Background: Influenza may impair respiratory exchange in the case of lower respiratory tract infections (LRTIs). Capillary blood gas (CBG) reflects arterial blood values but is a less invasive method than arterial blood sampling. We aimed to retrospectively verify the usefulness of CBG in pediatric influenza. Material and methods: CBG parameters (pH, pCO2, pO2, SatO2) in laboratory confirmed influenza cases hospitalized in 2013−2020 were verified in terms of LRTI, chest X-ray (CXR) performance, radiologically confirmed pneumonia (CXR + Pneumonia), prolonged hospitalization, and intensive care transfer. A theoretical CBG-based model for CXR performance was created and the odds ratios were compared to the factual CXR performance. Results: Among 409 children (aged 13 days−17 years 3/12, median 31 months), the usefulness of CBG decreased with the age. The SatO2 predicted the LRTI with AUC = 0.74 (95%CI: 0.62−0.86), AUC = 0.71 (0.61−0.82), and AUC = 0.602 (0.502−0.702) in children aged <6 months old (mo), 6−23 mo, 24−59 mo, respectively, while pO2 revealed AUC = 0.73 (0.6−0.85), AUC = 0.67 (0.56−0.78), and AUC = 0.601 (0.501−0.702), respectively. The pCO2 predicted the LRTI most precisely in children <6 months with AUC = 0.75 (0.63−0.87), yet not in older children. A high negative predictive value for CXR + Pneumonia was seen for SatO2 < 6 mo (96.7%), SatO2 6−23 mo (89.6%), pO2 < 6 mo (94.3%), pO2 6−23 mo (88.9%). The use of a CBG-driven CXR protocol (based on SatO2 and pO2) would decrease the odds of an unnecessary CXR in children <2 years old (yo) by 84.15% (74.5−90.14%) and 86.15% (66.46−94.28%), respectively. SatO2 and pO2 also predicted a prolonged hospitalization <6 mo AUC = 0.71 (0.59−0.83) and AUC = 0.73 (0.61−0.84), respectively, and in 6−23 mo AUC = 0.66 (0.54−0.78) and AUC = 0.63 (0.52−0.75), respectively. Conclusions: The CBG is useful mainly in children under two years, predicts the risk of LRTI, and can help exclude the risk of CXR + pneumonia. Children under six months of age represent the group that would benefit the most from CBG. A CBG-based protocol for the performance of CXR could significantly decrease the number of unnecessary CXRs.
Keywords: acidosis; capillary blood gas; children; hypercapnia; influenza; pneumonia.