Most anesthesia complications are preventable, and the steps that matter most happen before you ever reach the operating room. Modern anesthesia is remarkably safe, but the risks that remain, including breathing problems, heart events, dangerous nausea, and rare emergencies like malignant hyperthermia, are closely tied to how well your medical team understands your body going in. Here’s what you can do, and what your care team should be doing, to keep you safe.
Give a Complete Medical History
The single most important thing you can do to prevent anesthesia complications is provide a thorough, honest medical history during your preoperative screening. This isn’t just a formality. Your anesthesiologist uses it to choose medications, adjust doses, plan your airway management, and prepare for emergencies specific to your body. Leaving something out, even something that seems minor, can remove a safety net your team didn’t know they needed.
Expect to be asked about conditions across nearly every organ system: heart disease, lung problems, liver or kidney disease, bleeding disorders, diabetes, thyroid issues, neurological conditions, and chronic pain. You’ll also be asked about sleep apnea and snoring, whether you use oxygen at home, and whether you’ve had chemotherapy or radiation therapy. All of these change how anesthesia affects you.
Two questions deserve special attention. First, whether you or any blood relative has ever had a reaction to anesthesia, particularly malignant hyperthermia (a rare, inherited condition where certain anesthetics cause a dangerous spike in body temperature and muscle rigidity). Second, whether you’ve ever had difficulty with breathing tubes during previous surgeries. Problems with neck mobility, jaw opening, or loose teeth all affect how safely your airway can be managed. If you know about any of these issues, say so clearly and early.
Stop Herbal Supplements Well Before Surgery
Many people don’t think to mention herbal supplements, but these are among the most common hidden causes of anesthesia complications. The most frequently used supplements among surgical patients, garlic, ginseng, ginkgo, St. John’s wort, and echinacea, can all interfere with anesthesia in serious ways. Depending on the supplement, the risks include excessive bleeding during surgery, dangerous drops or spikes in blood pressure, heart rhythm disturbances, prolonged sedation, seizures, and altered breakdown of anesthetic drugs in the liver.
The American Society of Anesthesiologists and the American Association of Nurse Anesthetists recommend stopping all herbal medications one to two weeks before any elective surgery. That timeline matters because many of these substances have long-lasting effects on blood clotting and drug metabolism that don’t clear overnight. Tell your surgical team about every supplement you take, including ones you consider harmless.
Follow Fasting Rules Precisely
Fasting before surgery prevents one of the most dangerous anesthesia complications: pulmonary aspiration, where stomach contents enter your lungs while you’re unconscious. The rules are straightforward but specific, and they apply to all ages.
- Clear liquids (water, black coffee, pulp-free juice, clear tea, sports drinks): stop at least 2 hours before your procedure.
- A light meal (toast with clear liquids, for example): stop at least 6 hours before.
- Fatty foods, fried foods, or meat: allow 8 or more hours, because these take significantly longer to leave your stomach.
Both the type and amount of food matter. A slice of toast six hours before surgery is very different from a steak dinner six hours before. When in doubt, give yourself more fasting time rather than less, and follow your surgical team’s specific instructions if they differ from these general guidelines.
Understand Your Risk Category
Before surgery, you’ll be assigned a physical status classification on a scale from 1 to 6. This system, developed by the American Society of Anesthesiologists, gives your care team a quick way to communicate how much your underlying health increases anesthesia risk.
A healthy, fit person with no medical conditions and a normal weight is classified as ASA 1, the lowest risk category. Someone with a mild, well-controlled condition like reflux or a slightly elevated BMI falls into ASA 2. ASA 3 applies when a condition is more severe: significant obesity (a BMI above 40, for instance) or poorly managed diabetes. ASA 4 means a life-threatening condition is present, such as advanced lung disease that limits you to walking only a few meters before becoming short of breath. Emergency surgeries get an “E” added to the classification, which independently raises risk.
You won’t necessarily be told your ASA class, but you can ask. Understanding where you fall helps you have a more informed conversation with your anesthesiologist about what precautions they’re taking and whether your chronic conditions are as well-controlled as possible before the procedure.
Manage Sleep Apnea Before and After Surgery
Obstructive sleep apnea is one of the most significant risk factors for breathing complications under anesthesia, and it’s also one of the most underdiagnosed. If you snore loudly, feel exhausted during the day, or have been told you stop breathing in your sleep, bring this up with your surgical team even if you’ve never had a formal diagnosis.
Patients with sleep apnea face a higher risk of airway obstruction both during and after anesthesia. Their airways are already prone to collapsing, and anesthetic drugs relax the muscles that keep the airway open even further. People who are also obese desaturate (lose oxygen in their blood) much more rapidly during any period of obstructed breathing, because their lungs hold less reserve air.
If you already use a CPAP machine at home, bring it to the hospital. Using CPAP after surgery significantly reduces the risk of airway obstruction and breathing depression during recovery. Your care team should also position you with your head elevated at least 30 degrees rather than flat on your back throughout recovery. Guidelines recommend that sleep apnea patients be monitored for at least three hours longer than other patients before discharge, with continuous (not intermittent) oxygen monitoring during that time.
Reduce Nausea and Vomiting Risk
Postoperative nausea and vomiting affects a large proportion of surgical patients and, beyond being miserable, can cause dehydration, wound complications, and aspiration. Current guidelines recommend that anyone with even one risk factor receive preventive treatment using multiple medications that work through different pathways in the body. Previously, the threshold for treatment was higher, so this is a meaningful shift toward more aggressive prevention.
Common risk factors include being female, having a history of motion sickness or previous postoperative nausea, being a nonsmoker, and the use of opioid pain medications after surgery. If several of these apply to you, tell your anesthesiologist. They can adjust your anesthetic plan in several ways: using intravenous anesthesia instead of inhaled gases (which cuts nausea risk by roughly 40%), minimizing opioid use, and combining anti-nausea medications that target different receptors. A large meta-analysis of over 23,000 patients confirmed that intravenous anesthesia produces significantly less nausea and vomiting than inhaled anesthesia, along with less confusion upon waking and better overall recovery scores.
Know the Signs of Malignant Hyperthermia
Malignant hyperthermia is rare but potentially fatal. It’s an inherited condition in which certain inhaled anesthetics and a specific muscle relaxant trigger uncontrolled muscle contractions, rapidly rising body temperature, and metabolic crisis. If you have a family history of this condition, or if a blood relative has ever had an unexplained dangerous reaction to anesthesia, this information is critical to share.
Genetic testing can identify mutations in two genes (RYR1 and CACNA1S) associated with susceptibility, though a negative genetic test doesn’t completely rule it out. Muscle biopsy remains another diagnostic option. If susceptibility is confirmed or suspected, your anesthesiologist will avoid all known triggers and use alternative anesthetic agents. Environmental factors like heat, humidity, and physical stress can also contribute to episodes, so your care team will control the surgical environment accordingly.
Ask About Awareness Monitoring
Anesthesia awareness, being conscious during surgery while unable to move or speak, is rare but deeply distressing. Brain activity monitors that track consciousness levels during surgery exist, with the most widely used being the bispectral index (BIS) monitor. It reads electrical activity from the brain and converts it into a number from 0 to 100, with values between 40 and 60 considered the target range for adequate anesthesia.
However, a major trial of 2,000 high-risk patients published in the New England Journal of Medicine found that BIS-guided anesthesia was no better at preventing awareness than simply monitoring the concentration of anesthetic gas being delivered. Awareness occurred at the same rate in both groups, and it sometimes happened even when readings were within the target range. Where brain monitoring does add value is during total intravenous anesthesia, where there’s no gas concentration to measure. If your surgery will use only IV-based anesthetics, ask whether brain monitoring will be used.
Protect Your Heart During Surgery
Heart complications are the leading cause of perioperative death, accounting for roughly 34% of deaths related to surgery. Heart muscle injury occurs in about 13% of non-cardiac surgeries, often silently, increasing the risk of heart failure, stroke, and cardiac arrest in the days that follow.
Your risk depends on factors like existing heart disease, history of heart failure, prior heart attacks or stents, implanted devices like pacemakers, and conditions like uncontrolled high blood pressure. If you have any of these, your team will use risk assessment tools to determine whether your heart conditions need to be better stabilized before proceeding, whether additional monitoring is needed during surgery, or whether the surgical approach should be modified. If you’re on blood thinners, the timing of when to stop and restart them is a critical conversation to have well before your surgery date. Don’t adjust these medications on your own.