OXYGENATION is not a problem if supplemental oxygen is provided to premature neonates because of the fetal Haemoglobin (Hb) having very high affinity for oxygen: P50 is 19 mm Hg compared to 26.8 mm Hg in adult.
P.S. The P50 is the partial pressure (PaO2) of oxygen at which 50% of the Haemoglobin is saturated with oxygen (SaO2 = 50%); lower the P50 higher the affinity of the Haemoglobin for oxygen. So, fetal Haemoglobin having lower P50 = 19 mm Hg, has higher affinity to bind oxygen.
A 2.0 kg premature neonate can have a blood volume of 2.0 x 100 ml/kg = 200 ml and if FFP (fresh frozen plasma) is transfused to build up the blood volume and also the coagulation factors instead of giving Vit K, the cardiac output would be adequate. The Hb level of 7.0 gm% would mean total Hb 200 ml x 7.0 gm% = 14.0 gm, which would carry 14.0 x 1.34 ml O2/gm of Hb = 18.8 ml oxygen content in the total blood volume of 200 ml if all the Haemoglobin is saturated with oxygen (SpO2 = 100%), which can be approximately the oxygen flux (oxygen delivered in one cardiac output, that is in one minute) because generally cardiac output is approximately equal to the blood volume. Generally accepted value is 1.34 rather than 1.39 ml of oxygen per gm of Hb.
Enough oxygen can be delivered to the tissues provided supplemental oxygen is given but not too high because it can cause retrolental hyperplasia.
The premature lung is very compliant and fluid can collect easily. Strict monitoring and calculation of fluid loss and administration is very important.
Even in adults, Hb of 10 gm% is a good margin because generally advocated level for transfusion trigger is 7-8 gm%. Normally, an adult consumes 250 ml oxygen per minute which can be carried by just 187 gm of total Hb in a blood volume of say 5000 ml. Therefore, 5000 ml /187 gm Hb = 3.7 gm % Hb would be enough for the per minute oxygen consumption of 250 ml, which comes to 3-5 ml oxygen/kg body weight/minute considering average body weight of 50-70 kg.
The premature neonate can carry 18.8 ml oxygen in blood volume of 200 ml, weighing 2.0 kg. Therefore, the oxygen delivery will be 18.8/2.0 = 9.4 ml oxygen/kg/minute because the cardiac output is generally equal to blood volume. The amount of oxygen delivery 9.4 ml/kg/min is with a good safety margin, when the minimum required is 3-5 ml/kg/min.
THE FOUR MOST IMPORTANT EQUATIONS IN CLINICAL PRACTICE:
http://m.globalrph.com/?url=http%3A%2F%2Fwww.globalrph.com%2Fmartin_4_most2.htm&utm_referrer=#2852
Feral Haemoglobin:
https://en.m.wikipedia.org/wiki/Fetal_hemoglobin
Management of fluids in neonatal surgery:
https://bjaed.org/article/S2058-5349(18)30048-9/abstract
P.S. The P50 is the partial pressure (PaO2) of oxygen at which 50% of the Haemoglobin is saturated with oxygen (SaO2 = 50%); lower the P50 higher the affinity of the Haemoglobin for oxygen. So, fetal Haemoglobin having lower P50 = 19 mm Hg, has higher affinity to bind oxygen.
A 2.0 kg premature neonate can have a blood volume of 2.0 x 100 ml/kg = 200 ml and if FFP (fresh frozen plasma) is transfused to build up the blood volume and also the coagulation factors instead of giving Vit K, the cardiac output would be adequate. The Hb level of 7.0 gm% would mean total Hb 200 ml x 7.0 gm% = 14.0 gm, which would carry 14.0 x 1.34 ml O2/gm of Hb = 18.8 ml oxygen content in the total blood volume of 200 ml if all the Haemoglobin is saturated with oxygen (SpO2 = 100%), which can be approximately the oxygen flux (oxygen delivered in one cardiac output, that is in one minute) because generally cardiac output is approximately equal to the blood volume. Generally accepted value is 1.34 rather than 1.39 ml of oxygen per gm of Hb.
Enough oxygen can be delivered to the tissues provided supplemental oxygen is given but not too high because it can cause retrolental hyperplasia.
The premature lung is very compliant and fluid can collect easily. Strict monitoring and calculation of fluid loss and administration is very important.
Even in adults, Hb of 10 gm% is a good margin because generally advocated level for transfusion trigger is 7-8 gm%. Normally, an adult consumes 250 ml oxygen per minute which can be carried by just 187 gm of total Hb in a blood volume of say 5000 ml. Therefore, 5000 ml /187 gm Hb = 3.7 gm % Hb would be enough for the per minute oxygen consumption of 250 ml, which comes to 3-5 ml oxygen/kg body weight/minute considering average body weight of 50-70 kg.
The premature neonate can carry 18.8 ml oxygen in blood volume of 200 ml, weighing 2.0 kg. Therefore, the oxygen delivery will be 18.8/2.0 = 9.4 ml oxygen/kg/minute because the cardiac output is generally equal to blood volume. The amount of oxygen delivery 9.4 ml/kg/min is with a good safety margin, when the minimum required is 3-5 ml/kg/min.
THE FOUR MOST IMPORTANT EQUATIONS IN CLINICAL PRACTICE:
http://m.globalrph.com/?url=http%3A%2F%2Fwww.globalrph.com%2Fmartin_4_most2.htm&utm_referrer=#2852
Feral Haemoglobin:
https://en.m.wikipedia.org/wiki/Fetal_hemoglobin
Management of fluids in neonatal surgery:
https://bjaed.org/article/S2058-5349(18)30048-9/abstract
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