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Ann Thorac Surg 2001;72:731-734
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Tracheostomy: a risk factor for mediastinitis after cardiac operation

^a Department of Cardiothoracic Surgery, University of Missouri, Columbia, Missouri, USA

Address reprint requests to Dr Curtis, University Hospital and Clinics, #1 Hospital Dr, DC 011.00, Columbia, MO 65212
e-mail: curtisj{at}health.missouri.edu

Presented at the Forty-seventh Annual Meeting of the Southern Thoracic Surgical Association, Marco Island, FL, Nov 9–11, 2000.

	Abstract

Top Abstract Introduction Material and methods Results Comment Acknowledgments Discussion References

 
Background. We studied whether tracheostomy after coronary artery bypass grafting (CABG) is associated with higher incidence of mediastinitis and mortality, and whether shorter intervals between median sternotomy and tracheotomy are associated with higher incidence of mediastinitis.

Methods. Patients (n = 6,057) undergoing CABG since March 1977 were reviewed. Patients requiring tracheostomy and those developing mediastinitis were identified. Mediastinitis diagnosis required positive culture of mediastinal tissue or fluid.

Results. After CABG, 88 patients had tracheostomy performed (1.45%). Seven patients receiving tracheostomy after developing mediastinitis were excluded. Of the remaining 81 patients, 7 developed mediastinitis (8.6%) compared with 44 of 5,969 (0.7%) who did not require tracheostomy (p < 0.001). Mortality in tracheostomy patients was 24.7% (20 of 81) compared with 5.2% in patients not requiring tracheostomy (316 of 5,969; p < 0.001). Patients not developing mediastinitis had tracheostomy placement an average of 25 days after CABG compared with 18.7 days for those developing mediastinitis (p = 0.141).

Conclusions. Tracheostomy after CABG is associated with increased incidence of mediastinitis and mortality. In this review, the time interval between CABG and tracheostomy was not predictive of mediastinitis. A larger sample size would be required to be confident that there is no correlation.

	Introduction

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Mediastinitis is a dreaded complication after cardiac operation and is associated with increased hospital stay, cost, and mortality [1]. We studied whether patients who require tracheostomy after cardiac operation have an increased incidence of mediastinitis and mortality. Additionally, we tested the hypothesis that a shorter time interval between median sternotomy and tracheostomy placement is associated with a higher incidence of mediastinal wound infection.

	Material and methods

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After review by the University of Missouri Institutional Review Board and receipt of exempt status, a retrospective review of a computerized database maintained in the Division of Cardiothoracic Surgery at the University of Missouri Health Sciences Center formed the basis of this report. A standardized data registry form is compiled in a prospective manner on all patients undergoing cardiac operations. The hospital record of each patient identified from our database as having a tracheostomy or chest wound infection was then thoroughly reviewed to ensure completeness and accuracy of data entry.

Patients undergoing coronary artery bypass grafting alone or with other procedures since March 1977 were reviewed. Although techniques varied, all patients had surgical tracheostomy, and no patient in this report had a percutaneous tracheostomy. During this period, the general admonition was to place the tracheostomy below the second tracheal cartilage and avoid dissection inferiorly toward the median sternotomy incision. Most patients were returned to the operating theater for tracheostomy. The diagnosis of mediastinitis required a positive culture of mediastinal tissue or fluid.

The relationship between postoperative tracheostomy and the development of mediastinitis and mortality was analyzed using Fischer’s exact test. The strength of the relationship between the incidence of mediastinitis and time of tracheostomy placement was quantified using the Pearson product moment correlation coefficient. Timing of tracheostomy placement (days postoperatively) for each of the groups was compared using the Kruskal-Wallis one-way analysis of variance on ranks (normality test failed), followed by a pairwise multiple comparison using Dunn’s method.

	Results

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Records from 6,057 patients were reviewed. A tracheostomy was performed in 88 patients (1.45%), 7 to 78 days postoperatively. Sixty-two patients were men (70.5%), and patients’ ages ranged from 45 to 87 years (mean, 68.2 years). Seven patients received tracheostomy after exhibiting mediastinitis and were excluded from the analysis. Of the remaining 81 patients, 7 had mediastinitis after tracheostomy (8.6%). Tracheostomy was performed in these patients from 11 to 32 days (average, 18.7 days) after the initial cardiac surgical procedure. The diagnosis of mediastinitis was made 14 to 47 days (average, 32 days) after the cardiac surgical procedure. The interval between tracheostomy placement and the diagnosis of mediastinitis ranged from 1 to 31 days, with an average of 13.3 days (standard deviation, 12.8 days). The significant association of tracheostomy and the development of mediastinitis and mortality is shown in Table 1. Patients who required tracheostomy after cardiac operation had a mediastinitis incidence of 8.6%, compared with 0.7% in those patients who did not require tracheostomy (p < 0.001).

The impact of the time interval between median sternotomy and placement of tracheostomy and the subsequent development of mediastinitis is shown in Table 2. Patients who experienced mediastinitis had tracheostomy placement an average of 18.7 days after median sternotomy compared with 24.9 days in patients who did not have mediastinitis (p = 0.194). No significant relationship between incidence of mediastinitis and time of tracheostomy placement was identified (Pearson product moment correlation coefficient, 0.165; p = 0.723). The incidence of mediastinitis in patients who had tracheostomy during the first 2 weeks after cardiac operation was 15.4% compared with 7.4% in those in whom tracheostomy was delayed longer (p = 0.312).

Potential predictors for the development of postoperative mediastinitis are listed in Table 3 comparing their incidence in tracheostomy patients who did not develop mediastinitis (n = 74) and those who did (n = 7). There was no statistical difference in these patient characteristics and risk factors with regard to patients’ age, sex, cardiopulmonary bypass time, redo operation status, incidence of chronic obstructive pulmonary disease, forced expiratory volume in 1 s, or diabetes mellitus.

	Comment

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It is generally presumed that tracheostomy increases the risk for mediastinitis, particularly if it is performed early after median sternotomy when contamination can occur by contiguous extension through nonsealed tissue planes. The realization and documentation of contamination of median sternotomy wounds by tracheostomy comes from the early era of cardiac surgical procedures [7, 8]. In this early period, tracheostomy was often performed at the time of the cardiac procedure, with most patients exhibiting localized or general infection. This disastrous experience resulted in a standard practice of delaying tracheostomy for at least 1 or 2 weeks until tissue planes between the tracheostomy and median sternotomy have obliterated. Similarly, patients with existing tracheostomy stomas who require cardiac operation are approached with great concern for contamination of the median sternotomy and postoperative wound infection, leading to novel approaches to the heart, including bilateral thoracotomy incisions and limited median sternotomy approaches [9, 10]. Indeed, multiple observers have now shown that even nasal or nasopharyngeal cultures have correlated with the development of mediastinitis after cardiac operation [1, 11].

During the last decade, few authors have included tracheostomy among potential risk factors for development of mediastinitis, although chronic obstructive pulmonary disease and prolonged postoperative mechanical ventilation are understood to increase risk [2, 12–15]. A recent provocative article by Stamenkovic and colleagues [16] challenges the long-held belief that tracheostomy is associated with median sternotomy and infection after cardiac operation. In a contemporary review of their 9,900 patients with median sternotomy, 1.8% required tracheostomy, an incidence similar to the 1.45% in our series. They observed a 22% mortality in patients requiring tracheostomy, also similar to our 24.7%. However, despite the fact that 41% of their patients received tracheostomy on or before postoperative day 7, only 1 of their 174 patients experienced mediastinitis after the tracheostomy was placed. They concluded that there is no demonstrable relationship between early tracheostomy and mediastinitis. Some of their patients had percutaneous tracheostomy.

Others have minimized the risk of tracheostomy-associated mediastinitis by using a percutaneous tracheostomy technique [12, 17]. Hubner and colleagues [12] reported their experience in 45 patients who received percutaneous tracheostomy after cardiac operation with no incidence of mediastinitis.

In the present series, all tracheostomies were performed by standard or nonpercutaneous surgical techniques. The odds ratio of patients experiencing mediastinitis with a tracheostomy as compared with patients not requiring a tracheostomy was 13.0 (7 of 81 patients requiring tracheostomy had mediastinitis, whereas 41 of 5,697 patients not requiring tracheostomy had mediastinitis). Mortality among patients receiving tracheostomy was significantly higher than among those who did not (24.7% versus 5.3%; p < 0.001). Our hypothesis that earlier tracheostomy increases the risk of mediastinitis was not proven in this series (Table 2). The incidence of mediastinitis in patients receiving tracheostomy before 2 weeks was 14.3% compared with 7.5% after 2 weeks (p = 0.312).

This retrospective review, despite the prospective nature of data collection, has numerous opportunities for error. The requirement for a positive culture for the diagnosis of mediastinitis may underestimate the true incidence of mediastinitis in this series. Conversely, it is possible that some of the 81 patients who had tracheostomy were already infected, with subsequent diagnosis of mediastinitis being unrelated to tracheostomy placement. This would overestimate the impact of tracheostomy on the incidence of mediastinitis. Further, as it was not our intent to conduct a comprehensive epidemiologic study of the determining factors for tracheostomy, it is possible that unidentified confounding risk factors that resulted in the need for tracheostomy were present in a higher proportion in those who had mediastinitis.

Despite these limitations, we conclude that patients who require tracheostomy after cardiac operation have a higher incidence of mediastinitis and have a higher mortality than those patients who do not require tracheostomy. In this review, the time interval between cardiac operation and tracheostomy was shorter in those patients who subsequently experienced mediastinitis compared with those who did not. Although this did not reach statistical significance, a larger patient population would be necessary for us to confidently conclude that the interval is not important. Percutaneous tracheostomy techniques, despite their inherent morbidity, seem attractive in this situation and may result in a decreased incidence of posttracheostomy mediastinitis after cardiac operation.

	Acknowledgments

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The authors thank Bruce Richman, MD, who assisted in the development of the manuscript, and Anna Coleman for preparation of the manuscript.

	Discussion

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DR NORMAN J. SNOW (Chicago, IL): Doctor Curtis and his colleagues have studied whether the tracheostomy after coronary artery bypass grafting is associated with a higher incidence of mediastinitis, but I think we have to go one step further and try to ask ourselves whether there is any causal relationship or whether it is only incidental.

The authors have discussed the risk factors for mediastinitis that are commonly known and have been defined in the literature and found no difference between their two groups, but they did not really discuss, number one, the reason for the tracheostomy, and, second, the reasons why these patients were so sick. That is, other than the commonality of risk factors such as diabetes or redo operation, did they have low cardiac output, did they have adult respiratory distress syndrome, were they in renal failure, with pneumonia, did they use inotropic agents, one group as opposed to the other, or was there a perioperative myocardial infarction or mechanical support to account for the severity of illness in these patients?

Now, as you know, the Health Care Financing Administration considers the addition of a tracheostomy to almost any diagnosis related group as a surrogate for the severity of illness, and they bump up the compensation for any diagnosis related group when a tracheostomy is involved, and I think that is the same thing that may be happening here. The tracheostomy is a surrogate for how sick the patients really are and may not be the causal factor in the mediastinitis, but there may be other confounding factors to account for this.

The wide variation in the time of diagnosis and the time of tracheostomy after operation again calls into question whether the two are causally related or whether they are simply associated because the patients are sick to begin with.

The mortality in the group with tracheostomy, of course, is higher, but again, it is not just the presence of the tracheostomy. It may well have been the severity of illness, which we were not privy to in the presentation. Remember that the organisms were very similar in patients who had developed mediastinitis before and after the tracheostomy. We know that the nasal carrier state for many organisms, especially Staphylococcus aureus, does have an effect on the incidence of mediastinitis, and that is another factor that was not discussed in the paper and could well have important bearings on the conclusions.

I have two questions. First, what were the patient characteristics in the two groups in terms of their severity of illness rather than just their risk factors?

Second, do you think that a percutaneous tracheostomy or a cricothyroidotomy, for that matter, may obviate some of your concerns? We have performed percutaneous tracheostomy in 7 patients within 1 week of open heart operation and have not seen mediastinitis. Of course that is not a series and there is no statistical validity to it, but one wonders whether that might obviate some of the concerns that you have. Early tracheostomy might be beneficial to some patients with respiratory insufficiency, and we would hate to see patients denied the benefits of tracheostomy without a solid causal link being established between tracheostomy and mediastinitis. Tracheostomy is a surrogate often for the severity of illness, but not necessarily the cause.

DR JONES: Thank you very much. Those are very good questions. First, there is no question that having to perform a tracheostomy indicates that you are treating severely ill patients who are likely to have higher mortality and complication rates. The conditions for which tracheostomies were performed were not specifically described in this study. We looked at it primarily from the standpoint of when a standard tracheostomy should be done, and whether the tracheostomy was associated with mediastinitis.

As far as the causal relationship, certainly it would depend on many factors, including particularly the habitus of the patients, the surgical technique that was used, and whether or not a cricothyroidotomy was done. I think the answer to your final question can be found in two recent studies of the percutaneous method, obviating the need to dissect down in the tissue plane and having a separation. These patients did not have mediastinitis. We are adopting percutaneous tracheostomy as our routine now, and I think that it should be considered the standard of care in this clinical situation.

	References

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Jack J. Curtis Joseph T. Walls Richard A. Schmaltz Todd L. Demmy James W. Jones William R. Wilson, Jr Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Curtis, J. J. Articles by Wagner-Mann, C. C. Search for Related Content PubMed PubMed Citation Articles by Curtis, J. J. Articles by Wagner-Mann, C. C. Related Collections Cardiac - other