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. 2023 Mar:184:109679.
doi: 10.1016/j.resuscitation.2022.109679. Epub 2022 Dec 24.

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

Henry E Wang  1 , Xabier Jaureguibeitia  2 , Elisabete Aramendi  3 , Michelle Nassal  4 , Ashish Panchal  5 , Erik Alonso  6 , Graham Nichol  7 , Tom Aufderheide  8 , Mohamud R Daya  9 , Jestin Carlson  10 , Ahamed Idris  11
Affiliations

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

Henry E Wang et al. Resuscitation. 2023 Mar.

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.

Keywords: Airway management; Cardiopulmonary arrest; Emergency medical services; Intubation; Ventilation.

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Conflict of interest statement

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 Clara, CA), Kestra Medical Technologies Inc. (Kirkland, WA), Invero Health LLC. (Montvale, NJ), Orixha Inc. (Saint Cyr Au Mont d’Or, France), and ZOLL Circulation (San Jose, CA).

Figures

FIGURE 1
FIGURE 1
Example of “measured” (panel a) and “counted” (panel b) strategies for calculating ventilation rate (VR). For measured VR, we first calculated the instantaneous ventilation rate (VRinst) as 60/Δt, with Δt representing the time difference between two consecutive ventilations. We then calculated VR for a given time epoch as the integral average of VRinst over the corresponding time window length (WL). For the counted strategy, we determined VR from the number of ventilations within the given time epoch; (counted VR = [ (number of ventilations × 60) / (time epoch)]). We repeated the analysis using analytical time epochs of 10, 20, 30 and 60 seconds.
FIGURE 2
FIGURE 2
Violin plots depicting the duration and proportion of post-airway time with hypoventilation. Graphs illustrate differences in calculated hypoventilation using different ventilation rate calculation methods (measured vs. counted) and time epochs (10, 20, 30, 60 seconds). Violin plots include box plot (median, interquartile range) and probability density distribution of the ventilation data smoothed by a kernel density estimator. Plots show that the differences in hypoventilation estimates between the measured and counted methods are smallest with a time epoch of 60 seconds.
FIGURE 3
FIGURE 3
Violin plots depicting the duration and proportion of post-airway time with hyperventilation. Graphs illustrate differences between in calculated hyperventilation using different ventilation rate calculation methods (measured vs. counted) and time epochs (10, 20, 30, 60 seconds). Plots show that the differences in hyperventilation estimates between the measured and counted methods are smallest with a time epoch of 60 seconds.
FIGURE 4
FIGURE 4
Examples of “counted” (panel a) and “measured” (panel b) calculations of ventilation rate (VR) in a case with frequent ventilations. Upper panels illustrate VR calculations with time epochs of 60 seconds. Lower panels illustrate VR calculations with time epochs of 20 seconds. In this case, the use of 60-second time epochs resulted in the classification of all time segments as normoventilation (VR 6–12 breaths/minute). However, the use of 20-second time epochs resulted in time segments classified as hyperventilation (VR>12 breaths/minute).
FIGURE 5
FIGURE 5
Examples of “counted” (panel a) and “measured” (panel b) calculations of ventilation rate (VR) in a case with infrequent ventilations. Upper panels illustrate VR calculations with time epochs of 60 seconds. Lower panels illustrate VR calculations with time epochs of 20 seconds. In this case, the use of 60-second time epochs resulted in the classification of all time segments as hypoventilation (VR <6 breaths/minute). However, the use of 20-second time epochs resulted a mixture of time segments classified as hypoventilation (VR<6 breaths/minute) and normoventilation (VR 6–12 breaths/minute).
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