Smaller tidal volumes with room-air are not sufficient to ensure adequate oxygenation during bag-valve-mask ventilation

Emergency medicine updates: Cardiac arrest airway management

INTRODUCTION

Cardiac arrest is the loss of systemic circulation. The approach to airway management is an important component of the resuscitation of patients in cardiac arrest.

OBJECTIVE

This paper evaluates key evidence-based updates concerning airway management in cardiac arrest.

DISCUSSION

Management of cardiac arrest focuses on cardiopulmonary resuscitation (CPR), including high-quality chest compressions and ventilation. Resuscitation should prioritize circulation with high-quality compressions, but as the resuscitation continues, airway management is necessary to provide ventilation. During initial CPR efforts, a compression to ventilation ratio of 30:2 is recommended. Bag-valve-mask (BVM) ventilation is an effective means of ventilation during CPR efforts, though providers should ensure appropriate mask seal with a two-person BVM strategy (one person holding the mask and one person ventilating) if possible. Breaths should be provided over less than 1 s with enough tidal volume to cause chest rise. Advanced airways include a supraglottic airway (SGA) or endotracheal tube via endotracheal intubation (ETI). If an advanced airway is present, one asynchronous ventilation should be provided every 8-10 s. An advanced airway may be considered with an asphyxial cause of arrest, those with prolonged arrest or transport, and cases managed with limited numbers of experienced personnel, though compressions must not be interrupted for placement of an advanced airway. An SGA is a viable option for an advanced airway. In settings with high ETI success rate, ETI may be performed, but in other settings SGA is recommended. If performing ETI, video laryngoscopy is associated with an improved view of the glottis and higher first pass success compared to direct laryngoscopy. Cricoid pressure is not recommended. Confirmation of ETI is necessary. Following ETI and return of spontaneous circulation, a lung protective strategy of ventilation is recommended while avoiding hypoxia.

CONCLUSIONS

An understanding of literature updates regarding airway management can improve the ED care of patients in cardiac arrest.

Ventilation during cardiopulmonary resuscitation: A narrative review

Ventilation during cardiopulmonary resuscitation is vital to achieve optimal oxygenation but continues to be a subject of ongoing debate. This narrative review aims to provide an overview of various components and challenges of ventilation during cardiopulmonary resuscitation, highlighting key areas of uncertainty in the current understanding of ventilation management. It addresses the pulmonary pathophysiology during cardiac arrest, the importance of adequate alveolar ventilation, recommendations concerning the maintenance of airway patency, tidal volumes and ventilation rates in both synchronous and asynchronous ventilation. Additionally, it discusses ventilation adjuncts such as the impedance threshold device, the role of positive end-expiratory pressure ventilation, and passive oxygenation. Finally, this review offers directions for future research.

Automatic Mechanical Ventilation vs Manual Bag Ventilation During CPR: A Pilot Randomized Controlled Trial

BACKGROUND

There is insufficient evidence supporting the theory that mechanical ventilation can replace the manual ventilation method during CPR.

RESEARCH QUESTION

Is using automatic mechanical ventilation (MV) feasible and comparable to the manual ventilation method during CPR?

STUDY DESIGN AND METHODS

This pilot randomized controlled trial compared MV and manual bag ventilation (BV) during CPR after out-of-hospital cardiac arrest (OHCA). Patients with medical OHCA arriving at the ED were randomly assigned to two groups: an MV group using a mechanical ventilator and a BV group using a bag valve mask. Primary outcome was any return of spontaneous circulation (ROSC). Secondary outcomes were changes of arterial blood gas analysis results during CPR. Tidal volume, minute volume, and peak airway pressure were also analyzed.

RESULTS

A total of 60 patients were enrolled, and 30 patients were randomly assigned to each group. There were no statistically significant differences in basic characteristics of OHCA patients between the two groups. The rate of any return of spontaneous circulation was 56.7% in the MV group and 43.3% in the BV group, indicating no significant (P = .439) difference between the two groups. There were also no statistically significant differences in changes of PH, Pco2, Po2, bicarbonate, or lactate levels during CPR between the two groups (P values = .798, 0.249, .515, .876, and .878, respectively). Significantly lower tidal volume (P < .001) and minute volume (P = .009) were observed in the MV group.

INTERPRETATION

In this pilot trial, the use of MV instead of BV during CPR was feasible and could serve as a viable alternative. A multicenter randomized controlled trial is needed to create sufficient evidence for ventilation guidelines during CPR.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; No.: NCT05550454; URL: www.

CLINICALTRIALS

gov.

Cardiopulmonary Resuscitation: The Importance of the Basics

Cardiac arrest is the loss of organized cardiac activity. Unfortunately, survival to hospital discharge is poor, despite recent scientific advances. The goals of cardiopulmonary resuscitation (CPR) are to restore circulation and identify and correct an underlying etiology. High-quality compressions remain the foundation of CPR, optimizing coronary and cerebral perfusion pressure. High-quality compressions must be performed at the appropriate rate and depth. Interruptions in compressions are detrimental to management. Mechanical compression devices are not associated with improved outcomes but can assist in several situations.

Airway Management of the Cardiac Arrest Victim

Appropriate airway management is critical to successful cardiac arrest resuscitation. However, the timing and method of airway management during cardiac arrest have traditionally been guided by expert and consensus opinion informed by observational data. In the last 5 years, recent studies, including several randomized controlled trials (RCTs), have provided additional clarity to help guide airway management. This article will review both current data and guidelines for airway management in cardiac arrest, a stepwise approach to airway management, the utility of various airway adjuncts, and best practices for oxygenation and ventilation in the peri-arrest period.

Effect of Early Supraglottic Airway Device Insertion on Chest Compression Fraction during Simulated Out-of-Hospital Cardiac Arrest: Randomised Controlled Trial

Early insertion of a supraglottic airway (SGA) device could improve chest compression fraction by allowing providers to perform continuous chest compressions or by shortening the interruptions needed to deliver ventilations. SGA devices do not require the same expertise as endotracheal intubation. This study aimed to determine whether the immediate insertion of an i-gel^® while providing continuous chest compressions with asynchronous ventilations could generate higher CCFs than the standard 30:2 approach using a face-mask in a simulation of out-of-hospital cardiac arrest. A multicentre, parallel, randomised, superiority, simulation study was carried out. The primary outcome was the difference in CCF during the first two minutes of resuscitation. Overall and per-cycle CCF quality of compressions and ventilations parameters were also compared. Among thirteen teams of two participants, the early insertion of an i-gel^® resulted in higher CCFs during the first two minutes (89.0% vs. 83.6%, p = 0.001). Overall and per-cycle CCF were consistently higher in the i-gel^® group, even after the 30:2 alternation had been resumed. In the i-gel^® group, ventilation parameters were enhanced, but compressions were significantly shallower (4.6 cm vs. 5.2 cm, p = 0.007). This latter issue must be addressed before clinical trials can be considered.

Tidal volume measurements via transthoracic impedance waveform characteristics: The effect of age, body mass index and gender. A single centre interventional study

BACKGROUND AND AIM

Measuring tidal volumes (TV) during bag-valve ventilation is challenging in the clinical setting. The ventilation waveform amplitude of the transthoracic impedance (TTI-amplitude) correlates well with TV for an individual, but poorer between patients. We hypothesized that TV to TTI-amplitude relations could be improved when adjusted for morphometric variables like body mass index (BMI), gender or age, and that TTI-amplitude cut-offs for ventilations with adequate TV (>400ml) could be established.

MATERIALS AND METHODS

Twenty-one consenting adults (9 female, and 9 overall overweight) during positive pressure ventilation in anaesthesia before scheduled surgery were included. Seventeen ventilator modes were used (⩾ five breaths per mode) to adjust different TVs (150-800 ml), ventilation frequencies (10-30 min^-1) and insufflation times (0.5-3.5 s). TTI from the defibrillation pads was filtered to obtain ventilation TTI-amplitudes. Linear regression models were fitted between target and explanatory variables, and compared (coefficient of determination, R²).

RESULTS

The TV to TTI-amplitude slope was 1.39 Ω/l (R²=0.52), with significant differences (p<0.05) between male/female (1.04 Ω/l vs 1.84 Ω/l) and normal/overweight subjects (1.65 Ω/l vs 1.04 Ω/l). The median (interquartile range) TTI-amplitude cut-off for adequate TV was 0.51 Ω(0.14-1.20) with significant differences between males and females (0.58 Ω/0.39 Ω), and normal and overweight subjects (0.52 Ω/0.46 Ω). The TV to TTI-amplitude model improved (R²=0.66) when BMI, age and gender were included.

CONCLUSIONS

TTI-amplitude to TV relations were established and cut-offs for ventilations with adequate TV determined. Patient morphometric variables related to gender, age and BMI explain part of the variability in the measurements.

Effect on Chest Compression Fraction of Continuous Manual Compressions with Asynchronous Ventilations Using an i-gel® versus 30:2 Approach during Simulated Out-of-Hospital Cardiac Arrest: Protocol for a Manikin Multicenter Randomized Controlled Trial

The optimal airway management strategy during cardiopulmonary resuscitation is uncertain. In the case of out-of-hospital cardiac arrest, a high chest compression fraction is paramount to obtain the return of spontaneous circulation and improve survival and neurological outcomes. To improve this fraction, providing continuous chest compressions should be more effective than using the conventional 30:2 ratio. Airway management should, however, be adapted, since face-mask ventilation can hardly be carried out while continuous compressions are administered. The early insertion of a supraglottic device could therefore improve the chest compression fraction by allowing ventilation while maintaining compressions. This is a protocol for a multicenter, parallel, randomized simulation study. Depending on randomization, each team made up of paramedics and emergency medical technicians will manage the 10-min scenario according either to the standard approach (30 compressions with two face-mask ventilations) or to the experimental approach (continuous manual compressions with early insertion of an i-gel® supraglottic device to deliver asynchronous ventilations). The primary outcome will be the chest compression fraction during the first two minutes of cardiopulmonary resuscitation. Secondary outcomes will be chest compression fraction (per cycle and overall), compressions and ventilations quality, time to first shock and to first ventilation, user satisfaction, and providers' self-assessed cognitive load.

A review of ventilation in adult out-of-hospital cardiac arrest

Out-of-hospital cardiac arrest continues to be a devastating condition despite advances in resuscitation care. Ensuring effective gas exchange must be weighed against the negative impact hyperventilation can have on cardiac physiology and survival. The goals of this narrative review are to evaluate the available evidence regarding the role of ventilation in out-of-hospital cardiac arrest resuscitation and to provide recommendations for future directions. Ensuring successful airway patency is fundamental for effective ventilation. The airway management approach should be based on professional skill level and the situation faced by rescuers. Evidence has explored the influence of different ventilation rates, tidal volumes, and strategies during out-of-hospital cardiac arrest; however, other modifiable factors affecting out-of-hospital cardiac arrest ventilation have limited supporting data. Researchers have begun to explore the impact of ventilation in adult out-of-hospital cardiac arrest outcomes, further stressing its importance in cardiac arrest resuscitation management. Capnography and thoracic impedance signals are used to measure ventilation rate, although these strategies have limitations. Existing technology fails to reliably measure real-time clinical ventilation data, thereby limiting the ability to investigate optimal ventilation management. An essential step in advancing cardiac arrest care will be to develop techniques to accurately and reliably measure ventilation parameters. These devices should allow for immediate feedback for out-of-hospital practitioners, in a similar way to chest compression feedback. Once developed, new strategies can be established to guide out-of-hospital personnel on optimal ventilation practices.

Comparing Surf Lifeguards and Nurse Anesthetists' Use of the i-gel Supraglottic Airway Device - An Observational Simulation Study

Purpose

Using a supraglottic airway (SGA) may provide more effective ventilations compared with a mouth-to-pocket-mask for drowning victims. SGAs are widely used by nurse anesthetists but it is unknown whether surf lifeguards can use SGAs effectively. We aimed to compare the use of SGA by surf lifeguards and experienced nurse anesthetists.

Materials and Methods

Surf lifeguards inserted a SGA (i-gel O₂, size 4) in a resuscitation manikin during cardiopulmonary resuscitation (CPR) and nurse anesthetists inserted a SGA in a resuscitation manikin placed on a bed, and performed ventilations. Outcome measures: time to first ventilation, tidal volume, proportion of ventilations with visible manikin chest rise, and ventilations within the recommended tidal volume (0.5–0.6 L).

Results

Overall, 30 surf lifeguards and 30 nurse anesthetists participated. Median (Q1–Q3) time to first ventilation was 20 s (15–22) for surf lifeguards and 17 s (15–21) for nurse anesthetists (p=0.31). Mean (SD) tidal volume was 0.55 L (0.21) for surf lifeguards and 0.31 L (0.10) for nurse anesthetists (p<0.0001). Surf lifeguards and nurse anesthetists delivered 100% and 95% ventilations with visible manikin chest rise (p=0.004) and 19% and 5% ventilations within the recommended tidal volume, respectively (p<0.0001).

Conclusion

In a simulated setting, there was no significant difference between surf lifeguards and experienced nurse anesthetists in time to first ventilation when using a SGA. Surf lifeguards delivered a higher tidal volume, and a higher proportion of ventilations within guideline recommendations, but generally ventilations caused visible manikin chest rise for both groups.

Effect of tidal volume on gas exchange during rescue ventilation

Tidal volume V_T required for mouth-to-mouth (MTM) and bag-valve-mask (BVM) rescue ventilation remains debatable owing to differences in physiology and end-point objectives. Analysis of gas transport may clarify minimum necessary V_T and its determinants. Alveolar and arterial O₂ and CO₂ responses to MTM and air BVM ventilation for V_T between 0.4 and 1.2 liters were computed using a model of gas exchange that incorporates inspired gas concentrations, airway dead space, cardiac output, pulmonary shunt, blood gas dissociation curves, tissue compartments, and metabolic rate. Parameters were adjusted to match published human data. Steady state arterial oxygen saturation reached plateaus at V_T above 0.7 liters with MTM and 0.6 liters with air ventilation at 12 breaths per minute. Increasing shunt shifted oxygenation plateaus downward, but larger tidal volumes did not improve oxygen saturation. Carbon dioxide retention occurred at V_T below 2.3 liters for MTM ventilation and 0.6 liters for air ventilation. Results establish a physiological foundation for tidal volume requirements during resuscitation.

Can EMS Providers Provide Appropriate Tidal Volumes in a Simulated Adult-sized Patient with a Pediatric-sized Bag-Valve-Mask?

INTRODUCTION

In the prehospital setting, Emergency Medical Services (EMS) professionals rely on providing positive pressure ventilation with a bag-valve-mask (BVM). Multiple emergency medicine and critical care studies have shown that lung-protective ventilation protocols reduce morbidity and mortality. Our primary objective was to determine if a group of EMS professionals could provide ventilations with a smaller BVM that would be sufficient to ventilate patients. Secondary objectives included 1) if the pediatric bag provided volumes similar to lung-protective ventilation in the hospital setting and 2) compare volumes provided to the patient depending on the type of airway (mask, King tube, and intubation).

METHODS

Using a patient simulator of a head and thorax that was able to record respiratory rate, tidal volume, peak pressure, and minute volume via a laptop computer, participants were asked to ventilate the simulator during six 1-minute ventilation tests. The first scenario was BVM ventilation with an oropharyngeal airway in place ventilating with both an adult- and pediatric-sized BVM, the second scenario had a supraglottic airway and both bags, and the third scenario had an endotracheal tube and both bags. Participants were enrolled in convenience manner while they were on-duty and the research staff was able to travel to their stations. Prior to enrolling, participants were not given any additional training on ventilation skills.

RESULTS

We enrolled 50 providers from a large, busy, urban fire-based EMS agency with 14.96 (SD = 9.92) mean years of experience. Only 1.5% of all breaths delivered with the pediatric BVM during the ventilation scenarios were below the recommended tidal volume. A greater percentage of breaths delivered in the recommended range occurred when the pediatric BVM was used (17.5% vs 5.1%, p < 0.001). Median volumes for each scenario were 570.5mL, 664.0mL, 663.0mL for the pediatric BMV and 796.0mL, 994.5mL, 981.5mL for the adult BVM. In all three categories of airway devices, the pediatric BVM provided lower median tidal volumes (p < 0.001).

CONCLUSION

The study suggests that ventilating an adult patient is possible with a smaller, pediatric-sized BVM. The tidal volumes recorded with the pediatric BVM were more consistent with lung-protective ventilation volumes.

Effectiveness and safety of in-water resuscitation performed by lifeguards and laypersons: a crossover manikin study

OBJECTIVE

Drowning is associated with a high mortality and morbidity and a common cause of death. In-water resuscitation (IWR) in the case of drowning accidents has been recommended by certain resuscitation guidelines in the last several years. IWR has been discussed controversially in the past, especially with regard to the delay of chest compressions, effectiveness of ventilation, and hazard to the rescuer. The aim of the present study was to assess the effectiveness and safety of IWR.

METHODS

In this crossover manikin study, 21 lifeguards and 21 laypersons performed two rescue procedures in an indoor swimming pool over a 50-meter distance: In random order, one rescue procedure was performed with in-water ventilation and one without. Tidal and minute volumes were recorded using a modified Laerdal Resusci Anne (Laerdal Medical, Stavanger, Norway) and total rescue duration, submersions, water aspiration by the victim, and physical effort were assessed.

RESULTS

IWR resulted in significant increases in rescue duration (lifeguards: 106 vs. 82 seconds; laypersons: 133 vs. 106 seconds) and submersions (lifeguards: 3 vs. 1; laypersons: 5 vs. 0). Furthermore, water aspiration (lifeguards: 112 vs. 29 mL; laypersons: 160 vs. 56 mL) and physical effort (lifeguards: visual analog scale [VAS] score 7 vs. 5; laypersons: VAS score 8 vs. 6) increased significantly when IWR was performed. Lifeguards achieved significantly better ventilation characteristics and performed both rescue procedures faster and with lower side effects. IWR performed by laypersons was insufficient with regard to both tidal and minute volumes.

CONCLUSIONS

In-water resuscitation is associated with a delay of the rescue procedure and a relevant aspiration of water by the victim. IWR appears to be possible when performed over a short distance by well-trained professionals. The training of lifeguards must place particular emphasis on a reduction of submersions and aspiration when IWR is performed. IWR by laypersons is exhausting, time-consuming, and inefficient and should probably not be recommended. Key words: drowning; near-drowning; hypoxia; ventilation, artificial; respiration, artificial; resuscitation, in-water.

Duration of Ventilations During Cardiopulmonary Resuscitation by Lay Rescuers and First Responders

Background—

The 2010 guidelines for cardiopulmonary resuscitation allow 5 seconds to give 2 breaths to deliver sufficient chest compressions and to keep perfusion pressure high. This study aims to determine whether the recommended short interruption for ventilations by trained lay rescuers and first responders can be achieved and to evaluate its consequence for chest compressions and survival.

Methods and Results—

From a prospective data collection of out-of-hospital cardiac arrest, we used automatic external defibrillator recordings of cardiopulmonary resuscitation by rescuers who had received a standard European Resuscitation Council basic life support and automatic external defibrillator course. Ventilation periods and total compressions delivered per minute during each 2 minutes of cardiopulmonary resuscitation cycle were measured, and the chest compression fraction was calculated. Neurological intact survival to discharge was studied in relation to these factors and covariates. We included 199 automatic external defibrillator recordings. The median interruption time for 2 ventilations was 7 seconds (25th–75th percentile, 6–9 seconds). Of all rescuers, 21% took <5 seconds and 83% took <10 seconds for a ventilation period; 97%, 88%, and 63% of rescuers were able to deliver >60, >70, and >80 chest compressions per minute, respectively. The median chest compression fraction was 65% (25th–75th percentile, 59%–71%). Survival was 25% (49 of 199), not associated with long or short ventilation pauses when controlled for covariates.

Conclusions—

The great majority of rescuers can give 2 rescue breaths in <10 seconds and deliver at least 70 compressions in a minute. Longer pauses for ventilations are not associated with worse outcome. Guidelines may allow longer pauses for ventilations with no detriment to survival.

Efficacy of ventilation and ventilation adjuncts during in-water-resuscitation--a randomized cross-over trial

INTRODUCTION

Drowning is a common cause of death in young adults. The 2010 guidelines of the European Resuscitation Council call for in-water-resuscitation (IWR). There has been controversy about IWR amongst emergency and diving physicians for decades. The aim of the present study was assessing the efficacy of IWR.

METHODS

In this randomized cross-over trial, nineteen lifeguards performed a rescue manoeuvre over a 100 m distance in open water. All subjects performed the procedure four times in random order: with no ventilation (NV) and transportation only, mouth-to-mouth ventilation (MMV), bag-mask-ventilation (BMV) and laryngeal tube ventilation (LTV). Tidal volumes, ventilation rate and minute-volumes were recorded using a modified Laerdal Resusci Anne manikin. Furthermore, water aspiration and number of submersions of the test mannequin were assessed, as well as the physical effort of the lifeguard rescuers.One lifeguard subject did not complete MMV due to exhaustion and was excluded from analysis.

RESULTS

NV was the fastest rescue manoeuvre (advantage ∼40s). MMV and LTV were evaluated as efficient and relatively easy to perform by the lifeguards. While MMV (mean 199 ml) and BMV (mean 481 ml) were associated with a large amount of aspirated water, aspiration was significantly lower in LTV (mean 118 ml). The efficacy of ventilation was consistently good in LTV (Vt=447 ml), continuously poor in BMV (Vt=197) and declined substantially during MMV (Vt=1,019 ml initially and Vt=786 ml at the end). The physical effort of the lifeguards was remarkably higher when performing IWR: 3.7 in NV, 6.7 in MMV, 6.4 in BMV and 4.8 in LTV as measured on the 0-10 visual analogue scale.

CONCLUSION

IWR in open water is time consuming and physically demanding. The IWR training of lifeguards should put more emphasis on a reduction of aspiration. The use of ventilation adjuncts like the laryngeal tube might ease IWR, reduce aspiration of water and increase the efficacy of ventilation during IWR.

Update on cardiopulmonary resuscitation guidelines of interest to anesthesiologists

BACKGROUND AND OBJECTIVES

The new cardiopulmonary resuscitation (CPR) guidelines emphasize the importance of high-quality chest compressions and modify some routines. The objective of this report was to review the main changes in resuscitation practiced by anesthesiologists.

CONTENTS

The emphasis on high-quality chest compressions with adequate rate and depth allowing full recoil of the chest and with minimal interruptions is highlighted in this update. One should not take more than ten seconds checking the pulse before starting CPR. The universal relationship of 30:2 is maintained, modifying its order, initiating with chest compressions, followed by airways and breathing (C-A-B instead of A-B-C). The procedure "look, listen, and feel whether the patient is breathing" was removed from the algorithm, and the use of cricoid pressure during ventilations is not recommended any more. The rate of chest compressions was changed for at least one hundred per minute instead of approximately one hundred per minute, and its depth in adults was changed to 5 cm instead of the prior recommendation of 4 to 5 cm. The single shock is maintained, and it should be of 120 to 200 J when it is biphasic; and 360 J when it is monophasic. In advanced cardiac life support, the use of capnography and capnometry to confirm intubation and monitoring the quality of CPR is a formal recommendation. Atropine is no longer recommended for routine use in the treatment of pulseless electrical activity or asystole.

CONCLUSIONS

Updating the phases of the new CPR guidelines is important, and continuous learning is recommended. This will improve the quality of resuscitation and survival of patients in cardiac arrest.

Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

The goal of therapy for bradycardia or tachycardia is to rapidly identify and treat patients who are hemodynamically unstable or symptomatic due to the arrhythmia. Drugs or, when appropriate, pacing may be used to control unstable or symptomatic bradycardia. Cardioversion or drugs or both may be used to control unstable or symptomatic tachycardia. ACLS providers should closely monitor stable patients pending expert consultation and should be prepared to aggressively treat those with evidence of decompensation.

Comparison of three modes of positive pressure mask ventilation during induction of anaesthesia: a prospective, randomized, crossover study

BACKGROUND

Mask ventilation of apnoeic patients may be associated with alveolar hypoventilation, hyperventilation and gastric insufflation, which may be affected by the mode of ventilation during induction of anaesthesia. This study is to compare the effect of three modes of positive pressure mask ventilation during induction of anaesthesia regarding ventilatory variables and gastric insufflation.

METHODS

Ninety (90) patients, ASA I-II were included in this prospective, randomized, crossover study. Patients were divided into three groups of different sequence of modes of ventilation. Each patient was ventilated with pressure-controlled ventilation (PCV), manual-controlled ventilation (MCV), and volume-controlled ventilation (VCV) during the induction of anaesthesia. Respiratory and haemodynamic variables were monitored. Gastric insufflation was detected with a stethoscope applied to epigastric area.

RESULTS

Haemodynamic variables showed no significant differences between the three modes of ventilation. PCV was associated with lower peak airway pressures (11.4 +/- 1.2 cmH2O) compared with MCV and VCV (14.3 +/- 1.7 and 13.3 +/- 1.5 cmH2O; respectively P < 0.0001). Inspiratory and expiratory tidal volumes showed no significant differences between the three modes. Gastric insufflation was detected in one patient (1.1%) in the PCV group compared to three patients (3.3%) in the MCV group and three patients (3.3%) in the VCV group.

CONCLUSION

We concluded that in this model of apnoeic patients with an unprotected airway, PCV was associated with lower peak airway pressure which may provide additional patient safety.

Predictors of Intubation Success andTherapeutic Value of Paramedic Airway Management in a Large, Urban EMS System

BACKGROUND

Endotracheal intubation (ETI) is commonly used by paramedics for definitive airway management. The predictors of success and therapeutic value with regard to oxygenation are not well studied.

OBJECTIVES

1) To explore the relationship between intubation success and perfusion status, Glasgow Coma Scale (GCS) score, and end-tidal carbon dioxide (EtCO2); 2) to describe the incidence of unrecognized esophageal intubations with use of continuous capnometry; and 3) to document the incremental benefit of invasive versus noninvasive airway management techniques in correcting hypoxemia.

METHODS

This was a prospective, observational study conducted in a large urban emergency medical services system. Paramedics completed a telephone debriefing interview with quality assurance personnel following delivery of all patients in whom invasive airway management had been attempted. Continuous capnometry was used for confirmation of tube position in all patients. Descriptive statistics were used to document airway management performance, including first-attempt ETI success, overall ETI success, and Combitube insertion (CTI) success. In addition, the incidence of unrecognized esophageal intubation was recorded. The relationship between intubation success and perfusion status, GCS score, and initial EtCO2 value was explored using logistic regression. Finally, recorded SpO2 values and the incidence of hypoxemia (SpO2 < 90%) at baseline, following noninvasive airway maneuvers, and after invasive airway management were compared for perfusing patients.

RESULTS

A total of 703 patients were enrolled over 12 months. First-attempt ETI success was 61%, and overall ETI success was 81%; invasive airway management (ETI or CTI) was unsuccessful in 11% of patients. A single unrecognized esophageal intubation was observed (0.1%). A clear relationship between airway management success and perfusion status, GCS score, and initial EtCO2 value was observed. Only EtCO2 demonstrated an independent association with ETI success after adjusting for the other variables. Significant improvements in mean SpO2 and the incidence of hypoxemia over baseline were observed with both noninvasive and invasive airway management techniques in 168 perfusing patients.

CONCLUSIONS

A relationship between intubation success and perfusion status, GCS score, and initial EtCO2 value was observed. Capnometry was effective in eliminating unrecognized esophageal intubations. Both noninvasive and invasive airway management strategies were effective in increasing SpO2 values and decreasing the incidence of hypoxemia, with additional benefit observed with invasive airway maneuvers in some patients.

Comparison of ventilation and chest compression performance by bystanders using the Impact Model 730 ventilator and a conventional bag valve with mask in a model of adult cardiopulmonary arrest

"Bystanders" or lay persons are typically the first caregivers to attend to a victim of out-of-hospital cardiopulmonary arrest. Astronaut crew medical officers (CMO) play a similar role to bystanders aboard the International Space Station (ISS). Studies have demonstrated the importance of bystander cardiopulmonary resuscitation (BCPR) for patient survival before the arrival of emergency medical care. Recent apprehension from bystanders about the threat of contracting communicable diseases during BCPR, however, has led to the consideration of other ventilation systems such as the bag-valve mask (BVM) and automatic transport ventilators (ATV). BVM use is called for during CPR aboard the ISS. This study evaluated the ventilation and compression performance of 40 basic CPR-trained bystanders using either a BVM (adult-sized self-inflating bag with face mask) or an ATV (Model 730 ventilator (M730), Impact Instrumentation, Inc., West Caldwell, NJ). Each two-bystander team gave BCPR to a simulated cardiopulmonary arrest victim using the 2-breath/15-compression cycle for 4 min and then switched roles for another 4-min interval. Compared to BVM use, the M730 led to significantly (p<0.05) lower number of breaths, smaller tidal volumes, airway flows, airway pressures, volume of gas entering the stomach per breath and chest compressions for the 4-min period. The M730 also enabled a bystander to meet the recommendation of 4-breath and compression cycles per minute as per Guidelines 2000. Lastly, ease-of-use scores were significantly higher for the M730 compared to the BVM. Overall, the data suggest that the M730 improves the quality of performance for a bystander performing BCPR.

Acute management of sudden cardiac death in adults based upon the new CPR guidelines

PURPOSE OF THE REVIEW

The aim of this article is to provide a comprehensive description of interventions that can improve outcomes in adults with sudden cardiac death. The new American Heart Association 2005 Guidelines introduced a number of changes for the initial management of cardiorespiratory arrest based on new data that accumulated over the last 5 years.

ACUTE MANAGEMENT OF SUDDEN CARDIAC DEATH

Appropriate interventions targeting the three phases of cardiopulmonary resuscitation (CPR) (electrical, circulatory, and metabolic) should be implemented. Early defibrillation in early witnessed arrest with one shock is very effective and can improve survival outcomes. When resuscitation efforts are delayed and CPR is performed by paramedics, 2 min of CPR before shock is recommended. Emphasis has been placed on fast and forceful continuous compressions with minimal interruptions, adequate decompression, and decrease in the rate of ventilations to 8-10/min for intubated patients with two rescuers and a universal increase in compression to ventilation ratio to 30:2 for lone rescuers. Mechanical adjuncts to improve circulation have been adapted in the recommendations. The inspiratory impedance threshold device that enhances negative intrathoracic pressure and improves venous preload has been recommended for application in intubated and bag-mask ventilated patients. Owing to the difficulty of endotracheal intubation, airway management devices (Combitube and Laryngeal Mask Airway) can be used as alternatives with minimal extra training.

CONCLUSION

The new guidelines for CPR have focused on early defibrillation, uninterrupted compressions, complete decompression, fewer ventilations, and simplification and uniformity of the process.

Airway management in emergency situations

Securing and monitoring the airway are among the key requirements of appropriate therapy in emergency patients. Failures to secure the airways can drastically increase morbidity and mortality of patients within a very short time. Therefore, the entire range of measures needed to secure the airway in an emergency, without intermediate ventilation and oxygenation, is limited to 30-40 seconds. Endotracheal intubation is often called the 'gold standard' for airway management in an emergency, but multiple failed intubation attempts do not result in maintaining oxygenation; instead, they endanger the patient by prolonging hypoxia and causing additional trauma to the upper airways. Thus, knowledge and availability of alternative procedures are also essential in every emergency setting. Given the great variety of techniques available, it is important to establish a well-planned, methodical protocol within the framework of an algorithm. This not only facilitates the preparation of equipment and the training of personnel, it also ensures efficient decision-making under time pressure. Most anaesthesia-related deaths are due to hypoxaemia when difficulty in securing the airway is encountered, especially in obstetrics during induction of anaesthesia for caesarean delivery. The most commonly occurring adverse respiratory events are failure to intubate, failure to recognize oesophageal intubation, and failure to ventilate. Thus, it is essential that every anaesthesiologist working on the labour and delivery ward is comfortable with the algorithm for the management of failed intubation. The algorithm for emergency airway management describing the sequence of various procedures has to be adapted to internal standards and to techniques that are available.

In-water resuscitation: a pilot evaluation

INTRODUCTION

The first and most important treatment for the apnoeic drowning victim is the rapid alleviation of hypoxia by artificial ventilation. Recent studies have suggested that commencing resuscitative efforts with the victim still in the water may be beneficial. The aim of this pilot study was to evaluate the feasibility and efficacy of in-water unsupported rescue breathing.

METHODS

Three lifeguards were taught how to perform in-water unsupported rescue breathing. Ventilation volume, inflation duration were recorded from a modified Laerdal resuscitation manikin. The rescue duration was recorded and compared to a rescue undertaken without in-water resuscitation.

RESULTS

The three lifeguards performed between seven and nine ventilations during each simulated rescue. This gave average inflation volumes for each lifeguard of 711 ml (S.D. 166), 750 ml (S.D. 108), 629 ml (S.D. 182) and average inflation duration of 0.8s (S.D. 0.3), 0.9s (S.D. 0.2) and 0.6s (S.D. 0.1). The rescue duration was increased from an average time of 1 min 10 s to 1 min 24 s by performing in-water resuscitation.

CONCLUSION

This study has demonstrated the feasibility and potential efficacy of in-water unsupported rescue breathing with a victim in deep water. Furthermore, the technique was not associated with an undue prolongation of the rescue duration over a 50 m rescue. In circumstances where the trained lifeguard finds themselves with an apnoeic victim in the water, with no buoyant rescue aid available, they may consider the application of in-water, unsupported rescue breathing, especially if recovery to dry land is likely to be delayed. The effectiveness of this technique, however, remains to be proven in the open water environment.

Two-rescuer CPR results in hyperventilation in the ventilating rescuer

The "Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care--International Consensus on Science" recommend a tidal ventilation volume of 10 ml/kg body-weight without the use of supplemental oxygen during two-rescuer adult cardiopulmonary resuscitation (CPR). This relates to a ventilation volume of about 6.4 l/min. Additionally, the first aid provider ventilating the victim will breathe for him/herself during the external chest compression period adding another 3.2 l/min of ventilation. Finally, a deep breath is recommended before each ventilation to increase the end-expiratory oxygen concentration of the air exhaled. To investigate the effects of these recommendations, 20 healthy volunteers were asked to perform two-rescuer CPR in a lung model connected to a BLS-manikin. End-tidal carbon dioxide, oxygen saturation, and heart rate were recorded continuously. Capillary blood gas samples were collected and non-invasive blood pressure was recorded prior to the start of external chest compressions and immediately after the end of each measurement period. Furthermore, hyperventilation related symptoms reported by the volunteers were also recorded. The data reveal a significant decrease in capillary and end-tidal carbon dioxide pressure in the volunteers (P < 0.001). Additionally, in 75% of test persons multiple hyperventilation associated symptoms occurred. Ventilation during two-rescuer CPR performed according to the Guidelines 2000 may cause injury to the health of first aid providers. To minimize hyperventilation, both rescuers should exchange their positions at intervals of 3-5 min. These data challenge the recommendation to take a deep breath prior to each ventilation.

Effects of decreasing inspiratory times during simulated bag-valve-mask ventilation

During CPR, an inspiratory time of 2 s is recommended when the airway is unprotected; indicating that approximately 30% of the resuscitation attempt is spent on ventilation, but not on chest compressions. Since survival rates may not decrease when ventilation levels are relatively low, and uninterrupted chest compressions with a constant rate of approximately 100/min have been shown to be lifesaving, it may be beneficial to cut down the time spent on ventilation, and instead, increase the time for chest compressions. In an established bench model of a simulated unprotected airway, we evaluated if inspiratory time can be decreased from 2 to 1 s at different lower oesophageal sphincter pressure (LOSP) levels during ventilation with a bag-valve-mask device. In comparison with an inspiratory time of 2 s, 1 s resulted in significantly (p < 0.001) higher peak airway pressure and peak inspiratory flow rate, while lung tidal volumes at all LOSP levels were clinically comparable. Neither ventilation strategy produced stomach inflation at 20 cmH2O LOSP, and 1 s versus 2 s inspiratory time did not produce significantly higher (mean +/- S.D.) stomach inflation at 15 (8 +/-9 ml versus 0 +/- 0 ml; p < 0.01) and 10 cmH2O LOSP (69 +/- 20 ml versus 34 +/- 18 ml; p < 0.001), and significantly lower stomach inflation at 5 cmH2O LOSP (219 +/- 16 ml versus 308 +/- 21 ml; p < 0.001) per breath. Total cumulative stomach inflation volume over constantly decreasing LOSP levels with an inspiratory time of 2 s versus 1 s was higher (6820 ml versus 5920 ml). In conclusion, in this model of a simulated unprotected airway, a reduction of inspiratory time from 2 to 1 s resulted in a significant increase of peak airway pressure and peak inspiratory flow rate, while lung tidal volumes remained clinically comparable (up to approximately 15% difference), but statistically different due to the precise measurements. Theoretically, this may increase the time available for, and consequently the actual number of, chest compressions during CPR by approximately 25% without risking an excessive increase in stomach inflation.

A strategy to optimise the performance of the mouth-to-bag resuscitator using small tidal volumes: effects on lung and gastric ventilation in a bench model of an unprotected airway

When ventilating an unintubated patient with a standard adult self-inflating bag, high peak inspiratory flow rates may result in high peak airway pressures with subsequent stomach inflation. In a previous study we have tested a newly developed mouth-to-bag-resuscitator (max. volume, 1500 ml) that limits peak inspiratory flow, but the possible advantages were masked by excessive tidal volumes. The mouth-to-bag-resuscitator requires blowing up a balloon inside the self-inflating bag that subsequently displaces air, which then flows into the patient's airway. Due to this mechanism, gas flow and peak airway pressures are reduced during inspiration when compared with a standard bag-valve-mask-device. In addition, the device allows the rescuer to use two hands instead of one to seal the mask on the patient's face. The purpose of the present study was to assess the effects of the mouth-to-bag-resuscitator, which was modified to produce a maximum tidal volume of 500 ml, compared with a paediatric self-inflating bag (max. volume, 380 ml), and a standard adult self-inflating bag (max. volume, 1500 ml) in an established bench model simulating an unintubated patient with respiratory arrest. The bench model consisted of a face mask, manikin head, training lung (lung compliance, 100 ml/0.098 kPa (100ml/cm H2O); airway resistance, 0.39 kPa/(l s) (4 cm H2O/(l s)), and a valve simulating lower oesophageal sphincter pressure, 1.47 kPa (15 cm H2O). Twenty critical care nurses volunteered for the study and ventilated the manikin for 1 min with a respiratory rate of 20 min(-1) with each ventilation device in random order. The mouth-to-bag-resuscitator versus paediatric self-inflating bag resulted in significantly (P < 0.05) higher lung tidal volumes (302 +/- 41 ml versus 233 +/- 22 ml), and peak airway pressure (10 +/- 1 cm H2O versus 9 +/- 1 cm H2O), but comparable inspiratory time fraction (28 +/- 5% versus 27 +/- 5%, Ti/Ttot), peak inspiratory flow rate (0.6 +/- .01 l/s versus 0.6 +/- 0.2 l/s), and stomach inflation (149 +/- 495 ml/min versus 128 +/- 278 ml/min). In comparison with the adult self-inflating bag, there was significantly (P < 0.05) less gastric inflation (3943 +/- 4896 ml/min versus 149 +/- 495 ml/min versus 128 +/- 278 ml/min, respectively) with both devices, but the standard adult self-inflating bag had significantly higher lung tidal volumes (566 +/- 77 ml), peak airway pressure (13 +/- 1 cm H2O), and peak inspiratory flow rate (0.8 +/- 0.11 l/s). In conclusion, comparing the mouth-to-bag-resuscitator with small tidal volumes versus the paediatric self-inflating-bag during simulated ventilation of an unintubated patient in respiratory arrest resulted in comparable marginal stomach inflation, but significantly reduced the likelihood of gastric inflation compared to the adult self-inflating-bag. Lung tidal volumes were improved from approximately 250 ml with the paediatric self-inflating-bag to approximately 300 ml with the mouth-to-bag-resuscitator.

Mechanical versus manual ventilation via a face mask during the induction of anesthesia: a prospective, randomized, crossover study

One approach to make ventilation safer in an unprotected airway has been to limit tidal volumes; another one might be to limit peak airway pressure, although it is unknown whether adequate tidal volumes can be delivered. Accordingly, the purpose of this study was to evaluate the quality of automatic pressure-controlled ventilation versus manual circle system face-mask ventilation regarding ventilatory variables in an unprotected airway. We studied 41 adults (ASA status I-II) in a prospective, randomized, crossover design with both devices during the induction of anesthesia. Respiratory variables were measured with a pulmonary monitor (CP-100). Pressure-controlled mask ventilation versus circle system ventilation resulted in lower (mean +/- SD) peak airway pressures (10.6 +/- 1.5 cm H(2)O versus 14.4 +/- 2.4 cm H(2)O; P < 0.001), delta airway pressures (8.5 +/- 1.5 cm H(2)O versus 11.9 +/- 2.3 cm H(2)O; P < 0.001), expiratory tidal volume (650 +/- 100 mL versus 680 +/- 100 mL; P = 0.001), minute ventilation (10.4 +/- 1.8 L/min versus 11.6 +/- 1.8 L/min; P < 0.001), and peak inspiratory flow rates (0.81 +/- 0.06 L/s versus 1.06 +/- 0.26 L/s; P < 0.001) but higher inspiratory time fraction (48% +/- 0.8% versus 33% +/- 7.7%; P < 0.001) and end-tidal carbon dioxide (34 +/- 3 mm Hg versus 33 +/- 4 mm Hg; not significant). We conclude that in this model of apneic patients with an unprotected airway, pressure-controlled ventilation resulted in reduced inspiratory peak flow rates and peak airway pressures when compared with circle system ventilation, thus providing an additional patient safety effect during mask ventilation.

IMPLICATIONS

In this model of apneic patients with an unprotected airway, pressure-controlled ventilation resulted in reduced inspiratory peak flow rates and lower peak airway pressures when compared with circle system ventilation, thus providing an additional patient safety effect during face-mask ventilation.

Ventilation performance of a mixed group of operators using a new rescue breathing device—the glossopalatinal tube

INTRODUCTION

We studied how effectively a mixed group of helpers could ventilate a manikin with a new rescue breathing device after a short period of instruction. The device consists of a mouthcap, a "glossopalatinal tube" (GPT) reaching between tongue and palate and a connector for a bag, ventilator or the rescuers mouth. Rather than reaching behind the tongue like an oropharyngeal airway (OP), it is able to scoop the tongue off the posterior pharyngeal wall when tilted by the rescuer. It was compared with a conventional face mask with an OP.

METHODS

The study made use of an anaesthesia simulator (MedSim Ltd., Israel) and a manikin. 46 subjects with different professional backgrounds (anaesthesia nurses, medical students, emergency medical technicians (EMTs), physicians training for anaesthesiology) underwent a standard introduction to the GPT and OP (lecture with demonstration on an intubation trainer, illustrated brochure). They ventilated the manikin for 5 min each using the bag plus GPT and the OP plus face mask, respectively, in random order after the simulator had been made apnoeic and the simulated arterial oxygen saturation (S(aO(2))) had dropped to 80%. The actions and the results (tidal volumes (V(t)), S(aO(2))) were recorded on video. The subjects graded difficulty of operation and fatigue on a visual analogue scale (VAS).

RESULTS AND CONCLUSIONS

Mean V(t) with the OP plus mask amounted to 463 (230-688 ml), with GPT to 426 (243-610 ml) (median [10-90% percentiles]) (P=0.047). No differences were observed with respect to the time a S(aO(2))> or =90% was maintained (OP plus mask: 255 (139-266 s), GPT: 255 (90-269 s)) or the grades for fatigue (OP plus mask: 58% of VAS, GPT: 48% of VAS, median) and difficulty (OP plus mask: 16% of VAS, GPT: 21% of VAS). Performance and grades were scattered over a wide range. Success with the two devices was correlated, but the subjects judgement tended to diverge. The GPT is an easy to learn alternative to conventional devices and might be helpful in clinical emergencies, including situations of unexpectedly difficult ventilation.

Artificial ventilation for basic life support leads to hyperventilation in first aid providers

The 'Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care - International Consensus on Science' recommend an artificial ventilation volume of 10 ml/kg bodyweight (equivalent to a tidal volume of 700-1000 ml) without the use of supplemental oxygen in adults with respiratory arrest. For first aid providers using the mouth-to-mouth or mouth-to-nose-ventilation technique, respectively, a ventilation volume of approximately 9.6 l/min results. Additionally, a deep breath is recommended before each ventilation to increase the end-expiratory oxygen concentration of the air exhaled by the first aid provider. To investigate the effects of these recommendations in healthy volunteers, test persons were asked to ventilate an artificial lung model for a period of up to 10 min. The tidal volume was set at 800 ml at a breathing rate of 12/min. End-tidal carbon dioxide, oxygen saturation (measured by pulse oximetry), and heart rate were measured continuously. Capillary blood gas samples were collected and non-invasive blood pressure readings were recorded prior to the start of ventilation and immediately after the end of the measuring period. The data reveal a statistically significant and clinically relevant decrease in end-tidal carbon dioxide pressure (P<0.001, median decrease 14 mmHg), and the occurrence of hyperventilation-associated symptoms such as paraesthesia, dizziness, and carpopedal spasms in more than 75% of the participants. Clinically and statistically significant hyperventilation results in first aid providers performing artificial ventilation according to the guidelines. This artificial ventilation is associated with a significant decrease in capillary and end-tidal carbon dioxide pressure as well as with multiple symptoms of an acute hyperventilation syndrome. Ventilation performed according to these guidelines may cause injury to the health of the first aid provider. Rescuers ventilating the victim should be replaced at regular intervals and the recommendation to take a deep breath before each ventilation should not be upheld in order to minimise the risk of hyperventilation.

Comparison of different airway management strategies to ventilate apneic, nonpreoxygenated patients

OBJECTIVE

Endotracheal intubation is the gold standard for providing emergency ventilation, but acquiring and maintaining intubation skills may be difficult. Recent reports indicate that even in urban emergency medical services with a high call volume, esophageal intubations were observed, requiring either perfect intubation skills or development of alternatives for emergency ventilation.

DESIGN

Simulated emergency ventilation in apneic patients employing four different airway devices that used small tidal volumes.

SETTING

University hospital operating room.

SUBJECTS

Forty-eight ASA I/II patients who signed written informed consent before being enrolled into the study.

INTERVENTIONS

In healthy adult patients without underlying respiratory or cardiac disease who were breathing room air before undergoing routine induction of surgery, 12 experienced professional paramedics inserted either a laryngeal mask airway (n = 12), Combitube (n = 12), or cuffed oropharyngeal airway (n = 12) or placed a face mask (n = 12) before providing ventilation with a pediatric (maximum volume, 700 mL) self-inflating bag with 100% oxygen for 3 mins.

MEASUREMENTS AND MAIN RESULTS

In three of 12 cuffed oropharyngeal airway patients, two of 12 laryngeal mask airway patients, and one of 12 Combitube patients, oxygen saturation fell below 90% during airway device insertion, and the experiment was terminated; no oxygenation failures occurred with the bag-valve-mask. Oxygen saturation decreased significantly (p <.05) during insertion of the Combitube and laryngeal mask but not with the bag-valve-mask and cuffed oropharyngeal airway; however, oxygen saturation increased after 1 min of ventilation with 100% oxygen. No differences in tidal lung volumes were observed between airway devices.

CONCLUSIONS

Paramedics were able to employ the laryngeal mask airway, Combitube, and cuffed oropharyngeal airway in apneic patients with normal lung compliance and airways. In this population, bag-valve-mask ventilation was the most simple and successful strategy. Small tidal volumes applied with a pediatric self-inflating bag and 100% oxygen resulted in adequate oxygenation and ventilation.

Advances in airway management

Emergency ventilation is an essential component of basic life support. Respiratory emergencies occur far more frequently than cardiac arrest and, if not treated promptly and effectively, may lead to cardiac arrest. Many respiratory emergencies require assisted ventilation to prevent the occurrence of hypoxemia, hypercarbia, and cardiac decompensation. Emergency assisted ventilation is often difficult to perform and is associated with several adverse complications, such as gastric inflation, regurgitation, and pulmonary aspiration. The American Heart Association sponsored conferences in 1999 and 2000 to review and revise guidelines for cardiopulmonary resuscitation. This article reviews the science behind guideline changes related to pulmonary resuscitation and discusses recent advances in emergency airway management, focusing on noninvasive techniques for ventilation (mouth-to-mouth ventilation, bag-mask ventilation) and alternative airway devices (laryngeal mask airway, the Combitube).

Effects of decreasing inspiratory flow rate during simulated basic life support ventilation of a cardiac arrest patient on lung and stomach tidal volumes

If the airway of a cardiac arrest patient is unprotected, basic life support with low rather than high inspiratory flow rates may reduce stomach inflation. Further, if the inspiratory flow rate is fixed such as with a resuscitator performance may improve; especially when used by less experienced rescuers. The purpose of the present study was to assess the effect of limited flow ventilation on respiratory variables, and lung and stomach volumes, when compared with a bag valve device. After institutional review board approval, and written informed consent was obtained, 20 critical care unit registered nurses volunteered to ventilate a bench model simulating a cardiac arrest patient with an unprotected airway consisting of a face mask, manikin head, training lung [with lung compliance, 50 ml/0.098 kPa (50 ml/cmH(2)O); airway resistance, 0.39 kPa/l/s (4 cmH(2)O/l/s)] oesophagus [lower oesophageal sphincter pressure, 0.49 kPa (5 cmH(2)O)] and simulated stomach. Each volunteer ventilated the model with a self-inflating bag (Ambu, Glostrup, Denmark; max. volume, 1500 ml), and a resuscitator providing limited fixed flow (Oxylator EM 100, CPR Medical devices Inc., Toronto, Canada) for 2 min; study endpoints were measured with 2 pneumotachometers. The self-inflating bag vs. resuscitator resulted in comparable mean +/- SD mask tidal volumes (945 +/- 104 vs. 921 +/- 250 ml), significantly (P < 0.05) higher peak inspiratory flow rates (111 +/- 27 vs. 45 +/- 21 l/min), and peak inspiratory pressure (1.2 +/- 0.47 vs. 78 +/- 0.07 kPa), but significantly shorter inspiratory times (1.1 +/- 0.29 vs. 1.6 +/- 0.35 s). Lung tidal volumes were comparable (337 +/- 120 vs. 309 +/- 61 ml), but stomach tidal volumes were significantly (P < 0.05) higher (200 +/- 95 vs. 140 +/- 51 ml) with the self-inflating bag. In conclusion, simulated ventilation of an unintubated cardiac arrest patient using a resuscitator resulted in decreased peak flow rates and therefore, in decreased peak airway pressures when compared with a self-inflating bag. Limited flow ventilation using the resuscitator decreased stomach inflation, although lung tidal volumes were comparable between groups.

[New aspects and perspectives on cardiac arrest]

OBJECTIVES

To analyse the current knowledge based on the experimental and the clinical research studies focused on the main fields of cardiopulmonary resuscitation.

DATA SOURCES

International guidelines and recent review articles. Data collected from the Medline database with the key word: cardiac arrest.

STUDY SELECTION

Research studies published during the last ten years were reviewed. Relevant clinical information was extracted and discussed when it induced changes in guidelines.

DATA SYNTHESIS

Promising improvements on basic and advanced life supports are proposed. Chest compressions prevail over ventilation. Alternatives to classical chest compressions are tested. Ventilatory volume must be reduced from 1000 to approximatively 500 mL for each breath with oxygen. Biphasic waveform defibrillators and automated external defibrillators will be considered as the best devices in the near future. Some non-catecholaminergic vasopressors could reduce the use of epinephrine for advanced cardiac life support. Lidocaine could be replaced by amiodarone as anti-arrhythmic drug of choice. New post-resuscitation therapeutic strategies are evaluated, especially coronary reperfusion when the cause of cardiac arrest is cardiac.

CONCLUSION

Many fields of cardiopulmonary resuscitation are investigated. Some relevant informations are included in the last international guidelines published in 2000, but most of them need complementary studies before other changes could be recommended for routine practice.

Alternative ventilation strategies in cardiopulmonary resuscitation

The introduction of the 2000 Guidelines for Cardiopulmonary Resuscitation emphasizes a new, evidence-based approach to the science of ventilation during cardiopulmonary resuscitation (CPR). New laboratory and clinical science underemphasizes the role of ventilation immediately after a dysrhythmic cardiac arrest (arrest primarily resulting from a cardiovascular event, such as ventricular defibrillation or asystole). However, the classic airway patency, breathing, and circulation (ABC) CPR sequence remains a fundamental factor for the immediate survival and neurologic outcome of patients after asphyxial cardiac arrest (cardiac arrest primarily resulting from respiratory arrest). The hidden danger of ventilation of the unprotected airway during cardiac arrest either by mouth-to-mouth or by mask can be minimized by applying ventilation techniques that decrease stomach gas insufflation. This goal can be achieved by decreasing peak inspiratory flow rate, increasing inspiratory time, and decreasing tidal volume to approximately 5 to 7 mL/kg, if oxygen is available. Laboratory and clinical evidence recently supported the important role of alternative airway devices to mask ventilation and endotracheal intubation in the chain of survival. In particular, the laryngeal mask airway and esophageal Combitube proved to be effective alternatives in providing oxygenation and ventilation to the patient in cardiac arrest in the prehospital arena in North America. Prompt recognition of supraglottic obstruction of the airway is fundamental for the management of patients in cardiac arrest when ventilation and oxygenation cannot be provided by conventional methods. "Minimally invasive" cricothyroidotomy devices are now available for the professional health care provider who is not proficient or comfortable with performing an emergency surgical tracheotomy or cricothyroidotomy. Finally, a recent device that affects the relative influence of positive pressure ventilation on the hemodynamics during cardiac arrest has been introduced, the inspiratory impedance threshold valve, with the goal of maximizing coronary and cerebral perfusion while performing CPR. Although the role of this alternative ventilatory methodology in CPR is rapidly being established, we cannot overemphasize the need for proper training to minimize complications and maximize the efficacy of these new devices.

Basic life support cardiopulmonary resuscitation

CPR represents the primary intervention used during cardiac arrest for maintaining perfusion and extending the potential resuscitation period. Effective CPR, however, requires careful attention to detail by the resuscitation team, including (1) effective control of the airway using manual maneuvers or airway adjuncts, (2) delivery of effective ventilation that assures adequate oxygenation, while reducing the chance for gastric inflation, and (3) chest compressions delivered at the appropriate depth and rate using a duty cycle of 50% compression and 50% release. During the resuscitation effort team leaders should closely monitor the performance of CPR, rotate rescuers frequently to avoid fatigue, and provide continuous feedback based upon direct (transmitted pulse, chest rise) and indirect (end-tidal CO2) measures of effectiveness. A careful and measured approach to CPR performance, combined with a strong chain of survival, provides victims of cardiac arrest the best chance for survival.

The effects of different mouth-to-mouth ventilation tidal volumes on gas exchange during simulated rescue breathing

The American Heart Association recommends tidal volumes of 700 to 1000 mL during mouth-to-mouth ventilation, but smaller tidal volumes of 500 mL may be of advantage to decrease the likelihood of stomach inflation. Because mouth-to-mouth ventilation gas contains only 17% oxygen, but 4% carbon dioxide, it is unknown whether 500-mL tidal volumes given during rescue breathing may result in insufficient oxygenation and inadequate carbon dioxide elimination. In a university hospital research laboratory, 20 fully conscious volunteer health care professionals were randomly assigned to breathe tidal volumes of 500 or 1000 mL of mouth-to-mouth ventilation gas (17% oxygen, 4% carbon dioxide, 79% nitrogen), or room air control (21% oxygen, 79% nitrogen) for 5 min. Arterial blood gases were taken immediately before, and after breathing 5 min of the experimental gas composition. When comparing 500 versus 1000 mL of mouth-to-mouth ventilation tidal volumes with 500 mL of room air, 500 mL of mouth-to-mouth ventilation tidal volume resulted in significantly (P < 0.05) lower mean +/- SEM arterial oxygen partial pressure (70 +/- 1 versus 85 +/- 2 versus 92 +/- 3 mm Hg, respectively), and lower oxygen saturation (94 +/- 0.4 versus 97 +/- 0.2 versus 98 +/- 0.2%), but increased arterial carbon dioxide partial pressure (46 +/- 1 versus 40 +/- 1 versus 39 +/- 1 mm Hg, respectively). Sixteen of 20 volunteers had to be excluded from the experiment with 500 mL of mouth-to-mouth ventilation gas after about 3 min instead of after 5 minutes as planned because of severe nervousness, sweating, and air hunger. We conclude that during simulated mouth-to-mouth ventilation, only large (approximately 1000 mL), but not small (approximately 500 mL) tidal volumes were able to maintain both sufficient oxygenation and adequate carbon dioxide elimination.

IMPLICATIONS

To provide efficient mouth-to-mouth ventilation, it is important to administer tidal volumes of 1000 mL; tidal volumes of 500 mL were not adequate.

The respiratory system during resuscitation: a review of the history, risk of infection during assisted ventilation, respiratory mechanics, and ventilation strategies for patients with an unprotected airway

The fear of acquiring infectious diseases has resulted in reluctance among healthcare professionals and the lay public to perform mouth-to-mouth ventilation. However, the benefit of basic life support for a patient in cardiopulmonary or respiratory arrest greatly outweighs the risk for secondary infection in the rescuer or the patient. The distribution of ventilation volume between lungs and stomach in the unprotected airway depends on patient variables such as lower oesophageal sphincter pressure, airway resistance and respiratory system compliance, and the technique applied while performing basic or advanced airway support, such as head position, inflation flow rate and time, which determine upper airway pressure. The combination of these variables determines gas distribution between the lungs and the oesophagus and subsequently, the stomach. During bag-valve-mask ventilation of patients in respiratory or cardiac arrest with oxygen supplementation (> or = 40% oxygen), a tidal volume of 6-7 ml kg(-1) ( approximately 500 ml) given over 1-2 s until the chest rises is recommended. For bag-valve-mask ventilation with room-air, a tidal volume of 10 ml kg(-1) (700-1000 ml) in an adult given over 2 s until the chest rises clearly is recommended. During mouth-to-mouth ventilation, a breath over 2 s sufficient to make the chest rise clearly (a tidal volume of approximately 10 ml kg(-1) approximately 700-1000 ml in an adult) is recommended.

Basic and advanced life support, acute resuscitation, and cardiac resuscitation

The global approach to resuscitation has changed dramatically in the past year. The groundwork for these changes began a decade ago with the development of the Utstein guidelines for uniform reporting of critical events. Consistency in data collection was necessary to enable evidence-based review and comparison of current practice. Resuscitation protocols have been significantly altered based upon these data. Basic life support (BLS) protocols have been simplified. Early access to electrical cardioversion is the key to survival. Mobilization of AED technology in the community is essential. Several issues were identified as crucial to future improvement of resuscitation statistics. Prevention strategies should be developed for high-risk patients. There is a need to identify cases in which resuscitation should not be started. Enhancement of educational methods to improve performance and retention of skills is key. Finally, the roadblocks for performance of ethical prospective research must be minimized.

Emergency airway management by non-anaesthesia house officers--a comparison of three strategies

OBJECTIVES

The purpose of this study was to determine effects of different airway devices and tidal volumes on lung ventilation and gastric inflation in an unprotected airway.

METHODS

Thirty one non-anaesthesia house officers volunteered for the study, and ventilated a bench model simulating an unintubated respiratory arrest patient with bag-valve-facemask, laryngeal mask airway, and combitube using paediatric and adult self inflating bags.

RESULTS

The paediatric versus adult self inflating bag resulted with the laryngeal mask airway and combitube in significantly (p<0.001) lower mean (SEM) lung tidal volumes (376 (30) v 653 (47) ml, and 368 (28) v 727 (53) ml, respectively). Gastric inflation was zero with the combitube; and 0 (0) v 8 (3) ml with the laryngeal mask airway with low versus large tidal volumes. The paediatric versus adult self inflating bag with the bag-valve-facemask resulted in comparable lung tidal volumes (245 (19) v 271 (33) ml; p=NS); but significantly (p<0.001) lower gastric tidal volume (149 (11) v 272 (24) ml).

CONCLUSIONS

The paediatric self inflating bag may be an option to reduce the risk of gastric inflation when using the laryngeal mask airway, and especially, the bag-valve-facemask. Both the laryngeal mask airway and combitube proved to be valid alternatives for the bag-valve-facemask in this experimental model.