Affiliations: Ostschweizer Kinderspital,
St. Gallen, Switzerland ,
Vanderbilt University School of Medicine,
Correspondence to: Bernhard Frey, MD, Intensivpflegestation, Ostschweizer Kinderspital, CH-9006 St. Gallen, Switzerland; e-mail: firstname.lastname@example.org
To the Editor:
We read with interest the study of Hartert et al (February
1999)1on the use of pulse oximetry for assessing pulsus
paradoxus. We performed a very similar study in children,2
notably with the same brand of pulse oximeter, and gained the same
results: there is a close association between pulsus paradoxus (in our
study, measured by intra-arterial pressure monitoring) and the
fluctuations of the plethysmographic respiratory wave (r = 0.85; 95%
confidence interval, 0.76 to 0.91). Hartert et al1 made an
important contribution toward the routine application of pulse
oximetry by working out the technical basis of the phenomenon.
Obviously, this phenomenon is not restricted to a single device. The
authors documented their observations in four different monitoring
systems. After calibration of the device, which entails a specific
association between the number of millimeters of change in the
plethysmographic baseline and the number of millimeters of Hg recording
pulsus paradoxus, electronic analysis of the plethysmographic
fluctuations can show a continuous measurement of pulsus
About half of the patients studied by Hartert et al1 were
receiving mechanical ventilation. The authors did not mention that in
patients receiving positive-pressure ventilation the lowest BP values
are recorded during expiration (reversed pulsus paradoxus), whereas in
spontaneous breathing they are recorded during inspiration. The
correlation between pulsus paradoxus and pulse oximetry in tracing
fluctuations might not be influenced by the state of respiration
(spontaneous or mechanical ventilation). However, (reversed) pulsus
paradoxus might not be a good parameter of disease severity in patients
receiving mechanical ventilation, as the magnitude of pulsus paradoxus
depends at least partly on the applied ventilator
I thank Dr. Frey for his thoughts and comments in regard to our
study of the use of pulse oximetry in assessing pulsus paradoxus
(February 1999).1The confirmation of our study by his
series2 in children is important in validating pulse
oximetry as a useful tool in individuals who are critically ill. In
regard to our utilization of the respiratory waveform variation in
persons receiving mechanical ventilation, I concur that there are
limitations. However, I feel that this finding is useful even in those
patients receiving mechanical ventilation as it suggests that either
the applied ventilator pressures or the work of breathing are such that
they impact the inspiratory fall in systolic BP.
I apologize for not having referenced the work of Frey and
Butt2 in our manuscript, and thanks to Dr. Frey once again
for his thoughtful comments.
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