We know the right ventricle is a weak pump compared to LV. This is evident from the triangular pressure-volume loop of RV. RV not only generates less pressure, its thin wall and its direct connectivity to the extrathoracic compartment make it vulnerable to hemodynamic fluctuations whenever Intrathoracic pressure swings.
Note the lowly lying pressure-volume loop of the right ventricle. RV is a too gentle chamber and needs to be handled with extreme care especially when it is failing acutely.
Patients on ventilators are typically exposed to iatrogenic rise and fall in right heart pressure. If continuous airway pressure is kept high it’s directly add on to RV afterload. The second adverse event is through interrupting venous return (preload).
Effect of mechanical ventilation on RV
- RV preload is reduced (If they drop too low – they are equivalent to be in “Status Valsalva maneuver” )
- RV afterload increases when Inspiratory airway pressure is increased. (
- If RV is grossly dilated it may encroach LV and interfere with its function (Reversed Bernheim effect )
- Many of the unexplained hypotension and reduced cardiac index are due to suboptimal ventilator setting
- Ventilator increases the mean RA pressure, and if there is PFO, it can shunt right to left and aggravate the preexisting systemic hypoxia.
In some of the situations where RV is already in the fighting mode for survival, imagine its plight when it had to take on the adverse setting of the ventilator as well. This happens in RV infractions. Pulmonary embolism, dilated cardiomyopathies, Post heart transplant, and in general in many ARDS patients. Discussing the ventilatory settings and a sound understanding of the prevailing hemodynamics of patients is so important.
Settings need to be optimized (Good to acquire a basic knowledge of from an Intensivist/Anesthetist)
- .Optimal PEEP (Often dynamic but <18cm H2o)
- Tidal volume
- Avoid Hypoxic pulmonary vasoconstriction and hypercarbia (<60mmhg)
- RV dysfunction can be an independent indication Proning the patient (Apart from PaO2/Fio2 ratio)
Final message
It is a paradox, for patients with LV, failure ventilators instantly help as it unloads the left ventricle and relieves pulmonary congestion on the go. The same can’t be said about RV dysfunction. Ventilators interfere with RV in multiple complex ways. However, simple settings change can improve blood pressure dramatically. Always aim for an RV protective ventilation strategy. Many times It’s in our hands to let the tired RV free, from fighting its friend (or foe).
Reference
A comprehensive resource
Dr.S.Venkatesan MD 