Editing Anatomy and Physiology – RN Flashcards (section)

== Respiratory and Acid-Base ==

;Distinguish oxygenation from ventilation and give the corresponding measurements.
:Oxygenation is oxygen loading onto hemoglobin, measured by PaO2 (80 to 100 mmHg) and oxygen saturation (95% to 100%). Ventilation is carbon dioxide clearance, measured by PaCO2 (35 to 45 mmHg). A patient can be adequately oxygenated on supplemental oxygen while dangerously hypercapnic.

;Give the four-step approach to arterial blood gas interpretation.
:First, classify the pH (below 7.35 acidosis, above 7.45 alkalosis). Second, evaluate PaCO2 for the respiratory component and bicarbonate for the metabolic component. Third, identify which value explains the pH abnormality; if PaCO2 moves opposite to the pH, the cause is respiratory, and if bicarbonate moves with the pH, the cause is metabolic. Fourth, determine compensation: none, partial (pH still abnormal), or full (pH back in range).

;What is ventilation-perfusion mismatch, and give one example of each type?
:A mismatch between alveolar ventilation and capillary perfusion. Ventilation without perfusion (dead space) occurs in pulmonary embolism. Perfusion without ventilation (shunt) occurs in pneumonia, atelectasis, and pulmonary edema.

;Why does a normal pulse oximetry reading not exclude respiratory failure?
:Pulse oximetry measures only hemoglobin saturation. It gives no information about carbon dioxide retention, and it can read falsely normal in carbon monoxide poisoning, and unreliably in poor perfusion, hypothermia, and motion.

;Explain the "good lung down" principle and its exception.
:Gravity increases perfusion to the dependent lung, so positioning the healthier lung down matches perfusion to the better-ventilated tissue and improves oxygenation. The exception is unilateral lung abscess or hemorrhage, where the affected lung is placed down to prevent spillage into the healthy lung.