Purpose of the study
The in-hospital cardiac arrest (IHCA) is a common event with a poor prognosis. Many studies show a higher mortality for patients admitted at weekend or night at hospital. Only a few publications analyzed the influence of daytime on incidence and outcome of IHCA.

Materials and methods
We analyzed all cases with IHCA and resuscitation from the German Resuscitation Registry (GRR) between 2010 and 2017. Primary outcome was ROSC. We build four groups: (1) weekdays (Mo-Fr), 8am-8pm; (2) weekdays, 8pm-8am; (3) weekend, 8am-8pm; (4) weekend, 8pm-8am. 

Results
In the study period 15,277 IHCA were registered in the GRR. 2,730 cases must be excluded due to missing variables. The study includes 12,547 cases. 54.3% of all IHCA take place on weekdays between 8am and 8pm. Group 2 covers 20.7% of all IHCA cases, group 3 18.0% and group 4 7.1%. The ROSC rate differs significantly between the four groups: (1) 63.2%, (2) 54.4%, (3) 60.2%, (4) 54.4% (p<0.001). In group 1 in 68.3% a consultant was the leading member of the medical emergency team (MET). In group 2 in 60.5% of all cases a consultant was present, 64.8% in group 3 and 58.4% in group 4. The rate of witnessed cardiac arrest differs although: (1) 72.7%, (2) 62.1%, (3) 70.8%, (4) 63.2% (p<0.001).  
The rate of resuscitation started by visitors or staff members are similar: (1) 62.2%, (2) 66.7%, (3) 63.6%, (4) 65.4%.

Conclusions
This study shows that the short-term survival after IHCA depends on the daytime. At night the resuscitation team is often not leaded by a consultant and the rate of unwitnessed cardiac arrest is higher. We need more engagement to optimize the observation of the patient on the ward (especially at night) and the qualification of the MET in the hospitals in Germany.

4 - Influence of daytime on survival after in-hospital cardiac arrest in Germany