Canis ISSN: 2398-2942

Ventilation-perfusion mismatching

Contributor(s): John Dodam, Prof Stephen Greene, Daniel H Lewis

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 V-P mismatch: atelectic alveolus.

Hypoxemia

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Other causes of ventilation-perfusion mismatching:

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Treatment

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Further Reading

Publications

Refereed papers

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.


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