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Risk factors for postoperative pulmonary complications in coronary artery

bypass graft surgery patients

Louise Jensen a,, Liyan Yang b

a Faculty of Nursing, University of Alberta, 3rd Floor, Clinical Sciences Building, Edmonton, AB, Canada T6G 2G3b Faculty of Nursing, Edmonton, AB, Canada T6G 2G3

Received 30 March 2006; received in revised form 2 November 2006; accepted 6 November 2006

Available online 7 March 2007

Abstract

Background: Despite numerous advances in anesthesia, surgical techniques, and postoperative care for coronary artery bypass graft (CABG)

surgery, postoperative pulmonary complications (PPCs) still account for postoperative morbidity.

Objective: To determine current risk factors for PPCs in CABG surgery patients.

Methods: A retrospective cohort design was used. Health records were reviewed for patients ( n =315) who had CABG surgery at a large

quaternary healthcare center over a 4 month period. Pre-, peri-, and postoperative risk factors for PPCs were recorded as binary variables.

Data were further assessed according to PPCs and non-PPCs using logistic regression models.

Results: PPCs occurred in 99.4% of this CABG surgical cohort. Atelectasis, pleural effusion, atelectasis with pleural effusion, and pneumonia

were the most frequent PPCs post CABG surgery. Age N65 years, diabetes, and ASA classification N3 were found to be related to the

presence of atelectasis. No significant risk factors were related to the development of pleural effusion or atelectasis with pleural effusion.

Postoperative pneumonia was associated with previous myocardial infarction, ventilation N10 h, and hospital stay N5 days. History of

bronchitis and COPD were related to postoperative pneumothorax; history of heart failure, COPD, and other lung diseases were related to

postoperative pulmonary edema.Conclusion: These findings contribute to the understanding of PPCs in post-CABG surgery patients and assist in identification of patients at

risk for developing PPCs.

2006 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.

Keywords: Pulmonary complications; CABG postoperative complications

Coronary artery bypass graft (CABG) surgery is a

common treatment for patients with ischemic heart disease.

Postoperative complications significantly contribute to

prolonged hospitalization and intensive care unit (ICU)

stay following CABG surgery [1,2]. Despite numerousadvances in anesthesia, surgical techniques, and postopera-

tive care, postoperative pulmonary complications (PPCs)

still account for major CABG surgery postoperative

morbidity [3]. Furthermore, as patients referred for CABG

surgery today are older with more complex comorbidities, it

was postulated that development of PPCs related to pre-

operative, peri-operative, and postoperative factors may have

changed. Therefore, the purpose of this study was to

determine current risk factors associated with PPCs from

these three operative time periods. Determining predisposing

factors for PPCs could assist in identifying patients at riskand in the development of prevention strategies.

1. Background

Since cardiac surgery was introduced in the 1950s, the

characteristics of patients undergoing CABG surgery have

changed substantially. Patients are older, female, have unstable

angina, pulmonary hypertension, and poorer left ventricular

function [4,5]. This changing profile may predispose some

cardiac surgical patients to develop PPCs, especially in the

European Journal of Cardiovascular Nursing 6 (2007) 241246

www.elsevier.com/locate/ejcnurse

Corresponding author. Tel.: +1 780 492 6795; fax: +1 780 492 2551.

E-mail address: [email protected] (L. Jensen).

1474-5151/$ - see front matter 2006 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.

doi:10.1016/j.ejcnurse.2006.11.001
mailto:[email protected]://dx.doi.org/10.1016/j.ejcnurse.2006.11.001http://dx.doi.org/10.1016/j.ejcnurse.2006.11.001mailto:[email protected]

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elderly where the capacity to meet additional workloads

postoperatively is limited [6]. PPCs also have a higher

incidence in patients undergoing CABG surgery (25%) than

valvular surgery (17%) [2]. Also, PPCs contribute significant-

ly to prolonged length of ICU and hospital stay [1,2].

The reported incidence of PPCS following CABG

surgery varies from 5

90% [7]. This variation dependslargely on how PPCs are defined [712]. Johnson and

McMahan [2] found the incidence of PPCs to be 25% based

on 121 CABG surgery patients, versus 13.3% based on 7306

patients by Pederson, Eliason, and Henriken [9]. Diagnosis

of PPCs requires patients to have pulmonary dysfunc-

tion and associated clinical findings that meet diagnostic

criteria. However, the conditions included in PPCs ranged

from atelectasis only [11] to atelectasis, pneumonia, bron-

chospasm, respiratory failure with prolonged mechanical

ventilation, non-cardiogenic (permeability) pulmonary edema,

pulmonary emboli, and cardiogenic pulmonary edema

[7,8,12]. Atelectasis and pneumonia are the most common

PPCs based on an analysis of 80 studies investigating PPCs

post cardiac surgery, and noted a lack of data on the

frequency of types of PPCs [7]. Furthermore, the frequency

of specific PPCs has not been linked to the type of cardiac

surgery [10], which may vary due to surgical complexityand duration of anesthesia, and hence the potential for

complications [7].

Risk factors for PPCs previously identified in the

literature are history of smoking, chronic obstructive

pulmonary disease, chronic heart failure, emergency cardiac

surgery, previous cardiac surgery, hypercapnia, American

Society of Anesthesiologist (ASA) classification 2, age N

59 years, weight N114 kg, low serum albumin, diabetes

mellitus, or preoperative hospital stay N4 days [3,1315]. In

117 adult elective CABG surgery patients, a risk model for

Fig. 1. Definition of variables.

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PPCs was developed by logistic regression analysis

(sensitivity=87%; specificity=56%), with age, productive

cough, diabetes mellitus, and a history of smoking identifiedas risk factors [15]. However, the pre-, peri-, and

postoperative risk factors specifically related to PPCs for

CABG surgery patients remain unclear.

2. Purpose of the study

The purpose of this study was to examine the PPCs in a

cohort of CABG surgical patients. Specifically, the research

questions were:

1. What is the incidence of PPCs?

2. What types of PPCs occur and their frequency?

3. What pre-, peri-, and postoperative factors are related to

the development of PPCs?

4. Are PPCs related to increased ICU and hospital stay?

3. Methods

A retrospective cohort design was used to examine therelationship between the pre-, peri-, and postoperative risk

factors and the development of PPCs in a cohort of patients

who had undergone CABG surgery. Health records were

reviewed on all patients (n =315) who had CABG surgery at a

large quaternary healthcare center from January to April, 2002,

with an independent random review of 100 health records to

verify consistency in data coding. All patients undergoing

CABG surgery at this institution have standardized pre-

operative education specifically related to pulmonary function.

Data retrieved included risk factors, PPCs, and outcomes as

recorded on the health record. Variableswere coded as binary for

purposes of analysis, with cut-off values determined from the

literature a priori or from median values post hoc (see Fig. 1).The pre-operative risk factors recorded were age, smoking

history, body mass index (BMI), American Society of

Anesthesiologists (ASA) classification, history of hypertension,

blood pressure on admission, previous myocardial infarction

(MI), history of heart failure, diabetes mellitus, and history of

lung disease [chronic obstructive lung disease (COPD),

bronchitis, other lung disease]. The peri-operative risk factors

included surgical approach, duration of anesthesia, duration of

cardiopulmonary bypass (CPB), and number of coronary

vessels bypassed. Postoperative risk factors recorded were

presence of nasogastric (NG) tube, duration of ventilation, and

postoperative complications other than pulmonary such asbleeding, arrhythmias, renal insufficiency, and infection. PPCs

Table 1

Cohort characteristics

Variables Frequency Percent

Age

65 years 171 54.3

N65 years 144 45.7

GenderMale 249 79.0

Female 66 21.0

Smoking

Never/quitN6 months 220 69.8

Current smoking 95 30.2

Body Mass Index

25 83 26.3

N25 232 73.7

Hypertension on admission

130/80 233 74.0

N130/80 82 26.0

History of hypertension 198 62.9

History of heart failure 65 20.6

Previous myocardial infarction 166 52.7

Diabetes 96 30.5History of lung disease 62 19.7

American Society of Anesthesiologists

(ASA) Classification

3 157 49.8

N3 158 50.2

Duration of anesthesia

270 min 163 51.7

N270 min 152 43.8

Bypass time (n =307)

95 min 168 54.7

N95 min 139 45.3

Number of vessels bypassed

3 181 57.5

N3 134 42.5

Duration of ventilation (n =313)10 h 201 64.2

N10 h 112 35.8

ICU stay

24 h 190 60.3

N24 h 125 39.7

Hospital stay

5 days 166 52.7

N5 days 149 47.3

Table 2

Postoperative pulmonary complications

N %

Atelectasis 307 97.5

Pleural effusion 238 75.6

Atelectasis and pleural effusion 232 73.7

Pneumonia 37 11.7Pulmonary edema 33 10.5

Pneumothorax 23 7.3

Hemothorax 1 0.3

Pulmonary embolus 1 0.3

Table 3

Predictors of postoperative pneumonia

Variable Risk coefficient SE P Odds ratio

Previous MI 0.846 0.428 0.048 2.331

VentilationN10 h 0.990 0.395 0.012 5.647

Hospital stayN5 days 1.515 0.481 0.002 4.550

Intercept 4.515 0.585

Model 2 =43.282, df= 5, pb0.001. Hosmer and Lemeshow goodness-of-

fit statistic=2.360, df= 7, p =0.937.

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(atelectasis, pneumonia, pleural effusion, pneumothorax,

hemothorax, pulmonary embolus, pulmonary edema, respira-

tory failure) were identified from progress notes, laboratory

reports, and diagnostic imaging reports. Outcomes identified

were of length of ICU stay and length of hospital stay.

4. Data analysis

Descriptive statistics were computed for all risk factors,PPCs, and outcomes. Pre- peri- and postoperative risk factors

were first examined separately using univariate logistic

regression analysis. Data were assessed according to PPCs

and non-PPCS. All statistically significant univariate

predictors of PPCs were then entered into a stepwise

multivariate logistic regression model. Risk factors were

considered significant at pb0.05.

5. Results

5.1. Risk factors for postoperative pulmonary complications

The age of this CABG surgical cohort ranged from 29 to87 years (M= 63.1 11 years). The mean age for males

(n = 249) was 63.5 10.1 years and for females (n =66) was

61.9 11.1 years. In this cohort, 95(30.2%) patients were still

smoking at the time of surgery or had just quit within

6 months. Other pre-operative risk factors were history of

hypertension (62.9%), history of heart failure (20.6%),

previous myocardial infarction (52.7%), diabetes mellitus

(30.5%), and history of lung disease (19.7%) (Table 1).

Peri-operatively, 49.8% of the patients had an ASA

classification 3. Surgical approach was excluded from

analysis as all patients had a mid-sternal surgical approach.

The length of anesthesia ranged from 150 to 630 min(M=276.53.3 min), with a median duration of 270 min.

Total cardiopulmonary bypass time ranged from 27 to

226 min (M=951.7 min), with a median of 93 min. The

majority of patients had 3 or 4 coronary vessels bypassed.

All patients had an NG tube, therefore NG tube postoper-

atively was excluded from further analysis.

Postoperatively, the duration of mechanical ventilation

ranged from 3 to 460 h (M=15.92.1 h), ICU stay rangedfrom 12 to 502 h (M=40.42.9 h), and hospital stay ranged

from 3 to 57 days (M= 6.7 0.3 days). The majority of

subjects (52.7%) stayed in hospital less than 5 days (Table 1).

5.2. Incidence of postoperative pulmonary complications

Overall, 313 (99.4%) CABG surgery patients developed a

PPC. The majority of patients developed atelectasis (97.5%),

pleural effusion (75.6%), or atelectasis with pleural effusion

(73.7%). Thirty-seven (11.7%) patients developed pneumo-

nia, 33 (10.5%) patients had pulmonary edema, and 23

(7.3%) patients had a pneumothorax. There was only 1 casefor each of the remaining PPCs noted in Table 2.

5.3. Predictors of postoperative pulmonary complications

Predictors of PPCs were examined from pre- peri- and

postoperative patient variables. No significant predictors

were found for pleural effusion or atelectasis with pleural

effusion. Age N65 years, diabetes mellitus, and ASA

classification 3 were found to be significantly related to

the presence of atelectasis in the univariate model, but did

not remain significant predictors in multivariate analysis.

Previous myocardial infarction, history of COPD or

bronchitis, duration of anesthesia N270 min, duration ofventilationN10 h, and hospital stay N5 days were found to be

associated with the presence of pneumonia. However, in the

multivariate regression model, only previous myocardial

infarction (OR=2.3, p =.05), ventilation N10 h (OR=5.6,

p = .01), and hospital stay N5 days (OR= 4.6, p =.00)

remained significant predictors of pneumonia (Table 3).

Only two pre-operative risk factors were significant

univariate predictors and remained predictors of a postop-

erative pneumothorax in the multivariate model, history of

bronc hitis (OR = 5.4, p =.02) and history of COPD

(OR=4.8, p =.03) (Table 4). Finally, history of heart failure

(OR=3.6, p =.00), history of COPD (OR=4.6, p = .02), and

Table 4

Predictors of postoperative pneumothorax


Bronchitis 1.678 0.712 0.018 5.353

COPD 1.572 0.704 0.026 4.818


Model 2 =7.692, df= 2, p =0.021. Hosmer and Lemeshow goodness-of-fit statistic=0, df= 3, model perfectly fit data.

Table 5

Predictors of postoperative pulmonary edema


History of heart failure 1.281 0.399 0.001 3.599

History of COPD 1.519 0.663 0.022 4.570

History of other lung disease 2.128 0.671 0.002 8.402




Table 6

Predictors of ICU stayN24 h


Pneumonia 0.774 0.384 0.044 2.169

Pulmonary edema 1.211 0.412 0.003 3.358

Atrial fibrillation 0.901 0.292 0.002 2.462

Renal insufficiency 1.841 0.591 0.002 6.300

Ventricular tachycardia 2.205 1.119 0.049 9.067





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history of other lung diseases (OR = 8.4, p = .00) were

significant risk factors for postoperative pulmonary edema

(Table 5).

6. Predictors of prolonged ICU and hospital stay

All postoperative complications recorded, includingPPCs, were considered risk factors for prolonged ICU stay

(N24 h) and hospital stay (N5 days), and subsequently,

entered into the stepwise multivariate regression model.

Pneumonia (OR= 2.2, p = 0.04), pulmonary edema

(OR=3.4, p = 0.00), atrial fibrillation (OR= 2.5, p =0.00),

renal insufficiency (OR= 6.3, p = 0.00), and ventricular

tachycardia (OR=9.1, p =0.05) were significant predictors

of prolonged ICU stay N24 h (Table 6). Atelectasis with

pleural effusion (OR = 1.8, p =0.05), pneumonia (OR=6.4,

p =0.00), atrial fibrillation (OR=4.0, p =0.00), and sternal

wound infection (OR=5.0, p = 0.04) significantly predicted

a prolonged hospital stay N5 days (Table 7).

7. Discussion

Atelectasis, pleural effusion, atelectasis with pleural

effusion, pneumonia, pulmonary edema, and pneumothorax

were present in this postoperative CABG surgery cohort.

This is similar with Schuller and Morrow's [3] conclusion

that the most commonly seen pulmonary complications after

coronary revascularization are pleural effusion, hemothorax,

atelectasis, pulmonary edema, and pneumonia.

Atelectasis accounted for the highest incidence of PPCs,

similar to the findings of others [3,12,15]. However, the

majority of patients were asymptomatic or recovered by thetime of discharge. Three risk factors were found to be related

to the presence of atelectasis, yet, they were not confirmed

with multivariate analysis. This may be due to the skewed

distribution of only 7 patients not having atelectasis.

Pleural effusion with atelectasis was the second most

commonly occurring PPC. Although older age, lower serum

albumin concentration, higher APACHE scores during the

initial 24 h of ICU stay, longer ICU stay, and longer

mechanical ventilation have been found to be related to

pleural effusion [16], there were no significant predictors of

pleural effusion found in this study. This may be in part due

to the unknown pathogenesis of pleural effusion post CABG

surgery, which most likely is related to surgical trauma [17].

However in this study cohort, pleural effusion did contribute

to prolonged hospital stay.

The incidence of pneumonia ranges from 3% to 34% after

various surgical procedures, with a mortality between 20%

and 50% [18]. Although only 37 (11.7%) CABG surgery

patients in this study developed postoperative pneumonia, itcontributed to both prolonged ICU stay and postoperative

hospital stay. Similar to Croce's [19] findings, advanced age,

history of COPD, and prolonged ventilation were risk factors

for postoperative pneumonia. Previous myocardial infarc-

tion, however, was a unique variable found to predict

postoperative pneumonia in this study. Leal-Noval et al. [20]

found that a perioperative myocardial infarction was a risk

factor for pneumonia postoperatively, in addition to previous

treatment with broad-spectrum antibiotics, enteral nutrition,

and reintubation. Finally, ventilation N10 h was found to be a

strong predictor of postoperative pneumonia. Transmission

of organisms causing pneumonia can take place throughcontamination of respiratory equipment or devices, aspira-

tion, and ineffective oral hygiene [21,22].

Pneumothorax is a frequent complication of cardiac

surgery and is more common if postoperative mechanical

ventilation is prolonged or if high levels of PEEP are required

[3]. Urschel et al. [23] concluded that patients with COPD are

more likely to suffer prolonged morbidity and require a

thoracotomy. This is similar to the results of this study, in that

a history of COPD and history of bronchitis were related to

the development of a postoperative pneumothorax. Other

potential causes for postoperative pneumothorax in cardiac

surgery patients include lung perforation during central line

insertion, direct pulmonary injury by needle puncture throughthe pericardium, puncture of the lung during chest closure, or

other forms of direct injury to the lung [24].

Postoperative pulmonary edema is commonly found in

patients with chronic pulmonary disease and in those with

postoperative infection [25]. Accumulation of extravascular

lung water may be excreted by leaky alveolar-capillary

membranes following cardiopulmonary bypass and by

hypoalbuminemia [26]. History of heart failure and history

of COPD and other lung diseases were found to be predictors

of postoperative pulmonary edema. Pulmonary vascular

congestion may be caused by impaired leftventricular function

with subsequent elevation of pulmonary capillary pressure [3].

8. Implications of the findings

Risk factors for PPCs were examined pre- peri- and

postoperatively. Pre-operative risk factors identified were

consistent with those reported in the literature. No peri-

operative risk factors were found related to any PPC. Also,

the results suggest that in addition to PPCs, atrial fibrillation,

renal dysfunction, and infection are reasons contributing to

prolonged ICU or hospital stay. An understanding of the most

common PPCs allows for earlier identification of complica-

tions, prompt intervention, and the decrease of adverse

Table 7

Predictors of hospital stayN5 days

Variable Risk

coefficient

SE P Odds

ratio

Atelectasis with pleural effusion 0.566 0.286 0.048 1.761

Pneumonia 1.852 0.482 0.000 6.371

Atrial fibrillation 1.390 0.315 0.000 4.014Sternal infection 1.607 0.797 0.044 4.989




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patient outcomes. The priority concerns of pre-operative care

include knowing the pre-operative risk factors examined in

this study; knowing that the elderly may be prone to

conditions such as aspiration; providing sufficient respiratory

care for patients with a history of COPD, bronchitis, or other

lung diseases to optimize pulmonary function before surgery;

teaching patients about airway clearance techniques and earlypostoperative mobilization; and monitoring of patients with a

history of myocardial infarction or heart failure. However,

indicators that nurses use to identify PPCs and instigate

treatment needs exploration. Actual preventive strategies and

the effect of interventions on the course of PPCs are largely

unknown. Furthermore, risk prediction models for the

development of PPCs in homogeneous groups of patients

must be tested to enhance clinical applicability and hence

outcomes.

9. Limitations of the study

As one of the limitations for this study, the convenience

sample drawn from a single institution could affect

generalizability of the findings. Since this study was a

retrospective design, risk factors were reviewed from the

literature, independent outcomes were defined, and the data

were collected from health records, the major drawbacks

were missing data and the difficulty of interpreting

information recorded by different health personnel. For

instance, 20 (6.4%) patients were missing an NYHA

classification, 8 (2.5%) patients were missing cardiopulmo-

nary bypass time, and 2 (0.6%) patients were missing

duration of ventilation. In addition, pain management was not

included due to the difficulty of interpreting documentationand lack of information. Skewed distribution of outcomes

may account for a bias in data analysis, in that PPCs

developed in 313 (99.4%) patients, with atelectasis occurring

in 308 (97.8%). Among the previous studies, definitions of

postoperative pulmonary complications varied widely. Re-

finement of the definition of pulmonary complications to a

narrower spectrum of clinically relevant and related out-

comes needs to be addressed in further studies.

10. Conclusions

The majority of this CABG surgery patient cohort (99.4%)developed PPCs, with atelectasis, pleural effusion, or both

being the most common. However, only atelectasis with

pleural effusion contributed to a hospital stay N5 days. Age N

65 years, diabetes, ASA classification N3 were found to be

related to the presence of atelectasis. No risk factors were

found to be related to pleural effusion or atelectasis with

pleural effusion. Previous myocardial infarction, ventilation N

10 h, and hospital stay N5 days were found to be associated

with postoperative pneumonia. Finally, history of heart failure,

COPD, and other lung diseases predicted postoperative

pulmonary edema. These findings further contribute to the

understanding of PPCs in post-CABG patients.

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