Introduction

• Ventilation of alveoli is, ideally, matched to their perfusion. Normally, the overall ratio of pulmonary ventilation to perfusion (V/Q) is close to 1 (V/Q = 0.8 in humans).
• Ventilation-perfusion mismatching describes conditions in which changes in ventilation and/or perfusion lead to inadequacies in gas exchange. However, it should be remembered that physiologic ventilation-perfusion mismatching exists in normal, healthy lungs.
• Extremes of ventilation-perfusion mismatching include:
  • Atelectatic alveolus with normal perfusion (physiological shunt with V/Q = zero)
  • Lack of blood flow around an alveolus with normal ventilation (dead space ventilation with V/Q = infinity, eg. pulmonary embolism).
    It is important to distinguish between these conditions because hypoxemia due to true right-to-left shunt is not responsive to treatment with increased inspired oxygen concentration while high V/Q conditions should respond to oxygen therapy .

Hypoxemia

Other causes of ventilation-perfusion mismatching:

Treatment

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.

Other sources of information

• Durbin C G (2001) Arterial blood gas analysis and monitoring. In: Clinical Monitoring: Practical applications for anesthesia and critical care. Eds C L Lake, R L Hines and C D Blitt. W B Saunders Co, Philadelphia. pp 335-354.
• West J B (1990) Ventilation-perfusion relationships. In: Respiratory Physiology - the essentials. Fourth ed. Williams & Wilkins, Baltimore. pp 51-68.
• Harrison R A (1989) Respiratory function and anesthesia. In: Clinical Anesthesia. Eds P G Barash, B F Cullen and R K Stoelting. J B Lippincott, Philadelphia. pp 877-904.