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Free Paper presentations
at the January 2006 Scientific Symposium
Abstracts
Contents
adequate passive ventilation during CPR?
2. Teaching recognition of agonal breathing
improves diagnosis of cardiac arrest
3. Modelling the effects of interrupted compressions:
- less is better
4. Radiological measurement of the adult chest:
implications for chest compression depth
5. Evaluation of ambulance telephone CPR advice
for adult cardiac arrests
Does external chest compression generate adequate passive
ventilation during cardiopulmonary resuscitation? A clinical study.
Dr Charles Deakin
Medical Director
Hampshire Ambulance Service, Winchester
Other authors:
JF O’Neill, T Tabor ABSTRACT:
Aims: To determine whether compression-only CPR provides adequate passive ventilation in adult cardiac arrest patients.
Methodology: Adult cardiac arrest patients admitted to the Emergency Department by ambulance were treated according to ILCOR advanced life support guidelines, including tracheal intubation. Chest compressions were performed using an automated chest compression device (LUCAS) but without active decompression. During cardiac massage, positive pressure ventilation was paused for 30 seconds, allowing tidal volumes and CO2 minute volume during thumper-generated passive ventilation to be calculated.
Results: Data were collected on 17 patients (11 male), age 47-82 years. Average time from emergency call to arrival at hospital was 39.4 min. The median tidal volume per compression was 11.6ml (range 0.3 – 118.7 ml) and the median CO2 minute volume was 12.6 ml (range 2.4 – 107.3).
Conclusions: These are the first human data demonstrating the effects of external chest compression on passive ventilation. Our findings show that very little ventilation occurs; the tidal volumes are small, and certainly less than physiological dead space. CO2 minute volumes are also low (normal range 150-180 ml). Compression-only CPR does not produce adequate passive ventilation approximately 30 minutes into a cardiac arrest. Although chest compliance at the time of the study is likely to be less than at the time of collapse, the ability of bystander CPR to generate adequate gas exchange immediately after collapse is unlikely.
improves diagnosis of cardiac arrest
Dr Gavin Perkins
(Represented by C Christensen and G Walker)
Division of Medical Sciences
University of Birmingham
Other authors:
K Christensen, J Hulme, K G Monsieurs, G Walker
ABSTRACT:
Aims: Agonal breathing is present in up to 40% of pre-hospital cardiac arrests and is mistaken as a sign of circulation leading to omission of bystander resuscitation. The aim of this study was to test if tuition on recognizing agonal breathing could improve the diagnosis of cardiac arrest.
Methodology: First year medical students were randomised to control (taught standard CPR) or intervention (standard CPR plus tuition on recognising agonal breathing) groups. Two weeks after initial training, the students ability to recognise cardiac arrest were tested using a simulated victim demonstrating normal, absent or agonal breathing.
Results: Sixty-four students were randomised equally to intervention and control groups. The intervention group had superior diagnostic accuracy for cardiac arrest compared to the control group (90% vs 78%, P=0.03). The intervention group were more likely to correctly recognise cardiac arrest and initiate CPR than the standard control group (sensitivity 90% vs 78%, P=0.02). The improved results were predominantly due to recognition that agonal breathing is a sign of cardiac arrest (75% intervention group vs 43% control group, P=0.01).
Conclusion: This study demonstrates improved diagnostic accuracy and sensitivity of “checking for signs of circulation” by actively teaching CPR providers to recognise agonal breathing as a sign of cardiac arrest.
Modelling the effects of interrupted compressions: - less is better
Dr Gerrit J Noordergraaf
Anaesthesiologist
St Elisabeth Hospital, Nijmegen Medical Centre
The Netherlands
Other authors:
A Noordergraaf, GJ Scheffer, WHA Schilders ABSTRACT:
Aims: To investigate the effect of major and minor interruptions of chest compressions on coronary blood flow using a mathematical model.
Methodology: Using the Donders model, a physiology based model designed for investigations in CPR, we evaluated the effects of interruption of chest compressions (pe) under steady state CPR conditions. The pe, chosen for optimal output, was terminated and reinstituted after set periods of times (compression free time (CFT)). We noted pressures and flows in the circuit during CFT. The time needed to re-establish steady state was also calculated. This cycle was also done with interposed ventilations as an alternative source of pe, during CFT.
Results: Interruption of the steady state in CPR, shows an exponential decrease in flows in the direction of the initial state. Pulsatile pressures and flows are lost in the arterial system within ± 5 seconds. Flows in the venous system are disproportionally maintained. Coronary flow ceases almost immediately, but does not become negative. Interposed ventilation does little to attenuate these effects, with limited consequence of one or more ventilation.
Conclusion: The importance of adequate and uninterrupted chest compressions cannot be overstated. Mathematical models in CPR can be a useful tool for clinicians.
Radiological measurement of the adult chest:implications for chest compression depth
Dr Amelia Pickard
Southmead Hospital
North Bristol NHS Trust, Bristol
Other authors:
M Darby, J Soar
ABSTRACT:
Aims: The recommended depth of chest compression during adult cardiopulmonary resuscitation (CPR) is 4-5 cm, and for children one third the anterior-posterior (AP) chest diameter. A one third AP chest diameter compression depth has also been suggested for adult CPR. We have assessed chest CT scans to measure what proportion of the AP chest diameter is compressed during adult CPR.
Method: Measurements of AP diameter of chest CT scans were taken from the skin anteriorly at the middle of the lower half of the sternum, perpendicularly to the skin on the posterior thorax. Anatomical structures found at this level were also noted.
Results: One hundred consecutive CT scans were examined (66 males and 34 females). The age (mean ± SD) was 68 ± 12 years. AP chest diameter was 253 ± 27 mm for males and 235 ± 30 mm for females. Proportion of total AP chest diameter achieved with current compressions is 15.8-19.8% for males and 17.0-21.3% for females. The commonest anatomical structure found was the ascending aorta and the top of the left atrium.
Conclusion: The current recommended depth for chest compressions in adults is approximately one fifth the AP diameter of the chest.
Evaluation of ambulance telephone-CPR advice for adult cardiac arrests
Dr Charles Deakin
Medical Director
Hampshire Ambulance Service, Winchester
Other authors:
JF O’Neill ABSTRACT:
Introduction: When performed correctly, bystander cardiopulmonary resuscitation (CPR) can triple the chance of survival from out-of-hospital cardiac arrest 1. However, the number of patients who receive CPR is still low. Dispatcher-assisted CPR aims to improve the provision of CPR by giving telephone instructions to witnesses of cardiac arrest. We analysed emergency calls to calculate the time spent on each of the components of CPR.
Methodology: Recordings of ‘999’ calls to Hampshire Ambulance Service were retrospectively analysed over a six month period. Calls were selected using the Advanced Medical Priority Dispatch System (AMPDS) codes corresponding to adult cardiac arrest, and prompting the call handler to provide CPR instructions.
Results: 123 ‘999’ calls at which CPR instructions were given were analysed. Of these, 90 callers (73%) agreed to attempt CPR, 71 (58%) progressed to opening the airway, 57 (46%) performed mouth to mouth, and 32 (26%) began chest compressions. From the start of the call, the median time taken to perform each intervention was: open airway 2.1 min (range 1.0 - 8.0 min), start rescue breaths 4.1 min (range 1.3 – 10.6 min) and start chest compressions 5.25 min (range 2.6 – 12.5 min). Of those attempting CPR, 20% stopped because they could not move the patient onto a hard surface as instructed and 7% stopped because they did not wish to perform mouth-to-mouth ventilation. Gasping respirations were reported in 15% of calls.
Conclusions: The time spent opening the airway and attempting ventilations, resulted in significant delays in delivery of chest compression. Difficulty moving the patient to a hard surface and refusal to perform mouth-to-mouth ventilation were the commonest reasons for stopping CPR. Telephone CPR is limited in its ability to deliver effective CPR.
Reference: 1. Gallagher EJ et al. Effectiveness of bystander cardiopulmonary resuscitation and survival following out-of-hospital cardiac arrest. JAMA 1995; 274: 1922-5
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© Resuscitation Council (UK) 2006  This page last updated: 30 January 2006 |
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