Study objective: To characterize fatigue-induced deterioration in the adequacy of closed-chest compressions performed over a period of 5 minutes and to determine whether CPR providers can recognize the effects of fatigue on compression adequacy. Design: Prospective evaluation of study subjects performing closed-chest compressions on an electronic mannequin that assesses compression placement and depth. Setting: Major resuscitation room in rural university hospital emergency department. Participants: Eleven experienced nursing assistants who regularly provide CPR in the ED. Results: Each study participant performed 5 minutes of closed-chest compressions. Compression adequacy (for placement and depth) was assessed with the mannequin and reported on an attached monitor out of view of the study subjects. Subjects were asked to verbally indicate the point during their 5-minute compression period at which they felt too fatigued to provide effective compressions (arbitrarily defined as a minimum of 90% of all compressions being judged correct by the mannequin). We used one-way repeated-measures ANOVA and regression analysis to determine whether compression adequacy diminished over time. ANOVA was also used to determine whether the total compressions performed per minute diminished over time. The percentage of correct chest compressions decreased significantly after 1 minute of compressions (P =.0001). We found 92.9% of compressions performed during minute 1 to be correct. The percentages for minutes 2 through 5 were as follows: 67.1%, 39.2%, 31.2%, and 18.0%. Regression analysis revealed a decrement in compression adequacy of 18.6% per minute after the first minute of compressions. The number of total compressions attempted per minute did not decrease (P =.98). Study subjects did not accurately identify the point during their 5-minute sessions at which their fatigue caused compressions to become impaired. Whereas mean compression adequacy declined below 90% after only 1 minute, the time of indicated fatigue was 253±40 seconds (mean±SD). Conclusion: Although compression rate was maintained over time, chest compression quality declined significantly over the study period. Because CPR providers could not recognize their inability to provide proper compressions, cardiac arrest team leaders should carefully monitor compression adequacy during CPR to assure maximally effective care for patients receiving CPR. [Hightower D, Thomas SH, Stone CK, Dunn K, March JA: Decay in quality of closed-chest compressions over time. Ann Emerg Med September 1995;26:300-303.]