The Modified Bohr Equation

Hosts:Pradip Kamat, Children’s Healthcare of Atlanta/Emory University School of MedicineRahul Damania, Cleveland Clinic Children’s HospitalCase Introduction:6-year-old patient admitted to PICU with severe pneumonia complicated by pediatric Acute Respiratory Distress Syndrome (pARDS).Presented with respiratory distress, hypoxemia, and significant respiratory acidosis.Required intubation and mechanical ventilation.Despite initial interventions, condition remained precarious with persistent hypercapnia.Physiology Concept: Dead SpaceDefined as the volume of air that does not participate in gas exchange.Consists of anatomic dead space (large airways) and physiologic dead space (alveoli).Physiologic dead space reflects ventilation-perfusion mismatch.Pathological Dead Space:Occurs due to conditions disrupting pulmonary blood flow or ventilation.Common in conditions like pulmonary embolism, severe pneumonia, or ARDS.Clinical Implications:Increased dead space fraction (DSF) in PARDS is a prognostic factor linked to severity and mortality.Elevated DSF indicates worse lung injury and inefficient gas exchange.DSF can be calculated using the formula: DSF = (PaCO2 – PetCO2) / PaCO2.Practical Management:Optimize Mechanical VentilationEnhance PerfusionConsider Positioning (e.g., prone positioning)Summary of Physiology Concepts:Bohr equation for physiologic dead space.Importance of lung-protective ventilation strategies.Monitoring and trending dead space fraction.Strategies to improve airway patency and mucociliary clearance.Connect with us!PICU Doc on Call provides concise explanations of critical concepts in pediatric intensive care.Feedback, subscriptions, and reviews are encouraged.Visit picudoconcall.org for episodes and Doc on Call infographics.Hosted by Dr. Pradip Kamat and Dr. Rahul Damania.Reference:Yehya N, Bhalla AK, Thomas NJ, Khemani RG. Alveolar Dead Space Fraction Discriminates Mortality in Pediatric Acute Respiratory Distress Syndrome. Pediatr Crit Care Med. 2016 Feb;17(2):101-9. doi: 10.1097/PCC.0000000000000613. PMID: 26669646; PMCID: PMC4740261.