The effects of bed height and time on the quality of chest compressions during simulated Cardiopulmonary
Resuscitation
Sherren PB, Lewinsohn A, Wijayatilake DS
Department of Anaesthesia and Intensive Care, Queen’s Hospital, UK
Background
• Sudden cardiac arrest is a leading cause of death in Europe, affecting about 700,000 individuals every year1.
• Despite all the research and education that has gone into the field of CPR, survival rates remain relatively bleak2.
• Although ILCOR make efforts to discuss the appropriate patient and rescuer position, these are based largely on expert opinion with only a small evidence base3.
• Cardiac vs Thoracic pump theories4.
The objectives of this study were to:
•Investigate the effect of bed height on the quality of chest compressions (Primary outcome).
•Investigate if fatigue occurs during the first two minutes of chest compressions.
Objectives
Methods• Participants were selected from a range of specialities
following approval from R&D department.
• Exclusion criterion:• No previous Basic Life Support training in past 1 year.• Refused verbal consent to take part in study.
• A size 9 portex ETT was used to intubate a Laerdal ALS manikin, and the cuff was inflated with 10ml of air. This was connected to a Dragor series Evita 4 Ventilator.
• IPPV was set to VCV with a tidal volume of 500ml, a rate of 10bpm, an inspiratory time of 1.7 seconds and no PEEP (as per ALS protocols).
Methods•The manikin was placed on a standard hospital recovery trolley, and chest compressions were performed at 3 different bed heights (relative to the rescuer).
•Between each set of readings an appropriate rest period was given.
•The 3 bed heights used were 1) Mid Thigh 2) ASIS 3) Xiphisternal area*
Methods•Chest compressions were performed for 30 seconds at each bed level until measurements were taken. At the ASIS level chest compression were continued for 2 minutes.
•At 30 seconds and 2 minutes the inspiratory Pawp and residual/trough pressures were measured.
•The intra thoracic pressure change (ΔITP) was obtained
ΔITP = Pawp – Residual/trough awp during inspiration.
• On the basis of a preliminary work it was calculated that a sample of size of 98 would be required to detect a 20% increase in the mean Pawp from the xiphisternal level to the other bed heights (The primary outcome).
• The sample size was calculated using an α level of 0.05 and a 80% power.
• The intrathoracic pressures generated at the 3 bed heights were analysed with a three way ANOVA test.
• When comparing the means obtained at 30 seconds and 2 minutes, a one-tailed paired student t-test was used.
• P- values of <0.05 were deemed to be statistical significant.
Statistics
Results
Table 1 : Spread of specialties involved in the trial, n=101
Grade/position Number of candidates
Doctors: Juniors (Foundation year) Seniors (Specialist trainees / Registrars) Consultants
93511
Nurses: Band 5 Band 6
1110
Prehospital: Paramedics EMT’s
86
Others: including physiotherapists, students, porters, health care assistants and operating department assistants.
11
Results
Xiphisternal ASIS Mid Thigh P – Value
Mean Pawp at 30 seconds, cmH2O (SD)
15.36
(2.52)
17.69
(2.91)
18.89
(2.80)
<0.01*
Mean ΔITP at 30 seconds,
cmH2O (SD)
11.14
(2.69)
13.34
(2.74)
14.36
(2.83)
<0.01*
Table 2 : Effects of bed height position on intrathoracic pressure generated after 30 seconds of CPR (N=101). *signifies statistical significance.
Results
30 seconds CPR
2 minutes CPR P –Value
Mean Pawp, cmH2O (SD)
17.69
(2.91)
14.51
(2.89)
<0.01*
Table 3 : Mean Pawp generated during CPR at 30 seconds as compared to 2 minutes (N=101). * signifies statistical significance.
Conclusions
• The results suggest that the highest quality chest compressions were achieved when the patient’s chest is in line with the operator’s mid-thigh.
• Chest compression effectiveness deteriorates significantly within 2 minutes, as providers fatigue. Providers should be changed every cycle of CPR and not be allowed to continue, despite any subjective absence of feeling fatigued.
• Using intrathoracic pressures as a surrogate measure of chest compression effectiveness is not as well established/validated as MCD.
• Our study used a manikin model to simulate the human chest wall cavity, and we understand that this may not exactly mirror the pressures generated during CPR in a live subject.
• The time-related results indicated a significant drop in CPR effectiveness from 30 seconds to 2 minutes but, without more time interval measurements, it is impossible to quantify a trend or identify the exact time at which CPR effectiveness drops off significantly
Limitations
Any Questions?
Thank you
References1. Sans S, Kesteloot H, Kromhout D. The burden of cardiovascular
diseases mortality in Europe. Task Force of the European Society of Cardiology on Cardiovascular Mortality and Morbidity Statistics in Europe. Eur Heart J 1997;18:1231-48.
2. Eisenberg MS, Mengert TJ. Cardiac resuscitation. N Engl J Med 2001; 344:1304—1313.
3. International Liaison Committee on Resuscitation. International Consensus on cardiopulmonary resuscitation and emergency cardiovascular science with treatment recommendations. Part 2. Adult basic life support. Resuscitation 2005; 67: 187-201.
4. Rudikoff MT, Maughan WL, Effron M, Freund P, Weisfeldt ML. Mechanisms of blood flow during cardiopulmonary resuscitation. Circulation 1980;61:345-352.
