Table 1.
Intraoperative medications in the Procedural Sedation and General Anaesthesia cohorts.
Table 2.
Subject cohort anthropometrics and comorbidities.
Table 3.
Subject cohort respiratory metrics.
Fig 1.
Representative correlations between MV and EtCO2.
Data from three individual patients are included, one from each group: Procedural Sedation (red), General Anesthesia (blue) and Awake Volunteer (green). Each data point corresponds to a single 30 sec measurement pair (MV and EtCO2). The lines (Deming regressions) and confidence ellipses (±1 SD) show the best-fits to the data. In a representative patient from the General Anesthesia cohort, a 1 L/min increase in MV resulted in a 13.2 mmHg decrease in EtCO2 (EtCO2 instrument sensitivity (i.e., slope) = 13.2 mmHg/L/min = θGA = -85.7°). In a patient from the Awake Volunteers group, across a range of breathing patterns, a 1 L/min increase in MV resulted in a 0.27 mmHg decrease in EtCO2 (EtCO2 instrument sensitivity = 0.27 mmHg/L/min = θAV = -14.9°). The patient from the Procedural Sedation group falls between the patients from General Anesthesia and Awake Volunteers groups. Specifically, a 1 L/min increase in MV led to 2.0 mmHg decrease in EtCO2 (EtCO2 instrument sensitivity = 2.0 mmHg/L/min, corresponding with θPS = -63.5°).
Fig 2.
Distributions of EtCO2 instrument sensitivity to changes in MV.
For each patient group (General Anesthesia (top, blue), Procedural Sedation (middle, red), and Awake Volunteers (bottom, green)), the distribution of EtCO2 instrument sensitivity is presented as both a box-plot and histogram. Each box-plot shows the median EtCO2 instrument sensitivity (middle vertical line), the box extends from the 25th to 75th percentile, the whiskers extend to the most extreme non-outlier data points, and statistical outliers are plotted individually (plus signs). The median EtCO2 instrument sensitivities were -85.1°, -38.1°, and -20.2° for the General Anesthesia, Procedural Sedation, and Awake Vounteer cohorts, respectively. The General Anesthesia and Awake Volunteer cohorts had unimodal distributions of EtCO2 instrument sensitivity and single normal distributions were fit to these data (black lines). EtCO2 instrument sensitivities were significantly higher in the intubated patients under General Anesthesia (θ = -83.6 ± 9.9°, vertical dashed blue line) compared to non-intubated Awake Volunteers over a range of prescribed breathing patterns (θ = -24.7 ± 19.7°, vertical dashed green line, p < 0.0001). The distribution of EtCO2 instrument sensitivity for the Procedural Sedation cohort was bimodal. Therefore, a mixture of two normal distributions was therefore fit to these data. Approximately half of the patients experienced high EtCO2 instrument sensitivity (θ = -96.6 ± 15.0°), consistent with the General Anesthesia patients, while the remaining patients had low instrument sensitivity (θ = -1.2 ± 22.4°), consistent with the awake volunteers. Clinically-relevant EtCO2 is indicated by the shaded gray area. The majority of General Anesthesia patients (43/54, 80%) had clinically-relevant EtCO2 instrument sensitivity. In contrast, less than half of Procedural Sedation patients (24/58, 41%) and no patients in the Awake Volunteer cohort demonstrated clinically-relevant EtCO2 instrument sensitivity of -76°.
Fig 3.
Distributions of average EtCO2 measurements.
For each patient group (General Anesthesia (top, blue), Procedural Sedation (middle, red), and Awake Volunteers (bottom, green)), the distribution of average EtCO2 is presented as both a histogram and box-plot. Each box-plot shows the median EtCO2 instrument sensitivity (middle vertical line), the box extends from the 25th to 75th percentile, the whiskers extend to the most extreme non-outlier data points, and statistical outliers are plotted individually (plus signs). EtCO2 values for all three groups were unimodal and a single normal distribution was fit to each group (black lines). The average EtCO2 in the General Anesthesia cohort (37.2 ± 4.3 mmHg) was significantly higher than in the Awake Volunteers (31.4 ± 5.2 mmHg) which in turn was higher than the Procedural Sedation groups (23.3 ± 4.8 mmHg) (p < 0.0001). The normal range of EtCO2 (35–45 mmHg) is indicated by the shaded yellow area. The majority of General Anesthesia patients (37/54, 69%) had an average EtCO2 measurement within this normal range. In contrast, only 27% (13/48) of Awake Volunteers across the range of prescribed respiratory patterns and 5% (3/58) of Procedural Sedation patients had an average EtCO2 measurement within the normal range.