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The pulmonary physician in critical care • 2: Oxygen delivery and consumption in the critically ill
  1. R M Leach,
  2. D F Treacher
  1. Department of Intensive Care, Guy's & St Thomas' NHS Trust, London SE1 7EH, UK
  1. Correspondence to:
    Dr D Treacher;
    David.Treacher{at}gstt.sthames.nhs.uk

Abstract

Early detection and correction of tissue hypoxia is essential if progressive organ dysfunction and death are to be avoided. However, hypoxia in individual tissues or organs caused by disordered regional distribution of oxygen delivery or disruption of the processes of cellular oxygen uptake and utilisation cannot be identified from global measurements. Regional oxygen transport and cellular utilisation have an important role in maintaining tissue function. When tissue hypoxia is recognised, treatment must be aimed at the primary cause. Supplemental oxygen may be life saving in some situations but cannot correct inadequate oxygen delivery caused by a low cardiac output or impaired ventilation. Recent innovations include artificial oxygen carrying proteins and “haemoglobin” molecules designed to improve tissue blood flow by reducing viscosity. Regulating cell metabolism using different substrates or drugs has so far been poorly explored but is an exciting area for further research. A minimum level of global oxygen delivery and perfusion pressure must be maintained in the critically ill patient with established “shock”, but advances in the understanding and control of regional distribution and other “downstream” factors in the oxygen cascade are needed to improve outcome in these patients.

  • intensive care
  • oxygen delivery
  • So2, oxygen saturation (%)
  • Po2, oxygen partial pressure (kPa)
  • Pio2inspired Po2
  • Peo2mixed expired Po2
  • Peco2mixed expired Pco2
  • Pao2alveolar Po2
  • Pao2arterial Po2
  • Sao2arterial So2
  • Svo2mixed venous So2
  • Qt, cardiac output
  • Hb, haemoglobin
  • Cao2, arterial O2 content
  • Cvo2, mixed venous O2 content
  • Vo2, oxygen consumption
  • Vco2, CO2 production
  • O2R, oxygen return
  • Do2, oxygen delivery
  • Vi/e, minute volume, inspiratory/expiratory
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