The relationship between minute ventilation and end tidal CO2 in intubated and spontaneously breathing patients undergoing procedural sedation

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

Background

Monitoring respiratory status using end tidal CO ₂ (EtCO ₂), which reliably reflects arterial PaCO ₂ in intubated patients under general anesthesia, has often proven both inaccurate and inadequate when monitoring non-intubated and spontaneously breathing patients. This is particularly important in patients undergoing procedural sedation (e.g., endoscopy, colonoscopy). This can be undertaken in the operating theater, but is also often delivered outside the operating room by non-anesthesia providers. In this study we evaluated the ability for conventional EtCO ₂ monitoring to reflect changes in ventilation in non-intubated surgical patients undergoing monitored anesthesia care and compared and contrasted these findings to both intubated patients under general anesthesia and spontaneously breathing volunteers.

Methods

Minute Ventilation (MV), tidal volume (TV), and respiratory rate (RR) were continuously collected from an impedance-based Respiratory Volume Monitor (RVM) simultaneously with capnography data in 160 patients from three patient groups: non-intubated surgical patients managed using spinal anesthesia and Procedural Sedation (n = 58); intubated surgical patients under General Anesthesia (n = 54); and spontaneously breathing Awake Volunteers (n = 48). EtCO ₂ instrument sensitivity was calculated for each patient as the slope of a Deming regression between corresponding measurements of EtCO ₂ and MV and expressed as angle from the x-axis (θ). All data are presented as mean ± SD unless otherwise indicated.

Results

While, as expected, EtCO ₂ and MV measurements were negatively correlated in most patients, we found gross systematic differences across the three cohorts. In the General Anesthesia patients, small changes in MV resulted in large changes in EtCO ₂ (high sensitivity, θ = -83.6 ± 9.9°). In contrast, in the Awake Volunteers patients, large changes in MV resulted in insignificant changes in EtCO ₂ (low sensitivity, θ = -24.7 ± 19.7°, p < 0.0001 vs General Anesthesia). In the Procedural Sedation patients, EtCO ₂ sensitivity showed a bimodal distribution, with an approximately even split between patients showing high EtCO ₂ instrument sensitivity, similar to those under General Anesthesia, and patients with low EtCO ₂ instrument sensitivity, similar to the Awake Volunteers.

Conclusions

When monitoring non-intubated patients undergoing procedural sedation, EtCO ₂ often provides inadequate instrument sensitivity when detecting changes in ventilation. This suggests that augmenting standard patient care with EtCO ₂ monitoring is a less than optimal solution for detecting changes in respiratory status in non-intubated patients. Instead, adding direct monitoring of MV with an RVM may be preferable for continuous assessment of adequacy of ventilation in non-intubated patients.

Related collections

Most cited references 27

Record: found
Abstract: found
Article: not found

Oscillation mechanics of the respiratory system.

Charles Irvin, Zoltán Hantos, Ramon Farré … (2011)

The mechanical impedance of the respiratory system defines the pressure profile required to drive a unit of oscillatory flow into the lungs. Impedance is a function of oscillation frequency, and is measured using the forced oscillation technique. Digital signal processing methods, most notably the Fourier transform, are used to calculate impedance from measured oscillatory pressures and flows. Impedance is a complex function of frequency, having both real and imaginary parts that vary with frequency in ways that can be used empirically to distinguish normal lung function from a variety of different pathologies. The most useful diagnostic information is gained when anatomically based mathematical models are fit to measurements of impedance. The simplest such model consists of a single flow-resistive conduit connecting to a single elastic compartment. Models of greater complexity may have two or more compartments, and provide more accurate fits to impedance measurements over a variety of different frequency ranges. The model that currently enjoys the widest application in studies of animal models of lung disease consists of a single airway serving an alveolar compartment comprising tissue with a constant-phase impedance. This model has been shown to fit very accurately to a wide range of impedance data, yet contains only four free parameters, and as such is highly parsimonious. The measurement of impedance in human patients is also now rapidly gaining acceptance, and promises to provide a more comprehensible assessment of lung function than parameters derived from conventional spirometry. © 2011 American Physiological Society.

0 comments Cited 49 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: not found

Microstream capnography improves patient monitoring during moderate sedation: a randomized, controlled trial.

Adrienne Newburg, D Goldmann, Jenifer Lightdale … (2006)

Investigative efforts to improve monitoring during sedation for patients of all ages are part of a national agenda for patient safety. According to the Institute of Medicine, recent technological advances in patient monitoring have contributed to substantially decreased mortality for people receiving general anesthesia in operating room settings. Patient safety has not been similarly targeted for the several million children annually in the United States who receive moderate sedation without endotracheal intubation. Critical event analyses have documented that hypoxemia secondary to depressed respiratory activity is a principal risk factor for near misses and death in this population. Current guidelines for monitoring patient safety during moderate sedation in children call for continuous pulse oximetry and visual assessment, which may not detect alveolar hypoventilation until arterial oxygen desaturation has occurred. Microstream capnography may provide an "early warning system" by generating real-time waveforms of respiratory activity in nonintubated patients. The aim of this study was to determine whether intervention based on capnography indications of alveolar hypoventilation reduces the incidence of arterial oxygen desaturation in nonintubated children receiving moderate sedation for nonsurgical procedures. We included 163 children undergoing 174 elective gastrointestinal procedures with moderate sedation in a pediatric endoscopy unit in a randomized, controlled trial. All of the patients received routine care, including 2-L supplemental oxygen via nasal cannula. Investigators, patients, and endoscopy staff were blinded to additional capnography monitoring. In the intervention arm, trained independent observers signaled to clinical staff if capnograms indicated alveolar hypoventilation for >15 seconds. In the control arm, observers signaled if capnograms indicated alveolar hypoventilation for >60 seconds. Endoscopy nurses responded to signals in both arms by encouraging patients to breathe deeply, even if routine patient monitoring did not indicate a change in respiratory status. Our primary outcome measure was patient arterial oxygen desaturation defined as a pulse oximetry reading of 5 seconds. Secondary outcome measures included documented assessments of abnormal ventilation, termination of the procedure secondary to concerns for patient safety, as well as other more rare adverse events including need for bag-mask ventilation, sedation reversal, or seizures. Children randomly assigned to the intervention arm were significantly less likely to experience arterial oxygen desaturation than children in the control arm. Two study patients had documented adverse events, with no procedures terminated for patient safety concerns. Intervention and control patients did not differ in baseline characteristics. Endoscopy staff documented poor ventilation in 3% of all procedures and no apnea. Capnography indicated alveolar hypoventilation during 56% of procedures and apnea during 24%. We found no change in magnitude or statistical significance of the intervention effect when we adjusted the analysis for age, sedative dose, or other covariates. The results of this controlled effectiveness trial support routine use of microstream capnography to detect alveolar hypoventilation and reduce hypoxemia during procedural sedation in children. In addition, capnography allowed early detection of arterial oxygen desaturation because of alveolar hypoventilation in the presence of supplemental oxygen. The current standard of care for monitoring all patients receiving sedation relies overtly on pulse oximetry, which does not measure ventilation. Most medical societies and regulatory organizations consider moderate sedation to be safe but also acknowledge serious associated risks, including suboptimal ventilation, airway obstruction, apnea, hypoxemia, hypoxia, and cardiopulmonary arrest. The results of this controlled trial suggest that microstream capnography improves the current standard of care for monitoring sedated children by allowing early detection of respiratory compromise, prompting intervention to minimize hypoxemia. Integrating capnography into patient monitoring protocols may ultimately improve the safety of nonintubated patients receiving moderate sedation.

0 comments Cited 44 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: not found

Automated graphic assessment of respiratory activity is superior to pulse oximetry and visual assessment for the detection of early respiratory depression during therapeutic upper endoscopy.

John J. Vargo, Ryan J. Morrow, Gregory Zuccaro … (2002)

Recommendations from the American Society of Anesthesiologists suggest that monitoring for apnea using the detection of exhaled carbon dioxide (capnography) is a useful adjunct in the assessment of ventilatory status of patients undergoing sedation and analgesia. There are no data on the utility of capnography in GI endoscopy, nor is the frequency of abnormal ventilatory activity during endoscopy known. The aims of this study were to determine the following: (1) the frequency of abnormal ventilatory activity during therapeutic upper endoscopy, (2) the sensitivity of observation and pulse oximetry in the detection of apnea or disordered respiration, and (3) whether capnography provides an improvement over accepted monitoring techniques. Forty-nine patients undergoing therapeutic upper endoscopy were monitored with standard methods including pulse oximetry, automated blood pressure measurement, and visual assessment. In addition, graphic assessment of respiratory activity with sidestream capnography was performed in all patients. Endoscopy personnel were blinded to capnography data. Episodes of apnea or disordered respiration detected by capnography were documented and compared with the occurrence of hypoxemia, hypercapnea, hypotension, and the recognition of abnormal respiratory activity by endoscopy personnel. Comparison of simultaneous respiratory rate measurements obtained by capnography and by auscultation with a pretracheal stethoscope verified that capnography was an excellent indicator of respiratory rate when compared with the reference standard (auscultation) (r = 0.967, p < 0.001). Fifty-four episodes of apnea or disordered respiration occurred in 28 patients (mean duration 70.8 seconds). Only 50% of apnea or disordered respiration episodes were eventually detected by pulse oximetry. None were detected by visual assessment (p < 0.0010). Apnea/disordered respiration occurs commonly during therapeutic upper endoscopy and frequently precedes the development of hypoxemia. Potentially important abnormalities in respiratory activity are undetected with pulse oximetry and visual assessment.

0 comments Cited 36 times – based on 0 reviews      Review now

Bookmark

All references

Author and article information

Contributors

Jaideep H. Mehta:

ORCID: http://orcid.org/0000-0001-9274-7010

Role: ConceptualizationRole: Formal analysisRole: MethodologyRole: Project administrationRole: SupervisionRole: ValidationRole: Writing – original draftRole: Writing – review & editing

George W. Williams II: Role: ConceptualizationRole: Formal analysisRole: MethodologyRole: Project administrationRole: SupervisionRole: Writing – original draftRole: Writing – review & editing

Brian C. Harvey:

ORCID: http://orcid.org/0000-0002-4349-6304

Role: Formal analysisRole: ValidationRole: VisualizationRole: Writing – original draftRole: Writing – review & editing

Navneet K. Grewal: Role: MethodologyRole: Writing – original draftRole: Writing – review & editing

Edward E. George: Role: ConceptualizationRole: Data curationRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: Project administrationRole: ResourcesRole: SupervisionRole: Writing – original draftRole: Writing – review & editing

Yu Ru Kou: Role: Editor

Journal

Journal ID (nlm-ta): PLoS One

Journal ID (iso-abbrev): PLoS ONE

Journal ID (publisher-id): plos

Journal ID (pmc): plosone

Title: PLoS ONE

Publisher: Public Library of Science (San Francisco, CA USA )

ISSN (Electronic): 1932-6203

Publication date (Electronic): 29 June 2017

Publication date Collection: 2017

Volume: 12

Issue: 6

Electronic Location Identifier: e0180187

Affiliations

[1 ]Department of Anesthesiology, The University of Texas Health Science Center at Houston, Houston, Texas, United States of America

[2 ]Respiratory Motion, Inc. Waltham, Massachusetts, United States of America

[3 ]Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States of America

National Yang-Ming University, TAIWAN

Author notes

Competing Interests: I have read the journal's policy and the authors of this manuscript have the following competing interests: JHM owns stock in Respiratory Motion, Inc. BCH was an employee of Respiratory Motion, Inc. at the time the manuscript was written and collaborated with co-authors on data analysis and manuscript preparation. Respiratory Motion, Inc. provided the respiratory volume monitors used for data collection in this Study. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

* E-mail: Jaideep.H.Mehta@ 123456uth.tmc.edu

Author information

Jaideep H. Mehta http://orcid.org/0000-0001-9274-7010

Brian C. Harvey http://orcid.org/0000-0002-4349-6304

Article

Publisher ID: PONE-D-17-15967

DOI: 10.1371/journal.pone.0180187

PMC ID: 5491149

PubMed ID: 28662195

SO-VID: 50aee746-804a-4f51-89a1-266be3662462

License:

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 25 April 2017

Date accepted : 12 June 2017

Page count

Figures: 3, Tables: 3, Pages: 14

Funding

Funded by: Respiratory Motion, Inc.

Respiratory Motion, Inc. ( www.respiratorymotion.com) provided the respiratory volume monitors used for data collection in this study. BCH, an employee of Respiratory Motion, Inc., collaborated with co-authors on data analysis and manuscript preparation. Respiratory Motion, Inc. provided support for author BCH in the form of salary, but did not have any additional role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Custom metadata

Data Availability Data are from the "Comparison of an Impedance-Based Respiratory Monitor with Ventilator Volumes in the Operative Setting" and “Evaluation of ExSpironTM Respiratory Volume Monitor (RVM)” studies. Data are available from the Partners Healthcare Institutional Data Access / Ethics Committee for researchers who meet the criteria for access to confidential data. Qualified researchers can send data requests to rpdrhelp@ 123456partners.org .