Post Operative Physiologic Disorders

Post Operative Physiologic Disorders

A variety of physiologic disorders affecting multiple organ systems must be diagnosed and treated in the PACU during emergence from anesthesia and surgery

Upper Air Way Obstruction

Airway obstruction is a common and potentially devastating complication in the postoperative period. The most frequent cause of airway obstruction in the PACU is the loss of pharyngeal tone in a sedated or obtunded patient. The residual depressant effects of inhaled and intravenous anesthetics and the persistent effects of neuromuscular blocking drugs contribute to the loss of pharyngeal tone in the immediate postoperative period. This effort to breathe against an obstructed airway is characterized by a paradoxic breathing pattern consisting of retraction of the sternal notch and exaggerated abdominal muscle activity. Collapse of the chest wall plus protrusion of the abdomen with inspiratory effort produces a rocking motion that becomes more prominent with increasing airway obstruction. Obstruction secondary to loss of pharyngeal tone can be relieved by simply opening the airway with the "jaw thrust maneuver" or continuous positive airway pressure applied via a face mask (or both). Support of the airway is needed until the patient has adequately recovered from the effects of drugs administered during anesthesia. In selected patients, placement of an oral or nasal airway, laryngeal mask airway, or endotracheal tube may be required.

Pain Control

Preoperative administration of nonsteroidal anti-inflammatory drugs (NSAIDs) alone or with acetaminophen can significantly reduce postoperative opioid requirements for selected procedures. Moderate to severe postoperative pain in the PACU can be managed with parenteral opioid. When opioids are used, titration of small intravenous doses is generally safest. Although considerable variability may be encountered, most patients are quite sensitive to opioids within the first hour after general anesthesia. Adequate analgesia must be balanced against excessive sedation. Opioids of intermediate to long duration, such as meperidine, 10 - 20 mg (0.25 - 0.5 mg/kg in children), or morphine, 2 - 4 mg (0.025 - 0.05 mg/kg in children), are most commonly used. Analgesic effects usually peak within 4 - 5 min. Maximal respiratory depression, particularly with morphine may not be seen until 20 - 30 min later.

Agitation

Agitation, a state of being very nervous and anxious, before the patient is fully responsive, pain is often manifested as postoperative restlessness. Serious systemic disturbances (such as hypoxemia, acidosis, or hypotension), bladder distention, or a surgical complication (such as occult intra abdominal hemorrhage) should always be considered as well. Marked agitation may necessitate arm and leg restraints to avoid self-injury, particularly in children. When serious physiological disturbances have been excluded in children, cuddling and kind words from a sympathetic attendant or the parents (if they are allowed in the PACU) often calm the pediatric patient. Other contributory factors include marked preoperative anxiety and fear as well as adverse drug effects (large doses of central anticholinergic agents, phenothiazines, or ketamine). Physostigmine, 1 - 2 mg intravenously (0.05 mg/kg in children), is most effective in treating delirium due to atropine and scopolamine but may also be useful in other cases. If serious systemic disturbances and pain can be excluded, persistent agitation may require sedation with intermittent intravenous doses of midazolam, 0.5 - 1 mg (0.05 mg/kg in children).

Nausea & Vomiting

Postoperative nausea and vomiting (PONV) are a common problem following general anesthesia, occurring in 20 - 30% of all patients. The etiology of PONV is usually multifactorial, involving anesthetic agents, the type of procedure, and patient factors. It is important to recognize that nausea is a common complaint that is reported at the onset of hypotension, particularly following spinal anesthesia.

An increased incidence of nausea is reported following opioid administration during anesthesia and intraperitoneal surgery. The highest incidence appears to be in young women; studies suggest nausea is more common during menstruation. Increased vagal tone manifested as sudden bradycardia commonly precedes or coincides with emesis. Propofol anesthesia decreases the incidence of PONV, as does a preoperative history of smoking. Ondansetron 4 mg (0.1 mg/kg in children) is effective in preventing PONV and in treating established PONV. Metoclopramide, 0.15 mg/kg intravenously, is somewhat less effective but is a good alternative to ondanestron.

Dexamethasone, 4 - 10 mg (0.10 mg/kg in children), when combined with another antiemetic is particularly effective for refractory nausea and vomiting. Moreover, it appears to be effective for up to 24 h and thus may be useful for post discharge nausea and vomiting.

Shivering & Hypothermia

Shivering occurs in the PACU as a result of intraoperative hypothermia or the effects of anesthetic agents. It is also common in the immediate postpartum period. The most important cause of hypothermia is a redistribution of heat from the body core to the peripheral compartments. A cold ambient temperature in the operating room, prolonged exposure of a large wound, and the use of large amounts of unwarmed intravenous fluids or high flows of un humidified gases can also be contributory. Nearly all anesthetics, particularly volatile agents, decrease the normal vasoconstrictive response to hypothermia. Although anesthetic agents also decrease the shivering threshold, shivering is commonly observed during or after emergence from general anesthesia. Shivering in such instances represents the body's effort to increase heat production and raise body temperature and may be associated with intense vasoconstriction.

Spinal anesthesia also lowers the shivering threshold and vasoconstrictive response to hypothermia; shivering may also be encountered in the recovery room following regional anesthesia. Other causes of shivering should be excluded, such as sepsis, drug allergy, or a transfusion reaction.

Hypothermia should be treated with warming lights or heating blankets, to raise body temperature to normal. Intense shivering causes precipitous rises in oxygen consumption, CO2 production, and cardiac output. These physiological effects are often poorly tolerated by patients with preexisting cardiac or pulmonary impairment. Hypothermia has been associated with an increased incidence of myocardial ischemia, arrhythmias, and increased duration of muscle relaxant effects. Small intravenous doses of meperidine, 10 - 50 mg, can dramatically reduce or even stop shivering. Intubated and mechanically ventilated patients can also be sedated until normothermia is reestablished and the effects of anesthesia have dissipated.

Cardiovascular Instability

Patients with a history of essential hypertension are at greatest risk for significant systemic hypertension in the PACU. Additional factors include pain, hypoventilation and associated hypercapnia, emergence excitement, advanced age, a history of cigarette smoking, and preexisting renal disease. Systemic hypotension in the PACU is usually due to decreased intravascular fluid volume and preload, and as such, responds favorably to intravenous fluid administration. The most common causes of decreased intravascular volume in the immediate postoperative period include ongoing third-space translocation of fluid, inadequate intraoperative fluid replacement (especially in patients who undergo major intra-abdominal procedures or preoperative bowel preparation), and loss of sympathetic nervous system tone as a result of neuraxial (spinal or epidural) blockade.

Discharge From PACU

All patients must be evaluated by an anesthetist prior to discharge from the PACU unless strict discharge criteria are adopted. Criteria for discharging patients from the PACU are established by the department of anesthesia and the hospital's medical staff. They may allow PACU nurses to determine when patients may be transferred without the presence of a physician provided all criteria have been met (Table 5.2).

Before discharge, patients should have been observed for respiratory depression for at least 20 - 30 min after the last dose of parenteral narcotic. Other minimum discharge criteria for patients recovering from general anesthesia usually include the following:

1. Easy arousability
2. Full orientation
3. The ability to maintain and protect the airway
4. Stable vital signs for at least 15 - 30 min
5. The ability to call for help if necessary
6. No obvious surgical complications (such as active bleeding).

Patients receiving regional anesthesia should also show signs of resolution of both sensory and motor blockade. Complete resolution of the block is generally desirable to avoid inadvertent injuries due to motor weakness or sensory deficits; some medical centers have nursing protocols that allow earlier discharge to appropriately staffed areas. Documenting resolution of the block is also critically important. Failure of a spinal anesthesia to resolve after 6 h raises the possibility of spinal cord or epidural hematoma, which should be excluded by radiological imaging.