Implantable Doppler Probe
The Cook-Swartz Doppler Flow Monitoring System (CDSP) is a technique
introduced in 1988 by Swartz et al. [74] This method involves
securing a 1.0-mm Doppler probe to a cuff of expanded
polytetrafluoroethylene (e.g., GORE-TEX), which is then placed around
the flap vessel and sutured in place. [75]
The Doppler probe utilizes a 20-MHz ultrasonic frequency and features a
1-mm2 piezoelectric crystal embedded within a soft
silicone sleeve. It connects to a battery-operated or line-powered
portable monitor. The probe is secured around the vessel with a small
8x5 mm2 thin silicone sheet cuff, using sutures or
clips. Its proximal end exits as a thin wire through the wound and
connects to an intermediate extension cable, sutured to the patient
using specially designed retention tabs. This cable plugs into a
transportable monitor at the patient’s bedside, powered by either
battery or mains.[76]
This design ensures precise detection of blood flow velocity and
facilitates secure attachment to the blood vessel distal to the
anastomosis site, ensuring compatibility with surrounding
tissue.[74] During operation, the probe enables simultaneous
measurement of velocity and blood flow, establishing a direct
correlation between flow and velocity with a relatively low error
margin, even under varying flow conditions. [74]
Some authors postulate the addition of implantable systems such as the
Cook-Schwartz Doppler probe to the clinical assessment of free tissue
transfers. [77] Several cohort studies have demonstrated their
usefulness in terms of sensitivity, specificity and false-negative and
positive results. This technology can quickly detect compromise,
especially in flaps that are not visible and therefore cannot be
assessed clinically. [78] However, in a large cohort of 398 breast
reconstruction patients, other authors recognized no advantage in the
use of Cook-Schwartz Doppler probes; on the contrary, false negative
findings of flap compromise were significantly increased. [8]
Comparative Analysis
In the domain of flap surgery, reconstructive surgeons employ a spectrum
of both invasive and non-invasive techniques. We provided a comparative
analysis of these different techniques where we delve into the nuanced
strengths and weaknesses of each approach, with a keen focus on factors
such as accuracy, cost-effectiveness, ease of use, and clinical
applicability.
Non-invasive techniques offer diverse options. Acoustic Doppler
Sonography (HHD) and colour-coded duplex sonography (DS) provide
cost-effective solutions, particularly valuable for identifying
perforators. HHD excels in breast surgery but may yield false positives,
while DS, offering detailed data, can be time-consuming and technically
challenging due to its requirement for extensive anatomical knowledge.
Near Infrared Spectroscopy (NIRS) effectively measures oxygen level
changes and distinguishes between venous and arterial compromise in free
flaps, yet lacks dedicated flap assessment systems. Thermal Imaging
(TI), a smartphone-based technique, enables early detection of vascular
insults but is limited to surface temperature changes, with variable
specificity. Photoplethysmography (rPPG) assists in differentiating
between venous and arterial thrombosis but may require prior
visualization of vascular anatomy.
Invasive techniques introduce different considerations.
Contrast-enhanced ultrasound (CEUS) provides accuracy in locating
small-lumen perforating vessels but carries risks associated with
intravenous contrast agents. Computed Tomography Angiography (CTA)
offers high accuracy and shorter examination times but involves ionizing
radiation, limiting its use in specific patient populations. NIRF with
ICG, an invasive method, enables real-time visualization of vessel
structure but entails potential risks associated with intravenous
injection. The implantable Doppler probe rapidly detects compromise,
especially in non-visible flaps, though controversial findings regarding
sensitivity and false-negative results raise concerns about its
advantages.
In the overall evaluation, each technique, be it non-invasive or
invasive, presents a unique set of advantages and limitations.
Non-invasive methods excel in accessibility and safety but may sacrifice
specificity. Invasive techniques offer high accuracy but introduce
additional risks. The selection between these approaches necessitates a
tailored decision-making process, taking into account the specific
clinical scenario, patient characteristics, procedural requirements, and
the surgeon’s expertise. A concise overview of the strengths and
weaknesses of each flap-assessment technique, categorized by
non-invasive and invasive approaches, is provided in table 1.