Performance of manual ventilation: how to define its efficiency in bench studies? A review of the literature

The Role of Chest Compressions on Ventilation during Advanced Cardiopulmonary Resuscitation

Background: There is growing interest in the quality of manual ventilation during cardiopulmonary resuscitation (CPR), but accurate assessment of ventilation parameters remains a challenge. Waveform capnography is currently the reference for monitoring ventilation rate in intubated patients, but fails to provide information on tidal volumes and inspiration-expiration timing. Moreover, the capnogram is often distorted when chest compressions (CCs) are performed during ventilation compromising its reliability during CPR. Our main purpose was to characterize manual ventilation during CPR and to assess how CCs may impact on ventilation quality. Methods: Retrospective analysis were performed of CPR recordings fromtwo databases of adult patients in cardiac arrest including capnogram, compression depth, and airway flow, pressure and volume signals. Using automated signal processing techniques followed by manual revision, individual ventilations were identified and ventilation parameters were measured. Oscillations on the capnogram plateau during CCs were characterized, and its correlation with compression depth and airway volume was assessed. Finally, we identified events of reversed airflow caused by CCs and their effect on volume and capnogram waveform. Results: Ventilation rates were higher than the recommended 10 breaths/min in 66.7% of the cases. Variability in ventilation rates correlated with the variability in tidal volumes and other ventilatory parameters. Oscillations caused by CCs on capnograms were of high amplitude (median above 74%) and were associated with low pseudo-volumes (median 26 mL). Correlation between the amplitude of those oscillations with either the CCs depth or the generated passive volumes was low, with correlation coefficients of -0.24 and 0.40, respectively. During inspiration and expiration, reversed airflow events caused opposed movement of gases in 80% of ventilations. Conclusions: Our study confirmed lack of adherence between measured ventilation rates and the guideline recommendations, and a substantial dispersion in manual ventilation parameters during CPR. Oscillations on the capnogram plateau caused by CCs did not correlate with compression depth or associated small tidal volumes. CCs caused reversed flow during inspiration, expiration and in the interval between ventilations, sufficient to generate volume changes and causing oscillations on capnogram. Further research is warranted to assess the impact of these findings on ventilation quality during CPR.

Low-Grade Thermal Energy Harvesting and Self-Powered Sensing Based on Thermogalvanic Hydrogels

Thermoelectric cells (TEC) directly convert heat into electricity via the Seebeck effect. Known as one TEC, thermogalvanic hydrogels are promising for harvesting low-grade thermal energy for sustainable energy production. In recent years, research on thermogalvanic hydrogels has increased dramatically due to their capacity to continuously convert heat into electricity with or without consuming the material. Until recently, the commercial viability of thermogalvanic hydrogels was limited by their low power output and the difficulty of packaging. In this review, we summarize the advances in electrode materials, redox pairs, polymer network integration approaches, and applications of thermogalvanic hydrogels. Then, we highlight the key challenges, that is, low-cost preparation, high thermoelectric power, long-time stable operation of thermogalvanic hydrogels, and broader applications in heat harvesting and thermoelectric sensing.

Use of a novel "Split" ventilation system in bench and porcine modeling of acute respiratory distress syndrome

Split ventilation (using a single ventilator to ventilate multiple patients) is technically feasible. However, connecting two patients with acute respiratory distress syndrome (ARDS) and differing lung mechanics to a single ventilator is concerning. This study aimed to: (1) determine functionality of a split ventilation system in benchtop tests, (2) determine whether standard ventilation would be superior to split ventilation in a porcine model of ARDS and (3) assess usability of a split ventilation system with minimal specific training. The functionality of a split ventilation system was assessed using test lungs. The usability of the system was assessed in simulated clinical scenarios. The feasibility of the system to provide modified lung protective ventilation was assessed in a porcine model of ARDS (n = 30). In bench testing a split ventilation system independently ventilated two test lungs under conditions of varying compliance and resistance. In usability tests, a high proportion of naïve operators could assemble and use the system. In the porcine model, modified lung protective ventilation was feasible with split ventilation and produced similar respiratory mechanics, gas exchange and biomarkers of lung injury when compared to standard ventilation. Split ventilation can provide some elements of lung protective ventilation and is feasible in bench testing and an in vivo model of ARDS.

Using gel for difficult mask ventilation on the bearded patients: a simulation-based study

The beard is a well-known cause of difficult mask ventilation due to excessive air leaks. Various techniques have been proposed to overcome this difficulty, such as applying a gel on the mask edge. Our objective was to determine whether the gel technique will improve ventilation and to assess the comfort of the provider. A randomized crossover design was conducted to assess the efficacy of gel in a bearded simulation model. Respiratory therapists (RT) were recruited by convenience sampling to hold the mask using a two-handed technique for a two-minute ventilation session. During the session, the ventilator provided a fixed Tidal Volume (TV) of 550 mL and a respiratory rate of 12 per minute, and the simulated model measured the received volumes. We compared the median TV and number of failed ventilation attempts with or without the gel. The comfort level while using the gel was assessed with constructed questions. We recruited 74 respiratory therapists working in Riyadh city. More than half of the participants had more than 5 years experience. The median tidal volume for standard mask ventilation without the gel was 283 mL [interquartile range (IQR) 224, 327], whereas that with the gel was 467 mL [451, 478], respectively (p < 0.01). The number of successful ventilations was recorded out of 24 breaths during the 2-min ventilation period for each technique; the proportion of successful ventilations increased significantly by 65% (95% CI 51-75%, p < 0.01) with the gel. In addition, only nine participants believed the technique was not comfortable, while the remaining individuals found it comfortable or natural. In our bearded simulation model, applying the gel significantly improved ventilation without negatively affecting comfort. Further studies and education are encouraged in the field of basic airway management.

The Articulated Oral Airway as an aid to mask ventilation: a prospective, randomized, interventional, non-inferiority study

Background

Oropharyngeal airways are used both to facilitate airway patency during mask ventilation as well as conduits for flexible scope intubation, though none excel at both. A novel device, the Articulated Oral Airway (AOA), is designed to facilitate flexible scope intubation by active displacement of the tongue. Whether this active tongue displacement also facilitates mask ventilation, thus adding dual functionality, is unknown. This study compared the AOA to the Guedel Oral Airway (GOA) in regards to efficacy of mask ventilation of patients with factors predictive of difficult mask ventilation. The hypothesis was that the AOA would be non-inferior to the GOA in terms of expiratory tidal volumes by a margin of 1 ml/kg, thus demonstrating dual functionality.

Methods

In this randomized controlled clinical trial, fifty-eight patients with factors predictive of difficult mask ventilation were mask ventilated with both the GOA and the AOA. Video of the anesthetic monitors were evaluated by a blinded member of the research team, noting inspiratory and expiratory tidal volumes and expiratory CO2 waveforms.

Results

The AOA was found to be non-inferior to the GOA at a margin of 1 ml/kg with a mean weight-standardized expiratory tidal measurement 0.45 ml/kg lower (CI: 0.34–0.57) and inspiratory tidal measurement 0.109 lower (CI: − 0.26-0.04). There was no significant difference in expiratory waveforms (p = 0.2639).

Conclusions

The AOA was non-inferior to the GOA for mask ventilation of patients with predictors of difficult mask ventilation and there was no significant difference in EtCO2 waveforms between the groups. These results were consistent in the subset of patients who were initially difficult to mask ventilate.

Trial registration

ClinicalTrials.gov, NCT03144089, May 2017.

Ventilating the Bearded: A Randomized Crossover Trial Comparing a Novel Bag-Valve-Guedel Adaptor to a Standard Mask

INTRODUCTION

Emergency field ventilation using bag-valve face mask devices can be difficult to perform, especially in bearded individuals. In view of the increasing numbers of servicemen and civilians sporting a beard or moustache, the issue of finding a technical solution for ventilation in this population has gained importance. We therefore developed a novel adaptor that enables the direct connection of a bag-valve device to a Guedel-type oropharyngeal airway device thereby directly connecting the oral airway to the bag valve, eliminating the need for a face mask. The objective of this study was to compare the efficacy of the bag-valve-Guedel adaptor (BVGA) to the common face mask in healthy bearded volunteers.

METHODS

This study was a randomized-by-sequence, crossover-controlled trial (NCT02768246) approved by the local IRB (0051-16-HMO). All subjects signed an informed consent before participation. Twenty-five healthy bearded men (age 28 ± 7) were recruited. After randomization, the first group (mask then BVGA, n = 12) began breathing room air through the face mask, followed by 100% O2. After washout in room air, the procedure was repeated with the BVGA. The second group (BVGA then mask, n = 13) began with the BVGA followed by the face mask. Subjects were awake and breathed spontaneously throughout the experiment. Therefore, a Guedel was not used. Physiological and respiratory parameters were monitored continuously. The primary endpoint was the presence of suspected leak as determined by end-tidal-CO2 (EtCO2 < 20 mmHg). Secondary endpoints included tidal volume and safety.

RESULTS

The order of device use did not affect the results significantly (p > 0.05 by Mann-Whitney-U test); therefore, the data were pooled. There were no cases of suspected leak while breathing through the BVGA. By contrast, while breathing through a face mask, there were 8 of 25 (32%) and 5 of 25 (20%) cases of suspected leak in air and 100% O2, respectively (air: p = 0.002; 100% O2: p = 0.014 by McNemar test). No adverse events were observed.

CONCLUSIONS

In bearded individuals, the BVGA provides significantly more efficient (less leak) ventilation compared to a face mask. This is also of particular importance in view of the increasing number of bearded individuals serving in the armed forces. Moreover, since effective ventilation with a mask requires experience, the relatively easy-to-apply BVGA will enable less experienced first responders to achieve higher success rates in this critical phase of treatment. Further studies are planned to evaluate the efficacy of the BVGA in the prehospital setting.

Comparison of the Effectiveness and Comfort Level of Two Commonly Used Mask Ventilation Techniques in a Model

BACKGROUND

Mask ventilation is an important rescue airway skill for providing oxygenation and ventilation. Maintaining a good face mask seal is a fundamental factor for successful ventilation. Therefore, the aim of this study was to compare the effectiveness and comfortability of 2 commonly used mask ventilation techniques.

METHODS

A randomized crossover study was performed to compare the 2-handed C-E and 2-handed V-E techniques on a simulation model. Respiratory therapists were recruited by convenience sampling to hold the mask during mechanical ventilation with a fixed tidal volume (V_T) of 500 mL, a rate of 12 breaths/min and a PEEP of zero were provided. Each participant performed a 2-min ventilation session, with a total of 24 breaths for each technique. For each technique, we recorded the median V_T and the number of successful breaths (≥300 mL). Provider comfort was assessed by using a 5-point Likert scale at the end of the 2 techniques. Subgroup analyses were conducted for sex, experience, and height of the participants.

RESULTS

Of the 75 respiratory therapists recruited, 74 participants were included in the analysis. There was no statistically significant difference in the median V_T between the V-E (417 mL [interquartile range, 396-427] mL) and C-E techniques (410 [interquartile range, 391-423] mL) (P = .82). Approximately 74% of breaths delivered by the C-E technique were effective, whereas only 68% of those delivered by the V-E technique were effective (P < .001). Most of the participants reported that using the 2-handed C-E technique was more comfortable.

CONCLUSIONS

In our study, the median V_T did not differ significantly between the 2 techniques. However, the C-E technique seemed to be superior to the V-E technique in terms of the number of effectively delivered breaths and comfortability. Further studies are recommended for basic airway management techniques.

The impact of ventilation rate on end-tidal carbon dioxide level during manual cardiopulmonary resuscitation

AIM

Ventilation rate is a confounding factor for interpretation of end-tidal carbon dioxide (ETCO₂) during cardiopulmonary resuscitation (CPR). The aim of our study was to model the effect of ventilation rate on ETCO₂ during manual CPR in adult out-of-hospital cardiac arrest (OHCA).

METHODS

We conducted a retrospective analysis of OHCA monitor-defibrillator files with concurrent capnogram, compression depth, transthoracic impedance and ECG. We annotated pairs of capnogram segments presenting differences in average ventilation rate and average ETCO₂ value but with other influencing factors (e.g. compression rate and depth) presenting similar values within the pair. ETCO₂ variation as a function of ventilation rate was adjusted through curve fitting using non-linear least squares as a measure of goodness of fit.

RESULTS

A total of 141 pairs of segments from 102 patients were annotated. Each pair provided a single data point for curve fitting. The best goodness of fit yielded a coefficient of determination R² of 0.93. Our model described that ETCO₂ decays exponentially with increasing ventilation rate. The model showed no differences attributable to the airway type (endotracheal tube or supraglottic King-LT-D).

CONCLUSION

Capnogram interpretation during CPR is challenging since many factors influence ETCO₂. For adequate interpretation, we need to know the effect of each factor on ETCO₂. Our model allows quantifying the effect of ventilation rate on ETCO₂ variation. Our findings could contribute to better interpretation of ETCO₂ during CPR.

Effectiveness of a Real-Time Ventilation Feedback Device for Guiding Adequate Minute Ventilation: A Manikin Simulation Study

Background and objectives: It is often challenging even for skilled rescuers to provide adequate positive pressure ventilation consistently. This study aimed to investigate the effectiveness of a newly developed real-time ventilation feedback device (RTVFD) that estimates tidal volume (TV) and ventilation interval (VI) in real time. Materials and methods: We conducted a randomised, crossover, manikin simulation study. A total of 26 medical providers were randomly assigned to the RTVFD-assisted ventilation (RAV) first group (n = 13) and the non-assisted ventilation (NV) first group (n = 13). Participants provided ventilation using adult and paediatric bag valves (BVs) for 2 min each. After a washout period, the simulation was repeated by exchanging the participants’ groups. Results: The primary outcome was optimal TV in the RAV and NV groups using adult and paediatric BVs. A secondary outcome was optimal VI in the RAV and NV groups using adult and paediatric BVs. The proportions of optimal TV values were higher for the RAVs when using both adult and paediatric BVs (adult BV: 47.29% vs. 18.46%, p < 0.001; paediatric BV: 89.51% vs. 72.66%, p < 0.001) than for the NVs. The proportions of optimal VI were significantly higher in RAVs when using both adult and paediatric BVs than that in NVs (adult BV: 95.64% vs. 50.20%, p < 0.001; paediatric BV: 95.83% vs. 57.14%, p < 0.001). Additionally, we found that with paediatric BVs, the simulation had a higher OR for both optimal TV (13.26; 95% CI, 9.96–17.65; p < 0.001) and VI (1.32; 1.08–1.62, p = 0.007), regardless of RTVFD use. Conclusion: Real-time feedback using RTVFD significantly improves the TV and VI in both adult and paediatric BVs in a manikin simulation study.

The effect of neuromuscular blockade on the efficiency of facemask ventilation in patients difficult to facemask ventilate: a prospective trial

Facemask ventilation of the lungs can be an important rescue intervention in a 'cannot intubate' scenario. We assessed the effect of neuromuscular blockade on expiratory tidal volumes in patients with expected difficulty in mask ventilation. The lungs of patients with at least three predictors of difficulty in mask ventilation were ventilated using a facemask held with two hands, with mechanical ventilation set in a pressure-controlled mode. Tidal volumes were recorded before and after the establishment of complete neuromuscular block. In 113 patients, median (IQR [range]) tidal volume increased from 350 (260-492 [80-850]) ml initially, by 48% to 517 (373-667 [100-1250]) ml 30 s after rocuronium administration, (p < 0.001). After the onset of the complete neuromuscular block, a median tidal volume of 600 (433-750 [250-1303]) ml was observed, corresponding to an increase of 71% from baseline values (p < 0.001), and 16% from values obtained 30 s after rocuronium administration, respectively; p = 0.003). No decrease in the tidal volume during the measurements was observed. We conclude that the administration of rocuronium at a dose of 0.6 mg.kg^-1 was able to improve facemask ventilation in all cases with a potentially clinically relevant increase in tidal volume. The early use of a neuromuscular blocking agent can be considered as a therapeutic option in case of difficulty with mask ventilation.

Real-time tidal volume feedback guides optimal ventilation during simulated CPR

PURPOSE

We performed this study to investigate whether real-time tidal volume feedback increases optimal ventilation and decreases hyperventilation during manikin-simulated cardiopulmonary resuscitation (CPR).

BASIC PROCEDURES

We developed a new real-time tidal volume monitoring device (TVD) which estimated tidal volume in real time using a magnetic flowmeter. The TVD was validated with a volume-controlled mechanical ventilator with various tidal volumes. We conducted a randomized, crossover, manikin-simulation study in which 14 participants were randomly divided into a control (without tidal volume feedback, n = 7) and a TVD group (with real-time tidal volume feedback, n = 7) and underwent manikin simulation. The optimal ventilation was defined as 420-490 mL of tidal volumes for a 70-kg adult manikin. After 2 weeks of the washout period, the simulation was repeated via the participants' crossover.

MAIN FINDINGS

In the validation study, 97.6% and 100% of the difference ratios in tidal volumes between the mechanical ventilator and TVD were within ±1.5% and ±2.5%, respectively. During manikin-simulated CPR, TVD use increased the proportion of optimal ventilation per person. Its median values (range) of the control group and the TVD group were 37.5% (0.0-65.0) and 87.5% (65.0-100.0), respectively, P < .001). TVD use also decreased hyperventilation. The proportions of hyperventilation in the control group and the TVD group were 25.0% vs 8.9%, respectively (P < .001).

PRINCIPAL CONCLUSIONS

Real-time tidal volume feedback using the new TVD guided the rescuers to provide optimal ventilation and to avoid hyperventilation during manikin-simulated CPR.

Evaluation of Bag-Valve-Mask Ventilation in Manikin Studies: What Are the Current Limitations?

Introduction. Manikin-based studies for evaluation of ventilation performance show high heterogeneity in the analysis and experimental methods used as we pointed out in previous studies. In this work, we aim to evaluate these potential limitations and propose a new analysis methodology to reliably assess ventilation performance. Methods. One hundred forty healthcare providers were selected to ventilate a manikin with two adult self-inflating bags in random order. Ventilation parameters were analysed using different published analysis methods compared to ours. Results. Using different methods impacts the evaluation of ventilation efficiency which ranges from 0% to 45.71%. Our new method proved relevant and showed that all professionals tend to cause hyperventilation and revealed a significant relationship between professional category, grip strength of the hand keeping the mask, and ventilation performance (p = 0.0049 and p = 0.0297, resp.). Conclusion. Using adequate analysis methods is crucial to avoid many biases. Extrapolations to humans still have to be taken with caution as many factors impact the evaluation of ventilation performance. Healthcare professionals tend to cause hyperventilation with current devices. We believe this problem could be prevented by implementing monitoring tools in order to give direct feedback to healthcare professionals regarding ventilation efficiency and ventilatory parameter values.