A summary of complications associated with general anesthesia including their incidence, mechanism, risk factors, prevention strategies, and management is presented.
Key points
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General anesthesia has potential complications that may contribute to perioperative morbidity.
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Cardiorespiratory complications are the most common in the perioperative period.
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Thorough preoperative assessment is essential to identify patients at risk of complications.
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Minor complications such as sore throat and dental damage are common and can lead to patient dissatisfaction.
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Delayed discharge and unplanned admission as a result of perioperative complications are important quality outcome measures, particularly in ambulatory surgery.
Introduction
Each year, increasing numbers of people are undergoing surgery. Many of these patients are older and have multiple comorbidities. General anesthesia is a reversible state of unconsciousness that allows patients to undergo surgical procedures in a safe and humane way. Although it is increasingly safe, general anesthesia is not without risks and complications. Anesthesia-related mortality is rare and has declined significantly over the past 5 decades. Morbidity associated with general anesthesia ranges from minor complications that affect the patient’s experience with no long-term consequences to complications with long-term repercussions resulting in permanent disability.
Cardiovascular and respiratory complications are the most common. Myocardial infarction, interference with lung mechanics, and exacerbation of preexisting comorbidities can all occur. Other serious complications include acute renal impairment and the development of long-term postoperative cognitive dysfunction. Minor but important complications of general anesthesia include postoperative nausea and vomiting, sore throat, and dental damage. All these complications can have a significant impact on patients and may result in prolonged hospital stay and expense.
By being aware of potential complications related to general anesthesia, many can be predicted and prevented. Thorough preoperative assessment is the key to identifying risk factors and stratifying patients so that optimization and planning can occur preoperatively.
Introduction
Each year, increasing numbers of people are undergoing surgery. Many of these patients are older and have multiple comorbidities. General anesthesia is a reversible state of unconsciousness that allows patients to undergo surgical procedures in a safe and humane way. Although it is increasingly safe, general anesthesia is not without risks and complications. Anesthesia-related mortality is rare and has declined significantly over the past 5 decades. Morbidity associated with general anesthesia ranges from minor complications that affect the patient’s experience with no long-term consequences to complications with long-term repercussions resulting in permanent disability.
Cardiovascular and respiratory complications are the most common. Myocardial infarction, interference with lung mechanics, and exacerbation of preexisting comorbidities can all occur. Other serious complications include acute renal impairment and the development of long-term postoperative cognitive dysfunction. Minor but important complications of general anesthesia include postoperative nausea and vomiting, sore throat, and dental damage. All these complications can have a significant impact on patients and may result in prolonged hospital stay and expense.
By being aware of potential complications related to general anesthesia, many can be predicted and prevented. Thorough preoperative assessment is the key to identifying risk factors and stratifying patients so that optimization and planning can occur preoperatively.
Cardiovascular complications with general anesthesia
Perioperative cardiac complications include myocardial ischemia or infarction (MI), heart failure (HF), and cardiac arrest.
Myocardial Infarction
Recent studies suggest up to 5% of patients undergoing elective noncardiac surgery have MI. In the presence of 1 cardiac risk factor, the incidence is 4.4%, with the risk of cardiovascular death approximately 1.6%. Most perioperative ischemic events are silent and may have no clinically appreciable signs or symptoms. The true incidence of ischemia in the perioperative period is likely underestimated.
Perioperative MI is common but can be hard to predict and prevent. It usually occurs in the first 48 hours postoperatively. Most perioperative MIs result from oxygen supply-demand mismatch. Anesthesia and surgery confer a physiologic stress test to the patient that increases O 2 demand. Hypotension, anemia, and coronary artery disease prevent this demand from being met. Thrombus formation or plaque rupture account for only one-third of events.
Several risk indices allow the stratification of patients according to the likelihood of perioperative cardiac complications. The most commonly used is the Revised Cardiac Risk Index (RCRI). This identifies 6 independent predictors of major cardiac complications: high-risk surgery, history of ischemic heart disease, history of HF, history of cerebrovascular disease, diabetes requiring insulin, and chronic renal impairment. Risk increases with the presence of each additional risk factor.
The American Heart Association devised a stepwise approach to help manage patients undergoing noncardiac surgery. Their recommendations incorporate assessment of patients for risk factors, rational use of investigations that influence patient treatment, and provision of recommendations for preoperative optimization.
Certain drugs in the perioperative period can influence cardiac outcomes. β-Blockers have been shown to decrease the incidence of perioperative MI but the potential for harm (most notably stroke) means no recommendations can be made at present. There is also insufficient data on the potential benefit of commencing statins perioperatively. Use of nitrous oxide can lead to impairment of methionine synthase and inhibition of folate synthesis resulting in hyperhomocysteinemia, which has been associated with myocardial ischemia and infarction. Studies are ongoing to determine whether the use of clonidine and aspirin are effective in reducing the incidence of major cardiovascular events perioperatively.
Heart Failure
HF occurs in 1% to 6% of patients after major surgery. It is most common in patients with underlying cardiovascular disease. Negative pressure pulmonary edema results from high-pressure respiratory effort in the setting of an obstructed airway. It occurs in approximately 0.1% of patients undergoing general anesthesia and complete recovery occurs in most patients.
Arrhythmia
Bradyarrythmias and ventricular arrhythmias are rare in the perioperative period. Less than 1% of all surgical patients (including cardiac surgery) experience a bradyarrhythmia or ventricular arrhythmia that is severe enough to require treatment. Atrial fibrillation is the most common perioperative arrhythmia with an incidence of 0.37% to 20% in noncardiac surgery patients. The incidence is highest in patients undergoing major vascular and open abdominal surgery and least in those having ophthalmic or superficial minor surgery. Preoperative risk factors for development of atrial fibrillation include increasing age, male gender, preexisting heart disease, American Society of Anesthesiologists Class 3 or 4, and preoperative electrolyte disturbances.
New-onset arrhythmias in the perioperative period are usually self-limiting with more than 80% reverting to sinus rhythm before discharge. Management consists of recognizing the arrhythmia and instituting rate and rhythm control methods under expert medical guidance.
Thromboembolism
Venous thromboembolism (VTE) includes both deep vein thrombosis (DVT) and pulmonary embolism (PE) and is a significant cause of morbidity and mortality in the perioperative period. In patients undergoing plastic surgery, the overall incidence of VTE is 1.69%, however this varies according to the presence of risk factors. Several tools exist to help assess and stratify the risk of VTE for each patient. The Carprini Risk Assessment Model ( Fig. 1 ) has been validated for use in plastic surgery patients and endorsed by the American Society of Plastic Surgeons. Current recommendations on thromboprophylaxis in surgical patients are based on the calculated risk of VTE and consideration of the risk of bleeding associated with any intervention. These recommendations are summarized in Table 1 .
| Caprini RAM Score | Risk of VTE (%) | Recommended Thromboprophylaxis |
|---|---|---|
| 0 | <0.5 | Nil/ambulate early |
| 1–2 | 1–5 | Mechanical prophylaxis (IPC) |
| 3–4 | 3.0 | If not high risk for major bleeding: LMWH or LDUH or mechanical prophylaxis (IPC) If high risk for major bleeding: mechanical prophylaxis (IPC) |
| >5 | 6.0 | LMWH or LDUH and mechanical prophylaxis (IPC) |
Cardiac Arrest
The risk of anesthesia-related cardiac arrest is 1.86:10,000. It is more likely in patients at the extremes of age (neonates, elderly), patients with poor physical function, and emergency surgery. General anesthesia is a risk factor for cardiac arrest. More than 90% of anesthesia-related cardiac arrests are related to airway management or medication administration. Respiratory causes are more common in the pediatric population, whereas cardiac arrest after administration of medications causing cardiovascular depression occurs more commonly in adults.
Respiratory complications
Perioperative respiratory complications are an important predictor of morbidity and mortality and affect the financial burden of health care by increasing the length of hospital stay. The incidence is similar to that for perioperative cardiac complications at 6.8%; serious complications occur in 2.6%. Anesthesia-related complications include atelectasis, aspiration, and bronchospasm; exacerbation of existing lung disease and infection are less relevant in the intraoperative period.
Atelectasis
Atelectasis accounts for up to 70% of severe postoperative hypoxemia and is a risk factor for the development of pneumonia and acute lung injury. Within minutes of induction of general anesthesia, mechanical compression of alveoli, reabsorption of alveolar gases, and paralysis cause diaphragm displacement. Functional residual capacity and lung compliance is reduced, increasing airway resistance. These changes can progress throughout general anesthesia and manifest clinically as V/Q mismatch (or shunt), impaired gas exchange, hypoxemia, diaphragm dysfunction, decreased respiratory drive, inhibition of cough, and impaired mucociliary clearance.
Several patient and surgical factors increase the risk of perioperative respiratory complications; these include advanced age, an American Society of Anesthesiologists status greater than 2, functional dependence, congestive cardiac failure, and a history of chronic obstructive pulmonary disease. Risk increases with emergency surgery and procedures in close proximity to the diaphragm. Cigarette smoking has recently been shown to be associated with increased 30-day mortality and perioperative respiratory complications.
Prevention of perioperative complications is facilitated by accurate risk stratification and preoperative optimization with a multidisciplinary team approach. Intraoperative ventilatory strategies to reduce atelectasis including postinduction recruitment maneuvers and minimizing intraoperative inspired oxygen concentrations are beneficial. Preoperative respiratory muscle training, incentive spirometry, and chest physiotherapy may confer some benefit although this has not been proved. Smoking cessation for 4 to 8 weeks preoperatively reduces the risk of respiratory complications to baseline and cessation for shorter periods is likely to decrease risk.
Aspiration
Aspiration of gastric contents into the airway is the most common cause of airway-related death during anesthesia. It occurs in 1:4000 patients undergoing general anesthesia, increasing to 1:900 in emergency surgery. The highest risk is at intubation and extubation. Identifying patients at risk of aspiration is key to its prevention. Risk factors and methods to modify them are outlined in Table 2 .
| Risk Factor | Intervention | |
|---|---|---|
| Patient |
| Routine preoperative fasting Empty stomach with oro/nasogastric tube Administer prokinetic premedication |
| Surgical |
| |
| Anesthetic | Difficult intubation Gastric insufflation Inadequate depth of anesthesia | Avoid general anesthesia; consider regional Rapid sequence induction Monitor depth of anesthesia Ensure paralysis reversal |
Bronchospasm
Bronchospasm is caused by the constriction of bronchial smooth muscle and edema, which untreated can result in hypoxia, hypotension, or death. It occurs in 0.2% of patients undergoing general anesthesia. Preexisting airway disease, recent or active upper respiratory tract infection, smoking history, and atopy all increase risk. The key triggers are airway instrumentation or delivery of inhalational anesthetic agents. Early surgical stimulation without adequate depth of anesthesia, airway soiling, and medications (eg, β-blockers, neostigmine, morphine, atracurium) can also induce bronchospasm. Prevention relies on the optimization of underlying airway disease, being aware of drug sensitivities, encouraging smoking cessation, delaying surgery if recent upper respiratory infection, and avoiding unnecessary airway manipulation. Algorithms exist for the management and diagnosis of bronchospasm, the mainstay of which consist of removing the trigger, supplying high flow oxygen, and administering bronchodilators to facilitate the relaxation of airway smooth muscle relaxation.
Neurologic complications
Postoperative Cognitive Dysfunction
Postoperative cognitive dysfunction (POCD) is defined as a decline in cognitive levels from preoperative function as detected by changes on neuropsychological testing. It occurs in approximately 9.9% of patients. Postoperative delirium is defined as an acute change in cognition and attention, which may include alterations in consciousness and disorganized thinking. The incidence varies according to the type of surgery and is highest (35%–65%) in patient’s undergoing hip fracture surgery.
Patient factors may be the most important in the development of POCD. Advanced age is an independent risk factor both acutely and in the long term. Recent studies demonstrate that the development of POCD is independent of major changes in blood pressure and oxygenation. Cardiac surgery is associated with an increased incidence at 7 days postoperatively, but this difference does not exist by 3 months suggesting the development of POCD is independent of the type of procedure or anesthetic.
The exact mechanisms of POCD are yet to be elucidated and no specific treatment exists for either POCD or postoperative delirium. Neuroinflammatory mediators such as tumor necrosis factor α may play a role and are potential therapeutic targets. Screening patients postoperatively, minimizing analgesic medications, early reestablishment of routines, and early mobilization and discharge may help.
Awareness
Awareness is defined as consciousness under general anesthesia with subsequent recall of the events experienced. It has been reported to occur in 0.03% of patients. In a recent survey of anesthesiologists, it was reported as 1 in 15,000 implying that many cases of awareness are not identified nor reported. Up to 26% of patients have significant long-term sequelae after an episode of awareness. The sequelae include anxiety, depression, and, in severe cases, posttraumatic stress disorder.
Awareness results from an inadequate depth of anesthesia. Several risk factors have been identified for the development of awareness and are listed in Box 1 . Most cases occur at induction/emergence when the anesthetic is being titrated to surgical conditions. Risk is highest when neuromuscular blocking drugs are used.
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