title: Compression force-depth relationship during out-of-hospital cardiopulmonary resuscitation.
abstract: BACKGROUND
  Recent clinical studies reporting the high frequency of inadequate chest compression depth (<38 mm) during CPR, have prompted the question if adult human chest characteristics render it difficult to attain the recommended compression depth in certain patients.
  
  
  METHODS
  Using a specially designed monitor/defibrillator equipped with a sternal pad fitted with an accelerometer and a pressure sensor, compression force and depth was measured during CPR in 91 adult out-of-hospital cardiac arrest patients.
  
  
  RESULTS
  There was a strong non-linear relationship between the force of compression and depth achieved. Mean applied force for all patients was 30.3+/-8.2 kg and mean absolute compression depth 42+/-8 mm. For 87 of 91 patients 38 mm compression depth was obtained with less than 50 kg. Stiffer chests were compressed more forcefully than softer chests (p<0.001), but softer chests were compressed more deeply than stiffer chests (p=0.001). The force needed to reach 38 mm compression depth (F38) and mean compression force were higher for males than for females: 29.8+/-14.5 kg versus 22.5+/-10.2 kg (p<0.02), and 32.0+/-8.3 kg versus 27.0+/-7.0 kg (p<0.01), respectively. There was no significant variation in F38 or compression depth with age, but a significant 1.5 kg mean decrease in applied force for each 10 years increase in age (p<0.05). Chest stiffness decreased significantly (p<0.0001) with an increasing number of compressions performed. Average residual force during decompression was 1.7+/-1.0 kg, corresponding to an average residual depth of 3+/-2 mm.
  
  
  CONCLUSIONS
  In most out-of-hospital cardiac arrest victims adequate chest compression depth can be achieved by a force<50 kg, indicating that an average sized and fit rescuer should be able to perform effective CPR in most adult patients.
authors.affiliation: Institute for Experimental Medical Research, Ulleval University Hospital, N-0407 Oslo, Norway.
authors.forename: A E
authors.initials: AE
authors.lastname: Tomlinson
authors.forename: J
authors.initials: J
authors.lastname: Nysaether
authors.forename: J
authors.initials: J
authors.lastname: Kramer-Johansen
authors.forename: P A
authors.initials: PA
authors.lastname: Steen
authors.forename: E
authors.initials: E
authors.lastname: Dorph
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000552:Ambulances; D016887:Cardiopulmonary Resuscitation / Q000295:instrumentation*; D004548:Elasticity; D004739:England; D004867:Equipment Design; D005260:Female; D006323:Heart Arrest / Q000503:physiopathology / Q000628:therapy*; D006336:Heart Massage / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway; D010045:Outpatients; D011312:Pressure; D012307:Risk Factors; D013548:Sweden; D013909:Thorax / Q000503:physiopathology; D016896:Treatment Outcome