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Mortality Associated with Anesthesia
By Henry Rosenberg, M.D., Professor of Anesthesiology, Thomas Jefferson University. E-mail: email@example.com
A Brief History of Anesthesia
On October 16, 1846, William Thomas Green Morton demonstrated that a chemical compound can produce insensibility to pain in a predictable and controlled manner at the Masschusetts General Hospital. This remarkable accomplishment changed the practice of medicine forever. The introduction of diethyl ether (originally called "Letheon") by Morton revolutionized the practice of medicine and surgery. Early in the 20th century, the famous physician, Sir William Osler, listed anesthesia as one of the great events in modern medicine.
However soon after ether anesthesia was introduced, people started to die during surgery. Soon thereafter, chloroform was demonstrated by Simpson to have anesthetic properties. These drugs and others that were introduced over the ensuing years caused changes in physiology that were never seen and were unanticipated. For example, one of the causes of death that unfortunately still occurs during anesthesia administration is aspiration of stomach contents. What was not appreciated for many years was that anesthetic agents depress the normal reflex response to foreign compounds entering the airway.
The 150+ years since the introduction of anesthesia have been marked by the struggle to improve the safety of anesthesia care. New drugs were introduced that are not explosive, that do not depress vital functions to as great extent as older agents, local anesthetics were developed and introduced, devices were devised to monitor blood pressure, activity of the heart and lungs and measure oxygen content of the blood, to name a few, and a formal rigorous training program was introduced in order to prepare qualified nurses and physicians in the complexities of managing patients undergoing ever-more complex surgical procedures. Anesthesiology (the study of the science of anesthesia) has branched into subspecialties such as pain management, critical care of patients, operating room management, to name a few.
When mortality from anesthesia began to be studied in the 1950s and it is often difficult to sort out mortality due to surgery and patient disease from that due to administration of anesthesia drugs, the rate was somewhere in the vicinity of 1 death related to anesthesia for every 10,000 administrations in otherwise healthy patients. The malpractice premium for anesthesiologists was about as high as that of surgical specialties. However, due to the introduction of sophisticated monitoring devices, better training, understanding of the physiologic effects of anesthetics and better transmission of information concerning causes of anesthesia mortality, the mortality rate has fallen into the range of 5-6 deaths/million anesthetic administrations. At the same time, the malpractice premium has fallen close to the range of primary care physicians.
Why Do Patients Die from Anesthesia?
Despite the remarkable growth in understanding of how anesthetic drugs work, not everything is known or predictable about how a patient will respond to these potentially toxic agents.
I will present some of my views as a practicing anesthesiologist who has spent most of his career in a University environment on this subject.
Airway Management: It is well known that if a patient is deprived of oxygen for 4-6 minutes they will experience brain death. Longer periods will lead to cardiac arrest.
During most anesthetic administrations using general anesthesia (drugs that produce total loss of consciousness), the airway is protected and guaranteed by inserting a device called an endotracheal tube into the trachea (windpipe). This is done by direct visualization of the inlet (glottis) to the trachea.
Just behind the tracheal opening is the esophagus. If the tube is placed in the esophagus, obviously oxygen is not delivered to the lungs and after a brief period the patient will turn blue and suffer a cardiac arrest.
These devices have greatly reduced the incidence of misplacement of the endotracheal tube. However, if a device is not present (such as in an office where surgery is performed) or not working, then an error may be made in assessing whether the tube is correctly placed.
Why, you may ask, doesn't the patient breathe by himself if the tube is not in the right place? This is because patients are usually paralyzed in order to place the tube.
Another airway problem that can lead to hypoxia (lack of oxygen) is the failure to appreciate that the patient's anatomical structures may make the placement of the tube difficult or impossible. Repeated attempts at intubation will lead to airway trauma, and unless an emergency tracheotomy is done (hole in the windpipe), the patient may develop fatal hypoxia. A profusion of devices have been developed to help in such an emergency situation including the fiberoptic bronchoscope--a thin fiberoptic bundle that allows the anesthesiologist to get a view of the trachea--and the laryngeal mask airway (LMA). The LMA is an innovative device that opens up the upper airway (above the trachea) and allows for temporary ventiliation in such critical situations.
As mentioned above, aspiration of gastric contents in a patient with a full stomach is a potential cause of mortality. All pregnant patients, very obese patients, trauma victims and patients with bowel obstruction have a full stomach. Precautions, through use of drugs to hasten onset of anesthesia and paralysis, along with pressure over the neck to prevent gastric contents from coming up the esophagus, will minimize the risk of aspiration.
Ventilation: In addition to establishing a patient airway to deliver oxygen and other gases, gas exchange needs to take place so that oxygen may be delivered and carbon dioxide removed from the body. Usually this is accomplished with a mechanical device called a ventilator.
Patients may get into trouble not so much during the anesthetic delivery but shortly thereafter if the paralyzing drugs used by the anesthesiologist or CRNA (nurse anesthetist) are not "reversed"--i.e., their actions terminated with the use of antagonists. Patients who are deeply anesthetized or paralyzed will not breathe and may become hypoxic.
A more common cause of death has been the administration of potent sedative drugs in order to make patients comfortable during "minor" procedures. Often these potent agents are administered by poorly trained persons without the supervision of an anesthesiologist. In addition to sedation, these agents may cause respiratory depression (the patient stops breathing) leading to hypoxia. One of the targets of educational programs has been "conscious sedation" protocols. That is, sedation should produce only mental relaxation but not loss of consciousness. However, the margin between one effect and the other blurs and the same dose of drug in one patient may produce loss of consciousness in another patient.
In some cases, the ventilator may malfunction and not deliver gases in an appropriate manner.
Increased pressure in the lungs will cause a hole in the lung (a pneumothorax). Such pressure may continue to build up outside the lungs and cause pressure on the blood vessels returning blood to the heart and therefore reduce the cardiac output (this is called a tension pneumothorax). Unless the pneumothorax is recognized and treated by placing tube through the chest wall into the area just outside the lung itself, the patient may go on to die.
Pneumothorax is not easy to diagnose in many cases. Patients who have suffered trauma are the ones most at risk to pneumothorax. Other causes may be puncture of the lining of the lung from outside the chest incident to placing a needle into one of the major vessels in order to establish an IV access route--usually the subclavian or internal jugular vein.
Circulation: The heart propels blood around the body. When the heart stops, organs do not get blood and oxygen.
Patients often bleed during surgery and it is vital that the anesthesia provider administer blood and fluid to keep up with the losses. Often this means that the anesthesiologist must recognize that a particular procedure is associated with much blood and fluid loss and prepare for that eventually by inserting extra intravenous lines and making sure the blood bank has blood for transfusion.
The circulation may be stopped by many of the anesthetic drugs that are used. These agents are all toxic in concentrations, slightly higher than those that produce loss of consciousness. Overdose of anesthetic gases or intravenous drugs will stop the heart. All patients respond slightly differently to the anesthetics. A "normal" dose of an anesthetic will lead to a problem in some special situations such as the patient who is very sick or has a reduced blood volume. Anesthesia providers must know and recognize when this problem may arise.
Allergic Reactions: Allergies to drugs are life threatening. Fortunately, the anesthetic gases do not produce allergic reactions. The drugs that do produce allergy with the response of marked drop in blood pressure and wheezing leading to inability to ventilate, are generally drugs that are used incident to anesthesia, such as muscle relaxants (paralyzing agents), intravenous anesthetic drugs, and antibiotics. Latex may also cause life-threatening allergic reactions. Latex containing gloves may lead to an allergic response when the surgeon puts his/her hands into the patient's body.
The steps for treatment of allergic response are well known, but treatment must be begun promptly and in adequate doses.
Malignant Hyperthermia (MH): Every now and then a patient would develop high body temperature, increased heart rate, muscle rigidity and die during anesthesia. When investigated, it turned out that this problem is inherited in a predictable manner and results from a defect in the metabolism of skeletal muscle when exposesd to certain general anesthetics and one paralyzing agent. The disorder was named Malignant Hyperthermia because 80% of patients who developed this problem died. MH was found to occur in anywhere from one in 10,000 to one in 50,000 anesthetic administrations. Further research demonstrated that the patients were, in general, free of any outward signs of abnormality in the muscles or any other organ.
In the late 1970s, an antidote drug was found--dantrolene sodium. The signs and symptoms of MH were categorized and the anesthesia community was made aware of how to recognize and treat the problem by a patient advocacy organization, the Malignant Hyperthermia Association of the United States (MHAUS). Further information about this disorder may be obtained from the website http://www.mhaus.org or by calling 1-800-98-mhaus.
Death and disability occurs infrequently from MH now, perhaps in only 5% of cases. However, if a facility stocks dantrolene and is familiar with the signs of the disorder, there should be no fatalities.
With the emphasis on cost reduction, more surgery is being performed in offices and outpatient centers. Many of these sites are not prepared to treat MH because dantrolene is felt to be too expensive!
At least 400 MH cases occur in the US each year and at least 2-3 young healthy patients die.
Testing for MH is available by a special muscle biopsy test that is performed in nine centers in the U.S., including Thomas Jefferson University.
Other Muscle Diseases: In the early 1990s, the MHAUS noted reports of death in young, apparently healthy children undergoing minor surgery. Further investigation showed that these children had muscular dystrophy, but were as yet asymptomatic. In this case, death was due to elevated potassium incident to the administration of the paralyzing agent succinylcholine. Elevated potassium stops the heart. This led to a change in the package insert for this drug advising against the routine use of succinylcholine in children.
Elevated Potassium After Succinylcholine: In addition to patients suffering from muscle disease, burn patients, trauma patients, spinal cord-injured patients may develop fatal elevation of potassium after administration of succinylcholine. What is not generally appreciated is that this phenomenon may happen weeks after major trauma if the patient is immobilized for several weeks.
Local Anesthetics: Local anesthetics were first discovered about 100 years ago. These are the "caine" drugs, novocaine, bupivicaine, etc. These drugs are injected or used topically (such as hemorrhoid creams) to produce analgesia. Local anesthetics are used commonly by anesthesiologists as well as non-anesthesiologists.
If the local anesthetic is injected into a vessel in large amounts, the patient may experience a seizure and cardiac arrest. Anesthesiologists are especially aware of this problem because they use these drugs in spinal, epidural, and a variety of nerve block procedures. Rapid diagnosis and treatment should prevent mortality.
However, sometimes surgeons and gastroenterologists, or dermatologists, may not appreciate the potential toxicity of these agents and may be unprepared to treat the complications. For example, a liposuction technique has been developed using large amounts of dilute local anesthetics injected under the skin. If the drug is absorbed rapidly or too high a concentration of drug is used, then toxicity may result. Several deaths have been described from this problem recently.
Mechanical Problems: Over the past 75 years, the devices designed to administer anesthetic agents (the anesthesia machine) has undergone mechanical and human engineering changes so that machine malfunction is a very uncommon cause of anesthesia mortality. A check-out list is to be followed by the practitioner prior to using the machine. This check-out will detect most every problem with the machine.
Human Factors: Modern anesthesia is more than administration of drugs. The anesthesiologist must anticipate and react to changes induced by surgery and be familiar with changes that occur in the response to drugs in sick patients. Extensive training is required of anesthesia providers, be they nurse anesthetists, anesthesia assistants or anesthesiologists. Attention and vigilance is required in even the most straightforward cases, because unanticipated problems may happen at any moment. Fatigue, stress, lack of sleep may slow responses to critical events. The role of such human factors in anesthesia mishaps is poorly understood.
There is also a debate that centers on whether the safety record of nurse anesthetists supervised by surgeons is similar to or different from that of anesthesiologists performing anesthesia by himself/herself (as in almost all countries in the western world) or supervising nurse anesthetists. Recent data suggest that a better safety record is provided when a trained anesthesiologist supervises anesthesia care.
Anesthesiology is often cited as a medical specialty where safety has been a central focus with dramatic improvements in mortality and morbidity over the past thirty years. As someone who has practiced the specialty since the early 1970s, I feel that the technological advancements and growth in knowledge has enabled anesthesiologists to care for ever sicker patients in a safer manner. For example, when I started training, electrocardiograph monitoring was not available for all patients. Now it is unthinkable to provide anesthesia without EKG, pulse oximetry, blood pressure, and capnography.
In recent years, computer technology has led to the creation of full scale mannikin simulators. The belief is that, like pilots, anesthesiologists and CRNAs should be trained in emergency situations using a simulator, so that he/she can be prepared to treat the rare and unusual anesthetic problem.
In addition, pharmaceutical companies continue to improve the available agents that are used to produce anesthesia.
The goal is a zero defect product.