Elsevier

Resuscitation

Volume 184, March 2023, 109679
Resuscitation

Clinical paper
Methods for calculating ventilation rates during resuscitation from out-of-hospital cardiac arrest

https://doi.org/10.1016/j.resuscitation.2022.109679Get rights and content

Abstract

Objective

Ventilation control is important during resuscitation from out-of-hospital cardiac arrest (OHCA). We compared different methods for calculating ventilation rates (VR) during OHCA.

Methods

We analyzed data from the Pragmatic Airway Resuscitation Trial, identifying ventilations through capnogram recordings. We determined VR by: 1) counting the number of breaths within a time epoch (“counted” VR), and 2) calculating the mean of the inverse of measured time between breaths within a time epoch (“measured” VR). We repeated the VR estimates using different time epochs (10, 20, 30, 60 sec). We defined hypo- and hyperventilation as VR <6 and >12 breaths/min, respectively. We assessed differences in estimated hypo- and hyperventilation with each VR measurement technique.

Results

Of 3,004 patients, data were available for 1,010. With the counted method, total hypoventilation increased with longer time epochs ([10-s epoch: 75 sec hypoventilation] to [60-s epoch: 97 sec hypoventilation]). However, with the measured method, total hypoventilation decreased with longer time epochs ([10-s epoch: 223 sec hypoventilation] to [60-s epoch: 150 sec hypoventilation]). With the counted method, the total duration of hyperventilation decreased with longer time epochs ([10-s epochs: 35 sec hyperventilation] to [60-s epoch: 0 sec hyperventilation]). With the measured method, total hyperventilation decreased with longer time epochs ([10-s epoch: 78 sec hyperventilation] to [60-s epoch: 0 sec hyperventilation]). Differences between the measured and counted estimates were smallest with a 60-s time epoch.

Conclusions

Quantifications of hypo- and hyperventilation vary with the applied measurement methods. Measurement methods are important when characterizing ventilation rates in OHCA.

Introduction

Optimal control of ventilation is important for successful resuscitation from out-of-hospital cardiac arrest (OHCA).1 Potential adverse effects of inadequate ventilation can include hypoxemia, hypercapnia, acidemia, alveolar atelectasis and pulmonary shunting.1, 2 Over-ventilation can result in increased intrathoracic pressure, decreased venous return, cardiac output and coronary perfusion, and cerebral vasoconstriction.3, 4, 5 Prior studies have characterized ventilation quality over the entirety of resuscitation without considering shorter but potentially important episodes of hypo- or hyperventilation.3 Previously we demonstrated the feasibility of using the continuous capnography signal from modern portable cardiac monitors to characterize ventilation rate during OHCA.6, 7, 8, 9, 10, 11, 12

Important considerations in the analysis of the capnogram include the methods used to calculate the ventilation rate and the resulting estimates of hypo- and hyperventilation. For example, measurements of respiratory rate may be accomplished by counting individual ventilations occurring during a defined time epoch.13, 14 Another approach is to estimate the instantaneous ventilatory rate by calculating the time interval between breaths.13, 15, 16 The different ventilation rate measurement techniques may result in varying estimates of hypo- and hyperventilation. The optimal analysis approach to calculating ventilation rate is unclear.

The Pragmatic Airway Resuscitation Trial (PART) found improved outcomes with an airway strategy of initial laryngeal tube (LT) insertion compared with endotracheal intubation (ETI) in patients with OHCA.17 In this study, we sought to evaluate different techniques for estimating hypo- and hyperventilation during OHCA resuscitation.

Section snippets

Study design

We conducted a post hoc analysis of data from the PART trial.17 The Institutional Review Boards of participating institutions approved the parent study under federal regulations for Exception from Informed Consent for Emergency Research (21 CFR 50.24). The current analysis was approved by the Office of Responsible Research Practices of The Ohio State University.

Setting – The PART trial

The PART trial involved 27 emergency medical services (EMS) agencies from the Birmingham (Alabama), Dallas-Fort Worth (Texas),

Results

The parent trial enrolled a total of 3,004 patients. CPR process files were available for 2,020 patients, and capnography files of sufficient quality were available for 1,010 patients. Among patients with adequate capnography data, 538 (53%) originated from Philips monitors, 436 (43.2%) from Zoll monitors, and 36 (3.6%) from PhysioControl monitors. There were 13 randomization clusters in the parent trial; 1 cluster had only 3 cases with suitable capnography data, and 3 had no cases with

Discussion

Our analysis has important implications for clinical care. Resuscitation guidelines emphasize control of ventilation rates during OHCA resuscitation, with avoidance of hypo- and hyperventilation.23 However, we found that the estimates of ventilation rates vary with measurement methods. We also showed influences upon the resulting estimates of hypo- and hyperventilation.

There are many technologies for identifying clinical respirations, including spirometry, capnometry, impedance pneumography,

Limitations

Capnography files of adequate length and quality were available for only one-third of cases enrolled in the parent trial. As previously reported, survival rates were much lower for cases with than without capnography; the exact reasons for this selection bias are unclear.31 We observed few files from PhysioControl monitors; PhysioControl monitors must be configured to continuously record the capnography signal, potentially explaining the low capture rate. If outcomes were better among EMS

Conclusions

In resuscitation from OHCA, estimates of ventilation rates and hypo- and hyperventilation depend upon the applied analytic methods. Measurement methods are important considerations when characterizing ventilation rates in OHCA.

Sources of funding

Research supported by Grant UH2/UH3-HL125163 from National Heart Lung and Blood Institute, Spanish Ministerio de Ciencia, Innovación y Universidades under Grant PID2021-122727OB-I00, and by the Basque Government under Grants IT1717-22 and PRE 2019 0209.

Disclosures

All authors have made substantial contributions to all of the following: (1) the conception and design of the study, or acquisition of data, or analysis and interpretation of data, (2) drafting the article or revising it critically for important intellectual content, (3) final approval of the version to be submitted.

There is no overlap with previous publications other than the parent PART study and we confirm that the manuscript, including related data, figures and tables, has not been

CRediT authorship contribution statement

Henry Wang: Conceptualization, Data curation, Formal analysis, Funding acquisition, Methodology, Project administration, Resources, Supervision, Investigation, Writing – original draft, Writing – review & editing. Xabier Jaureguibeitia: Conceptualization, Data curation, Formal analysis, Methodology, Software, Investigation, Writing – review & editing. Elisabete Aramendi: Conceptualization, Formal analysis, Methodology, Software, Investigation, Writing – review & editing. Michelle Nassal:

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Graham Nichol has research funding from Abiomed Inc. (Danvers, MA), Vapotherm Inc. (Exeter, NH), and ZOLL Medical (Chelmsford, MA). He is a member of the steering committee of the PRINCESS 2 Trial of Ultrafast Hypothermia After Cardiac Arrest. He is also a consultant to CPR Therapeutics (Putney, VT), Heartbeam Inc. (Santa

Acknowledgements

None.

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