Proportional Assist Ventilation and Neurally Adjusted Ventilatory Assist—Better Approaches to Patient Ventilator Synchrony?

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Understanding the regulation of breathing in the critical care patient is multifaceted, especially in ventilator-dependent patients who must interact with artificial respiration. Mechanical ventilation originally consisted of simple, manually-driven pump devices, but it has developed into advanced positive pressure ventilators for continuous support of patients in respiratory failure. This evolution has resulted in mechanical ventilators that deliver assist intermittently, attempting to mimic natural breathing. Recently, modes of mechanical ventilation that synchronize not only the timing, but also the level of assist to the patient's own effort, have been introduced. This article describes the concepts related to proportional assist ventilation and neurally adjusted ventilatory assist, and how they relate to conventional modes in terms of patient-ventilator synchrony.

Section snippets

Transmission of respiratory motoneuron output to ventilation: the neuroventilatory coupling

To recognize the complexity of patient-ventilator interaction, the chain-of-events that take place during spontaneous breathing are presented in Fig. 1 and explained in the rest of this section.

Voluntary and involuntary control of the respiratory muscles originate from separate sites in the central nervous system and have separate descending pathways. Voluntary control arises from the motor and premotor cortex, whereas involuntary control is mediated by both rhythmic and nonrhythmic systems

Neural feedback from the respiratory system

Respiration is regulated by a very complete feedback system, including many reflex loops, which are often not considered in the clinical application of mechanical ventilation of spontaneously breathing patients.

Integration of a mechanical ventilator

Mechanical ventilation mainly accomplishes two tasks: it provides adequate ventilation and it unloads the respiratory muscles. If mechanical ventilation is applied without coordination to inspiratory muscle activity (asynchronous), ventilation can reduce respiratory drive primarily via a chemoreceptor response. If the assist is delivered synchronously with inspiratory effort, it will overcome increased elastic and resistive loads and compensate for muscle weakness.

To ensure that assist is

Summary

Patient-ventilator interaction is a complex topic, where interaction between patient effort, triggering, assist levels, off-cycling, and sedation all play a role. Patient-ventilator asynchrony prolongs the duration of mechanical ventilation and this may be interrelated with sedation practice. It is therefore important to raise the awareness of how mechanical ventilation affects breathing pattern and effort via on-line monitoring, allowing us to better understand how to best tailor the assist

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    Dr. Sinderby and Dr. Beck have made inventions related to neural control of mechanical ventilation that are patented. The license for these patents belongs to Maquet Critical Care. Future commercial uses of this technology may provide financial benefit to Dr. Sinderby and Dr. Beck through royalties. Dr. Sinderby and Dr. Beck each own 50% of Neurovent Research Inc., a research and development company that builds the equipment and catheters for research studies. Neurovent Research Inc. has a consulting agreement with Maquet Critical Care.

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