Objective To explore the fluctuation trend of carbon dioxide (CO₂) during sleep in children with moderate and severe obstructive sleep apnea hypopnea syndrome (OSAHS), and to analyze the correlation between CO₂ and polysomnographic (PSG) indexes.Methods Twenty-one children with moderate and severe OSAHS confirmed by PSG and transcutaneous partial pressure of carbon dioxide monitoring (TcpCO₂) (OSAHS group) and 25 healthy children (control group) were selected. The general situation, respiratory events and TcpCO₂ trend during sleep were compared between the two groups. The correlations between variables of TcpCO₂ and PSG were analyzed.Results There were no significant differences in gender and age between the OSAHS group and the control group. The body mass index (BMI)[(27.9±6.8) kg/m² vs (16.8±2.9) kg/m²], apnea hyponea index (AHI)[(21.6±17.2) times/h vs (1.3±1.0) times/h], obstructive apnea index (OAI) (1.1times/h vs 0.0 time/h), obstructive apnea hyponea index (OAHI) (19.2 times/h vs 0.2 times/h), oxygen desaturation index (ODI)[(19.5±16.9) times/h vs (1.1±1.0) times/h], the average and highest values of TcpCO₂[(46.8±3.8) mmHg vs (44.7±2.5) mmHg、(54.8±5.3) mmHg vs (48.9±3.3) mmHg], TcpCO₂ in non-rapid eye movement (NREM)[(47.0±3.8) mmHg vs (45.1±2.4) mmHg] and TcpCO₂ in rapid eye movement (REM)[(48.0±5.2) mmHg vs (44.4±2.8) mmHg] stage of OSAHS children were higher than those of the control group. The averages of oxygen saturation (SaO₂)[(96.5±1.2)% vs (97.6±0.9)%] and lowest SaO₂[(82.6±8.7)% vs (92.2±2.9)%] in OSAHS children were lower than those in the control group. The differences in BMI, AHI, OAI, OAHI, ODI, average and lowest SaO₂, average and highest TcpCO₂, NREM TcpCO₂ and REM TcpCO₂ between the two groups were all statistically significant (all P<0.05). There were no correlations among the average and highest TcpCO₂ and the BMI, OAI, ODI.Conclusions TcpCO₂ monitoring can reflect the dynamic changes of CO₂ in the whole night. CO₂ in OSAHS children has a rising trend during sleep, and the level of CO₂ in REM sleep is also higher than that in NREM sleep. CO₂ level can not be judged according to the PSG indexes, but needs to be evaluated by objective inspection.