A randomized controlled triple blinded clinical trial with repeated measurements. The reporting of this study complies with the CONSORT (Consolidated Standards of Reporting Trials) statement for trials of non-pharmacological treatments.

The first aim of the study was to evaluate the effectiveness of the three competing interventions on the critical care nurses' knowledge of, attitudes toward and adherence to 17 ventilator bundle components; the second aim was to determine the effectiveness of adherence to 17 ventilator bundle components with pre-defined ventilator bundle on the psychological factors of critical care nurses including nurses' stressors in intensive care unit (ICU), perceived stress, trait and state anxieties; the third aim was to evaluate their impact on the clinical outcomes; and the fourth aim was comparing KAP and psychological factors with clinical outcomes.

The multi-center study was conducted in four academic teaching hospitals in Tehran, Iran. The study consisted of a 3-month baseline observation period (October 2011-December 2011, Period 1), followed by a 6-month intervention period (January 2012 to June 2012) and a 3 (July 2012-September 2012, Period 2), 15 (October 2012-December 2013, Period 3) and 21-months (January 2014-June 2015, Period 4) follow-up periods. The protocol for Evidence based guidelines (EBGs) for preventing VAP remained unchanged throughout the study period in every ICU.

Consecutive adult patients (age ≥18 years) who were admitted to the mixed medical-surgical ICUs (>72 hours) and received invasive ventilation (>48 hours) were enrolled and monitored daily for the development of ventilator-associate pneumonia (VAP) until ICU discharge or death. Patients with any limitation of code status were excluded from the study. Convenience sample of critical care nurses were recruited through letters and telephone and face-to-face invitations. Inclusion criteria were holding a degree qualification as a registered nurse and being a direct care provider (bedside). Nurses with less than one year experience in critical care unit or working less than whole study period were excluded. An investigator at each participating medical center was responsible for initial screening and enrollment.

The sample size was determined through power analysis, which revealed that a sample size of 40 participants was required to detect a 20% difference between VAP rates in each group (α = 0.05, 1-β = 0.9; dropout = 20%). The estimation of the effect size based on a previous VAP surveillance, conducted from March 2010 to December 2010 (unpublished data).

Included nurses were randomly assigned to control or one of the three competing intervention group (allocation ratio of 1:4). Randomization was accomplished using Random Allocation Software© (RAS; Informer Technologies, Inc.). Block randomization was performed by a computer-generated randomization list prepared by blinded biostatistician who had no clinical involvement in the trial. All nurses, data collectors, and statistician were blinded to group assignment.

Inclusion Criteria:

• Holding a degree qualification as a registered nurse
• being a direct care provider (bedside)

Exclusion Criteria:

• Nurses with less than one year experience in critical care unit
• working less than whole study period were excluded