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J Thorac Cardiovasc Surg 1998;116:1081-1082
© 1998 Mosby, Inc.
LETTERS TO THE EDITOR |
To the Editor:
Benedetti and colleagues
1 imply that a causal relationship exists between their findings from neurophysiologic assessment of abdominal muscle reflexes and sensory and evoked potentials of the operative thoracotomy scar and intercostal nerve impairment. They subsequently infer that intercostal nerve impairment is more severe in posterolateral thoracotomy than muscle-sparing thoracotomy, accounting for the greater level of pain associated with the muscle-splitting incision. I wish to present some observations, as a result of my subjective experience with 180 consecutive muscle-sparing incisions performed in the last 2 years, that call into question this interesting concept regarding postthoracotomy pain.
Despite my extensive use of the muscle-sparing approach, the preferred incision for all except chest wall resections (including lung resections, sleeve resections, posterior mediastinal mass excisions, video-assisted thoracoscopic surgical procedures, and esophageal procedures), I believe that postoperative pain is only slightly less than with muscle splitting. Immediate postoperative arm movement, however, does appear to be improved. Hazelrigg and associates 2 have documented similar objective findings.
My difficulty with the study of Benedetti and colleagues 1 begins with the muscle-splitting thoracotomy they employ. They have chosen to compare the posterolateral thoracotomy with a muscle-sparing incision through the auscultatory triangle, with a skin incision 5 cm smaller than the muscle-splitting posterolateral incision. Their statement that muscle-sparing thoracotomy causes less pain and fewer complications is supported by 8 references; however, only 2 of these used the auscultatory triangle approach. In addition, only 1 of these references objectively measured pain in 50 patients and concluded that there was a statistically significant, albeit small, difference between muscle-splitting and muscle-sparing groups. 2 Furthermore, this single reference did not use the auscultatory triangle approach but rather employed the standard lateral incision.
I further propose that the trauma of the 2 approaches is the same, other than the skin incision and cutting of muscles. Although without doubt I agree that nerve damage plays an important role in acute postthoracotomy pain, I do not believe that intercostal nerve impairment and postoperative pain intensity are solely related to the trauma produced by the incision of muscle groups. The standard posterolateral incision does indeed incise muscles of the back and chest wall (latissimus dorsi, serratus anterior, and trapezius), which does not occur with the muscle-sparing approach. After observing, however, that some patients show relatively little difference in postoperative pain between approaches, and indeed some patients after video-assisted thoracoscopic surgical procedures have pain equivalent to that seen with a full thoracotomy, I would argue that a significant component of pain is produced at the time of rib spreading. I would assume that stretching or damage of the intercostal nerves are the same during rib spreading in the 2 procedures described in the article under discussion.
The anatomy of the proposed nerve impairment is also difficult to conceptualize. The superficial abdominal reflexes are mediated by lower intercostal nerves T7 through T12. Presumably the skin incision made by Benedetti and colleagues 1 was either in the T5 or T6 dermatome, with the fifth or sixth intercostal space entered. How this could affect the lower intercostal nerves is unclear. In my own experience, I perform a vertical midaxillary skin incision as described by Ginsberg. 3 I would expect such an incision to cut across several dermatomes, being almost in a direct line with T3 through T6 lateral cutaneous branches of the intercostal nerves. Interestingly, although almost all the patients describe anesthesia in the T5 or T6 dermatome after the operation, this appears to depend on which intercostal space was entered. One woman has reported loss of sensation to the affected nipple, and I have observed 2 cases of ipsilateral rectus weakness, both of which occurred earlier in my experience, when the vertical incision was carried down to the level of T8 or T9 to reflect the lower border of the serratus anterior. Since that experience, I have carried the incision to T7 and then split the serratus over the intercostal space to be entered, with no untoward effects noted. I believe that this experience indicates that the location of the skin incision is not as important as the intercostal space that is entered and spread.
I agree with Benedetti and colleagues 1 that the data show that electromyographic responses, somatosensory evoked potentials, and tactile electrical thresholds are related to pain, but I am concerned that this was true for patients undergoing both posterolateral and muscle-sparing thoracotomy (Fig. 5 in Benedetti and colleagues 1), with variability within each group being high (Figs. 2, 3, and 4 in Benedetti and colleagues 1). Indeed, in a recent article by this same group examining superficial abdominal reflexes in muscle-incising posterolateral incisions, 55% of patients had reflexes present and 19 of 42 had absence. 4 If intercostal nerve impairment is implicated, should not a greater percentage of patients undergoing posterolateral incision lose this reflex?
The pathophysiology of postthoracotomy pain is complex. Benedetti and colleagues 1 are to be commended for their work with such a difficult, multifactorial problem. I look forward to their further investigations in this area.
Peter Fonseca, MD, PhD
Department of Cardiothoracic Surgery
National Naval Medical Center
8901 Wisconsin Ave
Bethesda, MD 20889
12/8/92803
References
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