Component reductions in oxygen delivery generate variable haemodynamic and stress hormone responses.
BACKGROUND
In clinical practice, global oxygen delivery (DO2) is often considered as a whole; however pathological and adaptive responses after a decrease in individual constituents of the DO2 equation (cardiac output, haemoglobin, oxyhaemoglobin saturation) are likely to be diverse. We hypothesized that an equivalent decrease in DO2 after reductions in each separate component of the equation would result in different haemodynamic, tissue oxygenation, and stress hormonal responses.


METHODS
Anaesthetized, fluid-resuscitated male Wistar rats were subjected to circulatory, anaemic, or hypoxic hypoxia (by haemorrhage, isovolaemic haemodilution, and breathing a hypoxic gas mix, respectively), produced either rapidly over 5 min or graded over 30 min, to a targeted 50% decrease in global oxygen delivery. Sham-operated animals acted as controls. Measurements were made of haemodynamics, skeletal muscle tissue oxygen tension, blood gas analysis, and circulating stress hormone levels.


RESULTS
Whereas haemorrhage generated the largest decrease in cardiac output, and the greatest stress hormone response, haemodilution had the most marked effect on arterial pressure. In contrast, rapid hypoxaemia produced a minor impact on global haemodynamics yet induced the greatest decrease in regional oxygenation. A greater degree of hyperlactataemia was observed with graded insults compared with those administered rapidly.


CONCLUSIONS
Decreasing global oxygen delivery, achieved by targeted reductions in its separate components, induces varying circulatory, tissue oxygen tension, and stress hormone responses. We conclude that not all oxygen delivery is the same; this disparity should be emphasized in classical teaching and re-evaluated in patient management.
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.
A
A
Dyson
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.
N
N
Ekbal
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK Centre for Perioperative Medicine and Critical Care Research, Imperial College Healthcare NHS Trust, St Mary's Hospital, London, UK.
M
M
Stotz
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.
S
S
Barnes
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.
J
J
Carré
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.
S
S
Tully
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.
S
S
Henderson
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK.
L
L
Barrett
Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London, UK m.singer@ucl.ac.uk.
M
M
Singer
D000465:Algorithms; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation; D000818:Animals; D001784:Blood Gas Analysis; D001810:Blood Volume / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D017666:Deuterium Oxide / Q000378:metabolism; D006438:Hemodilution; D006439:Hemodynamics / Q000502:physiology*; D006454:Hemoglobins / Q000378:metabolism; D006470:Hemorrhage / Q000378:metabolism; D006728:Hormones / Q000378:metabolism*; D007530:Isoflurane; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D010108:Oxyhemoglobins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013315:Stress, Psychological / Q000378:metabolism*; D014563:Urodynamics / Q000502:physiology
D018685:Anesthetics, Inhalation; D006454:Hemoglobins; D006728:Hormones; D010108:Oxyhemoglobins; D007530:Isoflurane; D017666:Deuterium Oxide
cardiac output; haemodynamics; haemoglobin; stress hormones; tissue oxygenation