Primary Examination SAQs

Study notes for the ANZCA Primary Examination SAQs

Mother & Baby

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Written by primarysaqs

December 31, 2009 at 11:46 am

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  1. Hi Amanda, thank you so much for maintaining your wonderful site – it’s been incredibly useful. I had a query about the diagram on the double Haldane effect on 2007a(14) – I think the umbilical vessels should be above the uterine vessels in relation to the Y axis? (As in I think they carry more CO2). Cheers, Monica

    Monica Diczbalis

    February 3, 2016 at 8:43 pm

    • Hi Monica!
      Thanks for contributing with such a great question about the Double Haldane Effect and the graph! The confusion with this graph (shamelessly copied from p355 Power and Kam, 1st ed), lies in the y-axis displaying CO2 content. The maternal circulation, from my reading, contains a much higher CO2 content /100ml blood due to the larger capacity of the bicarbonate system (which is responsible for the carriage of 90% of CO2 in the blood). This complicates understanding the Haldane Effect, as the carbamino compounds, which are responsible for 70% of the Haldane effect, are in and of themselves only responsible for a small proportion overall of the CO2 carriage (<10%).

      I believe the overall CO2 content of the fetal blood is in fact lower because of the immaturity of the bicarbonate system (which plays a greater role with increasing gestational age, but who knows the age of the fetus for this graph!!). I think the important effect of the double Haldane effect to take on is still that there is a profound change in the affinity of both maternal and fetal Hb for CO2 which results in a large partial pressure gradient facilitating the movement of CO2 from the fetus to maternal circulation. That is why the x-axis indeed shows that fetal pCO2 is higher than maternal pCO2. I hope this clarifies the reason why the graph is actually correct!



      February 5, 2016 at 10:25 pm

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