Chapter 36 Postanesthesia Recovery
1. What is the postanesthesia care unit (PACU)?
2. What are the requirements for monitoring in the PACU?
3. What are the American Society of Anesthesiologists (ASA) practice guidelines for post anesthesia care?
4. What are some postoperative physiologic disorders that may manifest in the PACU?
Airway obstruction
5. What is the usual mechanism of airway obstruction in the post general anesthesia patient? How does it present clinically?
6. What is the initial intervention to deal with airway obstruction?
7. How may residual neuromuscular blockade manifest in an awake patient?
8. How is residual neuromuscular blockade assessed in an awake patient?
9. What are some factors that contribute to prolonged nondepolarizing neuromuscular blockade in the PACU?
10. What are some factors that contribute to prolonged depolarizing neuromuscular blockade in the PACU?
11. What operative factors may result in life-threatening airway edema in the immediate postoperative period?
12. What leak tests can be performed to evaluate airway patency in patients at risk for airway edema prior to extubation of the trachea?
13. What are some special considerations for patients with obstructive sleep apnea for postanesthesia care?
Hypoxemia in the PACU
14. What are some potential causes of hypoxemia in the PACU? Which of these is most common?
15. What are some potential causes of postoperative hypoventilation?
16. What is the ventilatory response to carbon dioxide?
17. In the PACU, how can hypoxemia secondary to hypercapnia be reversed?
18. What is diffusion hypoxia?
19. Describe the hypoxic pulmonary vasoconstriction (HPV) response and list the conditions and medications that may inhibit it.
20. What is the significance of an increased venous admixture in the PACU?
Oxygen supplementation
25. What is the FIO2 that can be delivered through simple nasal cannula? What are some other options for oxygen delivery in the PACU?
26. What is a high flow nasal cannula? What is its advantage?
27. Is there a role for continuous positive airway pressure (CPAP) and noninvasive positive-pressure ventilation (NIPPV) in the PACU?
Hemodynamic instability
28. What is the significance of hypertension in the PACU?
29. What are some factors associated with significant hypertension in the PACU?
30. What are some causes of hypotension in the PACU?
31. How is myocardial ischemia detected in the PACU?
32. What are some factors which may contribute to cardiac arrhythmias in the PACU?
33. What are some possible causes of sinus tachycardia in the PACU?
34. How should new-onset atrial fibrillation be managed in the PACU?
35. What drugs may contribute to ventricular tachycardia in the PACU?
36. What are some possible causes of bradycardia in the PACU?
Renal dysfunction
40. What is the differential diagnosis of postoperative renal dysfunction?
41. How is oliguria defined? What are some causes of oliguria in the PACU?
42. What are the risk factors for postoperative urinary retention?
43. What are some specific causes of oliguria presenting in the PACU that require immediate attention to prevent ongoing injury?
Answers*
1. The postanesthesia care unit (PACU) is the area equipped and staffed to monitor and care for patients as they emerge from general anesthesia and surgery. Clinical monitoring in the unit is focused on the cardiopulmonary system, with vigilant attention to airway patency and protection, oxygenation, and ventilation, as well as hemodynamic stability. Vital signs are recorded at the minimum every 15 minutes. The unit is located adjacent to the operating room to allow for prompt intervention by anesthesia and surgical staff if needed. (632)
2. Standards and practice parameters for postanesthesia care have been adopted by the ASA. The Standards for Postanesthesia Care is a document that delineates the minimal requirements for monitoring and care in the unit. These are minimal standards that are to be exceeded when deemed appropriate by the judgment of the anesthesia caregiver.
3. Unlike the general ASA standards, the ASA practice guidelines for postanesthesia care provide specific recommendations for clinical evaluation and therapeutic intervention for physiologic disorders that may present in the PACU. (632)
4. A number of postoperative physiologic disorders may manifest in the PACU. These include nausea and vomiting, oliguria, hypoventilation, bleeding, hypothermia, delirium, pain, and delayed awakening. Not surprisingly, data from the U.S. closed claims database show that the most devastating outcomes are the result of airway, respiratory, or cardiovascular compromise. Hypertension or hypotension, cardiac arrhythmia, airway obstruction, hypoventilation, and hypoxemia require immediate attention and intervention. (632, Table 39-1)
Airway obstruction
5. Airway obstruction in the PACU is most often due to the loss of pharyngeal tone resulting from the residual depressant effects of inhaled and intravenous anesthetics and/or the persistent effects of neuromuscular blocking drugs. In awake patients, the pharyngeal muscles contract synchronously with the diaphragm. This activity serves to pull the tongue forward and tent the airway open as the diaphragm creates the negative pressure for inspiration. In the PACU, this pharyngeal muscle activity may be lost and the resultant compliant pharyngeal tissue collapses with negative inspiratory pressure causing obstruction. When this occurs there is a characteristic paradoxic breathing pattern consisting of retraction of the sternal notch and exaggerated abdominal muscle activity. This rocking motion becomes more prominent with increasing airway obstruction. Airway obstruction can be associated with arterial hypoxemia and desaturation on pulse oximetry. (632)
6. Airway obstruction can usually be treated by the jaw thrust maneuver. When this is not sufficient to relieve the obstruction, CPAP can be applied via face mask. If necessary, this can be followed by placement of nasal and oral airways, and in extreme cases laryngeal mask airway or endotracheal tube placement. (632)
7. Residual neuromuscular blockade in the awake patient may manifest as a struggle to breathe. In a patient whose mental status is not clear enough to communicate clearly the patient may appear agitated. (633)
8. Clinical assessment of residual neuromuscular blockade is preferred to the application of the train-of-four ratio and titanic stimulation in awake patients, as both are painful interventions. Clinical evaluation includes grip strength, tongue protrusion, the ability to lift the legs off the bed, and the ability to lift the head off the pillow for a full 5 seconds. Of these, the sustained head lift most directly reflects the ability of the patient to maintain and protect the airway. An extubated patient’s ability to oppose and fix the incisor teeth against a tongue depressor is another clinically reliable indicator to pharyngeal tone. This maneuver correlates with an average train-of-four ratio of 0.85. (633)
9. Factors which may contribute to prolonged nondepolarizing neuromuscular blockade include drugs, diseases, and metabolic states. Drugs which prolong neuromuscular blockade include residual inhaled anesthesia, local anesthetics (lidocaine and other sodium channel blockers), cardiac antiarrhythmic drugs (procainamide), antibiotics (aminoglycosides most commonly), calcium channel blockers, furosemide, and corticosteroids. Metabolic states which may prolong neuromuscular blockade include hypothermia, respiratory acidosis, renal or hepatic failure, hypermagnesemia, and hypocalcemia. Of these, hypothermia and respiratory acidosis are easily recognized and reversible. (633, Table 39-2)
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