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 dynamic response of human lungs due to underwater shock wave exposure

Since the 19th century, underwater explosions have posed a significant threat to service members. While there have been attempts to establish injury criteria for the most vulnerable organs, namely the lungs, existing criteria are highly variable due to insufficient human data and the corresponding inability to understand the underlying injury mechanisms. This study presents an experimental characterization of isolated human lung dynamics during simulated exposure to underwater shock waves. We found that the large acoustic impedance at the surface of the lung severely attenuated transmission of the shock wave into the lungs. However, the shock wave initiated large bulk pressure-volume cycles that are distinct from the response of the solid organs under similar loading. These pressure-volume cycles are due to compression of the contained gas, which we modeled with the Rayleigh-Plesset equation. The extent of these lung dynamics was dependent on physical confinement, which in real underwater blast conditions is influenced by factors such as rib cage properties and donned equipment. Findings demonstrate a potential causal mechanism for implosion injuries, which has significant implications for the understanding of primary blast lung injury due to underwater blast exposures.

Spanish Society of Anesthesiology, Reanimation and Pain Therapy (SEDAR), Spanish Society of Emergency and Emergency Medicine (SEMES) and Spanish Society of Otolaryngology, Head and Neck Surgery (SEORL-CCC) Guideline for difficult airway management. Part II

The Airway Management section of the Spanish Society of Anesthesiology, Resuscitation, and Pain Therapy (SEDAR), the Spanish Society of Emergency Medicine (SEMES), and the Spanish Society of Otorhinolaryngology and Head and Neck Surgery (SEORL-CCC) present the Guide for the comprehensive management of difficult airway in adult patients. Its principles are focused on the human factors, cognitive processes for decision-making in critical situations, and optimization in the progression of strategies application to preserve adequate alveolar oxygenation in order to enhance safety and the quality of care. The document provides evidence-based recommendations, theoretical-educational tools, and implementation tools, mainly cognitive aids, applicable to airway management in the fields of anesthesiology, critical care, emergencies, and prehospital medicine. For this purpose, an extensive literature search was conducted following PRISMA-R guidelines and was analyzed using the GRADE methodology. Recommendations were formulated according to the GRADE methodology. Recommendations for sections with low-quality evidence were based on expert opinion through consensus reached via a Delphi questionnaire.

Preintubation Machine-Delivered Pressure Support Ventilation With Positive End-Expiratory Pressure Versus Manual Bag-Mask Ventilation for Oxygenation in Overweight and Obese Patients: A Randomized, Pilot Study

BACKGROUND

Noninvasive positive pressure ventilation (NIPPV) maintains mean airway pressures well, and its usability for preoxygenation is well described. Anesthesia machine-delivered NIPPV-based preoxygenation has recently been evaluated against the traditional manual bag-mask ventilation (BMV). The efficiency of such a technique over the traditional one is yet to be established well. The present study evaluated the feasibility of machine-delivered preoxygenation using pressure support ventilation (PSV) with positive end-expiratory pressure (PEEP) and compared the effectiveness with BMV.

METHODS

Thirty overweight and obese adults belonging to the American Society of Anesthesiologist's physical status I-II were randomized to receive PSV+PEEP or BMV for preintubation preoxygenation targeted to a fraction of expired oxygen (FeO2) of 85% and 90% or for a maximum period of five minutes, whichever came first. Postintubation, the patient was observed for the time taken until 1% desaturation without ventilation. Arterial blood gases, respiratory variables, FeO2 achieved, and different times were collected and compared.

RESULTS

The baseline characteristics and arterial blood gases were similar between the two groups. The PSV+PEEP group had consistent and favorable tidal volume and airway pressure delivery. The difference in time to reach a FeO2 of 85% between the two groups was not statistically different. Only two patients achieved a FeO2 of 90% in the PSV+PEEP group versus none in the BMV group. However, partial pressure of oxygen at 1% desaturation (217.42±109.47 versus 138.073±71.319 mmHg, p 0.0259) was higher in the PSV+PEEP group. Similarly, the time until 1% desaturation was significantly prolonged in the PSV+PEEP group (206.6±76.952 versus 140.466±54.245 seconds, p 0.0111).

CONCLUSION

The present pilot study findings indicate that preintubation machine-delivered PSV+PEEP-based preoxygenation is feasible and might be more effective than traditional BMV in overweight and obese patients.

Six-Hour Manual Ventilation with a Bag-Valve-Tube Device by Briefly Trained Non-Medical Personnel is Feasible

RATIONALE

Manual ventilation with a bag-valve device (BVD) is a Basic Life Support skill. Prolonged manual ventilation may be required in resource-poor locations and in severe disasters such as hurricanes, pandemics, and chemical events. In such circumstances, trained operators may not be available and lay persons may need to be quickly trained to do the job.

OBJECTIVES

The current study investigated whether minimally trained operators were able to manually ventilate a simulated endotracheally intubated patient for six hours.

METHODS

Two groups of 10 volunteers, previously unfamiliar with manual ventilation, received brief, structured BVD-tube ventilation training and performed six hours of manual ventilation on an electronic lung simulator. Operator cardiorespiratory variables and perceived effort, as well as the quality of the delivered ventilation, were recorded. Group One ventilated a "normal lung" (compliance 50cmH2O/L, resistance 5cmH2O/L/min). Group Two ventilated a "moderately injured lung" (compliance 20cmH2O/L, resistance 20cmH2O/L/min).

RESULTS

Volunteers' blood pressure, heart rate (HR), respiratory rate (RR), and peripheral capillary oxygen saturation (SpO2) were stable throughout the study. Perceived effort was minimal. The two groups provided clinically adequate and similar RRs (13.3 [SD = 3.0] and 14.1 [SD = 2.5] breaths/minute, respectively) and minute volume (MV; 7.6 [SD = 2.1] and 7.7 [SD = 1.4] L/minute, respectively).

CONCLUSIONS

The results indicate that minimally trained persons can effectively perform six hours of manual BVD-tube ventilation of normal and moderately injured lungs, without undue effort. Quality of delivered ventilation was clinically adequate.

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.

Regurgitation and pulmonary aspiration during cardio-pulmonary resuscitation (CPR) with a laryngeal tube: A pilot crossover human cadaver study

Background

High-quality chest compressions are imperative for Cardio-Pulmonary-Resuscitation (CPR). International CPR guidelines advocate, that chest compressions should not be interrupted for ventilation once a patient’s trachea is intubated or a supraglottic-airway-device positioned. Supraglottic-airway-devices offer limited protection against pulmonary aspiration. Simultaneous chest compressions and positive pressure ventilation both increase intrathoracic pressure and potentially enhances the risk of pulmonary aspiration. The hypothesis was, that regurgitation and pulmonary aspiration is more common during continuous versus interrupted chest compressions in human cadavers ventilated with a laryngeal tube airway.

Methods

Twenty suitable cadavers were included, and were positioned supine, the stomach was emptied, 500 ml of methylene-blue-solution instilled and laryngeal tube inserted. Cadavers were randomly assigned to: 1) continuous chest compressions; or, 2) interrupted chest compressions for ventilation breaths. After 14 minutes of the initial designated CPR strategy, pulmonary aspiration was assessed with a flexible bronchoscope. The methylene-blue-solution was replaced by 500 ml barium-sulfate radiopaque suspension. 14 minutes of CPR with the second designated ventilation strategy was performed. Pulmonary aspiration was then assessed with a conventional chest X-ray.

Results

Two cadavers were excluded for technical reasons, leaving 18 cadavers for statistical analysis. Pulmonary aspiration was observed in 9 (50%) cadavers with continuous chest compressions, and 7 (39%) with interrupted chest compressions (P = 0.75).

Conclusion

Our pilot study indicate, that incidence of pulmonary aspiration is generally high in patients undergoing CPR when a laryngeal tube is used for ventilation. Our study was not powered to identify potentially important differences in regurgitation or aspiration between ongoing vs. interrupted chest compression. Our results nonetheless suggest that interrupted chest compressions might better protect against pulmonary aspiration when a laryngeal tube is used for ventilation.

Discrimination ability of the endotracheal tube location using real-time palpation during intubation using an endotracheal tube with a preloaded stylet

Purpose

Palpation during intubation could be used as an ancillary method of providing real-time information of the endotracheal tube (ETT) placement before manual ventilation. This study aimed to evaluate the ability to discriminate the ETT location using a modified real-time palpation method with a preloaded stylet during intubation.

Patients and methods

The examiner performing the real-time palpation method placed three fingers on the lateral sides of the trachea between the sternal notch and the thyroid cartilage to determine if endotracheal intubation was successful. Endotracheal intubation was confirmed by auscultation and quantitative carbon dioxide waveform using capnography.

Results

Eighty-eight patients were enrolled in this study. The discrimination accuracy of the real-time palpation method was 98.9% (95% CI: 93.8–99.8) for identifying the location of ETT between the trachea and esophagus. There was one false negative, reported as esophageal intubation rather than tracheal intubation.

Conclusion

The real-time palpation method during intubation using an ETT with a preloaded stylet is an instantly applicable technique with good discrimination ability. The addition of real-time information through this palpation method to the conventional intubation process, especially in patients with poor vocal cord visualization, would be useful to facilitate the process of safe and careful endotracheal intubation.

Effects of Stomach Inflation on Cardiopulmonary Function and Survival During Hemorrhagic Shock: A Randomized, Controlled, Porcine Study

BACKGROUND

Ventilation of an unprotected airway may result in stomach inflation. The purpose of this study was to evaluate the effect of clinically realistic stomach inflation on cardiopulmonary function during hemorrhagic shock in a porcine model.

METHODS

Pigs were randomized to a sham control group (n = 9), hemorrhagic shock (35 mL kg over 15 min [n = 9]), and hemorrhagic shock combined with stomach inflation (35 mL kg over 15 min and 5 L stomach inflation [n = 10]).

RESULTS

When compared with the control group, hemorrhagic shock (n = 9) increased heart rate (103 ± 11 vs. 146 ± 37 beats min; P = 0.002) and lactate (1.4 ± 0.5 vs. 4.0 ± 1.9 mmol L; P < 0.001), and decreased mean arterial blood pressure (81.3 ± 12.8 vs. 35.4 ± 8.1 mmHg; P < 0.001) and stroke-volume index (38.1 ± 6.4 vs. 13.6 ± 4.8 mL min m; P < 0.001). Hemorrhagic shock combined with stomach inflation (n = 10) versus hemorrhagic shock only (n = 9) increased intra-abdominal pressure (27.0 ± 9.3 vs. 1.1 ± 1.0 mmHg; P < 0.001), and decreased stroke-volume index (9.9 ± 6.0 vs. 20.8 ± 8.5 mL min m; P = 0.007), and dynamic respiratory system compliance (10.8 ± 4.5 vs. 38.1 ± 6.1 mL cmH2O; P < 0.001). Before versus after stomach evacuation during hemorrhagic shock, intra-abdominal pressure decreased (27.0 ± 9.3 vs. 9.8 ± 5.4 mmHg; P = 0.042). Survival in the sham control and hemorrhagic shock group was 9 of 9, respectively, and 3 of 10 after hemorrhagic shock and stomach inflation (P < 0.001).

CONCLUSIONS

During hemorrhagic shock stomach inflation caused an abdominal compartment syndrome and thereby impaired cardiopulmonary function and aerobic metabolism, and increased mortality. Subsequent stomach evacuation partly reversed adverse stomach-inflation triggered effects.

Hospital resuscitation teams: a review of the risks to the healthcare worker

Background

“Code blue” events and related resuscitation efforts involve multidisciplinary bedside teams that implement specialized interventions aimed at patient revival. Activities include performing effective chest compressions, assessing and restoring a perfusing cardiac rhythm, stabilizing the airway, and treating the underlying cause of the arrest. While the existing critical care literature has appropriately focused on the patient, there has been a dearth of information discussing the various stresses to the healthcare team. This review summarizes the available literature regarding occupational risks to medical emergency teams, characterizes these risks, offers preventive strategies to healthcare workers, and highlights further research needs.

Methods

We performed a literature search of PubMed for English articles of all types (randomized controlled trials, case-control and cohort studies, case reports and series, editorials and commentaries) through September 22, 2016, discussing potential occupational hazards during resuscitation scenarios. Of the 6266 articles reviewed, 73 relevant articles were included.

Results

The literature search identified six potential occupational risk categories to members of the resuscitation team—infectious, electrical, musculoskeletal, chemical, irradiative, and psychological. Retrieved articles were reviewed in detail by the authors.

Conclusion

Overall, we found there is limited evidence detailing the risks to healthcare workers performing resuscitation. We identify these risks and offer potential solutions. There are clearly numerous opportunities for further study in this field.

Comparison of learning performance of 2 intubating laryngeal mask airways in novice: A randomized crossover manikin study

BACKGROUND

Intubating laryngeal mask airways (LMAs) such as i-gel and Aura-i could serve as rescue devices in resuscitation and further ensure the airway by facilitating trachea intubation without ventilation interruption. But data regarding intubating LMAs in novice are limited and skill degeneration without regular training has not been evaluated. So we designed this prospective randomized crossover manikin study to compare the learning performance of 2 intubating LMAs (i-gel and Aura-i).

METHODS

In total, 46 novice doctors participated in this study. After standardized training and finishing 3 consecutive successful intubations with both LMAs on manikin, each participant applied intubation with both LMAs in random order for initial evaluation. To evaluate skill retention, participants were reassessed 90 days later on the same manikin without retraining between times. Primary outcome was time to successful ventilation (TTV).

RESULTS

The TTV for i-gel was significantly shorter than Aura-i (initial evaluation 11.8 ± 2.9 seconds vs 22.4 ± 5.2 seconds, 90-days reevaluation 14.9 ± 3.6 seconds vs 28.9 ± 10.0 seconds, initial evaluation, P = .001; second evaluation, P < .001); during re-evaluation, TTV taken for i-gel and Aura-i were both significantly longer (initial evaluation, P = .001; second evaluation, P < .001) and ease score of insertion both increased profoundly (i-gel P = .025; Aura-i P < .001). In both assessments, participants preferred i-gel as easier alternative (initial evaluation, P = .001; second evaluation, P < .001). There was no difference in successful intubation rate, first attempt success rate, bronchoscopy assessment, and insertion score for 2 LMAs.

CONCLUSION

Compared with Aura-i, i-gel showed a faster and easier intubation by novice doctors in this manikin study; the skill retention of intubation performance after 3 months was acceptable for both intubating LMAs, but TTV prolonged significantly.

Evaluation of six different airway devices regarding regurgitation and pulmonary aspiration during cardio-pulmonary resuscitation (CPR) - A human cadaver pilot study

BACKGROUND

Chest compressions and ventilation are lifesaving tasks during cardio-pulmonary resuscitation (CPR). Besides oxygenation, endotracheal intubation (ETI) during CPR is performed to avoid aspiration of gastric contents. If intubation is difficult or impossible, supraglottic airway devices are utilized. We tested six different airway devices regarding their potential to protect against regurgitation and aspiration during CPR in a randomized experimental human cadaver study.

METHODS

Five-hundred ml of 0.01% methylene-blue-solution were instilled into the stomach of 30 adult human cadavers via an oro-gastric tube. The cadavers were then randomly assigned to one of six groups, resulting in 5 cadavers in each group. Airway management was performed with either bag-valve ventilation, Laryngeal Tube, EasyTube, Laryngeal Mask (Classic), I-Gel, or ETI. Thereafter 5min of CPR were performed according to the 2010 Guidelines of the European Resuscitation Council. Pulmonary aspiration was defined as the presence of methylene-blue-solution below the vocal cords or the ETI cuff as assessed by fiber-optic bronchoscopy.

RESULTS

Thirty cadavers were included (14 females, 16 males). Aspiration was detected in three out of five cadavers receiving bag-valve ventilation and in two out of five intubated with LMA or I-Gel. In cadavers intubated with the LT, aspiration occurred in one out of five cases. No aspiration could be detected in cadavers intubated with ETI and EasyTube.

CONCLUSION

This study provides experimental evidence that, during CPR, ETI offers superior protection against regurgitation and pulmonary aspiration of gastric contents than supraglottic airway devices or bag-valve ventilation.

Cardiopulmonary resuscitation, chest compression only and teamwork from the perspective of medical doctors, surgeons and anesthesiologists

Background:

New resuscitation guidelines that were proposed by the European Resuscitation Council in 2010 have introduced a new method of cardiopulmonary resuscitation (CPR) by chest compressions only for untrained individuals.

Objectives:

We conducted this study to evaluate differences in attitudes towards CPR among medical doctors, surgeons and anesthesiologists in Osijek University Hospital. A call for help, chest-compression-only resuscitation, mouth-to-mouth ventilation and team-work were recognized as critical points that may influence the outcome. Unfamiliarity with these methods may be indicative of a lack of education in resuscitation and may result in poor outcomes for victims.

Patients and Methods:

An anonymous survey was conducted on 190 medical professionals: 93 medical doctors, 70 surgeons, and 27 anesthesiologists during year 2012 (mean age 41.9 years). The questions were related to previous education in resuscitation, current resuscitation practices and attitudes towards cardiopulmonary resuscitation. Data were analyzed using ANOVA and Fisher exact test. A P value of < 0.05 was considered statistically significant.

Results:

The only difference between groups was regarding the male and female ratio, with more male surgeons (45, 55, and 11, P < 0.001). All doctors considered CPR as important, but only anesthesiologists knew how often guidelines in CPR change. Approximately 45% of medical doctors, 48% of surgeons and 77% of anesthesiologists reported that they have renewed their knowledge in CPR within the last five years, whereas 34%, 25% and 22% had never renewed their knowledge in the CPR (P = 0.01 between surgeons anesthesiologists). Furthermore, chest-compression-only was recognized as a valuable CPR technique by 25.8% of medical doctors, 14.3% of surgeons and 59.3% of anesthesiologists (P < 0.001). Anesthesiologists estimated a high risk of infection transmission (62%) and were more likely to refuse mouth-to-mouth ventilation when compared to surgeons (25% vs.10%, P = 0.01). Anesthesiologists are most often called for help by their colleagues, only rarely surgeons call their departmental colleagues and nurses to help in CPR.

Conclusions:

An insufficient formal education in CPR was registered for all groups, reflecting the lack of familiarity with new CPR methods. A team education, involving doctors and nurses may improve familiarity with CPR and patient outcomes.

Impact of A Pressure-Responsive Flow-Limiting Valve on Bag–valve–mask Ventilation in an Airway Model

Objective:

Using a simulated airway model, we compared ventilation performance by emergency medical services (EMS) providers using a traditional bag–valve–mask (Easy Grip®) resuscitator to their performance when using a new device, the SMART BAG® resuscitator, which has a pressure-responsive flow-limiting valve.

Methods:

We recruited EMS providers at an EMS educational forum and performed a randomized, non-blinded, prospective crossover comparison of ventilation with 2 devices on a non-intubated simulated airway model. Subjects were instructed to ventilate a Mini Ventilation Training Analyzer® as they would an 85-kg adult patient in respiratory arrest. After being randomized to order of device use, they performed ventilation for 1 minute with each device. Primary outcomes were ventilation rates and peak airway pressures. We also measured average tidal volume, gastric inflation volume, minute ventilation and inspiratory:expiratory (I:E) ratio, and compared our results to the American Heart Association standards (2005 edition).

Results:

We observed statistically significant differences between the SMART BAG® and the traditional bag–valve–mask for respiratory rate (12 v. 14 breaths/min), peak airway pressure (15.6 v. 18.9 cm H2O), gastric inflation (239.6 v. 1598.4 mL), minute ventilation (7980 v. 8775 mL), and I:E ratio (1.3 v. 1.1). Average tidal volume was similar with both devices (679.6 v. 672.2 mL).

Conclusion:

The SMART BAG® provided ventilation performance that was more consistent with American Heart Association guidelines and delivered similar tidal volumes when compared with ventilation with a traditional bag–valve–mask resuscitator.

Preoxygenation reduces desaturation events and improves intubation success

OBJECTIVE

Oxygen desaturation occurs frequently in the course of prehospital rapid sequence intubation (RSI) and is associated with increased morbidity and mortality. Preoxygenation with positive pressure ventilation by bag valve mask may delay the onset of desaturation. The purpose of this study was to evaluate implementation of a targeted preoxygenation protocol including the use of positive pressure ventilation on desaturation events and intubation success during air medical RSI.

METHODS

The RSI air medical program airway training model was modified to target an oxygen saturation as measured by pulse oximetry value of ≥ 93% before initial laryngoscopy. A review of oxygen saturation as measured by pulse oximetry tracings was performed for 2 years before and 2 years after implementation of this protocol. The incidence of desaturation events and overall intubation success rates were compared before and after the intervention.

RESULTS

One hundred fifty-five RSI procedures were evaluated over the study period. Desaturation events decreased from 58% in the 2 years before algorithm changes to 28% in the first year and 14% in the second year after implementation (P < .01). Intubation success rates increased from 89% to 98% (P < .01). There were no self-reports of aspiration events during the study period.

CONCLUSION

A preoxygenation protocol dramatically reduced the incidence of desaturation events and increased intubation success without an increase in the number of reported aspiration events.

Effective CPR Procedure With Real Time Evaluation and Feedback Using Smartphones

Timely cardio pulmonary resuscitation (CPR) can mean the difference between life and death. A trained person may not be available at emergency sites to give CPR. Normally, a 9-1-1 operator gives verbal instructions over the phone to a person giving CPR. In this paper, we discuss the use of smartphones to assist in administering CPR more efficiently and accurately. The two important CPR parameters are the frequency and depth of compressions. In this paper, we used smartphones to calculate these factors and to give real-time guidance to improve CPR. In addition, we used an application to measure oxygen saturation in blood. If blood oxygen saturation falls below an acceptable threshold, the person giving CPR can be asked to do mouth-to-mouth breathing. The 9-1-1 operator receives this information real time and can further guide the person giving CPR. Our experiments show accuracy >90% for compression frequency, depth, and oxygen saturation.

Comparison of the i-gel™ and the Laryngeal Mask Airway Classic™ in terms of clinical performance

PURPOSE

The i-gel™ is one of the second generation supraglottic airway devices. Our study was designed to compare the i-gel and the Laryngeal Mask Airway Classic™ with respect to the clinical performance.

METHODS

We compared the performance of the i-gel with that of the Laryngeal Mask Airway Classic in 120 patients undergoing urologic surgery during general anesthesia without muscle relaxant with respect to the number of attempts for successful insertion, insertion time, peak airway pressure, incidence of regurgitation, fiberoptic glottic view and postoperative complications. Second generation supraglottic airway devices were inserted by the same anesthesiologist, experienced in use of both devices (>200 uses and first time failure rate <5%). Methylene blue method was used to detect gastric regurgitation.

RESULTS

There was no statistical difference between the two groups regarding the success of insertion of second generation supraglottic airway device (p=0.951). The laryngeal mask insertion time for the i-gel group was significantly shorter than that for the Laryngeal Mask Airway Classic group (11.6±2.4s versus 13.1±1.8s [p=0.001]). The fiberoptic glottic view scores for the i-gel group was significantly better than that for the ones for the Laryngeal Mask Airway Classic group (p=0.001). On fiberoptic view, there was no sign of methylene blue dye at any time point in either group. In addition, there was no difference between the groups in patient response regarding the presence of a sore throat when questioned 24h after the procedure (p=0.752).

CONCLUSION

Both devices had good performance with low postoperative complications and without occurrence of regurgitation. The i-gel provided a shorter insertion time and a better fiberoptic view than the Laryngeal Mask Airway Classic.

Performance of supraglottic airway devices and 12 month skill retention: a randomized controlled study with manikins

PURPOSE

Airway management for successful ventilation by laypersons and inexperienced healthcare providers is difficult to achieve. Bag-valve mask (BVM) ventilation requires extensive training and is performed poorly. Supraglottic airway devices (SADs) have been successfully introduced to clinical resuscitation practice as an alternative. We evaluated recently introduced (i-gel™ and LMA-Supreme™) and established SADs (LMA-Unique™, LMA-ProSeal™) and BVM used by laypeople in training sessions on manikins.

METHODS

In this randomized controlled study, 267 third-year medical students participated with informed consent and IRB approval. After brief standardized training, each participant applied all devices in a randomized order. Success of device application and ventilation was recorded. Without further training, skill retention was assessed in the same manner 12 months later. Outcome parameters were the number of application attempts, application time, tidal volume and gastric inflation rate recorded at successful attempts, and subjective ease-of-use rating by the participants.

RESULTS

i-gel™ and LMA-Supreme™ were the most successful in the first attempt at both assessments and in the subjective ease-of-use rating. The shortest application time was found with BVM (8 ± 5s in 2008 vs. 9 ± 5s in 2009) and i-gel (10 ± 3s vs. 12 ± 5s). Tidal volumes were disappointing with no device reaching 50% volume within the recommended range (0.4-0.6L). Gastric inflation rate was highest with BVM (18% vs. 20%) but significantly lower with all SADs (0.4-6%; p < 0.001 for 2008 and 2009).

CONCLUSION

SADs showed clear advantages over BVM. Compared with LMA-Unique™ and LMA-ProSeal™, i-gel™ and LMA-Supreme™ led to higher first-attempt success rates and a shorter application time.

Anaesthesia in prehospital emergencies and in the emergency room

AIMS

To review anaesthesia in prehospital emergencies and in the emergency room, and to discuss guidelines for anaesthesia indication; pre-oxygenation; anaesthesia induction and drugs; airway management; anaesthesia maintenance and monitoring; side effects and training.

METHODS

A literature search in the PubMed database was performed and 87 articles were included in this non-systematic review.

CONCLUSIONS

For pre-oxygenation, high-flow oxygen should be delivered with a tight-fitting face-mask provided with a reservoir. In haemodynamically unstable patients, ketamine may be the induction agent of choice. The rocuronium antagonist sugammadex may have the potential to make rocuronium a first-line neuromuscular blocking agent in emergency induction. An experienced health-care provider may consider prehospital anaesthesia induction. A moderately experienced health-care provider should optimise oxygenation, fasten hospital transfer and only try to intubate a patient in extremis. If intubation fails twice, ventilation should be resumed with an alternative supra-glottic airway or a bag-valve-mask device. A lesser experienced health-care provider should completely refrain from intubation, optimise oxygenation, fasten hospital transfer and only in extremis ventilate with an alternative supra-glottic airway or a bag-valve-mask device. With an expected difficult airway, the patient should be intubated awake. With an unexpected difficult airway, bag-valve-mask ventilation should be resumed and an alternative supra-glottic airway device inserted. Senior help should be called early. In a "can-not-ventilate, can-not-intubate" situation an alternative airway should be tried and if unsuccessful because of severe upper airway pathology, a surgical airway should be performed. Ventilation should be monitored continuously with capnography. Clinical training is important to increase airway management skills.

Optimising the unprotected airway with a prototype Jaw-Thrust-Device--a prospective randomised cross-over study

Despite being a standard procedure during induction of anaesthesia, facemask ventilation can be a major challenge especially for inexperienced anaesthetists. We manufactured a Jaw-Thrust-Device designed to keep the patient's jaws in an optimised position, and thus to maintain the airway in a permanently patent state. Using a cross over design, we compared the influence of using the Esmarch manoeuvre (bimanual jaw-thrust), a nasopharyngeal airway, an oropharyngeal airway, or the Jaw-Thrust-Device on airway physiology in 50 healthy adults with body mass index < 35 kg.m(-2), undergoing standard facemask ventilation for routine induction of anaesthesia. The main study endpoints were expiratory tidal volumes, airway resistances, and gas flow rates. The Jaw-Thrust-Device was more effective in increasing expiratory tidal volumes and peak inspiratory flow than a standard Esmarch manoeuvre, and was more effective than both nasopharyngeal and oropharyngeal airways in decreasing airway resistance.

A comparison of the i-gel with the LMA-Unique in non-paralysed anaesthetised adult patients

SUMMARY

This study assessed two disposable devices; the newly developed supraglottic airway device i-gel and the LMA-Unique in routine clinical practice. Eighty patients (ASA 1-3) undergoing minor routine gynaecologic surgery were randomly allocated to have an i-gel (n = 40) or LMA-Unique (n = 40) inserted. Oxygen saturation, end-tidal carbon dioxide, tidal volume and peak airway pressure were recorded, as well as time of insertion, airway leak pressure, postoperative sore-throat, dysphonia and dysphagia for each device. Time of insertion was comparable with the i-gel and LMA-Unique. There was no failure in the i-gel group and one failure in the LMA-Unique group. Ventilation and oxygenation were similar between devices. Mean airway pressure was comparable with both devices, whereas airway leak pressure was significantly higher (p < 0.0001) in the i-gel group (mean 29 cmH(2)O, range 24-40) compared with the LMA-Unique group (mean 18 cmH(2)O, range 6-30). Fibreoptic score of the position of the devices was significantly better in the i-gel group. Post-operative sore-throat and dysphagia were comparable with both devices. Both devices appeared to be simple alternatives to secure the airway. Significantly higher airway leak pressure suggests that the i-gel may be advantageous in this respect.

Effect of decreased inspiratory times on tidal volume. Bench model simulating cardiopulmonary resuscitation

BACKGROUND

During cardiopulmonary resuscitation (CPR) with a chest compression rate of 60-100/min the time for secure undisturbed ventilation in the chest decompression phase is only 0.3-0.5 s and it is unclear which tidal volumes could be delivered in such a short time.

OBJECTIVES

Attempts were made to assess the tidal volumes that can be insufflated in such a short time window.

METHODS

In a bench model tidal volumes were compared in simulated non-intubated and intubated patients employing an adult self-inflating bag-valve with inspiratory times of 0.25, 0.3, and 0.5 s. Respiratory system compliance values were 60 mL/cmH(2)O being representative for respiratory system conditions shortly after onset of cardiac arrest and 20 mL/cmH(2)O being representative for conditions after prolonged cardiac arrest.

RESULTS

With a respiratory system compliance of 60 mL/cmH(2)O, tidal volumes (mean+/-SD) in non-intubated versus intubated patients were 144+/-13 mL versus 196+/-23 mL in 0.25 s (p<0.01), 178+/-10 versus 270+/-14 mL in 0.3 s (p<0.01), and 310+/-12 mL versus 466+/-20 mL in 0.5 s (p<0.01). With a respiratory system compliance of 20 mL/cmH(2)O, tidal volumes in non-intubated patient versus intubated patients were 128+/-10 mL versus 186+/-20 mL in 0.25 s (p<0.01), 158+/-17 versus 250+/-14 mL in 0.3 s (p<0.01) and 230+/-21 mL versus 395+/-20 mL in 0.5 s (p<0.01).

CONCLUSIONS

Ventilation windows of 0.25, 0.3, and 0.5 s were too short to provide adequate tidal volumes in a simulated non-intubated cardiac arrest patient. In a simulated intubated cardiac arrest patient, ventilation windows of at least 0.5 s were necessary to provide adequate tidal volumes.

The mouth-to-bag resuscitator during standard anaesthesia induction in apnoeic patients

AIM

Ventilation of a non-intubated emergency patient by inexperienced rescuers with a standard bag-valve device may result in high inspiratory flow rates and subsequently high airway pressures with stomach inflation. Therefore, a self-inflating bag has been developed that requires lay rescuers to blow up a single-use balloon inside an adult bag-valve device, which, in turn, displaces air within the bag towards the patient. This concept has been compared to standard adult bag-valve devices earlier in bench models but not in patients.

METHODS

An anaesthetist who was blinded to all monitor tracings ventilated the lungs of 40 apnoeic patients during routine anaesthesia induction either with a standard bag-valve device or with the mouth-to-bag resuscitator in a random order. Study endpoints were peak inspiratory flow rates, peak airway pressure, tidal volumes and inspiratory time.

RESULTS

Peak inspiratory flow was 40+/-10lmin(-1) for the standard bag-valve device versus 33+/-13lmin(-1) for the mouth-to-bag resuscitator (P<0.0001); peak airway pressure was 17+/-5cmH(2)O versus 14+/-5cmH(2)O (P<0.0001); inspiratory tidal volume was 477+/-133ml versus 644+/-248ml (P<0.001) and inspiratory time was 1.1+/-0.3s versus 1.9+/-0.6s (P<0.0001).

CONCLUSION

Employing the mouth-to-bag resuscitator during simulated ventilation of a non-intubated patient in respiratory arrest significantly decreased peak inspiratory flow and peak airway pressure and increased inspiratory tidal volume and inspiratory times compared to a standard bag-valve device.

Naloxone Use in a Tiered-Response Emergency Medical Services System

OBJECTIVE

To examine the delivery and effect of naloxone for opioid overdose in a tiered-response emergency medical services (EMS) system and to ascertain how much time could be saved if the first arriving emergency medical technicians (EMTs) could have administered intranasal naloxone.

METHODS

This was case series of all EMS-treated overdose patients who received naloxone by paramedics in a two-tiered EMS system during 2004. The system dispatches basic life support-trained fire fighter-EMTs and/or advanced life support-trained paramedics depending on the severity of cases. Main outcomes were geographic distribution of naloxone-treated overdose, severity of cases, response to naloxone, and time interval between arrival of EMTs and arrival of paramedics at the scene.

RESULTS

There were 164 patients who received naloxone for suspected overdose. There were 75 patients (46%) initially unresponsive to painful stimulus. Respiratory rate was <10 breaths/min in 79 (48%). Death occurred in 36 (22%) at the scene or during transport. A full or partial response to naloxone occurred in 119 (73%). Recognized adverse reactions were limited to agitation/combativeness in 25 (15%) and emesis in six (4%). Average EMT arrival time was 5.9 minutes. Average paramedic arrival time was 11.6 minutes in most cases and 16.1 minutes in 46 cases (28%) in which paramedics were requested by EMTs at the scene.

CONCLUSIONS

There is potential for significantly earlier delivery of naloxone to patients in opioid overdose if EMTs could deliver intranasal naloxone. A pilot study training and authorizing EMTs to administer intranasal naloxone in suspected opioid overdose is warranted.

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.

Ventilation strategies in the obstructed airway in a bench model simulating a nonintubated respiratory arrest patient

BACKGROUND

The Smart Bag MO(R) is an adult flow-limited bag-valve device designed to reduce the risk of stomach inflation in an unprotected airway. Its properties in severe airway obstruction are as yet unknown.

METHODS

In a bench model, we evaluated respiratory mechanics and delivered tidal volumes although ventilating at airway resistances of 4, 10, and 20 cm H(2)O . L(-1) . s(-1) once with a flow-limited bag-valve device and once with a standard bag-valve device to simulate a respiratory arrest patient with an unprotected airway.

RESULTS

Inspiratory times were always longer with the flow-limited bag-valve device than with the standard bag-valve device. Lung tidal volume in the simulated unobstructed airway was 750 +/- 70 mL using the flow-limited bag-valve device versus 780 +/- 30 mL using the standard bag-valve device (n.s.); in the simulated medium obstructed airway it was 800 +/- 70 versus 850 +/- 20 mL (n.s.), and in the simulated severely obstructed airway it was 210 +/- 20 versus 170 +/- 10 mL (P < 0.01). Peak airway pressure in the simulated unobstructed airway was 15 +/- 2 cm H(2)O using the flow-limited bag-valve device versus 22 +/- 4 cm H(2)O using the standard bag-valve device (P < 0.01); in the simulated medium obstructed airway it was 22 +/- 1 versus 39 +/- 7 cm H(2)O (P < 0.01), and in the simulated severely obstructed airway it was 26 +/- 1 versus 61 +/- 3 cm H(2)O (P < 0.01). Stomach inflation in the simulated unobstructed airway was 0 mL/min using both bag-valve devices; in the simulated medium obstructed airway it was 0 mL/min for the flow-limited bag-valve device versus 200 +/- 20 mL/min for the standard bag-valve device (P < 0.01), and in the simulated severely obstructed airway it was 0 versus 1240 +/- 50 mL/min (P < 0.01).

CONCLUSION

In a simulated severely obstructed unprotected airway, the use of a flow-limited bag-valve device resulted in longer inspiratory times, higher tidal volumes, lower inspiratory pressures, and no stomach inflation compared with a standard bag-valve device.

Automated emergency ventilation devices in a simulated unprotected airway

BACKGROUND

Automated ventilation devices are becoming more popular for emergency ventilation, but there is still not much experience concerning the optimal ventilation mode.

METHODS

In a bench model representing a non-intubated patient in respiratory and cardiac arrest, we compared a pressure-cycled with a time- and volume-cycled automated ventilation device in their completely automated modes. The main study endpoints were inspiratory time, respiratory rate, stomach inflation, and lung tidal volumes.

RESULTS

The pressure-cycled device inspired for 6.7 s in the respiratory arrest setting (respiratory rate 5.6/min), and never reached its closing pressure in the cardiac arrest setting (respiratory rate 1 breath/min). The time- and volume-cycled device inspired in both settings for 1.7 s (respiratory rate 13 breaths/min). In the respiratory arrest setting, mask leakage was 620 ± 20 mL for the pressure-cycled device vs. 290 ± 10 mL for the time- and volume-cycled device (p < 0.0001); lung tidal volume was 1080 ± 50 mL vs. 490 ± 20 mL, respectively (p < 0.0001); and there was no stomach inflation for either device. In the cardiac arrest setting, pressure-cycled device mask leakage was 5460 ± 60 mL vs. 240 ± 20 mL (p < 0.0001) for the time- and volume-cycled device (p < 0.0001); stomach inflation was 13,100 ± 100 mL vs. 90 ± 10 mL, respectively (p < 0.0001); and lung tidal volume 740 ± 60 mL vs. 420 ± 20 mL, respectively (p < 0.0001).

CONCLUSION

In a simulated respiratory arrest setting, ventilation with an automated pressure-cycled ventilation device resulted in lower respiratory frequency and larger tidal volumes compared to a time- and volume-cycled device. In a simulated cardiac arrest setting, ventilation with an automated pressure-cycled ventilation device, but not a time- and volume-cycled device, resulted in continuous gastric insufflation.

Device capable of reducing gastric inflation during artificial ventilation in a manikin model

Gastric inflation is a significant issue when ventilation is performed in cases of unprotected airway. The objective of this study was to compare the amounts of gastric insufflation and tidal volumes produced by a hose-extended bag-valve-mask (BVM) device supplemented by an interposed reservoir bag with a similar BVM without the reservoir in a simulated human model. Fourteen academic dental staff members performed 10 ventilations on a manikin using the reservoir-supplemented device in comparison to the control BVM in a randomized order. Lung compliance was adjusted to 45 (high) and 4.5 mL/mbar (low), and the lower esophageal sphincter pressure (LOSP) simulator to a pressure of 15 and 3 mbar, respectively, in different settings. Lower tidal volumes were observed with the new device than with the control BVM at high compliance with LOSP of 15 mbar (median 506 vs. 787 mL, respectively; p = 0.0002) and LOSP of 3 mbar (median 544 vs. 794 mL, respectively; p = 0.0006), as well as during ventilation at low lung compliance and LOSP of 3mbar (median 131 vs. 163 mL, respectively; p = 0.0342). No differences were detected at low lung compliance and LOSP of 15 mbar (median 175 vs. 194 mL; p = 0.3804). Gastric inflation almost exclusively occurred in case of low lung compliance, being markedly lower with the new device than with the control device at 15 mbar LOSP (300 vs. 2225 mL, respectively; p = 0.0006), and at 3 mbar LOSP (1138 vs. 3050 mL, respectively; p = 0.0001). Application of the hose-extended bag-valve-mask device supplemented with a reservoir bag reduces tidal volumes. Marked reduction of gastric inflation by use of this device becomes effective under conditions with low lung compliance.

Minimizing stomach inflation versus optimizing chest compressions

In a bench model, we evaluated a bag-valve device (Smart Bag MO) with limited maximum inspiratory gas flow developed to reduce the risk of stomach inflation in an unprotected airway. During simulated cardiopulmonary resuscitation with uninterrupted chest compressions, ventilation with the "disabled" Smart Bag MO or an adult self-inflating bag-valve device provided only adequate tidal volumes if inspiratory time was 0.5 s. Ventilation with the "enabled" Smart Bag MO, even in ventilation windows of 0.5 s, provided inadequate tidal volumes during simulated cardiopulmonary resuscitation and would result in hypoventilation in a patient.

In-hospital resuscitation

A recent world expert conference on resuscitation and emergency cardiac care led to evidence-based international guidelines for cardiopulmonary resuscitation (CPR). Several changes to CPR interventions were recommended, and will have to be implemented into clinical practice. The poor prognosis of patients who suffer in-hospital cardiac arrest may be improved with developments in CPR interventions. In the present review the most important changes recommended by the new CPR guidelines and the latest promising CPR investigations are described, focusing on their impact on in-hospital resuscitation.

Analysis of non-invasive ventilation effects on gastric inflation using a non-linear mathematical model

A non-linear mathematical model of the oesophagus was developed to study the effects of non-invasive ventilation variables on the severity of gastric inflation. The model was based on the non-linear physical characteristics of biological tissue. The model simulated oesophageal mechanical function during non-invasive ventilation in cardiac arrest (2:30 ventilations/chest compressions cycles) and respiratory arrest (1:5 ventilations/s) as recommended by the European Resuscitation Council (ERC) in its 2005 guidelines for adult basic and advanced life support. Model predictions establish a strong correlation between the expiratory time and the occurrence of gastric inflation. For cardiac arrest, when using ventilation pressure lower than 12 cmH2O, expiratory time between consequent ventilations and time until the occurrence of gastric inflation were linearly dependent (r = 0.98). This linear correlation changed abruptly when airway pressure exceeded the threshold pressure of 12 cmH2O, indicating that air had entered the stomach during the first ventilation. The interval at which the pressure at the distal section of the oesophagus was above the lower oesophageal sphincter (LES) opening pressure was significantly prolonged in the model of cardiac arrest (approximately 5.5 s compared to 3 s in respiratory arrest), thus allowing a greater amount of air to enter the stomach at relatively low airway pressures. During cardiac arrest, the mean pressure at the distal section of the oesophagus and the amplitude of air backflow were higher compared to the mean pressure and amplitude during respiratory arrest. This is also due to the shorter expiratory intervals in the 2:30 ventilations/chest compressions technique. The model indicates that the time required for the air trapped in the oesophagus to completely deflate is approximately 2 s. This may be longer than the expiratory time recommended by the 2005 guidelines. Model predictions support the 2005 guidelines regarding the decrease in the tidal volume and in the inspiratory pressure in an effort to minimise gastric inflation.

Reflection on a patient's airway management during a ward-based resuscitation

BACKGROUND

The bag-valve-mask (BVM) system is a common adjunct used during adult resuscitation to ventilate the lungs and deliver oxygen to patients in cardiopulmonary arrest. Gastric inflation, regurgitation and aspiration are well-documented complications of BVM ventilation, which can have serious consequences for patients.

AIM

The aim of this paper is to review the cause of gastric inflation, regurgitation and aspiration during BVM ventilation and to consider techniques that have been suggested to reduce these problems.

METHOD

Using a reflective model, the author revisits an actual cardiac arrest, and within a structured framework considers the event itself, the context of the event and looks at ways in which practice could be improved in future.

RESULTS

It is clear from the evidence that a reduction in peak airway pressure can reduce the risk of gastric inflation, regurgitation and aspiration. A review of the available research strongly suggests that in expert hands, the most effective means of reducing peak airway pressure is by reducing tidal volume by using a smaller bag.

CONCLUSION

Although the evidence, as presented, for a reduction in bag size is convincing, there appears to be a problem that less regular users do not appear to be able to produce effective tidal volumes when using a smaller bag. If a reduced bag size is standardized, further research using a diverse group of health care workers with the BVM is required before a clear policy can be achieved. It is likely that training and practice will be shown to be important for nursing staff expected to use the smaller BVM.

New airways for resuscitation?

Over the last 15 years supraglottic airway devices (SADs), most notably the classic laryngeal mask airway (LMA) have revolutionised airway management in anaesthesia. In contrast for resuscitation, both in and outside hospital, facemask ventilation and tracheal intubation remain the mainstays of airway management. However there is evidence that both these techniques have complications and are often poorly performed by inexperienced personnel. Tracheal intubation also has the potential to cause serious harm or death through unrecognised oesophageal intubation. SADs may have a role in airway management for resuscitation as first responder devices, rescue devices or for use during patient extraction. In particular they may be beneficial as the level of skill required to use the device safely may be less than for the tracheal tube. Concerns have been expressed over the ability to ventilate the lungs successfully and also the risk of aspiration with SADs. The only SADs recommended by ILCOR in its current guidance are the classic LMA and combitube. Several SADs have recently been introduced with claims that ventilation and airway protection is improved. This pragmatic review examines recent developments in SAD technology and the relevance of this to the potential for using SADs during resuscitation. In addition to examining research directly related to resuscitation both on bench models and in patients the review also examines evidence from anaesthetic practice. SADS discussed include the classic, intubating and Proseal LMAs, the combitube, the laryngeal tube, laryngeal tube sonda mark I and II and single use laryngeal masks.

Over-the-head cardiopulmonary resuscitation improves efficacy in basic life support performed by professional medical personnel with a single rescuer: a simulation study

Two-rescuer cardiopulmonary resuscitation (CPR) is considered the best method for professional basic life support (BLS). However, in many prehospital cardiac arrest situations, one rescuer has to begin CPR alone while the other performs additional tasks. In theory, over-the-head CPR is a suitable alternative in this situation, with the added benefit of allowing the single rescuer to use a self-inflating bag for ventilation. In this trial, we compared standard single-rescuer CPR with over-the-head CPR in manikins. We planned this study using a crossover study design where each participant administered both CPR techniques in a randomized order. Ventilation and chest compression data were collected with analysis software during a 2-min CPR test for each technique. Sixty-seven emergency medical technician students participated in this trial. Over-the-head CPR allowed for superior ventilation compared to standard CPR (number of correct ventilations: 330 of 760 versus 279 of 779; P = 0.002). The quality of delivered chest compressions did not differ between the two groups (correct chest compressions: 4293 of 6304 versus 4313 of 6395; P = 0.44). In conclusion, our study has shown that over-the-head CPR may be an effective alternative BLS technique when a single professional rescuer has to perform CPR, likely offering superior ventilation and comparable chest compression quality compared with standard BLS.

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.

Should there be a change in the teaching of airway management in the medical school curriculum?

OBJECTIVE

To evaluate the use of the Laryngeal Mask Airway (LMA), the oesophageal-tracheal combitube (ETC) and the tracheal tube (TT) by medical students, with a view to recommend changes to the medical school curriculum.

METHODS

A prospective cohort study of 93 third-year medical students were taught the use of LMA, ETC and TT on manikins and had their skills tested at 0 and 6 months.

RESULTS

Overall, LMA insertion was the fastest technique with a mean time taken for successful insertion of 32.2 s, compared to that for ETC (55.0 s, P = 0.000) and TT (71.5s, P = 0.000). There was a significant delay in the time taken for insertion at 6 months for all three devices: 13.5 s for the LMA (P = 0.000), 29.6 s for the ETC (P = 0.000) and 31.8 s for the TT (P = 0.001). Both the ETC and the TT had a significantly lower first-attempt success rate at 6 months (ETC: 91% versus 63%, P = 0.000 and TT: 80% versus 55%, P = 0.003) but not the LMA (96% versus 92%, P = 0.549). At 6 months, the overall success rate was 99% for the LMA, 100% for the ETC and 93% for the TT. Complication rate was higher for the ETC (9% versus 46%, P = 0.000) and the TT (38% versus 78%, P = 0.005) but not for the LMA (3% versus 10%, P = 0.688).

CONCLUSIONS

The use of the TT is difficult and the skills acquired by the medical students deteriorate significantly over time. The LMA and the ETC seem to have an advantage over the TT in that they are more easily learnt and the skills better retained. It is recommended that these alternative devices be included in the medical school curriculum for airway management.

Effects of decreasing peak flow rate on stomach inflation during bag-valve-mask ventilation

Reducing inspiratory flow rate and peak airway pressure may be important in order to minimise the risk of stomach inflation when ventilating an unprotected airway with positive pressure ventilation. This study was designed to yield enough power to determine whether employing an inspiratory gas flow limiting bag-valve device (SMART BAG, O-Two Medical Technologies Inc., Ontario, Canada) would also decrease the likelihood of stomach inflation in an established bench model of a simulated unintubated respiratory arrest patient. The bench model consists of a training lung (lung compliance, 50 ml/cm H2O; airway resistance, 4 cm H2O/l/s) and a valve simulating lower oesophageal sphincter opening at a pressure of 19 cm H(2)O. One hundred and ninety-one emergency medicine physicians were requested to ventilate the manikin utilising a standard single-person technique for 1 min (respiratory rate, 12/min; Vt, 500 ml) with both a standard adult bag-valve-mask and the SMART BAG. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The SMART BAG versus standard bag-valve-mask resulted in significantly (P < 0.001) lower (mean +/- S.D.) mean airway pressure (14 +/- 2 cm H2O versus 16 +/- 3 cm H2O), respiratory rates (13 +/- 3 breaths per min versus 14 +/- 4 breaths per min), incidence of stomach inflation (4.2% versus 38.7%) and median stomach inflation volumes (351 [range, 18-1211 ml] versus 1426 [20-5882 ml]); lung tidal volumes (538 +/- 97 ml versus 533 +/- 97 ml) were comparable. Inspiratory to expiratory ratios were significantly (P < 0.001) increased (1.7 +/- 0.5 versus 1.5 +/- 0.6). In conclusion, the SMART BAG reduced inspiratory flow, mean airway pressure and both the incidence and actual volume of stomach inflation compared with a standard bag-valve-mask device while maintaining delivered lung tidal volumes and increasing the inspiratory to expiratory ratio.

Arterial blood gases with 700 ml tidal volumes during out-of-hospital CPR

The optimal tidal and minute ventilation during cardiopulmonary resuscitation (CPR) is not known. In the present study seven adult, non-traumatic, out-of-hospital cardiac arrest patients were intubated and mechanically ventilated at 12 min(-1) with 100% oxygen and a tidal volume of 700 ml (10 +/- 2 ml kg(-1)). Arterial blood gas samples were analysed after 6-8 min of unsuccessful resuscitation and mechanical ventilation. Mean PaCO2 was 5.2 +/- 1.3 kPa and mean PaO2 30.7 +/- 17.2 kPa. The patient with the highest (14 ml kg(-1)) and lowest (8 ml kg(-1)) tidal volumes per kg had the lowest and highest PaCO2 values of 2.6 and 6.8 kPa, respectively. Linear regression analysis confirmed a significant correlation between arterial pCO2 and tidal volume in ml/kg, r2 = 0.87. We conclude that aiming for an estimated ventilation of 10 ml kg(-1) tidal volume at frequency of 12 min(-1) might be expected to achieve normocapnia during ALS.

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.