Definitions
The first qualifying arterial blood gas for the diagnosis of PARDS was
used for the AVDSf calculation and was considered the onset of PARDS for
purposes of this study. AVDSf was calculated using the Enghoff
modification of the Bohr formula: AVDSf = (PaCO2 -
PetCO2) / PaCO2. Echocardiograms were
analyzed as previously described (Himebauch 2018). Echocardiographic
measures of RV systolic function included: qualitative assessment
(normal or mildly, moderately, or severely diminished), fractional area
change (FAC), tricuspid annular plan systolic excursion (TAPSE), RV peak
systolic global longitudinal strain (RV GLS), and RV peak systolic
strain (also known as free wall strain). Abnormal FAC was defined as
less than 35%. Abnormal TAPSE was defined as a value less than -2
standard deviations below published pediatric normal values for
age14 and calculated through an online calculator
(parameterz.blogspot.com). Abnormal RV GLS and strain were defined as
values greater than -18% and greater than -21%, respectively, as less
negative values reflect worse function. As pulmonary arterial catheters
are rarely used in clinical practice, echocardiographic surrogates of
pulmonary hypertension were defined as flattening or bowing of the
septal position in systole in the parasternal short-axis view, tricuspid
regurgitant velocity > 2.8 m/s2, or RV
systolic pressure estimate greater than ½ systemic systolic pressure at
the time of echocardiogram.