What is the reason for increased blood pressure after injection of norepinephrine?

Blood pressure elevation after injection of norepinephrine is usually caused by factors such as excessive drug dosage, increased heart rate, and constriction of small veins and arteries. A detailed analysis is as follows:

1. Excessive drug dosage

Since this medication is primarily used to treat acute hypotension and shock due to peripheral vasodilation, administering too high a dose may lead to adverse effects such as elevated blood pressure and local tissue necrosis.

2. Rapid heart rate

After injecting norepinephrine, patients may experience increased myocardial contraction and tachycardia, resulting in excessive cardiac output. This can trigger a reflexive enhancement of the vagus nerve activity, ultimately leading to elevated blood pressure.

3. Constriction of small veins and arteries

Norepinephrine exerts a significant vasoconstrictive effect through activation of alpha receptors, causing constriction of small veins and arteries in areas such as the skin, mucous membranes, and glomeruli. This increases systemic vascular resistance, thereby inducing hypertension.

In addition, other underlying diseases may also contribute to elevated blood pressure, including hyperthyroidism, renal failure, renal artery stenosis, and Cushing's syndrome. It is important to note that if a patient develops adverse symptoms after injection, they should promptly seek medical evaluation. Under a physician’s guidance, an appropriate treatment plan should be selected. Self-medication should be strictly avoided to prevent potential harm to the body.