Incidence of hypo- and hypercarbia in severe traumatic brain injury before and after 2003 pediatric guidelines

Objective: To examine the incidence of severe hypocarbia (PaCO2 < 30 mm Hg) in patients with severe pediatric traumatic brain injury before and after publication of the 2003 pediatric guidelines (PG). Design: Retrospective cohort analysis. Setting. Harborview Medical Center, Seattle, Washington (January 1, 1995, to December 31, 2005). Patients: Children < 15 yrs of age with severe pediatric traumatic brain injury. Interventions: None. Measurements and Main Results: The pre-PG group (before August 1, 2003) included 375 patients and the post-PG group included 89 patients. Post PG guidelines, there was a trend toward earlier (45 vs. 32 mins; p =.05) and more frequent (7.1 vs. 8.4 samples; p =.06) PaCO2 sampling within 48 hrs of admission. Children 0-2 yrs had a longer time (75.0 mins) between admission and first PaCO2 sample than older children (44.3 mins; p <.01). The youngest children also had the highest incidence of severe hypocarbia on the first PaCO2 sample (31% vs. 19%; p =.02). Incidence of severe hypocarbia was high and did not decline (60% vs. 52%; p =.2) after the PG guidelines. However, over the 11 yrs, the odds of severe hypocarbia decreased (adjusted odds ratio 0.9; 95% confidence interval 0.84-0.96). During both periods, the incidence of severe hypocarbia was highest during the first 2 hrs after hospital admission. Intracranial pressure monitors were used more frequently post-PG. In 62 of 82 (77%) patients with severe hypocarbia in whom an intracranial pressure monitor was in place, the preceding intracranial pressure was < 20 mm Hg. Severe hypocarbia independently predicted inpatient mortality (adjusted odds ratio 2.8; 95% confidence interval 1.3-5.9). Conclusions: Although PaCO2 sampling was more frequent during the post-PG period and severe hypocarbia decreased during successive study years, the incidence of severe hypocarbia remained high during the first 48 hrs after hospital admission during the post-PG period. Time to PaCO2 sampling was longer in young children and associated with more severe hypocarbia. The presence of severe hypocarbia predicted mortality.