Pulmonary abnormalities after cardiac surgery are better explained by atelectasis than by increased permeability oedema.
BACKGROUND
Cardiac surgery can be complicated by pulmonary abnormalities, but it is unclear how various manifestations interrelate.


METHODS
A prospective study in the intensive care unit was performed on 26 mechanically ventilated patients without cardiac failure within 3 h after elective cardiac surgery involving cardiopulmonary bypass. Oedema (extravascular lung water, EVLW) was measured by the thermal-dye technique and permeability by a dual radionuclide technique, yielding a pulmonary leak index (PLI). Radiographic, mechanical and gas exchange features were used to calculate the lung injury score (LIS), ranging between 0 and 4. Evidence for left lower lobe atelectasis was obtained from plain radiographs. The plasma colloid osmotic pressure (COP) was measured by an oncometer.


RESULTS
The EVLW (normal, <7 ml/kg) was elevated in 36% of patients and the PLI (normal, <14.1 x 10(-3)/min) in 44%, but the variables did not interrelate directly. Patients with a supranormal EVLW had a lower COP than patients with normal EVLW. The duration of mechanical ventilation was prolonged in patients (20%) with EVLW > 10 ml/kg. There was no difference in EVLW and PLI in patients with LIS < 1 and LIS > 1 (31% of patients). In patients with radiographic evidence for atelectasis (46%), the positive end-expiratory pressure and inspiratory O2 fraction to maintain oxygenation were higher than in those without.


CONCLUSIONS
After cardiac surgery, mild pulmonary oedema is relatively common, even in the absence of high filling pressures, and is mainly attributable to a low COP, irrespective of increased permeability in about one-half of patients. It may prolong mechanical ventilation at EVLW > 10 ml/kg. However, pulmonary radiographic and ventilatory abnormalities may result, at least in part, from atelectasis rather than increased permeability oedema.
Verheij
J
J
Department of Intensive Care, Institute for Cardiovascular Research, Vrije Universiteit Medical Centre, Amsterdam, the Netherlands.
van Lingen
A
A
Raijmakers
P G H M
PG
Spijkstra
J-J
JJ
Girbes
A R J
AR
Jansen
E K
EK
van den Berg
F G
FG
Groeneveld
A B J
AB
D000328:Adult; D000368:Aged; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D002315:Cardiopulmonary Bypass; D003422:Critical Care; D015633:Extravascular Lung Water / Q000502:physiology; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008171:Lung Diseases / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009997:Osmotic Pressure; D010539:Permeability; D011446:Prospective Studies; D001261:Pulmonary Atelectasis / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D011654:Pulmonary Edema / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D011859:Radiography; D012129:Respiratory Function Tests