The comfort of breathing: A study with volunteers assessing the influence of various modes of assisted ventilation

Objective: To assess the subjective feeling of comfort of healthy volunteer s breathing on various modes of ventilation used in intensive care. Design:A randomized, prospective, double-blinded, crossover trial using vol unteers. Setting: An intensive care unit (ICU) in a teaching hospital. Interventions: We compared, by using healthy volunteers, the subjective fee ling of comfort of three modes of ventilation used during the weaning phase of critical illness. We used healthy volunteers to avoid other distracting influences of intensive care that may confound the primary feeling of comf ort. The modes we compared were synchronized intermittent mandatory ventila tion, assisted spontaneous breathing, and biphasic positive airway pressure . The imposed ventilation was comparable with 50% of the volunteers' normal respiratory effort. The volunteers breathed via a mouthpiece through a ven tilator circuit, and the modes of ventilation were introduced in a randomiz ed manner. Measurements and Main Results: We measured visual analog scores for comfort for the three modes of ventilation and collected a ranking order and open- ended comments. We demonstrated that at the level of support we imposed, as sisted spontaneous breathing was the most comfortable mode of ventilation a nd that synchronized intermittent mandatory ventilation was the most uncomf ortable. These results were strongly supported by both the ranking scale an d comments of the volunteers. Conclusions: Assisted spontaneous breathing was the most comfortable mode o f ventilation because the pattern was primarily determined by the volunteer . Synchronized intermittent mandatory ventilation was the most uncomfortabl e because the ventilatory pattern was imposed on the volunteers, leading to ventilator-volunteer dyssynchrony. We also conclude there is wide individu al variation in the subjective feeling of comfort. Whereas the mode of vent ilation in ICUs is based primarily on the physiologic needs of the patient, the feeling of comfort may be considered when choosing an appropriate mode of ventilation during the weaning phase of critical illness.