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Abstract
Introduction The purpose of inflations during cardiopulmonary resuscitation (CPR) is to deliver an adequate tidal volume (VT) to facilitate gas exchange. However, no study has examined VT delivery during chest compression (CC) in detail to understand the effect of CC on lung aeration. The aim of the study was to examine VT changes during CC and their effect on lung aeration.
Methods Piglets were anaesthetised, instrumented and intubated with zero leak. They were then randomly assigned to CPR using either 3:1 compression:ventilation ratio (C:V) (n=6), continuous CC with asynchronous ventilations (CCaV) (90 CC/min with 30/min asynchronous ventilations) (n=6) or continuous CC superimposed with 30 s sustained inflations (CC+SI) with a CC rate of 120/min (n=5). A respiratory function monitor (NM3, Respironics, Philips, Andover, Massachusetts, USA) was used to continuously measure inspiration tidal volume (VTi) and expirational tidal volume (VTe). ANOVA with Bonferroni post-test were used to compare variables of all three groups.
Results During the inflation in the 3:1 C:V group, the mean (SD) VTi and VTe was 23.5 (5.3) mL/kg and 19.4 (2.7) mL/kg (p=0.16), respectively. During the CC, we observed a significant VT loss in the 3:1 group with VTi and VTe being 4.1 (1.2) mL/kg and 11.1 (3.3) mL/kg (p=0.007), respectively. In the CCaV group, VTe was higher compared with VTi, but this was not significant. In the CC+SI group, a VT gain during each CC with VTi and VTe of 16.3 (3.2) mL/kg and 14 (3) mL/kg (p=0.21), respectively, was observed.
Conclusions VT delivery is improved using CC+SI compared with 3:1 C:V. This improvement in VT delivery may lead to better alveolar oxygen delivery and lung aeration.
- Resuscitation
- Neonatology
- Respiratory
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Introduction
According to the current neonatal resuscitation guidelines, chest compressions (CC) are recommended if heart rate remains <60 bpm despite adequate ventilation with supplementary oxygen for 30 s.1 Current best practice is to provide 90 CC and 30 ventilations that are coordinated during a pause.1 The purpose of inflations during CC is to deliver an adequate tidal volume (VT) to facilitate gas exchange.1 Solevåg et al2 reported an increase in expiratory VT once CC were started compared with mask ventilation alone. Roehr et al examined different auditory prompts during simulated neonatal cardiopulmonary resuscitation (CPR) using a leak-free manikin and reported higher expiratory VTs in all groups compared with baseline.3 These studies suggest a change in expiratory VT once CCs are initiated. A loss in expiratory VT could cause lung derecruitment, which could hamper oxygenation and therefore return of spontaneous circulation. However, no study has examined VT delivery during CC in detail to understand the effect of CC on lung aeration. The aim of the study was to examine changes in VT during CC and their effect on lung aeration in our porcine model of neonatal resuscitation.
Methods
This is a secondary analysis of our previously published randomised controlled animal trials.4 ,5 The original trials were conducted in accordance with the Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines and approved by the Animal Care and Use Committee (Health Sciences), University of Alberta—AUP00000237. For this secondary analysis, we included 17 newborn mixed breed piglets (1–4 days of age, weighing 1.6–2.1 kg) from the original study with respiratory function data. The piglets were instrumented according to our previously described experimental protocol of neonatal resuscitation.4 ,5 Briefly, piglets were exposed to 45 min normocapnic hypoxia, followed by an asphyxia period until heart rate decreased to 25% of baseline, which was achieved by disconnecting the ventilator and clamping the endotracheal tube. Fifteen seconds after the heart rate reached 25% of baseline, positive pressure ventilation was commenced for 30 s with a Neopuff T-Piece (Fisher & Paykel, Auckland, New Zealand). The default settings for the Neopuff were peak inflation pressure (30 cm H2O), positive end expiratory pressure (5 cm H2O) and gas flow 8 L/min. Piglets were randomly assigned to CPR using either 3:1 C:V (n=6), continuous CC with asynchronous ventilations (CCaV) (n=6) or continuous CC superimposed with sustained inflations (CC+SI) (n=5). Piglets in the 3:1 group received CPR according to the current resuscitation guidelines: 90 CC/min and 30 inflations.1 In the CCaV group, CC were continuously delivered at a rate of 90 CC/min with asynchronous ventilations at a rate of 30 inflations/min.5 ,6 In the CC+SI group, piglets received a SI with a peak inflation pressure of 30 cm H2O for the duration of 30 s, which superimposed CC at a rate of 120/min.4 SI was interrupted for 1 s every 30 s before the next SI. In all groups, CC were continued until return of spontaneous circulation, defined as heart rate increase >150/min for more than 15 s was achieved. In all piglets, CC was performed using he two-thumb encircling technique by a single operator (GMS).
Respiratory parameters
A respiratory function monitor (NM3, Respironics, Philips, Andover, Massachusetts, USA) was used to continuously measure inspiratory VT (VTi) and expiratory VT (VTe), airway pressures and gas flow. The gas flow sensor was placed between the endotracheal tube and the ventilation device. VT was calculated by integrating the flow signal.
Data collection and analysis
Demographics of study piglets were recorded. Airway pressures, gas flow, VT and exhaled CO2 (ECO2) were measured and analysed using Flow Tool Physiologic Waveform Viewer (Philips Healthcare, Wallingford, Connecticut, USA). For this study, an inflation-by-inflation analysis of respiratory parameter waveforms was performed for each inflation for the duration of CPR. The data are presented as mean±SD for normally distributed continuous variables and median (IQR) when the distribution was skewed. The data were tested for normality and compared using ANOVA with Bonferroni post-test. ANOVA with Bonferroni post-test were used to compare parametric variables of all three groups. p Values are two-sided and p<0.05 was considered statistically significant. Statistical analyses were performed with Stata (Intercooled 10, Statacorp, Texas, USA).
Results
Seventeen piglets were available for analysis. Baseline characteristics and time to return of spontaneous circulation are presented in table 1.
Characteristics at baseline and prior to commencement of cardiopulmonary resuscitation
During the ventilation in the 3:1 C:V group, the mean (SD) VTi and VTe was 23.5 (5.3) mL/kg and 19.4 (2.7) mL/kg (p=0.16), respectively (figure 1A). The first CC occurred during expiration and therefore no separate VTi and VTe could be calculated. During the second CC, we observed a VT loss with VTi and VTe being 1.5 (0.4) mL/kg and 8.1 (1.5) mL/kg (p=0.003), respectively. Similar VT losses were observed with the third CC, with VTi and VTe being 2.2 (0.4) mL/kg and 4.2 (0.7) mL/kg, (p=0.040), respectively (figure 1A). This cumulated to a total VT loss of 4.5 mL/kg for each 3:1 cycle.
Tidal volume (VT) (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.
In the CCaV group, the VTi and VTe during the inflation was 16.1 (2.4) mL/kg and 14.9 (1.6) mL/kg (p=0.69), respectively (figure 1B). During CC, the VTe was higher compared with VTi, but this did not reach statistical significance. During the second CC, VTi and VTe was 6.3 (2.9) mL/kg and 12.6 (3.4) mL/kg (p=0.19), respectively, and during the third CC, VTi and VTe was 6 (2.3) mL/kg and 10 (2.9) mL/kg (p=0.30), respectively (figure 1B). This cumulated to a total VT loss of 9.1 mL/kg for each cycle of three CC and one inflation.
In comparison, in the CC+SI group, we observed a VT gain during each CC with a VTi and VTe of 16.3 (3.2) mL/kg and 14 (3) mL/kg (p=0.21), respectively (figure 1C). ECO2 was also significantly higher in the CC+SI group (30 (11) mm Hg) compared with 3:1 (10 (4) mm Hg) or CCaV (13 (2) mm Hg) group during expiration (p<0.01) (figure 1A–C). During CC, the CC+SI group had the same ECO2 values (30 (11) mm Hg), which were always significantly higher compared with 3:1 or CCaV (p<0.01). During CC, ECO2 in the 3:1 group was (10 (4) mm Hg—first CC); (10 (4) mm Hg—second CC) and (9 (3) mm Hg—third CC) and in the CCaV group, ECO2 was (15 (2) mm Hg—first CC); (13 (2) mm Hg—second CC) and (10 (1) mm Hg—third CC).
Discussion
The results of this study can be summarised as follows: (i) with each CC a higher VTe was expired as VTi was gained (figure 1A, B). In comparison, similar inspiratory and expiratory VTs were delivered with each CC during CC+SI and CCaV (figure 1B, C). The current resuscitation guidelines recommend a C:V ratio of 3:1 with a pause after every third CC to deliver one inflation.1 The purpose of inflations during CPR is to deliver an adequate VT to facilitate gas exchange.1 Several studies examined mask leak, VT and minute ventilation during simulated neonatal CPR.2 ,3 Roehr et al3 examined different auditory prompts during simulated neonatal CPR and reported similar higher VTs in all groups compared with baseline. In addition, the figure in Roehr et al's3 article is strikingly similar to our figure 1A, suggesting that similar observations have been made in a manikin. Li et al6 reported a significant increase in mask leak once CC were initiated in a 24-week premature infant receiving CPR in the delivery room. These studies suggest a change in mask leak or VT once CCs are started. In the current study, we demonstrated that more air was forced out of the chest during 3:1 or CCaV CPR (figure 1A, B). The passive chest recoil during 3:1 only contributed to dead space ventilation (figure 1A). During CCaV, some VT was delivered, suggesting better lung ventilation and potentially better gas exchange compared with 3:1 C:V. In comparison, using CC+SI provided an adequate VT as no VT loss occurred (figure 1C). Figure 1C clearly demonstrates that when CC+SI are performed, air moves in and out of the chest and ventilation is passively achieved during CC. This is a novel finding that has not been reported previously. Our data suggest that minute ventilation, and therefore increased alveolar oxygen delivery can be achieved with improved CC techniques.
Clinical relevance
When using CC+SI, passive lung ventilation/aeration can be achieved. This is of considerable clinical relevance because newborn infants have fluid filled lungs at birth and adequate ventilation techniques are required to achieve lung aeration.7 Although 3:1 CPR delivers VT, there is a relative loss of VT per 3:1 cycle of up to 4.5 mL/kg. Using CC+SI will improve lung aeration resulting in increases in pulmonary blood flow; hence, increase in oxygenated blood flow returning from the lungs restoring cardiac function and resulting in better tissue oxygen delivery during resuscitation. This is of considerable clinical relevance because improved respiratory and haemodynamic parameters potentially minimise morbidity and mortality in newborn infants needing CC.
Limitations
All piglets were anaesthetised and sedated which differ from delivery room resuscitations. Piglets were intubated using a tightly sealed endotracheal tube to prevent any endotracheal tube leak, which allowed accurate assessment of respiratory function for the purpose of this study. During delivery room resuscitation, the loss of VT might be even higher as mask leak exacerbates. We only studied a peak inflation pressure of 30 cm H2O and a SI length of 30 s; different peak inflation pressure setting or length of an SI might yield different results and need further studies. In addition, the data present a piglet study and the impact of these findings to infants remains unknown.
Conclusion
VT delivery is improved using CC+SI compared with 3:1 C:V. This improvement in VT delivery may lead to better alveolar oxygen delivery and lung aeration. Future studies in animal models and/or during neonatal resuscitation are needed to examine techniques that minimise VT loss during CC.
Footnotes
Contributors Conception and design: GMS and P-YC. Collection and assembly of data; analysis and interpretation of the data; drafting of the article; critical revision of the article for important intellectual content and final approval of the article: GMS, ESL, MOR and P-YC.
Funding The study was supported by a grant from the Laerdal Foundation for Acute Medicine, Norway. ESL is supported in part by the Northern Alberta Clinical Trials and Research Centre Faculty of Medicine and Dentistry, University of Alberta, and Neonatal Research Fund, Northern Alberta Neonatal Program, Alberta Health Services. MOR is supported by a Fellowship of Molly Towell Perinatal Foundation. GMS is a recipient of the Heart and Stroke Foundation/University of Alberta Professorship of Neonatal Resuscitation and a Heart and Stroke Scholarship.
Competing interests Respironics (Philips, USA) provided a respiratory function monitor for the study and Fisher & Paykel (Auckland, New Zealand) provided the Neopuff T-Piece for the study. Neither company was involved in the design of the study, was present during data acquisition, data analysis, statistical analysis or interpretation of results, and both companies were not involved in writing of the manuscript.
Provenance and peer review Not commissioned; externally peer reviewed.