How often should we perform arterial blood gas analysis during thoracoscopic surgery?

Abstract Study Objectives To continuously measure arterial blood gases (ABGs), to calculate the percentage of anticipated changes over time, and to develop recommendations for sampling frequencies of arterial blood gases in patients undergoing thoracoscopic surgery. Design Prospective, observational clinical trial. Setting University hospital. Patients 43 consecutive elective patients undergoing thoracoscopic surgery with one-lung ventilation. Interventions and Measurements A Paratrend 7 probe for continuous arterial partial pressure of oxygen and arterial partial pressure of carbon dioxide measurement was introduced through a radial artery cannula in the awake patient before surgery. Data were collected throughout the procedure until patients left the operating room. Afterward, time courses of arterial blood gas values were transformed into frequency space by fast Fourier transform analysis, and the expected deviations in arterial blood gases were calculated over time. Main Results Forty-three consecutive patients undergoing thoracoscopic surgery were included, and arterial blood gas values were measured during a total of 141.5 h. Critical arterial partial pressure of oxygen values ≤60 mmHg were recorded in 16 patients for a total of 4.5 hours. Fourier amplitude spectra showed comparable characteristics of arterial partial pressure of oxygen and arterial partial pressure of carbon dioxide time courses in all patients. It takes only 5, 10, or 20 minutes for the arterial partial pressure of oxygen to change 10%, 20%, or 40%, respectively (95% confidence). Conclusions Current standards to monitor arterial blood gases are not sufficient to detect and prevent hypoxemic events during thoracoscopic surgery with one-lung ventilation. Intermittent arterial blood gas analyses must be performed more frequently, up to every 10 minutes, to detect changes of 20% in arterial partial pressure of oxygen.