Perioperative adherence to continuous positive airway pressure and its effect on postoperative nocturnal hypoxemia in obstructive sleep apnea patients: a prospective cohort study

Table 2 Linear regression for perioperative overnight oximetry using a linear fixed effects model

Variable	Parameter estimate	SEM	T-statistic	P-value
Mean SpO₂
Intercept	92.98	1.6	58.17	< 0.0001
CPAP Adherence	0.54	0.78	0.69	0.49
N1 vs. Pre-op	1.13	0.495	2.27	0.025
N2 vs. Pre-op	1.12	0.56	3.01	0.076
O₂ therapy	1.69	0.561	3.01	0.003
Minimum SpO₂
Intercept	84.45	9.6	8.8	< 0.0001
CPAP Adherence	2.15	4.7	0.46	0.65
N1 vs. Pre-op	−2.04	2.98	−0.69	0.49
N2 vs. Pre-op	−7.45	3.76	−1.98	0.0497
O₂ therapy	−6.17	3.37	−1.83	0.070
ODI
Intercept	18.75	6.63	2.83	0.0055
CPAP Adherence	−11.8	3.55	−3.33	0.0011
N1 vs. Pre-op	−7.96	2.32	−3.44	0.0008
N2 vs. Pre-op	−4.51	3.49	−1.29	0.19
CPAP adherence × N1	9.14	2.81	3.25	0.0015
CPAP adherence × N2	4.4	2.88	1.53	0.13
O₂ therapy	−0.78	2.56	−0.3	0.76
CT90
Intercept	2.95	13.53	0.22	0.83
CPAP Adherence	−0.35	6.62	−0.05	0.96
N1 vs. Pre-op	0.22	4.22	0.05	0.96
N2 vs. Pre-op	0.083	5.3	0.02	0.99
O₂ therapy	−4.53	4.75	−0.95	0.34

Statistical analysis using linear fixed effects model where the time-varying covariate CPAP adherence only utilizes within-subject variation. By definition the time invariant covariates are assumed stable over time, and thus are removed from consideration. Abbreviations: CPAP continuous positive airway pressure, ODI oxygen desaturation index, CT90 cumulative time percentage with SpO2 < 90%, N1 postoperative night 1, N2 postoperative night 2, SEM standard error of the mean.

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