Since its introduction in 1846, anesthesia has allowed for medical miracles. Limbs can be removed, tumors examined, organs replaced—and a patient will feel and remember nothing. Or so we choose to believe. In reality, tens of thousands of patients each year in the United States alone wake up at some point during surgery. Since their eyes are taped shut and their bodies are usually paralyzed, they cannot alert anyone to their condition. In efforts to eradicate this phenomenon, medicine has been forced to confront how little we really know about anesthesia’s effects on the brain. The doctor who may be closest to a solution may also answer a question that has confounded centuries’ worth of scientists and philosophers: What does it mean to be conscious?
This experience is called “intraoperative recall” or “anesthesia awareness,” and it’s more common than you might think. Although studies diverge, most experts estimate that for every 1,000 patients who undergo general anesthesia each year in the United States, one to two will experience awareness. Patients who awake hear surgeons’ small talk, the swish and stretch of organs, the suctioning of blood; they feel the probing of fingers, the yanks and tugs on innards; they smell cauterized flesh and singed hair. But because one of the first steps of surgery is to tape patients’ eyes shut, they can’t see. And because another common step is to paralyze patients to prevent muscle twitching, they have no way to alert doctors that they are awake. (...)
An anesthesiologist’s job is surprisingly subjective. The same patient could be put under general anesthesia a number of different ways, all to accomplish the same fundamental goal: to render him unconscious and immune to pain. Many methods also induce paralysis and prevent the formation of memory. Getting the patient under, and quickly, is almost always accomplished with propofol, a drug now famous for killing Michael Jackson. It is milky and viscous, almost like yogurt in a fat syringe. When injected, it has a nearly instant hypnotic effect: blood pressure falls, heart rate increases, and breathing stops. (Anesthesiologists use additional drugs, as well as ventilation, to immediately correct for these effects.)
Other drugs in the anesthetic arsenal include fentanyl, which kills pain, and midazolam, which does little for pain but induces sleepiness, relieves anxiety, and interrupts memory formation. Rocuronium disconnects the brain from the muscles, creating a neuromuscular blockade, also known as paralysis. Sevoflurane is a multipurpose gaseous wonder, making it one of the most commonly used general anesthetics in the United States today—even though anesthesiologists are still relatively clueless as to how it produces unconsciousness. It crosses from the lungs into the blood, and from the blood to the brain, but … then what?
Other mysteries have been untangled. Redheads are known to feel pain especially acutely. This confused researchers, until someone realized that the same genetic mutation that causes red hair also increases sensitivity to pain. One study found that redheaded patients require about 20 percent more general anesthesia than brunettes. Like redheads, children also require stronger anesthesia; their youthful livers clear drugs from the system much more quickly than adults’ livers do. Patients with drug or alcohol problems, on the other hand, may be desensitized to anesthesia and require more—unless the patient is intoxicated at that moment, in which case less drug is needed.
After delivering the appropriate cocktail, anesthesiologists carefully monitor a patient’s reactions. One way they do this is by tracking vital signs: blood pressure, heart rate, and temperature; fluid intake and urine output; oxygen saturation in arteries. They also observe muscles, pupils, breathing, and pallor, among many other indicators.
One organ, however, has remained stubbornly beyond their watch. Even though anesthesiologists are not entirely sure how their drugs work, they do know where they go: the brain. All changes in your vital signs are only the peripheral reverberations of anesthetic drugs’ hammering on the soft mass inside your skull. Determining consciousness by measuring anything besides brain activity is like trying to decide whether a friend is angry by studying his or her facial expressions instead of asking directly, “Are you mad?”
In lamenting how little we know about the anesthetized brain, Gregory Crosby, a professor of anesthesiology at Harvard, wrote in The New England Journal of Medicine in 2011, “The astonishing thing is not that awareness occurs, but that it occurs so infrequently.”
An anesthesiologist’s job is surprisingly subjective. The same patient could be put under general anesthesia a number of different ways, all to accomplish the same fundamental goal: to render him unconscious and immune to pain. Many methods also induce paralysis and prevent the formation of memory. Getting the patient under, and quickly, is almost always accomplished with propofol, a drug now famous for killing Michael Jackson. It is milky and viscous, almost like yogurt in a fat syringe. When injected, it has a nearly instant hypnotic effect: blood pressure falls, heart rate increases, and breathing stops. (Anesthesiologists use additional drugs, as well as ventilation, to immediately correct for these effects.)
Other drugs in the anesthetic arsenal include fentanyl, which kills pain, and midazolam, which does little for pain but induces sleepiness, relieves anxiety, and interrupts memory formation. Rocuronium disconnects the brain from the muscles, creating a neuromuscular blockade, also known as paralysis. Sevoflurane is a multipurpose gaseous wonder, making it one of the most commonly used general anesthetics in the United States today—even though anesthesiologists are still relatively clueless as to how it produces unconsciousness. It crosses from the lungs into the blood, and from the blood to the brain, but … then what?
Other mysteries have been untangled. Redheads are known to feel pain especially acutely. This confused researchers, until someone realized that the same genetic mutation that causes red hair also increases sensitivity to pain. One study found that redheaded patients require about 20 percent more general anesthesia than brunettes. Like redheads, children also require stronger anesthesia; their youthful livers clear drugs from the system much more quickly than adults’ livers do. Patients with drug or alcohol problems, on the other hand, may be desensitized to anesthesia and require more—unless the patient is intoxicated at that moment, in which case less drug is needed.
After delivering the appropriate cocktail, anesthesiologists carefully monitor a patient’s reactions. One way they do this is by tracking vital signs: blood pressure, heart rate, and temperature; fluid intake and urine output; oxygen saturation in arteries. They also observe muscles, pupils, breathing, and pallor, among many other indicators.
One organ, however, has remained stubbornly beyond their watch. Even though anesthesiologists are not entirely sure how their drugs work, they do know where they go: the brain. All changes in your vital signs are only the peripheral reverberations of anesthetic drugs’ hammering on the soft mass inside your skull. Determining consciousness by measuring anything besides brain activity is like trying to decide whether a friend is angry by studying his or her facial expressions instead of asking directly, “Are you mad?”
In lamenting how little we know about the anesthetized brain, Gregory Crosby, a professor of anesthesiology at Harvard, wrote in The New England Journal of Medicine in 2011, “The astonishing thing is not that awareness occurs, but that it occurs so infrequently.”
by Joshua Lang, The Atlantic | Read more:
Image: Max Aguilera-Hellweg
