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Efficiency of ventilation of Pulmomat has been examined in 48 patients under general anaesthesia and relaxation during normoventilation and hyperventilation of 15 and 30% degree. For criteria the acid-base status of arterial blood has been used. In normoventilation acid-base status remained unchanged within the normal range providing a regular control respectively correction of ventilationvolumes. There was no significant difference between results of 15 and 30% hyperventilation. In both situations arterial pCO-2 was reduced 15-20%. There was a tendency to acidosis in all kinds of ventilation presumably as a consequence of surgical effects. For security using the Pulmomat as respirator, a hyperventilation of 15% degree is recommanded in clinical use.

The efficiency of ventilation provided by the Engstrom-Respirator ER 300 was examined in 35 patients under general anaesthesia and relaxation during normoventilation and hyperventilation of 15% and 30%. For criteria the acid-base-status of arterial blood was used. There was a tendency to acidosis in all kinds of ventilation, probably as a consequence of surgical effects. During normoventilation the acid-base-status showed changes of low hyperventilation which are desired for security. During hyperventilation of 15% and 30%, arterial pCO2 was reduced to 30 and 27 Torr. Both situations showed no advantage over normoventilation. Using the Engstron-Respirator, normoventilation should be preferred during general anesthesia. Higher degrees of hyperventilation should be avoided because of their effects in lowering cerebral blood flow.

Efficiency of ventilation of Spiromat 650 (Dräger) has been examined in 54 patients under general anaesthesia and relaxation during normoventilation and hyperventilation of 15 and 30% degree. Changes in the acid-base status of arterial blood were used as criteria. There was a tendency to metabolic acidosis in all kinds of ventilation-probably as a consequence of surgical trauma-which was covered by an respiratory alkalosis. In all groups arterial PCO2 was reduced about 25%, without any significant difference between results of normo- 15%-and 20% hyperventilation. Using the Spiromat 650 (Drger) as respirator to normovolemic ventialtion is recommanded for clinical use.