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Arquivos Brasileiros de Cardiologia

Print version ISSN 0066-782X

Arq. Bras. Cardiol. vol.95 no.4 São Paulo Oct. 2010  Epub Aug 27, 2010

http://dx.doi.org/10.1590/S0066-782X2010005000115 

ORIGINAL ARTICLE

 

Incidence of pulmonary complications in myocardial revascularization

 

 

Leila D. N. OrtizI; Camila W. SchaanI; Camila P. LeguisamoI; Katiane TremarinI; Waldo L. L. D. MattosI,II; Renato A. K. KalilI,II; Lucia C. PellandaI,II

IInstituto de Cardiologia do Rio Grande do Sul/Fundação Universitária de Cardiologia
IIUniversidade Federal de Ciências da Saúde de Porto Alegre, Porto Alegre, RS - Brazil

Mailing address

 

 


ABSTRACT

BACKGROUND: Despite the increasingly careful attempts to reduce perioperative risks, pulmonary complications following surgery are still very common, leading to longer length of hospital stays or death.
OBJECTIVE: To describe the incidence of pulmonary complications and identify their association with duration of extracorporeal circulation (ECC), surgery and ischemia, number of bypass grafts performed, location of drains and length of drainage following myocardial revascularization (MRV).
METHODS: This contemporaneous cohort consisted of 202 patients undergoing elective myocardial revascularization (MRV) with saphenous vein graft and internal mammary artery graft and ECC, at a referral university cardiology hospital in Southern Brazil, from April 2006 to November 2007. The following outcomes were analyzed: duration of mechanical ventilation; pneumonia onset; atelectasis; pleural effusion; location of drains and time of removal; and length of hospital stay.
RESULTS: Of the 202 patients, 90 developed some sort of pulmonary complication. The incidence of pleural effusion was 84%, whereas atelectasis was 65%. The following variables were associated with pulmonary complications: duration of ECC (p = 0.003), surgery (p = 0.040) and ischemia (p = 0.001); length of drainage (p = 0.050) and location of pleural drains (p = 0.033); age (p = 0.001); ejection fraction (p = 0.010); diagnosis of asthma (p = 0.047) and preoperative abnormal chest X-ray findings (p = 0.029).
CONCLUSION: Variables related to the complexity of the surgery and preexisting comorbidities are associated with a high incidence of postoperative pulmonary complications. These data reinforce the importance of having patients undergo perioperative clinical assessment to detect early respiratory complications after MRV. (Arq Bras Cardiol. 2010; [online]. ahead print, PP.0-0)

Key words: Myocardial revascularization; postoperative complications; thoracic surgery; pleural effusion; perioperative care.


 

 

Introduction

Advances in myocardial revascularization surgery (MRV), as well as in the development and enhancement of perioperative care, led to a drop in morbidity-mortality rates during the procedure, allowing MRV to be used to treat increasingly complex cases1-3. However, studies show that despite these advances, impairment of pulmonary function is still very common after surgery. This impairment has a multifactorial origin, including, among others: surgical variables, such as duration of extracorporeal circulation (ECC); duration of surgery; duration of ischemia; number of grafts performed; length of drainage and location of drains as potential predictive factors for pulmonary complications following MRV4-7.

Thus, it is important to look for factors potentially associated with pulmonary complications in order to devise preventive strategies that are more effective in reducing these complications.

Physical therapy can help prevent postoperative (PO) complications, especially when the physical therapist is aware of the changes that took place during the surgery and their consequences, thus making their work more effective with that specific patient8.

Therefore, the aim of this study was to evaluate the potential association between surgical variables and postoperative respiratory complications following MRV, at a referral university cardiology hospital.

 

Materials and methods

This contemporaneous cohort study was conducted at the Instituto de Cardiologia do Rio Grande do Sul/Fundação Universitária de Cardiologia - ICFUC (Rio Grande do Sul State Institute of Cardiology/University Cardiology Foundation), in Porto Alegre, Brazil, and was approved by the institution's Research Ethics Committee. Data collection was performed by qualified investigators from April 2006 to November 2007. Data were collected from 202 patients undergoing elective MRV surgery with saphenous vein grafting (SVG) and internal mammary artery grafting (IMG) and ECC; these patients signed an informed consent form and were followed from the preoperative phase through discharge from the hospital. Some variables could not be used since information was lacking in the patient's medical chart. Exclusion criteria were: patients who refused to participate in the study, emergency surgeries, surgeries performed without ECC and MRV with concomitant valve surgery.

Preoperative evaluation

Data were collected on two days of the week, which were selected through a table with random numbers. Patient data were collected from medical charts and recorded in detail in an evaluation chart containing: identification; admission date; date of surgery; weight and height; calculation of body mass index (BMI): weight/height2, considering as normal = 24.9 kg/m2, overweight = 25 to 29.9 kg/m2 and obese > 30 kg/m2; risk factors for coronary disease (systemic arterial hypertension, diabetes mellitus; previous associated diseases such as cerebrovascular accident (CVA), angina, acute myocardial infarction (AMI), chronic obstructive pulmonary disease (COPD)). The routine procedures performed by the physician as preoperative evaluation were also recorded: New York Heart Association (NYHA) Functional Classification; ejection fraction (EF); arterial gasometry; complete blood count; chest X-ray (all reports showing abnormal findings as evaluated by the radiologist). The patient was asked about his/her alcohol consumption and smoking status and was classified as: ex-smoker - patient who used to smoke and quit smoking up to 6 months before surgery; smoker - patient who currently smoked or used to smoke up to 6 months before MRV, and non-smoker - patient who never smoked.

Perioperative evaluation

MRV was performed via median sternotomy, using saphenous vein graft (SVG) and internal mammary artery graft (IMG). All patients underwent general anesthesia, orotracheal intubation, controlled mechanical ventilation and ECC. During the surgical procedure, the following information was recorded on the medical chart: duration of surgery, ECC and ischemia, number and type of grafts used, and drain placement.

Postoperative evaluation

At the postoperative unit, the following data on patient's clinical status were recorded on the medical chart: weaning from mechanical ventilation; onset of pathological conditions such as pneumonia (defined as the presence of a recent or chronic pulmonary infiltrate); high temperature; leukocytosis; purulent tracheal secretion and medical diagnosis from the medical chart9; atelectasis (defined as insufficient lung aeration in a part of the lung or the whole lung)10 based on the radiological report; pleural effusion (characterized by the collection of excess fluid in the pleural cavity, as detected by anteroposterior and lateral chest radiographs)10,11; acute respiratory distress syndrome (ARDS) (defined as being of acute onset, oxygenation with a partial pressure arterial oxygen/fraction of inspired oxygen ratio of < 200 mmHg despite positive end-expiratory pressure (PEEP)); bilateral pulmonary infiltrate detected by chest radiographs, pulmonary artery wedge pressure < 18 mmHg or no clinical evidence of left atrial hypertension12; length of hospitalization, and death during this period. During the postoperative period, patients underwent routine tests again: chest X-ray, arterial gasometry and complete blood count.

Statistical analysis

The sample size was based on data from literature with an approximate 30% incidence of complications following MRV5-7, a confidence interval amplitude of 10, alpha 0.05, and statistical power of 80%.

The analyses were performed using the version 15.0 of the SPSS statistical software.

The quantitative variables were presented as means and standard deviations or medians and interquartile ranges (25th to 75th percentile). The qualitative variables were presented as distribution of absolute and relative frequencies.

The Spearman's Coefficient of Rank Correlation was used to evaluate the correlation between the quantitative outcomes and the quantitative predictive variables or quantitative clinical profile. In order to evaluate the difference between the quantitative variables and qualitative variables (dichotomous) or qualitative clinical profile (dichotomous), the Student's t test was used whenever the outcomes had a normal distribution; for the other cases, the nonparametric Mann-Whitney test was used.

The chi-square test was used to evaluate the relationship between qualitative outcomes and the qualitative predictive variables or qualitative clinical profile. The nonparametric Kruskal-Wallis test was used to evaluate the quantitative outcomes relative to the patients' smoking status.

A p value of < 0.05 was considered statistically significant.

Multiple Linear Regression Analysis was used with automatic stepwise selection to evaluate the relationship between the length of hospital stay/duration of mechanical ventilation and the clinical profile/surgical predictive variables statistically significant on bivariate analysis.

 

Results

The sample consisted of 202 patients undergoing MRV, and their characteristics are shown on Table 1. Their mean age was 62 years, 70% of them were men, 45% were ex-smokers and 13% had a previous history of chronic obstructive pulmonary disease (COPD).

 

 

Table 2 shows the surgical variables. The average number of grafts was 2.8 per surgery, and the mean duration of surgery was 4.3 hours.

 

 

Table 3 shows the incidence of postoperative complications that occurred during hospitalization. Of the 202 patients, 90 developed some sort of pulmonary complication. The frequency of pleural effusion was 84%, whereas atelectasis was 65%. Patients received mechanical ventilation for a median of 11 hours (8-16) and their average length of hospital stay was 12.7 days. Eleven patients died after MRV (5.4%).

 

 

Table 4 shows the correlations between the duration of mechanical ventilation (DMV) and length of hospital stay and pre- and perioperative variables. Statistically significant associations have been observed among the duration of mechanical ventilation, ejection fraction, previous history of asthma, and duration of ECC and ischemia, and time in the operating room. As to the length of hospital stay, associations with age, ex-smoker status, abnormal chest X-ray findings, previous history of hypertension and asthma, and duration of ischemia were significant. The correlations between duration of mechanical ventilation and length of hospital stay were weak; however, the correlations between clinical characteristics and surgical variables were significant.

 

 

Table 5 shows bivariate analyses between mechanical ventilation over 24 hours, pneumonia, atelectasis and pleural effusion and pre- and perioperative variables. Associations were observed between mechanical ventilation over 24 hours and length of drainage, pneumonia and preoperative abnormal chest X-ray findings, atelectasis and location of drains, and pleural effusion and time in the operating room.

Table 6 shows the results after the adjustments made to the multiple linear regression model, showing that age, preoperative abnormal chest X-ray findings, asthma, SAH and previous CVA remained independently associated with the length of hospital stay.

 

 

Discussion

In this contemporaneous cohort, pulmonary complications were frequent. More than 87% of the patients experienced at least one pulmonary complication during hospitalization. The occurrence of postoperative pulmonary complications is closely related to the presence of risk factors inherent to the surgical procedure, anesthesia and preexisting comorbidities4,5.

Consistent with the literature, an association was observed between postoperative complications, complexity of the surgical procedure, and previous comorbidities in MRV.

It is noteworthy that the criteria used for the establishment of a diagnosis of pulmonary complications were quite comprehensive, without necessarily considering their clinical relevance.

In this study, a mortality rate of 5.4% was recorded after MRV, similar to that reported in literature for elective surgeries at a referral center7.

Independent of other factors, general anesthesia combined with the surgical procedure accounts for the changes in pulmonary function that take place in the postoperative period. Due to the fact that general anesthesia depresses the function of respiratory centers, the longer the sedation time the higher the risk of pulmonary impairment13,14.

Use of ECC triggers physiological changes secondary to the exposure of blood to the plastic surface of tubes, oxygenators and filters. This, in turn, leads to an increase in extravascular fluid volume in pulmonary circulation, resulting in the filling of the alveoli by inflammatory cells and inactivation of pulmonary surfactant and collapse of some areas. This picture may result in changes in the ventilation/pulmonary perfusion relationship, reduction of compliance, and changes in respiratory work during the postoperative period, making it difficult to wean the patient and increasing the time on mechanical ventilation15.

As per our findings, prolonged mechanical ventilation (over 24 hours) was associated with length of drainage. There are reports in the literature about the damages chest drains can cause to pulmonary function, especially those inserted in the intercostal region, which can change the ventilatory mechanics and lead to pulmonary hypoventilation. These patients are thus more susceptible to developing pulmonary complications, as well as experiencing pain caused by the drain itself, potentially prolonging mechanical ventilation15,16.

The use of pleural drain tubes may be required due to potential injuries caused to the pleura during the removal of the internal mammary artery. However, the use of drains may impair the pulmonary function, since it increases the respiratory work through alterations in gas exchanges and lung mechanics, reducing lung volumes, allowing secretions to collect, leading to potential airflow obstruction and, thus, development of atelectasis4,16-18. This study observed an association between the location of drain tubes and the development of atelectasis. This complication was further worsened in patients who had two drains inserted both in the mediastinum and in the pleural cavity, compared to patients who had a drain tube inserted only in the mediastinum. This data also show that the greater the number of chest drains inserted the higher the potential for pulmonary complications.

Besides the preexisting comorbidities, a long surgery may be directly related to the complexity of the case, since it presupposes that a large number of procedures was performed. Thus, surgeries taking longer than 210 minutes are considered an important risk factor for the development of postoperative pulmonary complications14. Consistent with literature data, we observed that in our sample longer surgeries were associated with a higher incidence of pleural effusions, possibly due to the pleural inflammatory responses triggered by the surgical procedure itself11,18. In our sample, the high incidence of pleural effusion observed was probably due to the use of strictly radiological criteria, independently of their dimension and clinical repercussion. In other studies, the criteria employed were also based on radiographic exams, however with classifications according to the degree of the pulmonary impairment11,18.

In our study, an association was found between preoperative abnormal chest X-ray findings and pneumonia; however, there are few studies in the literature that have evaluated this association in MRV19. It is also noteworthy that all radiographic abnormal findings were taken into account, whether or not they were clinically relevant, and this can represent a bias for the evaluation of this variable.

Other factors have also been observed, such as preexisting comorbidities and the patients' clinical status before the surgery, which prolonged the length of hospital stay due to their higher susceptibility to pre- and postoperative complications5,20.

The limitations of this study are inherent to its design, since cohort studies are prone to selection and analysis bias. The fact that different professionals collected the data and recorded them on the patient medical charts was a limitation for the investigator, since it meant that he/she had to rely on the recorded information, rather than directly accompanying patient progress during the postoperative phase. Moreover, observational studies are prone to residual confounding factors not considered in the multivariate analysis. Nevertheless, a detailed review of the medical chart was conducted in an attempt to extract the best quality information possible.

All pulmonary complications observed in this study were taken into account independently of the degree of the impairment, through radiographic reports and diagnoses made by the medical team during the progression of the patient, which can justify the high number of outcomes.

In conclusion, over the past several decades, MRV and pre-, peri- and postoperative care have advanced greatly, reducing the occurrence of postoperative complications. However, surgeries are being performed on increasingly complex cases, thus leading to the development of complications following MRV, especially in the respiratory tract, such as those reported in this and in other studies20-22.

Therefore, concomitantly with technological advances, there is a need to conduct better clinical assessments in light of the potential risk factors, seeking to further improve the status of the patient in the postoperative phase.

Thus, there are many aspects to be studied in this area, in the search for effective physiotherapeutic interventions to further reduce the clinical outcomes which are significant to the patients. Other studies have shown that physical therapy can play an important role both in preventing and reducing postoperative complications, through techniques such as pulmonary expansion and ventilation, bronchial hygiene andrespiratory muscle training, among other resources capable of ensuring better recovery after MRV23,24.

Potential Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Sources of Funding

There were no external funding sources for this study.

Study Association

This article is part of the thesis of master submitted by Leila D. N. Ortiz, from Instituto de Cardiologia do RS/FUC.

 

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Mailing address:
Leila D. N. Ortiz
Av. Princesa Isabel, 395 - Santana
Porto Alegre, RS - Brazil
E-mail: ldnortiz@ibest.com.br, ppgfuc@cardiologia.org.br

Manuscript received April 28, 2009; received manuscript revised August 31, 2009; accepted February 22, 2010.

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