Outline the determinants of oxygen delivery to the tissues.
An opening statement such as oxygen delivery = cardiac output x oxygen content then allowed
a more detailed description of the determinants of both oxygen content and cardiac output. It
was expected candidates could detail the formula for Oxygen Content = Sat O2 % x 1.34 x Hb
x 10 (depending on units) + PaO2 x .003, or x .03 (units) and accurately describe each
element. Determinant of cardiac output completed the answer, often starting with CO = HR x
SV while discussing the importance of preload, afterload and contractility.
Many candidates spent little time on cardiac output which cost valuable marks. Some
candidates provided a lot of detail on how oxygen is managed within the lung, the majority of
which was not required as part of the answer. Some candidates answered the question
describing the oxygen cascade only which was not sufficient to score well.
Total DO2 = Cardiac output (L/min) × Oxygen content (ml/L)
= HR × SV
Where SV is influenced by preload, afterload and contractility.
= (sO2 × ceHb × BO2 ) + (PaO2 × 0.003)
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