Respiratory Function During Chest Compressions

Abstract

Chest compression (CC) is an infrequent event (0.08%) in newborns delivered at near-term and term gestation, and occurs at a higher frequency (10%) in preterm deliveries. In addition, outcome studies of deliveries requiring resuscitation or chest compression have reported high rates of mortality and neurodevelopmental impairment in surviving children. A respiratory function monitor (RFM) can help guide a resuscitator during cardiopulmonary resuscitation (CPR) in a neonate and help assess the quality and efficacy of chest compression. Utilizing a non-invasive respiratory function monitor during chest compression may decrease high mortality rates in addition to having many distinct advantages, which will benefit both the newborn and the resuscitators. There are several different ways that a respiratory function monitor can assist a resuscitator during chest compression; these include confirming and ensuring adequate lung ventilation, analyzing the efficacy and quality of chest compression and exhaled CO2 monitoring.

1. Introduction

Fortunately, the need for chest compression (CC) or medications in the delivery room is rare. Only about 0.1% of term infants receive these interventions, resulting in approximately 1 million newborn deaths annually worldwide. In addition, chest compression or medications is more frequent in the preterm population (~15%) due to birth asphyxia [1, 2]. Fortunately, the majority of newborn infants successfully make the transition from fetal to neonatal life without any help [3]. An estimated 10% of newborns need help to establish effective ventilation (e.g., positive pressure ventilation, PPV), which remains the most critical step of neonatal resuscitation [3]. However, clinicians struggle to deliver an adequate tidal volume (V_T) [4]. In addition, mask positive pressure ventilation is often impaired by either mask leak or airway obstruction [5]. Manikin studies have further demonstrated that initiation of chest compression increases mask leak and therefore impedes effective ventilation [6, 7]. It is imperative to give optimal ventilation during chest compression to maximize efficacy [8]. Recently, a respiratory function monitor (RFM) has been described to be support the clinical team during simulated [9, 10] and real-time neonatal resuscitation [11–14]. This chapter discusses how an RFM can aid during neonatal resuscitation.

2. Respiratory function monitor

2.1. V_T, gas flow, airway pressure, and exhaled CO₂ monitor

Gas flow, V_T, airway pressure, and exhaledCO₂ (ECO₂) can be measured by any respiratory function monitor using a flow sensor placed between a ventilation device and facemask or endotracheal tube [11, 14]. Inspiratory and expiratory tidal volume passing through the sensor can be calculated by any flow sensor (e.g., fixed orifice pneumotach or a hot wire anemometer) by integrating the flow signal [11, 14]. Airway pressure is measured by directly connecting a line to the circuit, which displays peak inflation pressure and positive end expiratory pressure. Any respiratory function monitor continuously displays waves (e.g., pressure, flow, and tidal volume) and numerical values (e.g., airway pressure, tidal volume, and respiratory rate) [11, 14]. In addition, the percentage of mask leak or around a tracheal tube is calculated and displayed. ECO₂ is measured using a non-dispersive infrared absorption technique. According to manufacturers, the accuracy for gas flow is ±0.125 L/min and for ECO₂ is ±2 mmHg.

3. Mask leak

Mask ventilation studies in the delivery room have reported variable mask leak during positive pressure ventilation [4], which can be significantly decreased if mask leak is displayed on an RFM [13]. Using a manikin, Binder-Heschl et al. reported that mask leak significantly increased from 15% during positive pressure ventilation to 32% after chest compression was started [6]. This is further supported by a study by Solevåg et al. who reported that tidal volume delivery is significantly decreased using continuous chest compression with non-synchronized ventilation compared to the current 3:1 cardiopulmonary resuscitation (CPR) [7]. However, when a resuscitation used an RFM to asses mask leak, it was significantly reduced [6]. Unfortunately, the data in newborn infants are sparse and limited to a case report by Li et al. [12]. During chest compression, mask leak was 100% and did not result in an increase in heart rate, suggesting that adequate tidal volume was not delivered (Figure 1) [12].

Figure 1.

As CC is initiated in an extremely preterm infant, the traces indicate large mask leak. This results in ineffective ventilation and noV_T delivered, which could lead to failure of achieving ROSC.

4. Tidal volume

The purpose of inflations during chest compression is to deliver an adequate tidal volume to facilitate gas exchange [3]. A manikin study reported that tidal volume increases once chest compression was started compared to mask ventilation alone [7]. Interestingly, a further manikin study examined different auditory prompts during simulated neonatal cardiopulmonary resuscitation and reported higher tidal volumes in all groups compared to baseline [15]. These studies suggest a change in tidal volume once chest compressions are initiated. An increase or decrease in tidal volume could cause lung derecruitment, which could hamper oxygenation and therefore return of spontaneous circulation (ROSV) [12]. In a porcine model of neonatal resuscitation, Li et al. recently described that using the current recommendation of 3:1 chest compression to ventilation ratio (Figure 2) [3], lung derecruitment occurs [8]. The study further compared continuous chest compressions with asynchronous ventilations and found similar results [8], however, when chest compression superimposed by sustained inflation (CC + SI) (Figure 3) [16] improved tidal volume delivery and continuous lung recruitment was observed, potentially leading to better alveolar oxygen delivery and lung aeration.

Figure 2.

V_T (mL/kg) changes during 3:1 chest compression:ventilation ratio (3:1 C:V) (A), continuous chest compressions and asynchronous ventilations (CCaV) (B), and continuous chest compressions superimposed by sustained inflations (CC + SI) (C). #p < 0.05 exhaled CO₂ (ECO₂) compared with CC + SI [8] (with permission).

Figure 3.

CC superimposed by sustained inflation; adequate lung ventilation andV_T delivery are displayed: (i) adequate gas flow towards and away from the infant; (ii) averageV_T of 4 mL/kg is delivered without leak.

5. Exhaled carbon dioxide (ECO₂)

There is increasing evidence that continuous monitoring of exhaled carbon dioxide (ECO₂) can predict rise of heart rate during neonatal transition [17], monitor lung aeration at birth [11, 18–20], and predict return of spontaneous circulation during neonatal cardiopulmonary resuscitation (Figure 4) [21]. Blank et al. used a Pedi-Cap during mask positive pressure ventilation and reported a significant increase in heart rate once the Pedi-Cap turned yellow [17]. Similar results have been described in animal models and a further delivery room study [18]. During neonatal cardiopulmonary resuscitation ECO₂ is a reliable parameter to examine return of spontaneous circulation. Chalak et al. reported that an ECO₂ of 14 mmHg was the most reliable indicator for return of spontaneous circulation with 92% sensitivity and 81% specificity [21]. This study suggests that monitoring ECO₂ during cardiopulmonary resuscitation would allow uninterrupted chest compression and potentially could be an indirect indicator of the CC effectiveness. This has been further supported by a recent animal study by Li et al., suggesting that either ECO₂, rate of elimination of CO₂ (VCO₂) or partial pressure of exhaled (PeCO₂) could be used to monitor the return of spontaneous circulation [12]. A recent case report of neonatal cardiopulmonary resuscitation in an extremely preterm infant supports this hypothesis where a significant increase in ECO₂ preceded an increase in heart rate and return of spontaneous circulation [12]. ECO₂ monitoring is a non-invasive tool that can be used to predict the return of spontaneous circulation during cardiopulmonary resuscitation.

Figure 4.

Increasing ECO₂ values suggesting imminent ROSC.

5.1. Partial pressure of exhaled (PeCO₂) and rate of elimination of CO₂ (VCO₂)

A recent animal study described VCO₂ and PECO₂ values as a clinical indicator during chest compression to achieve the return of spontaneous circulation. VCO₂, or the volume of expired CO₂, reflects changes in both ventilation and perfusion, and therefore ventilation/perfusion (V/Q) matching [22]. Palme-Kilander et al. reported that low VCO₂ values could be due to residual lung fluid, very low tone, or deficient perfusion of the lungs [23]. A recent study in preterm infants reported that higher VCO₂ levels were associated with lung aeration and successful establishment of functional residual capacity [19]. During chest compression, increasing VCO₂ values reflects adequate ventilation, perfusion, and lung aeration [22]. Thus, VCO₂ potentially provides valuable information during neonatal resuscitation.

PeCO₂ is a continuous, non-invasive measurement. Since the physiological dead space/tidal volume (V_D/V_T) ratio is never zero, PeCO₂ is always lower than the ETCO₂ [22]. During resuscitation, there is poor ventilation to perfusion matching, and therefore dead space/tidal volume increases, independent of whether mismatching is either due to impaired perfusion, impaired ventilation, or a mixture of impaired perfusion and ventilation, causing lower PeCO₂ [22]. Therefore, PeCO₂ is decreased under all conditions of impaired ventilation/perfusion. In the case of ventilation mismatch, PeCO₂ is dilute relative to ETCO₂, and the PeCO₂/ETCO₂ ratio is reduced. In the case of reduced or maldistributed pulmonary blood flow without airway defects, both PeCO₂ and ETCO₂ would be reduced, resulting in a near normal PeCO₂/ETCO₂ ratio. A recent animal study described PeCO₂ for the first time in the neonatal population. Newborn piglets who successfully achieved return of spontaneous circulation had significantly higher PeCO₂ levels in the latter portion of cardiopulmonary resuscitation, indicating sufficient gas exchange was occurring [22]. Low levels of PeCO₂ can only be attributed to poor or low quality of ventilation during cardiopulmonary resuscitation, while decreased levels of both PeCO₂ and ETCO₂ may signify inadequate pulmonary perfusion due to poor circulation [22]. These findings suggest that monitoring PeCO₂ and ETCO₂ continuously during cardiopulmonary resuscitation, the clinical team would be able to determine changes in ventilation or perfusion and adjust ventilation to improve either.

6. Conclusion

Using a respiratory function monitor to assess mask leak and tidal volume delivery during neonatal cardiopulmonary resuscitation can help improve mask ventilation. In addition, using exhaled carbon dioxide can predict return of spontaneous circulation during neonatal cardiopulmonary resuscitation.

Abbreviations

CPR  cardio pulmonary resuscitation

CC   chest compression

CC+SI  continuous chest compressions with sustained inflations

ECO₂  exhaled carbon dioxide

PPV   positive pressure ventilation

ROSC  return of spontaneous circulation

V_T    tidal volume

VD/VT  physiological dead space/tidal volume

Acknowledgments

MOR is supported by a Molly Towell Perinatal Research Foundation Fellowship. ALS is supported by the Canadian Institute of Health Research (MOP299116) and the South-Eastern Norway Regional Health Authority. GMS is a recipient of the Heart and Stroke Foundation/University of Alberta Professorship of Neonatal Resuscitation and Heart and Stroke Foundation Canada Research Scholar.

Conflict of Interest: None declared by the authors.