Answer to the case of CHD: ToF
1. Why is spo2 directly related to blood pressure?VSD is a component of ToF. Normally, owing to the greater pressure in the left ventricle, there is a left to right shunt of blood in each systole. If left ventricular pressure decreases to a degree lower than that of the right ventricle, the shunting will occur from right to the left. This results in the mixing up of the deoxygenated blood from the right ventricle with the oxygenated blood in the left ventricle resulting in a decreased spo2. So, every time the pressure in the left ventricle, and hence the arterial blood pressure drops, it is accompanied by a drop in spo2.
2. Can we use sevofluorane (inhaled general anesthetic) to induce general anesthesia?
Inhaled anesthetics work by diffusing into the blood in the pulmonary circulation and producing anesthetic effects when they reach the brain. Patients with ToF have pulmonary stenosis. this is associated with decreased perfusion of the pulmonary capillaries. So even if we use inhaled anesthetics, they cannot diffuse very well into the blood and hence cannot produce the desired effects. So in these cases we cannot useinhaled anesthetics to for induction.
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