Science / Medicine : General Anesthesia: Balancing Act in Operating Room
When Jeffrey B. Cooper says that in general anesthesia, “someone takes you to the brink of death, basically, with lethal drugs,” the pioneer in the study of anesthesia safety is hardly exaggerating.
General anesthesia indeed can be one of medicine’s most precarious procedures. It involves the use of some of the most dangerous drugs around--typically a combination of at least six agents--all of which grant very little margin for error.
The potential dangers of general anesthesia have long been recognized, and today efforts are still under way to establish better guidelines intended to further reduce such risks.
When a person undergoes it, control of breathing, circulation of the blood and pumping of the heart all are turned over to an anesthesiologist, who must monitor that patient’s vital signs for any hints of abnormality, using an assortment of monitors.
In a typical case, a patient first receives an oral premedication to produce drowsiness and allay anxiety. Intravenous sodium pentothal might be given to induce sleep.
Then muscle-paralyzing drugs are administered for relaxation and so that a tube can be inserted in the trachea to control breathing. The endotracheal tube is connected to a ventilator, which controls the patient’s breathing throughout the operation and delivers oxygen to the lungs.
Depress Vital Functions
Through the endotracheal tube, in addition to oxygen for breathing, nitrous oxide and potent inhalation anesthetics are given. Nitrous oxide contributes to amnesia, and the potent inhalation agents, such as halothane, aid in the three functions of anesthesia: amnesia, analgesia (elimination of pain) and relaxation. Supplemental opiates such as morphine might then be added to enhance analgesia and relaxation.
These agents also depress vital functions: They can decrease respiration and reflexes, lower blood pressure, reduce the amount of blood pumped out by the heart and slow the rate of the heart.
But there’s more to general anesthesia than that.
Endotracheal intubation, surgical incision and manipulation and blood loss all have profound stimulatory effects on the body, and its response to such stimuli is to pour out adrenalin. This, in turn, requires the administration of additional drugs to counter such effects; without suppression of the physiologic responses to pain and stress, the heart rate would race and blood pressure would skyrocket.
“It takes a lot of experience to get the drugs balanced in just the right way so the patient is asleep and not moving and not dead, and will wake up at the end of surgery,” said Cooper, a biomedical engineer in the department of anesthesia at Massachusetts General Hospital in Boston. This is particularly true when the patient is seriously ill and the operation is complicated.
In addition, technical problems and unpredictable patient reactions to drugs and stress during anesthesia can occur to further complicate things.
Since 1846, when a dentist demonstrated at Massachusetts General Hospital that ether inhalation can produce unconsciousness and insensibility to pain, the dangers of anesthetic agents have been widely recognized.
The first anesthetic death was reported only two years later in 1848. In the early days, deaths resulting from drug-induced respiratory and cardiac failure were not at all uncommon.
But even today, it is estimated that in the United States one in 10,000 cases of anesthesia results in death--a rate that many still regard as unacceptable. The majority of such deaths, they say, are preventable.
This does not include the untold numbers of patients who suffer permanent disability, such as brain or heart damage, as the result of undergoing anesthesia.
Even as recently as 10 years ago, infrequent patient deaths and other bad outcomes were regarded as regrettable consequences of anesthesia, according to Dr. James Philip of the Brigham and Women’s Hospital in Boston and Harvard Medical School. “Anesthesia was considered to be so dangerous that once in a while it was acceptable to lose someone,” he said.
The current climate has changed drastically, however. Patients, family members, and physicians no longer accept bad outcomes of anesthesia as a necessary evil. “The feeling now is that one death is too many,” Cooper said.
In October, 1986, the American Society of Anesthesiologists promulgated an unprecedented set of recommendations to govern patient monitoring during anesthesia on a minute-to-minute basis.
Although it is still up to individual physicians and hospitals to decide whether to follow these standards, the recommendations do carry a lot of weight. For instance, some insurance companies will not cover physicians and hospitals that do not follow these standards.
Most authorities maintain that anesthesia is still amazingly safe, all things considered. “It is extraordinarily safe when one considers how many people are anesthetized and how dangerous anesthesia really is,” Cooper said.
“The reality is, for a healthy patient coming to the hospital for an elective procedure--what most people go to the hospital for--the risk of death (from anesthesia) is probably about one in several hundred thousand,” he said.
The exact mechanism of anesthetic agents remains a topic of debate. Although it is known that such drugs change the way nerve impulses are transmitted and processed in the brain, how this is achieved on a molecular level remains unclear.
One impetus for the 1986 guidelines was the work of Cooper and others at Harvard who, beginning in the mid-1970s, showed that, in the vast majority of cases, the cause of “critical incidents” during anesthesia was human error.
They examined in great detail more than 1,000 critical incidents taken from four Boston-area hospitals in which human error or equipment failure could have led to, or did lead to, injury or death. These studies, which elucidated many of the causes of negative outcomes in anesthesia, had begun as an investigation of the causes of equipment failure, with the objective of designed a better anesthesia machine, Cooper said.
But, he explained, “it became clear that the majority of problems that people have in anesthesia are related to the human operators.”
The most common error, which accounted for more than 11% of the total mistakes, was a breathing circuit disconnection during mechanical ventilation. During such a procedure, the patient’s muscles are paralyzed so that he cannot breathe on his own. A disconnection of the breathing circuit results in no oxygen being delivered to the patient.
After performing its own study, a risk-management committee at Harvard concluded that more meticulous monitoring would help prevent injuries and deaths. And it set forth standards for minimal monitoring during anesthesia, which were implemented at the nine Harvard-affiliated hospitals.
The standards went into effect in July, 1985, and since that time, only one anesthesia accident has occurred (out of about 100,000 anesthetics given annually). This incident occurred in August, 1985, and was caused because the standards apparently were not followed, according to Dr. John H. Eichhorn of Beth Israel Hospital and Harvard Medical School, who was a member of the committee that formulated the standards.
Not long afterward, the American Society of Anesthesiologists adopted a revised set of standards for basic intra-operative monitoring to apply nationwide.