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Intrapulmonary shunting

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    Can anyone explain this to me in simple terms and its implications. Im getting very confused.

    If blood is shunted away from the lungs then the V/Q ratio should be greater than 1, however books tell me that it tends to 0.

    What causes the blood to be shunted away from the lungs?
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    Tetralogy of Fallot.

    But I have no idea about V/Q ratios.
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    No its not about congenital abnormalities.

    Ive got a PBL case about respiratory failure, and mechanical ventilation. The patient is in the ICU and requires positive end expiratory pressure (PEEP) ventilation. And it says:

    In the extreme case when the V/Q ratio equals 0, pulmonary blood flow does not participate in gas exchange because the perfused lung unit receives no ventilation. This condition is intrapulmonary shunting and is calculated by comparing the oxygen contents in arterial blood, mixed venous blood, and pulmonary capillary blood (see Other Tests). In healthy people, the percentage of intrapulmonary shunt is less than 10%. When the intrapulmonary shunt is greater than 30%, resultant hypoxemia does not improve with supplemental oxygenation because the shunted blood does not come in contact with the high oxygen content in the alveoli. Instead, treatment consists of recruiting and maximizing lung volume with positive pressure. PaO2 continues to fall proportionately as the shunt increases.

    Where V/Q is the ratio between ventilation and perfusion in the lungs.
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    What is the question again? Why is it zero? The ratio is V/Q so if you have a bit of the lung that it is not ventilated you get 0/Q=0 This area of the lung that is not ventilated is called the intrapulmonary shunt. Perfusion is normal-it is ventilation that is the problem.
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    Oh ok, i get it. So what would cause these areas to not be ventilated. Collapsed alveoli from infection or trauma? Something like that?
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    Exactly. Most common scanario is alveoli feeling with fluid from pneumonia, pulmonary odeama or trauma. It is a common complication from mechanical ventilation +lying unconcious in bed to get basal collapse. Bases of the lungs are not ventilated properly and gunk collects down there.

    Good chest physio and repositioning plus skillfull adjustments of the vent (and I do not pretend to understend those) seem to be usual plan of action.
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    (Original post by joshwaah)
    Oh ok, i get it. So what would cause these areas to not be ventilated. Collapsed alveoli from infection or trauma? Something like that?
    In an ITU punter? Atelectasis, collapse, mucus plug, consolidation, etc.
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    (Original post by belis)
    Good chest physio and repositioning plus skillfull adjustments of the vent (and I do not pretend to understend those) seem to be usual plan of action.
    Stick a 5L bag of fluid on their chest.

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