10/15/2023 0 Comments Shunt vs dead space usmle redditThey all impact how well a patient ventilates. There are three types of dead space: anatomic, physiologic, and that dead space belonging to any airway equipment being used to assist ventilation. Dead space is the portion of the respiratory system where tidal volume doesn’t participate in gas exchange: it is ventilated but not perfused. One important contributor to ventilation perfusion mismatch is dead space. It will help you understand how you can use these concepts to care for your patient. This article will describe how dead space is different from shunt. Physiologic dead space is ventilation of poor perfused alveoli. Collateral ventilation in the obstructed segments prevents absorption atelectasis and subsequent shunt formation by keeping the alveoli ventilated.Shunt is perfusion of poorly ventilated alveoli. The factor that prevents the development of shunt is collateral ventilation. The shunt is an uncommon mechanism of hypoxemia in COPD patients. However, emphysema severity on quantitative chest computed tomography scan did not predict hypoxemia. In the COPD gene study, female sex, higher body mass index, lower FEV1 were independent risk factors for hypoxemia development in patients with moderate to very severe COPD. It may be due to the lesser involvement of small airway as small airway obstruction may cause atelectasis resulting in the perfusion of poorly ventilated lung areas and development of hypoxemia. study is the presence of normal or near normal PaO2 in 80% of patients despite having moderate to severe emphysema on HRCT in 75% of patients. Blood flow is also reduced due to compression by the overinflated alveolar walls. The reduced perfusion causes modest V/Q mismatch and explains the lack of correlation with extent of emphysema. also reported reduced pulmonary capillary blood volume across all spectrum of emphysema. measured blood volume on the basis of positron emission tomography scan and found lower tissue density and peripheral vascular volume within lungs in emphysematous patients. Severe V/Q mismatch does not develop in COPD patients as the destruction of the alveolar surface is associated with a reduction in perfusion also. COPD is a shunt since the alveoli are being destroyed despite being adequately perfused correct?
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