stress index in ventilators
- related: basic understanding of ventilators
- tags: #permanent
- Stress index vs flow dysynchrony
- Stress index is how much recruitable lung is left in volume control
- Premature cycle: TV too low
This parameter is the slope of the airway pressure graphic during inflation with a volume controlled breath (no patient effort) using a constant inspiratory flow. Under these conditions, the airway pressure slope represents respiratory system compliance during the tidal breath. If it slopes upward (worsening compliance) it suggests tidal overdistention. If it slopes downward (improving compliance) it suggests recruitment during the tidal volume. Ideally, the slope should be linear, suggesting a stable compliance during the tidal breath. Three examples are given in Figure 1. However, in the case presented, the only PEEP choice given was to inappropriately eliminate it (choice B is incorrect). Respiratory rate adjustments in the presence of adequate expiratory times will have no effect on DP (choice C is incorrect).
Importantly, using DP to target tidal volumes settings has not been subjected to a prospective randomized trial as yet. Such a trial would randomize patients with a plateau pressure <30 cm H2O and receiving a Vt of 6 mL/kg IBW but with a high DP to either remain on 6 mL/kg or have the Vt reduced further to reduce DP.
Constant flow, volume controlled breaths (no patient effort) during three levels of PEEP to assess the stress index – the slope of the airway pressure tracing. In tracing A (PEEP = 5), the airway pressure graphic slopes downward indicating recruitment is taking place and suggests adding PEEP. In tracing C (PEEP = 25), the airway pressure graphic slopes upward indicating overdistention is occurring and suggests reducing PEEP. In tracing B (PEEP = 15), the airway pressure graphic is linear, indicating compliance is constant during the breath and suggests PEEP is appropriate.1