In their work the authors observed the influence of controlled hypotension by means of sodium nitroprusside on the acidobasic balance, the oxygenation parameters, pulmonary shunt and lactatemia in patients with idiopathic scoliosis in the course of dorsal fusion by Harrington instrumentation. In comparison with the control group of patients there had not occurred significant - from the viewpoint of statistics - changes in ph, paCO2 and pvO2. However, the pulmonary shunt (Qva/Qt) doubled (p less than 0.002) which resulted in a significant decrease of paO2 (p less than 0.02) but in no case there occurred hypoxemia. The values of the lactate both in the venous and arterial blood were increased (p less than 0.001, or p less than 0.02) in contrast to the control group of patients, but they did not mean the increased production of lactate during intracellular hypoxia. As a result the regulated hypotension by means of sodium nitroprusside can be applied also in patients with altered pulmonary functions.