General Risk Factors

Several variables are general risk factors for anesthetic complications, such as:

Age

Children are not just "little adults." They have physiologic differences, which change how anesthesia is delivered and how they tolerate it. First, a few definitions: Newborn is defined as the first 24 hours after birth, neonate is the first 30 days after birth, infant is 1 to 12 months of age, and child is 1 year of age to puberty.

Children use more oxygen than adults, nearly double in the case of neonates. Neonates also have about a 30-60% increase in cardiac output to meet their increased oxygen requirements, and both increased cardiac output and high hemoglobin level (about 17 g/dl) are needed to compensate for the diminished release of oxygen by fetal hemoglobin to tissues. Because of limited distensibility of the left ventricle, cardiac output in neonates is heart rate dependent. The oxyhemoglobin curve begins to approximate that of adults by four to six months of age.

Age and affect a patient's response to anesthesia.

Other physiological differences in neonates and infants include increased alveolar ventilation, increased proportion of extracellular fluid volume to body weight, more difficulty maintaining body temperature, and decreased ability to concentrate urine. Neonates and infants aren't able to compensate for extreme shifts in fluid balance as well as adults.

These physiological differences, along with differences in skeletal muscle mass, metabolic rate, and receptor maturity affect how neonates, infants, and children respond to anesthetics and other drugs.

Similarly, elderly patients have physiological differences that affect their response to anesthesia. "Elderly" describes individuals age 65 or older, and "aged" describes those age 80 or over. Age-related organ decline and pre-existing diseases give older patients a decreased physiologic reserve for acute stress such as that imposed by surgery. Morbidity and mortality tend to be higher in elderly patients compared to younger people, but this is related more to co-existing diseases rather than age. Older patients do better when other health problems are controlled prior to surgery, but sometimes, as in the case of emergency surgery, this isn't possible. Older patients are also prone to delirium as a result of almost any physical illness, and because of diminished renal and hepatic function, drug effects are prolonged.

Co-Morbidities

Anesthetic and surgical safety can be increased by optimally controlling pre-existing medical conditions, and persuading patients to stop smoking, lose weight, and cut down on alcohol or other drug use before elective surgical procedures.

It's approximated that 40% of adults undergoing surgery each year in the U.S. either have, or are at risk for, coronary artery disease (Stoelting & Miller, 2006). Anesthesia for patients with cardiovascular disease must be tailored to the disease process to avoid cardiac-associated morbidity and mortality, including understanding of the disease process, suitable anesthetic drug selection, and use of appropriate monitoring equipment. Preoperative assessment is key, including a complete history and physical exam, radiographic imaging, echocardiography, laboratory studies, and/or cardiac catheterization to determine the heart's functional status. The more the anesthesiologist knows about the patient's cardiac status, the better the patient can be managed during surgery.

Pulmonary complications are as common as cardiac complications following noncardiac surgery and are more costly (Smetana, 2009). Since anesthesia and surgery may produce hypoventilation, hypoxemia, and retention of secretions, patients with chronic pulmonary disease are at increased risk for postoperative respiratory failure. This risk can be lowered by thorough preoperative assessment, optimal medical therapy, and starting chest physiotherapy before surgery. Patients with chronic pulmonary disease often also have co-existing cardiac disease and/or essential hypertension. The surgical sites including aortic, thoracic and upper abdominal area are a predictor of risk for postoperative pulmonary complications, even in healthy patients. Obstructive sleep apnea, and pulmonary hypertension may also be factors to increase risk (Smetana, 2009).

The administration of general anesthesia may induce a reduction in renal blood flow in up to 50% of patients, resulting in the impaired excretion of nephrotoxic drugs. In addition, the function of cholinesterase, an enzyme responsible for breaking down certain anesthetic agents, may be impaired, resulting in prolonged respiratory muscle paralysis if neuromuscular blocking agents are used (Salifu, 2011).

Approximately 5% of adults in the U.S. have renal disease, which could increase the risk of perioperative morbidity (Hurford, Bailin, Davison, Haspel, Rosow & Vassallo, 2006). Acute renal failure is a sudden decrease in renal function and can be prerenal (volume depletion/low cardiac output), intrarenal (acute tubular necrosis), or postrenal (obstructive uropathy). Mortality related to acute renal failure is greater than 30% in surgical and trauma patients (Hurford et al., 2006). All inhalational anesthetics and many induction agents cause myocardial depression, hypotension, and an increase in renal vascular resistance, leading to temporary renal dysfunction even in patients with normal kidneys. With brief anesthesia, these changes reverse within a few hours, but prolonged anesthesia can cause renal dysfunction that lasts for days. There's also concern that some fluorinated agents may cause nephrotoxicity (sevoflurane, haloflurane). However, this is a theoretical concern, and hasn't been proven to be clinically significant.

Again, preoperative assessment with history and physical, laboratory studies, and radiographic studies help in perioperative management. Anesthesia for these patients usually consists of nitrous oxide, oxygen, desflurane, and isoflurane. Those at increased risk for acute renal failure include the elderly, patients with pre-existing renal disease or congestive heart failure, patients undergoing high-risk surgery or who have experienced major trauma or burns, patients with prolonged renal hypoperfusion (shock, sepsis), and patients who have undergone procedures with injectable dye. Medications that are metabolized primarily by the kidneys should be avoided in these patients. Use of demerol (meperidine) for postoperative pain control should be avoided because accumulation of its metabolite normeperidine can cause seizures in patients with CKD (Chronic Kidney Disease), especially those on dialysis (Salifu, 2011).

Because the liver serves a role in drug elimination and production of clotting factors, patients with hepatic disease are also at higher risk for anesthetic complications. Perioperative morbidity and mortality depends on the extent of liver disease and the type of surgery. Again, preoperative history, physical, and laboratory tests are crucial to guiding care and enhancing the patient's outcome. Pre-existing abnormalities related to hepatic disease should be corrected as much as possible before surgery, including coagulopathy, poorly controlled ascites, electrolyte and volume imbalances, encephalopathy, renal function, and nutritional status.

Patients with diabetes mellitus are at increased risk for complications due to glucose and electrolyte management issues and the stress of surgery. Ketoacidosis and hyperosmolar coma are acute diabetic complications that must be corrected before elective surgery. Diabetic patients with peripheral neuropathy are also at risk for positioning injuries.

Obesity (defined as more than 100 pounds above ideal body weight) predisposes patients to anesthetic complications in almost every organ system. Hypertension, increased blood volume, and coronary artery disease affect cardiac function. Pulmonary hypertension is common in obese patients and can cause right ventricular failure. Restrictive ventilation leads to a decreased functional residual capacity; the supine position during surgery causes ventilation-perfusion mismatch and atelectasis with desaturation. Gastroesophageal reflux and aspiration are more common in obese patients, and since surgery is more technically challenging, obese patients are also at higher risk for extensive blood loss. Positioning injuries are also common, and extra padding and skin protection should be used.

History of Smoking, Alcohol, or Other Drug Use

Patients undergoing elective procedures should be encouraged to stop smoking, drinking alcohol, and/or using other drugs a few weeks before surgery. Smokers have increased airway hyperreactivity and are at higher risk for perioperative pulmonary complications. A productive cough, wheezing, shortness of breath, or hemoptysis may indicate a need for pulmonary testing or treatment before surgery.

Alcohol abuse can affect anesthesia amounts required during procedures.

Alcohol intoxication lowers the amount of anesthesia required and predisposes the patient to hypoglycemia and hypothermia. Alcohol withdrawal can cause acute hypertension, delirium, tremors, and seizures, and can greatly increase the anesthetic requirement. Chronic alcohol use can increase benzodiazepine requirements.

Routine use of drugs such as benzodiazepines and narcotics may increase the anesthetic requirement, as well as the postoperative analgesia needed to provide adequate pain control. Stimulant abuse can predispose the patient to palpitations, angina, dysrhythmias, and seizures.

Self-reporting of smoking, alcohol, and/or drug use tends to underestimate reality, but it still helps caregivers to know what substances the patient uses and, especially, when the last use occurred.

Family History

Any family history of adverse reactions to anesthesia should be considered. Malignant hyperthermia, a hypermetabolic syndrome, is the most dangerous, and occurs in genetically predisposed patients after exposure to an anesthetic triggering drug. These include halothane, isoflurane, desflurane, sevoflurane, and succinylcholine. Symptoms result from sustained muscle contraction and include tachycardia, acidosis, hypoxemia, hypercarbia, and hyperthermia. These signs usually start in the operating room, but may not be apparent until the patient is in the postanesthesia care unit or the postoperative floor. Dantrolene is the drug of choice for treatment of malignant hyperthermia; it's not recommended for pre-treatment of susceptible patients, but should be readily available when these patients have surgery. Local or regional anesthesia is used for these patients when possible, although general anesthesia with non-triggering drugs is safe too (i.e., propofol, barbiturates, narcotics, benzodiazepines, and nitrous oxide). Succinylcholine is a depolarizing neuromuscular blocking agent – nondepolarizing neuromuscular blockade can be safely used in patients predisposed to malignant hyperthermia.

Other adverse drug effects experienced by the patient and/or family should be noted before surgery, but it's important to differentiate between true allergic reactions and adverse side effects (like nausea). Common after-effects of anesthesia will be discussed later.

The chart below summarizes general risk factors for anesthetic complications.

Age Co-Morbidities Social History Family History
  • Children
  • Elderly
  • Cardiovascular disease
  • Respiratory disease
  • Renal failure
  • Liver failure
  • Diabetes Mellitus
  • Obesity
  • Smoking
  • Alcohol abuse
  • Other drug abuse
  • Malignant hyperthermia
  • Adverse drug effects

The ASA has created a physical status classification to help determine a patient's perioperative risks. The levels are described in the chart below (PS = Physical Status).

PS-1

Normal, health patient

PS-2

Patient with mild systemic disease that results in no functional limitations

PS-3

Patient with severe systemic disease that results in no functional limitations

PS-4

Patient with severe systemic disease that is a constant threat to life

PS-5

Moribund patient who is not expected to survive without the operation

PS-6

Declared brain-dead patient whose organs are being removed for donor purposes

If the procedure is done as an emergency, an "E" is added to the appropriate class.



Case Study

In reviewing Mrs. Parks' medical history, you find that she has emphysema from smoking for most of her life. She admits to smoking and drinking "occasionally" at social functions when others are partaking, but denies keeping cigarettes at home. She has not needed home oxygen. She is also obese, at 5'4" and 260 pounds. She has diabetes mellitus and peripheral vascular disease, with a chronic wound on her left heel. Mrs. Parks says her doctor told her about a month ago that unless her diabetes became better controlled, she might end up with an amputation of her foot. She says she has been trying since then to take better care of herself, and her blood glucose diary does indeed seem to be more regular. Her husband and daughter are supportive with this, and frequently remind her to check her blood sugar. So far, her kidney function is intact.

Mrs. Parks' general risk factors that increase her chance for anesthetic complications are:

Mrs. Parks' physical status classification, according to the ASA, is PS-3.

Mrs. Parks' daughter is currently going to nursing school and asks you what the statistics are for mortality related to anesthesia. Your response: 1 in 250,000.



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