intrapulmonary shunt vs dead space usmle

The A-a gradient can be calculated by subtracting the alveolar partial pressure of oxygen, which is calculated using the alveolar gas equation, by the arterial partial pressure of oxygen, measured with arterial blood gas (ABG). All three of these conditions can contribute to an increase in A-a gradient and cause hypoxemia. Diffusion problems can occur when the alveolar walls are fibrosed and oxygen cannot diffuse across the alveolar wall into the blood stream.

High V/Q is also called dead space and low V/Q is called shunting. Normally approximately 2 to 5 of the cardiac output bypasses the pulmonary capillaries because the following veins empty into the left side of the heart: (1) Bronchial (2) Pleural (3) Thebesian b. V/Q mismatch means a mismatch of ventilation to perfusion (V/Q) ratio and can represent either too little perfusion due to blood flow obstruction (high V/Q) or too little ventilation due to airway obstruction (low V/Q). Anatomic shunt: The portion of the total cardiac output that bypasses the pulmonary capillary bed. An increase in A-a gradient can occur in hypoxemia and the causes include V/Q mismatch such as dead space or shunting and diffusion problems. The normal A-a gradient is 10 to 15 mmHg. The A-a gradient represents the difference in partial pressure of oxygen between the alveoli and the arteries.

Intrapulmonary shunt vs dead space usmle