Ventilatory muscle fatigue is a reversible loss of the ability to generate force or velocity of contraction in response to increased elastic and resistive loads. Mechanical ventilation should provide support without imposing additional loads from the ventilator (dys-synchrony). Interactive breaths optimize this relationship but require that patient effort and the ventilator response be synchronous during breath initiation, flow delivery, and termination. Proper delivery considers all 3 phases and uses clinical data, ventilator graphics, and sometimes a trial-and-error approach to optimize patient-ventilator interactions. Newer modes optimize interactions but await good clinical outcome data before routine use.