Sequence analysis of capnography waveform abnormalities during nurse-administered procedural sedation and analgesia...

Identifying common patterns in capnography waveform abnormalities and the factors that influence these patterns could yield insights to optimize responses to sedation-induced respiratory depression. Respiratory state sequences for 102 patients who had a procedure in a cardiac catheterisation laboratory with procedural sedation and analgesia were developed by classifying each second of procedures into a state of normal breathing or other capnography waveform abnormalities based on pre-specified cut-offs for respiratory rate and end-tidal CO₂ concentration. Hierarchical clustering identified four common patterns in respiratory state sequences, which were characterized by a predominance of the state assigned normal breathing (n = 42; 41%), hypopneic hypoventilation (n = 38; 38%), apnea (n = 15; 15%) and bradypneic hypoventilation (n = 7; 7%). A multivariable distance matrix regression model including demographic and clinical variables explained 28% of the variation in inter-individual differences in respiratory state sequences. Obstructive sleep apnea (R² = 2.4%; p = 0.02), smoking status (R² = 2.8%; p = 0.01), Charlson comorbidity index score (R² = 2.5%; p = 0.021), peak transcutaneous carbon dioxide concentration (R² = 4.1%; p = 0.002) and receiving an intervention to support respiration (R² = 5.6%; p = 0.001) were significant covariates but each explained only small amounts of the variation in respiratory state sequences. Oxygen desaturation (SpO₂ < 90%) was rare (n = 3; 3%) and not associated with respiratory state sequence trajectories.