The use of capnometry to predict arterial partial pressure of CO(2) in non-intubated breathless patients in the emergency department

Bias between capnometry and venous carbon dioxide during initial assessment of pediatric emergency department patients: A video-based study

Objective

The bias of capnometry (ETCO2) and venous carbon dioxide (vpCO2) among pediatric emergency department (PED) patients triaged to critical care areas is unknown. We aimed to explore correlations and bias between ETCO2 and vpCO2¸and identify predictors of bias.

Methods

This was an observational, video-based, retrospective study comparing ETCO2 and vpCO2. Pediatric patients with simultaneous ETCO2 and vpCO2 data were included. Our primary aim utilized linear regressions to determine correlations and Bland-Altman analysis to assess bias. Our secondary aim utilized multiple regression to identify clinical covariates contributing to bias. Covariates included age, respiratory rate, heart rate, mean arterial blood pressure, capnometry interface, PED diagnosis, and PED disposition.

Results

A total of 200 PED patients with ETCO2 and vpCO2 data were included. The median (interquartile range [IQR]) ETCO2, vpCO2, and ΔCO2 in mmHg were 38 (32, 46), 49 (41, 61), and 11 (4, 20), respectively. ETCO2 (r = 0.76) and ΔCO2 (r = 0.71) were highly correlated with vpCO2. The mean bias between ETCO2 and vpCO2 was -14.1 mmHg (95% confidence interval [CI], -41.9 -13.7). The bias between ETCO2 and vpCO2 increased at higher values of each measure. ETCO2 sampling interface was the only independent predictor of vpCO2 in our multivariate analysis. Patients requiring bag-valve mask (BVM) ventilation had the highest median bias between ETCO2 and vpCO2 (29 mmHg, IQR 15, 37).

Conclusion

ETCO2 and vpCO2 were highly correlated. However, bias increased at higher levels of both ETCO2 and vpCO2. Among PED patients, ETCO2's ability to approximate vpCO2 diminishes with worsening hypercarbic respiratory failure.

Effects of Prone Position and Positive End-Expiratory Pressure on Noninvasive Estimators of ICP: A Pilot Study

BACKGROUND

Prone positioning and positive end-expiratory pressure can improve pulmonary gas exchange and respiratory mechanics. However, they may be associated with the development of intracranial hypertension. Intracranial pressure (ICP) can be noninvasively estimated from the sonographic measurement of the optic nerve sheath diameter (ONSD) and from the transcranial Doppler analysis of the pulsatility (ICPPI) and the diastolic component (ICPFVd) of the velocity waveform.

METHODS

The effect of the prone positioning and positive end-expiratory pressure on ONSD, ICPFVd, and ICPPI was assessed in a prospective study of 30 patients undergoing spine surgery. One-way repeated measures analysis of variance, fixed-effect multivariate regression models, and receiver operating characteristic analyses were used to analyze numerical data.

RESULTS

The mean values of ONSD, ICPFVd, and ICPPI significantly increased after change from supine to prone position. Receiver operating characteristic analyses demonstrated that, among the noninvasive methods, the mean ONSD measure had the greatest area under the curve signifying it is the most effective in distinguishing a hypothetical change in ICP between supine and prone positioning (0.86±0.034 [0.79 to 0.92]). A cutoff of 0.43 cm was found to be a best separator of ONSD value between supine and prone with a specificity of 75.0 and a sensitivity of 86.7.

CONCLUSIONS

Noninvasive ICP estimation may be useful in patients at risk of developing intracranial hypertension who require prone positioning.

Correlation Between Partial Pressure of Arterial Carbon Dioxide and End Tidal Carbon Dioxide in Patients with Severe Alcohol Withdrawal

BACKGROUND

Respiratory depression is a common adverse effect of benzodiazepine administration to patients with severe alcoholic withdrawal. This study was conducted to assess the value of end tidal carbon dioxide (ETCO2) levels compared to partial pressure of arterial carbon dioxide (PaCO2) levels in monitoring respiratory depression secondary to benzodiazepine treatment in patients with severe alcohol withdrawal.

METHODS

We retrospectively analyzed 36 patients admitted to the intensive care unit for severe alcohol withdrawal who had been administered sedative agents.

RESULTS

We observed a statistically significant correlation between PaCO2 and ETCO2 at time 1 (r=0.74, P<0.01) and time 3 (r=0.52, P=0.02) but not at time 2 (r=0.22, P=0.31).

CONCLUSION

Our study confirms a positive correlation between PaCO2 and ETCO2 levels in patients experiencing severe alcohol withdrawal.

Accuracy of end-tidal CO2 measurement through the nose and pharynx in nonintubated patients during digital subtraction cerebral angiography

OBJECTIVE

To determine the accuracy of end-tidal CO2 (PETCO2) obtained in the nose through the Smart CapnoLine and in the pharynx through the modified Filterline H Set with supplemental oxygen at 5 L/min in nonintubated patients undergoing digital subtraction cerebral angiography (DSA).

TYPE OF STUDY

Prospective, observational.

PATIENTS

Twenty patients with disturbance of consciousness because of brain disease, who will receive DSA.

METHODS

PETCO2 was measured in the nose through the Smart CapnoLine and in the pharynx using the modified Filterline H Set that was inserted through the nasopharyngeal airway. Oxygen was administered through the Smart CapnoLine at a rate of 5 L/min. Five minutes after a constant and normally shaped capnography waveform, arterial blood was drawn from an indwelling femoral catheter for analyzing arterial CO2 partial pressure (PaCO2), and PETCO2 that was measured through the nose and the pharynx were simultaneously recorded. After the DSA procedure, PaCO2 was analyzed again. Data were analyzed with Pearson correlation and Bland-Altman analysis.

RESULTS

PETCO2 sampled from both the nose and the pharynx was significantly correlated with PaCO2, and the correlation coefficients had approximate values, 0.832 (P<0.0001) for PaCO2 with PETCO2 through the nose and 0.836 (P<0.0001) for PaCO2 with PETCO2 through the pharynx. The mean bias±SD for PETCO2 and PaCO2 was 4.53±2.76 mm Hg (nose) and 3.22±2.86 mm Hg (pharynx). The 95% level of agreement for PETCO2 and PaCO2 ranged from -0.90 to 9.95 mm Hg (nose) and from -2.39 to 8.82 mm Hg (pharynx). End-tidal CO2 measurements through the nose and the pharynx had comparable performance. The correlation of PETCO2 measured through the nose and the pharynx was 0.971 (P<0.001). The difference between PETCO2 measured through the nose and the pharynx was 1.31±1.25 mm Hg, and t test results showed that arterial to end-tidal CO2 pressure difference (Pa-ETCO2) in sampling through the nose was significantly greater than Pa-ETCO2 sampling through the pharynx (P<0.05).

CONCLUSIONS

In a clinical setting, end-tidal CO2 measurements sampled from the nose and the pharynx were accurate and reliable in nonintubated patients with a nasopharynx airway in place during DSA.