Substantial changes in arterial blood gases during thoracoscopic surgery can be missed by conventional intermittent laboratory blood gas analyses

Substantial and clinically relevant changes in arterial blood gases are likely to occur during thoracoscopic surgery with one-lung ventilation (OLV). We hypothesized that they may be missed when using the conventional intermittent blood gas sampling practice. Therefore, during 30 thoracoscopic procedures with OLV, the sampling intervals between consecutive intermittent laboratory blood gas analyses (BGA) were evaluated with respect to changes of Pao(2) Paco(2) and pHa ([H+]) using a continuous intraarterial blood gas monitoring system. Frequency and timing of EGA were based on the clinical judgment of 16 experienced anesthesiologists who were blinded to the continuously measured values. Extreme fluctuations of Pao(2) (37-625 mm Hg), Paco(2) (27-56 mm Hg), and pHa (7.24-7.51) were observed by continuous blood gas monitoring. During 63% of all sampling intervals, Pao(2) decreased >20% compared with the preceding EGA value, which remained undetected by intermittent analysis. In 10 patients with a continuously measured minimal Pao(2) value less than or equal to 60 mm Hg, the preceding EGA overestimated this minimal Pao(2) by >47%. Correspondingly, Pace, increases of >10% were observed in 35% of all sampling intervals, and [H+] increases of >10% were observed in 24% of all sampling intervals. Because these blood gas changes were not reliably detected by using noninvasive monitoring and their magnitude is not predictable during OLV, intermittent EGA with short sampling intervals is warranted. In critical cases, continuous blood gas monitoring may be helpful. Implications: The magnitude of blood gas changes during thoracoscopic surgery with one-lung ventilation is not predictable and not reliably detected by noninvasive monitoring. Using a continuous intraarterial blood gas monitoring device, we demonstrated that intermittent laboratory blood gas analysis with short sampling intervals is warranted to detect arterial hypoxemia.