DISCUSSION
Several studies showed a reduction in forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC) in heart failure patients 8-11. Factors responsible for the restrictive pattern are increased lung stiffness, respiratory muscle fatigue, cardiac enlargement and constriction of under perfused alveoli leading to reduced lung compliance in a low cardiac output state. Elsobkey and Gomaa 12 showed that both valvular and ischemic patients had lower than normal PFT results pre-operatively with a predominant restrictive pattern. The authors also noticed that patients with rheumatic heart disease had lower values compared to patients with ischemic heart disease and this was explained by the fact that patients with rheumatic heart disease are more prone to develop pulmonary congestion in which the lung compliance is reduced and the resistance to airflow is increased with resultant decreased gas exchange and pulmonary function. This finding had also been confirmed in patients with mitral valve disease by Saxena et al. 8. Importantly, restrictive or obstructive lung impairment can be identified that is solely due to cardiac decompensation in the absence of any intrinsic lung disease 13.
The question is whether these reduced spirometry readings in surgical patients represent a real risk for postoperative respiratory complications or it is just a reflection of the heart failure status that would improve postoperatively after fixing the surgical problem. In order to answer this problem, we included in this study only coronary patients with left ventricular dysfunction and patients with severe left-sided valvular problems causing congestive heart failure. Despite the small percentage of patients with a history of asthma or COPD in our cohort, we demonstrated that the group of patients with moderate to severe impairment of pulmonary function test has a significantly longer duration of intubation and higher hospital mortality.
Our findings go in line with other studies that support the routine use of PFT in cardiac surgery patients. In a prospective cohort study14, performing spirometry on all comers for cardiac surgery irrespective of smoking or COPD history, preoperative spirometry reclassified 18% of the patients. A reduced FEV1 independently doubled the risk of death. They concluded that the inclusion of preoperative spirometry in routine screening of cardiac surgical patients may improve risk prediction and identify high-risk patients. Alam et al.15 observed that predicted FVC% and predicted FEV1% were most strongly associated with poor postoperative outcomes including postoperative respiratory failure, atelectasis and pulmonary infection but not with postoperative mortality.
On the other hand, a small study by Spivak et al. 16and another one by Bando et al. 17, found that PFT should not be used as exclusion criteria for CABG and that postoperative cardiac function and occurrence of complications are more significant than preoperative PFT in determining the duration of ventilation after cardiac surgery and that routine spirometry is unnecessary for most adult cardiac patients. Manganas et al. 18 found that patients with severe COPD can undergo CABG without increased mortality risk when compared with patients with normal PFT or with mild to moderate COPD. However, they have an increased risk of pulmonary infections, a tendency towards atrial fibrillation and slightly increased length of hospital stay. Whether to add PFT and different classifications of COPD to the STS risk model for predicting outcomes after cardiothoracic surgery was studied by Ivanov et al.19 and it came with only little utility.