ABSTRACT
BACKGROUND: The monitoring of end-tidal carbon dioxide tension (PETCO2) and oxygen supply may be required in spontaneously breathing patients during spinal anesthesia, particulary in cases involving high spinal block, underlying pulmonary disease, and use of a sedative drug. We investigated changes in PETCO2 and arterial oxygen tension versus oxygen flow rate via a nasal cannula, and the correlation between arterial carbon dioxide tension (PaCO2) and PETCO2 in spontaneously breathing patients during spinal anesthesia. METHODS: Thirty adult patients participated in this study. We performed spinal anesthesia with an optimal dose of heavy marcaine. After determining the sensory blockade level, PETCO2 was sampled from hub of a 14-gauge central catheter piercing one of the two nasal oxygen prongs, and oxygen flow rates (2, 3, 4 or 5 L/min) were measured by on-line capnography. The oxygen flow rates were varied every 5 minutes, and PETCO2 values and arterial samples for PaCO2 and arterial oxygen tension (PaO2) analysis were obtained at the end of each 5-minute period. RESULTS: No significant difference in PETCO2 was observed at the different oxygen flow rates. The results show that PETCO2 correlates closely with PaCO2 irrespective of oxygen flow rate. The PaO2 values were; 155.7 +/- 26.3, 192.7 +/- 36.6, 217.0 +/- 40.6 and 241.4 +/- 51.3 mmHg at nasal oxygen flow rates of 2, 3, 4 and 5 L/min, respectively. CONCLUSIONS: The measurement of PETCO2 via this nasal cannula was useful for continuous, noninvasive monitoring during spinal anesthesia irrespective of oxygen flow rate.