title: Monitoring of partial and full venous outflow obstruction in a porcine flap model using laser speckle contrast imaging.
abstract: BACKGROUND
  In microsurgery, there is a demand for more reliable methods of post-operative monitoring of free flaps, especially with regard to tissue-threatening obstructions of the feeding arteries and draining veins. In this study, we evaluated laser speckle contrast imaging (LSCI) and laser Doppler flowmetry (LDF) to assess their possibilities to detect partial and full venous outflow obstruction, as well as full arterial occlusion, in a porcine flap model.
  
  
  METHODS
  Cranial gluteal artery perforator flaps (CGAPs) were raised, and arterial and venous blood flow to and from the flaps was monitored using ultrasonic flow probes. The venous flow was altered with an inflatable cuff to simulate partial and full (50% and 100%) venous obstruction, and arterial flow was completely obstructed using clamps. The flap microcirculation was monitored using LSCI and LDF.
  
  
  RESULTS
  Both LDF and the LSCI detected significant changes in flap perfusion. After partial (50%) venous occlusion, perfusion decreased from baseline, LSCI: 63.5 ± 12.9 PU (p = 0.01), LDF 31.3 ± 15.7 (p = 0.64). After 100% venous occlusion, a further decrease in perfusion was observed: LSCI 54.6 ± 14.2 PU (p < 0.001) and LDF 16.7 ± 12.8 PU (p < 0.001). After release of the venous cuff, LSCI detected a return of the perfusion to a level slightly, but not significantly, below the baseline level 70.1 ± 11.5 PU (p = 0.39), while the LDF signal returned to a level not significant from the baseline 36.1 ± 17.9 PU (p > 0.99). Perfusion during 100% arterial occlusion decreased significantly as measured with both methods, LSCI: 48.3 ± 7.7 (PU, p < 0.001) and LDF: 8.5 ± 4.0 PU (p < 0.001). During 50% and 100% venous occlusion, LSCI showed a 20% and 26% intersubject variability (CV%), respectively, compared to 50% and 77% for LDF.
  
  
  CONCLUSIONS
  LSCI offers sensitive and reproducible measurements of flap microcirculation and seems more reliable in detecting decreases in blood perfusion caused by venous obstruction. It also allows for perfusion measurements in a relatively large area of flap tissue. This may be useful in identifying areas of the flap with compromised microcirculation during and after surgery.
authors.affiliation: Department of Hand and Plastic Surgery and Burns, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden. Electronic address: johan.zotterman@regionostergotland.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Zötterman
authors.affiliation: Department of Hand and Plastic Surgery and Burns, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
authors.forename: Max
authors.initials: M
authors.lastname: Bergkvist
authors.affiliation: Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
authors.forename: Fredrik
authors.initials: F
authors.lastname: Iredahl
authors.affiliation: Department of Radiation Physics, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Tesselaar
authors.affiliation: Department of Hand and Plastic Surgery and Burns, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
authors.forename: Simon
authors.initials: S
authors.lastname: Farnebo
mesh_terms: D000818:Animals; D001157:Arterial Occlusive Diseases / Q000175:diagnosis / Q000503:physiopathology; D001158:Arteries / Q000000981:diagnostic imaging / Q000503:physiopathology; D001783:Blood Flow Velocity; D058752:Free Tissue Flaps / Q000009:adverse effects / Q000098:blood supply; D006439:Hemodynamics; D017078:Laser-Doppler Flowmetry / Q000379:methods; D008866:Microsurgery / Q000009:adverse effects* / Q000379:methods; D008953:Models, Anatomic; D011183:Postoperative Complications / Q000175:diagnosis / Q000503:physiopathology / Q000517:prevention & control; D019651:Plastic Surgery Procedures / Q000009:adverse effects* / Q000379:methods; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D013552:Swine; D014654:Vascular Patency; D014680:Veins / Q000000981:diagnostic imaging / Q000503:physiopathology
keywords: Arterial occlusion; Free flaps; Laser Doppler; Laser speckle contrast imaging; Venous occlusion