Figure 5 shows simultaneous recordings of TcPco2 and PaC02 in all six patients, while initiating or interrupting NPPV. TcPco2 followed the same trend as PaC02, with a few minutes of delay, as expected. In all six patients, the first changes in TcPco2 were observed during the first 60 s following the ventilatory event. In four patients, a new steady state for PaC02 was reached after starting or interrupting NPPV, and lasted for up to 20 min. We computed an exponential fit for PaC02 and TcPco2 values, and calculated the t90% for each curve. The difference between t90% for PaC02 and TcPco2 indicates the lag time of the latter over the former. This lag time averaged 5±3 min (range, 1 to 9 min). In two patients (cases 4 and 6), PaC02 did not become sufficiently stable after the start of NPPV and this precluded computation of an exponential fit with calculation of the lag time. However, it can be estimated from the graph on Figure 5 that the response time of TcPco2 in case 6 did not lag over PaC02 by more than a few minutes. In case 4, there was an initial drop in TcPco2 without concomitant change in PaC02, for the first 5 min; then both graphs followed a similar trend.
We have shown that TcPco2 values, measured with the capnograph (Fastrac), showed a good agreement with simultaneous arterial measurements of PaC02, without significant drift after 4 h of continuous recording. buy zyrtec online
A review of published studies, as summarized in Table 1, shows conflicting results regarding agreement between TcPco2 and PaC02. Five studies, however, gave excellent correlation, two of them indicating Pearson’s coefficient of correlation (r) equal to 0.97, and three others reporting bias values2 of 1.5 mm Hg with SDs2 of 3.5 mm Hg. Thus, the results that we obtained in the present study are among the best reported so far, and they seem appropriate for clinical application.
Table 1—Correlation Between TcPco2 and PaC02, Bias, and Limits of Agreement for Different Capnographs According to Available Published Data
|No. of||d,||s,||Limits of Agreement1 l|
|First Author||Patients||r||mm Hg||mm Hg||d-2 s||d+2 s||Capnograph|
|Lanigan||12||0.52||0.0||7.9||-15.7||15.7||Novametrix 850 Commonsensor|
|Hoffmann||9||0.84||NA||NA||NA||NA||Radiometer TINA TCM-3|
|Kesten||20||0.90||NA||NA||NA||NA||Radiometer TINA TCM-3|
|Lanigan||12||0.91||-0.5||2.8||–6.2||5.2||Kontron, Microgas Combisensor|
|Reid||22||0.92||NA||NA||NA||NA||Sensormedics TM TcCOa monitor|
|Palmisano||251||0.93||1.3||3.9||—6.5||9.1||Radiometer TINA TCM-3|
|Mahutte||47||0.93||NA||NA||NA||NA||Sensormedics, Transcutaneous Gas System|
|Pilsbury||28||0.97||NA||NA||NA||NA||Kontron Sensor 51|
|Sridhar||24||NA||0.2||1.0||-1.7||2.2||Radiometer TINA TCM-3|
|Blanchette||30||NA||-0.5||5.2||–11.0||9.9||Sensormedics Transcend Po2—Pco2 monitor|
Figure 5. Time response of TcPco2 after a ventilatory event inducing a change in PaC02. Simultaneous recordings of TcPco2 and PaC02 before and after interrupting NPPV (case 3) or initiating NPPV (cases 1, 2, 4, 5, and 6). Exponential fit curves are shown for cases 1, 2, 3, and 5. Data are expressed in mm Hg.5.2
Blog invites submissions of review articles, reports on clinical techniques, case reports, conference summaries, and articles of opinion pertinent to the control of pain and anxiety in dentistry.