The study data will be analyzed using the Bland Altman technique for assessing agreement between two methods of clinical measurement6. Consistency between the PaCO2 and TCCO2 methods will be quantified by constructing limits of agreement (LoA). These limits are determined by using the observed mean and standard deviations of the differences between the two methods. A scatterplot will be constructed in which the Y-axis contains the differences in the paired measurements for each case (TCCO2 - PaCO2) and the X-axis contains the means of the same paired measurements ((TCCO2 + PaCO2)/2). A line representing the observed mean difference will be constructed parallel to the X-axis, as will two more lines at the points ± 1.96SD of the mean difference. These lines represent the LoA. 95% confidence intervals for the upper and lower LoA will be calculated. The pre-defined maximum acceptable difference between the methods of measurement has been determined as 10 mmHg. If the upper 95% confidence interval of the upper LoA and the lower 95% confidence interval of the lower LoA are both less than 10 mmHg from the observed mean difference, the H_0 will be accepted and the two measurement methods will be said to be in agreement.