Elsevier

Resuscitation

Volume 81, Issue 11, November 2010, Pages 1544-1549
Resuscitation

Clinical paper
Does change in thoracic impedance measured via defibrillator electrode pads accurately detect ventilation breaths in children?

https://doi.org/10.1016/j.resuscitation.2010.07.010Get rights and content

Abstract

Introduction

Resuscitation guidelines recommend rescue ventilations consist of tidal volumes 7–10 ml/kg. Changes in thoracic impedance (ΔTI) measured using defibrillator electrode pads to detect and guide rescue ventilations have not been studied in children.

Aim

We hypothesized that ΔTI measured via standard anterior–apical (AA) position can accurately detect ventilations with volume >7 ml/kg in children. We also compared standard AA position with alternative anterior–posterior (AP) position.

Methods

IRB-approved, prospective, observational study of sedated, subjects (6 months to 17 years) on conventional mechanical ventilation. Thoracic impedance (TI) was obtained via Philips MRx defibrillator with standard electrode pads for 5 min each in AA and AP positions. Ventilations were simultaneously measured by pneumotachometer (Novametrix CO2SMO Plus).

Results

Twenty-eight subjects (median 4 years, IQR 1.7–9 years; median 16.3 kg, IQR 10.5–39 kg) were enrolled. Data were available for 21 episodes in AA position and 22 episodes in AP position, with paired AA and AP data available for 18. For ventilations with volume <7 ml/kg, the defibrillator algorithm detected 80.0% for both AA and AP (p = 0.99). For ventilations ≥7 ml/kg, detection was 95.1% for AA and 95.7% for AP (p = 0.38).

Conclusions

Changes in thoracic impedance obtained via defibrillator pads can accurately detect ventilations above 7 ml/kg in stable, mechanically ventilated children, corresponding to rescue ventilations recommended during CPR. Both AA and AP pad positions were less sensitive to detect smaller volumes (<7 ml/kg) than higher volumes (≥7 ml/kg), suggesting that shallow ventilations during CPR might be missed. There were no differences in impedance measurements between standard AA pad position and commonly used alternative AP pad position.

Introduction

Studies of adults and children experiencing cardiac arrest demonstrate that providers frequently deliver poor quality cardiopulmonary resuscitation (CPR) in both in-hospital and out-of-hospital settings.1, 2, 3, 4, 5, 6 Specifically, over-ventilation during CPR is common and related to poor outcomes from cardiac arrest.7, 8 Published guidelines recommend that rescue ventilations consist of tidal volumes per kilogram bodyweight (Vts) of 7–10 ml/kg for optimal CPR and emphasize the importance of avoiding over-ventilation during CPR.9, 10 While there is evidence to suggest that CPR feedback/prompt devices to guide compressions and ventilations may improve skill acquisition and retention by providers, it is not known if such devices improve actual patient outcomes during CPR.11

Recent improvements in defibrillator and monitor technology make it feasible to provide audiovisual feedback on quality of CPR to providers in both adult and pediatric settings.12, 13, 14, 15 While studies in adults have demonstrated that changes in thoracic impedance (ΔTI) measured by defibrillator electrode pads are accurate in measuring presence and rate of ventilations delivered during CPR,16, 17 it is unknown if this technology is feasible to detect and guide rescue ventilations in children.

In this study, we investigated the relationship between tidal volume (Vt) and changes in thoracic impedance (TI) in children. We hypothesized that impedance would be predictive of tidal volume in a clinically useful way, and in particular, delta-TI could allow accurate detection of tidal volumes less than, equal to, or greater than 7 ml/kg. Thus, as our primary objective, we tested whether delta-TI measured through standard anterior–apical (AA) defibrillator electrode pad placement can accurately detect ventilations of >7 ml/kg in children. We also compared the AA position with the commonly used alternative anterior–posterior (AP) position to detect similar ventilations.

Section snippets

Methods

This prospective observational study was approved by the Institutional Review Board at the Children's Hospital of Philadelphia. Data were collected in compliance with the guidelines of the Health Insurance Portability and Accountability Act to ensure subject confidentiality. Parental/guardian informed consent and, if capable, child assent was obtained from all subjects.

Results

A total of 28 subjects met eligibility criteria and were enrolled in the study. Table 1 displays subject demographics and admission diagnosis. Median age was 4 years (range 6 months to 17 years; IQR 1.7–9). Three subjects were excluded due to irregular and dyssynchronous breathing patterns that resulted in both CO2SMO + and MRx signals that were too noisy to analyze. Simultaneous CO2SMO+ and MRx recordings (see Fig. 1 for an example) were available for 21 subjects in the AA position and for 22

Discussion

Our study is the first to examine the feasibility and accuracy of changes in thoracic impedance (using standard defibrillator electrode pads) to detect ventilations and quantify tidal volumes in the pediatric age group. We also examined the impact of different pad positions (AA vs. AP) to determine if there were differences in estimation of ventilation volumes. In addition to verifying that defibrillator electrode pads could accurately detect guideline recommended ventilations in the 7–10 ml/kg

Conclusions

This study demonstrates that changes in thoracic impedance obtained via defibrillator pads can accurately detect and guide ventilations in stable, mechanically ventilated children, corresponding to rescue ventilations recommended during cardiopulmonary resuscitation. The observed variability in the thoracic impedance coefficient between subjects precludes the use of a single average impedance coefficient to accurately estimate tidal volumes. As lower tidal volume provides less impedance change

Conflict of interest

The authors acknowledge the following potential conflicts of interest. Dana Niles and Vinay Nadkarni receive unrestricted research grant support from the Laerdal Foundation for Acute Care Medicine. Mette Stavland, Joar Eilevstjønn and Jon Nysæther were employed by Laerdal Medical during this work.

Acknowledgments

We wish to thank Stephanie Tuttle MBA, Raymond Matthews RRT, and the staff of the pediatric intensive care unit and perioperative complex at CHOP for their support and contributions to this study. We also thank Robert Berg MD for his support on the manuscript.

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  • A novel technique to assess the quality of ventilation during pre-hospital cardiopulmonary resuscitation

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    A number of clinical and laboratory investigations showed a nearly linear relationship between tidal volume and thoracic bioimpedance [13,14]. In addition, studies also suggest that tidal volumes of about 4 mL/kg or about 300 mL produce a bioimpedance waveform amplitude of about 0.5 Ω across different devices [7,18,19,22,23]. We confirmed a similar relation between a tidal volume of 300 mL measured by a ventilator and 0.5 Ω amplitude in the bioimpedance waveform recorded simultaneously by the LP12, which were the devices used by our EMS agencies at the time of our study (right panel in Fig. 1).

  • Reliability and accuracy of the thoracic impedance signal for measuring cardiopulmonary resuscitation quality metrics

    2015, Resuscitation
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    As a limitation, the volume of the ventilations was not considered in this approach. Although the guidelines recommend ventilations of 7–10 ml/kg of tidal volume, only the use of a flow monitoring system would provide such information.29,32 Our method unifies the detection of both CCs and ventilations in a single temporal method based on different preprocessing and adaptive thresholding, but common feature extraction.

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“A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2010.07.010”.

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