An intravascular oxygen tension monitoring device used in myocutaneous transplants: A preliminary report

An intravascular oxygen tension (PO₂) sensor (Continucath 1000) was used to assess flap viability in microsurgically revascularized free flaps for 36 hours postoperatively. In vitro, long term stability, linearity, and response time of the PO₂ sensor proved to be excellent. In 14 patients with sound flaps tissue PO₂ values were found to be between 15 and 35 mm Hg. In three cases a failing flap needed reexploration. In these cases the PO₂ sensor was accurate in detecting circulatory failure while in other cases it traced a number of physiological changes. The device holds promise for free flap monitoring but further studies are indicated. © 1993 Wiley-Liss Inc.     

The effect of glutathione, superoxide dismutase and adenosine triphosphate on venous flap survival

Oxygen-derived free radicals and the energy supply for resynthesis are important factors that affect flap survival. An experimental rabbit model was designed to investigate the effects of the free radical scavengers, glutathione (GSH), superoxide dismutase (SOD), and adenosine triphosphate (ATP-MgCL₂), on venous flap survival. Four 4×6 cm flaps were elevated in each animal along the axis of the thoraco-epigastric veins. Postoperatively, the agents were administered intravenously and relative flap survival was measured after two weeks. Mean flap survival, using the free radical scavengers, ranged between 76 and 87%, which showed a significant improvement over saline controls (68.73%, p<0.01). The respective mechanisms of the individual agents are discussed.     

Neutrophil function and pO2 in irradiated skin- and skin-muscle-flaps

Results of earlier investigations have demonstrated impaired function of polymorph-nuclear cells (PMN) in previously irradiated tissue. This study was designed to examine the effect of local oxygen pressure (pO₂) on neutrophil function in irradiated tissue. By choosing a pig model of irradiated and non-irradiated high perfusion wound environment (i.e. musculo-cutaneous (MC) flap) vs. a poor perfusion wound environment (i.e. random pattern (RP) skin flap), the effect of different pO₂ levels on neutrophil phagocytosis and respiratory burst (H₂O₂ production) were measured at 6, 12, and 16 weeks after irradiation. In both kinds of irradiated flaps, pO₂ levels and neutrophil function were significantly lower (RP: <20 mmHg; MC: 30 mmHg) than in corresponding flaps from non-irradiated tissue (RP: 26–28 mmHg; MC: 30–40 mmHg) and showed a progressive decline with increasing time interval after irradiation. Correlation between pO₂ and phagocytosis (p=0.001) and H₂O₂ production (p=0.02) proved to be statistically significant for the irradiated random pattern flaps, but not for musculocutaneous flaps.     

Transcutaneous Po2 monitoring for assessing viability and predicting survival of skin flaps: Experimental and clinical correlations

Rectangular skin flaps based on the right superficial epigastric vessels were designed on the groins of 36 rats. Preoperative control, intraoperative, and postoperative readings of oxygen tension (Po₂) were made atproximal, central, and distal sites on the flaps with a transcutaneous Po₂ (tcPo₂) monitor under various conditions of oxygen inspiration. The results of this experimental work indicated that the tcPo₂ monitor was useful in continuously and rapidly measuring changes in oxygen concentration in skin flaps in a noninvasive fashion. The monitoring demonstrated that the response time of the flaps to changes in the concentration of inspired oxygen was rapid (less than 15 seconds). The monitoring also was valuable in assessing viability of the flaps, in predicting flap survival, and in detecting any systemic factors influencing oxygen transport, such as pneumonia. As a result of the experimental series, tcPo₂ monitoring was used clinically to evaluate 18 flaps in 16 patients. As in the experimental series, the clinical measurements were significant and reproducible. They demonstrated that the tcPo₂ monitor provides safe, reliable monitoring of peripheral oxygenation in the microcirculation that is rapid, continuous, and totally noninvasive. It is concluded that simultaneous tcPo₂ measurements at control and flap sites provides a continuous record of the status of a flap that can improve the postoperative management of the surgical patient.     

Transcutaneous oxygen tension in flaps

Summary Transcutaneous oxygen tension (pTcO₂) in various types of flap is described and compared. Random and arterial flaps showed different pTcO₂ patterns. The value of delay was shown. The results indicated the potential of the pTcO₂ technique for flap research and for clinical monitoring of flap circulation.     

Current evidence on the use of near-infrared spectroscopy for postoperative free flap monitoring: A systematic review

BackgroundAlthough the surgical outcomes of free flap reconstruction have improved over time, vascular compromise remains a devastating complication. Near-infrared spectroscopy (NIRS) is a promising new free flap monitoring technique with the potential for better outcomes than clinical monitoring (CM). This systematic review aims to provide a comprehensive review of the current evidence regarding the use of NIRS for free flap monitoring.MethodsA systematic literature review was performed, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, on existing NRIS studies, including the clinical outcomes of NIRS monitoring, speed of detection, diagnostic accuracy, variables affecting NIRS accuracy, and cost-effectiveness.ResultsA total of 24 articles were included in this analysis. In most instances of flap compromise, NIRS enabled earlier detection of compromise than did CM, by an average of 8.1 (0.5–32.0) h. The flap salvage rate of flaps monitored with CM and NIRS (87.2%) was significantly higher than that of flaps monitored with CM alone (50.0%) (P<0.01). The overall survival rate for flaps monitored with CM and NIRS (98.1%) was also significantly higher than that for flaps monitored with CM alone (96.3%) (P=0.02). Blood oxygen saturation was the only variable with a significant effect on NIRS results.ConclusionNIRS is an objective and reliable flap monitoring technique that provides superior flap salvage and survival rates compared with CM, which translates to cost savings and a reduction in workload for healthcare staff. Further large-scale studies are needed to standardize flap compromise criterion values and efficacy for different flap types.     

Infrared surface temperature monitoring in the postoperative management of free tissue transfers

BACKGROUND:

Early identification of failing free flaps may allow for potential intervention and flap salvage. The predictive ability of flap temperature monitoring has been previously questioned. The present study investigated the ability of an infrared surface temperature monitoring device to detect trends in flap temperature and correlation with anastomotic thrombosis and flap failure.

METHODS:

Postoperative measurement of surface temperature was obtained in 47 microvascular free flaps. Differences in temperature between survival and failure groups were evaluated for statistical significance using Student’s t test (P<0.05). In addition, a single variable analysis was performed on 30 different flap characteristics to evaluate their prediction of flap failure.

RESULTS:

In total, eight flaps failed. Five of these were re-explored, of which one was salvaged. The three other flaps died a progressive death secondary to presumed thrombosis of the microcirculation despite adequate Doppler signals. Temperatures of the flap failure group during the last 24 h yielded a mean difference of 2°C (3.56°F) compared with surviving flaps (P<0.05). The temperature of the failing flaps began to decline at the eighth postoperative hour. Single variable analysis identified prior radiation to be a predictor of flap failure.

CONCLUSIONS:

A surface temperature measurement device provides reproducible digital readings without physical contact with the flap. Technical difficulties encountered in previous research with implantable or surface contact temperature probes are obviated with this noncontact technique. Flap temperature monitoring revealed a trend in temperature that correlates with anastomotic thrombosis and eventual flap failure.     

Continuous free flap monitoring: a modification of the Licox catheter probe system

Early recognition of flap failure is the solution for flap salvage. Many methods have been used to monitor free flaps. The Licox Catheter pO ₂ Micro-Probe instrument is used for continuous determination of oxygen partial pressure in body fluids (pO ₂) and tissues (p _tiO ₂). Minimally invasive catheter microprobes are used as sensors. Based on our experiences with this kind of tissue-oxygen measurement and according to our clinical experience, the Licox catheter probe system was modified. An online alarm system was developed to inform medical staff at the exact moment when the Licox software detects a definite fall in the p _tiO ₂ level in the transferred flap tissue. This modified device not only allows staff-saving free flap monitoring but is also time saving and facilitates online monitoring with the possibility of an immediate surgical intervention if vascular impairment should occur. This is a relevant factor for the success of a surgical revision     

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. © 2014 Wiley Periodicals, Inc. Microsurgery 35:123–128, 2015.     

Postoperative monitoring of lower limb free flaps with the Cook–Swartz implantable Doppler probe: A clinical trial

Background: Free flaps to the lower limb have inherently high venous pressures, potentially impairing flap viability, which may lead to limb amputation if flap failure ensues. Adequate monitoring of flap perfusion is thus essential, with timely detection of flap compromise able to potentiate flap salvage. While clinical monitoring has been popularized, recent use of the implantable Doppler probe has been used with success in other free flap settings. Methods: A comparative study of 40 consecutive patients undergoing microvascular free flap reconstruction of lower limb defects was undertaken, with postoperative monitoring achieved with either clinical monitoring alone or the use of the Cook‐Swartz implantable Doppler probe. Results: The use of the implantable Doppler probe was associated with salvage of 2/2 compromised flaps compared to salvage of 2/5 compromised flaps in the group undergoing clinical monitoring alone (salvage rate 100% vs. 40%, P = 0.28). While not statistically significant, this was a strong trend toward an improved flap salvage rate with the use of the implantable Doppler probe. There were no false positives or negatives in either group. One flap loss in the clinically monitored group resulted in limb amputation (the only amputation in the cohort). Conclusion: A trend toward early detection and salvage of flaps with anastomotic insufficiency was seen with the use of the Cook–Swartz implantable Doppler probe. These findings suggest a possible benefit of this technique as a stand‐alone or adjunctive tool in the clinical monitoring of free flaps, with further investigation warranted into the broader application of these devices. © 2009 Wiley‐Liss, Inc. Microsurgery 30:354–360, 2010.     

Analysis of 49 cases of flap compromise in 1310 free flaps for head and neck reconstruction

Background.

The purpose of this study was to analyze the causes of flap compromise and failure in head and neck free flap reconstruction.

Methods.

We retrospectively reviewed 1310 free flap reconstructions for head and neck defects performed between July 1995 and June 2006.

Results.

Forty‐nine cases of flap compromise due to vascular obstruction (3.7%) were identified, and 27 flaps were lost (2%). Arterial occlusions occurred in 12 flaps, with a salvage rate of 33%. Eight flaps failed within the first 24 hours, and only 1 of these was salvageable. Five of the 8 flaps had intraoperative thrombosis due to technical difficulties. Venous occlusions occurred in 31 flaps, with a salvage rate of 58%. Twenty‐two venous occlusions occurred within the first 72 hours. The main reason for venous failure was mechanical obstruction due to compression, twisting, kinking, or stretching of the vein. The most common cause of late failures (after 7 days) was unrecognized failure of a buried flap owing to the lack of reliable monitoring. Overall, there was no correlation between surgeon experience and flap failure, but the flap failure rate was lower in surgeons who had performed more than 70 free flap procedures.

Conclusion.

Precise surgical techniques, avoidance of mechanical obstruction, and better monitoring of buried flaps may further improve the success rate of free tissue transfer in complex head and neck reconstruction. © 2008 Wiley Periodicals, Inc. Head Neck, 2009     

Continuous mixed venous oxygen saturation monitoring during general anesthesia

Clinical evaluation of continuous Sv¯_{O 2} monitoring during general anesthesia was made in 21 surgical patients utilizing a fiberoptic reflectometry system combined with a pulmonary artery flow-directed balloon catheter. On-line in vivo values for Sv¯_{O 2} by the system were closely related to those obtained in vitro from a Radiometer ABL-300. There was a good correlation between changes of in vivo Sv¯_{O 2} and corresponding changes in cardiac index. We also observed that there were significant correlations between Sv¯_{O 2} and oxygen extraction ratio, and Sv¯_{O 2} and oxygen delivery. These data indicate that continuous monitoring of Sv¯_{O 2} during general anesthesia can provide on-line information not only about hemodynamic state but also on oxygen transport, which will be especially helpful in managing hemodynamicaly unstable patients during anesthesia.(Kemmotsu O, Yokota S, Mizushima M et al.: Continuous mixed venous oxygen saturation monitoring during general anesthesia. J Anesth 3: 188–193, 1989)     

Value of polarography in the control of viability of free compound flaps

Time course of oxygen tension in 30 free compound flaps was studied by the polarographic method. The use of two types of polarographic electrodes--open needle and closed membrane epicutaneous--in control over the viability of free compound flaps revealed essential differences in the obtained results. Zero pO2 value in measurement with an epicutaneous electrode is not always evidence of flap non-viability. A negative "oxygen test" in measurement with an open needle electrode was an indication for a repeated operation. Repeated operations were undertaken for circulatory disorders after transplantation of 13 flaps and were successful in 8 cases. In 10 of these 13 cases the circulatory disorder was detected in the stage of subcompensation.     

Free flap microcirculatory monitoring correlates to free flap temperature assessment

Introduction

Salvage rates of free flaps have been reported to be inversely related to the time interval between the onset of ischaemia and its clinical recognition. Consecutively, monitoring of free flaps remains of major importance. The aim of this study was to analyse the correlation of postoperative free flap microcirculation and free flap skin temperature as a potential tool of postoperative flap monitoring.

Hypothesis

Free flap skin temperature correlates to free flap capillary microcirculation.

Methods

Fifty-four free flaps were prospectively monitored during the study. Postoperative flap monitoring was performed using a regular digital infrared surface thermometer (Medisana FTD, Germany) simultaneously to microcirculatory assessment using combined Laser-Doppler and photospectrometry (Oxygen-to-see, Lea Medizintechnik, Germany).

Results

Mean microcirculatory blood flow was 105 ± 35 arbitrary units (AU). Mean temperature was 34.9 ± 2.2 °C. We found a significant correlation between free flap temperature and free flap capillary blood flow (Pearson correlation r = 0.48; p < 0.001) and postcapillary venous filling pressure (r = −0.32; p = 0.021) in 54 free flaps. A 1 °C less free flap temperature was associated with a decrease of the mean microcirculatory capillary blood flow by 37 relative units.

Conclusion

Our study demonstrates free flap skin temperature related to capillary microcirculation. Our primary hypothesis was confirmed. We postulate an acute temperature drop of 3 °C at the centre of the skin island as indicative of arterial thrombosis, whereas a 1–2 °C uniform temperature drop of the flap is indicative of venous compromise. Consecutively, free flap skin temperature assessment might be a reliable and inexpensive adjunct monitoring method in plastic reconstructive surgery to improve patients’ safety.     

Tissue oxygen tension measurement for monitoring musculocutaneous and cutaneous flaps

In pigs, latissimus dorsi musculocutaneous island flaps and buttock skin island flaps were raised. Subcutaneous (PscO2) and intramuscular oxygen tension (PimO2) were measured using a non-heated needle electrode before, during and after repeated occlusion of the supplying artery or the draining vein. During arterial and venous occlusion, the tissue oxygen tension in the musculocutaneous flap dropped rapidly. A plateau was reached after 15 min. After arterial occlusion the mean value was 20 mmHg (SEM = +/- 5 mmHg, N = 6) in the subcutis and 16 mmHg in the muscle (SEM = +/- 4 mmHg, N = 10). After venous occlusion the mean value was 11 mmHg (SEM = +/- 3 mmHg, N = 6) in the subcutis. In the skin flap the drop of PscO2 was slower, and after 30 min of arterial occlusion the mean value was 29 mmHg (SEM = +/- 9 mmHg, N = 6). This study has shown that tissue oxygen tension measurement can be used as a sensitive indicator of acute impairment of the supplying vessels in island flaps. The method seems to have potential for monitoring free tissue transfers. A comparable decrease in PscO2 was found for arterial and venous impairment.     

Early recognition of ischaemia with continuous real-time tissue oxygen monitoring in head and neck microvascular flaps

Aim of this study was to evaluate the reliability of a continuous real-time tissue oxygen monitoring method (Licox?) for postoperative follow-up of free microvascular flaps after ablative head and neck tumour surgery. We also wanted to establish and test accurate alarm levels for this monitoring method. One hundred eighteen head and neck cancer patients, operated in Tampere University Hospital, Finland, were analysed. Tissue oxygen (P_tiO₂) levels were continuously monitored with the Licox? system. Receiver operating characteristic analysis was performed considering following alarming signals: a clear change in the trend of the curve leading to a decline more than 50% in 1?h or a decline below 10?mmHg in the P_tiO₂ level. Licox? recognized all the patients who needed re-operation with sensitivity of 100% and specificity of 88%. The overall success rate was 99.2% (117 of 118) and flap salvage rate 88% (seven of eight), respectively. The Licox? tissue oxygen pressure monitoring system is a reliable method for detecting early postoperative circulation problems in free microvascular flaps. The suggested alarm signals are a clear change in the trend of the curve leading a decline more than 50% in an hour or a decline below 10?mmHg.     

Brain oxygen monitoring: in-vitro accuracy,long-term drift and response-time of Licox- and Neurotrend sensors

Summary Background. Oxygen tension sensors have been used to monitor tissue oxygenation in human brain for several years. The working principals of the most frequently used sensors, the Licox (LX) and Neurotrend (NT), are different, and they have never been validated independently for correct measurement in vitro. Therefore, we tried to clarify if the two currently available sensors provide sufficient accuracy and stability.Method. 12 LX oxygen tension sensors and NT sensors were placed into a liquid-filled tonometer chamber. The solution was kept at 37 ± 0.2 °C and equilibrated with five calibration gases containing different O₂- and CO₂-concentrations. After equilibration, readings were taken for each gas concentration (accuracy test). Afterwards, the sensors were left in 3% O₂ and 9% CO₂ and readings were taken after 24, 48, 72, 96 and 120 hours (drift test). Thereafter, a 90% response time test was performed transferring sensors from 1% to 5% oxygen concentration and back, using pre-equilibrated tonometers.Findings. All Licox oxygen probes [12] were used for this study. Two of 14 Neurotrend sensors did not calibrate, revealing a failure rate of 14% for NT. Oxygen tension during the accuracy test was measured as follows: 1% O₂ (7.1 mmHg): LX 6.5 ± 0.4, NT 5.3 ± 2.3 mmHg, 2% O₂ (14.2 mmHg): LX 12.9 ± 0.6, NT 12.1 ± 2.2 mmHg, 3% O₂ (21.4 mmHg): LX 19.8 ± 0.7, NT 19.4 ± 2.4 mmHg, 5% O₂ (35.8 mmHg): LX 33.4 ± 1.0 mmHg, NT 33.5 ± 2.9 mmHg, 8% O₂ (57.0 mmHg): 53.8 ± 1.5, NT 53.6 ± 3.3 mmHg. After 120 hours in 3% O₂ (21 mmHg), LX measured 19.8 ± 1.9 mmHg, NT 17.9 ± 4.7 mmHg. 90% response time from 1% to 5%/5% to 1% oxygen concentration was 129 ± 27/174 ± 26  sec for LX, 55 ± 19/98 ± 39 sec for NT.Conclusions. Both systems are measuring oxygen tension sufficiently, but more accurately with LX probes. NT sensors read significantly lower pO₂ in 1% O₂ and show an increasing deviation with higher oxygen concentrations which was due to two of twelve probes. A slight drift towards lower oxygen tension readings for both sensors but more pronounced for the NT does not impair long-term use. NT measures pCO₂ and pH very accurately.     

Identification of perioperative risk factor by laser‐doppler spectroscopy after free flap perfusion in the head and neck: A prospective clinical study

The aim of this study was to evaluate perioperative flap perfusion using noninvasive monitoring with a laser‐Doppler flowmetry and spectrophotometry unit (O2C) and identify whether perioperative blood flow, velocity, hemoglobin level (Hb), and oxygen saturation (SO₂) measured could be used as indicators of free flap success. Measurements of blood flow, velocity, Hb, and SO₂ were performed in 196 microvascular flaps, which had been transferred into the oral cavity to reconstruct ablative defects after surgery for oral cancer. The values were calculated superficially on the skin surface and at a depth of 8 mm. The results showed that perioperative absolute values measured were not associated with an increased rate of microvascular revisions or free flap failure. Independent predictors of microvascular revisions at the first postoperative day were the development of a falling trend in superficial and deep blood flow, and velocity in comparison with baseline values of variables measured. On day 2, all superficial and deep values of Hb, flow, and velocity were independent prognostic factors (P < 0.01), demonstrated as a downward trend were associated with a need for revision. The superficial and deep values of SO₂ (P = 0.59 and 0.43, respectively) were not associated with ultimate free flap failure. This is the first clinical study to demonstrate that during early free flap integration to the recipient site different parameters of perfusion and oxygenation play an important role at different points of time. Within the first two postoperative days, changes in these parameters can help influence the decision to revise microvascular anastomoses. © 2013 Wiley Periodicals, Inc. Microsurgery 34:345–351, 2014.     

Variations in flap blood flow and tissue PO2: a new technique for monitoring flap viability

An implantable and disposable tissue oxygen tension (PO2) probe, useful as a clinical monitor following free-tissue transfer, is described. Experimentally, using the rabbit epigastric groin flap model, we have found it to be a sensitive indicator of arterial and venous occlusion. Oxygen can be given to verify the integrity of the monitoring technique and check any abnormal reading. Animals administered oxygen will have a rapid increase in tissue PO2 when the pedicle is intact. If compromised by arterial or venous occlusion, the low readings demonstrate no change. The application of this new technique for monitoring free flaps in 12 patients is presented. In 2 patients the tissue PO2 monitor successfully detected early vessel thrombosis, resulting in reexploration of the anastomoses and salvage of the free flaps.     

Intracapillary haemoglobin oxygenation and interstitial pO2 in venous flaps: An experimental study in rats

In order to be able to objectively evaluate capillary perfusion of venous flaps, we created arterialised venous flaps, venous flow-through flaps, and unilateral pedicled venous island flaps in the epigastric vascular system of Wistar rats and determined their oxygen supply with two different methods. Interstitial pO₂ was polarographically measured with a probe placed in tracutaneously in the center of the 4 × 2.5 cm flaps and continuously recorded on a connected computer. Moreover, we also noninvasively determined the oxygenation of the intracapillary haemoglobin with a micro-lightguide spectrophotometer. The statistical evaluation showed comparable results for both measurement methods: Arterialised venous flaps had a better oxygen supply with a pO₂ of 16 mmHg and an Hb oxygenation of 23% than the other types of venous flaps, but they have a poorer oxygen supply than conventionally perfused flaps (pO₂: 24 mmHg, Hb oxygenation: 30%). Venous flow-through flaps (pO₂: 9 mmHg, Hb oxygenation: 17%) and unilateral pedicled venous island flaps had a significant better oxygen supply than skin flaps without any vascular connection. The results show that the capillary system in all types of venous flaps is reached by some of the inflowing oxygenated haemoglobin over the entire flap surface to different degrees. © 1998 Wiley-Liss, Inc. MICROSURGERY 18:324–330, 1998