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0592. Metabolic acidosis induced by haemorrhage and hydrochloric acid generates different cardiorespiratory responses


Metabolic acidosis is classically thought to induce an enhanced ventilatory pattern, irrespective of the underlying aetiology.


To induce a similar level of acidaemia in a rat model, by either infusion of an acidic solution or by blood withdrawal, and to assess the physiological responses to these insults.


Isoflurane-anaesthetised, tracheotomized rats were instrumented with left common carotid arterial and right jugular venous lines for blood sampling/BP monitoring and fluid/blood administration, respectively. OxyliteTM probes (Oxford Optronix, UK) placed in thigh muscle were used to monitor tissue oxygen tension (tPO2). Animals were subjected to either continuous 0.1 M hydrochloric acid (HCl) infusion or 60% withdrawal of estimated blood volume in six 10% steps over three hours to induce an equivalent fall in arterial base excess (BE). All animals (including a control group) received n-saline throughout. Hourly measurements were made of haemodynamics, tPO2 and arterial blood gas analysis.


See figure 1.

Figure 1
figure 1

Results. BL= baseline, SaO2= arterial oxygen saturation. Data shown as mean (SEM). Hydrochloric acid (HCl) n=6, Haemorrhage n=8, Controls n=10/group, *p< 0.05 comparing treated to controls, §p< 0.05 comparing haemorrhage to HCl. Statistics: repeated measures two-way ANOVA and Bonferroni's test for multiple comparisons.

HCl induced a metabolic acidosis with arterial hypoxaemia yet a preserved muscle tPO2, no tachypnoea nor fall in PaCO2. By contrast, haemorrhage to achieve a similar acidaemia, resulted in significant falls in blood pressure and tPO2, hyperlactataemia, a small rise in SaO2 and a decrease in respiration rate with a concomitant fall in PaCO2 probably related to higher tidal volumes.


Tissue hypoperfusion (and not just acidaemia per se) is an important component that triggers an enhanced ventilatory drive.

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Sabbatini, G., Dyson, A. & Singer, M. 0592. Metabolic acidosis induced by haemorrhage and hydrochloric acid generates different cardiorespiratory responses. ICMx 2 (Suppl 1), P36 (2014).

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