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The anesthesiologist meets with patients on the morning of surgery to explain anesthetic options, risks, and benefits. There are multiple different types of anesthesia that are used, and sometimes a combination may even be employed, depending on many factors such as the patient and their health, what type of anesthesia is needed for the surgery, how deep the anesthesia needs to be, whether muscle relaxation is also needed, and other variables.

For all types of anesthesia, modern techniques and monitoring are typically very safe, with the risks of major complications often being quoted as one in ten thousand or more (depending on the literature source you are quoting). Many patients still have some fear of anesthesia because of risks that were present in the early days of anesthesia. In fact, most of the patients that do have problems while under anesthesia tend to have them not because of the anesthesia, but because the patients are frequently ill and undergoing major surgery for heart, bowel, kidney, vascular, or other problems. Orthopaedic patients, on the other hand, are usually in reasonably good health and additionally are optimized before elective surgery (usually with a complete medical clearance and evaluation prior to large elective surgeries), so anesthesia complications are even less frequent with orthopaedic surgeries.

This chapter discusses the principal types of anesthesia used for most hip and knee surgeries. The majority of our patients have spinal anesthesia for joint replacements, and either regional or local anesthesia with arthroscopic procedures (with or without mild sedation). General anesthesia is sometimes needed for medical reasons or patient preference. At other hospitals across the country, slightly different methods may be used (e.g., all general anesthesia, epidurals instead of spinals for joint surgeries, etc.) and vary by region.

Spinal Anesthesia

Spinal anesthesia is a safe and effective means of anesthesia during surgery, and this is the method most commonly used for most joint replacement surgeries. It involves an injection of medication (usually a local anesthetic) into the lower portion of the spine which numbs and paralyzes the lower half of the body (usually below the navel). Many patients are initially disturbed by this concept, but in fact, spinal anesthesia is usually significantly more pleasant and safer than general anesthesia, with fewer side effects.

Most spinal injections are quick and delivered with a numbing anesthetic (lidocaine) around the skin. The injection itself can contain several different medications, depending on how long the anesthesia needs to last. The injection is usually made at the lower end of the spine below where the spinal cord itself ends; this is important, because it is very rare to have any sort of spinal cord injury for this reason.

Advantages of Spinal Anesthesia

There are a number of advantages to spinal anesthesia. It is safer for patients with any sort of pulmonary (lung) disease, since a breathing tube is not needed. Without the need for an airway, there are fewer risks of airway complications such as obstruction or aspiration of stomach contents.

Spinal anesthesia usually produces excellent muscle relaxation for lower limb surgery, which is important when ligamentous balancing and work on the hip or knee is needed.

Blood loss is usually less for the same operation performed with spinal anesthesia rather than with general anesthesia. This is because of circulatory effects that result in lower blood pressure and heart rate, and thus there is less bleeding at the operative site. Post-operative deep venous thromboses (clots) and pulmonary emboli are also usually decreased with spinal surgery.

Normal gut function also rapidly returns after spinal anesthesia because peristalsis, or the motion of the bowels, continues through spinal anesthesia.

It is important to know that having a spinal does not necessarily mean that you will be awake for surgery (unless you want to be). Most patients elect to have a mild sedative with the spinal so that they doze off for the surgery, then awaken on arriving in the recovery room. However, this level of sedation is mild and does not entail the deep anesthesia of general anesthesia that requires a breathing tube. Patients are usually not as groggy after surgery and have significantly less issues with nausea. It is also more pleasant because it gradually wears off, allowing patients to get situated in their bed and room before fully wearing off.

Disadvantages of Spinal Anesthesia

There are some disadvantages to spinal anesthesia despite all of the above advantages. For the right patient, it is a very good method of anesthesia, but not all patients are good candidates for a spinal anesthesia. Sometimes it can be difficult to get the spinal in if a patient has a very arthritic spine or has had previous spine surgery.

There is a small chance of a spinal headache. This occurs because of leakage of spinal fluid. It usually resolves with lying flat, caffeine, and time, but sometimes a blood patch (injection of the patient's own blood into the spinal cord to form a small clot - it is not as bad as it sounds) is needed to resolve the headache.

Spinals are usually only effective for surgeries lasting several hours or less. Beyond that, general anesthesia is usually needed. This is usually more than enough time for most hip and knee replacement surgeries with experienced joint surgeons, but revision surgeries and complex surgeries are usually planned to last longer and may necessitate other anesthesia arrangements. Sometimes the spinal anesthesia needs to be supplemented with general anesthesia if not fully effective or if it begins to wear off.

Spinal anesthesia sometimes cannot be used if the patient has a condition known as aortic stenosis (narrowing of the aortic valve and outflow region of the heart). This is because the normal blood pressure drop with spinal anesthesia can be severe and problematic if they do not have a sustained after-load (systemic blood pressure).

Spinal anesthesia cannot be used if there are clotting disorders or if the patient has recently (within 24 hours) been on major blood thinners, as this causes some risk of a hematoma and bleeding within the spinal cord area.

Finally, there cannot be any sores or ulcers in the region of the back where the injection must pass through (sometimes a problem for nursing home patients with hip fractures).

Epidural Anesthesia

Epidural anesthesia is similar to spinal anesthesia, except that the injection is given into the epidural space, positioned in the soft tissues just behind the spinal cord. Because of this, it usually takes longer to take effect, but also may not be as likely to produce a drop in blood pressure as a true spinal block.

Sometimes a tiny catheter is introduced into the epidural space and left in place, similar to an IV. This allows for continuous anesthesia for as long as needed, sometimes even days, by continuing to inject small amounts of anesthetic into the epidural space.

Epidural anesthesia essentially has the same advantages and disadvantages of a spinal, except that it can be a sort of continuous spinal that can be used for a prolonged period rather than a single shot lasting a few hours. It also employs a larger volume of anesthetic, and thus it is possible that there can be some complications if this is injected into the wrong space (in a vein, it can possibly cause convulsions or rarely cardiac arrest). While some hospitals use this technique routinely for joint replacement surgeries, we typically prefer the use of a spinal because it does not leave the patient tethered to an epidural catheter. The epidural also needs to be discontinued as postoperative anticoagulants are started.

General Anesthesia

General anesthesia refers to the patient going "completely under," typically requiring placement of a breathing tube and having the ventilator machine breath for them while they are asleep. The term "general" applies because it affects the entire body, with loss of consciousness and motionlessness.

The general anesthetic itself may come in several forms; some are gases that are mixed with oxygen and delivered via a breathing tube or mask (e.g., isofluorane or other volatiles). Other general anesthetics are administered intravenously (e.g., propofol).

For most patients, the last thing remembered is the medication going into the I.V. The breathing tube is typically inserted after sedation and before awakening, so you generally do not remember the tube (although you might have a sore throat afterwards). Because of the use of the breathing tube, there are some risks introduced with this, including loose or chipped teeth and problems with the airway or with the tube being improperly positioned.

General anesthesia can be used for many hours if necessary, and it is needed for very large and complex surgeries. However, it is more likely to produce nausea and vomiting after surgery, and most patients feel drowsy or weak for several days after the anesthesia (like a hangover). It is also more likely to produce mental status changes after surgery in elderly patients.

Regional or Local Anesthesia

These forms of anesthesia are usually used for smaller, outpatient procedures such as knee arthroscopy. Regional anesthesia can be accomplished by several methods, such as femoral and sciatic nerve blocks which specifically block the nerves in the leg. Local anesthesia means that anesthetic (lidocaine or similar agent) is simply injected into the area that is being worked on.

Most simple knee arthroscopy procedures can actually be performed with just a local anesthetic injection. In fact, I have had patients who opted to stay awake with the local anesthetic and watch the video monitor with great interest and enthusiasm. However, in the course of each year, there are usually only a few takers with this option (usually only two or three out of hundreds of patients).

Most patients undergoing arthroscopy instead opt for light sedation with the local injection, which usually proves adequate. Not only is it a safe and effective means of rapid anesthesia, but the local anesthetic frequently lasts for several hours, allowing them to get home comfortably and situated with the knee iced and elevated.

Conscious Sedation

This type of anesthesia refers to very light sedation that lasts just a few minutes, typically used in the emergency room for setting fractures, reducing dislocated hips, and manipulating stiff knees under quick anesthetic.

The patient actually remains awake enough to breath on their own but is unconscious enough that they do not remember setting the fracture or performing the procedure. It is usually performed in the emergency room or recovery room, usually with one physician (often an anesthesiologist or emergency room physician) giving the sedation, watching the patient, and monitoring for signs of oversedation while the orthopaedic surgeon does his work. There is a small chance that some patients can become oversedated and may have to be given reversal agents and oxygen via a hand bag until they awaken again, and a very small percentage of patients may require intubation if they stop breathing on their own. However, it is generally safe and performed hundreds of times every day across the country in emergency rooms.

General Considerations

There are a number of options available for anesthesia with hip and knee surgery, and the type selected for a particular patient and surgery depends on the type and anatomical location of the surgery, the length of the surgery, patient factors and other medical issues that may affect the choice of anesthesia, and patient preference.

Typically, most joint replacement and resurfacing procedures will use spinal or epidural anesthesia and secondarily general anesthesia if the anesthesiologist and/or surgical team deems it to be a better choice for the patient and surgery. Knee arthroscopy usually uses regional or light general anesthesia, sometimes being performed with only local anesthetic.

Regardless of the type of anesthesia used, there are a few important things to remember. When discussing anesthesia with the anesthesiologist, it is a good idea to mention any allergies, problems with medications in the past, and any prior experiences with anesthesia. It is also important to mention all medications normally taken as well as to inform the anesthesiologist of any herbal supplements you may be taking.

If you drink alcohol on a regular (i.e., daily) basis, or certainly if you use any recreational substances such as marijuana, it is vital to be honest and let the anesthesiologist know this. The information is kept in confidence, and a potential reaction can be very serious. It is also important to let the anesthesiologist know if any blood relatives have had bad anesthesia reactions in the past, and if you have any loose teeth or dentures. Finally, if you have had anything to eat or drink since the evening before, be sure to let the anesthesiologist know.
