new_n_lost
Politically InCorrect
Topics: 650
Posts: 6,061
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My 2 Cents
In TOF we have a normal Shunt left to right ==>
The ventricular septal defect (VSD) is typically large; thus, systolic pressures in the right and left ventricles (and in the aorta) are the same. Pathophysiology depends on degree of right ventricular outflow obstruction. A mild obstruction may produce a left-to-right shunt through the VSD;
a severe obstruction produces a right-to-left shunt, resulting in low systemic arterial saturation (cyanosis) that is unresponsive to supplemental O2.
Sudden episodes of profound cyanosis (“tet spell”) may occur, which may be lethal. A spell may be triggered by any event that slightly decreases O2 saturation (eg, crying, defecating) or that suddenly decreases systemic vascular resistance (eg, playing, kicking legs when awakening) or by sudden onset of tachycardia or hypovolemia. A vicious circle may develop: The initial fall in arterial Po2 stimulates the respiratory center and produces hyperpnea. Hyperpnea increases systemic venous return to the right ventricle by making the negative thoracic pump more efficient. In the presence of a fixed right ventricular outflow obstruction or decreased systemic vascular resistance, the increased systemic venous return to the right ventricle goes out the aorta, further decreasing arterial O2 saturation and thus creating the vicious circle of the hypoxic spell.
The child is placed on his or her back in the knee-to-chest position to increase aortic resistance. The increased aortic and left ventricular pressure reduces the rush of blood through the septal hole from the right ventricle and improves blood circulation to the lungs, so more red blood reaches the tissues.
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| shalini.ravi
Forum Senior
Topics: 17
Posts: 153
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THANKS SO much nnl 
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mediocricity aint my style
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