When the duration between inspirations is too short for the patient to exhale to their functional residual capacity, a condition known as intrinsic PEEP arises. Intrinsic PEEP can arise from a variety of factors, including increased expiratory resistance (RE), a high respiratory rate (both patient and ventilator), or a prolonged ratio of inspiratory to expiratory time (TI/TE). The work of breathing and patient-ventilator asynchrony (PVA) can increase with intrinsic PEEP during patient-triggered breaths. It is researchers’ working hypothesis that the trigger asynchrony caused by the disparity between intrinsic PEEP and ventilator PEEP necessitates higher respiratory muscle pressure (Pmus) to be overcome. To show that increased RE causes a rise in intrinsic PEEP beyond ventilator PEEP, they constructed a passive model using a servo lung model (ASL 5000) and an LTV 1200 ventilator in pressure control mode. Moreover, they built an interactive model to explore how RE and intrinsic PEEP influence trigger asynchrony (expressed as a percentage of patient-initiated breaths that failed to trigger). Then, they looked into whether or not higher Pmus could mitigate trigger asynchrony. The correlation between RE and intrinsic PEEP was quite high (r=0.97, P=.006). The levels of RE and negative Pmus were found to affect trigger asynchrony in a multivariate logistic regression analysis (P<.001). Rising intrinsic PEEP with increasing RE at a constant ventilator breathing rate is described by a passive lung model. Since the Pmus required to trigger a breath increases with increased RE due to the inspiratory muscles’ having to overcome intrinsic PEEP, an active lung model demonstrates how this might lead to trigger asynchrony. This model will be helpful in ventilator simulation scenarios for PVA and will allow for the research of intrinsic PEEP induced by a greater ventilator breathing rate and TI/TE. The model also indicates that decreasing RE can be achieved by increasing ventilator PEEP to match intrinsic PEEP.
Source: rc.rcjournal.com/content/early/2022/09/20/respcare.09484
