The introduction of anesthesia for surgical procedures was a monumental discovery and has allowed for necessary procedures to be performed in a humane, controlled and comfortable manner. While anesthesia today is the safest it has ever been, even for the sickest patients, its administration is not without risks.
The specific risks of anesthesia vary with the kind of anesthesia, type of surgery (elective or emergent), and patient specific factors, including age and pre-existing medical conditions. The risk of long-term complications, including death, from anesthesia itself is very small. Complications are more closely related to the surgical procedure and a patient’s general health.
Complications of General Anesthesia
Most healthy people tolerate general anesthesia without issue. Those who do suffer side-effects or complications typically have mild, transient symptoms that are easily managed. The following are possible complications of general anesthesia:
- Sore throat
- Nausea and vomiting
- Damage to teeth
- Lacerations (cuts) to the lips, tongue, gums, throat
- Nerve injury secondary to body positioning
- Awareness under anesthesia
- Anaphylaxis or allergic reaction
- Malignant hyperthermia
- Aspiration pneumonitis
- Respiratory depression
- Stroke
- Hypoxic brain injury
- Embolic event
- Cardiovascular collapse, cardiac arrest
- Death
Post-operative Nausea and Vomiting (PONV)
Post-operative nausea and vomiting or PONV is any nausea, vomiting or retching in the first 24-48 hours following surgery. It is one of the most common side effects of anesthesia, occurring in up to 30% of all post-operative patients, and a leading cause for patient dissatisfaction after anesthesia. While the physiology of PONV is complex and not well understood, some risk factors and triggering agents have been identified. Two scoring systems have been developed, one each for adults and children, to try to identify those patients at higher risk of developing PONV, thus allowing anesthesiologists to decide who may benefit from prophylactic therapies.
In adults, predictive risk factors include: female gender, non-smoker, history of PONV or motion sickness, surgery duration > 60 minutes and use of post-operative opioids. The more risk factors present, the higher the likelihood of developing PONV.
In children, predictive factors include: history of PONV in the child or relatives, surgery duration > 30 minutes, age > 3 years, and strabismus surgery.
The type of surgery has traditionally been thought to also contribute to the occurrence of PONV. While this association has not been reliably reproduced in studies, anecdotally there appears to be an increase in PONV following gynecological, ophthalmological (eye surgery), otological (ear surgery) and thyroid surgeries.
Awareness Under Anesthesia
Awareness during general anesthesia seems to be one of the biggest concerns for patients, but is very rare. Approximately 1-2 patients per 1000 general anesthetics may briefly become aware of their surroundings, but usually do not feel pain.
In extremely rare instances, a patient can have awareness of their situation and experience pain while under general anesthesia. Because of paralytics given to facilitate surgery, the patient may not be able to move to make others aware of their distress. People who truly experience this level of awareness may develop psychological issues similar to post-traumatic stress disorder (PTSD).
Certain situations are associated with a higher risk of some level of awareness. Also known as unintended intra-operative awareness, it may occur with:
- Emergency surgery
- Trauma surgery
- Cesarean surgery under general anesthesia
- Heart surgery involving cardiopulmonary bypass
- Depression
- Daily alcohol use
- Errors by the anesthesiologist-may may include improper monitoring of the patient and/or the amount of anesthesia administered during a procedure
Aspiration pneumonitis
Under general anesthesia the ability to protect one’s airway is reduced. This means that if a patient were to regurgitate stomach contents while anesthetized, the reflexes which seal off the airway to inhibit vomitus from entering the lungs may not be fully functional. Stomach content entering the lungs is referred to as aspiration and the inflammation within the tissue it causes is referred to an aspiration pneumonitis. If an infection were to develop in the inflamed area of the lungs following an aspiration event, this is known as aspiration pneumonia.
The risk of an aspiration event is higher in certain patients. These patients include people with moderate to severe reflux, those who have eaten within the previous 6-8 hours, pregnant women, and diabetic patients whose stomachs do not empty properly.
Anesthesiologists can attempt to reduce the risk of aspiration by administering medications that enhance gastric emptying (speed up the movement of food from the stomach into the intestines) or increase the pH of the gastric contents (make them less acidic, and therefore less damaging to lung tissue). They may also apply cricoid pressure (pressure on the cartilage of your trachea or windpipe) during intubation (placement of an endotracheal tube). Theoretically, this pressure can compress the esophagus (food pipe) and prevent regurgitation during manipulation of the airway.
Peripheral Nerve Damage
Peripheral nerve damage can occur with any type of surgery and is the result of nerve compression. It is most commonly caused by extensive periods of time in an exaggerated or awkward position. The ulnar nerve of the arm (runs along the little finger side of the forearm) and the peroneal nerve of the lower leg (runs along the outside of the leg between the knee and ankle) are affected most often. The severity of damage and recovery of function are variable and may be prolonged.
Both the anesthesiologist and surgeon are aware of this potential complication and take steps to prevent it. When possible, extreme postures are avoided and the body placed in a neutral position. Padding is placed under pressure points, particularly the elbows, hips, knees, heels, and any other dependent body region during patient positioning. These pressure points are reassessed throughout the procedure to ensure the padding and body is properly positioned. When possible, the patient’s limbs can be moved or repositioned during the surgery.
If nerve damage is suspected post-operatively, the patient is followed up and may be referred for further testing, such as electromyography.
Complications of Regional Anesthesia (Nerve Blocks)
Complications from regional anesthesia or nerve blocks have been reduced with the utilization of ultrasound-guided placement. Because all nerve blocks require the use of needles, there is always the potential for bleeding, hematoma formation, bruising at the puncture site, or infection. Direct visualization of the needle tip may aid identification of arteries and veins in the area. This decreases the likelihood of inadvertently puncturing a blood vessel during block placement. The area where the needle is inserted is antiseptically cleaned and a sterile cover is placed on the ultrasound probe to help minimize infection risk.
Nerve damage after a regional block is a rare occurrence. It can be caused by injury to the nerve directly from the needle, or related to secondary complications, such as infection or hematoma formation. To prevent injury, the anesthesiologist will ask you to tell them if you feel sharp or radiating pain while they are positioning the needle and during injection of the local anesthetic. After the nerve block has worn off, you should seek medical attention if you experience any new symptoms such as tingling, numbness, or motor dysfunction. These could indicate the formation of a hematoma or infection.
Nerve blocks performed for shoulder, arm and hand surgery involve the brachial plexus (a complex of nerves in the shoulder area) and are generally well tolerated. There are some symptoms that one may notice that are sometimes used to indicate a “good block”. Some patients experience Horner’s syndrome, which can include a change in pupil size, a droopy eyelid or nasal stuffiness on the same side as the block was performed. Some patients may also have a certain degree of hoarseness. It is possible to partially block one of the nerves going to the diaphragm. This can make a patient feel as though they need to make a stronger effort to breathe. All of these symptoms are temporary and should resolve as the nerve block wears off.
A rare, but important, complication of brachial plexus blocks is the development of a pneumothorax (entrapment of air between the lung and chest wall). While symptoms can occur immediately, they may take up to 24 hours to develop. These include shortness of breath, problems breathing, chest pain or persistent coughing. A chest x-ray will confirm the diagnosis of a pneumothorax. Depending on the size, placement of a chest tube is sometimes needed to evacuate the entrapped air.
Sometimes a nerve block just does not work. The anesthesiologist who places the block will assess the sensation and motor abilities of the blocked area. If the anesthesia is insufficient, sometimes a “rescue block” can be performed either in the same area as the failed block or at a different site that will cover the surgical area. When all else fails, a patient general anesthesia can be administered, if a regional nerve block was the planned surgical anesthetic.
Complications of Neuraxial Anesthesia (Spinal/Epidural)
In general, there is a low incidence of serious complications related to neuraxial anesthesia, but those that occur may be temporary or permanent. Complications are related to either exaggerated physiologic responses or needle/catheter insertion and include:
- Pain
- Post-dural-puncture headache
- Hypotension and bradycardia secondary to sympathetic blockade
- Hypothermia
- Respiratory failure resulting from a “high spinal/block”
- Urinary retention
- Spinal infection, including aseptic meningitis
- Spinal or epidural hematoma
- Nerve or spinal cord damage, possibly resulting in paralysis
Post-dural-puncture Headache
A post-dural-puncture headache (PDPH) results from the leakage of cerebrospinal fluid (CSF) following spinal anesthesia or inadvertent dural puncture with epidural placement. It is occurs commonly, particularly in the young, female obstetric (pregnant) population. PDPH symptoms may include headache, nausea, vomiting, photophobia (light sensitivity), diplopia (blurred or “double” vision), dizziness or tinnitus (“ringing in the ears”). The characteristic headache is positional, worsening with sitting or standing, and usually relieved with lying down. Onset of symptoms is typically within 12-72 hours after the leak starts.
If left untreated, symptoms will usually resolve in about a week. Conservative treatment includes bed rest, adequate hydration, analgesics (pain medications) and caffeine ingestion. When conservative management fails, an epidural blood patch may be offered by an anesthesiologist. This involves injecting a patient’s own blood into the back around the site of the fluid leak. When performed in the setting of a true post-dural-puncture headache, a blood patch has been shown to resolve symptoms almost immediately in upwards of 90% of cases.
Hypotension (Low Blood Pressure)
A majority of patients receiving spinal anesthesia, and many receiving epidurals, will develop some degree of hypotension. This occurs secondary to the blockage of the sympathetic nerves in the lower body that are responsible maintaining blood pressure. The decrease in blood pressure usually responds to a fluid bolus, but does occasionally require the use of vasopressors as well. While most healthy patients tolerate this transient hypotension, there are reports of cardiac arrest occurring following the placement of spinal or epidural anesthetics. Extra care must be taken in patients receiving neuraxial anesthesia that have a cardiac history. These patients may develop myocardial ischemia (decreased blood flow and oxygen to the heart muscle) with minor decreases in blood pressure. This type of anesthesia is actually contraindicated for several cardiac conditions for this very reason.
High Spinal or Total Spinal
A high spinal occurs when the level of anesthesia spreads into the upper thoracic or cervical regions, or in the case of a total spinal, into the base of the brain. It can result from the administration of too much local anesthetic or excessive spread of the medication. While not as common, a high block can also occur with epidural anesthesia. As the spinal level moves up, it begins to affect the nerves of the arms, resulting in tingling in the fingers or weakening of hand grips. A patient may complain of shortness of breath as the nerves to the accessory muscles used to breathe are affected. At higher levels, the nerves that aid in increasing heart rate are blocked, and bradycardia (slow heart rate) occurs, which can further lead to hypotension (low blood pressure). If the anesthetic moves all the way to the base of the brain it can inhibit the centers that control breathing.
Treatment for a high spinal involves supportive measures, which include administering fluids and medications to increase blood pressure and/or heart rate and likely intubation when the nerves affecting breathing are involved. Positioning a patient more head up to stop the flow of anesthetic toward the brain and turning off any continuous medications through a spinal or epidural catheter are also performed. These measures are continued until the local anesthetic wears off and normal function returns.
Complications of Local Anesthesia
Local anesthesia has similar complications to regional anesthesia. Since a needle is being utilized, the risks of bleeding, hematoma formation, bruising at the injection site, and infection are all possible. Nerve damage from direct needle contact or secondarily to hematoma or infection can also occur. Pain at the injection site is a possibility, as well as failure of the local anesthetic to provide sufficient anesthesia.