Spinal blocks often offer several advantages over general anesthesia for procedures involving the lower body, according to the 2006 edition of "Clinical Anesthesiology." As with any medical procedure, however, the use of spinal blocks in surgery sometimes results in side effects. Most of these side effects arise from disruption of signals from the sympathetic nervous system that controls such essential involuntary functions as blood pressure, heart rate and breathing.
Blood Pressure
Spinal blocks always induce a variable decrease in blood pressure, notes "Clinical Anesthesiology." Just how much depends on patient position, dose of medication and individual sensitivity to medication. Although anesthesiologists monitor blood pressure intraoperatively, since spinal anesthesia allows patients to remain awake, low blood pressure may be experienced as sudden feelings of weakness, sleepiness or nausea.
Heart Rate
Sometimes decreases in blood pressure are accompanied by decreases in the number of heart beats per minutes or a decrease in the force with which the heart contracts. Low heart rate produces similar symptoms as low blood pressure, although low heart rate may also induce mild chest pain or a feeling of palpitations as the heart slows down.
Respiratory Insufficiency
Respiratory insufficiency due to spinal blocks may result from inadequate perfusion of the brain centers that control breathing due to low blood pressure, or from inhibition of those centers by opioid drugs. In most cases, says "Clinical Anesthesiology," patients initially complain of difficulty breathing or breathing that seems to require more effort than normal, usually accompanied by numbness in the arms. Without treatment, patients may lose consciousness and miss breaths altogether, a condition know as apnea.
Treatment
Anesthesiologists use drugs called vasopressors to restore blood pressure while a drug known as atropine rapidly corrects low heart rate. Reassurance and supplemental oxygen are usually all that is needed to correct respiratory insufficiency. According to a 2004 report in the journal "Anesthesiology," stopping sedative medications can also help.
Prevention
Since some degree of sympathetic nervous system inhibition is always expected with the use of spinal blocks in surgery, anesthesiologists often load patients with 1 to 2 L of fluid around the time that they start the block. In addition, it also helps to tilt the table slightly towards the head, to prevent blood from pooling in the lower body. According to the American Society of Anesthesiology, patients can help by maintaining adequate fluid intake in the days leading up to surgery and telling the anesthesiologist about any past history of side effects due to anesthesia.
References
- "Clinical Anesthesiology, Fourth edition;" G.E. Morgan et al. (eds); 2006
- American Society of Regional Anesthesia and Pain Medicine: Patient Information
- American Society of Anesthesiologists: Anesthesia and Me
- "Anesthesiology;" Injuries Associated with Regional Anesthesia in the 1980s and 1990s; L.A. Lee et al.; 2004
