title: Evidence-based guidelines for the use of defibrillation pads.
abstract: OBJECTIVE
  Defibrillation pads are used routinely at both cardiac arrests and cardioversion procedures. There are currently no evidence-based guidelines on how often pads should be replaced, although it has been suggested that they should be changed as often as every three shocks to maintain optimal performance. Previously, we have shown that on exposure to air, pad mass diminishes over time due to evaporation--an effect likely to lead to poorer conduction between skin and paddle. This prospective study was designed to determine if evaporation is accelerated by the passage of a defibrillation current and to formulate evidence-based guidelines for defibrillation pad replacement.
  
  
  METHODS
  3M defibrillation pads (2346N) were collected from acute wards and emergency departments in two hospitals in the UK over a 2 month period. The duration of exposure to air, number and energy of shocks, and type of procedure were recorded. When no longer required, pad masses were determined and the loss of pad mass due to evaporation calculated.
  
  
  RESULTS
  26 pairs of pads were collected from 14 cardiac arrests and 12 cardioversions. The total defibrillation energy used ranged from 150 to 5080 J and evaporative drying time from 4 to 38 min. The rate of evaporation from these pads (86.1 mg x min(-1)) was not significantly different from pads previously studied on volunteers in the absence of a defibrillation current (99.4 mg x min(-1)). Of the defibrillation pads exposed to air for less than 30 min, in only one of 49 pads was the loss of mass due to evaporation consistent with a significant increase in transthoracic impedance (TTI). Correspondingly, of two pads used for more than 30 min, both attained a mass consistent with a significant increase in TTI.
  
  
  CONCLUSIONS
  Defibrillation pads can be used for up to 30 min without evaporation causing a clinically significant increase in TTI. The passage of a defibrillation current across pads does not further accelerate water loss.
authors.affiliation: Shackleton Department of Anaesthetics, Southampton University Hospitals NHS Trust, SO16 6YD, Southampton, UK.
authors.forename: N E
authors.initials: NE
authors.lastname: Drury
authors.forename: G W
authors.initials: GW
authors.lastname: Petley
authors.forename: F
authors.initials: F
authors.lastname: Clewlow
authors.forename: C D
authors.initials: CD
authors.lastname: Deakin
mesh_terms: D004554:Electric Countershock / Q000295:instrumentation*; D019317:Evidence-Based Medicine; D005782:Gels; D006801:Humans; D017410:Practice Guidelines as Topic; D011446:Prospective Studies; D013997:Time Factors
chemical_list: D005782:Gels