The effect of different ventilation regimes on jugular venous oxygen saturation in elective neurosurgical patients

Since the concept of hyperventilation on neurosurgical and neurotraumatological patients has been contested, our analysis was aimed at its scrutiny on the basis of easily accessible parameters of perisurgical monitoring. Furthermore, the influence of an improved oxygen supply was tested on hyperventilationally induced cerebral changes and to what extent recommendations could be derived for clinical application. In 50 patients (normoventilation FiO2 = 0.4, 0.6; moderate hyperventilation up to a value of paCO2 = 31 mmHg and FiO2 = 0.4, 0.6 and 0.8), who underwent an elective neurosurgical operation at the central nervous system, a fiberoptical catheter was inserted into the bulb of the jugular vein for the continuous monitoring of the jugular venous oxygen saturation (sjvO2), additionally to the regular measures of perioperative monitoring. Approval for this study was given by the Ethics Committee of the University of Leipzig. At five defined times an analysis of arterial and jugular venous blood gas samples was made and their lactate and glucose concentration determined: 1. Immediately after inducing anesthesia; 2. After dura opening; 3. Sixty minutes after dura opening; 4. At dura closing; 5. Sixty minutes after the end of the operation. The lactate oxygen index (LOI) as well as the cerebral oxygen extraction (CEO2) were calculated from primary data. Hyperventilation with a value of FiO2 = 0.4 leads to a significant decrease of the jugular venous oxygen saturation below 55%. It can be positively influenced by increasing the inspiratory oxygen concentration from 40% to 60%. The CEO2 increases, above values of 42% under a hyperventilation of FiO2 = 0.4. This effect can be reversed by increasing the FiO2 value up to 0.6. Under hyperventilation the LOI reaches 'pre-ischemic' values (LOI > 0.03) prior to dura opening. Further decrease of FiO2 to 0.8 has no positive additional effect. Normoventilation with FiO2 = 0.6 induces a decrease of sjvO2 but also a decrease of LOI. Hyperventilation as a routine procedure during elective neurosurgery shall be applied critically and be combined with an increased inspiratory oxygen concentration if necessary. A longterm normoventilation with increased FiO2 should be avoided.