“hypercapnea in Children with Status Asthmaticus Requiring PICU Care: A Retrospective Cohort Study”

Background: Status asthmaticus (SA) is a condition characterized by severe airway obstruction. As most patients with SA have normal compensatory responses to rising pCO2, hypercarbia has been used as an indication for intubation and mechanical ventilation. However, the risk of complications during invasive mechanical ventilation (IMV) for SA, combined with our successful experience non-invasively managing patients with a significant degree of hypercarbia necessitates exploration of the phenomenon.

Methods: We conducted this exploratory, hypothesis-generating, retrospective cohort study using the database of the PICU at IWK Health, Halifax NS to identify all patients aged 2 to 16 years admitted with a primary diagnosis of status asthmaticus from 2000 to 2019, who had no history of chronic CO2 retention (baseline bicarbonate >30mmol/L). Hypercapnea was defined as a corrected peak CO2 prior to invasive mechanical ventilation (IMV) greater than 45mmHg (corrected = arterial CO2, capillary CO2, venous CO2-5mmHg). Baseline and outcome data were abstracted from medical charts.

Results: Of 7624 patients admitted during the study period, 200 patients met inclusion criteria, with 1 exclusion. There were 44 patients in the HC group (median [interquartile range{IQR}] peak pCO2 (50 [47-62] mmHg ) and 155 patients in the NC group (median [IQR] peak pCO2 36 [33-39] mmHg). The two groups also differed significantly in the median (IQR) pCO2 at presentation (49 [41-56] mmHg versus 35 [32-38] mmHg respectively). The groups were similar for other baseline characteristics including age, previous asthma diagnosis, previous PICU admission, origin prior to PICU, presence of barotrauma (pre-intubation), and medications received within the first 24 hours (hydrocortisone equivalents, aminophylline, MgSO4). Five (11%) in the HC group and 1 (0.6%) of the normocapneic group received IMV (p=0.003). Non-invasive ventilation (NIV) was used in 13 (30%) HC and 42 (27%) NC patients (p=0.80). Among the HC group, baseline characteristics including peak CO2 were similar for those who required mechanical ventilation (invasive or non) and those who did not. Of the seven who developed superhypercapnea (peak corrected CO2 > 60mmHg, pH <7.25), five did not receive IMV.

Conclusion: IMV was more frequently used in the HC group. Beyond clinical exam, which was not captured in this study, baseline characteristics do not appear to be associated with hypercapnea. Hypercapnea and superhypercapnea do not necessarily imply a need for intubation and mechanical ventilation.