Primary Outcome Measures:
- Detection of SpO2-oscillations caused by cyclic recruitment and derecruitment of atelectasis. [ Time Frame: 20 min ] [ Designated as safety issue: Yes ]
As stated above cyclical recruitment and derecruitment has been shown a mechanism of VALI. It has further been demonstrated that PaO2-oscillations in the systemic circulation are transmitted to endorgans (i.e. brain, kidney and other peripheral organs). There have no studies quantifying PaO2- or SpO2-oscillations in human subjects. The rationale of this study is to measure non-invasively SpO2-oscillations throughout the respiratory cycle as PaO2 oscillations cannot easily be detected. We will analyse SpO2-oscillations in a cohort of post-operative patients. Atelectasis is a major risk factor for pulmonary complications. As it occurs in up to 90% of surgical patients this phenomenon is highly relevant. Patients with large areas of atelectatic lung tissue are prone to cyclical recruitment and derecruitment and consecutive SpO2-oscillations.
There will be two groups of patients: One with a high risk for atelectasis and one with low risk for atelectasis. The patients are stratified by the type of surgery. Upper abdominal surgery with a duration of more than 2 hours has been shown to be an independent risk factor for atelectasis. Therefore, we chose to assign patients scheduled for abdominal surgery with an anticipated duration of surgery of more than 4 hours for the high-risk group. Patients with neurosurgical procedures with more than 4 hours will be assigned to the low risk group. In each patient the SpO2-oscillations will be measured at three different respiratory rates (RR). The rationale for this is that previous studies showed that cyclical recruitment and derecruitment is dependent on the RR.