Study objectives: The purpose of this cross-sectional
study was to confirm the observation that pulse oximetry tracing
correlates with pulsus paradoxus, and is therefore a measure of the
severity of air trapping in obstructive airway disease.
Design: Cross-sectional survey.
The ICU in a tertiary care academic hospital.
Patients: Twenty-six patients consecutively admitted to the
ICU with obstructive airway disease, either asthma or COPD.
Measurements and results: Forty-six percent of the study
patients required mechanical ventilation, and 69% had an elevated
pulsus paradoxus. We defined the altered pulse oximetry baseline
tracing as the respiratory waveform variation (RWV). The RWV was
measured in numerical form as the change in millimeters from the
baseline. Pulsus paradoxus was significantly correlated with the RWV of
the pulse oximetry tracing (p < 0.0001). An analysis of the
respiratory variations in the pulse oximetry waveforms in obstructive
lung disease patients reflects the presence and degree of auto-positive
end-expiratory pressure (auto-PEEP; p < 0.0001).
Conclusions: We describe the characteristic alterations in
the pulse oximetry tracings that occur in the presence of pulsus
paradoxus and auto-PEEP. Since pulse oximetry is available universally
in ICUs and emergency departments, it may be a useful noninvasive means
of continually assessing pulsus paradoxus and air trapping severity in
obstructive airway disease patients.
Abbreviations: AC = alternating current;
auto-PEEP = auto-positive end-expiratory pressure; DC = direct
current; RWV = respiratory waveform variation; VMICU = Vanderbilt
Medical Intensive Care Unit; WOB = work of breathing