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Ann Thorac Surg 2000;70:2045-2049
© 2000 The Society of Thoracic Surgeons

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Original article: cardiovascular

Pain pattern and left internal mammary artery grafting

^a Clinic for Cardiovascular Surgery, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland
^b Surgical Intensive Care Unit, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland

Accepted for publication April 25, 2000.

Address reprint requests to Dr Mueller, Clinic for Cardiovascular Surgery, Centre Hospitalier Universitaire Vaudois (CHUV), CH-1011 Lausanne, Switzerland
e-mail: xavier.mueller{at}chuv.hospvd.ch

	Abstract

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Background. This study was designed to determine whether the pain pattern in patients with an internal mammary artery (IMA) harvest differs from that in other cardiac operations and whether these patients present specific characteristics with clinical implications.

Methods. One hundred patients with left IMA grafting (IMA group) were compared prospectively with 100 patients who had a heart operation without IMA harvest (non-IMA group). Pain assessment was performed on postoperative days (POD) 1, 2, 3, and 7, and included pain intensity (10-point scale) and pain localization.

Results. In the IMA group, pain intensity was higher on POD 2 (4.2 ± 2.4 versus 3.2 ± 2.3, p < 0.01), and there were more patients without pain on POD 7 (32 versus 19, p = 0.03). In the IMA group, more patients had left basal thoracic pain throughout the entire study period and had sternal pain on POD 7, whereas more patients in the non-IMA group complained about back pain during the early postoperative period.

Conclusions. The impact of IMA harvest on pain intensity is moderate, but the pain localization pattern of each group exhibits specific features that could help to better target pain management.

	Introduction

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Since the introduction of coronary artery bypass grafting in the treatment of coronary artery disease [1], coronary artery revascularization has become the fastest growing form of surgery. Over many years, reversed saphenous veins were the preferred graft material for coronary artery revascularization. In the meanwhile, however, higher long-term patency rates have been achieved with internal mammary artery (IMA) grafts than with saphenous vein grafts [2, 3]. These observations led to an exponential increase in the use of IMA for coronary artery revascularization and the emergence of a number of new techniques, increasing its versatility.

Although most aspects of postoperative care for patients with IMA grafting and for patients who undergo other cardiac operations are similar, some features such as increased incidence of atelectasis and postoperative shunting [4], postoperative bleeding of the harvest bed [5], or inadequate flow of the IMA [6] deserve special attention. Because of the specific retraction required for IMA harvest and the additional chest wall trauma of the harvesting itself, pain pattern in IMA patients may differ from other cardiac operation patients and present specific characteristics with clinical implications. Therefore, we compared pain localization and intensity of patients with left IMA harvest versus patients with other cardiac procedures.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Patients
This study involved two groups of 100 adult patients each. One group (IMA group) included 100 consecutive patients who underwent coronary artery bypass grafting involving the left IMA. The other group (non-IMA group) included 100 consecutive patients who had heart operation without IMA harvest. The data were collected prospectively and patient inclusion started January 1998.

Methods
All the patients underwent median sternotomy for open heart operation and fulfilled selection criteria chosen to minimize heterogeneity of the sample and to ensure proper data collection. These criteria included an extubation before the first postoperative morning, the absence of alterations in cognitive functioning at any time during the hospital stay as well as fluent French speaking and reading ability. Moreover patients were excluded if they required a ventricular assist device, an intraaortic balloon counterpulsation, a postoperative pneumothorax requiring thoracic drainage, or a second operative procedure (cardiac or noncardiac) during the same hospital stay.

All patients had standard bypass procedures with membrane oxygenation and moderate hypothermia. Patients with IMA grafting had the left IMA harvested but neither the right one nor both, as it is our policy to perform unilateral left IMA grafting only on the left anterior descending artery. The Delacroix-Chevalier retractor (Delacroix-Chevalier, Paris, France) [7], allowing anteroposterior retraction without external support, was used for IMA exposure. The arms were positioned along the body on the operating table. Sternum was closed with five peristernal wires. Mediastinal and thoracic drains were passed through the rectus abdominis muscles just below the xyphoid area.

Basically the analgesic regimen included, during the first 24 hours, intravenous morphine sulfate at a dose of 1 mg/h when the body weight was less than 90 kg and 2 mg/h for heavier patients. From the first postoperative day (POD) till the removal of the drain (POD 2 or 3), 500 mg paracetamol was given four times a day orally, and 5 to 10 mg morphine was injected subcutaneously as needed. Then paracetamol was administered as needed alternating with tramadol tablets of 50 mg up to four times a day.

Pain location and intensity were documented between 7 and 9 a.m. on the first, second, third, and seventh POD. The nurse in charge was instructed to report exactly the painful areas of the thorax and its surroundings on a specially designed diagram as shown in Figure 1. There were 18 anatomic areas. Boundaries between areas were drawn at anatomic landmarks when possible. It was expected that these divisions would approximate those used by patients when asked to describe their pain location. The distribution of pain was quantified by counting the number of areas involved. A numeric rating scale from 0 to 10, with 0 representing "no pain" and 10 representing "the worst possible pain," was used to assess the subject’s maximal pain intensity. Importantly, all the nurses involved had received uniform instructions before the beginning of the patient recruitment. All the pain data were collected by the nurse in charge on a separate sheet every observational day. Each sheet included the drawings of Figure 1.

View larger version (15K): [in this window] [in a new window]   Fig 1. Picture of the body with the 18 anatomic areas as found on the observational sheet for pain localization analysis.

	Results

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
The patients characteristics are shown on Table 1. The surgical procedure of the IMA group included 93 revascularizations with the left IMA and saphenous vein grafts, 5 revascularizations with the left IMA, and 2 revascularizations with the left IMA combined with aortic valve replacement. In the non-IMA group the following operations were performed: 52 aortic valve replacements or procedures on the ascending aorta (or both), 27 procedures on the mitral valve, 10 aortic and mitral valve replacements, 10 revascularizations with saphenous vein grafts, and 2 closures of an atrial septal defect.

Maximal pain intensity is shown on Figure 2. In both groups and for every observational day, the minimal value was 0 and the maximal value varied between 8 and 10. When both groups were compared, only the values of POD 2 exhibited a significant difference (p < 0.01). When comparisons were made between consecutive observations in the IMA group,a statistically significant difference was found between POD 1 and 2 (p = 0.049) and between POD 2 and 3 (p < 0.01), whereas the difference between POD 3 and 7 was not statistically significant (p = 0.1). When the same comparisons were performed in the non-IMA group, a statistically significant difference was found between POD 1 and 2 (p = 0.049) and between POD 3 and 7 (p = 0.01), whereas the difference between POD 2 and 3 was not statistically significant (p = 0.87).

View larger version (14K): [in this window] [in a new window]   Fig 2. Data of maximal pain intensity. ( = internal mammary artery (IMA) group; = non-IMA group; POD = postoperative day.)

Figures 3 and 4 show the number of patients who did not mention any pain area and those with more than one pain area, respectively. The following comparisons were statistically significant. On POD 7, there were more patients with no pain in the non-IMA group than in the IMA group (p = 0.03). When the observational days were compared, there were more patients without pain on POD 7 than on POD 1, 2, or 3 (p < 0.01 for all comparisons) in the non-IMA group. Notably, when the patients with more than one pain area were considered, there were neither between-group difference at any time, nor difference between observational days within the each group.

View larger version (11K): [in this window] [in a new window]   Fig 3. Number of patients with no pain area. ( = internal mammary artery (IMA) group; = non-IMA group.)

View larger version (14K): [in this window] [in a new window]   Fig 4. Number of patients with more than one pain area. ( = internal mammary artery (IMA) group; = non-IMA group.)

	Comment

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

Maximal pain intensity was moderate in both groups and throughout the first postoperative week. On POD 2, patients of the IMA group complained of significantly higher pain intensity than the non-IMA group (4.2 ± 2.4 versus 3.2 ± 2.3, respectively, p < 0.01), whereas there were no between-group differences on POD 1, 3, and 7. Therefore, there is an impact of IMA harvesting on pain intensity, which is, however, limited in time and in amount. Moreover there were more patients without pain on POD 7 in the non-IMA group, although overall pain intensity was similar in both groups. Importantly, among the patient characteristics that could bear an influence on pain perception, namely age and sex, age was found to be significantly different with older patients in the IMA group. This finding is likely to be related to the underlying coronary artery disease involving usually older patient than other cardiac surgical diseases. Increasing age has been recognized to decrease pain sensation [8–10], strengthening the finding that pain sensation was increased on POD 2 in the IMA group.

Few other studies have reported on IMA harvest-related pain. Two studies [11, 12] were retrospective case reports of small groups of patients with late chest pain and without any comparison group. Meehan and colleagues [13] in a prospective sample of 50 cardiac operation patients, 18 of whom with IMA harvest and 10 with vein grafts only, found a higher overall visual analogue scale score in the early postoperative period for the IMA group (4.42 versus 3.46, respectively, p = 0.04). These results on a small group of patients are in keeping with our figures.

The maximal intensity was reported on POD 2 in the IMA group (4.2 ± 2.4) and on POD 1 in the non-IMA group (3.8 ± 2.4), whereas the lower pain intensity was reported on POD 7 in both groups (2.7 ± 2 and 2.5 ± 2.3, respectively). This finding emphasizes the importance of the initial postoperative phase for pain management, which can be improved further. Moreover, at the end of the first postoperative week, pain sensation, although moderate, is still present and deserves consideration especially for elderly and patients with decreased pulmonary capacity, who are at higher risk to develop pulmonary complications.

The analyses of the pain areas shed a new light on pain sensation in each group. The area most frequently involved throughout all the study period is obviously the incisional area (area 3). A difference between both groups with regard to the sternal area was found on POD 7 when all pain areas were considered, with more IMA group patients complaining of pain (74 versus 50, respectively). When the different observational times were compared, a significant difference was found in the non-IMA group between POD 1 and POD 7, with more patients involved on POD 1. These findings may find a common explanation when the chest trauma of the operation is considered. On POD 1, incisional sternotomy area is understandably the area most likely to be involved with pain. After 1 week, it is expected that the frequency of incisional pain decreases as shown in the non-IMA group. However in the IMA group there was no decrease but rather an increase, although this increase was not statistically significant. Moore and colleagues [14] found that IMA harvesting was associated with a significantly greater incidence of sternal fractures, with 16 fractures among 94 patients with IMA mobilization versus 8 fractures among 194 patients with other cardiac operations. This increased incidence of sternal fracture is presumably due to the vertical forces applied by the sternal retraction device for IMA harvesting. This additional trauma may explain the frequency of sternal pain on POD 7, when mobilization of the patient awakens unrecognized fracture pain. Importantly, the absence of significant difference of the sternotomy area involvement between both groups during the first 3 POD argue against a significant role of mammary bed dissection in postoperative chest pain.

The left anterior basal thoracic area (area 6) was more often involved in the IMA group during the first 3 POD. This difference might have been caused by factors such as the more extreme retraction of the chest wall during IMA harvest and the greater likelihood of having a pleural chest tube.

Patients reported pain in the epigastric area (area 8) more often on the first 2 POD than on POD 7. This finding is easily explained by the mediastinal and chest tubes, which exit at this level and have all been removed by POD 7.

The posterior shoulder areas (areas 11 and 13) were more often involved at the end of the first postoperative week than early after the operation in both groups. In patients undergoing median sternotomy, retraction of the sternum applies an indirect force to the upper ribs and often results in fracture of the posterior and lateral aspects of the ribs [15–17]. Greenwald and coworkers [15], in a bone scan study of 24 cardiac operation patients, found that the first rib was fractured 15 times (12 posteriorly and 3 laterally); 1 patient had a bilateral fracture of the first rib; and the second rib was fractured 13 times. The mobilization of the patient awakens fracture-related pain, explaining their higher frequency at the end of the first postoperative week. An autopsy study suggested that placement of the sternal retractor as low as possible commensurate with adequate exposure should reduce the number of rib fractures [18].

More patients of the non-IMA group described pain of the median back areas (areas 12 and 17) in the early postoperative period. Moreover, the frequency of these complaints decreased significantly at the end of the first postoperative week. One hypothesis is that the non-IMA group may require wider sternal retraction more often, because of the access to deeper structures such as the mitral valve. Such a wider retraction would apply constraint on the costovertebral joints with subsequent paravertebral muscle contracture, and the related pain is likely to be more frequent while the patient is lying supine.

In conclusion, there is an impact of IMA harvesting on pain intensity, which is however limited in time (to POD 2 only) and in intensity (1 point higher on a 10-point scale than non-IMA cardiac surgical groups). However, the analysis of pain localization shows specific features within each group. In the IMA group, more patients had sternal pain at the end of the first postoperative week, with basal thoracic pain throughout all the study period, whereas in the non-IMA group more patients complained of back pain during the early postoperative period. Such a topographic analysis allows a more precise description of postoperative pain patterns. Importantly, pain management may be better targeted according to the different areas involved: incisional pain may be better relieved by opiates and nonsteroidal antiinflammatory (NSA) agents, early back pain may be alleviated by NSA drugs and active mobilization, and late shoulder pain may be attenuated by NSA drugs and gentle progressive mobilizations. Lastly, with the advent of minimal invasive operation, such a topographic description might be a useful tool to assess the pain pattern of this new approach. This technique requires greater retraction force to gain a proper access through a smaller incision, with subsequent chondrocostal distraction or rib fractures. As may be expected, pain sensation may be increased in the postoperative period, and this problem with important clinical implication deserves an appropriate evaluation.

	Acknowledgments

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
We thank the nurses of the Surgical Intensive Care Unit and the Clinic for Cardiovascular Surgery (CHUV-Lausanne) who recorded the patient data.

	References

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 

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