The effects of bed height and time on the quality of chest compressions (andresultant intrathoracic pressures) during Cardio Pulmonary Resuscitation (CPR).

Dr Asher Lewinsohn, BSc, MB BS (Hons), Dr Peter Sherren MB BS,Dr Asher Lewinsohn, BSc, MB BS (Hons), Dr Peter Sherren MB BS, Dr Dhuleep Sanjay Wijayatilake, BSc, MB BS, FRCADr Dhuleep Sanjay Wijayatilake, BSc, MB BS, FRCA

Department of Anaesthesia & Intensive Care Medicine, Queens HospDepartment of Anaesthesia & Intensive Care Medicine, Queens Hospital, Essex, England.ital, Essex, England.

IntroductionIntroduction� Sudden cardiac arrest is a leading cause of death in Europe, affecting about 700,000individuals every year1.

� Although current guidelines on effective CPR try to take most factors into account, alack of a comprehensive evidence base means that most guidelines are still basedmainly on expert opinion2.

The objectives of this study were to:

1. Investigate if there is a difference in effectiveness of chest compression at differentbed heights relative to the person performing chest compressions.

2. Investigate if fatigue occurs when performing chest compressions, and its effect onintra thoracic pressures generated.

ß Due to ethical constraints in obtaining consent for patients having CPR, it was decidedto use a manikin model (Laerdal ALS) to provide comparability and reproducibility.

ß Participants were randomly selected from a range of various specialities includingparamedics, doctors, nurses and support staff, following institutional ethics boardapproval.

ß Exclusion criterion: 1. No previous Basic Life Support training in past 1 year.

2. Refused verbal consent to take part in study.

ß The standard lungs of the Laerdal manikin were replaced with a set of lungs from theµresus annie¶ series. This allowed direct intubation and a limit on the number ofconnecting parts in the system.

ß A size 9 portex endo tracheal tube was used to intubate the manikin, and the cuff wasinflated with 10ml of air. This was connected to a Dragor series Evita 4 Ventilator.

ß Ventilation was set to a tidal volume of 500ml, a rate of 10bpm and an inspiratory timeof 1.7 seconds with no PEEP applied (as per ALS protocols). FiO2=30%.

ß The manikin was placed on a standard hospital recovery trolley, and CPR wasperformed for 2 minutes at 3 different bed heights relative to the subjects beforerecording data: 1) Xiphisternal area (Fig 1), 2) ASIS (Anterior Superior Iliac Spine (Fig2),3) Mid Thigh (Fig 3). Between each set of readings, a 2 minute rest period was given.

ResultsResults

ConclusionsConclusions

Materials and MethodsMaterials and Methods

ß There is now a significant growing evidence base which indicates that there is anoptimal bed height for effective CPR.

ß Our results suggest that this height is with the top of the bed in line with the operatorsknee.

ß This would have the patient¶s chest approximately in line with the operator¶s mid-thigh.

ß The second part of our study suggests that CPR would be more effective if the personperforming it changed every 2 minutes (1 cycle of the ALS protocol) .

ß This simple change can easily be achieved by a team approach.

ReferencesReferences1. 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 MorbidityStatistics in Europe. Eur Heart J 1997;18:1231-48.

2. International Liaison Committee on Resuscitation. International Consensus oncardiopulmonary resuscitation and emergency cardiovascular science with treatmentrecommendations. Part 2. Adult basic life support. Resuscitation 2005; 67: 187-201

Fig 4 Setup of ALS Resus manikin andDrager Evita series 4 ventilator.

Bed Height Mean Pmax at 30 seconds Standard Deviation

1) Xiphisternal area 15.36 * 2.52

2) ASIS 17.69 * 2.91

3) Mid Thigh 18.89 * 2.80

Fig 1. Fig 2. Fig3.

Table 1 : Effects of bed height position on intrathoracic pressure generated after 30seconds of CPR. N=100. * signifies statistical significance. (by way of ANOVA variancetesting, p < 0.01.)

30 seconds CPR 2 minutes CPR

Pmax Mean 17.52* 14.5 *

Table 2: Mean intrathoracic pressures generated during CPR at 30 seconds as comparedto 2 minutes. * signifies statistical significance. (by way of a one-tailed paired student t-test, p < 0.01.)

ß The intra thoracic pressures generated were detected by the ventilator, and used as anindication of the effectiveness of CPR.

ß In the second part of the study, subjects were asked to perform CPR for a total of 2minutes. The intra thoracic pressures generated at 30 seconds and 2 minutes wererecorded.

Limitations of StudyLimitations of Studyß Our study used a manikin model to simulate the human chest wall cavity and weunderstand that this may not exactly mirror the pressures generated during CPR in a livesubject.

ß We decided not to use a cadaveric model because, after death, the elastic recoil of thechest wall cavity is lost.

ß In the future, it would be interesting to repeat the study using human subjects, butobtaining consent (which will likely be retrospective) will of course be difficult.