Reverse Triggering: An Introduction to Diagnosis, Management, and Pharmacologic Implications

Abstract

Reverse triggering is an underdiagnosed form of patient-ventilator asynchrony in which a passive ventilator-delivered breath triggers a neural response resulting in involuntary patient effort and diaphragmatic contraction. Reverse triggering may significantly impact patient outcomes, and the unique physiology underscores critical potential implications for drug-device-patient interactions. The purpose of this review is to summarize what is known of reverse triggering and its pharmacotherapeutic consequences, with a particular focus on describing reported cases, physiology, historical context, epidemiology, and management. The PubMed database was searched for publications that reported patients presenting with reverse triggering. The current body of evidence suggests that deep sedation may predispose patients to episodes of reverse triggering; as such, providers may consider decreasing sedation or modifying ventilator settings in patients exhibiting ventilator asynchrony as an initial measure. Increased clinician awareness and research focus are necessary to understand appropriate management of reverse triggering and its association with patient outcomes.

Keywords: acute respiratory distress syndrome; critical care; mechanical ventilation; respiratory failure; reverse triggering; sedation.

FIGURE 1

Simplified pressure-time curve for possible reverse triggering event. This simplified schematic provides an overview of a reverse triggering event. (A) Passive ventilator breaths followed by a discordant diaphragmatic effort during expiration in a 1:1 entrainment ratio. Such diaphragmatic efforts, if initiated in or persisting beyond the ventilator refractory period and significant enough to exceed the set trigger, will result in double-triggering as shown. (B) Passive ventilator breath with a diaphragmatic effort during the inspiratory phase in a 1:2 entrainment ratio. In this example, the diaphragmatic effort during the ventilator refractory period results in an apparent early or ineffective trigger.

FIGURE 2

The three principles of critical care: A proposed schematic of balancing risks and harms of various interventions. Two special objects (must be kept) in view with regard to disease, namely, to do good or to do no harm—Hippocrates. With the three principles of critical care, the two principles of treatment of the underlying cause and provision of supportive care must be counterbalanced by the third principle of minimizing iatrogenic harm. When applied to a mechanically ventilated patient, treating the underlying cause may include pharmacotherapy (e.g., antibiotics) and non-pharmacotherapy (e.g., chest tubes); supportive care may be providing adequate oxygenation and ventilation while the therapies reverse the underlying cause (e.g., invasive positive pressure ventilation); and minimizing harm may include preventing VILI or ventilator associated infections. In the case of reverse triggering, two supportive care modalities (mechanical ventilation and sedation) may increase risk of iatrogenic harm, and careful consideration is warranted to maintain appropriate balance. Source Hanna Azimi, PharmD. Created with Biorender.com.

FIGURE 3

Theoretical depiction of a waveform tracing for a reverse triggering event. Key elements of this waveform tracing to note include: 1) a maximal patient effort occurring during lung inflation, 2) a larger tidal volume during the reverse trigger event, 3) inspiratory effort resulting in a slight negative dip in airway pressure, 4) sharply increased flow during the reverse trigger event, and increased transpulmonary pressures (both mean and end-inspiratory) during the reverse triggering event.

FIGURE 4

Proposed approach to the patient with ventilator asynchrony and possible reverse triggering.