The relationship between end-tidal CO 2 (ETCO 2), mean arterial blood pressure (MAP) and neuroendocrine response was investigated in experimentally induced haemorrhagic shock in six anaesthetized, spontaneously breathing dogs. One third of the calculated whole blood volume, i.e. 30 ml/kg was gradually withdrawn in 32 minutes. After 16 minutes, the blood was transfused to the dogs. Blood samples were taken regularly for plasma adrenaline, noradrenaline, beta-endorphin and serum cortisol levels.

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... AP and ETCO 2 decreased simultaneously during the withdrawal period. MAP increased before resuscitation commenced due to the increased sympathetic response, confirmed by high adrenalin levels. ETCO 2 remained low, suggesting that ETCO 2 reflects changes in cardiac output earlier during resuscitation when compared to MAP. Adrenaline, noradrenaline, beta-endorphin and cortisol levels increased during haemorrhagic shock and slowly decreased during resuscitation. The results of the study proved a good correlation and clinical relevance of ETCO 2 and MAP during development of haemorrhagic shock while the difference between ETCO 2 and MAP increased during resuscitation, suggesting the influence of sympathetic response, confirmed by increased levels of adrenaline. According to a proven positive correlation between ETCO 2 and cardiac output during haemorrhagic shock, the results suggest that ETCO 2 may be used as a better indicator of haemodynamic events when compared to MAP during a resuscitation period in haemorrhagic shock.