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Transcutaneous monitoring for managing patients undergoing non-invasive ventilation

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During the last decade, non-invasive ventilation (NIV) has proven to be a cornerstone in the treatment of acute respiratory failure in both intensive care units (ICU) and respiratory high-dependency units (RHDU) [1]. Studies have shown the usefulness of NIV in COPD exacerbations, acute respiratory failure, and lately, also in the management of hypoxemic acute respiratory failure in COVID-19 [1, 2].

During NIV it is critical to monitor the level of CO2 in the blood to observe treatment effect and titrate NIV treatment. The gold standard for CO2 monitoring is arterial blood gases (ABG) due to the accuracy and precision; but, the process of puncturing an artery can be painful for the patient and only shows single points in time of blood gas values [3]. Contrary to this, transcutaneous monitoring (TCM) of CO2 shows continuous values, is non-invasive, and less painful to the patient, and allows for proactive rather that reactive management of ventilation [1]. This allows transcutaneous monitoring to be a good supplement to arterial blood gases and, in specific cases, is able to replace them.


TCM in acute respiratory failure in the emergency department

Acute respiratory failure (ARF) is a common presentation in the emergency department (ED). Management and monitoring of patients with ARF is important for ED physicians which has been evident during the COVID-19 pandemic [4, 5].

During acute respiratory failure, it is vital to monitor the CO2 level to risk stratify patients and evaluate treatment effect [8]. Bobbia and colleagues found that transcutaneous CO2 values (tcpCO2) showed good agreement with arterial values for patients with ARF [6]. Horvath and colleagues showed that tcpCO2 was accurate compared to ABG for patients with acute respiratory failure starting NIV in the emergency department, both at baseline and after intervention [7]. They conclude that transcutaneous monitoring of CO2 is “a reliable, feasible, patient-friendly and safe alternative to repeated blood gas analysis for patients with severe hypoxaemic and/or hypercapnic respiratory failure receiving emergency NIV in the emergency department” [7].


TCM can help titrate NIV in intermediate/intensive care

After initial stabilization, patients receiving NIV are often treated in intermediate or intensive care units [1]. Monitoring of CO2 will often be done through indwelling arterial catheters or repeated arterial punctures [3].

van Oppen and colleagues examined the accuracy of TCM compared to repeated arterial samples for patients receiving NIV in a RHDU. They conclude that TCM is a “patient-friendly approach and a promising alternative to repeated arterial blood gas sampling in patients requiring NIV for acute hypercapnic respiratory failure” [3]. The British Thoracic Society/Intensive Care Society recommends transcutaneous monitoring of CO2 as a valuable supplement to ABG that might help facilitate titration and ceasing of NIV treatment [10].

In the review article by Ergan et al., transcutaneous monitoring of CO2 is recommended during NIV treatment of acute respiratory failure in the ICU and RHDU. They suggest that TCM during NIV can help facilitate “proactive (rather than reactive) ventilator titration” [1].


TCM of NIV during chronic respiratory failure & sleep studies

NIV is an effective treatment in chronic respiratory failure caused by chronic obstructive pulmonary disease (COPD), neuromuscular disorders, obesity hypoventilation syndrome (OHS) and central hypoventilation syndrome [8, 9]. Daytime and nighttime arterial CO2 is a predictor for respiratory mortality, but arterial values are not always available and can cause pain for the patient [8, 9].

Arrestad and colleagues compared tcpCO2 to arterial values in 67 patients receiving NIV for chronic respiratory failure. They found that tcpCO2 showed excellent agreement with daytime arterial values (bias 0.23 kPa, all values recorded within clinically acceptable range of +/- 1 kPa) without any clinically significant drift after overnight monitoring [9].

Storre and colleagues compared three different TCM in patients receiving NIV for chronic respiratory failure, and concluded that “overnight PtcCO2 -monitoring has become a reliable and robust tool for assessing alveolar ventilation during sleep in chronic HRF (hypoxic respiratory failure) patients receiving NPPV (non-invasive positive pressure ventilation)” [11].

AARC (American Association of Respiratory Care) recommends the use of transcutaneous monitoring for patients who “lack arterial access or have the need for continuous monitoring of oxygen and carbon dioxide with minimal blood draws”, including evaluating diagnostic and therapeutic interventions [12].


TCM compared to end-tidal monitoring of CO2

End-tidal monitoring of CO2 (etCO2) is commonly used in the operating room and in intubated patients, to monitor ventilation status and confirm endotracheal tube placement. Fujimoto and colleagues compared TCM and end-tidal monitoring in patients with hypoxemic respiratory failure, and found that tcpCO2 was more accurate and had a smaller bias than etpCO2 [13]. Likewise Lermuzeaux and colleagues found that tcpCO2 was more precise than etpCO2 in non-intubated patients in the ICU [15].


Patients prefer TCM over ABG

Arterial blood gas analysis remains the gold standard for measuring CO2 but can only be obtained through an indwelling catheter or an arterial puncture. Both carry risk of complications, and arterial punctures can be painful for the patient [3].

Two studies have compared pain scores and patient satisfaction comparing transcutaneous monitoring to arterial lines/punctures, and both found markedly better satisfaction/lower pain scores with TCM compared to arterial blood gas analysis [3, 14].



Transcutaneous monitoring of CO2 offers continuous values, shows good accuracy compared to arterial blood gases in both acute and chronic respiratory failure and is overwhelmingly preferred by patients over arterial blood gas analysis. Using TCM in NIV offers an opportunity to titrate settings and react proactive rather than reactive on ventilation status.



1. Ergan B, Nasiłowski J, Winck JC. How should we monitor patients with acute respiratory failure treated with noninvasive ventilation? European Respiratory Review 2018; 27, 148.
2. Franco C, Facciolongo N, Tonelli R, et al. Feasibility and clinical impact of out-of-ICU noninvasive respiratory support in patients with COVID-19-related pneumonia. Eur Respir J 2020; 56, 5.
3. van Oppen JD, Daniel PS, Sovani MP. What is the potential role of transcutaneous carbon dioxide in guiding acute noninvasive ventilation? Respir Care 2015; 60, 4: 484–91.
4. Wilcox SR, Condella A. Emergency Department Management of Severe Hypoxemic Respiratory Failure in Adults With COVID-19. J Emerg Med 2020.
5. Nee PA, Al-Jubouri MA, Gray AJ, et al. Critical care in the emergency department: Acute respiratory failure. Emerg Med J 2011; 28, 2: 94–97.
6. Bobbia X, Claret P-G, Palmier L et al. Concordance and limits between transcutaneous and arterial carbon dioxide pressure in emergency department patients with acute respiratory failure: A single-center prospective observational study. Scand J Trauma Resusc Emerg Med 2015; 23: 40.
7. Horvath CM, Brutsche MH, Baty F, Rüdiger JJ. Transcutaneous versus blood carbon dioxide monitoring during acute noninvasive ventilation in the emergency department - a retrospective analysis. Swiss Med Wkly 2016; 146: w14373.
8. Köhnlein T, Windisch W, Köhler D, et al. Non-invasive positive pressure ventilation for the treatment of severe stable chronic obstructive pulmonary disease: A prospective, multicentre, randomised, controlled clinical trial. Lancet Respir Med 2014; 2, 9: 698–705.
9. Aarrestad S, Tollefsen E, Kleiven AL, et al. Validity of transcutaneous PCO2in monitoring chronic hypoventilation treated with non-invasive ventilation. Respir Med 2016; 112: 112–18.
10. Davidson AC, Banham S, Elliott M, et al. BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults. Thorax 2016; 71 Suppl 2: ii1-35.
11. Storre JH, Magnet FS, Dreher M, Windisch W. Transcutaneous monitoring as a replacement for arterial PCO(2) monitoring during nocturnal noninvasive ventilation. Respir Med 2011; 105, 1: 143–50.
12. Restrepo RD, Hirst KR, Wittnebel L, Wettstein R. AARC clinical practice guideline: Transcutaneous monitoring of carbon dioxide and oxygen: 2012. Respir Care 2012; 57, 11: 1955–62.
13. Fujimoto S, Suzuki M, Sakamoto K et al. Comparison of End-Tidal, Arterial, Venous, and Transcutaneous PCO2. Respir Care 2019; 64, 10: 1208–14.
14. Mummery V, Rogers E, Padmanaban V, et al. Transcutaneous carbon dioxide measurement is not a reliable alternative to arterial blood gas sampling in the acute medical setting. Eur Respir J 2019; 53, 4.
15. Lermuzeaux M, Meric H, Sauneuf B, et al. Superiority of transcutaneous CO2 over end-tidal CO2 measurement for monitoring respiratory failure in nonintubated patients: A pilot study. J Crit Care 2016; 31, 1: 150–56.

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