Oxygen saturation fetal

Meperidine crosses the placental barrier and, even in reasonable analgesic doses, causes a significant increase in the percentage of babies who show delayed respiration, decreased respiratory minute volume, or decreased oxygen saturation, or who require resuscitation. Fetal and maternal respiratory depression induced by meperidine can be treated with naloxone. The fraction of drug that is bound to protein is lower in the fetus concentrations of free drug thus may be considerably higher than in the mother. Nevertheless,... 

The quantity P50, a measure of O2 concentration, is the partial pressure of Oj that half-saturates a given hemoglobin. Depending on the organism, P50 can vary widely, but in all instances it will exceed the PO2 of the peripheral tissues. For example, values of P50 for HbA and fetal HbF are 26 and 20 mm Hg, respectively. In the placenta, this difference enables HbF to extract oxygen from the HbA in the mother s blood. However, HbF is suboptimal postpartum since its high affinity for O2 dictates that it can deliver less Oj to the tissues. 

Studies of oxygen transport in pregnant mammals have shown that the 02-saturation curves of fetal and maternal blood are markedly different when measured under the same conditions. Fetal erythrocytes contain a structural variant of hemoglobin, HbF, consisting of two a and two y subunits (a2y2), whereas maternal erythrocytes contain HbA (a2/32). 

HbA now has a greater affinity for oxygen than does HbF. When BPG is reintroduced, the 02-saturation curves return to normal, as shown in the graph. What is the effect of BPG on the 02 affinity of hemoglobin How can the above information be used to explain the different 02 affinities of fetal and maternal hemoglobin ... 

Oxygen capacity of fetal blood at saturation, cm3 02/cm3 blood... 

Partial pressure of oxygen calculated from the space average fractional saturation of blood, torr Radius of fetal capillary, cm Radius of maternal channel, cm Radius of tissue cylinder, cm Dimensionless radial distance Variable radius, cm Time, sec... 

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