Overview of Complications Occurring in the Post-anesthesia Care Unit

Some of the most common complications occurring in the post-anesthesia care unit are respiratory, neuropsychiatric or cardiovascular. 

Neuropsychiatric complications — The most common central nervous system abnormality in the post-anesthesia care unit (PACU) is an altered state of consciousness. Postoperative patients can demonstrate excessive sedation or agitation, which, in some cases, may be alternating. Other neurologic problems that may be encountered include visual disturbances, complications related to regional anesthesia (epidural hematoma, neurapraxia), and intraoperative recall of the events of the operation. Early identification and treatment is important to lessen the impact of these uncommon, but potentially devastating complications. Each is discussed briefly.

Emergence delirium — Emergence delirium, also known as emergence agitation, refers to a prolonged (hours) change in mental status characterized by a dissociated state of consciousness in which the patient is irritable, uncooperative, uncompromising, thrashing, moaning, incoherent, or crying. The incidence of emergence agitation in children can be as high as 30 percent and is most common in children ages two to four. Emergence agitation is likely a response to a disorienting situation. Parental presence can smooth this transition and the child usually calms in less than 15 minutes. Pediatric emergence agitation has been attributed to the increased use of the rapid onset low-solubility inhaled anesthetic agents.

In the adult population, emergence agitation is less common, with an incidence of less than 5 percent. Transient agitation occurs in a wide range of adult postsurgical patients, but the development of delirium occurs most commonly in elderly patients, especially following major orthopedic procedures.

Emergence delirium can be a result of pain, hypoxia, hypercarbia, urinary retention, electrolyte imbalance (especially hyponatremia), and central, drug-induced anticholinergic activity. Preoperative substance abuse and poor functional status are also risk factors for postoperative delirium. Treatment should be directed first at the underlying cause. 

Somnolence — Somnolence in the PACU is most often due to the persistent effects of pharmacologic agents used during surgery, typically sedatives and neuromuscular blocking agents. 

It is important to rule out other causes of somnolence, such as hypotension, hypoxia, hypercarbia, hypoglycemia, and electrolyte abnormalities, before attributing the patient’s condition solely to a persistent anesthetic effect. A check of routine vital signs, complete blood count, blood gas analysis, and chemistry panel will differentiate most of the potential causes of postoperative somnolence. If a cerebrovascular injury is suspected, computed tomography (CT) of the head may be needed.

Visual disturbance — The most common cause of visual disturbance in the postoperative period is corneal abrasion. The patient typically complains of the sensation of a foreign body in the affected eye. The diagnosis is made by staining the cornea with fluorescein. Topical antibiotics and use of an eye patch usually result in full recovery.

Although rare, a patient may awaken from anesthesia with visual loss. Visual complications due to ischemic optic neuropathy or retinal artery occlusion can lead to total and permanent visual loss. Patients undergoing cardiac, spinal, and head and neck operations are at the highest risk. Risk factors include prone positioning, prolonged procedure duration, and significant blood loss or need for large volume resuscitation. An ophthalmology consultation is appropriate, but there may be little to offer the patient who has suffered this complication. 

Epidural hematoma — Epidural hematoma is an uncommon complication of neuraxial anesthesia with a reported incidence of 1 in 150,000. The risk increases in the setting of systemic anticoagulation. Epidural catheters are usually placed just prior to induction of anesthesia. If an epidural hematoma develops, it will not become apparent until the patient awakens in the PACU. Symptoms include back pain or back pressure, which can progress to muscle weakness, sensory loss, and urinary or bladder dysfunction. If an epidural hematoma is suspected, an emergent MRI of the spine and neurosurgical evaluation for possible decompression should be obtained, because permanent neurological injury can result in as little as six hours from the time of onset.

Intraoperative awareness — Awareness with recall following anesthesia refers to conscious awareness of intraoperative events and has become an important topic of discussion in the professional and lay press. As affected patients awaken from anesthesia, they may show evidence of awareness of the surgical procedure. Any patient suspected of having an awareness event should be offered psychiatric counseling. Awareness with recall following anesthesia is discussed in detail elsewhere. Respiratory complications — Respiratory problems are the second most common complication in the postoperative period. Patients with significant comorbidities, particularly neuromuscular, pulmonary, or cardiac dysfunction, are at a higher risk for respiratory compromise, but any patient can develop hypoxemia following surgery. 

In the immediate postoperative period, the most common causes of hypoventilation include airway obstruction, the effects of anesthetics, analgesics (eg, opioids), sedatives, residual neuromuscular blockade, and poorly controlled incisional pain impairing respiration. 

Impaired oxygen exchange in the postoperative period can occur as a result of intrapulmonary shunting, pulmonary edema, and pulmonary embolus. 

Airway obstruction — The most common cause of airway obstruction in the post-anesthesia care unit (PACU) is pharyngeal laxity due to weakness of the pharyngeal muscles. Other causes include laryngospasm, airway edema, hematoma, or a foreign body (eg, dentures). Postoperative stridor is an emergency that requires immediate evaluation by a healthcare provider experienced in advanced airway techniques. A surgical airway may be required in some cases. 

Following the relief of acute airway obstruction, pulmonary edema termed "negative pressure pulmonary edema," may result. The incidence is about 0.1 percent of all anesthesia cases and it occurs more often in young adults

Pharyngeal muscular weakness — Loss of pharyngeal motor tone leading to muscular laxity is due to residual neuromuscular blockade, residual anesthetic effect, or opioids. Preoperative medical conditions such as obstructive sleep apnea can also predispose to airway obstruction in the PACU. The diaphragm recovers more quickly from the effects of muscle relaxants than the pharyngeal musculature. Residual paralysis of pharyngeal muscles causes the base of the tongue and the tissues of the posterior oropharynx to move toward each other, obstructing the supraglottic inlet. As the patient attempts to draw in air, negative pressure generated in the thorax brings the pharyngeal tissues even closer together, further obstructing the airway. Clinically, the absence of airflow into the trachea is manifested as retraction at the sternal notch and paradoxical motion of the abdominal musculature.

The treatment of airway obstruction due to decreased pharyngeal muscle tone is the classic jaw thrust maneuver that brings forward the mandible and the base of the tongue, which is attached to it, thus opening the inlet to the posterior oropharynx. Continuous positive airway pressure (CPAP) via a facemask can also be given to hold the airway open until pharyngeal muscle tone returns to normal. 

If muscular weakness persists, the residual effects of muscle relaxants, sedatives, or opioids should be reversed. 

Laryngospasm — Laryngospasm as a cause of airway obstruction is more common in pediatric patients, but it can also occur in adults. Laryngospasm can occur abruptly following extubation in the patient who is no longer deeply anesthetized and not indifferent to laryngeal stimulation, but not awake enough to counteract the laryngeal reflex that results from vocal cord irritation (eg, tube removal, aspirated blood). Laryngospasm can also occur upon cessation of positive pressure ventilation via face mask, presumably due to sudden airway collapse.

The treatment of laryngospasm is positive pressure ventilation. If bag-mask ventilation is not successful, a small dose of succinylcholine (0.1 mg/kg IV) can be given to relax the cords. Vocal cord paralysis — Vocal cord paralysis due to bilateral recurrent laryngeal nerve injury can present in much the same way as laryngospasm and will not be apparent until the patient is extubated. Passage of air into the lungs is not possible.

The vocal cords will be seen to be in apposition at the midline with the laryngoscope. Attempted intubation in this setting is traumatic and often unsuccessful. Emergent tracheostomy is the appropriate initial intervention.

Airway edema — The airway can become edematous due to direct tissue trauma from multiple intubation attempts or surgical manipulation, or because of decreased venous drainage resulting from prolonged head-down or prone positioning

If airway edema is suspected, an endotracheal tube leak test can be performed once the patient is breathing spontaneously. The leak test is accomplished by deflating the cuff on the endotracheal tube and then covering the open end of the endotracheal tube to determine if the patient is capable of breathing around the tube. Alternatively, with the cuff deflated, the measured inspired volume can be compared with the exhaled volume on the ventilator. Significant airway edema is suggested if there is not a marked loss of tidal volume.

The endotracheal tube should remain in place if airway edema compromises the patency of the airway. The head is elevated to facilitate venous drainage. Steroids can also be given to decrease swelling associated with airway inflammation. Once an air leak around the endotracheal tube is apparent, extubation is reasonable.

Postoperative cervical hematoma — Following surgery in the neck, postoperative bleeding from vascular structures can lead to a cervical hematoma. As blood accumulates, it can compress the membranous posterior wall of the trachea and compromise the tracheal lumen. The lumen is often narrowed to less than 5 mm before the patient becomes clinically symptomatic.

Direct laryngoscopy will reveal only a dark mass along the posterior wall of the trachea. Attempts to intubate will be traumatic and unsuccessful. To secure a safe airway, the operative skin incision should be re-opened and the hematoma evacuated before attempting re-intubation.

Ideally, the patient should be taken emergently to the operating room, the neck prepped and draped, and the sutures or staples removed. The hematoma can then be evacuated from the wound, sponges placed into the wound and pressure applied to control bleeding while the patient is intubated. Once the airway is secured, surgical exploration can be continued to identify and control the source of bleeding, irrigate the wound, and re-close the incision. 

Foreign bodies — Dentures, teeth, surgical packs, or instruments can also obstruct the airway. Direct laryngoscopy or rigid bronchoscopy may be necessary to extract the obstructing object. Digital sweep through the mouth risks pushing the foreign body deeper into the airway and/or converting a partial obstruction to a complete obstruction, and should not be performed Residual effects of anesthesia — Following the completion of a procedure, the patient’s respiration is supported with positive pressure ventilation until the effects of the administered anesthetic agents wear off. 

One of the effects of volatile anesthetics, many intravenous sedative/hypnotic agents, and opioids is a decrease in the sensitivity of the respiratory center to rises in carbon dioxide, which then diminishes the respiratory drive. The intravenous sedatives ketamine and dexmedetomidine have less of a suppressive effect.

A diminished respiratory drive manifests as a reduced respiratory rate and/or tidal volume. As an example, the tidal volume is decreased but the respiratory rate may increase with the use of volatile anesthetic agents. In contrast, the respiratory rate decreases with the use of opioids while the tidal volume remains normal. The neuromuscular blockers have a direct effect on the musculature and reduce tidal volume because of reduced diaphragmatic movement. If prolonged, pharmacologic reversal may be necessary, as guided by the patient’s clinical condition. Patients with compromised renal or hepatic function are at an increased risk for persistent effects from sedatives, opioids, and neuromuscular blocking agents due to reduced drug clearance. Hypothermia and/or acidosis also slow enzymatic degradation of some agents (eg, cisatracurium). 

Cardiovascular complications — Cardiovascular complications in the postoperative patient are related to the severity of cardiovascular comorbidities (eg, coronary artery disease, hypertension), and the nature and course (eg, blood loss) of the operation.

Surgical patients with ischemic heart disease or a history of heart failure are less tolerant of the stress that surgery places on the heart, and these patients are more likely to present with cardiovascular complications in the post-anesthesia care unit (PACU). The surgical procedure can lead to cardiovascular complications through indirect and/or direct effects. As an example, blood loss during surgery may result in hypotension and hypoperfusion with cardiovascular injury as an indirect consequence. On the other hand, operations near the heart or mediastinum (eg, cardiac, pulmonary, or esophageal surgeries) can cause myocardial irritability and postoperative arrhythmias. Hypotension — There are many etiologies for hypotension in patients managed in the PACU. The most significant of these include hypovolemia, heart failure, sepsis, drug effects, anaphylaxis, and pulmonary embolus.

*Hypovolemia – Inadequate intravascular volume can be due to inadequate fluid replacement during the course of the operation. If intraoperative blood loss and/or ongoing blood loss is the cause of the hypovolemia, blood products are given as part of the ongoing resuscitation. It is important to remember that the postoperative hematocrit will not accurately reflect the degree of blood loss until adequate fluid resuscitation has occurred. 

•Myocardial ischemia/heart failure – In the perioperative period, hypotension can also be due to myocardial ischemia/infarction, heart failure, cardiac valvular dysfunction, and cardiac arrhythmia.

Patients with preexisting coronary artery disease and patients with drug-eluting stents whose antiplatelet therapy was prematurely withheld are at increased risk for perioperative myocardial ischemia . 

•Decreased vascular resistance – Hypotension related to decreased systemic vascular resistance is due to the combined effects of decreased atrial filling and reduced afterload. 

Iatrogenic causes of decreased vascular resistance are related to the administration of various pharmacologic agents such as the vasodilators sodium nitroprusside or hydralazine to treat hypertension, or the prolonged effect of long-acting anti-hypertensives (eg, lisinopril) taken by the patient on the morning of surgery. Epidural and spinal anesthetics also decrease peripheral vascular resistance by causing venodilation. When treating hypotension in patients with an epidural or spinal anesthetic, vasoconstricting agents are preferred over additional fluid, particularly in patients who will have trouble clearing the fluid load when vascular tone returns to normal (eg, patients with renal insufficiency, history of heart failure). 

Many disease states also decrease vascular resistance and can lead to postoperative hypotension. As examples, endotoxins released during surgery for intraabdominal sepsis, spinal shock due to spinal cord injury, and histamine release from mast cells during anaphylaxis can all cause profound hypotension mediated by a decrease in vascular resistance. Treatment is directed at the underlying cause (eg, antibiotics for sepsis, epinephrine to stabilize the mast cells in anaphylaxis), and symptomatic therapy includes intravenous vasoconstrictors (eg, vasopressin, norepinephrine, or phenylephrine) and fluid resuscitation; high fluid volumes are often needed.

Hypertension — Patients who develop hypertension in the PACU are at a higher risk for postoperative complications (eg, unplanned intensive care unit admission) compared with patients who experience an episode of hypotension. The most common cause of hypertension in the PACU is preoperative hypertension, particularly if the patient did not take their usual anti-hypertensive agent(s) on the morning of surgery. Other frequent causes of hypertension in the PACU include inadequate pain control, hypoventilation, urinary retention, and anxiety. Less commonly, delirium, which may be a manifestation of alcohol or drug withdrawal, can also contribute. These are reviewed briefly below. The general treatment of hypertension in the perioperative period is discussed in detail elsewhere. 

•Pain is a common cause of hypertension in the PACU. Inadequately treated surgical pain leads to sympathetic discharge which increases heart rate and blood pressure. A multimodal approach to pain management is preferred. Regional anesthetic techniques are useful when narcotics need to be avoided. 

•Urinary retention is an easily remedied cause of hypertension in the PACU, particularly for older men with known voiding problems due to prostatic hypertrophy or patients with decreased bladder muscle tone due to neuraxial anesthesia. If the patient has received a large volume of intravenous fluid and has not voided, the bladder should be palpated or scanned by ultrasound to determine if catheterization of the bladder is needed. 

•Hypoventilation is initially associated with an increase in sympathetic tone leading to a rise in blood pressure. Treatment is supportive with positive pressure ventilation via bag-mask ventilation or reintubation until the patient's respiratory drive returns to normal. 

•Postoperative anxiety and emergence delirium can also lead to elevated blood pressures. This problem is far more common in children. Prior to giving any sedatives, other causes of anxiety (eg, pain, respiratory insufficiency) must be identified and treated first. 

•Drug or alcohol withdrawal can also lead to hypertension in the PACU. Alcohol withdrawal can begin as early as 24 hours after consumption of the last alcoholic beverage. Early signs of withdrawal include hypertension and tachycardia. Narcotic abusers who have not received their usual dose may require additional dosing of their narcotic to manage withdrawal symptoms. The treatment of drug and alcohol withdrawal is discussed elsewhere. 

Arrhythmias — Cardiac arrhythmias in the postoperative period can be due to acute coronary insufficiency, hypoxia, electrolyte abnormalities (eg, hypokalemia, hypomagnesemia), anesthetics, and other pharmacologic agents. The uncoordinated cardiac contraction can lead to marked hypotension, particularly if ventricular function is already compromised such as in the patient with poor preoperative cardiac contractility. 

The most common postoperative ventricular arrhythmias are isolated premature ventricular contractions (PVCs) and ventricular bigeminy. These rhythms are unlikely to degenerate into life-threatening arrhythmias and they do not routinely require intervention. On the other hand, Torsade de Pointes (waveform 1) is a polymorphic ventricular tachycardia that results from prolongation of the Q-T interval in susceptible patients who become hypomagnesemic or receive certain medications (eg, class IA or III anti-arrhythmics, droperidol). Torsade de Pointes can cause hypotension or degenerate into ventricular fibrillation and sudden cardiac death. 

Atrial fibrillation is most likely to occur if a patient undergoes cardiac or thoracic surgery. The rate of new onset atrial fibrillation after pneumonectomy can be 50 percent or higher, and may be due to atrial irritability or the sudden cessation of chronic beta-blockade.

New onset postoperative bradyarrhythmias are due to excess administration of antihypertensive agents (eg, beta-blockers, alpha-2 agonists), excess opioid dosing, or related to high neuraxial anesthesia (suppression of cardiac accelerator fibers originating at the level of the first through fourth thoracic vertebrae [T1-T4]). 

The treatment of arrhythmias in the PACU first requires identification and correction of the underlying cause of the rhythm disturbance and thus, hypoxia, hypercarbia, ischemia, and electrolyte imbalances must be addressed. Medical management of the arrhythmias is usually enough to correct the arrhythmias, but if the tachyarrhythmias cause hemodynamic instability, electrical cardioversion may be required.

Symptomatic bradyarrhythmias that are not corrected may require temporary pacing (transvenous or transcutaneous). 

Hypothermia or hyperthermia — Hypothermia and hyperthermia have negative consequences. Decreases in body temperature as little as 2°C can slow drug metabolism (particularly degradation of neuromuscular blocking agents), and decrease platelet function impairing hemostasis. More profound decreases in body temperature cause somnolence. In contrast, excessive increases in body temperature cause a hypermetabolic state that increases the respiratory rate and heart rate, which can exacerbate underlying medical conditions.

Because maintenance of normothermia during recovery is important, the Joint Commission and the Surgical Care Improvement Project encourage warming all patients to 96.8°F (36°C) within 15 minutes of their arrival in the post-anesthesia care unit (PACU). Warming in the PACU is typically achieved using forced air warming devices. Despite this recommendation, a substantial proportion of patients become hypothermic perioperatively; in a large observational study, hypothermia (core temperature 36°C) occurred in 46 percent of patients admitted to the intensive care unit following elective non-cardiac surgery, and persisted over 24 hours in 1.2 percent .

Hypothermia — Causes of hypothermia in the PACU include :
●A cold environment
●Administration of room temperature IV fluids
●Medication-induced vasodilatation (eg, inhalation anesthetics)
●Decreased basal metabolic rate
●Anesthetic-induced impairment of the hypothalamic thermostat
●Exposure of body cavities to room temperature air
●Ventilation with unwarmed gasses

Shivering — Shivering in the postoperative period can occur with hypothermia, hyperthermia, or normothermia. Shivering causes patient discomfort and markedly increases myocardial oxygen consumption. Shivering is treated with a single dose of meperidine, 12.5 to 25 mg, intravenously. Alpha-2 agonists including clonidine (150 micrograms intravenously) and dexmedetomidine are used as second-line therapy.

Fever — Fever is defined as a core body temperature ≥102.2°F (39°C) (table 2). The potential causes of fever in the immediate operative and postoperative period are mainly limited to: medications or blood products to which the patient was exposed during care in the operating room or in the recovery area; trauma suffered prior to surgery or as part of surgery; infections that were present prior to surgery; and rarely, malignant hyperthermia. These entities are discussed elsewhere. 



Summary and recommendations●Postoperative complications are estimated to occur in about 25 percent of patients undergoing anesthesia. Complications may require additional treatment and may delay discharge from the post-anesthesia care unit (PACU). 

●The most common PACU complication is postoperative nausea or vomiting (PONV). The incidence following anesthesia ranges between 10 and 30 percent. Risk factors associated with higher rates of PONV include female gender, a history of motion sickness, absence of a history of smoking, prior PONV, and type of surgery, including neurological, head or neck, abdominal, and possibly breast surgery. 

●Prior to surgery, the patient should be assessed for their risk for PONV. We administer pharmacologic prophylaxis to patients with ≥1 risk factor for PONV. For patients with a single risk factor for PONV, a single agent is adequate, whereas patients with >1 risk factor generally require multiple agents. Prophylaxis is not necessary for patients who do not have risk factors. 

●When PONV develops in spite of pharmacologic prophylaxis, a different class of anti-emetics is chosen for rescue therapy from the class used for prophylaxis. 

●Respiratory problems are the second most common complication arising in the PACU. Patients with significant comorbidities, particularly cardiac, neuromuscular, or pulmonary dysfunction are at a higher risk for hypoxemia due to hypoventilation or impaired oxygen exchange. In postoperative patients, hypoventilation can be due to airway obstruction, poorly controlled incisional pain, and the residual effects of anesthetics, analgesics (eg, opioids), sedatives, or neuromuscular blocking agents. Impaired oxygen exchange is most commonly due to atelectasis from pulmonary splinting, but other causes for impaired oxygen exchange include pulmonary edema, or, more rarely, pulmonary embolus. 

●Cardiovascular complications in the postoperative patient are closely correlated to pre-existing cardiovascular disease. Hypotension can be due to hypovolemia, heart failure, sepsis, drugs, cardiac arrhythmia, anaphylaxis, and pulmonary embolus. Postoperative hypertension is most commonly related to pre-existing hypertension. Inadequately controlled pain is another common cause of hypertension. Other causes include urinary retention, hypoventilation, and drug or alcohol withdrawal. Cardiac arrhythmias (tachycardia, bradycardia) can be due to cardiac ischemia, hypoxia, electrolyte abnormalities (eg, hypokalemia, hypomagnesemia), anesthetics, and other pharmacologic agents. 

●Disturbances in thermoregulation are common, including hypothermia and hyperthermia. Shivering can occur in hypothermic, hyperthermic, or normothermic patients. Within 15 minutes of arrival in the PACU, all patients should be warmed to 96.8°F (36°C). Postoperative hypothermia is most often due to anesthetic induced vasodilation and impaired thermoregulation in conjunction with the cold operative environment. The potential causes of fever in the immediate operative and postoperative period are mainly limited to: medications or blood products to which the patient was exposed in the perioperative period; trauma suffered prior to surgery or as part of surgery; infections that were present prior to surgery; and rarely, malignant hyperthermia. 

●The most common central nervous system complication in the PACU is an altered state of consciousness (delirium, agitation, somnolence). Uncommon problems include visual disturbances, complications related to regional anesthesia (epidural hematoma, neurapraxia), and recall of intraoperative events. Early identification and treatment of these uncommon problems is important to lessen the impact of these potentially devastating complications. 

●Inability to void is common following anesthesia. The incidence varies widely, ranging from 5 to 70 percent depending upon patient, procedure, and anesthesia-specific factors. Patients with more than one risk factor for urinary retention should undergo assessment of urinary volume to determine if one-time catheterization is needed prior to discharge. All patients who have not spontaneously voided prior to discharge should seek medical attention if they have not spontaneously voided within eight hours of discharge.