63: Sedation and Anesthesia Outside the Operating Room

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CHAPTER 63 Sedation and Anesthesia Outside the Operating Room

Mark H. Chandler, MD

1 What procedures outside the operating room require sedation or general anesthesia?

image Radiologic procedures, including computed tomography, magnetic resonance imaging (MRI), and interventional radiology; often a lack of patient cooperation necessitates the need for anesthesia assistance
image Cardiac catheterizations, insertion of implantable cardiac defibrillators, coronary arteriography, radiofrequency ablation, and cardioversions
image Surgical procedures in office settings
image Extracorporeal shock-wave lithotripsy and cystoscopy
image Upper and lower gastrointestinal endoscopy, liver biopsy, and endoscopic retrograde cholangiopancreatography
image Therapeutic radiation
image Electroconvulsive therapy
image Any number of pediatric procedures
image Invasive procedures outside the operating room, including central venous line insertion, percutaneous tracheostomy, diagnostic peritoneal lavage, thoracocentesis, pericardiocentesis, tube thoracotomy, vascular cut down, and bronchoscopy
image Emergency airway management anywhere in the hospital
image Anesthesia in military settings, including on the battlefield

2 What equipment and standards are necessary for safely conducting an anesthetic outside the operating room?

image A reliable source of oxygen with a backup supply (e.g., green oxygen E-cylinder)
image Suction
image If inhalation anesthetics are to be used, an anesthesia machine complete with scavenging capabilities
image A self-inflating hand resuscitator (Ambu) bag capable of delivering at least 90% oxygen
image Standard anesthetic drugs, airway equipment, and monitoring necessary for the intended anesthetic and the subsequent transport
image Sufficient electrical outlets, including clearly labeled emergency electrical outlets
image Illumination, including battery-powered backup illumination (not simply a laryngoscope)
image An emergency cart with a defibrillator, emergency drugs, and other equipment adequate to provide cardiopulmonary resuscitation
image Staff trained to support the anesthesiologist and transport the patient and a reliable means of two-way communication to request assistance
image Appropriate postanesthesic management

This can be remembered with the mnemonic MAO IS SAME PEST:

M = Machine (with scavenger)
A = Ambu bag
O = Oxygen (with backup supply)
I = Illumination
S = Suction
S = Space
A = Anesthetic drugs and equipment
M = Monitors
E = Electricity
P = Postanesthesia care unit
E = Emergency cart
S = Staff
T = Telephone

3 What monitoring is necessary for administration of any anesthetic, regardless of whether it is in the operating room or elsewhere?

The American Society of Anesthesiologists (ASA) has established two basic monitoring standards for all anesthesia care, regardless of where it is administered:

1 Qualified anesthesia personnel must be present during the administration of any general anesthetics, regional anesthetics, and monitored anesthesia care.
2 Oxygenation, ventilation, circulation, and temperature shall be continually evaluated in any patient undergoing an anesthetic. Specifically the ASA requires the following:

image Oxygenation: During all anesthetics a quantitative method of assessing oxygenation such as pulse oximetry shall be used. When using an anesthesia machine, an oxygen analyzer with a low oxygen concentration limit alarm shall be used.
image Ventilation: At the very least, all patients undergoing an anesthetic will be assessed for qualitative clinical signs of ventilation such as observed chest excursion, movement of the reservoir breathing bag, or auscultation of breath sounds. When an endotracheal tube or laryngeal mask airway is inserted, its correct positioning must be verified by identification of carbon dioxide in the expired gas, and carbon dioxide must be monitored with capnography or capnometry.
image Circulation: Every patient receiving anesthesia shall have an electrocardiogram (ECG) continuously displayed throughout the anesthetic and shall have blood pressure and heart rate evaluated at least every 5 minutes. In addition, every patient receiving general anesthesia will have circulatory function continually evaluated by one of the following methods: palpation of a pulse, auscultation of heart sounds, monitoring of a tracing of intra-arterial pressure, or pulse oximetry.
image Body temperature: Whenever clinically significant changes in body temperature are expected, anticipated, or suspected, a patient receiving anesthesia shall have temperature monitored.

4 How might anesthesiologists be involved in establishing standards for sedation and analgesia conducted by nonanesthesiologists?

Given the rising cost of health care and the expense of operating room time, more and more procedures are now being performed in other areas of the hospital with nonanesthesiologists administering sedation and analgesia. Although this trend may help contain costs, it poses safety concerns. Anesthesiologists possess unique knowledge and expertise regarding the use of various pharmacologic agents and in the management of patients undergoing sedation and analgesia. For these reasons anesthesiologists are frequently called on (and indeed, necessary) to help establish hospital policies and procedures regarding sedation and analgesia by nonanesthesiologists.

5 Explain conscious sedation and the continuum of depth of anesthesia

The ASA Task Force on Sedation and Analgesia by Nonanesthesiologists states that sedation and analgesia comprise a continuum of states ranging from minimal sedation to general anesthesia. Understanding the concept of the continuum of anesthesia is a critical first step for nonanesthesiologists to administer sedation and analgesia. The term conscious sedation, which is often used by nonanesthesiologists to refer to sedation administered in settings other than the operating room, is considered moderate sedation/analgesia and is defined in Table 63-1.

TABLE 63-1 Definition of General Anesthesia and Levels of Sedation/Analgesia*

image

6 What are some of the requirements for the administration of moderate sedation by nonanesthesiologists?

Not surprisingly the Joint Commission, an accrediting agency, makes no distinction between the general perioperative requirements for the administration of anesthesia in the operating room and the administration of moderate sedation such as might be delivered by nonanesthesiologists outside of the operating room. These requirements are as follows:

image A presedation or preanesthesia assessment must be performed for each patient before beginning sedation or anesthesia.
image Before undergoing anesthesia or sedation, each patient must be provided preprocedural treatment, services, and education according to his or her plan of care.
image Before administering sedating medications, a licensed independent practitioner must plan, or must concur with the plan, for sedation or anesthesia.
image A sufficient number of qualified staff must be on hand to evaluate the patient, provide sedation/anesthesia, help with the procedure, and monitor and recover the patient.
image Individuals administering sedation or anesthesia must be qualified and have credentials to manage and rescue patients at whatever level is achieved, either intentionally or unintentionally. Thus a practitioner administering deep sedation/analgesia to a patient must be prepared for the patient to slip into general anesthesia, during which time the patient may require intubation, positive-pressure ventilation, and cardiovascular stabilization.
image Each patient’s physiologic status (oxygenation, ventilation, and circulation) is monitored continuously during administration of sedation or anesthesia.
image The patient’s postprocedure physiologic status is assessed as the patient recovers from sedation or anesthesia.

7 Is it advisable to have nonanesthesiogists administer deep sedation?

Because of the possibility of slipping into a deeper level of sedation/analgesia, the ASA recommends that privileges to administer deep sedation should only be granted to practitioners who are qualified to administer general anesthesia.

8 What is dexmedetomidine and what role does it serve in moderate sedation?

Dexmedetomidine (Precedex) is a relatively new, highly selective α2-agonist that has been shown to have excellent sedative and analgesic effects. The hypnotic effect of dexmetetomidine is thought to be from hyperpolarizing nonadrenergic neurons in the locus cereleus. Among the many qualities that make dexmeditomidine an excellent sedative for moderate sedation is that it has a predictable and stable hemodynamic effect, does not cause respiratory depression, and potentiates opioids and other sedatives. Moreover, when properly dosed, sedated patients are quickly aroused and oriented after the medication is discontinued, making it an ideal sedative for neurologic procedures and in the intensive care unit. Because it is also an antisialogue, dexmedetomidine is especially favored in the setting of awake fiber-optic intubations, creating a dry field for the anesthesiologist. Its cost relative to other sedative medications has probably limited greater use.

9 Why is soluble contrast media important to anesthesiologists?

Soluble contrast media have been used for years as a tool to aid radiologists in various radiologic studies. These media contain iodine, which, with its high atomic number (53), is particularly effective at absorbing x-rays. Despite higher costs, nonionized contrast media have recently begun to replace the older, toxic, hyperosmolar contrast media, thus significantly diminishing the occurrence of side effects. Nonetheless, side effects still do occur, ranging from fairly mild to severe life-threatening anaphylactic reactions. Most often these reactions occur within the first 5 to 10 minutes following the injection of contrast media. Thus it is advisable to keep the patient under close watch for at least 20 minutes following a contrast injection.

10 Besides anaphylaxis, what is a major risk with regard to contrast media?

Renal failure is a well-documented, severe reaction long associated with soluble contrast media, particularly in patients with disorders predisposing them to renal failure such as renal disease, diabetes, jaundice, multiple myeloma, hypovolemia and diminished renal blood flow from severe cardiac or vascular disease. Adequate hydration is absolutely necessary to decrease the impact on the patient. Furthermore, the necessity of the contrast study should always be considered. Particular caution must be used in patients taking metformin since renal failure in these patients can lead to severe, life-threatening lactic acidosis. For this reason it is recommended that metformin be held for 48 hours before performing any radiologic study in which contrast media are to be used.

11 Are there specific steps that can be taken to avoid and treat contrast media reactions?

Patients who have had adverse reactions to contrast media are at greater risk for more severe reactions with subsequent exposures. This risk can be somewhat mitigated by pretreatment with 50 mg of prednisolone the night before and the morning of surgery and 50 mg of intravenous (IV) diphenhydramine immediately before the procedure. If a severe reaction occurs during the procedure, treatment is supportive: oxygen, IV steroids, and treatment of the patient’s specific reaction (e.g., IV fluid and vasopressors for severe hypotension). Because reactions such as these are possible, all radiologic suites must be completely equipped with defibrillation and resuscitation equipment.

12 What are some of the more common manifestations of the reactions to soluble contrast media?

See Table 63-2.

TABLE 63-2 Reactions to Soluble Contrast Media

Mild Moderate Life-Threatening
Nausea Vomiting Glottic edema/bronchospasm
Headache Rigors Pulmonary edema
Perception of warmth Feeling faint Life-threatening arrhythmias
Mild urticaria
Chest pain
Severe urticaria
Bronchospasm
Dyspnea
Abdominal pain
Arrhythmias

Cardiac arrest
Seizures/unconsciousness
Renal failure

13 How is radiation exposure measured?

The roentgen equivalent in humans (rem) is a measure of equivalent dose and relates the absorbed radiation dose in human tissue to the effective biologic damage of the radiation. Equivalent doses are often expressed in terms of thousandths of a rem, or mrem. The Centers for Disease Control and Prevention recommends that the general adult public limit their annual radiation dose to 5000 mrem/year. The equivalent doses from various sources are listed in Table 63-3.

TABLE 63-3 Equivalent Radiation Doses for Medical Procedures

Medical Procedures Equivalent Doses
Chest x-ray 8 mrem
Extremities x-ray 1 mrem
Dental x-ray 10 mrem
Cervical spine x-ray 22 mrem
Pelvis x-ray 44 mrem
Upper gastrointestinal series 245 mrem
Lower gastrointestinal series 405 mrem
Computed tomography (whole body) 1100 mrem
Background Sources of Radiation  
Coast-to-coast airplane roundtrip 5 mrem
Average U.S. cosmic radiation 27 mrem/year
Average U.S. terrestrial radiation 28 mrem/year
Average dose to U.S. public from all sources 360 mrem/year
Recommended Radiation Exposure Limits  
Occupational dose limit 5000 mrem/year
Occupational exposure limit for minors 500 mrem/year
Occupational exposure limits for pregnant females 500 mrem/gestation

mrem, Roentgen equivalent in humans (in thousandths).

14 How can anesthesiologists protect themselves from radiation exposure?

Most institutions abide by the ALARA philosophy when it comes to protecting their workers: radiation exposure should be kept As Low As Reasonably Achievable. There are three basic strategies to the ALARA philosophy:

image Maximize the distance to the source: Newton’s inverse square law, which applies to any point source that spreads its influence in all directions (such as light, sound, gravitational field) tells us that the intensity of the radiation at a given radius is the source strength divided by the sphere area. Or, put more plainly, the intensity (I) of radiation is inversely related to the square of distance (d) from the source:

image

Thus increasing the distance from an x-ray machine or a fluoroscope when in use can profoundly affect the intensity of radiation exposure. Six feet of air provides the equivalent protection of 9 inches of concrete or 2.5 mm of lead.

image Minimize the time of exposure: Most medical occupational radiation exposure comes from x-rays scattered by both the patient and surrounding equipment. Obviously this scatter occurs only when the machine is on. A person’s radiation exposure is directly proportional to the length of exposure; thus every reasonable effort to limit the time of exposure is beneficial.
image Use shields: Most aprons contain the equivalent of 0.25 to 0.5 mm of lead, which is effective at blocking most scattered radiation in medical settings. Uncovered areas such as the lens of the eye still run the risk of radiation exposure. Other shields such as concrete walls and portable barriers should be used whenever possible. Lead aprons should be x-rayed periodically to determine if they are still effective barriers because they are known to deteriorate with lime particularly if mishandled.

15 Define the unique problems associated with providing an anesthetic in the magnetic resonance imaging suite

Difficulties in providing a safe anesthetic in the MRI suite arise from using a powerful magnetic field. The MRI suite is often located in a remote, isolated area of the hospital. The cylindric large-bore magnet surrounding the body limits access to the patient. Ferromagnetic objects may be hurled toward the scanner, creating lethal projectiles. Large metal objects may interfere with the quality of the image. Many electronic instruments may not function normally when placed in close proximity to the magnet. Implantable ferrous magnetic devices such as older cerebrovascular clips, surgical clips, and pacemakers, are hazardous.

16 What modifications in the anesthesia machine, ventilator, and monitoring equipment must be made to provide an anesthetic in the magnetic resonance imaging suite?

All monitoring equipment is affected by the magnetic fields generated by the MRI machine. Monitors with ferromagnetic components must be located outside the magnetic field. The distance depends on the strength of the field and shielding in the suite. If the anesthesia machine, monitoring equipment, and ventilator are located several meters from the patient, long monitoring leads and ventilation tubing, with a large compressible volume in the circuit, are required, and risk of disconnection is increased. Anesthetic and monitoring equipment with nonferromagnetic components is available and allows much closer proximity to the patient and MRI machine. Many newer institutions have anesthesia machines built into the structure of the MRI suite, which allows easier and safer conduction of anesthesia. Nonferromagnetic ventilators are also available.

The lack of availability of a piped oxygen source into the MRI suite in older institutions may be a significant problem, because many standard gas cylinders are ferromagnetic and may become dangerous projectiles when introduced into the magnetic environment. Aluminum cylinders are a safe alternative, but they cannot be recharged because metal fatigue from repeated pressurization predisposes these tanks to rupture. Ferromagnetic cylinders can be distinguished from aluminum cylinders in that the whole ferromagnetic cylinder is painted with the identification color of the gas contained therein (e.g., green for oxygen, yellow for air). Aluminum cylinders have only the neck of the cylinder painted with the appropriate color.

Many MRI manufacturers now produce ECGs and respiratory monitors compatible with their equipment. Unfortunately they tend to provide limited qualitative ECGs (as for detecting ischemic changes), but for rhythm and heart rate they suffice. If such equipment is not available, modification of existing equipment is necessary because, when unshielded ferromagnetic wiring is used, the ECG demonstrates artifact, particularly in the early T waves and late ST segments, mimicking the changes seen in hyperkalemia and pericarditis. The rapidly changing magnetic fields also may cause spikes in the ECG trace, which may falsely elevate the heart rate display. Positioning the electrodes as close as possible to the center of the magnetic field, keeping the limb leads close together and in the same plane, and braiding or twisting the leads help to minimize the changes produced by the magnetic field.

When using pulse oximetry, signal distortion is also a risk; the use of nonferromagnetic probes and shielded wiring minimizes the artifact. To function properly the capnograph should be placed outside of the magnetic field. The long connecting tubing causes significant lags in alarm times. The waveform may show a prolonged upslope, even in patients with healthy lungs. However, trends and respiratory rate may be observed. Noninvasive blood pressure readings may be obtained if all ferrous connections are removed from the cuff and tubing. Invasive pressure readings may be obtained if the signal from the pressure transducer is passed through a radiofrequency filter. Dampening of the waveform is minimized by resting the transducer within 1.5 m of the patient.

KEY POINTS: Anesthesia Outside the Operating Room image

1. Anesthesiologists are increasingly asked to administer anesthesia in nontraditional settings. Regardless of where an anesthetic is administered, the same standards exist for safety, monitors, equipment, and personnel.
2. Whenever a patient undergoes an anesthetic in any medical setting, qualified anesthesia personnel must be present, and oxygenation, ventilation, circulation, and temperature must be monitored.
3. Those medical professionals who administer moderate sedation (“conscious sedation”) must be well trained, prepared to evaluate and monitor their patient closely, and ready to manage their patient if their sedation and analgesia become deeper than intended.
4. Dexmedetomidine is a highly selective α2-agonist that has been shown to have excellent sedative and analgesic effects in a variety of settings.
5. Soluble contrast media can cause a whole range of reactions in patients, from the very mild such as urticaria and headaches to the severe and life threatening such as anaphylaxis, renal failure, and lactic acidosis.
6. Medical professionals keep their radiation exposure as low as reasonably achievable (ALARA), and below the CDC’s recommendation of less than 5000 mrem/year, by maximizing their distance to x-ray and fluoroscopes when in use, minimizing their time of exposure, and using shields.
7. Administering anesthesia to a patient undergoing an MRI poses several challenges, not the least of which is that any ferromagnetic object can become a projectile and that most monitors are affected by the powerful magnetic field.

Websites image

American Society of Anesthesiologists

http://www.asahq.org

American Society of Anesthesiologists

http://www.asahq.org/publicationsAndServices/standards/20.pdf

American Society of Anesthesiologists

http://www.asahq.org/publicationsAndServices/standards/02.pdf

Radiation Information Network of Idaho State University

http://www.physics.isu.edu/radinf

SUGGESTED READINGS

1. American Society of Anesthesiologists: Guidelines for nonoperating room anesthetizing locations (last amended on October 15). Park Ridge, Ill.

2. American Society of Anesthesiologists. Task Force on Sedation and Analgesia by Nonanesthesiologists: practice guidelines for sedation and analgesia by non-anesthesiologists. Anesthesiology. 2002;96:1004-1017.

3. Carollo D.S., Nossaman B.D., Ramadhyani U. Dexmedetomidine: a review of clinical applications. Curr Opin Anesthesiol. 2008;21:457-461.

4. Comprehensive Accreditation Manual for Hospitals: The Official Handbook, effective January 2009, Joint Commission on Accreditation of Healthcare Organizations, pp PC 17–18, RC 5–7, RI 5

5. Kotob F., Twersky R.S. Anesthesia outside the operating room: general overview and monitoring standards. Int Anesthesiol Clin. 2003;41:1-15.

6. MacKenzie R.A., Southom P., Stensrud P.E. Anesthesia at remote locations. In: Miller R.D., editor. Anesthesia. ed 5. New York: Churchill Livingstone; 2000:2241-2269.

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