TABLE 3.
Multivariable Mixed-Effect Model
| Variable | Coefficient (95% CI) in Bivariable Mixed-Effect Analysis (Paco2 ~ Tcco2 + x] | Coefficient (95% CI) in Multivariable Mixed-Effect Analysis (Paco2 ~ Tcco2 + Age [x] + Black/African American [yr] + VIS [z]) |
|---|---|---|
| Tcco2 | Variesa | 0.79 (0.77–0.80) |
| Age, mo | 0.01 (0.002–0.02)b | 0.02 (0.01–0.03) |
| Black/African American | –2 (–3.8 to –0.3)b | –1.9 (–3.5 to –0.24) |
| Pediatric Risk of Mortality III score | –0.07 (–1.4 to 0.01) | |
| Weight-for-age | –0.04 (–0.31 to 0.23) | |
| VIS | –0.18 (–0.22 to –0.13)b | –0.18 (–0.23 to –0.13) |
| Cumulative fluid overload | 0.01 (–0.01 to 0.03) | |
| Probe location | ||
| Chest | Reference | |
| Abdomen | 0.81 (–0.55 to 2.2) | |
| Back | 1.15 (–0.69 to 2.98) | |
| Thigh | 1.1 (–0.02 to 2.2) | |
| Other | 0.05 (–91 to 1) | |
| Respiratory support | ||
| Conventional mechanical ventilation | Reference | |
| High-frequency oscillatory or percussive ventilation | –0.57 (–1.5 to 0.37) | |
| Noninvasive ventilation | –0.70 (–2.6 to 1.2) |
Paco2 = partial pressure of carbon dioxide, Tcco2 = transcutaneous carbon dioxide, VIS = Vasoactive-Infusion Score.
Tcco2 coefficient varies across bivariable analyses. The Tcco2 coefficient in univariate mixed-effect analysis was 0.78 (95% CI, 0.76–0.80), implying that Tcco2 is highly correlated with Paco2 but tends to overestimate it.
A coefficient’s 95% CI that does not cross zero is considered statistically significant.
The intercept for the multivariable mixed-effect model was 8.5 (7.1–10). As an example, a 24-mo-old Black/African American child on vasoactive support with a VIS of 20 and a Tcco2 of 55 mm Hg would be expected to have a Paco2 of: 8.5 + 55 × 0.79 + 24 × 0.02 + 1 × –1.9 + 20 × –0.18 = 47 mm Hg.