Ventilation-Perfusion Inequality in Patients Undergoing Cardiac Surgery

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Abstract

Background

Impaired gas exchange is a major complication after cardiac surgery with the use of extracorporeal circulation. Blood gas analysis gives little information on underlying mechanisms, in particular if the impairment is multifactorial. In the current study we used the multiple inert gas technique with recordings of hemodynamics to analyze the separate effects of intrapulmonary shunt (JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr), ventilation-perfusion (JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png) mismatch, and low mixed venous oxygen tension on arterial oxygenation during cardiac surgery.

Methods

JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png distribution was studied in nine patients undergoing coronary artery revascularization surgery. The obtained data related to JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png distribution were perfusion of lung regions with JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png < 0.005 (JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr), perfusion of lung regions with 0.005 < JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png < 0.1 (“low”-JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png regions), ventilation of lung regions with 10 < JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png < 100 (“high”-JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png regions), and ventilation of lung regions with JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png > 100 (dead space [JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngD/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngT]). In addition, arterial and mixed venous oxygen and carbon dioxide tensions and systemic and pulmonary hemodynamics were analyzed. Recordings were made before and after induction of anesthesia, after sternotomy, 45 min after separation from extracorporeal circulation, 4 h postoperatively during mechanical ventilation, and on the 1st postoperative day during spontaneous breathing.

Results

In the awake state, JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr was 4 ± 4%, and perfusion of low-JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png regions was 3 ± 5%. The sum of JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr and low-JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png units correlated with the alveolar-arterial oxygen tension gradient (PA-ao2) (r = 0.63, P < 0.05). After induction of anesthesia, JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr increased to 10 ± 9% (P = 0.069). Sternotomy had little effect on shunt, but JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr increased to 22 ± 8% (P < 0.01) after separation from extracorporeal circulation, which was correlated with a significantly higher PA-ao2 (r = 0.77, P < 0.05). Postoperatively, gas exchange improved rapidly, as assessed by a decrease of PA-ao2 from 341 ± 77 to 97 ± 36 mmHg (P < 0.01) and a reduced JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr (5 ± 4%, P < 0.05). On the 1st postoperative day, arterial oxygen tension was significantly lower than preanesthesia values (58 ± 6 vs. 68 ± 8 mmHg, P < 0.05). JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr had increased to 11 ± 6% (P < 0.05), but little perfusion of low-JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png units was observed. A correlation was found between PA-ao2 and JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr (r = 0.82, P < 0.03).

Conclusions

JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr is a major component of impaired gas exchange before, during, and after cardiac surgery. JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr increases after induction of general anesthesia, probably because of development of atelectasis. After separation from extracorporeal circulation, accumulation of extravascular lung water or further collapse of lung tissue may aggravate JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngs/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-pngr-Postoperatively, oxygenation improves, possibly because of recruitment of previously nonventilated alveoli or resolution of extravascular lung water. During spontaneous breathing, additional mechanisms such as altered mechanics of the chest, perfusion of low-JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0312/v/2017-07-22T060122Z/r/image-pngA/JOURNAL/anet/04.02/00000542-199403000-00006/ENTITY_OV0422/v/2017-07-22T060122Z/r/image-png regions, and decreased mixed venous oxygen tension may contribute to impaired gas exchange.

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