A previously healthy factory worker was found unresponsive in his work place. He was afebrile, anicteric, tachypnoeic, drowsy and "blue" all over with clear lung fields and hyperdynamic cardiovascular findings. His ABG with 100% oxygen after intubation was:
pH = 7.30
pO2 = 580 mm Hg
pCO2 = 30 mm Hg
SaO2 = 50%
What is the most likely diagnosis?