E. Clyde Smoot HI, Beth A. Bergman, and Allan Roth
ASSESSMENT OF FLAP PERFUSION IN A PORCINE MODEL WITH A HEATED Downloaded by: National University of Singapore. Copyrighted material.
LASER DOPPLER PROBE ABSTRACT Skin and musculocutaneous flaps in a pig model were studied for their response to heating of the laser Doppler probe, both in the perfused state and in conditions of vascular occlusion. Even though heating the probe resulted in an elevation of perfusion of the flaps with no occlusions, it also increased the apparent perfusion of flaps that were occluded. The ability of flows to augment with heating, therefore, could not be perfectly correlated with impeded vascular flow. The addition of a heated perfusion reading for assessment of vascular occlusion did not improve the accuracy of the laser Doppler for monitoring of capillary-bed perfusion to detect vascular occlusion. The laser Doppler flowmeter has been used both in the laboratory and in the clinical setting for detection of changes in capillary blood flow in soft tissue. It is well established that changes in capillary flow within a cutaneous island flap have a linear relationship with the laser Doppler flow signal expressed in perfusion units.1 In a porcine model, the laser Doppler flow value has been shown to fall to a low level (but never to zero) in the presence of complete arterial or venous occlusion.2 This likely occurs because of a Doppler shift that is recorded from red blood cell oscillations even in the non-perfused state. Clinical experience for monitoring of free-tissue transfers with the laser Doppler has been variable. In a comparison of clinical assessment with laser Doppler monitoring to detect vascular occlusion. Walkinshaw et al3 concluded that measurements of flow state in free flaps did correlate with clinical observations. However, the flow patterns were not predictive nor sufficiently effective for indicating the need for clinical intervention to reexplore for pedicle occlusion. In that report, flow values never fell to zero but remained in a
low range of 20 mV, which was considered a physiologic zero. Unfortunately, in 17 patients who were monitored with an uneventful clinical course and survival of the flap, five had episodes in which the Doppler flow was indistinguishable from zero. Hence, it was concluded that there was a low specificity of the monitor, with many false readings indicating occlusion. On the other hand, Jenkins and colleagues4 concluded from clinical trials that the use of the laser Doppler monitor improved the salvage rate for free flap reexploration for pedicle occlusion from 50 percent to 85 percent. This study based monitoring on the detection of decreasing or low signal levels that decreased more than 50 percent from the control value during two consecutive 30 min readings. This would then trigger an evaluation by a physician for a clinical assessment and determination of need for early reexploration. It was the conclusion of this study that the laser Doppler more rapidly identified problems than did clinical monitoring, allowing for more timely correction and salvage. This method for monitoring has been confirmed and standardized by Clinton et al.5 as a
Division of Plastic and Reconstructive Surgery, Southern Illinois University of Medicine, Springfield, Illinois Reprint requests-. Dr. Smoot, Division of Plastic and Reconstructive Surgery, Southern Illinois University School of Medicine, 800 N. Rutledge St., P.O. Box 19230, Springfield, IL 62794-9230 Accepted for publication December 30, 1991 Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
131
sensitive method for monitoring for vascular occlusion. In addition, low flow readings noted by Doppler perfusion provided a more objective standard for nurses to evaluate the flaps in the perioperative period. Nonetheless, there remain problems of low specificity for Doppler readings used to determine pedicle occlusion. It has been observed that there is a non-linear response of laser Doppler flow readings to temperatureinduced changes in skin blood flow. When skin is heated, the response is an increase in the local blood flow that can be measured at the dermal capillary level.6 In the presence of a pedicle vascular occlusion, there have been indications from clinical experience that the skin may lose its ability to increase flow in response to heating. If this is a consistent finding, then failure to augment flow in response to a heat challenge may be a very early indication of the need to reexplore the pedicle for occlusion. Free flaps with no vascular compromise often have low perfusion in the immediate postoperative period. If an augmentation of flow from the low perfusion state can be produced by heating of the probe, an improvement in the specificity of the monitoring with the laser Doppler might be expected. Rather than rely on decreased flow readings to indicate a need for pedicle exploration, the clinician might monitor the response to heating. Failure to augment flow with heating would trigger suspicion of pedicle occlusion. This study was developed to investigate the skin and musculocutaneous flap response to heating of the laser Doppler probe in the perfused state and in conditions of venous or arterial occlusion. Flow augmentation patterns of the perfused and occluded pedicles were studied to establish whether augmented flow monitoring increases the specificity of the laser Doppler for clinical use.
132
MARCH 1992
superior gluteal vessels, respectively. Each flap was raised with an 8 x 8 cm2 skin island centered over the bulk of the flap. After isolating each pedicle, 2 percent Xylocaine was applied to the vessels. The flaps were allowed to perfuse for 20 min. At the end of this time, baseline laser Doppler (Med Pacific-LD 6000) readings at room temperature and after probe heating to 42° C for 2 min were completed. Each flap was then assigned by random drawing of prepared assignment slips to one of the following groups: (1) control, (2) venous occlusion or (3) arterial occlusion. The control flaps remained unoccluded. The appropriate artery or vein of the other groups was then ligated. Readings at room temperature and after probe heating were then taken at 15, 30, 60, 90, and 120 min. For clinical assessment of the flaps, three plastic surgery residents evaluated each at 15- and 30-min periods. Assessment included touching the flaps to assess temperature, capillary refill, and bleeding. Each flap was examined for the presence of vascular occlusion, and the evaluators were asked to determine whether arterial or venous occlusion was suspected for flaps determined to be failing. In this study of the sensitivity and specificity of the laser Doppler for various occlusions, heated and non-heated modes were compared to clinical assessment. For a given occlusion criterion (arterial occlusion, venous occlusion, or no occlusion), the ability to correctly determine the vascular status was compared with the clinical assessment.
RESULTS
Figure 1 is a summary of the results from all the pig flaps (n = 9 pigs). When the data are examined as a whole, two points can be made. First, it is apparent that the measurements taken at 15 min are not as definitive as those at 30 min following occlusion. MATERIALS AND METHODS Therefore, further analysis of the laser Doppler data was restricted to the 30-min time period. Second, it is Nine white domestic male pigs, weighing 40 to 50 apparent that even though heating the laser Doppler lb, were used for this experiment. Research was con- probe resulted in an elevation of the perfusion of flaps ducted in accordance with the guidelines established with no occlusions, it also increased the apparent perfuby the Southern Illinois University Laboratory Animal sion of the flaps that were occluded. Care and Use Committee. All animals were premediA more useful analysis of these data can be obcated with 0.02 mg/kg atropine sulfate, 2.2 mg/kg xy- tained by examining the success of the laser Doppler at lazine, and 11 mg/kg ketamine hydrochloride intra- signaling an occlusion of an individual flap, and commuscularly. Induction of anesthesia was then achieved paring the accuracy of this prediction with the assesswith 4 percent halothane in oxygen and nitrous oxide ment of the surgical residents. Table 1 lists five truth via nose cone. After endotracheal intubation, anesthe- tables so that a comparison of the sensitivity (detects sia was maintained using 1 percent halothane in oxy- occluded flaps) and specificity (detects only occluded gen and nitrous oxide. The pigs were then placed flaps) of the laser Doppler and residents can be made. prone, and the back and buttocks prepared and draped The perfusion levels at which a flap is called occluded in a sterile fashion. Two latissimus dorsi musculo- were determined by trial and error to give 100 percent cutaneous flaps and two gluteal skin flaps were raised sensitivity. The specificity percentage levels of the four and skeletonized to their thoracodorsal vessels and laser Doppler truth tables were not significantly differ-
Downloaded by: National University of Singapore. Copyrighted material.
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 2
ASSESSMENT OF FLAP PERFUSION/SMOOT, BERGMAN, ROTH
200
#
•
max
•
•
max
•
•
no occlusion venous occlusion arterial occlusion O flow 1 ^ A flow 1 D •
>i» 150
100 L. CL
50--
o
Table 1. Comparison of Laser Doppler and Clinical Assessment
Downloaded by: National University of Singapore. Copyrighted material.
30 60 90 120 Time from occlusion (0=no occlusion)
Figure 1. Summary of results from all pig flaps.
ent than those of the surgical residents (Fisher's exact test).
Laser Doppler Actual
Occluded Not occluded
A. Laser Doppler at 30 min following control period assuming that perfusion 50% from control is indicative of an occlusion. Occluded 20 0 Sensitivity (20/20) = 100% Not occluded 1 Specificity (6/7) = 85.7% Clinical Assessment Actual
Occluded Not occluded
E. Assessment by surgical residents. Occluded 80 0 Not occluded
26
Sensitivity (80/80) = 100% Specificity (26/29) = 89.6%
DISCUSSION From our clinical experience, we have noted three patterns in the objective monitoring of free-tissue transfers. The first is illustrated by patient 1 (Fig. 2). Initial low-flow states of the perfused flap increased several days after surgery, in the absence of vascular occlusion and uneventful healing. Initial flows immediately after surgery were in the range of 25 mV. These readings were hard to distinguish from physiologic zero (—20 mV), but the flows with heating augmented to 40 mV. This baseline perfusion and augmentation ability increased over the initial three days. Flows of 40 mV would augment by as much as 100 percent to levels of 80 mV at 10 hr. The ability to augment flow, however, was present throughout the postoperative period. The unheated flow baseline increased over the initial 36 hr, going from approximately 30 mV to an average of 90 mV, maintaining augmentation. An alternate pattern seen in the uncomplicated musculocutaneous flap of patient 2 (Fig. 3) showed augmentation of flow in the first 36 hr. The initial flow during the first 24 hr averaged 75 and then tapered after 36 hr, averaging a flow value of 30. The flap retained the ability to augment flow as much as ten times, to heated flow values of 300 mV. In the third patient example (Fig. 4), the flap failed because of venous occlusion, with ultimate flap necrosis despite reexploration. The patient showed initial flow augmentation in the first hour after surgery. However, by the third hour, the perfusion reading no longer
133
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 2
MARCH 1992
# •unheoted A — A heated (45 )
CO
D
40 Figure 2. Monitoring pattern of patient 1.
Time (hours)
^
300
E w
# — • unheated A — A heated (45 )
250
EZ 200
20
40
60
80
100 Figure 3. Monitoring pattern of patient 2.
Time (hours)
160 # •unheated A — A heated (45 )
134
60
Figure 4. Monitoring pattern of patient 3.
Downloaded by: National University of Singapore. Copyrighted material.
20
ASSESSMENT OF FLAP PERFUSION/SMOOT, BERGMAN, ROTH
force a reevaluation or reexploration for pedicle assessment. If a large absolute value of increased flow in the flap is noted with heating of the probe, this indicates a good flow reserve and less likelihood of pedicle problems. A large augmented flow can be reassuring in evaluating tissue perfusion. However, we have not found mere flow augmentation (in small increments) to indicate unimpeded flow. We were not able to improve the specificity of detecting vascular occlusion by adding a heated mode assessment, unless we were willing to sacrifice sensitivity. Overall accuracy could not be improved for monitoring of capillary-bed perfusion.
REFERENCES Fischer JC, Parker PM, Shaw WW: Laser Doppler flow meter measurements of skin perfusion changes associated with arterial or venous compromise in the cutaneous island flap. Microsurgery 6:238, 1985 Svensson H, Svedman P, Holmberg J, lacobsson S: Detecting arterial and venous obstruction in flaps. Ann Plast Surg 14: 20, 1985 Walkinshaw R, Holloway A, Bulkley A, Engraw LH: Clinical evaluation of laser Doppler blood flow measurements in free flaps. Ann Plast Surg. 18:212, 1987 Jenkins S, Sepka R, Barwick WJ: Routine use of laser Doppler flowmetry for monitoring autologous tissue transplants. Ann Plast Surg. 21:423, 1988 Clinton MS, Sepka RS, Bristol D, et ai: Establishment of normal ranges of laser Doppler blood flow in autologous tissue transplants. Plast Reconstr Surg 87:299, 1991 Neufeld GR, Galante SR, Whang JM, et al.: Skin blood flow from gas transport: Helium, xenon and laser Doppler compared. Microvasc Res 34:143, 1988
Downloaded by: National University of Singapore. Copyrighted material.
showed augmentation and the initial high flow values rapidly fell to zero. After exploration, the flap flow would not augment, and the perfusion readings varied from 20 to 40, without any increase seen when the heated probe was used. This flap ultimately necrosed and venous occlusion was diagnosed. The laser Doppler is beneficial for detecting immediate total occlusion, whether arterial or venous. In other studies, as well as in our experience with these flaps, the capillary flow values detected at the surface level fell to low levels near the physiologic zero range within minutes of occluding the vascular tree. However, creation of partial pedicle occlusions in the experimental flap could not be detected in capillary flow patterns. Laser Doppler flow signals can be monitored to detect early vascular occlusion with the same accuracy as resident physician clinical assessment. If the monitoring can be instituted with reliable nursing oversight and reporting, then the Doppler can be used with confidence for early detection of problems. The laser Doppler with the heated mode may be beneficial in monitoring flow as the flap is inset or dressed after immediate transfer (when flows may be low), to make sure that no correctable occlusion is created because of compression of the vessels. The Doppler can also be very helpful for use in the recovery room to detect early venous occlusion, when rapid refill of the skin is hard to distinguish from venous occlusion. Even the clinical assessment, based on flap appearance, is not completely accurate. In the low-flow states, the paleness of the flap may confuse the examiner. An acute venous occlusion may resemble capillary flow with blanching and refill noted, further misleading the clinician. The laser Doppler signal, if clear or absent, may reinforce the clinical assessment or
This study was carried out with a grant from the Plastic Surgery Educational Foundation. The authors thank Hans Suchy, Aruna Mathur, and Michelle Poole for their technical assistance in performing the animal surgery.
135
ASSESSMENT OF FLAP PERFUSION IN A PORCINE MODEL WITH A HEATED Downloaded by: National University of Singapore. Copyrighted material.
LASER DOPPLER PROBE ABSTRACT Skin and musculocutaneous flaps in a pig model were studied for their response to heating of the laser Doppler probe, both in the perfused state and in conditions of vascular occlusion. Even though heating the probe resulted in an elevation of perfusion of the flaps with no occlusions, it also increased the apparent perfusion of flaps that were occluded. The ability of flows to augment with heating, therefore, could not be perfectly correlated with impeded vascular flow. The addition of a heated perfusion reading for assessment of vascular occlusion did not improve the accuracy of the laser Doppler for monitoring of capillary-bed perfusion to detect vascular occlusion. The laser Doppler flowmeter has been used both in the laboratory and in the clinical setting for detection of changes in capillary blood flow in soft tissue. It is well established that changes in capillary flow within a cutaneous island flap have a linear relationship with the laser Doppler flow signal expressed in perfusion units.1 In a porcine model, the laser Doppler flow value has been shown to fall to a low level (but never to zero) in the presence of complete arterial or venous occlusion.2 This likely occurs because of a Doppler shift that is recorded from red blood cell oscillations even in the non-perfused state. Clinical experience for monitoring of free-tissue transfers with the laser Doppler has been variable. In a comparison of clinical assessment with laser Doppler monitoring to detect vascular occlusion. Walkinshaw et al3 concluded that measurements of flow state in free flaps did correlate with clinical observations. However, the flow patterns were not predictive nor sufficiently effective for indicating the need for clinical intervention to reexplore for pedicle occlusion. In that report, flow values never fell to zero but remained in a
low range of 20 mV, which was considered a physiologic zero. Unfortunately, in 17 patients who were monitored with an uneventful clinical course and survival of the flap, five had episodes in which the Doppler flow was indistinguishable from zero. Hence, it was concluded that there was a low specificity of the monitor, with many false readings indicating occlusion. On the other hand, Jenkins and colleagues4 concluded from clinical trials that the use of the laser Doppler monitor improved the salvage rate for free flap reexploration for pedicle occlusion from 50 percent to 85 percent. This study based monitoring on the detection of decreasing or low signal levels that decreased more than 50 percent from the control value during two consecutive 30 min readings. This would then trigger an evaluation by a physician for a clinical assessment and determination of need for early reexploration. It was the conclusion of this study that the laser Doppler more rapidly identified problems than did clinical monitoring, allowing for more timely correction and salvage. This method for monitoring has been confirmed and standardized by Clinton et al.5 as a
Division of Plastic and Reconstructive Surgery, Southern Illinois University of Medicine, Springfield, Illinois Reprint requests-. Dr. Smoot, Division of Plastic and Reconstructive Surgery, Southern Illinois University School of Medicine, 800 N. Rutledge St., P.O. Box 19230, Springfield, IL 62794-9230 Accepted for publication December 30, 1991 Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
131
sensitive method for monitoring for vascular occlusion. In addition, low flow readings noted by Doppler perfusion provided a more objective standard for nurses to evaluate the flaps in the perioperative period. Nonetheless, there remain problems of low specificity for Doppler readings used to determine pedicle occlusion. It has been observed that there is a non-linear response of laser Doppler flow readings to temperatureinduced changes in skin blood flow. When skin is heated, the response is an increase in the local blood flow that can be measured at the dermal capillary level.6 In the presence of a pedicle vascular occlusion, there have been indications from clinical experience that the skin may lose its ability to increase flow in response to heating. If this is a consistent finding, then failure to augment flow in response to a heat challenge may be a very early indication of the need to reexplore the pedicle for occlusion. Free flaps with no vascular compromise often have low perfusion in the immediate postoperative period. If an augmentation of flow from the low perfusion state can be produced by heating of the probe, an improvement in the specificity of the monitoring with the laser Doppler might be expected. Rather than rely on decreased flow readings to indicate a need for pedicle exploration, the clinician might monitor the response to heating. Failure to augment flow with heating would trigger suspicion of pedicle occlusion. This study was developed to investigate the skin and musculocutaneous flap response to heating of the laser Doppler probe in the perfused state and in conditions of venous or arterial occlusion. Flow augmentation patterns of the perfused and occluded pedicles were studied to establish whether augmented flow monitoring increases the specificity of the laser Doppler for clinical use.
132
MARCH 1992
superior gluteal vessels, respectively. Each flap was raised with an 8 x 8 cm2 skin island centered over the bulk of the flap. After isolating each pedicle, 2 percent Xylocaine was applied to the vessels. The flaps were allowed to perfuse for 20 min. At the end of this time, baseline laser Doppler (Med Pacific-LD 6000) readings at room temperature and after probe heating to 42° C for 2 min were completed. Each flap was then assigned by random drawing of prepared assignment slips to one of the following groups: (1) control, (2) venous occlusion or (3) arterial occlusion. The control flaps remained unoccluded. The appropriate artery or vein of the other groups was then ligated. Readings at room temperature and after probe heating were then taken at 15, 30, 60, 90, and 120 min. For clinical assessment of the flaps, three plastic surgery residents evaluated each at 15- and 30-min periods. Assessment included touching the flaps to assess temperature, capillary refill, and bleeding. Each flap was examined for the presence of vascular occlusion, and the evaluators were asked to determine whether arterial or venous occlusion was suspected for flaps determined to be failing. In this study of the sensitivity and specificity of the laser Doppler for various occlusions, heated and non-heated modes were compared to clinical assessment. For a given occlusion criterion (arterial occlusion, venous occlusion, or no occlusion), the ability to correctly determine the vascular status was compared with the clinical assessment.
RESULTS
Figure 1 is a summary of the results from all the pig flaps (n = 9 pigs). When the data are examined as a whole, two points can be made. First, it is apparent that the measurements taken at 15 min are not as definitive as those at 30 min following occlusion. MATERIALS AND METHODS Therefore, further analysis of the laser Doppler data was restricted to the 30-min time period. Second, it is Nine white domestic male pigs, weighing 40 to 50 apparent that even though heating the laser Doppler lb, were used for this experiment. Research was con- probe resulted in an elevation of the perfusion of flaps ducted in accordance with the guidelines established with no occlusions, it also increased the apparent perfuby the Southern Illinois University Laboratory Animal sion of the flaps that were occluded. Care and Use Committee. All animals were premediA more useful analysis of these data can be obcated with 0.02 mg/kg atropine sulfate, 2.2 mg/kg xy- tained by examining the success of the laser Doppler at lazine, and 11 mg/kg ketamine hydrochloride intra- signaling an occlusion of an individual flap, and commuscularly. Induction of anesthesia was then achieved paring the accuracy of this prediction with the assesswith 4 percent halothane in oxygen and nitrous oxide ment of the surgical residents. Table 1 lists five truth via nose cone. After endotracheal intubation, anesthe- tables so that a comparison of the sensitivity (detects sia was maintained using 1 percent halothane in oxy- occluded flaps) and specificity (detects only occluded gen and nitrous oxide. The pigs were then placed flaps) of the laser Doppler and residents can be made. prone, and the back and buttocks prepared and draped The perfusion levels at which a flap is called occluded in a sterile fashion. Two latissimus dorsi musculo- were determined by trial and error to give 100 percent cutaneous flaps and two gluteal skin flaps were raised sensitivity. The specificity percentage levels of the four and skeletonized to their thoracodorsal vessels and laser Doppler truth tables were not significantly differ-
Downloaded by: National University of Singapore. Copyrighted material.
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 2
ASSESSMENT OF FLAP PERFUSION/SMOOT, BERGMAN, ROTH
200
#
•
max
•
•
max
•
•
no occlusion venous occlusion arterial occlusion O flow 1 ^ A flow 1 D •
>i» 150
100 L. CL
50--
o
Table 1. Comparison of Laser Doppler and Clinical Assessment
Downloaded by: National University of Singapore. Copyrighted material.
30 60 90 120 Time from occlusion (0=no occlusion)
Figure 1. Summary of results from all pig flaps.
ent than those of the surgical residents (Fisher's exact test).
Laser Doppler Actual
Occluded Not occluded
A. Laser Doppler at 30 min following control period assuming that perfusion 50% from control is indicative of an occlusion. Occluded 20 0 Sensitivity (20/20) = 100% Not occluded 1 Specificity (6/7) = 85.7% Clinical Assessment Actual
Occluded Not occluded
E. Assessment by surgical residents. Occluded 80 0 Not occluded
26
Sensitivity (80/80) = 100% Specificity (26/29) = 89.6%
DISCUSSION From our clinical experience, we have noted three patterns in the objective monitoring of free-tissue transfers. The first is illustrated by patient 1 (Fig. 2). Initial low-flow states of the perfused flap increased several days after surgery, in the absence of vascular occlusion and uneventful healing. Initial flows immediately after surgery were in the range of 25 mV. These readings were hard to distinguish from physiologic zero (—20 mV), but the flows with heating augmented to 40 mV. This baseline perfusion and augmentation ability increased over the initial three days. Flows of 40 mV would augment by as much as 100 percent to levels of 80 mV at 10 hr. The ability to augment flow, however, was present throughout the postoperative period. The unheated flow baseline increased over the initial 36 hr, going from approximately 30 mV to an average of 90 mV, maintaining augmentation. An alternate pattern seen in the uncomplicated musculocutaneous flap of patient 2 (Fig. 3) showed augmentation of flow in the first 36 hr. The initial flow during the first 24 hr averaged 75 and then tapered after 36 hr, averaging a flow value of 30. The flap retained the ability to augment flow as much as ten times, to heated flow values of 300 mV. In the third patient example (Fig. 4), the flap failed because of venous occlusion, with ultimate flap necrosis despite reexploration. The patient showed initial flow augmentation in the first hour after surgery. However, by the third hour, the perfusion reading no longer
133
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 2
MARCH 1992
# •unheoted A — A heated (45 )
CO
D
40 Figure 2. Monitoring pattern of patient 1.
Time (hours)
^
300
E w
# — • unheated A — A heated (45 )
250
EZ 200
20
40
60
80
100 Figure 3. Monitoring pattern of patient 2.
Time (hours)
160 # •unheated A — A heated (45 )
134
60
Figure 4. Monitoring pattern of patient 3.
Downloaded by: National University of Singapore. Copyrighted material.
20
ASSESSMENT OF FLAP PERFUSION/SMOOT, BERGMAN, ROTH
force a reevaluation or reexploration for pedicle assessment. If a large absolute value of increased flow in the flap is noted with heating of the probe, this indicates a good flow reserve and less likelihood of pedicle problems. A large augmented flow can be reassuring in evaluating tissue perfusion. However, we have not found mere flow augmentation (in small increments) to indicate unimpeded flow. We were not able to improve the specificity of detecting vascular occlusion by adding a heated mode assessment, unless we were willing to sacrifice sensitivity. Overall accuracy could not be improved for monitoring of capillary-bed perfusion.
REFERENCES Fischer JC, Parker PM, Shaw WW: Laser Doppler flow meter measurements of skin perfusion changes associated with arterial or venous compromise in the cutaneous island flap. Microsurgery 6:238, 1985 Svensson H, Svedman P, Holmberg J, lacobsson S: Detecting arterial and venous obstruction in flaps. Ann Plast Surg 14: 20, 1985 Walkinshaw R, Holloway A, Bulkley A, Engraw LH: Clinical evaluation of laser Doppler blood flow measurements in free flaps. Ann Plast Surg. 18:212, 1987 Jenkins S, Sepka R, Barwick WJ: Routine use of laser Doppler flowmetry for monitoring autologous tissue transplants. Ann Plast Surg. 21:423, 1988 Clinton MS, Sepka RS, Bristol D, et ai: Establishment of normal ranges of laser Doppler blood flow in autologous tissue transplants. Plast Reconstr Surg 87:299, 1991 Neufeld GR, Galante SR, Whang JM, et al.: Skin blood flow from gas transport: Helium, xenon and laser Doppler compared. Microvasc Res 34:143, 1988
Downloaded by: National University of Singapore. Copyrighted material.
showed augmentation and the initial high flow values rapidly fell to zero. After exploration, the flap flow would not augment, and the perfusion readings varied from 20 to 40, without any increase seen when the heated probe was used. This flap ultimately necrosed and venous occlusion was diagnosed. The laser Doppler is beneficial for detecting immediate total occlusion, whether arterial or venous. In other studies, as well as in our experience with these flaps, the capillary flow values detected at the surface level fell to low levels near the physiologic zero range within minutes of occluding the vascular tree. However, creation of partial pedicle occlusions in the experimental flap could not be detected in capillary flow patterns. Laser Doppler flow signals can be monitored to detect early vascular occlusion with the same accuracy as resident physician clinical assessment. If the monitoring can be instituted with reliable nursing oversight and reporting, then the Doppler can be used with confidence for early detection of problems. The laser Doppler with the heated mode may be beneficial in monitoring flow as the flap is inset or dressed after immediate transfer (when flows may be low), to make sure that no correctable occlusion is created because of compression of the vessels. The Doppler can also be very helpful for use in the recovery room to detect early venous occlusion, when rapid refill of the skin is hard to distinguish from venous occlusion. Even the clinical assessment, based on flap appearance, is not completely accurate. In the low-flow states, the paleness of the flap may confuse the examiner. An acute venous occlusion may resemble capillary flow with blanching and refill noted, further misleading the clinician. The laser Doppler signal, if clear or absent, may reinforce the clinical assessment or
This study was carried out with a grant from the Plastic Surgery Educational Foundation. The authors thank Hans Suchy, Aruna Mathur, and Michelle Poole for their technical assistance in performing the animal surgery.
135
