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Atelectasis and gas exchange after cardiac surgery
A Tenling1, T Hachenberg, H Tydén
1Department of Cardiothoracic Anesthesia, University Hospital, Uppsala, Sweden. Arne.Tenling@KlinFys.uu.se
Anesthesiology
|August 26, 1998
Summary
Post-cardiac surgery, significant lung atelectasis was observed. However, this lung collapse did not directly correlate with the measured intrapulmonary shunt fraction in patients.
Area of Science:
- Cardiothoracic Surgery
- Pulmonary Physiology
- Medical Imaging
Background:
- A high intrapulmonary shunt and impaired lung function are common after cardiac surgery, persisting for up to a week.
- Animal studies suggest atelectasis may cause postoperative shunt.
- This study investigated whether atelectasis explains shunt in human cardiac surgery patients.
Purpose of the Study:
- To determine if atelectasis is the cause of intrapulmonary shunt after cardiac surgery.
- To quantify the extent of atelectasis and shunt in patients undergoing coronary artery bypass graft and mitral valve surgery.
Main Methods:
- The multiple inert gas elimination technique (MIGET) was used to measure shunt before and after surgery in nine coronary artery bypass graft and nine mitral valve surgery patients.
- Computed tomography (CT) scans of the thorax were performed on the first postoperative day to assess atelectasis.
Main Results:
- Postoperative shunt fraction increased significantly, from 2+/-3% preoperatively to 12+/-60% on postoperative day one.
- CT scans revealed bilateral dependent densities in all but one patient, indicating atelectasis.
- The mean area of atelectasis was 8+/-8% of total lung area, with basal regions showing 28+/-19% collapsed tissue. No clear correlation was found between atelectasis extent and shunt fraction.
Conclusions:
- Large dorsal lung atelectasis is present on the first postoperative day after cardiac surgery.
- Atelectasis does not appear to be the sole or primary cause of the measured intrapulmonary shunt fraction in these patients.