Oxygen delivery and return of spontaneous circulation with ventilation:compression ratio 2:30 versus chest compressions only CPR in pigs

Part 10: Pediatric basic and advanced life support: 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations

Note From the Writing Group: Throughout this article, the reader will notice combinations of superscripted letters and numbers (eg, “Family Presence During ResuscitationPeds-003”). These callouts are hyperlinked to evidence-based worksheets, which were used in the development of this article. An appendix of worksheets, applicable to this article, is located at the end of the text. The worksheets are available in PDF format and are open access.

Chest compressions versus ventilation plus chest compressions in a pediatric asphyxial cardiac arrest animal model

OBJECTIVE

To compare the ventilation achieved with chest compressions (CC) or ventilation plus compressions (VC) in a pediatric animal model of cardiac arrest.

DESIGN

Randomized experimental study.

SETTING

Experimental department of a University Hospital.

METHODS

Twelve infant pigs with asphyxial cardiac arrest. Sequential 3-min periods of VC and CC were performed for a total duration of 9 min. Tidal volume (TV), end-tidal CO(2) (EtCO(2)), mean arterial pressure (MAP), central venous pressure (CVP), mean pulmonary arterial pressure (mPAP), and peripheral, cerebral, and renal saturations were recorded and arterial and venous blood gases were analyzed.

RESULTS

VC achieved a TV similar to the preset parameters on the ventilator, whilst the TV in CC was very low (P < 0.001). EtCO(2) with VC was significantly higher than with CC (14.0 vs. 3.9 mmHg, P < 0.05). Arterial pH was higher with VC than with CC (6.99 vs. 6.90 mmHg, P < 0.05). Arterial PCO(2) was lower with VC than with CC (62.1 vs. 97.0 mmHg, P < 0.05). There were no significant differences in the MAP; CVP; mPAP; peripheral, renal, and cerebral saturations; or lactate concentrations between the two techniques.

CONCLUSIONS

VC achieves better ventilation than CC during cardiopulmonary resuscitation and has no negative effect on the hemodynamic situation.

Update on cardiopulmonary resuscitation and emergency cardiovascular care guidelines

PURPOSE

The key changes included in the 2005 cardiopulmonary resuscitation (CPR) and emergency cardiac care (ECC) guidelines are reviewed. Advances since publication of the current guidelines are also discussed.

SUMMARY

The 2005 CPR and ECC guidelines include several key changes from the previous version published in 2000. The new guidelines place an increased emphasis on chest compressions and recommend a compression:ventilation (C:V) ratio of 30:2. Current knowledge on defibrillation has also been incorporated by recommending that Emergency Medical Service (EMS) rescuers give two minutes of CPR before defibrillation when the response interval is greater than four to five minutes and EMS responders did not witness the arrest. Another major change is the recommendation for a single shock to be administered followed immediately by CPR with no check of the cardiac rhythm until two minutes of CPR has been performed postdefibrillation. The 2005 guidelines recommend that an automated external defibrillator should be implemented in public locations where there is a relatively high likelihood of witnessed cardiac arrest. In addition, the most recent guidelines highlight the shift from primary-rhythm-based therapies and resuscitation to a focus on neurologic outcomes.

CONCLUSION

Several evidence-based changes were included in the 2005 CPR and ECC guidelines, including a C:V ratio of 30:2 and mitigation of hands-off time, early defibrillation, administration of a single shock versus a three-shock sequence, use of public-access defibrillators, and a shift from primary-rhythm-based therapies to a focus on neurologic outcomes.

Optimizing chest compressions during delivery-room resuscitation

There is a paucity of data to support the recommendations for cardiac compressions for the newly born. Techniques, compression to ventilation ratios, hand placement, and depth of compression guidelines are generally based on expert consensus, physiologic plausibility, and data from pediatric and adult models.

Comparison of chest compression only and standard cardiopulmonary resuscitation for out-of-hospital cardiac arrest in Singapore

OBJECTIVE

Chest compression only cardiopulmonary resuscitation (CC-CPR) without ventilation has been proposed as an alternative to standard cardiopulmonary resuscitation (CPR) for bystanders. However, there has been controversy regarding the relative effectiveness of both of these techniques. We aim to compare the outcomes of cardiac arrest patients in the cardiac arrest and resuscitation epidemiology study who either received CC-CPR, standard CPR or no bystander CPR.

METHODS

This prospective cohort study involved all out-of-hospital cardiac arrest (OHCA) patients attended to by emergency medical service (EMS) providers in a large urban centre. The data analyses were conducted secondarily on these collected data. The technique of bystander CPR was reported by paramedics who arrived at the scene.

RESULTS

From 1 October 2001 to 14 October 2004, 2428 patients were enrolled into the study. Of these, 255 were EMS-witnessed arrests and were excluded. 1695 cases did not receive any bystander CPR, 287 had standard CPR and 154 CC-CPR. Patient characteristics were similar in both the standard and CC-CPR groups except for a higher incidence of residential arrests and previous heart disease sufferers in the CC-CPR group. Patients who received standard CPR (odds ratio (OR) 5.4, 95% confidence interval (CI) 2.1-14.0) or CC-CPR (OR 5.0, 95% CI 1.5-16.4) were more likely to survive to discharge than those who had no bystander CPR. There was no significant difference in survival to discharge between those who received CC-CPR and standard CPR (OR 0.9, 95% CI 0.3-3.1).

CONCLUSION

We found that patients were more likely to survive with any form of bystander CPR than without. This emphasises the importance of chest compressions for OHCA patients, whether with or without ventilation.

Basic life support

PURPOSE OF REVIEW

Bystander cardiopulmonary resuscitation increases the chances of survival after out-of-hospital cardiac arrest. Existing bystander cardiopulmonary resuscitation rates are poor. There are several strategies for increasing the frequency and effectiveness of bystander cardiopulmonary resuscitation. These include simplifying the technique for basic life support, emphasizing the importance of compressions over ventilation, reducing the length of training by using video-based self-instruction and widening the range of those trained to include school children.

RECENT FINDINGS

A change in compression-ventilation ratio from 15: 2 to 30: 2 increases the number of compressions delivered. There is some evidence that compression-only cardiopulmonary resuscitation may increase survival rates from out-of-hospital cardiac arrest. Video-based self-instruction enables laypeople to be trained in basic life support in a fraction of the time of traditional courses. School children can be taught basic life support and can be used to help disseminate the skill.

SUMMARY

The optimal basic life support technique that will generate the highest survival rates from out-of-hospital cardiac arrest has not been determined, but there is increasing evidence that the existing technique needs to be simplified. Bystander cardiopulmonary resuscitation increases survival but it needs to be undertaken more frequently if overall survival rates are to be improved significantly.

Cardiopulmonary resuscitation for out of hospital cardiac arrest

American Heart Association advocates chest compression without ventilation

Comparison of 15:1, 15:2, and 30:2 compression-to-ventilation ratios for cardiopulmonary resuscitation in a canine model of a simulated, witnessed cardiac arrest

OBJECTIVES

This experimental study compared the effect of compression-to-ventilation (CV) ratios of 15:1, 15:2, and 30:2 on hemodynamics and resuscitation outcome in a canine model of a simulated, witnessed ventricular fibrillation (VF) cardiac arrest.

METHODS

Thirty healthy dogs, irrespective of species (mean +/- SD, 19.2 +/- 2.2 kg), were used in this study. A VF arrest was induced. The dogs received cardiopulmonary resuscitation (CPR) and were divided into three groups based on the applied CV ratios of 15:1, 15:2, and 30:2. After 1 minute of untreated VF, 4 minutes of basic life support (BLS) was performed. At the end of the 4 minutes, the dogs were defibrillated with an automatic external defibrillator (AED) and advanced cardiac life support (ACLS) efforts were continued for 10 minutes or until restoration of spontaneous circulation (ROSC) was attained, whichever came first.

RESULTS

None of the hemodynamic parameters, and arterial oxygen profiles was significantly different between the three groups during BLS- and ACLS-CPR. Eight dogs (80%) from each group achieved ROSC during BLS and ACLS. The survival rate was not different between the three groups. In the 15:1 and 30:2 groups, the number of compressions delivered over 1 minute were significantly greater than in the 15:2 group (73.1 +/- 8.1 and 69.0 +/- 6.9 to 56.3 +/- 6.8; p < 0.01). The time for ventilation during which compressions were stopped at each minute was significantly lower in the 15:1 and 30:2 groups than in the 15:2 group (15.4 +/- 3.9 and 17.1 +/- 2.7 to 25.2 +/- 2.6 sec/min; p < 0.01).

CONCLUSIONS

In a canine model of witnessed VF using a simulated scenario, CPR with three CV ratios, 15:1, 15:2, and 30:2, did not result in any differences in hemodynamics, arterial oxygen profiles, and resuscitation outcome among the three groups. CPR with a CV ratio of 15:1 provided comparable chest compressions and shorter pauses for ventilation between each cycle compared to a CV ratio of 30:2.

Quality of chest compressions during 10min of single-rescuer basic life support with different compression: ventilation ratios in a manikin model

INTRODUCTION

Good quality basic life support (BLS) improves outcome during cardiac arrest. As fatigue may reduce BLS performance over time we wanted to examine the quality of chest compressions in a single-rescuer scenario during prolonged BLS with different compression:ventilation ratios (C:V ratios).

MATERIAL AND METHODS

Professional paramedics were asked to perform single-rescuer BLS with C:V ratios of 15:2, 30:2 and 50:2 for 10 min each in random order. A Laerdal Medical Resusci Anne Simulator with PC Skillreporting System was used for BLS quality analysis. Total number of chest compressions, compression depth and compression rate were measured and the differences between the C:V ratios were analysed with repeated measures ANOVA. For analysis of fatigue, chest compression variables for each 2-min period were analysed and compared with the first 2-min period using repeated measures ANOVA.

RESULTS

Altogether 50 paramedics completed the study. The mean number of chest compressions increased significantly from 604 to 770 and 862 with C:V ratios of 15:2, 30:2 and 50:2, respectively. Chest compression rate was significantly higher with C:V ratio of 15:2 compared to 30:2 and 50:2 but was above 100 per minute for all three ratios. However, the mean chest compression depth did not change significantly between the different C:V ratios. The number of chest compressions did not change significantly with time for any of the three C:V ratios. Compression depth did decline after the first 2-min period for 30:2 and 50:2 as did compression rate for all three ratios. However all were above the guideline limits for the entire test period.

CONCLUSION

Increasing the C:V ratio increases the number of chest compressions during 10 min of BLS. Compression depth and compression rate were within guideline recommendations for all three ratios. We found no decline in chest compression quality below guideline recommendations during 10 min of BLS with any of the three different C:V ratios.

Arterial blood gases during basic life support of human cardiac arrest victims

BACKGROUND

Ventilation with tidal volumes sufficient to raise the victim's chest is an integral part of guidelines for lay-rescuer basic life support, but optimal tidal volume, frequency and ratio to chest compressions are not known.

METHODS

Adults with non-traumatic, out-of-hospital cardiac arrest, who were not successfully resuscitated following advanced life support by the staff of a physician-manned ambulance, were included. Advanced life support comprised tracheal intubation and mechanical ventilation with tidal volume of 700 ml and 100% oxygen, 12 times per min. An arterial blood sample was drawn at the end of the resuscitation attempt and analysed on the scene. After the victim was declared dead, basic life support was initiated with chest compressions and mouth-to-mask or mouth-to-tracheal tube ventilation (15:2), with volumes sufficient to make the chest rise. The tracheal tube was equipped with an impedance valve to avoid passive ventilation secondary to chest compressions. Arterial blood samples were drawn after 7-8 min of basic life support and analysed on the scene.

RESULTS

Six men and two women, median (range) age 72 (32-86) years, were included in the study. Four of these received mouth-to-mask ventilation and four mouth-to-tracheal tube ventilation. Mean (S.D.) arterial blood carbon dioxide and oxygen tension during advanced life support were 6.4 (1.4)kPa and 22 (15)kPa, respectively. Similar values during basic life support were 9.6 (1.9)kPa and 8.5 (1.6)kPa, respectively, with no differences between the ventilation methods.

CONCLUSION

Ventilation during basic life support performed according to international guidelines (2000) resulted in arterial hypercapnia and hypoxia.

Compression-only cardiopulmonary resuscitation for bystanders and first responders

PURPOSE OF REVIEW

The current resuscitation guidelines consider ventilation and chest compression essential components of resuscitation and therefore only one methodology, standard cardiopulmonary resuscitation, is explicitly recommended for the treatment of both respiratory and cardiac arrests. Pathophysiological and experimental observations argue that this generalization results in suboptimal treatment for victims of cardiac arrest.

RECENT FINDINGS

For more than a decade animal studies have demonstrated that assisted ventilation is not essential during the initial treatment of a fibrillatory arrest; but only in the last year have these results been confirmed in humans. These new observations come from a handful of systems utilizing cardiocerebral resuscitation in their prehospital resuscitation of adult victims of presumed cardiac arrest. They have all demonstrated a dramatic increase in survival. Recent data also indicate that survival is significantly increased when laypersons perform chest-compression-only cardiopulmonary resuscitation.

SUMMARY

The current resuscitation guidelines regarding the prehospital treatment of victims of adult cardiac arrest should be modified to explicitly permit the use of continuous-chest-compression cardiopulmonary resuscitation.

The new American Heart Association cardiopulmonary resuscitation guidelines: should children and adults have to share?

PURPOSE OF REVIEW

The latest American Heart Association guidelines for pediatric cardiopulmonary resuscitation (CPR) were published in December 2005. Changes from the 2000 guidelines were directed toward simplifying CPR. Infants, children, and adults now share the same recommendation for the initial compression:ventilation ratio. This is a significant change for pediatricians trained in the importance of a respiratory etiology of pediatric cardiopulmonary arrest. The present review will focus on the rationale behind these guideline changes.

RECENT FINDINGS

The new guidelines for single rescuer CPR include a compression:ventilation ratio of 30: 2 for both adult and pediatric victims. The impetus for this recommendation is based on recent appreciation for the deleterious effects of hyperventilation as well as an attempt to increase bystander delivery of CPR. The physiologic results of hyperventilation are discussed. The new pediatric basic life support guideline changes are underscored. Research representing the spectrum of opinions on the optimal compression:ventilation ratio, including compression-only CPR, is presented.

SUMMARY

Although based primarily on adult, animal, and computational models, the new compression:ventilation ratio, recommended for both initial pediatric and adult CPR, is a reasonable recommendation. The simplified CPR guidelines released in 2005 will hopefully contribute to improved bystander delivery of CPR and improved outcome.

Resuscitation outcomes comparing year 2000 with year 2005 ALS guidelines in a pig model of cardiac arrest

BACKGROUND

Ventricular fibrillation remains the leading cause of death in western societies. International organizations publish guidelines to follow in case of cardiac arrest. The aim of the present study is to assess whether the newly published guidelines record similar resuscitation success with the 2000 Advanced Life Support Guidelines on Resuscitation in a swine model of cardiac arrest.

METHODS AND RESULTS

Nineteen landrace/large white pigs were used. Ventricular fibrillation was induced with the use of a transvenous pacing wire inserted into the right ventricle. The animals were randomized into two groups. In Group A, 10 animals were resuscitated using the 2000 guidelines, whereas in Group B, 9 animals were resuscitated using the 2005 guidelines. Both algorithms recorded similar successful resuscitation rates, as 60% of the animals in Group A and 44.5% in Group B were successfully resuscitated. However, animals in Group A restored a rhythm, compatible with a pulse, quicker than those in Group B (p=0.002). Coronary perfusion pressure (CPP) was not adversely affected by three defibrillation attempts in Group A.

CONCLUSIONS

Both algorithms' resulted in comparable resuscitation success, however, guidelines 2000 resulted in faster resuscitation times. These preliminary results merit further investigation.

Use of an inspiratory impedance threshold valve during chest compressions without assisted ventilation may result in hypoxaemia

INTRODUCTION

Although the concept of intermittent airway occlusion with the inspiratory impedance threshold valve (ITV) is a well-recognised strategy for improving efficiency of cardiopulmonary resuscitation (CPR), little is known about possible pulmonary side effects.

METHODS

After a baseline chest CT-scan, 24 pigs with beating hearts undergoing apnoeic oxygenation received an injection of a contrast medium and were then assigned randomly to either active compression-decompression CPR with ITV (ACD ITV CPR), ACD CPR alone, or standard-CPR with ITV (standard-ITV CPR), or standard-CPR alone. After a maximum of 5 min of chest compressions or if oxygen saturation dropped below 70%, the experiment was stopped, haemodynamic variables and blood gas values were measured, and another CT-scan was performed; all animals underwent a 30 min recovery-period and a third subsequent CT-scan.

RESULTS

At baseline arterial oxygen saturation by pulse oxymetry was 99% in all four groups; in both the ACD ITV CPR and the standard-ITV CPR groups, arterial oxygen saturation dropped below 70% within 126+/-9s, whereas chest compressions in all ACD CPR and standard-CPR pigs were performed over 5 min (P<0.001). Before stopping chest compressions arterial oxygen pressure decreased in the ACD ITV CPR group from 426+/-96 to 42+/-8 mmHg while it decreased in the ACD CPR group only from 415+/-116 to 197+/-127 mmHg (P<0.001 between groups); in the standard-ITV CPR group arterial oxygen partial pressure decreased from 427+/-109 to 34+/-5 mmHg while oxygen partial pressure decreased only from 467+/-44 to 144+/-98 mmHg in the standard-CPR group (P<0.004 between groups). After the second CT scan arterial oxygen partial pressure decreased further to 19+/-2 mmHg in the ACD ITV CPR versus 210+/-41 mmHg in the ACD CPR group; to 20+/-2 mmHg in the standard-ITV CPR versus 148+/-33 mmHg in the standard-CPR group. Lung-density values (Hounsfield units) were significantly higher in the ACD ITV CPR versus ACD CPR group (-134+/-54 versus -330+/-77) and standard-ITV CPR versus standard-CPR group (-98+/-50 versus -387+/-42). After a 30 min recovery-period, there were no significant differences in arterial oxygen partial pressure (ACD ITV CPR 275+/-110 mmHg versus ACD CPR 379+/-111 mmHg and standard-ITV CPR 265+/-138 mmHg versus standard CPR 367+/-55 mmHg). Furthermore, there were no differences in lung density values between groups after 30 min of recovery.

CONCLUSION

In this animal model with a beating heart, intermittent airway obstruction through an ITV combined with apnoeic oxygenation and without active ventilation resulted in hypoxaemia due to transiently impaired lung function.

Haemodynamic effects of adrenaline (epinephrine) depend on chest compression quality during cardiopulmonary resuscitation in pigs

BACKGROUND

Adrenaline (epinephrine) is used during cardiopulmonary resuscitation (CPR) based on animal experiments without supportive clinical data. Clinically CPR was reported recently to have much poorer quality than expected from international guidelines and what is generally done in laboratory experiments. We have studied the haemodynamic effects of adrenaline during CPR with good laboratory quality and with quality simulating clinical findings and the feasibility of monitoring these effects through VF waveform analysis.

METHODS AND RESULTS

After 4 min of cardiac arrest, followed by 4 min of basic life support, 14 pigs were randomised to ClinicalCPR (intermittent manual chest compressions, compression-to-ventilation ratio 15:2, compression depth 30-38 mm) or LabCPR (continuous mechanical chest compressions, 12 ventilations/min, compression depth 45 mm). Adrenaline 0.02 mg/kg was administered 30 s thereafter. Plasma adrenaline concentration peaked earlier with LabCPR than with ClinicalCPR, median (range), 90 (30, 150) versus 150 (90, 270) s (p = 0.007), respectively. Coronary perfusion pressure (CPP) and cortical cerebral blood flow (CCBF) increased and femoral blood flow (FBF) decreased after adrenaline during LabCPR (mean differences (95% CI) CPP 17 (6, 29) mmHg (p = 0.01), FBF -5.0 (-8.8, -1.2) ml min(-1) (p = 0.02) and median difference CCBF 12% of baseline (p = 0.04)). There were no significant effects during ClinicalCPR (mean differences (95% CI) CPP 4.7 (-3.2, 13) mmHg (p = 0.2), FBF -0.2 (-4.6, 4.2) ml min(-1)(p = 0.9) and CCBF 3.6 (-1.8, 9.0)% of baseline (p = 0.15)). Slope VF waveform analysis reflected changes in CPP.

CONCLUSION

Adrenaline improved haemodynamics during laboratory quality CPR in pigs, but not with quality simulating clinically reported CPR performance.

Simplified dispatch-assisted CPR instructions outperform standard protocol

OBJECTIVE

Dispatch-assisted chest compressions only CPR (CC-CPR) has gained widespread acceptance, and recent research suggests that increasing the proportion of compression time during CPR may increase survival from out-of-hospital cardiac arrest. We created a simplified CC-CPR protocol to reduce time to start chest compressions and to increase the proportion of time spent delivering chest compressions. This simplified protocol was compared to a published protocol, Medical Priority Dispatch System (MPDS) Version 11.2, recommended by the National Academies of Emergency Dispatch.

METHODS

Subjects were randomized to the MPDS v11.2 protocol or a simplified protocol. Data was recorded from a Laerdal Resusci Anne Skillreporter manikin. A simulated emergency medical dispatcher, contacted by cell phone, delivered standardized instructions for both protocols. Outcomes included chest compression rate, depth, hand position, full release, overall proportion of compressions without error, time to start of CPR and total hands-off chest time. Proportions were analyzed by Wilcoxon's Rank Sum tests and time variables with Welch ANOVA and Wilcoxon's Rank Sum test. All tests used a two-sided alpha-level of 0.05.

RESULTS

One hundred and seventeen subjects were randomized prospectively, 58 to the standard protocol and 59 to the simplified protocol. The average age of subjects in both groups was 25 years old. For both groups, the compression rate was equivalent (104 simplified versus 94 MPDS, p = 0.13), as was the proportion with total release (1.0 simplified versus 1.0 MPDS, p = 0.09). The proportion to the correct depth was greater in the simplified protocol (0.31 versus 0.03, p < 0.01), as was the proportion of compressions done without error (0.05 versus 0.0, p = 0.16). Time to start of chest compressions and total hands-off chest time were better in the simplified protocol (start time 60.9s versus 78.6s, p < 0.0001; hands-off chest time 69 s versus 95 s, p < 0.0001). The proportion with correct hand position, however, was worse in the simplified protocol (0.35 versus 0.84, p < 0.01).

CONCLUSIONS

The simplified protocol was as good as, or better than the MPDS v11.2 protocol in every aspect studied except hand position, and the simplified protocol resulted in significant time savings. The protocol may need modification to ensure correct hand position. Time savings and improved quality of CPR achieved by the new set of instructions could be important in strengthening critical links in the cardiac chain of survival.

Thoracic impedance changes measured via defibrillator pads can monitor ventilation in critically ill patients and during cardiopulmonary resuscitation

OBJECTIVE

Monitoring of ventilation performance during cardiopulmonary resuscitation would be desirable to improve the quality of cardiopulmonary resuscitation. To investigate the potential for measuring ventilation rate and inspiration time, we calculated the correlation in waveform between transthoracic impedance measured via defibrillator pads and tidal volume given by a ventilator.

DESIGN

Clinical study.

SETTING

Emergency department of a tertiary care university hospital.

PATIENTS

A convenience sample of mechanical ventilated patients (n = 32), cardiac arrest patients (n = 20), and patients after restoration of spontaneous circulation (n = 31) older than 18 were eligible.

INTERVENTIONS

The Heartstart 4000SP defibrillator (Laerdal Medical Cooperation, Stavanger, Norway) with additional capabilities of recording thoracic impedance changes was used.

MEASUREMENTS AND MAIN RESULTS

The relationship between impedance change and tidal volume (impedance coefficient) was calculated. The mean (sd) correlations between the impedance waveform and the tidal volume waveform in the patient groups studied were .971 (.027), .969 (.032), and .967 (.035), respectively. The mean (sd) impedance coefficient for all patients in the study was .00194 (.0078) Omega/mL, and the mean (sd) specific (weight-corrected) impedance coefficient was .152 (.048) Omega/kg/mL. The measured thorax impedance change for different tidal volumes (400-1000 mL) was approximately linear.

CONCLUSIONS

The impedance sensor of a defibrillator is accurate in identifying tidal volumes, when chest compressions are interrupted. This also allows quantifying ventilation rates and inspiration times. However this technology, at its present state, provides only limited practical means for exact tidal volume estimation.

The need for head rotation and abdominal compressions during bystander cardiopulmonary resuscitation

The current AHA-ECC guidelines for basic life support focus on the provision of good chest compressions with minimal interruptions for patients with presumed out-of-hospital cardiac arrest. Moreover, international consensus guidelines now support the use of chest compression-only cardiopulmonary resuscitation (CPR) instructions for dispatcher-assisted CPR given over the phone to untrained bystanders. However, evidence that strongly challenge these recommendations have been overlooked. A review of this evidence argues for the need for head rotation (a hands-free method of airway control) and abdominal compressions during bystander CPR.

Brain tissue oxygen pressure and cerebral metabolism in an animal model of cardiac arrest and cardiopulmonary resuscitation

OBJECTIVE

Direct measurement of brain tissue oxygenation (PbtO2) is established during spontaneous circulation, but values of PbtO2 during and after cardiopulmonary resuscitation (CPR) are unknown. The purpose of this study was to investigate: (1) the time-course of PbtO2 in an established model of CPR, and (2) the changes of cerebral venous lactate and S-100B.

METHODS

In 12 pigs (12-16 weeks, 35-45 kg), ventricular fibrillation (VF) was induced electrically during general anaesthesia. After 4 min of untreated VF, all animals were subjected to CPR (chest compression rate 100/min, FiO2 1.0) with vasopressor therapy after 7, 12, and 17 min (vasopressin 0.4, 0.4, and 0.8 U/kg, respectively). Defibrillation was performed after 22 min of cardiac arrest. After return of spontaneous circulation (ROSC), the pigs were observed for 1h.

RESULTS

After initiation of VF, PbtO2 decreased compared to baseline (mean +/- SEM; 22 +/- 6 versus 2 +/- 1 mmHg after 4 min of VF; P < 0.05). During CPR, PbtO2 increased, and reached maximum values 8 min after start of CPR (25 +/- 7 mmHg; P < 0.05 versus no-flow). No further changes were seen until ROSC. Lactate, and S-100B increased during CPR compared to baseline (16 +/- 2 versus 85 +/- 8 mg/dl, and 0.46 +/- 0.05 versus 2.12 +/- 0.40 microg/l after 13 min of CPR, respectively; P < 0.001); lactate remained elevated, while S-100B returned to baseline after ROSC.

CONCLUSIONS

Though PbtO2 returned to pre-arrest values during CPR, PbtO2 and cerebral lactate were lower than during post-arrest reperfusion with 100% oxygen, which reflected the cerebral low-flow state during CPR. The transient increase of S-100B may indicate a disturbance of the blood-brain-barrier.

The problem with and benefit of ventilations: should our approach be the same in cardiac and respiratory arrest?

PURPOSE OF REVIEW

Recent advances in cardiopulmonary resuscitation have led to greater understanding of cardio-cerebral-pulmonary interactions during the process. The purpose of this discussion is to update the physiologic understanding of these interactions during cardiopulmonary resuscitation, review the detrimental and beneficial effects of ventilation, and identify implications for clinical practice.

RECENT FINDINGS

There is an inversely proportional relationship between mean intrathoracic pressure, coronary perfusion pressure, and survival from cardiac arrest. Increased ventilation rates and increased ventilation duration impede venous blood return to the heart, decreasing hemodynamics and coronary perfusion pressure during cardiopulmonary resuscitation. It has also been shown that there is a direct and immediate transfer of the increase in intrathoracic pressure to the cranial cavity with each positive pressure ventilation, also reducing cerebral perfusion pressure. The reduced amount of blood flowing through the pulmonary bed during cardiopulmonary resuscitation tends to be overventilated, compromising hemodynamics to both the heart and brain and resulting in ventilation/perfusion mismatch.

SUMMARY

The fundamental hemodynamic principle of intrathoracic pressure defines cardio-cerebral-pulmonary interactions during cardiopulmonary resuscitation. Further research is essential to optimize these interactions during treatment of profound shock.

Clinical and hemodynamic comparison of 15:2 and 30:2 compression-to-ventilation ratios for cardiopulmonary resuscitation*

OBJECTIVE

To compare cardiopulmonary resuscitation (CPR) with a compression to ventilation (C:V) ratio of 15:2 vs. 30:2, with and without use of an impedance threshold device (ITD).

DESIGN

Prospective randomized animal and manikin study.

SETTING

Animal laboratory and emergency medical technician training facilities.

SUBJECTS

Twenty female pigs and 20 Basic Life Support (BLS)-certified rescuers.

INTERVENTIONS, MEASUREMENTS, AND MAIN RESULTS

ANIMALS

Acid-base status, cerebral, and cardiovascular hemodynamics were evaluated in 18 pigs in cardiac arrest randomized to a C:V ratio of 15:2 or 30:2. After 6 mins of cardiac arrest and 6 mins of CPR, an ITD was added. Compared to 15:2, 30:2 significantly increased diastolic blood pressure (20 +/- 1 to 26 +/- 1; p < .01); coronary perfusion pressure (18 +/- 1 to 25 +/- 2; p = .04); cerebral perfusion pressure (16 +/- 3 to 18 +/- 3; p = .07); common carotid blood flow (48 +/- 5 to 82 +/- 5 mL/min; p < .001); end-tidal CO2 (7.7 +/- 0.9 to 15.7 +/- 2.4; p < .0001); and mixed venous oxygen saturation (26 +/- 5 to 36 +/- 5, p < .05). Hemodynamics improved further with the ITD. Oxygenation and arterial pH were similar. Only one of nine pigs had return of spontaneous circulation with 15:2, vs. six of nine with 30:2 (p < 0.03). HUMANS: Fatigue and quality of CPR performance were evaluated in 20 BLS-certified rescuers randomized to perform CPR for 5 mins at 15:2 or 30:2 on a recording CPR manikin. There were no significant differences in the quality of CPR performance or measurement of fatigue. Significantly more compressions per minute were delivered with 30:2 in both the animal and human studies.

CONCLUSIONS

These data strongly support the contention that a ratio of 30:2 is superior to 15:2 during manual CPR and that the ITD further enhances circulation with both C:V ratios.

What is the optimal chest compression-ventilation ratio?

PURPOSE OF REVIEW

Despite a more widespread knowledge of basic cardiopulmonary resuscitation maneuvers in the community, the survival rate for patients with cardiac arrest has remained essentially unchanged in the past 30 years. Over the past few decades, many different compression-ventilation ratios have been studied in terms of best coronary and cerebral oxygen delivery, restoration of spontaneous circulation, and neurologic outcome. This article summarizes the recent evidence presented at the International Consensus on Resuscitation Science in January 2005.

RECENT FINDINGS

Recent data from animal and mathematical models suggest a move to a higher compression-ventilation ratio to maximize coronary and cerebral oxygen delivery during cardiac arrest and long-term neurologic outcome. Prospective randomized human data on alternative compression-ventilation ratios are missing and new evidence seems to indicate the inadequacy of both lay and professional rescuers in providing chest compression and ventilating the victim in cardiac arrest. Finally, observational and animal studies highlight the hidden danger of inadvertent hyperventilation during advanced cardiac life support as a reduction of both coronary and perfusion pressure secondary to increased intrathoracic pressure and decreased venous return.

SUMMARY

The optimal compression-ventilation ratio is still unknown and the best tradeoff between oxygenation and organ perfusion during cardiopulmonary resuscitation is probably different for each patient and scenario. A discrepancy between what is recommended by the current guidelines and the 'real world' of cardiopulmonary resuscitation has resulted in a near flat survival rate from cardiac arrest in the past few years.

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.

A comparison of CPR delivery with various compression-to-ventilation ratios during two-rescuer CPR

BACKGROUND

The number of chest compressions required for optimal generation of coronary perfusion pressure remains unknown although studies examining compression-to-ventilation ratios higher than 15:2 (C:V) in animals have reported higher C:V to be superior for return of spontaneous circulation and neurologic outcome. We examined human performance of two-rescuer CPR using various C:V.

METHODS

Thirty six EMT-Basic students in their final week of training performed two-rescuer CPR using C:V of 15:2, 30:2, 40:2, 50:2, and 60:2 on a recording resuscitation manikin. Compression and ventilation variables were recorded by computer while the number of pauses for ventilations and the hands-off time (time not spent performing chest compressions) were abstracted by hand. Data were analyzed by ANOVA and significant differences from the standard treatment of C:V = 15:2 were assessed by Tukey's HSD post hoc test.

FINDINGS

The number of compressions delivered per minute increased with increasing C:V while the hands-off time and pauses for ventilations decreased. All comparisons were significantly different from C:V = 15:2 (P < 0.001). The ventilation numbers decreased with increasing C:V although mean minute volume exceeded 1l for all C:V.

INTERPRETATION

A 15:2 compression-to-ventilation ratio when performed during two-rescuer CPR results in 26s of hands off time each minute while only delivering 60 compressions. Alternative C:V ratios of 30:2, 40:2, 50:2, and 60:2 all exceed the AHA recommended 80 compressions/min while still delivering a minute volume in excess of 1l.

Modified cardiopulmonary resuscitation (CPR) instruction protocols for emergency medical dispatchers: rationale and recommendations

BACKGROUND

International consensus guidelines now support the use of "chest compressions-only" cardiopulmonary resuscitation (CPR) instructions (CCOIs) by emergency medical dispatch (EMD) personnel providing telephone assistance to untrained bystanders at a cardiac arrest scene. These guidelines are based largely on evolving experimental data and a clinical trial conducted in one venue with distinct emergency medical services (EMS) system features. Accordingly, the Council of Standards for the National Academies of Emergency Dispatch was asked to adapt a modified telephone CPR protocol, and specifically one that could be applied more broadly to the spectrum of EMS systems.

METHODS

A group of international EMD specialists, researchers and professional association representatives analyzed available scientific data and considered variations in EMS systems, particularly those in Europe and North America.

RESULTS AND CONCLUSIONS

Several recommendations were established: (1) to avoid confusion, bystanders already providing CPR should continue those previously learned methods; (2) following a sudden collapse unlikely to be of respiratory etiology, CCOIs should be provided when the bystander is not CPR-trained, declining to perform mouth-to-mouth ventilation or unsure of actions to take; (3) following 4 min of CCOIs, ventilations can be provided, but, for now, only at a compression-ventilation ratio of 100:2 until EMS arrives; (4) until more data become available, dispatchers should follow existing compression-ventilation protocols for children and adult cases involving probable respiratory/trauma etiologies; (5) EMD CPR protocols should account for EMS system features and receive quality oversight and expert medical direction.

["Topless" cardiopulmonary resuscitation. Fashion or science?]

A decade after the onset of a discussion whether ventilation could be omitted from bystander basic life support (BLS) algorithms, the state of the evidence is reevaluated. Initial animal studies and a prospective randomized patient trial had suggested that omission of ventilation during the first minutes of lay cardiopulmonary resuscitation (CPR) did not impair patient outcomes. More recent studies demonstrate, however, that this may hold true only in very specific scenarios, and that the chest compression-only technique was never superior to standard BLS. Instead of calling basics of BLS training and practice into question, more and better training of lay persons and professionals appears mandatory, and targeted use of dispatcher-guided telephone CPR should be evaluated and, if it improves outcome, it should be encouraged. Future studies should focus much less on the omission but on the optimization of ventilation under the specific conditions of CPR.