L25 Acid Base 3

Question 1

Explain why a severe diarrhoea patient’s blood presssure is lower sitting up than lying down

Answer 1

They have lost Na and H2O–> hypovolaemia. CO is low giving rise to relatively low MAP when supine. This is exacerbated with postural change because increased hydrostatic pressures in the lower extremities lead to sequestration of blood in the superficial veins in this region, reducing venous return, SV, CO and MAP.

Question 2

Is hypokalaemia expected in acidosis : how can it happen

Answer 2

Normally increased H+ in the ECF will be buffered over hrs-days by K+ exchange with intracellular K+, thus causing hyperkalaemia.

However hypokalaemia can happen if circumstances leading to acidosis lead to RAAS activation: excretion of K, retention of Na.

Question 3

What is another reason for hyperventilation instead of resp compensation
and how can hypokalaemia affect breathing

Answer 3

Pleuritic pain when breathing due to pneumonia so shallow breathing with increased RR.

Anxiety (unable to be sustained)

Hypokalaemia can cause impaired contractility of muscle: impaired respiratory motor activity so can impair hyperventilation.