Reliability of Capnometry in Neonates on Patient Triggered Ventilation
Dr.Tushar B. Parikh (DNB),(DM)(Neonatology)Consultant & Incharge NICU,Oyster and Pearl Hospital, Pune
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Introduction: Capnometry is not well studied in neonates on Patient Triggered Ventilation (PTV). We conducted this study to determine the reliability of Main Stream (MS) and Side Stream (SS) Capnometry in neonates on PTV.
Method: Neonates on PTV were enrolled in the study. Before each Arterial Blood Gas (ABG) assessment, MS and SS capnometer readings were recorded. Lung mechanics were recorded from the online graphics. ABG was collected from the arterial line. The EtCO2 â€“ PaCO2 correlation was drawn for MS and SS capnometry under various disease conditions, ventilator settings and lung mechanics.
Results: A total of 74 ABGs were collected from 18 patients. The EtCO2 â€“ PaCO2 correlation was better with MS capnometry than with SS capnometry (r = 0.855 vs.0.68, p < 0.001 for both methods). Both methods correlated well with PaCO2 in Flow cycled SIMV (MS: r = 0.9 & SS: r = 0.82). However, in Flow Cycled Assist Control mode, SS capnometry correlated poorly (SS: r = 0.49 vs. MS: r = 0.76). The EtCO2 - PaCO2 correlation by MS capnometry holds good for RDS, Apnea, Pneumonia and Congenital cyanotic heart disease (r = 0.85, 0.97, 0.84, 0.84 respectively, p < 0.001), but not for PPHN(r = 0.37, p = 0.35). SS EtCO2 correlated well in RDS, Apnea, Pneumonia, (r = 0.75, 0.85, 0.94 respectively, p < 0.001), but not in PPHN (- 0.20, p = 0.629) and CCHD (r = 0.73, p = 0.1). At higher ventilator rates (> 60 /min), SS capnometry correlated poorly. The EtCO2 â€“PaCO2 correlation by both methods was better when lung compliance was > 1 ml / cmH2O than when lung compliance was < 1 ml / cmH2O.
Conclusions: MS capnometry is superior to SS capnometry for neonates on patient triggered ventilation.