Assessing PaCO2 in acute respiratory disease: accuracy of a transcutaneous carbon dioxide device

Transcutaneous carbon dioxide measurements in fruits, vegetables and humans: A prospective observational study

BACKGROUND

Transcutaneous carbon dioxide measurement (TcCO2) is frequently used as a surrogate for arterial blood gas sampling in adults and children with critical illness. Data from noninvasive TcCO2 monitoring assists with clinical decisions regarding mechanical ventilation settings, estimation of metabolic consumption and determination of adequate end-organ tissue perfusion.

OBJECTIVES

To report TcCO2 values obtained from various fruits, vegetables and elite critical care medicine specialists.

DESIGN

Prospective, observational, nonblinded cohort study.

SETTINGS

Single-centre, tertiary paediatric referral centre and organic farmers' market.

PARTICIPANTS

Vegetables and fruits included 10 samples of each of the following: red delicious apple (Malus domestica), manzano banana (Musa sapientum), key lime (Citrus aurantiifolia), miniature sweet bell pepper (Capsicum annuum), sweet potato (Ipomoea batatas) and avocado (Persea americana). Ten human controls were studied including a paediatric intensivist, a paediatric inpatient hospital physician, four paediatric resident physicians and four paediatric critical care nurses.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

TcCO2 values for each species and device response times.

RESULTS

TcCO2 readings were measurable in all study species except the sweet potato. Mean ± SD values of TcCO2 for human controls [4.34 ± 0.37 kPa (32.6 ± 2.8 mmHg)] were greater than apples [3.09 ± 0.19 kPa (23.2 ± 1.4 mmHg), P < 0.01], bananas [2.73 ± 0.28 kPa (20.5 ± 2.1 mmHg), P < 0.01] and limes [2.76 ± 0.52 kPa (20.7 ± 3.9 mmHg), P < 0.01] but no different to those of avocados [4.29 ± 0.44 kPa (32.2 ± 3.3 mmHg), P = 0.77] and bell peppers [4.19 ± 1.13 kPa (31.4 ± 8.5 mmHg), P = 0.68]. Transcutaneous response times did not differ between research cohorts and human controls.

CONCLUSION

We found nonroot, nontuberous vegetables to have TcCO2 values similar to that of healthy, human controls. Fruits yield TcCO2 readings, but substantially lower than human controls.

Transcutaneous Carbon Dioxide Monitoring During Apnea Testing for Determination of Neurologic Death in Children: A Retrospective Case Series

OBJECTIVES

Determination of neurologic death in children is a clinical diagnosis based on absence of neurologic function with irreversible coma and apnea. Apnea testing during determination of neurologic death assesses spontaneous respiration when PaCO2 increases to greater than or equal to 60 and greater than or equal to 20 mm Hg above pre-apneic baseline. The utility of transcutaneous carbon dioxide measurements during apnea testing in children is unknown. We seek to determine the degree of correlation between paired transcutaneous carbon dioxide and PaCO2 values during apnea testing for determination of neurologic death.

DESIGN

Single-center, retrospective case series.

SETTING

Twenty-eight bed PICU in a 259-bed, tertiary care, referral center.

PATIENTS

Children 0-18 years old undergoing determination of neurologic death between May 2017 and December 2018.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Primary outcomes were paired transcutaneous carbon dioxide and PaCO2 values obtained during determination of neurologic death. Primary analyses included Pearson correlation coefficient, Bland-Altman bias and limits of agreement, and comparative statistics. Descriptive data included demographics, admission diagnoses, hemodynamics, Vasoactive Inotropic Scores, and arterial blood gas measurement. Eight children underwent 15 determination of neurologic death examinations resulting in 31 paired transcutaneous carbon dioxide and PaCO2 values for study. Transcutaneous carbon dioxide and PaCO2 correlated well (r = 0.94; p < 0.01). Bias between transcutaneous carbon dioxide and PaCO2 was -3.29 ± 7.14 mm Hg. Differences in means did not correlate with Vasoactive Inotropic Score (r = 0.2) or patient temperature (r = 0.11). Receiver operator characteristic curve of transcutaneous carbon dioxide after 3-10 minutes of apnea to discriminate positive apnea testing by the standard of PaCO2 yielded an area under the curve of 0.91 and threshold of greater than or equal to 64 mm Hg (sensitivity, 91.7%; specificity, 100%; positive predictive value, 100%; negative predictive value, 92.3%; accuracy, 95.9%).

CONCLUSIONS

During apnea testing for determination of neurologic death in children, noninvasive transcutaneous carbon dioxide monitoring demonstrated high correlation, accuracy, and minimal bias when compared with PaCO2. Further validation is required before any recommendation to replace PaCO2 with noninvasive transcutaneous carbon dioxide monitoring can be proposed. However, concurrent transcutaneous carbon dioxide data may limit unnecessary apnea time and associated hemodynamic instability or respiratory decompensation by approximating goal arterial blood sampling to document target PaCO2.

Transcutaneous carbon dioxide monitoring as a predictive tool for all-cause 6-month mortality after acute pulmonary embolism

BACKGROUND

Pulmonary embolism (PE) frequently remains undiagnosed. The partial pressure of carbon dioxide (Pa_CO2)_, a surrogate of dead-space ventilation, is useful in the evaluation of the degree of pulmonary artery occlusion. At present, there is no knowledge about the prognostic role of Pa_CΟ2 variations during the first hours of an acute PE. Transcutaneous measurement of CO₂ (Ptc_CO2) is a simple, non-invasive method that correlates well with Pa_CO2 levels, evaluated in this study for the first time in patients with PE.

PURPOSE

To assess the correlation between Ptc_CO2 and Pa_CO2 levels in the acute phase of PE and the role of Ptc_CO2 in predicting 6-months mortality.

METHODS

This was a pilot study including 53 patients with acute PE who hospitalized in Respiratory Medicine Department at University Hospital of Larissa in central Greece during 15 months. Ptc_CO2 was constantly monitored for four hours after PE diagnosis with the TCM40 monitoring system (SmartCal). Simultaneous arterial blood gas measurements were performed. Each patient was prospectively recorded for six months via standard telephone calls.

RESULTS

Pa_CO2 and Ptc_CO2 values were well-correlated in the acute phase of PE. Decreased Ptc_CO2 levels in the first monitoring hour were associated with a higher risk of mortality. In the PE subgroup who died, the lower Ptc_CO2 level in the first hour of PE was a predictor of shorter survival time independently of gender, age, comorbidities, and smoking status.

CONCLUSION

Ptc_CO2 measurement, especially in the first hour after PE, seemed to be a valid tool in predicting all-cause 6-month mortality.

Estimating Arterial Partial Pressure of Carbon Dioxide in Ventilated Patients: How Valid Are Surrogate Measures?

The arterial partial pressure of carbon dioxide (Pa_CO2) is an important parameter in critically ill, mechanically ventilated patients. To limit invasive procedures or for more continuous monitoring of Pa_CO2, clinicians often rely on venous blood gases, capnography, or transcutaneous monitoring. Each of these has advantages and limitations. Central venous Pco₂ allows accurate estimation of Pa_CO2, differing from it by an amount described by the Fick principle. As long as cardiac output is relatively normal, central venous Pco₂ exceeds the arterial value by approximately 4 mm Hg. In contrast, peripheral venous Pco₂ is a poor predictor of Pa_CO2, and we do not recommend using peripheral venous Pco₂ in this manner. Capnography offers measurement of the end-tidal Pco₂ (Pet_CO2), a value that is close to Pa_CO2 when the lung is healthy. It has the advantage of being noninvasive and continuously available. In mechanically ventilated patients with lung disease, however, Pet_CO2 often differs from Pa_CO2, sometimes by a large degree, often seriously underestimating the arterial value. Dependence of Pet_CO2 on alveolar dead space and ventilator expiratory time limits its value to predict Pa_CO2. When lung function or ventilator settings change, Pet_CO2 and Pa_CO2 can vary in different directions, producing further uncertainty. Transcutaneous Pco₂ measurement has become practical and reliable. It is promising for judging steady state values for Pa_CO2 unless there is overt vasoconstriction of the skin. Moreover, it can be useful in conditions where capnography fails (high-frequency ventilation) or where arterial blood gas analysis is burdensome (clinic or home management of mechanical ventilation).

Non invasive monitoring in mechanically ventilated pediatric patients

Cardiopulmonary monitoring is a key component in the evaluation and management of critically ill patients. Clinicians typically rely on a combination of invasive and non-invasive monitoring to assess cardiac output and adequacy of ventilation. Recent technological advances have led to the introduction: of continuous non-invasive monitors that allow for data to be obtained at the bedside of critically ill patients. These advances help to identify hemodynamic changes and allow for interventions before complications occur. In this manuscript, we highlight several important methods of non-invasive cardiopulmonary monitoring, including capnography, transcutaneous monitoring, pulse oximetry, and near infrared spectroscopy.

Hypercapnia impairs lung neutrophil function and increases mortality in murine pseudomonas pneumonia

Hypercapnia, an elevation of the level of carbon dioxide (CO2) in blood and tissues, is a marker of poor prognosis in chronic obstructive pulmonary disease and other pulmonary disorders. We previously reported that hypercapnia inhibits the expression of TNF and IL-6 and phagocytosis in macrophages in vitro. In the present study, we determined the effects of normoxic hypercapnia (10% CO2, 21% O2, and 69% N2) on outcomes of Pseudomonas aeruginosa pneumonia in BALB/c mice and on pulmonary neutrophil function. We found that the mortality of P. aeruginosa pneumonia was increased in 10% CO2-exposed compared with air-exposed mice. Hypercapnia increased pneumonia mortality similarly in mice with acute and chronic respiratory acidosis, indicating an effect unrelated to the degree of acidosis. Exposure to 10% CO2 increased the burden of P. aeruginosa in the lungs, spleen, and liver, but did not alter lung injury attributable to pneumonia. Hypercapnia did not reduce pulmonary neutrophil recruitment during infection, but alveolar neutrophils from 10% CO2-exposed mice phagocytosed fewer bacteria and produced less H2O2 than neutrophils from air-exposed mice. Secretion of IL-6 and TNF in the lungs of 10% CO2-exposed mice was decreased 7 hours, but not 15 hours, after the onset of pneumonia, indicating that hypercapnia inhibited the early cytokine response to infection. The increase in pneumonia mortality caused by elevated CO2 was reversible when hypercapnic mice were returned to breathing air before or immediately after infection. These results suggest that hypercapnia may increase the susceptibility to and/or worsen the outcome of lung infections in patients with severe lung disease.

Accuracy of transcutaneous carbon dioxide monitoring in hypotensive patients

Objectives

Continuous blood gas monitoring is frequently necessary in critically ill patients. Our aim was to assess the accuracy of transcutaneous CO2 tension (PtcCO2) monitoring in the emergency department (ED) assessment of hypotensive patients by comparing it with the gold standard of arterial blood gas analysis (ABGA).

Methods

All patients receiving PtcCO2 monitoring in the ED were included. We excluded paediatric patients, patients with no ABGA results during a hypotensive event, patients whose ABGA was not performed simultaneously with PtcCO2 monitoring, and patients who received sodium bicarbonate for resuscitation. The included patients were classified into hypotensive patients and normotensive patients. A hypotensive patient was defined as a patient showing a mean arterial pressure under 60 mm Hg. The agreement in measurement between PaCO2 tension (PaCO2) and PtcCO2 were investigated in both groups.

Results

The mean difference between PaCO2 and PtcCO2 was 2.1 mm Hg, and the Bland–Altman limits of agreement (bias±1.96 SD) ranged from −15.6 to 19.7 mm Hg in the 28 normotensive patients. The mean difference between PaCO2 and PtcCO2 was 1.1 mm Hg, and the Bland–Altman limits of agreement (bias±1.96 SD) ranged from −19.5 to 21.7 mm Hg in the 26 hypotensive patients. The weighted κ values were 0.64 in the normotensive patients and 0.60 in the hypotensive patients.

Conclusions

PtcCO2 monitoring showed wider limits of agreement with PaCO2 in urgent situations in the ED environment. However, acutely developed hypotension does not affect the accuracy of PtcCO2 monitoring.

Concordance between transcutaneous and arterial measurements of carbon dioxide in an ED

BACKGROUND

Transcutaneous carbon dioxide pressure (PtcCO(2)) has been suggested as a noninvasive surrogate of arterial carbon dioxide pressure (PaCO(2)). Our study evaluates the reliability of this method in spontaneously breathing patients in an emergency department.

PATIENTS AND METHODS

A prospective, observational study was performed in nonintubated dyspneic patients who required measurement of arterial blood gases. Simultaneously and blindly to the physicians in charge, PtcCO(2) was measured using a TOSCA 500 monitor (Radiometer, Villeurbanne, France). Agreement between PaCO(2) and PtcCO(2) was assessed using the Bland-Altman method.

RESULTS

Forty-eight patients (mean age, 65 years) were included, and 50 measurements were done. Eleven (23%) had acute heart failure; 10 (21%), pneumonia; 7 (15%), acute asthma; and 7 (15%), exacerbation of chronic obstructive pulmonary disease. Median PaCO(2) was 42 mm Hg (range, 17-109). Mean difference between PaCO(2) and PtcCO(2) was 1 mm Hg with 95% limits of agreement of -3.4 to +5.6 mm Hg. All measurement differences were within 5 mm Hg, and 32 (64%) were within 2 mm Hg.

CONCLUSION

Transcutaneous carbon dioxide pressure accurately predicts PaCO(2) in spontaneously breathing patients.

Randomized controlled trial of high concentration oxygen in suspected community-acquired pneumonia

OBJECTIVE

To determine whether high concentration oxygen increases the PaCO(2) in the treatment of community-acquired pneumonia.

DESIGN

Randomized controlled clinical trial in which patients received high concentration oxygen (8 L/min via medium concentration mask) or titrated oxygen (to achieve oxygen saturations between 93 and 95%) for 60 minutes. Transcutaneous CO(2) (PtCO(2)) was measured at 0, 20, 40 and 60 minutes.

SETTING

The Emergency Departments at Wellington, Hutt and Kenepuru Hospitals.

PARTICIPANTS

150 patients with suspected community-acquired pneumonia presenting to the Emergency Department. Patients with chronic obstructive pulmonary disease (COPD) or disorders associated with hypercapnic respiratory failure were excluded.

MAIN OUTCOME VARIABLES

The primary outcome variable was the proportion of patients with a rise in PtCO(2) ≥4 mmHg at 60 minutes. Secondary outcome variables included the proportion of patients with a rise in PtCO(2) ≥8 mmHg at 60 minutes.

RESULTS

The proportion of patients with a rise in PtCO(2) ≥4 mmHg at 60 minutes was greater in the high concentration oxygen group, 36/72 (50.0%) vs 11/75 (14.7%), relative risk (RR) 3.4 (95% CI 1.9 to 6.2), P < 0.001. The high concentration group had a greater proportion of patients with a rise in PtCO(2) ≥8 mmHg, 11/72 (15.3%) vs 2/75 (2.7%), RR 5.7 (95% CI 1.3 to 25.0), P = 0.007. Amongst the 74 patients with radiological confirmation of pneumonia, the high concentration group had a greater proportion with a rise in PtCO(2) ≥4 mmHg, 20/35 (57.1%) vs 5/39 (12.8%), RR 4.5 (95% CI 1.9 to 10.6) P < 0.001.

CONCLUSIONS

We conclude that high concentration oxygen therapy increases the PtCO(2) in patients presenting with suspected community-acquired pneumonia. This suggests that the potential increase in PaCO(2) with high concentration oxygen therapy is not limited to COPD, but may also occur in other respiratory disorders with abnormal gas exchange.