Adult and pediatric studies provide conflicting data regarding whether post-cardiac arrest hypoxemia, hyperoxemia, hypercapnia, and/or hypocapnia are associated with worse outcomes. We sought to determine whether postarrest hypoxemia or postarrest hyperoxemia is associated with lower rates of survival to hospital discharge, compared with postarrest normoxemia, and whether postarrest hypocapnia or hypercapnia is associated with lower rates of survival, compared with postarrest normocapnia. An embedded prospective observational study during a multicenter interventional cardiopulmonary resuscitation trial was conducted from 2016 to 2021. Patients ⩽18 years old and with a corrected gestational age of ≥37 weeks who received chest compressions for cardiac arrest in one of the 18 intensive care units were included. Exposures during the first 24 hours postarrest were hypoxemia, hyperoxemia, or normoxemia-defined as lowest arterial oxygen tension/pressure (Pa ) <60 mm Hg, highest Pa ⩾200 mm Hg, or every Pa 60-199 mm Hg, respectively-and hypocapnia, hypercapnia, or normocapnia, defined as lowest arterial carbon dioxide tension/pressure (Pa ) <30 mm Hg, highest Pa ⩾50 mm Hg, or every Pa 30-49 mm Hg, respectively. Associations of oxygenation and carbon dioxide group with survival to hospital discharge were assessed using Poisson regression with robust error estimates. The hypoxemia group was less likely to survive to hospital discharge, compared with the normoxemia group (adjusted relative risk aRR = 0.71; 95% confidence interval CI =  0.58-0.87), whereas survival in the hyperoxemia group did not differ from that in the normoxemia group (aRR = 1.0; 95% CI = 0.87-1.15). The hypercapnia group was less likely to survive to hospital discharge, compared with the normocapnia group (aRR = 0.74; 95% CI = 0.64-0.84), whereas survival in the hypocapnia group did not differ from that in the normocapnia group (aRR = 0.91; 95% CI = 0.74-1.12). Postarrest hypoxemia and hypercapnia were each associated with lower rates of survival to hospital discharge.