Abdominal surgery commonly requires perioperative relaxation and therefore controlled mechanical ventilation. However, respiratory support can be associated with minor, yet clinically significant changes in blood gas content. The inadvertent hyperoxia (excessively high oxygen) and/or hypocapnia (excessively low carbon dioxide) can result in transient changes in cerebral blood flow and cognitive impair.

The moderate hyperventilation resulting in hypocapnia as well as hyperoxia are common features of mechanical ventilation during general anesthesia. While mild hyperventilation is routinely advocated in laparoscopic surgical interventions, increased FiO2 is set to reinforce safety of respiratory support. Hypocapnia may cause disturbances of cerebral blood flow due to narrowing of cerebral vessels and a decrease cerebral blood flow. Hypocapnia is particularly injurious to the brain in premature infants. Factors that may predispose the immature brain to such injury include poorly developed vascular supply to vulnerable areas, antioxidant depletion by excitatory amino acids, and the lipopolysaccharide and cytokine effects that potentiate destruction of white matter. Data from neonates clearly suggest that severe hypocapnia after hyperventilation contribute to adverse neurologic outcomes. The use of high concentrations of oxygen can lead to a number of events such as the formation of harmful free radicals and activation of lipid peroxidation, resulting in secondary brain injury due to hyperoxia, particularly after suffering anoxia of the brain in resuscitated victims of sudden cardiac arrest. It is recommended to use the fraction of oxygen to maintain saturation at the level of 94-98% when performing cardiopulmonary resuscitation (CPR), due to the risk of reperfusion injury. These disturbances of gas exchange, yet transient can interfere in cerebral blood flow and therefore mental functions.

The primary aim of this study was the assessment of the impact of intraoperative gas exchange (hypocapnia, hyperoxia and their combinations) on the state of higher nervous activity

Inclusion Criteria:

• Informed consent
• Age > 18 years and below 80 yrs
• Elective abdominal endoscopic intervention

Exclusion Criteria:

• Known cerebral disorder, incl. traumatic injury and severe vascular impairment
• Known psychiatric illness
• Severe drug or alcohol abuse
• Resent stroke (during last 6 months)
• Pregnancy
• Within the 30 days prior to this study, either entry into any other randomized therapeutic study of an agent not licensed for the intended use or administration of any other investigational agent for the treatment of ALI. Patients must not participate in such studies for at least 30 days after enrolment into this study.