Ventilation - perfusion relationship during hip arthroplasty.

Ventilation-perfusion relationships (VA/Q) were studied during hip arthroplasty, using a multiple inert-gas elimination technique. True shunt (VA/Q = O) increased on 10 out of 16 prosthesis-anchoring occasions, while "low" VA/Q values (O less than VA/Q less than 0.1) increased on 2 occasions only. Pao2 fell by 1-2 kPa. "High" VA/Q values (10 less than VA/Q less than 100) appeared or increased with the insertion of the prosthesis, while dead space (VA/Q greater than 100) was unaltered. Cardiac output did not change. Pulmonary artery pressure fell and airway peak pressure rose by approximately 2 mmHg. It is possible that the blood flow is forced from non-dependent to dependent lung regions by the altered pressure in airways and blood vessels, creating a "high" VA/Q in upper and shunt regions and a "low" VA/Q in lower lung regions.