Why does hyperventilation during CPR cause a decrease in venous return to the heart?
Because you are doing too much blowing and too little pumping. The reason for CPR is to keep blood going to the brain until the heart can be fixed. Hyperventilation causes the brain’s blood vessels to constrict (due to low carbon dioxide.) The brain can’t get as much blood, so the CPR becomes less effective. Also patients aren’t hyperventilated prior to intubation, they are pre-oxygenated to keep them from becoming too hypoxic.
