Am. J. Respir. Crit. Care Med., Vol 150, No. 3, 09 1994, 865-869.
Performance of a patient-dedicated, on-demand blood gas monitor in medical ICU patients
CK Mahutte, SA Sasse, PA Chen and M Holody
Department of Medicine, Veterans Affairs Medical Center, Long Beach, California 90822.
We examined the performance characteristics of a new bedside blood gas
monitor. This monitor's fluorescent pH, PCO2, and PO2 sensors are embedded
in a cassette, which is calibrated in vitro and then inserted into the
patient's radial artery tubing set. In 50 medical ICU patients, 683 paired
monitor and conventional blood gas analyzer values were obtained.
Performance was assessed via calculations of bias (mean monitor and
analyzer difference) and its standard deviation (SD), plots of monitor and
analyzer differences against the means (of monitor and analyzer), and
linear regression analysis of the sequential changes in monitor values
versus the corresponding sequential changes in analyzer values. The ex vivo
calibration, assessed using the initial paired blood samples, showed a bias
+/- SD of 0.02 +/- 0.02 for pH, -0.1 +/- 1.9 mm Hg for PCO2, and 4.3 +/-
6.0 mm Hg for PO2. For all paired samples (n = 683), the biases +/- SD were
0.004 +/- 0.023 for pH, 0.6 +/- 2.4 mm Hg for PCO2, and 2.7 +2- 6.4 mm HG
for PO2. The PO2 bias increased as PO2 increased. The standard deviations
(imprecision) of both PCO2 and PO2 also increased as the magnitudes of
these variables increased. Sequential changes in monitor values versus the
corresponding sequential changes in analyzer values revealed regression
lines close to the line of identity. Serum sodium had no effect on pH bias.
Daily drift of the sensors was inconsequential, with values of - 0.01/d for
pH, 1.7 mm Hg/d for PCO2, and 1.1 mm Hg/d for PO2. We conclude that the
performance of this monitor is comparable to that of conventional blood gas
analyzers.
