This is THE MOST IMPORTANT SLIDE IN THIS PRESENTATION! Accurately recognising and grading hypovolaemia is essential to being an effective emergency vet. MBS cardiovascular parameters change predictably and together as hypovolaemia worsens. You should try to grade them as mild, moderate or severe. What is the initial cardiovascular response to hypovolaemia? It is mild tachycardia and stronger cardiac contractions. Vasoconstriction may be occurring in non-essential beds but you will not see it in the gums yet. So in the mild (or compensated) stage, the heart rate is only mildly increased and the MMs will still be pink or even pinker than normal as the heart pumps the smaller volume of blood around faster. The CRT will be rapid and the pulses are taller than normal because of the increased cardiac contraction. As hypovolaemia worsens the heart rate rises more, pallor becomes apparent in the mucous membranes and the CRT is high normal (which you should be thinking totally doesn’t fit with the heart rate if it was just pain or stress). Pulses are becoming shorter and narrower because of their reduced volume. Once hypovolaemia is severe then there is no red in the MM, you struggle to see a CRT or to find a femoral pulse. If you need to put a number on the severity of their hypoperfusion, buy a lactate meter.