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Eur J Cardiothorac Surg 2004;25:548-552
© 2004 Elsevier Science NL

Long-term outcome and quality of life of patients requiring prolonged mechanical ventilation after cardiac surgery

^a Department of Cardiovascular Anesthesia and Intensive Care, San Raffaele Hospital, Vita-Salute University, Via Olgettina 60, 20132 Milano, Italy
^b Department of Cardiac Surgery, San Raffaele Hospital, Vita-Salute University, Milan, Italy

Received 1 October 2003; received in revised form 26 November 2003; accepted 27 November 2003.

^* Corresponding author. Tel.: +39-2-2643-7722; fax: +39-2-2643-7155
e-mail: pappalardo.federico{at}hsr.it

	Abstract

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 
Objectives: To study the long-term survival and quality of life of patients with a complicated post-operative course after cardiac surgery requiring prolonged (7 days) mechanical ventilation (MV), since they represent a heavy burden on hospital resources and their outcome has never been adequately evaluated. Methods: Out of 4827 consecutive cardiac surgical patients, 148 (3%) required prolonged post-operative MV: their hospital course was analysed and factors affecting prolonged MV and mortality were identified using multivariate analysis. Long-term survival was assessed using Cox proportional hazard method. Long-term (36±12 months) follow-up information was collected and quality of life was assessed by an ad hoc questionnaire. Results: Overall mortality in the study group was 45.3 versus 2% in the control population (P<0.0001). Predictors of death in the prolonged MV group were age (odds ratio, OR 1.049) and diabetes (OR 3.459). Long-term survival was significantly worse in those patients who were extubated after 21 days: 88.9 versus 70.9% at 1 year (P=0.03) and 80.9 versus 64.5% at 5 years (P=0.05). Mild or no limitation in daily living was referred by 69% of the survivors. Conclusions: The hospital mortality of patients requiring prolonged MV is high. The long-term survival of patients who are weaned from MV after 21 days is significantly lower. The great majority of the survivors can enjoy a good quality of life.

Key Words: Cardiac surgery • Mechanical ventilation • Outcome • Quality of life

	1. Introduction

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 
The burden on hospital resources of patients with a complicated post-operative course after cardiac operations is enormous. Although most patients have rapid recovery after cardiac surgery, there are few who die in the early post-operative period and others who require extended treatment in the intensive care unit (ICU): some of them eventually recover, while others suffer through prolonged organ support only to die or be severely disabled [1,2].

The aim of this study was to evaluate the hospital course and to collect follow-up information on patients who required prolonged post-operative mechanical ventilation (MV), defined as being on a ventilator for 7 days, to determine whether outcome was related to the duration of post-operative MV and whether the hospital treatment was cost-effective.

	2. Materials and methods

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 
A cohort of 4827 consecutive adult cardiac surgical patients operated from January 1998 to June 2001 at San Raffaele University Hospital, Milan, was analysed to study the effects of prolonged MV on outcome.

Patients who required prolonged MV (7 days) during hospitalisation have been identified from a database that prospectively collects information on all cardiac surgical procedures. Details on patient demographics, cardiac disease and co-morbidities, surgical procedure and post-operative events are registered in the database. Also the length of stay in ICU and the duration of respiratory support are recorded.

Patients who died in the operating room or within the first post-operative week were excluded from the analysis.

Patients in the prolonged MV group were compared to those who survived the operation and did not require prolonged MV. Hospital and long-term survival in the study group were analysed according to the duration of MV.

Patients were enrolled in the follow-up if they had left the hospital alive at least 1 year before the beginning of the study: they were interviewed by phone calls to assess their survival and quality of life. The questionnaire was administered by phone and was divided into seven dimensions of health: physical morbidity, functional status, emotional complications, need for re-admissions, activities of daily living, perception of life, pain [3,4]. Time from surgery to interview is variable (mean±SD follow-up 36±12 months).

Factors affecting prolonged MV as well as mortality in the study group were identified using multivariate analysis.

The amount of healthcare resources (duration of MV, length of ICU and hospital stay) consumed in the provision of care was recorded for each patient.

	3. Statistical analysis

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 
Descriptive statistics such as proportions, means, and SDs were used to summarise the results. Data were stored electronically and analysed by use of the software SPSS version 10.1 (SPSS, Chicago, IL). Long-term survival was analysed with the use of Kaplan–Meier estimates. Data on patients who withdrew from follow-up were censored at the time of withdrawal. Differences in mortality after extubation between patients undergoing less or more than 3 weeks of mechanical ventilation were analysed with use of a Cox proportional hazards model and a log-rank test.

Statistical comparison between groups was done with a two-tailed ²-test or the t-test when appropriate. Data are presented as mean±SD; nonnormally distributed variables were expressed as median (25th–75th percentile).

We used forward logistic regression to assess the independent correlates of prolonged mechanical ventilation among the overall cardiac surgery population and the independent correlates of hospital mortality for the group of patients who received prolonged mechanical ventilation. Variables with univariate significance (P<0.05) were entered into the regression. For this analysis we present the odds ratio (OR) and 95% CI for each significant pre-operative, intra-operative or post-operative variable.

	4. Results

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 
Of the 4827 patients who underwent cardiac surgery at our hospital from January 1998 to June 2001, 4679 (96.9%) were extubated within the first post-operative week (control group), 57 (0.1%) died in the operating room or in the first post-operative week and only 148 (3.0%) required prolonged (7 days) post-operative MV (study group). Pre-operative patients' characteristics, type of surgery and mortality for the control and study groups are shown in Tables 1 and 2. The complications which occurred in the two groups are shown in Table 3. The overall hospital mortality in the study group was 45.3 versus 2% in the control population. Predictors of prolonged MV were: pre-operative dialysis and renal failure, emergency, re-operation, female sex, age and the occurrence of post-operative low output syndrome (Table 4).

Actuarial overall survival of the study population is shown in Fig. 1 . Patient survival was further analysed according to the length of mechanical ventilation grouping patients into four subgroups: those extubated within 14 days, 20 days, 2 months and more than 2 months. We therefore arbitrarily separated patients into those who needed MV for more than 21 days and those who did not: long-term survival of these subgroups was statistically different. Analysis of survival at 1 year after liberation from MV, the period intuitively most affected by the hospital course, showed that the patients who were weaned from MV after 21 days had a survival rate of 65.6%, whereas those who were weaned before 21 days had a survival of 87% (P=0.03). The survival rate remains statistically different also at 5 years: 55.7% in the former versus 69% in the latter (P=0.05) (Fig. 2) . Causes of death among patients discharged from the hospital were mainly cardiovascular (Fig. 3) .

View larger version (10K): [in this window] [in a new window]   Fig. 1. Overall actuarial survival at long-term follow-up of the study population.

View larger version (12K): [in this window] [in a new window]   Fig. 2. Survival at 5 years of the study population according to the duration of MV.

View larger version (16K): [in this window] [in a new window]   Fig. 3. Causes of death among hospital survivors.

View larger version (14K): [in this window] [in a new window]   Fig. 4. Functional scale used to describe daily activities at long-term follow-up.

Only three patients suffered from severe chronic pain secondary to prolonged immobilisation and pressure ulcers.

Regarding hospital resources utilisation, the median length on mechanical ventilation was 360 h (240–648) in the study group versus 9 h (9–15) in the control group, the median length of ICU stay was 18 days (11–31) in the study group versus 1 day (1–2) in the control group and the median hospital stay was 25 days (16–42) in the study group versus 5 days (5–7) in the control group.

	5. Discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 
The main result of this study is that patients with a complicated post-operative course after cardiac surgery, requiring prolonged MV, have a dismal prognosis (50% chances of hospital survival) and that prognosis of survivors is significantly different at 1 and 5 years among those who are weaned or not from MV within 21 days after operation. Moreover the study reveals that survivors can enjoy a clinical improvement and a good quality of life without severe limitations after hospital discharge at long-term follow-up.

The vast majority of our cardiac surgical patients (89%) spend less than 24 h in the cardio-thoracic ICU; however, a small percentage of them develop post-operative organ system failure, requiring prolonged mechanical ventilation, and consume a disproportionate share of hospital resources with high morbidity and mortality rates. There are few studies, which evaluated survival according to the duration of post-operative MV in patients discharged after a prolonged and complicated ICU treatment after cardiac surgery [5–7].

Our study investigates hospital and long-term survival and functional status in a population of 148 patients undergoing prolonged mechanical ventilation after cardiac surgery. The decision to study patients requiring 7 days or more of ventilatory support was arbitrary: we feel that the need for mechanical ventilation 1 week after surgery is an ominous sign. The further subgrouping of patients into those who were liberated or not from MV within 21 days might describe the efficacy of the tracheostomy which is routinely performed at our institution after 14 days of endotracheal intubation; the continuing need for MV might reflect a complex scenario in which the respiratory failure is secondary to dysfunction of organ systems other than the lung.

In the clinical realm patients with very severe cardiac pump failure or neurologic dysfunction rarely survive 1 week after surgery; afterwards, the need for a tracheostomy sets the time of the occurrence of critically illness-related diseases (sepsis, MOF, muscle disorders). Perhaps, patients who have complicated surgery (for high pre-operative risk or for perioperative adverse events) either recover and are therefore liberated from mechanical ventilation with the aid of a tracheostomy, or suffer the consequences of ICU stay and prolonged ventilation itself. After 21 days the differentiation of complications secondary to surgery and those due to the need for long-term mechanical ventilation, such as nosocomial pneumonia, is difficult to discern. Nevertheless, from our data we cannot assume that there is a length of ventilation which is discriminatory for poor outcome (death or poor quality of life).

Our data show that even after a complicated post-operative course surviving patients may enjoy an improvement in their quality of life.

Risk factors for a complicated post-operative course (prolonged MV) in our series are the pre-existence of renal failure needing dialysis, age, priority of surgery, female sex, redo operation and the development of post-operative low output syndrome.

In the light of these data, despite the high mortality rate, acute complications occurring in this population need to be aggressively treated: we should not be desperate in front of sepsis, renal failure or GI complications. Acute CVA constitutes an extremely complex scenario which is out of the purpose of this study.

Early and extremely accurate prediction of outcome at ICU admission after cardiac surgery would allow the rational deployment of resources in favour of critically ill patients most likely to recover and facilitate limitation of aggressive intervention in patients with hopeless prognosis. Unfortunately patients recovering from the effects of CPB are not amenable to early stratification because the physiologic consequences of CPB usually resolve completely and do not impact outcome. Thus outcome prediction in cardiac surgical patients in the immediate post-operative period may be unreliable [8].

Ryan et al. [9] have shown that prediction of outcome is not possible from pre-operative data or severity of organ failure in the first 24 h of ICU stay in a population of 324 cardiac surgical admissions during at least 14 days.

Until outcome can be accurately predicted and failure to respond to extended intensive care can be recognised earlier and with certainty [10,11], a small proportion of critically ill patients will continue to require a disproportionately large number of ICU days at a high cost and still have poor outcome. In this study, however, most patients who successfully managed through a complicated ICU stay and discharged from the hospital had a good outcome in terms of post-discharge survival and functional capacity: hospital discharge, in our opinion, is an incomplete measure of outcome as, after discharge from hospital, the mortality rate for these patients continues to be high, as is the cost of their care.

Our study has several limitations: no pre-operative assessment of functional status was performed; no data is available on the severity of illness during prolonged MV; no cardiac evaluation has been recorded at follow-up.

In conclusion, the present study confirms that prolonged mechanical ventilation is a marker for a morbid post-operative course; however, the knowledge of long-term outcome in patients who have sustained major complications after cardiac surgery could help physicians to treat patients and permit more realistic counselling of relatives. Our observations can serve as a basis for discussions on treatment, resuscitation and even withdrawal of care when a patient is still critically ill 1 week after surgery and, furthermore, for a realistic approach with the relatives on the expectations of prolonged, aggressive medical support.

The strain these patients place on personal, system, and financial resources is extreme with disproportionate consumption of ICU resources (54% of ICU ventilators occupied by 3% of the population and 31% bed occupation of the cardio-thoracic ICU in the period studied), but it seems to be justified.

	Acknowledgments

 
We are indebted to Luigi Villani, Giuseppe Giardina and Monica Lischio for their technical support.

	Footnotes

 
Presented at the joint 17th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 11th Annual Meeting of the European Society of Thoracic Surgeons, Vienna, Austria, October 12–15, 2003.

	Appendix A. Conference discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 
Dr J. Revuelta (Santander, Spain): Nowadays, as you know, with the ICU fast track system, more than 48 hours is considered prolonged. Why do you move to seven days? This is really very prolonged period of time.

Dr Pappalardo: Actually the definition of prolonged mechanical ventilation in the literature is variable, especially after cardiac operations. The issues we have considered in setting this time were several. At first, we feel that on clinical grounds a patient who is still on a ventilator seven days after surgery is not working very well.

Second, by day seven we surely have resolved all the transient effects of anesthetics and cardiopulmonary bypass, and moreover, as it has been elegantly shown last year in a paper by the group from Duke University, noncardiac complications affect outcome more than cardiac complications alone. So probably by day seven we can move the site of our attention from the heart to the whole body.

Dr R. Dion (Leiden, The Netherlands): This is a most important paper. It is indeed our duty to demonstrate to the community that even complex, demanding, and therefore costly surgical procedures frequently are rewarded by excellent outcome.

	References

Top Abstract 1. Introduction 2. Materials and methods 3. Statistical analysis 4. Results 5. Discussion Appendix A. Conference... References

 

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