Physiological effects of spinal anesthesia

Spinal anesthesia refers to the injection of drugs into the subarachnoid space, so that an inhibitory effect can be achieved. This method of anesthesia is called spinal anesthesia, also known as spinal anesthesia. It will have a certain impact on physiology. After the drug enters the subarachnoid space, nerve block will occur. Because spinal anesthesia has no effect on gas exchange, it will have a certain impact on liver and kidney function, and may cause decreased liver and kidney perfusion.

Physiological effects

1. Nerve block

1. After the local anesthetic is injected into the subarachnoid space, the order, timing and range of the blockade will vary due to the different thickness of the nerves.

2. The sympathetic nerves are the thinnest, blocked the fastest, and have the highest plane; the sensory nerves are second, blocked later, and have a higher plane; the motor nerves are the thickest, blocked the latest, and have the lowest plane.

3. If the blocking plane exceeds thoracic 4, the heart rate will slow down, cardiac output will decrease, and blood pressure will drop due to the blocking of cardiac sympathetic fibers.

4. The symptoms are particularly severe in patients with hypovolemia, the elderly and those with venous reflux disorders (pregnancy).

3. Impact on breathing

1. During low spinal anesthesia, there is no effect on gas exchange.

2. When the plane rises to the chest, the intercostal muscles gradually become paralyzed. For general patients, the respiratory function will not be affected because of the diaphragm compensation, but it will have a serious impact on those with poor respiratory function reserves (obese, weak people).

3. Paralysis of the intercostal muscles and abdominal muscles can make the patient cough weakly.

4. Effects on liver and kidney function

During spinal anesthesia, renal perfusion may be increased due to renal vasodilation. If the anesthesia is not properly managed, short-term hypotension may reduce liver and kidney perfusion.

5. Effects on uterine contraction

When the anesthesia plane is below thoracic level 10, the cervical muscles relax and the contraction of the uterine muscles increases. When the plane exceeds thoracic level 6, the uterine muscles are also restricted. Prolonged hypotension may weaken uterine contractions.