MV and hemodynamic

Q: Which of the following may not be an effect of mechanical ventilation on hemodynamics? - select one

A) Decreased venous return

B) Reduced right ventricular output

C) Reduced left ventricular output

D) Compressed Aortic Valve (AV)

Answer: D

Almost half of the patients (43%) develop hemodynamic instability within one hour of intubation with 

• systolic blood pressure <65 mmHg at least once
• <90 mmHg for >30 minutes
• new or increased need for vasopressors or fluid bolus >15 mL/kg 

It is well known that positive pressure vеոtilatiоn decreases cardiac output, leading to hypotension. It is important to understand all three major mechanisms of action.

1. Decreased venous return: An increase in intrathoracic and right atrial pressure due to positive pressure vеոtilаtiοո reduces the gradient for venous return. This effect is further augmented by higher positive end-expiratory pressure (ΡЕЕР) or intravascular hypovolemia.

2. Reduced right ventricular output – Alveolar inflation during positive pressure vеոtilаtiοո compresses the pulmonary vascular bed. This increases pulmonary vascular resistance and reduces the right ventricular output. This effect can be mitigated by augmenting venous blood volume.

3. Reduced left ventricular output – Increased pulmonary vascular resistance can shift the interventricular septum to the left, impair diastolic filling of the left ventricle, and reduce left ventricular output. An interesting paradox may occur here: In Patients with left ventricular failure, the increased intrathoracic pressure from positive pressure vеntilatiοn may improve left ventricular function by decreasing both venous return and left ventricular afterload.

#hemodynamic

#ventilators

References:

1. Russotto V, Myatra SN, Laffey JG, et al. Intubation Practices and Adverse Peri-intubation Events in Critically Ill Patients From 29 Countries. JAMA 2021; 325:1164.

2. Fougères E, Teboul JL, Richard C, et al. Hemodynamic impact of a positive end-expiratory pressure setting in acute respiratory distress syndrome: importance of the volume status. Crit Care Med 2010; 38:802.

3. Bersten AD, Holt AW, Vedig AE, et al. Treatment of severe cardiogenic pulmonary edema with continuous positive airway pressure delivered by face mask. N Engl J Med 1991; 325:1825.