No one enjoys having surgery. But if you have to go under the knife, a chat with your anesthesiologist can help put your mind at ease and ensure you get the best medical care.
It’s also a chance to ask about the medications your doctors plan to use – and the factors that can affect how much (or how little) anesthesia you’ll need. Your age, genetics and even your hair color can play an important role in how your body responds to anesthesia during surgery and pain medications after.
That’s why it’s important to be completely honest about your medical history before any surgical procedure, said Daniel I. Sessler, a professor of anesthesiology and vice president for clinical and outcomes research at the University of Texas Health Science Center at Houston.
If you smoke marijuana every day, for instance, “We don’t care. We’re not going to make a moral judgment about that. But we need to know to optimize your anesthesia,” he said.
We asked experts to explain some of the most common reasons people need more – or less – anesthesia and pain control. Here’s what they said.
Your hair color
Some procedures require only sedation. But when you need to be completely out, you’re given general anesthesia. This requires a carefully curated cocktail of medications that may include inhaled anesthetic gases or intravenous drugs to maintain unconsciousness, said Miles Berger, a neuroanesthesiologist and professor of anesthesiology, perioperative and pain medicine at Stanford University. It also includes medications to relieve pain and relax or immobilize muscles to prevent movement on the operating table.
If you have naturally red hair, you may be more sensitive to certain types of pain. And in some cases, you may also need more anesthetics than non-redheads, research suggests.
“We don’t exactly know the reason, but it is true,” said Sessler, who for decades has been studying the increased anesthetic requirements in people with naturally red hair.
One theory is that variants in the melanocortin-1 receptor (MC1R) gene in people with red hair alter signaling pathways that may influence how the body responds to anesthetic drugs.
In one study, Sessler and his colleagues found that healthy, redheaded women needed nearly 20 percent more of a common inhaled anesthetic to induce and maintain unconsciousness than women with dark hair.
Their research also suggested that people with red hair may be more resistant to certain local anesthetics. In a separate study, Sessler and others measured pain sensitivity in 30 red-haired women and 30 dark-haired women and found that those with red hair were more sensitive to pain from cold and heat. Also, lidocaine injections used to numb the skin were notably less effective for the women with red hair than for those with dark hair.
Your alcohol, cannabis and opioid use
Chronic alcohol and cannabis use can increase the amount of anesthetics needed during and after surgery, Sessler said. The same is true for regular use of prescription opioids and other medications for severe chronic pain.
One reason this happens – with opioids, in particular – is because opioids bind to brain receptors that can become less responsive over time, meaning you need more medication to achieve the same effect. In such cases, “they’re going to need much higher doses” in the hospital, Sessler said.
Also, liver enzymes break down these substances so they can be more easily excreted. When you use them regularly, your body can become more efficient at breaking them down.
That can make some medications “much less effective at a given dose,” Sessler said, because your body breaks them down more quickly.
Research has also shown a link between cannabis use and how much anesthesia and pain medication you’ll need after the surgery. A 2024 study that looked at more than 1,600 cannabis users who were undergoing surgeries found that cannabis use was associated with higher pain scores and increased opioid use after surgery than those who didn’t use cannabis.
Your age
Younger, healthier adults may need more anesthesia than older people. As you age, you need less of the inhaled gases – roughly 6 percent less per decade after age 40, said Berger, who studies age-related changes in anesthetic requirements in older patients.
Research is still emerging, and the reason is not entirely understood. But Berger said that he and other researchers think that when older people require unusually low amounts of anesthesia, it may point to underlying brain or cognitive problems.
Your overall health
Research suggests people who are frail, have serious acute illnesses or infections such as sepsis, or have cirrhosis, may require less anesthesia. And those with obstructive sleep apnea, a condition in which a person’s airway collapses during sleep, may be at higher risk of breathing problems from opioid pain medications after surgery.
To reduce the need for opioids, anesthesiologists may suggest other approaches such as nonsteroidal anti-inflammatory drugs (NSAIDs) or, when appropriate, regional analgesic techniques such as epidurals or nerve blocks to numb parts of the body.
Knowing whether you have any factors that may affect your anesthesia needs helps your doctor guide management and gives you an effective and safe anesthetic, Sessler said.
But there’s no need to worry: Failing to tell your anesthesiologist about your real hair color, cannabis use or chronic disease probably isn’t going to lead to disaster in the operating room.
That’s because anesthesia isn’t applied using standardized doses. An anesthesiologist starts with an initial dose and tweaks it as needed based on your response, vital signs and, sometimes, brain monitoring, then continually adjusts it throughout the procedure, Sessler said.
“But everything an anesthesiologist knows about a patient combined with everything we monitor during anesthesia allows us to provide an optimal experience,” he said.
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