Rationale for the use of the implantable Doppler probe based on 7 years' experience

In head and neck microvascular reconstruction, a proportion of patients are at a higher risk of flap failure. These include salvage surgery after chemoradiotherapy, reconstruction for osteoradionecrosis and when difficulty is encountered in achieving flap perfusion intraoperatively. Several studies have shown that the Cook-Swartz Doppler (Cook Medical Inc, Bloomington, USA) enabled earlier detection of a compromised flap. We retrospectively reviewed microvascular reconstructions monitored with the Cook-Swartz implantable Doppler (2006-2012) and included patients' characteristics, comorbidity (American Society of Anesthesiologists' (ASA) grade), indication for operation, type of reconstruction, and indication for implantable Doppler. We also included details of surgical exploration, free flap salvage, and outcomes of flap salvage. These outcomes were compared with a group of low-risk patients (2005-2009) whose flaps were monitored clinically. A total of 75 free flaps in 73 patients were monitored with the implantable Doppler: 40 (53%) were in cases which required reconstruction following previous surgery/radiotherapy or flap perfusion difficulties, 10 (13%) buried flaps, 13 (17%) as routine flap monitors and 12 (17%) for other indications. The false negative rate was 5%, sensitivity 67%, the false positive rate was 25%, and specificity was 95%. Higher risk flaps monitored with the doppler had a higher return to theatre rate, 21% compared with 4% (p<0.001) and flap failure rate, 7% compared with 1% (p=0.002). Salvage rates for free flaps were similar in both groups (62% compared with 60%, p=1.0). There is not enough evidence to suggest that the implantable doppler reduces the rate of failed flaps in routine low-risk cases, and its value in monitoring high-risk reconstructions require evaluation in a prospective randomised study.