title: An investigation of thrust, depth and the impedance cardiogram as measures of cardiopulmonary resuscitation efficacy in a porcine model of cardiac arrest.
abstract: OBJECTIVE
  Optimising the depth and rate of applied chest compressions following out of hospital cardiac arrest is crucial in maintaining end organ perfusion and improving survival. The impedance cardiogram (ICG) measured via defibrillator pads produces a characteristic waveform during chest compressions with the potential to provide feedback on cardiopulmonary resuscitation (CPR) and enhance performance. The objective of this pre-clinical study was to investigate the relationship between mechanical and physiological markers of CPR efficacy in a porcine model and examine the strength of correlation between the ICG amplitude, compression depth and end-tidal CO2 (ETCO2).
  
  
  METHODS
  Two experiments were performed using 24 swine (12 per experiment). For experiment 1, ventricular fibrillation (VF) was induced and mechanical CPR commenced at varying thrusts (0-60 kg) for 2 min intervals. Chest compression depth was recorded using a Philips QCPR device with additional recording of invasive physiological parameters: systolic blood pressure, ETCO2, cardiac output and carotid flow. For experiment 2, VF was induced and mechanical CPR commenced at varying depths (0-5 cm) for 2 min intervals. The ICG was recorded via defibrillator pads attached to the animal's sternum and connected to a Heartsine 500 P defibrillator. ICG amplitude, chest compression depth, systolic blood pressure and ETCO2 were recorded during each cycle. In both experiments the within-animal correlation between the measured parameters was assessed using a mixed effect model.
  
  
  RESULTS
  In experiment 1 moderate within-animal correlations were observed between physiological parameters and compression depth (r=0.69-0.77) and thrust (r=0.66-0.82). A moderate correlation was observed between compression depth and thrust (r=0.75). In experiment 2 a strong within-animal correlation and moderate overall correlations were observed between ICG amplitude and compression depth (r=0.89, r=0.79) and ETCO2 (r=0.85, r=0.64).
  
  
  CONCLUSIONS
  In this porcine model of induced cardiac arrest moderate within animal correlations were observed between mechanical and physiological markers of chest compression efficacy demonstrating the challenge in utilising a single mechanical metric to quantify chest compression efficacy. ICG amplitude demonstrated strong within animal correlations with compression depth and ETCO2 suggesting its potential utility to provide CPR feedback in the out of hospital setting to improve performance.
authors.affiliation: Cardiovascular Research Unit, Craigavon Area Hospital, Portadown, UK. Electronic address: drandrewhowe@gmail.com.
authors.forename: Andrew
authors.initials: A
authors.lastname: Howe
authors.affiliation: HeartSine Technologies Ltd, Belfast, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: O'Hare
authors.affiliation: Veterinary Anaesthesia Consultancy, Larne, Co Antrim, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Crawford
authors.affiliation: Exploristics Ltd, Belfast, UK.
authors.forename: Bruno
authors.initials: B
authors.lastname: Delafont
authors.affiliation: University of Ulster, Newtownabbey, Belfast, Northern Ireland, UK.
authors.forename: Olibhear
authors.initials: O
authors.lastname: McAlister
authors.affiliation: HeartSine Technologies Ltd, Belfast, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Di Maio
authors.affiliation: Royal (Dick) School of Veterinary Studies, Dept. of Anaesthesia, University of Edinburgh, Edinburgh, UK.
authors.forename: Eddie
authors.initials: E
authors.lastname: Clutton
authors.affiliation: Belfast Heart Centre, Royal Victoria Hospital, Belfast, UK.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Adgey
authors.affiliation: Cardiovascular Research Unit, Craigavon Area Hospital, Portadown, UK.
authors.forename: David
authors.initials: D
authors.lastname: McEneaney
mesh_terms: D000818:Animals; D002307:Cardiography, Impedance / Q000379:methods*; D016887:Cardiopulmonary Resuscitation / Q000379:methods* / Q000592:standards; D004195:Disease Models, Animal; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods*; D058687:Out-of-Hospital Cardiac Arrest / Q000503:physiopathology / Q000628:therapy*; D013552:Swine; D013997:Time Factors
keywords: Automated external defibrillator (AED); Cardiopulmonary resuscitation (CPR); Chest compression depth; End-tidal carbon dioxide; Impedance cardiography; Transthoracic impedance