British Jmmal ofPlastic Surperv (19911. 44.27-29 0 1991 The T&tees of Brit&h’&so&tioh of Plastic Surgeons

Pulse oximetry in postoperative monitoring of free muscle flaps L. A. Lindsey, J. D. Watson and A. A. Quaba Plastic Surgery Unit, Bangour General Hospital, Broxburn, West Lothian SUMMARY. The use of a pulse oxhneter for monitoring free muscle transfers is described. Three cases are presented, two of which were uncomplicated and one in which the need for revision of anastomosis was identified by the oximeter. Observations on a pedicled muscle flap are also reported. Pulse oximeters provide an improved photoplethysmographic monitoring technique which is easily performed u&g completely standard operating theatre equipment.

now very reliable and user-friendly (Strohl et al., 1986). The pulse oximeter should therefore be an ideal device for monitoring free flaps. So far its use has been restricted to monitoring reimplanted digits (Gordon, 1988) but in fact equipment presently available is able to monitor a wide variety of flaps.

The use of free flap techniques has now become well established in plastic surgery and appears likely to increase. One problem, however, is the failure of flaps due to problems at the site of the anastomosis, particularly in post-traumatic reconstruction. The most critical period is usually the first 24-48 hours following surgery when venous or arterial obstruction can cause the rapid, often undetected demise of a flap. Although clinical observation remains the most important factor in postoperative care, this is more difficult in the case of muscle flaps. A number of monitoring techniques have been devised to facilitate the early detection of poor flap perfusion, allowing prompt surgical intervention where necessary. These methods include thermometry, ultrasound Doppler, laser Doppler, transcutaneous oxygen measurement, fluorescein photography (Sloan and Sasaki, 1985) photoplethysmography (Harrison et al., 1981) and needle electrode oxygen measurement (Hjortdal et al., 1990). Most of the above techniques rely on specialist equipment and require some experience in their use. Ideally a monitoring technique should be easy to use, sensitive and specific and require only standard equipment. The technique of photoplethysmography (Harrison et al., 1981) proved to be a good method, able to predict flap failure and to some extent distinguish between venous and arterial obstruction, but was hampered by the complexity of the equipment required. Photoplethysmography monitors blood flow indirectly by measuring the absorbance of light in tissue as blood volume changes with arterial pulsation. The result is a pulsatile waveform which is lost in arterial obstruction and becomes flattened in venous obstruction with an increased baseline. The recently introduced pulse oximeter works on an identical principle, but as it measures light absorbance at two carefully chosen wavelengths it can derive the oxygen saturation of arterial haemoglobin as a percentage as well as displaying the plethysmographic waveform. For this reason, pulse oximeters have gone into widespread use as anaesthetic monitors and are


An unmodified Ohmeda Biox 3700e pulse oximeter was used to monitor free muscle flaps in three cases and a pedicled muscle flap in one case. In all cases the ear probe was used with the jaws held slightly apart with adhesive tape to prevent pressure necrosis. The probe may be gas-sterilised or swabbed with alcohol but we initially achieved sterility by feeding the probe down adjacent fingers of a small-sized surgical glove, which does not affect the readings. The probe is then placed so that a portion of the flap rests between its jaws, shielded from excessive ambient light (e.g. theatre light) and kept as still as possible (Fig. 1). After a few seconds the plethysmographic waveform should appear; it is important to recognise its regular character (Fig. 2) and to distinguish it from irregular movement artefact. Any saturation readings displayed in the absence of a regular, clear waveform must be disregarded. If the waveform is very weak a saturation reading may not be displayed.

Case reports

Case 1 A 17-year-old girl sustained a crush fracture to her right calcaneus with degloving skin loss over her heel. This was covered with a free rectus abdominis muscle flap based on the inferior epigastric vessels. The probe was applied at the end of the procedure and a clear but low-strength plethysmographic waveform was obtained with initial saturation of 80%. The saturation (see Fig. 3) and waveform strength continued to rise slowly and the flap survived without complication. 27


British Journal of Plastic Surgery Case 2 A 39-year-old man sustained a pylon fracture to his left ankle with skin loss over the fibula. A free rectus flap was used as for Case 1, but despite fresh bleeding from the muscle no reading could be obtained on the oximeter postoperatively. A decision was made to observe the flap but after 20 hours it was clear that the flap was not viable. Exploration revealed a blocked artery and reanastomosis produced a clear plethysmographic waveform with saturation of 80%. Saturation soon began to fall, however (Fig. 3); signal strength fell and extensive debridement was performed 2 days later, leaving about a tenth of the flap intact. This proved sufficient to cover the defect. Fig. 1

Case 3 A 17-year-old boy sustained soft tissue and tendon loss over his right fibula. A latissimus dorsi flap was used to cover the defect and immediately following anastomosis a clear low strength waveform with a saturation of 90% was achieved. The distal portion seemed poorly perfused at first and no reading could be obtained from it. After the muscle was stretched into place the distal part became pink and its saturation was recorded as 90%. Following this, saturation remained high (Fig. 3) and signal strength rose. The flap survived uneventfully.

Case 4 During the raising of a latissimus dorsi musculocutaneous flap for a breast reconstruction, readings were taken from the muscle. Oxygen saturation was found to be 95% before and after elevation, with clear plethysmographic waveforms. Clamping of the vessels abolished the waveform immediately in a reversible fashion.

Fig. 2 Figure l-Probe attached to muscle flap (Case 3). Figure 2-Pulse oximeter showing plethysmographic waveform (Case 3).



















90 Hours

Fig. 3 Figure SPlot

of oxygen saturation versus time for Cases 1 to 3.

Pulse Oximetry in Postoperative Monitoring of Free Muscle Flaps Discussion

The cases presented demonstrate the usefulness of pulse oximetry in monitoring free flaps. In Case 2 the oximeter identified the inadequacy of the initial anastomosis while the patient was still in theatre, but unfortunately insufficient importance was accorded to this at the time. Secondly, the oximeter predicted the flap’s subsequent partial failure, presumably due to the initial ischaemia. It would seem that absence of a plethysmographic waveform or an oxygen saturation much below about 80% would be a cause for concern, and the automatic alarms on the oximeter should be set accordingly. Previous experience with free flaps (Harrison et al., 1981) demonstrated the validity of standard photoplethysmography as a monitoring technique. The addition of saturation measurement with the advent of the pulse oximeter has clearly extended its use. The standard oximeter probes have the advantage of being readily available and may be used on digits or muscle flaps. When used on the latter they do require some elevation of the edge of the flap. It is likely that purpose-built surface mounting probes would overcome this problem, providing a completely non-invasive monitoring technique.


References Gordon,L. (1988). Microsurgical Reconstruction of the Extremities. New York: Springer-Verlag, p. 179. Harrison, D., Giriiag, M. aad Mot& G. (1981). Experience in monitoring the circulation in free flap transfers. Plastic and Reconstructive Surgery, 68,543. yjortdal, V. E., Awaad, A. M., Tiienga, E. J., Hansen, E. S., Kjolseth, D. K., Hearikaea, T. B. aad Gottrap, F. (1990). Tissue oxygen tension measurement for monitoring musculocutaneous and cutaneous flaps. Paper presented at British Microsurgical Society meeting, Canniesburn Hospital, Glasgow, January 1990. Sloan, G. M. and Sasaki, G. H. (1985). Noninvasive monitoring of tissue viability. Clinics in Plustic Surgery, 12, 185. Stroll, K., House, P., Holic, J., Fottke, J. and Chetutg, P. (1986). Comparison of three transmittance oximeters. Medical Instrumentation, 20, 143.

The Authors L. A. Lindsey, MB C&B, B.Med.Sci., SHO in Plastic Surgery J. D. Watson, FRCSG(Plast), FRCSEd, Consultant Plastic Surgeon A. A. Quaba, FRCSF.d(Plast), Consultant Plastic Surgeon Plastic Surgery Unit, Bangour Lothian EH52 6LR. Requests

for reprints


to Mr J. D. Watson.

Paper received 26 May 1990. Accepted 11 July 1990.




Pulse oximetry in postoperative monitoring of free muscle flaps.

The use of a pulse oximeter for monitoring free muscle transfers is described. Three cases are presented, two of which were uncomplicated and one in w...
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