<prompt> Which one of the following distinguishes ARDS acuteadult respiratory distress syndrome from cardiogenic pulmonary oedema?Normal Pao2Normal pulmonary aerial pressureNormal aeriala-alveolar gradientNormal Paco2  <response>: Cardiogenic pulmonary edema is characterised by increased pulmonary aerial pressure with evidence of increased intracardiac pressuresS3 gallop,elevated JVP,peripheral edema which are absent in ARDS-pulmonary edema. The chest radiograph in cardiogenic edema shows an enlarged cardiac silhouette,vascular redistribution,interstitial thickening and perihilar alveolar infiltrates;pleural effusions are common.In ARDS-pulmonary edema,hea size is normal,alveolar infiltrates are distributed more uniformly throughout the lungs,and pleural effusions are uncommon. Finally,the hypoxaemia of cardiogenic pulmonary edema is largely due to VQ mismatch and responds to athe administration of supplemental oxygen.In contrast,hypoxaemia in ARDS-pulmonary edema is due to intra pulmonary shunting and typically persists despite high concentrations of inhaled O2. Reference:Harrisons Medicine-20th edition,page no:2032 