.

Table 1.

A comparison of current screening diagnostics for peripheral arterial disease

Identified Criteria for Comparison	Microcirculatory Assessment Skin Perfusion Pressure	Macrocirculatory Assessment Transcutaneous Oxygen Tension	Pulse Volume Recording	Peripheral Pressure Measurements (ABI, TBI, and Segmental Pressures)
Assessment parameter	Microcirculatory perfusion	O2 saturation	Macrocirculatory perfusion	Macrocirculatory perfusion
Useful in patients with
Calcified arteries	Yes	Yes	Yes5	No
Inaudible pulses/Doppler	Yes	Yes	Yes	No
Edema	Yes	No	Yes	Sometimes
Callus	Yes	No	Yes	No
Able to perform testing in the presence of
Anemia	Yes	No	Yes	Yes
Hypoxia	Yes	No	Yes	Yes
Labor intensive/time consuming	No	Yes	No	Yes
Approximate procedure times	3–5 min	30–60 min	≤1 min	10–20 min
Calibration required	No	Yes	No	No
Contact gel/solution required	No	Yes	No	Yes
Use of electrodes required	No	Yes, warmed to 42°C–44°C	No	No
Testing procedure is challenging	No	Yes	No	Yes
Training requirements	Minimal	Extensive	Minimal	Extensive

ABI, ankle brachial index; TBI, toe-brachial index.

Caution, Critical Remarks, and Recommendations

SensiLase System testing should be used in conjunction with other diagnostic information including other circulatory tests, clinical observations, and symptoms. Patients with severe tremors may not be amenable to testing with SensiLase System, because laser Doppler is sensitive to extreme, repetitive motion; the system software may not permit a result to be reported.

SensiLase Studycast System provides a perfusion diagnostic system and permits seamless integration of vascular ultrasound data into final reports. This is coupled with systematic structures, tools, and processes that assist creation, transfer, receipt, and recognition between PCPs and limb preservation centers to support management of patients with chronic illness.

Abbreviations and Acronyms

ABI

ankle brachial index

CLI

critical limb ischemia

DM

diabetes mellitus

HIT

health information transfer

LPC

limb preservation center

PAD

peripheral arterial disease

PCP

primary care physician

PVR

pulse volume recording

SD

standard deviation

SPP

skin perfusion pressure

TBI

toe-brachial index

TcPO₂

transcutaneous partial pressure oxygen or transcutaneous oxygen tension

Acknowledgments and Funding Sources

No financial support or compensation was received for development of this article.

Author Disclosure and Ghostwriting

The authors have no conflicts of interest. The content of this article was expressly written by the author listed. No ghostwriters were used to write this article.