Doppler Signal Interpretation in Free Tissue Transfer: A Computer Simulator for Resident and Nursing Education

Over the past three decades, free tissue transfer has evolved into a highly reliable technique for the reconstructive surgeon. With better instrumentation, increasing experience of microsurgeons, refinement of microsurgical techniques, and development of more reliable flaps, the failure rate of free-tissue transfer has been reduced significantly since its introduction. Success rates greater than 91 percent have been reported in single institution and muliticenter studies with re-exploration rates between 6 and 25 percent.[1] [2] [3] [4] [5] However, despite improving success rates, free flap failure remains a clinical, financial, and emotional disaster. The ability to effectively monitor free flaps in the postoperative period is essential for early detection of the failing flap to maximize salvage potential. One muliticenter survey of current practices of free-flap monitoring reported an initial failure rate of 6.7 percent in 2825 free flaps.[6] Of the failing flaps, 41 percent were salvaged, resulting in a final failure rate of only 4 percent. Of 95 respondents to this survey, 90 percent of surgeons rely on adjunctive monitoring devices in addition to clinical assessment. The most common monitoring device reported was hand-held Doppler ultrasonography, used by 29 percent of the responding microsurgeons.

Salvaging a failing free flap depends on the early detection of compromised vascular flow or anastomosis and immediate surgical intervention. Hand-held Doppler ultrasonography, combined with clinical observation, are proven, inexpensive, and reliable techniques for postoperative monitoring.[7] [8] [9] [10] However, clinical expertise is necessary for accurate correlation of Doppler signals with flap vascular status based on clinical observations.

At our institution, responsibility of postoperative flap evaluation falls largely on residents and nurses. To be assured that those residents and nurses involved with postoperative free-flap assessment have a consistent educational foundation, we have developed a computer-based simulator for those frontline residents and nurses involved in postoperative care of free flaps at our institution. The simulator contains a brief history and understanding of Doppler ultrasonography; an interactive portion that differentiates between arterial and venous signals, and reinforces clinical observations with reference to flap edema, color, and temperature. A pre-test was administered to nurses who underwent simulator training and data were collected on multiple parameters.

Sixty-three nurses who routinely take part in immediate postoperative intensive care unit free-flap monitoring were polled on experience, years in nursing, and education in the nuances of free-flap monitoring. Seventy-seven percent (49/63) of those polled had been in nursing less than 5 years. When asked how many flaps they had seen during their career, 66.7 percent had taken care of 5 to 15 free flaps. When asked how many free flaps they had monitored in the last month, 39.7 percent had monitored no flaps, with the remaining 60.3 percent monitoring less than five flaps (Table [1]). When polled on what was the most important clinical parameter to monitor, the majority thought either flap color (47.6 percent) or the Doppler signal (44.4 percent) (Table [2]). When polled if a Doppler ultrasound probe could be used to distinguish between an artery and a vein, 39.7 percent responded yes with 60.3 percent responding no. From this survey, we concluded that postoperative monitoring was being performed by nursing personnel with less than 5 years of nursing experience and relative inexperience in postoperative free-flap care and evaluation. After reviewing these data, we believed there was a need for standardized formal education to monitor the patient and flap following free-tissue transfer procedures.

Table 1 Number of Flaps Nurses have Taken Care of During their Career and in the Last Month Number of Flaps Evaluated 0 1-5 6-15 16-30 > 31 Career 0 4 (6.3 percent) 42 (66.7 percent) 14 (22.2 percent) 3 (4.8 percent) Last Month 25 (39.7 percent) 38 (60.3 percent) 0 0 0

Table 2 Most Important Clinical Attribute when Monitoring Free Tissue Transfer Color Temperature Doppler Signal Flap Edema Flap Bleeding 30 (47.6 percent) 2 (3.2 percent) 28 (44.4 percent) 2 (3.2 percent) 1 (1.6 percent)

With that in mind, we developed a computer simulator to help train and educate nursing personnel, as well as residents and medical students, in the postoperative care of free-flap monitoring (Figs. [1-5]). The computer simulator was developed in an HTML format and compiled into a Macromedia Flash executable file that is less than 10 megabytes in size. Intraoperative Doppler ultrasonography was performed during microsurgery cases and recorded directly to an attached laptop computer. These unmodified signals were imported into the program to educate the user on the differences between arterial and venous signals. The simulator will run on any computer that is running a Windows platform and takes less than 30 min to complete.

Figure 1 Introduction page for the Doppler simulator.

Figure 2 Part I: Doppler terminology section. A historical review of physicist Christian Doppler and basic terminology.

Figure 3 Part II: Doppler physics. A basic mathematical review of Doppler physics.

Figure 4 Part III: Doppler shift and flow. Multimedia interactive portion of the simulator allowing simulated movement of the Doppler hand-piece to hear the difference between tangential and obtuse angles, and with regard to blood-flow direction in an artery.

Figure 5 Part IV: Advanced Doppler section. Discussion regarding triphasic arterial signals and venous hum are reviewed.

Success in free-tissue transfer is the expected result with microsurgical procedures performed today. However, occasional failure of a free flap remains a devastating loss for the patient, family and the surgical team. The potential to salvage a failing free flap is dependent on making an accurate and timely diagnosis and being able to promptly return the patient to the operating room.

At our institution, most of the postoperative monitoring of free flaps is performed by the residents and nurses. However, with the advent of the 80-hr work-week constraints, residents may not receive valuable clinical experience in free-flap monitoring, and more of the onus falls on the nursing personnel. The results of our poll suggest that the experience level of the nursing personnel is quite inconsistent and limited in the care and monitoring of patients who have undergone free flaps.

The ideal monitoring technique should be straightforward, and any data collected on the free flaps should be unambiguous and easily interpreted, satisfying the criteria proposed by Creech and Miller in 1975.[11] However, adjunctive monitoring techniques are effective only when used by personnel with the appropriate educational background and experience. We have therefore proposed and introduced this educational tool as a means to enhance the understanding and capability of our clinical personnel.

As Gillies suggested, perhaps the most significant advance in the development of modern plastic surgery was photography.[12] Since Spear and Little[13] emphasized the importance of the 35-mm slide projector in preoperative planning and the teaching of residents, technical innovations have continued at a rapid pace, bringing us to the digital images of today. Clearly the next advancement in surgical education will be the development of sophisticated computer simulators for educating medical students, residents, and nurses in the ever-increasing sophisticated care of patients. We believe that the Doppler computer simulator contributes significantly to the education of residents and nurses involved with the care and monitoring of patients undergoing free-tissue transfer. We think that this may contribute to a higher salvage rate of compromised flaps at institutions utilizing this device. Computer simulation may also prove useful and necessary to compensate for the loss of clinical experience of residents training under the 80-hour work week.

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