Limitation on %MinVol in INTELLiVENT®-ASV®

Mechanical ventilation is considered a supportive therapy that is often lifesaving. However, the last 20 years of research have shown that it is associated with potential risks, which may lead to ventilatior induced lung injury (VILI). The application of a lung-protective strategy (low tidal volume, permissive hypercapnia and low driving pressure) is mandatory for mechanically ventilated patients, in order to lower the risk of deterioration and improve their outcome. The continuous clinical assessment of the patient’s condition by the caregiver is essential, as mechanical ventilation is only one part of the treatment.

In spontaneously breathing patients, the chemo reflex control system (i.e., related to changes in pH and PaO2) is the main controller of the respiratory drive under normal conditions. During critical illness however, other factors modify respiratory drive. These include metabolic acidosis, anxiety, pain, delirium, drugs (e.g., sedatives and opioids), increased ventilation-perfusion mismatch, sepsis, shivering, and a higher metabolic rate. High respiratory drive leads to excess loading of the diaphragm, stress and strain to the lungs, and places the patients at risk of lung and diaphragm injury (i.e., patient self-inflicted lung injury (P-SILI) and myotrauma, respectively).

In fact, there is no technique available for direct measurement of the drive arising from the brainstem. Therefore, it is always inferred on the basis of its output, which includes muscular effort. Respiratory drive controls the magnitude of the inspiratory effort. Therefore, measurements of respiratory drive (e.g., airway occlusion pressure) can be used to estimate inspiratory effort and measurements of effort (e.g., esophageal pressure) to estimate drive.

INTELLiVENT-ASV (Not available in the US and some other marketsA​)​ continuously adjusts the %MinVol based on the patient’s PetCO2 and/or respiratory rate (RR) - depending on whether the patient is passive or active - and selects an optimal breathing pattern (tidal volume and respiratory rate) according to the minimal work and force of breathing concept. Automatic increases in %MinVol above 200% are not possible for safety purposes, as the inputs for INTELLiVENT-ASV are limited to the PetCO2 and the respiratory rate. Once this limit is reached, the system warns the user with the alarm Ventilation controller at Limit.

In this scenario, it is the responsibility of the caregiver to check the patient’s clinical condition, in order to detect the primary cause behind the increase in the minute ventilation. The caregiver has to treat the underlying cause in such a way that the overall ventilator workload and demand are reduced. However, if the clinician decides that the patient requires higher minute ventilation, it is possible to set the %MinVol controller to manual and increase the %MinVol as required.

Relevant devices: HAMILTON-G5/S1 (Not available in all countriesB​), HAMILTON-C3, HAMILTON-C6
Relevant software: HAMILTON-G5/S1 SW v2.81 and lower, HAMILTON-C3 SW v2.0.5 and lower, HAMILTON-C6 SW v1.1.4 and lower