How we do it: Postoperative tissue oxygen monitoring in microvascular free flaps

Use of Near-infrared Spectroscopy and Implantable Doppler for Postoperative Monitoring of Free Tissue Transfer for Breast Reconstruction: A Systematic Review and Meta-analysis

BACKGROUND

Failure to accurately assess the perfusion of free tissue transfer (FTT) in the early postoperative period may contribute to failure, which is a source of major patient morbidity and healthcare costs. This systematic review and meta-analysis aim to evaluate and appraise current evidence for the use of near-infrared spectroscopy (NIRS) and/or implantable Doppler (ID) devices compared with conventional clinical assessment (CCA) for postoperative monitoring of FTT in reconstructive breast surgery.

METHODS

A systematic literature search was performed in accordance with the preferred reporting items for systematic reviews guidelines. Studies in human subjects published within the last decade relevant to the review question were identified. Meta-analysis using random-effects models of FTT failure rate and STARD scoring was then performed on the retrieved publications.

RESULTS

Nineteen studies met the inclusions criteria. For NIRS and ID, the mean sensitivity for the detection of FTT failure is 99.36% and 100% respectively, with average specificity of 99.36% and 97.63%, respectively. From studies with sufficient reported data, meta-analysis results demonstrated that both NIRS [OR = 0.09 (0.02-0.36); P < 0.001] and ID [OR = 0.39 (0.27-0.95); P = 0.04] were associated with significant reduction of FTT failure rates compared with CCA.

CONCLUSIONS

The use of ID and NIRS provided equivalent outcomes in detecting FTT failure and were superior to CCA. The ability to acquire continuous objective physiological data regarding tissue perfusion is a perceived advantage of these techniques. Reduced clinical staff workload and minimized hospital costs are also perceived as positive consequences of their use.

Modern postoperative monitoring of free flaps

PURPOSE OF REVIEW

Flap failure in microvascular reconstruction is a costly complication with total flap loss being the worst-case scenario. With the aim to rapidly identify a postoperative circulatory problem, some susceptible flaps can be saved by careful clinical monitoring or by various technical monitoring methods. In head and neck surgery, where the flaps are often buried and difficult to monitor clinically, a reliable technical monitoring method would be useful. A broad range of different techniques are in use varying according to practical and personal preferences among clinics and surgeons. However, no evidence for any particular technique being superb has emerged. We review reports of some frequently used and modern free flap monitoring techniques.

RECENT FINDINGS

Clinical monitoring is still the gold standard to which other techniques are compared to. Laser Doppler flowmetry and near-infrared spectroscopy have been reported to identify early circulatory problems, but both techniques are not well suited for buried flaps. Implantable Doppler, flow coupler, partial tissue oxygen pressure and microdialysis are invasive monitoring methods suitable for buried flaps.

SUMMARY

More research with practical and clinically relevant parameters, that is flap salvage rate, false positive rate and cost-efficiency are needed before objective comparisons between different monitoring techniques can be made.

The Effect of Norepinephrine and Dopamine on Radial Forearm Flap Partial Tissue Oxygen Pressure and Microdialysate Metabolite Measurements: A Randomized Controlled Trial

BACKGROUND

Patients undergoing ablative and reconstructive head and neck surgery with a microvascular flap have multiple factors that potentially decrease postoperative mean arterial pressure, which may endanger flap survival. The safety of vasopressor use has long been a topic of discussion. The authors analyzed the effect of vasopressors on microvascular flap perfusion after head and neck cancer reconstruction.

METHODS

A total of 27 patients were enrolled in a randomized, controlled, clinical trial. A microvascular radial forearm flap was used for reconstruction. Patients were allocated into one of three groups: dopamine, norepinephrine, and control. The intervention groups received the vasoactive drug, aiming to maintain the mean arterial pressure between 80 and 90 mmHg. Normovolemia was maintained according to central venous pressure. Flap perfusion was monitored with continuous tissue partial pressure of oxygen and microdialysate metabolite (lactate-to-pyruvate ratio) measurements.

RESULTS

No adverse effects were observed, and postoperative recovery was free of complications in all groups. Neither the lactate-to-pyruvate ratio nor continuous tissue partial pressure of oxygen values differed significantly between groups during the first 24 hours of the vasoactive drug infusion period or during the 72-hour follow-up.

CONCLUSIONS

Norepinephrine and dopamine are safe and effective vasopressors for use during the postoperative period following head and neck cancer surgery with microvascular reconstruction. Dopamine should be used with caution, however, because of the risk of side effects.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Variables affecting postoperative tissue perfusion monitoring in free flap breast reconstruction

Postoperative flap monitoring is a key component for successful free tissue transfer. Tissue oxygen saturation measurement (TOx) with near-infrared spectrophotometry (NIRS) is a method used for this purpose. The aim of this study was to identify external variables that can affect TOx. Patients who had breast reconstruction with free flaps were monitored prospectively and intra-operative details were recorded. Flap TOx was recorded with NIRS pre-extubation, postextubation, and then every four hours for 36 hours. At each of these time points, blood oxygen saturation (SO2), amount of supplemental oxygen, and blood pressure were recorded. Thirty flaps were monitored. Initially, a significant trend over time was detected such that for every increase of 24 hours, TOx decreased on average by 2.1% (P = 0.025). However, when accounting for SO2 levels, this decrease was no longer significant (P = 0.19). An increase by 1% in SO2 produced an increase in TOx reading of 0.36 (P = 0.007). The amount of supplemental O2, systolic blood pressure, and diastolic blood pressure did not have a significant impact on TOx (P > 0.05). The TOx values were highest in the free TRAM flaps and were lower in decreasing order in the muscle-sparing TRAM, DIEP, and SIEA flaps (P > 0.05). The TOx values did not significantly correlate with vessel size, perforator number, or perforator row. Postoperative flap TOx was found to correlate with SO2 and was not significantly dependent on blood pressure, supplemental O2, or surgical variables. Careful interpretation of oximetry values is essential in decision making during postoperative flap monitoring.

Comparison of tissue oxygenation and compartment pressure following tibia fracture

OBJECTIVE

We investigated the ability of direct continuous measurement of intramuscular tissue oxygenation (PmO(2)) to detect acute ischaemia in the leg in patients at risk for acute extremity compartment syndrome. Following tibia fracture treated by intramedullary nailing, we compared the proportions of PmO(2) and compartment pressure (CP) measurements that met the warning criteria for compartment syndrome.

METHODS

Participants included 10 patients sustaining acute isolated closed tibia shaft fractures treated by intramedullary nailing. A tissue oxygenation probe and a CP probe were percutaneously placed into the anterior compartment of the leg. PmO(2) and CP in the anterior compartment were measured in the injured leg for 48 h postoperatively. Measurements meeting the warning criteria were defined as PmO(2) < 10 mmHg, CP > 30 mmHg and perfusion pressure ΔP < 30 mmHg.

RESULTS

None of the patients developed compartment syndrome. Comparison of CP and PmO(2) showed a CP > 30 mmHg in 50.39% of CP measurements in all patients and a PmO(2) < 10 mmHg in 0.75% of PmO(2) measurements in two patients (P = 0.005). Comparison of ΔP and PmO(2) showed a ΔP < 30 mmHg in 31.01% of ΔP measurements in nine patients and a PmO(2) < 10 mmHg in 0.76% of PmO(2) measurements in one patient (P = 0.01).

CONCLUSION

In the absence of compartment syndrome, pressure measurements following tibia fracture treated with intramedullary nailing often met the warning criteria, whereas PmO(2) did not, suggesting that measurement of intramuscular tissue oxygenation may represent a potential method for the identification of acute compartment syndrome that deserves continued investigation.

Sympathetic innervation does not contribute to glycerol release in ischemic flaps

BACKGROUND

Extracellular glycerol as detected by microdialysis has been used as a surrogate marker for (ischemic) tissue damage and cellular membrane breakdown in the monitoring of free microvascular musculocutaneous flaps. One confounding factor for glycerol as a marker of ischemic cell damage is the effect of lipolysis and associated glycerol release as induced by sympathetic signalling alone. We hypothesized that extracellular glycerol concentrations in a microvascular flap with sympathetic innervation would be confounded by intact innervation per se as compared to denervated flap. Clinical relevance is related to the use of both free and pedicled flaps in reconstructive surgery. We tested the hypothesis in an experimental model of microvascular musculocutaneal flaps.

METHODS

Twelve pigs were anesthetized and mechanically ventilated. Two identical rectus abdominis musculocutaneal flaps were raised for the investigation. In the A-flaps the adventitia of the artery and accompanying innervation was carefully stripped, while in the B-flaps it was left untouched. Flap ischemia was induced by clamping both vessels for 60 minutes. The ischemia was confirmed by measuring tissue oxygen pressure, while extracellular lactate to pyruvate ratio indicated the accompanying anaerobic metabolism locally.

RESULTS

Intramuscular and subcutaneal extracellular glycerol concentrations were measured by microdialysate analyzer. Contrary to our hypothesis, glycerol concentrations were comparable between the two ischemia groups at 60 minutes (p = 0.089, T-test).

CONCLUSIONS

In this experimental model of vascular flap ischemia, intact innervation of the flap did not confound ischemia detection by glycerol. Extrapolation of the results to clinical setting warrants further studies.

Deep sedation with dexmedetomidine in a porcine model does not compromise the viability of free microvascular flap as depicted by microdialysis and tissue oxygen tension

BACKGROUND

Deep sedation is often necessary after major reconstructive plastic surgery in the face and neck regions to prevent sudden spontaneous movements capable of inflicting mechanical injury to the transplanted musculocutaneous flap(s). An adequate positioning may help to optimize oxygenation and perfusion of the transplanted tissues. We hypothesized that dexmedetomidine, a central alpha2-agonist and otherwise potentially ideal postoperative sedative drug, may induce vasoconstriction in denervated flaps, and thus increase the risk of tissue deterioration.

METHODS

Two symmetrical myocutaneous flaps were raised on each side of the upper abdomen in 12 anesthetized pigs. The sympathetic nerve fibers were stripped from the arteries in one of the flaps (denervated flap), while nerve fibers were kept untouched in the other (innervated flap). After simulation of ischemia and reperfusion periods, the animals were randomized to deep postoperative sedation with either propofol (n = 6) or dexmedetomidine (n = 6). Flap tissue metabolism was monitored by microdialysis and tissue-oxygen partial pressure. Glucose, lactate, and pyruvate concentrations were analyzed from the dialysate every 30 min for 4 h.

RESULTS

Mean arterial blood pressure was higher in the dexmedetomidine group (P = 0.036). Flap tissue metabolism remained stable throughout the experiment as measured by lactate-pyruvate and lactate-glucose ratios (median ranges 14.3-24.5 for lactate-pyruvate and 0.3-0.6 for lactate-glucose) and by tissue-oxygen partial pressure, and no differences were found between groups.

CONCLUSIONS

Our data suggest that dexmedetomidine, even if used for deep sedation, does not have deleterious effects on local perfusion or tissue metabolism in denervated musculocutaneous flaps.

Early reintervention of compromised free flaps improves success rate

INTRODUCTION AND AIM

To develop a protocolized monitor schedule in microvascular free flap reconstruction, we investigated a possible correlation between the outcome and the interval between clamp release and start of revision.

MATERIALS AND METHODS

All the charts of patients treated between 2000 and 2006 with a free flap were evaluated. The patients who underwent a flap revision were further analyzed.

RESULTS

A total of 608 free flaps were evaluated; 69 of these flaps were revised. Most vascular complications took place within the first 24 h; the latest complication was observed 8 days after surgery. After 6 days post surgery, the number of revisions decreased considerably. With regard to the salvaged flaps the mean time to start the revision was 46.5 h (SD 39). With regard to the failed revisions, the mean time to start the revision was 82.0 h (SD 47). This difference proved significant (P = 0.006).

CONCLUSION

Our data shows that the majority of anastomotic failures occur within the first 24 h. Thereafter, the frequency of failures decreases. We also found that the time between initial reconstruction and start of the salvage procedure influences the outcome of the revision negatively.