Basic data characteristics
According to the requirement of sample size, 500 cases were enrolled in the PHS group, and 400 cases were enrolled in the DABS group. Gender composition (64.80% and 65.25% of male ratio, respectively, P=0.944) and age distribution (63.55±16.82 and 62.86±15.65 years, respectively, P=0.532) in PHS and DABS group had no statistical difference (Table 1).
Almost all the venous indicators, e.g., K+ (4.11±0.72 mmol/L and 4.09±0.71 mmol/L, respectively,P=0.773), Na+ (138.09±4.87 mmol/L and 137.99±5.13 mmol/L, respectively, P=0.749), Hb (116.14±31.04 g/L and 118.73±30.82 g/L, respectively,P=0.213), and HCT (36.39±9.59% and 36.18±9.22%, respectively,P=0.742), in PHS and DABS group had no statistical difference except for Cl- (101.15 ±6.42 mmol/L and 102.28 ±6.45 mmol/L, respectively, P=0.009) (Table 1).
All the indicators in ABG, e.g., K+ (3.79±0.75 mmol/L and 3.89±0.70 mmol/L, respectively,P=0.035), Na+ (135.19 ±5.02 mmol/L and 136.80 ±5.69 mmol/L, respectively, P<0.0001), Cl- (108.74 ±7.42 mmol/L and 107.62 ±8.38 mmol/L, respectively, p=0.033), Hb (113.93 ±31.10 g/L and 119.62±32.28 g/L, respectively,P=0.007), and HCT (35.12±9.36% and 36.84±9.72%, respectively,P=0.007), in PHS and DABS group had a statistical difference.
Differences in biochemical indicators between venous results and ABG
Table 2 shows the difference in blood results between venous blood and arterial blood, which is an important index to reflect the accuracy and stability of ABG analysis. In the PHS group, the difference values were 0.318±0.396 mmol/L (P<0.0001, β=0.0001) for K+, 2.902±2.709 mmol/L (P<0.0001, β<0.0001) for Na+, –7.598±5.060 mmol/L (P<0.0001, β=0.0071) for Cl-, 2.212±7.992 g/L (P<0.0001, β=0.0001) for Hb, 1.269±2.861% (P<0.0001, β<0.0001) for HCT. In the DABS group, the difference values were 0.202±0.276 mmol/L (P<0.0001, β<0.0001) for K+, 1.187±2.346 mmol/L (P<0.0001, β<0.0001) for Na+, –5.336±6.116 mmol/L (P<0.0001, β=0.096) for Cl-, –0.898±9.998 g/L (P=0.073, β=0.021) for Hb, –0.659±3.228% (P<0.0001, β<0.0001) for HCT. The differences between arterial results of PHS and DABS were statistically significant in almost all indicators (K+, Na+, Cl-, and HCT).
Correlation of biochemical indicators between venous and arterial blood results
In the group of PHS, the blood results obtained by ABG analysis had a high consistency with those of venous blood at the same time, with Pearson’s correlation coefficient of 0.855 (P<0.0001) for K+, 0.850 (P<0.0001) for Na+, 0.742 (P<0.0001) for Cl-, 0.967 (P<0.0001) for Hb, and 0.955 (P<0.0001) for HCT. Whereas in the group of DABS, the consistency was higher in K+ and Na+, with correlation coefficient of 0.923 (P<0.0001) and 0.911 (P<0.0001), respectively, except for Cl- (0.688, P<0.0001), Hb (0.951, P<0.0001), and HCT (0.943, P<0.0001) (Table 3).
Sensitivity analysis
Through the analysis of box-plot, some abnormal values and extreme values were found, and some extreme values were quite different. However, to minimize the possibility of data entry errors, data were rechecked by multiple people. The possible reasons were measurement errors, special conditions of patients, or others. These abnormal and extreme values may have a great impact on the results. So, a sensitivity analysis was conducted by removing all the extreme values.
By comparison, there were 17 extreme values in the PHS group and 31 extreme values in the DABS group. After removing them, the average difference of the relative indicators between venous results and ABG collected by PHS or DABS was almost unaffected, but the standard deviation was obviously reduced. The results are shown in Table 4. In the PHS group, the adjusted difference values were 0.334±0.284 mmol/L (P<0.0001) for K+, 2.899±2.646 mmol/L (P<0.0001) for Na+, –7.359±4.542 mmol/L (P<0.0001) for Cl-, 2.211±6.018 g/L (P<0.0001) for Hb, and 1.250±2.371% (P<0.0001) for HCT. In the DABS group, the adjusted difference values were 0.193±0.255 mmol/L (P<0.0001) for K+, 1.158±2.219 mmol/L (P<0.0001) for Na+, –5.620±4.213 mmol/L (P<0.0001) for Cl-, –0.404±5.242 g/L (P=0.140) for Hb, and –0.434±1.953% (P<0.0001) for HCT.
At the same time, the adjusted correlation of results between venous and arterial blood samples also increased. The correlation coefficients were K+ (0.916, P<0.0001), Na+ (0.852, P<0.0001), Cl- (0.793, P<0.0001), Hb (0.981, P<0.0001), HCT (0.969, P<0.0001) in the PHS group and K+ (0.933, P<0.0001), Na+ (0.921, P<0.0001), Cl- (0.819, P<0.0001), Hb (0.986, P<0.0001), HCT (0.978, P<0.0001) in the DABS group (Table 5).