Chapter 35 Procedures Performed Outside the Operating Room
Characteristics of remote locations
1. What are some fundamental capabilities available in the operating room that must also be available for the delivery of anesthesia in remote locations?
2. What are some special challenges facing the anesthesiologist when delivering anesthesia and at the conclusion of anesthesia in remote locations?
3. What are some safety concerns facing the anesthesiologist delivering anesthesia in remote locations?
Noninvasive x-ray procedures
7. What is magnetic resonance imaging (MRI)? For what evaluations is it useful?
8. What are some contraindications to undergoing MRI?
9. What are some features of MRI that make it difficult for the patient to tolerate?
10. How should the patient be monitored when undergoing an anesthetic for MRI?
11. How must anesthetic equipment and monitors in the MRI center be altered for MRI compatibility? What are the risks of using standard operating room monitors?
12. How must accidental extubation of the trachea during MRI be managed?
13. Why is there an increased risk of hypothermia for patients in the MR imager?
14. What is computed tomography?
15. How does the management of anesthesia for patients undergoing computed tomography compare with the management of anesthesia for patients undergoing MRI?
Invasive x-ray procedures
16. Why more so in interventional radiology procedures than in diagnostic radiology procedures can there be a need for the anesthesiologist to suddenly change to the management of blood coagulation parameters by giving medications or taking new actions?
17. What drug should be immediately available for injection, and at what dose, in invasive radiology procedures where there has been administration of a full anticoagulation dose of heparin?
18. Patients taking antiplatelet drugs are often asked to stop taking those drugs several days before a surgical procedure to allow the body to generate new platelets unaffected by the drugs. However, interventional radiology procedures must sometimes be done in such patients before the effects of antiplatelet drugs have completely worn off. What action must the anesthesiologist take if serious bleeding occurs before antiplatelet agents have worn off, and the international normalized ratio, prothrombin time, partial prothrombin time, and fibrinogen are all normal?
Electroconvulsive therapy
21. What patients are candidates for electroconvulsive therapy (ECT)? How is ECT accomplished?
22. What are some cardiopulmonary effects of ECT? In what sequence might these effects occur?
23. What are the most common causes of mortality after ECT?
24. How is cerebral blood flow affected by ECT?
25. How is intragastric pressure affected by ECT?
26. What are some contraindications and relative contraindications to ECT?
27. What are some post-ECT manifestations in the patient?
28. What is the recommendation for the ingestion of solids and liquids before the performance of ECT?
29. Why is preoperative medication not recommended for the patient who is to undergo ECT?
30. What agents might be used for the induction of anesthesia in a patient undergoing ECT?
31. After unconsciousness results from the induction of anesthesia, why might succinylcholine be administered to the patient? Before this is done, why might a tourniquet be applied to an extremity of the patient?
32. How can the airway of the patient undergoing ECT be managed? What equipment should be available to the anesthesiologist?
33. What monitors should be used during the administration of an anesthetic for ECT?
Cardiac catheterization
34. Why might patients require anesthesia for cardiac catheterization? What adverse effects might the anesthetic have on cardiac function during these procedures?
35. What PaCO2 should be maintained during anesthesia for cardiac catheterization?
36. What complications can occur as a result of cardiac catheterization procedures?
37. How might anxiety be allayed during cardiac catheterization procedures?
38. Why might the onset of action of inhaled or injected anesthetics be altered in patients undergoing cardiac catheterization procedures?
Extracorporeal shock wave lithotripsy
42. What is extracorporeal shock wave lithotripsy (ESWL)?
43. What are the shock waves timed with during ESWL to avoid cardiac dysrhythmias?
44. Why is anesthesia required for patients undergoing ESWL?
45. What are some advantages of general anesthesia for patients undergoing ESWL?
46. What sensory level of regional anesthesia is recommended for patients undergoing ESWL with this anesthetic technique?
47. Why is intravenous fluid administration important during ESWL?
Dental surgery
49. What patients might require anesthesia for a dental procedure?
50. Why might an anticholinergic be administered to a patient before a dental procedure?
51. What agents can be used for the induction of anesthesia in patients requiring anesthesia for a dental procedure? What agent can be used in uncooperative patients when there is no intravenous access before the induction of anesthesia?
52. How is tracheal intubation usually accomplished to facilitate the dentist’s ability to perform dental procedures in patients requiring general anesthesia for the procedure?
53. What are some special concerns for the patient during emergence and in the recovery period after having undergone a dental procedure under general anesthesia?
Answers*
Characteristics of remote locations
1. Fundamental capabilities for monitoring, the delivery of supplemental oxygen, mechanical ventilation of the lungs, the delivery and scavenging of inhaled anesthetics, anesthesia equipment, and the availability of suction must all be available for the delivery of anesthesia in remote locations. (618)
2. Special challenges facing the anesthesiologist when delivering anesthesia in remote locations include limited access to the patient’s airway, poor availability of accessory help, and the potential difficulty in quickly obtaining emergency equipment. Special challenges facing the anesthesiologist at the conclusion of anesthesia in remote locations are based on the greater amount of distance the anesthesiologist must transport the patient before reaching the postanesthesia care unit. These may include a greater need for a supplemental oxygen supply and continuous monitoring. (618-619)
3. Some safety concerns that may face the anesthesiologist delivering anesthesia in remote locations include the possibility of exposure to increased radiation and the scavenging of waste anesthetic gases. (618-619)
Radiation safety
4. Patients, usually children, who cannot remain still or who cannot cooperate with instructions are most likely to require general anesthesia or sedation for diagnostic and therapeutic radiologic procedures. Adults may also require sedation or general anesthesia for radiologic procedures, especially patients who are developmentally delayed or have sustained trauma. (620)
5. The anesthesiologist should attempt to limit his or her exposure to radiation by wearing a lead apron and thyroid shield, through the use of movable lead glass screens, and by remaining as far away as possible from the radiation source, preferably at least 1 to 2 m. (619)
Allergic reactions
6. Common side effects associated with the administration of intravenous contrast agents are nausea and vomiting, a perception of warmth, headache, and mild urticaria. Severe reactions may include vomiting, rigors, feeling faint, bronchospasm, chest pain, arrhythmias, and renal failure. Life-threatening reactions include severe bronchospasm, glottic edema, pulmonary edema, arrhythmias, seizures, and cardiac arrest. The newer nonionic contrast dyes of lower osmolarity tend to be associated with fewer incidences of allergic reactions. Even so, patients at risk for an adverse reaction to a contrast agent should be pretreated with medicines to minimize the reaction to the contrast agent. Prednisolone can be administered at a dose of 50 to 100 mg intravenously both the night before and the morning of the procedure. Diphenhydramine, 50 mg, should also be given intravenously just before the procedure. Adequate hydration is necessary in these patients to maintain their intravascular volume because the intravenous contrast medium also acts as an osmotic load for the patient, inducing diuresis. (619-620)
Noninvasive x-ray procedures
7. MRI is a radiologic technology that provides digitalized tomographic images of the body by exposing the body to a very high-strength constant magnetic field and high-frequency alternating electric and magnetic fields. MRI does not produce any ionizing radiation. These studies are useful for the evaluation of neurologic and soft tissues, because they can distinguish between fat, vessels, and tumor. (620)
8. MRI is contraindicated in patients who have any implanted metals that are attracted or repelled by a magnetic field, or easily heated by alternating electromagnetic fields. Examples of metallic items include artificial cardiac pacemakers, aneurysm clips, some intravascular clips, and some biologic pumps. Contraindicated items with metals that can be dangerously heated and cause injury are standard pulse oximeter probes, standard electrocardiogram electrodes, temperature probes, pulmonary artery catheters containing wires, and epidural catheters containing wires. (621)
9. MRI is difficult for the patient to tolerate based on the positioning of the patient during the study. The patient must lie on a long thin table and then be moved into a long thin tube that has walls close to the face of the patient. Patients during MRI may become claustrophobic. In addition, the MR imager makes loud booming noises that may augment a patient’s discomfort. (621)
10. The patient undergoing an anesthetic during MRI should have his or her blood pressure, pulse oximeter oxygen saturation, and cardiac rhythm continually monitored with special MRI-compatible equipment. Capnograph monitors may also be used to detect end-tidal carbon dioxide, especially when monitoring from a distance. Extensions must be placed on all monitoring equipment because the patient moves into the MR imager during the study. (621)
11. Standard operating room monitors and anesthetic equipment must not be used. Special MRI-compatible monitoring equipment, such as a fiber-optic pulse oximeter, must be available for use in the MRI center. No ferromagnetic components are allowed for use near the scanner, because any ferromagnetic material will be forcefully attracted by the magnet and may cause injury to individuals in or near the scanner. Plastic, nonmagnetic steel, and aluminum components replace metal ones within special anesthetic machines, monitoring and intravenous infusion equipment, and ventilators specially made for compatibility with the MR imager. Aluminum gas cylinders must be used instead of standard iron gas cylinders. Again, traditional pulse oximeters must not be used in the MR imager, because they can cause very serious burns to the patient. (621)
12. Accidental extubation of the patient’s trachea during MRI must be managed by immediate discontinuation of imaging, removing the patient from the imager, and rapidly controlling the patient’s airway. In the event that resuscitative equipment is necessary in an emergency, the patient must be moved far enough away from the MR imager to prevent metal components of the resuscitative equipment from becoming attracted to the magnet. (621)
13. The airflow through the MR imager increases the amount of heat loss from the patient, placing the patient at an increased risk of hypothermia. This risk is of particular concern for pediatric patients undergoing MRI. (621-622)
14. Computed tomography (CT) is a radiologic imaging study that produces a two-dimensional image from data obtained by rotating an x-ray beam around the subject. Thus CT scanners emit ionizing radiation. (620)
15. Anesthesia for CT scanning is similar to that for MRI. That is, access to the patient is limited and monitoring is remote. Unlike with the MR imager, the avoidance of ferromagnetic equipment is not necessary. (620-621)
Invasive x-ray procedures
16. Interventional radiology cases can require sudden management changes in coagulation parameters because unforeseen bleeding in an anticoagulated patient can occur suddenly as a complication. If this occurs, the anticoagulation may need to be immediately reversed. If the bleeding is intracerebral, reversal of the coagulation can be essential for saving the patient’s life. (622-623)
17. When interventional radiology patients are heparinized during a procedure, the anesthesiologist must have protamine immediately available, preferably already drawn up and at a port where it can be injected safely and followed by a flush injection. (622-623)
18. If adequate platelet function prevents the cessation of bleeding in patients medicated with long-acting antiplatelet medications, then platelet transfusions are needed. There are no drugs available for suddenly reversing the effects of long-acting antiplatelet drugs. (622-623)
Radiation therapy
19. Patients undergoing radiation therapy may require anesthesia for immobilization during the procedure. Immobilization during radiation therapy is important because large doses of radiation are focused on specific target sites, and movement during the procedure can result in tissue damage to areas inadvertently radiated. The duration of the procedure is very brief, requiring that the patient must remain immobile for only a brief amount of time. (620)
20. Remote monitoring devices must be used for patients being sedated or anesthetized while undergoing radiation therapy because high doses of radiation require that all individuals must leave the area during the treatment period. (623)
Electroconvulsive therapy
21. Patients who have severe clinical depression that is refractory to medicines, patients who have become acutely suicidal, patients who are acutely psychotic or schizophrenic, and patients with acute mania are all candidates for electroconvulsive therapy (ECT). ECT is accomplished by administering an electric stimulus to the patient that is sufficient to induce a grand mal seizure. The mechanism for the short-term benefit derived from ECT is unknown, but is thought to be due to either the release or reestablishment of neurotransmitter levels. Controversy remains regarding the long-term benefit of ECT. (624)
22. Cardiopulmonary effects of ECT are reflected as stimulation of the parasympathetic nervous system followed by stimulation of the sympathetic nervous system. Initially, the anesthesiologist may see bradycardia and hypotension, followed by an increase in heart rate, an increase in blood pressure, and cardiac dysrhythmias. Apnea may also be seen during ECT. (624-625)
23. The most common causes of mortality after ECT are myocardial infarction and cardiac dysrhythmias. (625-626)
24. Dramatic increases in cerebral blood flow occur during ECT. (625-626)
25. Intragastric pressure is increased during ECT. (625)
26. Contraindications and relative contraindications to ECT include pheochromocytoma, increased intracranial pressure, recent cerebrovascular accident, cardiovascular conduction defects, high-risk intrauterine pregnancy, and aortic or cerebral aneurysms. (624-626)
27. After ECT, and the resultant grand mal seizure, the patient is likely to be postictal. Headache, confusion, agitation, cognitive impairment, and apnea may all be present after the procedure. (625-626)
28. Before the performance of ECT the patient must have fasted from solids and liquids just as a patient would before general anesthesia. This is to minimize the risk of the pulmonary aspiration of gastric contents, because protective airway reflexes will be lost with the induction of anesthesia and potentially during the seizure activity. (625)
29. Preoperative medication is not recommended before an ECT procedure because the duration of the preoperative medicine would likely be longer than the duration of the procedure itself. This may cause a delay in the awakening of the patient and a delay in the recovery of the patient from the procedure. An intravenous anticholinergic drug may be administered to a patient undergoing ECT before the administration of anesthesia to prevent the parasympathetic nervous system–mediated bradycardia that is frequently seen early in ECT. The anticholinergic drug would therefore have to be given 1 to 2 minutes before the induction of anesthesia. The routine administration of an anticholinergic is not recommended, however, because the duration of the bradycardia is typically brief. (625)
30. Most induction agents for general anesthesia may be used to induce anesthesia in patients undergoing ECT. These include propofol (1 to 1.5 mg/kg intravenously [IV]), thiopental (1.5 to 3 mg/kg IV), and methohexital (0.5 to 1 mg/kg IV). Careful hemodynamic monitoring must accompany the induction of anesthesia for ECT and continue throughout the entire procedure. (625)
31. After the induction of anesthesia and the onset of unconsciousness, succinylcholine is often administered in subclinical doses (0.3 to 1.0 mg/kg IV) to the patient undergoing ECT. The goal of succinylcholine administration is to attenuate the effects of seizure activity on skeletal muscle, mainly the tonic-clonic muscular contractions that may cause some harm to the patient. Because the administration of succinylcholine before ECT may mask the seizure activity that results from ECT, isolation of an extremity with a tourniquet is often done before succinylcholine administration. Physiologically, this prevents the administered succinylcholine from reaching the neuromuscular junctions in the isolated extremity distal to the tourniquet. Clinically, this allows for the physician to confirm that seizure activity has resulted from the ECT by observing the muscular contractions in the isolated extremity. (625)
32. The airway of the patient undergoing ECT can be managed by hand with a mask provided the patient is not at risk for the aspiration of gastric contents. Before the induction of anesthesia the patient must be well preoxygenated. The anesthesiologist must be prepared to ventilate by hand with bag and mask using supplemental oxygen before the onset of seizure activity and also in the postseizure period, given that apnea may follow seizure activity even after the termination of the effects of succinylcholine. The anesthesiologist must have all equipment needed to intubate the trachea of the patient should it become necessary. Suction must also be available in the event that the regurgitation of gastric contents or excessive oral secretions should occur. (625-626)
33. Routine monitors must be used during an ECT procedure, including pulse oximetry, blood pressure monitoring, and a continuous electrocardiogram. In addition to these, a peripheral nerve stimulator may be useful to confirm neuromuscular blockade and the recovery of skeletal muscle from neuromuscular blockade. An electroencephalogram may also be used to confirm grand mal seizure activity during ECT. (625)
Cardiac catheterization
34. Adults may undergo cardiac catheterization for a variety of procedures, including percutaneous valve procedures, pacemaker and/or implanted cardiac defibrillators (ICD), and angioplasty with or without stent placement. Anesthesia for these cases can be very challenging given that cardiac function may be severely compromised. In addition, the cardiologist may induce fibrillation during a procedure for ICD implant to test the new device. Children undergoing cardiac catheterization for the diagnosis of congenital cardiac lesions might require anesthesia for the procedure. The anesthetic employed must not have any significant effect on existing cardiac shunts so as not to interfere with the results of the study. The administration of anesthesia may cause myocardial depression or a decrease in preload by decreasing venous return, so care must be taken by the anesthesiologist to minimize these cardiovascular changes. (626)
35. The PaCO2 that should be maintained during anesthesia for patients undergoing cardiac catheterization should be equal to the patient’s resting PaCO2 so as not to influence myocardial activity or pulmonary pressure. (626)
36. Complications that can occur as a result of cardiac catheterization include bleeding at the vascular access site, perforation of the heart wall or great vessels, embolism, cardiac dysrhythmias, and heart block. In addition, thrombosis may occur in patients with a high hematocrit. (626)
37. Anxiety during cardiac catheterization procedures may be allayed by the administration of a benzodiazepine, possibly in combination with a short-acting opioid. This may be important in patients with coexisting cardiopulmonary problems because of the potential for the exacerbation of their underlying disease by the anxiety. (626)
38. The onset of action of inhaled or injected anesthetics may be altered in patients undergoing cardiac catheterization secondary to the influence of left-to-right or right-to-left shunts that may be present in this patient population. A left-to-right shunt causes the arterial partial pressure of an inhaled anesthetic to be higher than it otherwise would be because the blood that has passed ventilated alveoli does not pass through tissues before returning to the heart. Although the clinical effect of a left-to-right shunt is negligible, a right-to-left shunt can be serious because it has the opposite effect. A right-to-left shunt causes the arterial partial pressure of an inhaled anesthetic to be lower than it otherwise would be secondary to the dilutional effect of the blood that enters the systemic circulation without passing by ventilated alveoli after returning from the tissues. The rate of induction, and subsequent onset of action, of inhaled anesthetics may therefore be slowed in the presence of a right-to-left shunt. (626)
Cardioversion
39. Elective cardioversion can be painful during the electric shock, requiring the patient to have sedation and amnesia for a brief period during the administration of the shock. This can be accomplished by the intravenous injection of a short-acting induction drug such as etomidate or propofol after preoxygenation and just before the administration of the electric shock. (626-627)
40. The patient’s airway can be maintained during anesthesia before and after the cardioversion by hand with a mask provided the patient has fasted before the procedure. Equipment that should be available to the anesthesiologist providing anesthesia for cardioversion include a bag and mask for the support of ventilation, a supplemental oxygen source, suction, and the appropriate equipment for emergent intubation of the trachea. (626-627)
41. Monitoring of blood pressure, pulse oximetry, and the electrocardiogram should be the standard during anesthesia for cardioversion. (626-627)
Extracorporeal shock wave lithotripsy
42. Extracorporeal shock wave lithotripsy (ESWL) is a noninvasive method using shock waves for the disintegration of renal stones. All lithotripters have an energy source, a system to focus the shock wave, and a system to visualize and localize the renal stone. The first lithotripters required that patients be immersed in a water bath supported in a seated position. The immersion itself altered the patient’s physiology. For example, the central venous pressure often increased and the patient often became hypotensive after being immersed in warm water. Newer lithotripters do not require a water bath, are on multifunctional tables where cystoscopy and ureteral stent placement may also take place, and provide more focused shock waves to minimize pain at the entry site. (627)
43. Shock waves in ESWL are timed with the patient’s heart rate and are triggered by the R wave on the patient’s electrocardiogram. The shock waves are subsequently delivered during the refractory period of the heart muscle, thus minimizing the risk of cardiac dysrhythmias. Despite this, atrial and ventricular premature complexes, atrial fibrillation, and supraventricular tachycardia have all been reported. (627)
44. Anesthesia is required for patients undergoing ESWL for two reasons. First, the impact of the shock waves on the patient can be painful, especially in the immersion bath model of shock wave lithotripters. Second, immobilization of the patient is important for the success of the procedure. The shock waves are focused on the renal stones, and any movement of the patient can displace the focus of the shock wave so that it is no longer effectively targeting the renal stones. (627)
45. Advantages of general anesthesia for patients undergoing ESWL include rapid onset, better patient immobilization, and the control of ventilatory parameters to minimize stone movement with respiration. (627)
46. For a patient undergoing ESWL with a regional anesthetic, a T6 sensory level is necessary to ensure patient comfort during the procedure. Unfortunately this high level of anesthesia and sympathetic nervous system blockade may be associated with hypotension. This may be exacerbated by the sitting position necessary for some lithotripters. (627)
47. Intravenous fluid administration is important during ESWL for the maintenance of an adequate urine output. This helps facilitate the passage of stones that have been disintegrated by the shock waves. (627)
48. Contraindications to ESWL include pregnancy, coagulopathy, morbid obesity, and aortic aneurysms. Patients with pacemakers may undergo ESWL provided the pacemaker is placed above the diaphragm and not in the abdomen. (627)
Dental surgery
49. Anesthesia for a dental procedure is usually required for patients who are very young or developmentally delayed and unable to tolerate the procedure. (628)
50. An anticholinergic may be administered to a patient before a dental procedure for its antisialagogue effect. (628)
51. Any of the induction agents used to induce general anesthesia may be used for patients undergoing dental procedures, including methohexital, thiopental, propofol, and etomidate. When there is no intravenous access available, and the patient is uncooperative, the anesthesiologist may use intramuscular ketamine for the induction of anesthesia. (628)
52. Tracheal intubation is usually accomplished nasally to facilitate the dentist’s ability to perform dental procedures on those patients requiring general anesthesia for the procedure. (628)
53. During the emergence from general anesthesia for dental procedures the anesthesiologist must exercise caution with regard to the patient’s airway. The patient must have intact laryngeal reflexes for the safe extubation of the trachea. Oral bleeding and secretions that occurred intraoperatively may have led to gastric distention and irritation. Ongoing oozing and secretions may also place the patient at a greater risk for laryngospasm. The removal of oropharyngeal packing must be confirmed. In the recovery area, the patient’s airway must be closely observed by personnel with the appropriate equipment for airway management, including suction. (628)
