Chest
Volume 109, Issue 5, May 1996, Pages 1222-1230
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Preoperative Prediction of Postoperative Respiratory Outcome: Coronary Artery Bypass Grafting

https://doi.org/10.1378/chest.109.5.1222Get rights and content

Objective

The hypothesis that traditionally defined preoperative risk factors predict prolonged mechanical ventilation after coronary artery bypass graft surgery (CABG) was tested in our cohort. The predictive power of these factors was quantified, and specific patient subsets destined for prolonged mechanical ventilation after CABG surgery were defined.

Design

Five hundred thirteen consecutive patients undergoing CABG were prospectively evaluated. Preoperative pulmonary evaluation included clinical historic data, standard spirometry, and arterial blood gas. Preoperative cardiac parameters included clinical parameters and left ventricular function assessment. Nonthoracic organ (renal, endocrine, pancreas, liver) function was assessed.

Setting

University-based, tertiary referral center.

Interventions

None (observational only).

Outcomes measured

Duration of mechanical ventilation, duration of surgical ICU stay, and mortality.

Results

Multivariate regression analyses revealed that for the patient undergoing routine elective surgery and the patient undergoing urgent surgery, prolonged mechanical ventilation and death were rare events (8.3% and 2.0%, respectively). The combination of reduced left ventricular ejection fraction and the presence of selected preexisting comorbid conditions (clinical congestive heart failure, angina, current smoking, diabetes) served as modest risk factors for prolonged mechanical ventilation; their absence strongly predicted an uncomplicated postoperative respiratory course. No pulmonary diagnosis, mechanical lung function, or blood gas parameter substantially contributed to predicting adverse outcome. Classification and regression tree subgroup analysis refined specific factors important in specific subgroups.

Conclusion

With the exception of left ventricular ejection fraction, no preoperative factors emerge as good predictors across all subgroups. This series suggests that pulmonary diagnosis, lung mechanics, and blood gas parameters do not offer the clinician global rules in predicting postoperative respiratory outcome, nor should they be used as exclusion criteria for CABG surgery.

Section snippets

Subjects

Six hundred nineteen consecutive adult patients undergoing CABG surgery at the University of Vermont from April 1991 to March 1992 were considered for entry into the study. Inclusion criteria included the angiographic presence of bypassable coronary disease, and referral for anesthesia evaluation. All patients received clinical evaluation, cardiac evaluation, PFTs, including spirometry and arterial blood gas (ABG), and they were operated on. Excluded were those patients for whom PFTs could not

Cohort Characteristics

The cohort represents a typical group of CABG candidates at a referral center. Individual characteristics are described in Table 1. There were approximately equal numbers of routine and urgent procedures (n=219 vs 207, respectively). Approximately 71% of patients were male; most were 50 to 79 years old. Most were smokers at one time, but none admitted to current smoking at the time of preoperative anesthesia evaluation. Clinical congestive heart failure (CHF) was present in 19%, unstable angina

DISCUSSION

The ability to assess risk related to an intervention is central to any risk-benefit analysis in medicine. CABG surgery is both extraordinarily common and resource intensive. We have evaluated the risk for prolonged mechanical ventilation and ICU stay in a series of patients undergoing CABG surgery. Prospectively collected data on preoperative and perioperative variables suspected a priori to be risk factors for adverse respiratory outcome were examined. This was an observational study. No

APPENDIX 1

. Parameters and Ranges

ParametersAbnormal Range
Pulmonary function
FVC<75% predicted
FEV1<75% predicted
FEV1/FVC ratio<75%
PaCO2 in blood>45 mm Hg
PaO2 in blood<75 mm Hg
PaO2/FIo2 ratio<350 mm Hg
Cardiac function
LVEF<50%
Outcome
VENTHRS>48 h
SICU days>4 d

APPENDIX 2

. CART Addenda

COMFACIndex of the presence of any of four comorbid, clinically defined factors, including clinical CHF, angina, diabetes, and smoking history. Scale 0 to 1 (0.25 points per comorbid factor present).
AnginaCurrent, stable, or unstable.
AgeAge cutoffs vary depending on the subgroups examined.

APPENDIX 3

. Data Collected

Preoperative data
  • 1.

    Anthropometrics/demographics: age, sex, height, weight, surface area

  • 2.

    Smoking history: current, ever, never, pack-years, quit time (patient history)

  • 3.

    Pneumonia history: ever, recent (patient history)

  • 4.

    Bronchodilator use: current, frequency (patient history)

  • 5.

    ABG: pH, PaCO2, PaO2, FI02, measured HCO3

  • 6.

    Spirometry: FEV1, % predicted FEV1, FVC, % predicted FVC, FEV1/FVC, FEF25–75, % predicted FEF25–75.

  • 7.

    Cardiac: CHF, LVEF (radionuclide ventriculogram or

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