Table 2. Comparison of pH, pCO2 and pO2 of v-TAC and venous blood gas compared with arterial blood gas.
| Factor | All samples | Samples with SpO2≤90% | Samples with SpO2>90% | P-value between SpO2 groups * |
|---|---|---|---|---|
| Minutes between ABG and VBG, median (IQR) | 3 (2, 5) | 3 (2, 4) | 3 (2, 5) | 0.27 |
| pH | ||||
| N samples | 87 | 34 | 53 | |
| ABG, mean (SD) | 7.43 (0.05) | 7.42 (0.05) | 7.43 (0.05) | 0.65 |
| v-TAC, mean (SD) | 7.43 (0.05) | 7.42 (0.05) | 7.43 (0.05) | 0.31 |
| Difference ABG–v-TAC, mean (SD) | -0.001 (0.010) | -0.004 (0.009) | -0.0001 (0.011) | 0.50 |
| 95% limits of agreement | -0.017 to 0.016 | -0.015 to 0.014 | -0.015 to 0.013 | |
| VBG, mean (SD) | 7.41 (0.05) | 7.41 (0.06) | 7.41 (0.05) | 0.97 |
| Difference ABG-VBG, mean (SD) | 0.021 (0.023) | 0.016 (0.023) | 0.025 (0.023) | 0.087 |
| 95% limits of agreement | -0.018 to 0.060 | -0.012 to 0.043 | -0.010 to 0.059 | |
| pCO2 | ||||
| N samples | 87 | 34 | 53 | |
| ABG, mean (SD) | 6.08 (1.45) | 6.76 (1.41) | 5.64 (1.30) | 0.130 |
| v-TAC, mean (SD) | 6.21 (1.42) | 6.89 (1.39) | 5.78 (1.27) | 0.043 |
| Difference ABG–v-TAC, mean (SD) | -0.14 (0.21) | -0.13 (0.20) | -0.14 (0.21) | 0.97 |
| 95% limits of agreement | -0.46 to 0.19 | -0.44 to 0.18 | -0.41 to 0.13 | |
| VBG, mean (SD) | 6.78 (1.58) | 7.34 (1.56) | 6.42 (1.49) | 0.39 |
| Difference ABG–VBG, mean (SD) | -0.70 (0.60) | -0.58 (0.62) | -0.79 (0.58) | 0.158 |
| 95% limits of agreement | -1.66 to 0.25 | -1.32 to 0.16 | -1.61 to -0.04 | |
| pO2 | ||||
| N samples | 70 | 34 | 36 | |
| ABG, mean (SD) | 7.84 (1.11) | 7.06 (0.73) | 8.93 (1.03) | <0.001 |
| v-TAC, mean (SD) | 8.12 (0.96) | 7.37 (0.63) | 8.83 (0.63) | <0.001 |
| Difference ABG–v-TAC, mean (SD) | -0.28 (0.65) | -0.31 (0.56) | -0.25 (0.74) | 0.96 |
| 95% limits of agreement | -1.31 to 0.76 | -1.19 to 0.57 | -1.11 to 0.62 | |
| VBG, mean (SD) | 5.61 (1.52) | 5.60 (1.29) | 5.61 (1.66) | 0.92 |
| Difference ABG–VBG, mean (SD) | 2.59 (1.89) | 1.46 (1.41) | -3.32 (1.81) | <0.001 |
| 95% limits of agreement | -0.35 to 5.54 | -0.022 to 3.15 | 0.69 to 5.94 |
The 95% limits of agreement are adjusted for repeated measurements in the same patient.[18] The number of sample sets is lower for pO2 as v-TAC does not report values > 10 kPa.
* Means are compared between samples with SpO2 ≤ 90% and SpO2 > 90% using random effects regression which accounts for repeated measurements.
Abbreviations: ABG = arterial blood gas; IQR = interquartile range; pCO2 = partial pressure of carbon dioxide in blood; pO2 = partial pressure of oxygen in blood; SD = standard deviation; VBG = venous blood gas; SpO2 = oxygen saturation from pulse oximetry; v-TAC = calculated arterial blood gas values from VBG and pulse oximetry.