Cookies help us deliver our services. By using our services, you agree to our use of cookies. More information

Leach 1998 BMJ

From Bioblast
Publications in the MiPMap
Leach RM, Treacher DF (1998) ABC of oxygen. Oxygen transport-2. Tissue hypoxia. https://doi.org/10.1136/bmj.317.7169.1370

» BMJ 317:1370-3. PMID: 9812940 Open Access

Leach RM, Treacher DF (1998) BMJ

Abstract: Tissues vary considerably in their sensitivity to hypoxia. Neurological cells tolerate hypoxia for only a few minutes whereas bladder smooth muscle may survive for several days without oxygen. This has important implications in the management of oxygen transport and monitoring of tissue hypoxia in critically ill patients.

Bioblast editor: Gnaiger E

Selected quotations

  • Convective oxygen transport refers to the bulk movement of oxygen in air or blood and depends on active, energy consuming processes generating flow in the tracheobronchial tree and circulation. Diffusive transport refers to the passive movement of oxygen down its concentration gradient across tissue barriers, including the alveolar­capillary membrane, and across the extracellular matrix between the tissue capillaries and individual cells to mitochondria. The amount of diffusive oxygen movement depends on the oxygen tension gradient and the diffusion distance.
  • In many critically ill patients tissue hypoxia is due to disordered regional distribution of blood flow both between and within organs.
  • During critical illness tissue hypoxia is often caused by capillary microthrombosis after endothelial damage and neutrophil activation rather than by arterial hypoxaemia.
  • In healthy resting adults the overall extraction ratio of oxygen from capillary blood is about 25 % but may increase to 70­-80 % during maximal exercise in well trained athletes.
  • Various physicochemical factors affect the position of this sigmoid relation, which is defined by the oxygen concentration at which 50% of the haemoglobin is saturated (P50) — normally 3.5 kPa. A shift in the capillary oxygen­haemoglobin dissociation curve to the right enhances release of oxygen to tissues and improves oxygen availability. Provided that PaO2 does not fall much below 8 kPa the loss of oxygen uptake in the lungs is small but the increased release in the tissues is significant and the net effect is beneficial, increasing venous and tissue oxygen concentrations.
  • Mathematical models of tissue hypoxia show that the fall in cellular oxygen resulting from an increase in intercapillary distance is more severe if delivery of oxygen to tissues is reduced because of “hypoxic” hypoxia (a fall in PaO2) rather than “stagnant” (a fall in flow) or “anaemic” (reduced haemoglobin) hypoxia.
  • The mitochondrial partial pressure of oxygen required to generate the high energy phosphate bonds (ATP) that maintain aerobic cellular biochemical functions is only 0.13­-0.4 kPa.
  • Arterial oxygen saturation and PaO2 remain the principal clinical measures of arterial hypoxaemia, but the values may be normal despite tissue hypoxia in low output cardiac states and anaemia. In these circumstances mixed venous oxygen tension, measured in pulmonary artery blood, approximates to mean tissue oxygen tension and is a better index of tissue oxygenation.


Labels: MiParea: Respiration 

Stress:Hypoxia  Organism: Human 





MitoFit2022Hypoxia