Hypoxia and the General ITU Patient
Hypoxemia is a condition where low oxygen partial pressure in the blood leads to deranged cell function in peripheral tissues. Satisfactory hemoglobin oxygenation depends on adequate alveolar ventilation, diffusion from the alveoli into the pulmonary vasculature, and delivery of oxygenated blood by the circulation into cells. Admitting patients with worsening respiratory function and increasing shortness of breath despite oxygen insufflation is a common occurrence for any intensivist. Arriving at a diagnosis swiftly in order to initiate the appropriate therapy can involve a number of imaging modalities. The chest x-ray is the initial screening study in this scenario. It may identify disease of the lung parenchyma (infection, aspiration, inflammation, edema or tumor) or of the pleura (pneumothorax, or pleural effusion) and provides limited cardiac assessment. If the chest x-ray is normal, equivocal or non-specific early computed tomography is of great value in establishing accurate diagnosis to direct treatment in the deteriorating or critically ill patient. Computed tomography with intravenous contrast medium enables accurate assessment of the pulmonary arteries to evaluate for acute or chronic pulmonary embolism as well as enabling better evaluation of the lungs, heart and pleural space. CT can also be used to guide drainage. This chapter will cover this process in detail.