Importance of Communication

Remote locations are structured differently from the typical operating room, but clear communication is prudent for efficient and safe practice in either site. With clear communication, the actions of anesthesia personnel can be integrated with those of the procedural team involved in the NORA intervention. The anesthesia provider should have a detailed plan for communicating with more centrally located anesthesia colleagues and technicians, especially when help is required urgently. For instance, an unexpected difficult airway can be especially challenging because of the remote nature of many NORA locations. Additional anesthesia personnel and resources should be immediately available if needed. Sometimes the anesthesia providers in NORA locations feel isolated from the facilities available to operating room personnel. The lack of mutual experience and vocabulary presents challenges for anesthesia providers and other staff working in NORA locations. Anesthesia providers and proceduralists should have a mutual understanding of the specifics and challenges in the procedures as well as in medical care. Anesthesia providers working in an unfamiliar remote location must keep track of the identity and role of personnel participating in the interventional procedure or patient care. During times when the anesthesia provider may need experienced medical assistance (e.g., tracheal intubation, placement of an invasive monitor, or intravenous access), the availability of qualified staff members must be identified. Readily available preoperative documents for all patients in remote locations must include the attending proceduralist’s patient history and physical examination. Patient arrival and check-in arrangements should be similar to those for patients undergoing procedures in a traditional operating room setting.

Standard of Care and Equipment

Anesthesia care provided in remote locations must adhere to the same standards as the operating room. The American Society of Anesthesiologists (ASA) has issued a Statement on Nonoperating Room Anesthetizing Locations that posts minimal guidelines for NORA procedures. In summary, these guidelines recommend adequate monitoring capabilities, the means to deliver supplemental oxygen via a face mask with positive-pressure ventilation, the availability of suction, the equipment for providing controlled mechanical ventilation, an adequate supply of anesthetic drugs and ancillary equipment, and supplemental lighting for procedures that involve darkness. Although portable anesthesia machines should be placed in close proximity to the patient to facilitate breathing circuit connections, this is not always possible owing to the presence of equipment such as fluoroscopy “C-arms.”

If anesthetic gases are to be used, scavenging must be sufficient to ensure that trace amounts are below the upper limits set by the Occupational Safety and Health Administration (OSHA). Remote locations frequently involve additional hazards, such as exposure to radiation, loud sound levels, and heavy mechanical equipment. Advance preparation should be made to have all needed equipment available, such as lead aprons, portable lead-glass shields, and earplugs. At the end of the procedure one may often travel distances longer than the usual distance to the postanesthesia care unit or other patient units. So that patients can be safely and expeditiously transported to a recovery area, remote locations should always have available sufficient supplies of supplemental oxygen, transport monitors, and elevator and passageway keys. The anesthesia provider should always know the location of the nearest defibrillator, fire extinguisher, gas shutoff valves, and exits.

Radiation Safety Practices

Ionizing radiation and radiation safety issues are often encountered in these locations. Radiation intensity and exposure decrease with the inverse square of the distance from the emitting source. Frequently, the anesthesia provider can be located immediately behind a movable lead-glass screen. Regardless of whether this is possible or not, the anesthesia provider should wear a lead apron and a lead thyroid shield and remain at least 1 to 2 m from the radiation source. A 2011 study also highlighted the importance of eye protection for anesthesia providers working for a significant time in the radiology suite. Clear communication between the radiology and anesthesia teams is crucial for limiting radiation exposure.

Monitoring the Radiation Dose

Anesthesia providers, like all other health care workers who are at risk for radiation exposure, can monitor their monthly dosage by wearing radiation exposure badges. The physics unit of measurement for a biologic radiation dose is the sievert (Sv): 100 rem = 1 Sv. Because some types of ionizing radiation are more injurious than others, the biologic radiation dose is a product of the type-specific radiation weighting factor (or “quality factor”) and the ionizing energy absorbed per gram of tissue. Radiation exposure can be monitored with one or more film badges. In the United States, the average annual dose from cosmic rays and naturally occurring radioactive materials is about 3 mSv (300 mrem). Patients undergoing a chest radiograph receive a dose of 0.04 mSv, whereas those undergoing a computed tomography (CT) scan of the head receive 2 mSv. Federal guidelines set a limit of 50 mSv for the maximum annual occupational dose.

Adverse Reactions to Contrast Materials

Contrast materials are used in more than 10 million diagnostic radiology procedures performed each year. In 1990, fatal adverse reactions after the intravenous administration of contrast media were estimated to occur approximately once every 100,000 procedures, whereas serious adverse reactions were estimated to occur 0.2% of the time with ionic materials and 0.4% of the time with low osmolarity materials. Radiocontrast materials can produce anaphylactoid reactions in sensitive patients, and such reactions necessitate aggressive intervention, including the administration of oxygen, intravenous fluids, and epinephrine, with epinephrine being the essential component of therapy (also see Chapter 45 ).

Adverse drug reactions are more common after the injection of iodinated contrast agents (used for x-ray examinations such as CT) than after gadolinium contrast agents (used for magnetic resonance imaging [MRI]). The signs and symptoms of anaphylactoid reactions can be mild (nausea, pruritus, diaphoresis), moderate (faintness, emesis, urticaria, laryngeal edema, bronchospasm), or severe (seizures, hypotensive shock, laryngeal edema, respiratory distress, cardiac arrest) (also see Chapter 45 ). Prophylaxis against anaphylactoid reactions is directed against the massive vasodilation that results from mast cell and basophil release of inflammatory cytokines such as histamine, serotonin, and bradykinin. The main approach to prophylaxis is steroid and antihistamine administration on the night before and the morning of the procedure. A typical regimen for a 70-kg adult is 40 mg prednisone, 20 mg famotidine, and 50 mg diphenhydramine. Patients undergoing contrast procedures usually have induced diuresis from the intravenous osmotic load presented by the contrast agent. In this regard, adequate hydration of these patients is important to prevent aggravation of coexisting hypovolemia or azotemia. Chemotoxic reactions to contrast media are typically dose-dependent (unlike anaphylactoid and anaphylactic reactions) and related to osmolarity and ionic strength of the contrast agent.

Intravenous contrast material is often administered for radiologic imaging. A serious adverse reaction called nephrogenic systemic fibrosis (NSF) can occur after exposure to gadolinium-based MRI contrast agents. In NSF there is fibrosis of the skin, connective tissue, and sometimes internal organs. The severity of NSF can range from mild to severe and it can also be fatal. However, NSF apparently occurs only when severe renal impairment (e.g., dialysis-dependent renal failure) also exists. Anesthesia providers should not casually administer gadolinium-containing MRI contrast agent to patients with renal disease.

MRI Safety Considerations

Although ionizing radiation is not a safety issue because no x-rays or radioactive substances are involved, other safety issues are prominent in the magnet suite. Hearing loss may occur from high sound levels during the scan. Electrical burns can occur if incompatible monitoring equipment is attached to the patient. Similarly, patients with incompatible implanted devices or ferromagnetic material should never be placed inside a large magnetic field as device heating and malfunction can result in patient injury. Finally, missile injury can occur if ferromagnetic objects are brought within the vicinity of the magnetic field.

Objects in the magnet room need to be both MRI safe and MRI compatible. The term “MR conditional” was defined by the American Society for Testing and Materials to describe an item that poses no known hazards in a specified MRI environment (with specifications that include the static magnetic field strength and spatial gradient field generated by a particular MRI model). Before an MRI scan is started, the anesthesia provider should ensure the patient has been screened and cleared by MRI technicians responsible for knowing that the patient’s body does not contain susceptible metal objects such as incompatible orthopedic hardware, cardiac implantable electronic devices (CIEDs), wire-reinforced epidural catheters, or a pulmonary artery catheter with a temperature wire. Pulse oximetry is essential during MRI scans, and only an MRI-compatible fiberoptic pulse oximeter should be used. Patient burns can result at the point of attachment if one uses a standard pulse oximeter. Similar concerns pertain to any other monitoring or management devices that make actual or potential patient contact.

Missile injury in an MRI suite is a serious and life-threatening risk. The superconducting electrical currents that generate an MRI scanner’s large magnetic field are always “on.” Therefore, MRI scanners are always surrounded by large magnetic field gradients (up to 6 m away). Magnetic field gradients can pull metallic objects into the magnet with alarming speed and force. Certain metals such as nickel and cobalt are dangerous because they are magnetic, whereas other metals such as aluminum, titanium, copper, and silver do not pose a missile danger. These metals are used to make MRI-compatible intravenous poles, fixation devices, and nonmagnetic anesthesia machines. MRI-compatible intravenous infusion pumps are clinically available. If one must bring susceptible metal items such as infusion pumps into the MRI magnet room, they should be safely located and fixed, preferably bolted to a wall or floor. The additional equipment should be placed and verified as secure before the patient enters the MRI scanner. In the event that an object is pulled into the magnet causing patient injury and equipment damage, the superconducting magnet can be turned off immediately. This process, called quenching , should only be performed by MRI technicians. The superconducting magnet of an MRI operates at cryogenic temperatures near absolute zero and requires coolant (cryogen) such as liquid helium to maintain the low temperature. The quenching process involves a rise in temperature of the superconducting magnet with escape of cryogen into a venting system outside the MRI room. However, cryogen can escape into the MRI room and displace oxygen, which can cause cold injury and asphyxiation.

Monitoring Issues in MRI Suites

Many anesthesia providers prefer to be outside the magnet room during the scan. This practice is acceptable as long as the provider (1) has access to all vital sign monitor displays and (2) can view the patient through a window or video camera. Critically ill patients undergoing MRI may require an arterial line for blood pressure monitoring. If the pressure transducer is classified as “MR conditional” for the particular MRI scanner, then it may be used during the procedure along with an MRI-compatible pressure cable and monitoring system. Otherwise, long lengths of pressure tubing must be added so that pressure transducers and their electrical cables can be located far from the magnet, preferably outside the magnet room. The radiofrequency pulse from an MRI can cause a pressure transducer to generate artifactual spikes. This can lead to erroneously high arterial blood pressure readings that could mislead the anesthesia provider. Visual inspection of the waveform allows rapid detection of this artifact. All arterial and venous line stopcocks should be capped so that hemorrhage will not occur if the stopcock is inadvertently manipulated.

Compatible Equipment

The MRI-compatible equipment that goes into the magnet room functions as a second anesthesia workstation. Although suction, physiologic monitoring, and mechanical ventilation must be possible inside the magnet room, a primary anesthesia workstation must be located just outside the magnet room. If a potentially life-threatening problem arises, the patient must be promptly transferred from the scanner room to the primary anesthesia workstation so that optimal care and additional help can be provided.

Physiologic Monitoring

The ASA Standards of Basic Anesthetic Monitoring (also see Chapter 20 ) are applicable to all noninvasive imaging procedures. Anesthesia providers commonly use specially constructed nasal cannulas that have an integrated CO ₂ sampling line. Capnography can provide the respiratory rate and pattern, as well as the end-tidal CO ₂ concentration, although readings are more prone to artifacts in a nonintubated patient. If capnography is not possible, ventilation must be assessed by continuous visual inspection, auscultation, or both.

Oxygen Administration

Supplemental oxygen via a nasal cannula should come from a dedicated flowmeter instead of the anesthesia machine common gas outlet. This approach permits more rapid deployment of the anesthesia machine breathing circuit for delivering face mask oxygen or positive-pressure ventilation if the patient develops hypoventilation, hypoxemia, or apnea. For procedures of long duration, humidified oxygen should be given via nasal cannula to promote patient comfort by minimizing drying of the nasal and pharyngeal passages. Certain patients, including infants and small children, will not tolerate a nasal cannula but can receive oxygen with a “blow-by” technique.

Pharmacologically Induced Sedation

Many medications can be used to provide sedation for imaging procedures (also see Chapter 8, Chapter 9, Chapter 14 ). For example, sedation can usually be managed successfully with a continuous propofol infusion, with or without supplemental intravenous opioids or benzodiazepines (or both). For brief procedures, a small dose of a rapid-onset, short-acting opioid such as remifentanil or alfentanil is often an appropriate selection. Dexmedetomidine is another useful drug, primarily in procedures lasting more than an hour. Because dexmedetomidine has less frequent risk of respiratory depression compared to propofol, it is especially useful for patients with severe pulmonary hypertension, or those who require frequent assessment of mental status. Because dexmedetomidine tends to decrease systemic arterial blood pressure and has relatively long lasting duration, its use might require intravenous vasopressor support. Dexmedetomidine should be used cautiously in patients undergoing procedures that require arterial blood pressure to remain at baseline values or that require induced hypertension. Patients with atherosclerotic lesions in cerebral, cardiac, or renal arteries, as well as patients with brain or spinal cord compression from tumors, are particularly vulnerable.

Management of Anesthesia for Computed Tomography

CT is often used for intracranial imaging and for studies of the thorax and abdomen. Because CT is painless, noninvasive, and generally of short duration, adult patients undergoing elective diagnostic scans rarely require more than emotional support. In addition, the bore of the CT scan is much more open than an MRI, so claustrophobia is rarely an issue. CT scanning is a crucial diagnostic tool in several acute settings, including traumatic injury (head and abdominal), acute stroke, and acute altered mental status of unknown cause. CT scanning is also used for urgent assessments of gastrointestinal integrity in critically ill patients in the intensive care unit (ICU), who may require complex care during ICU transport. Sedation or general anesthesia is often essential for such patients, as well as for children and adults who have difficulty remaining motionless.

Unlike MRI, the concerns about magnetic fields are not present for CT scanning; however, the anesthesia provider is at risk for exposure to ionizing radiation. During the CT scan, the anesthesia provider should remain behind radiation shielding while the mechanized table moves the patient through the scanner. In addition to patient medical issues, complications during a CT scan could include disconnection of oxygen tubing or breathing circuits, inadvertent removal of intravenous catheters, and disconnection of monitors.

Management of Anesthesia for MRI

For pediatric patients (also see Chapter 34 ), a common technique consists of (1) inhaled induction of anesthesia with sevoflurane, (2) placement of intravenous catheter, (3) intravenous infusion of propofol, and (4) either nasal cannula, laryngeal mask airway, or endotracheal tube for airway management, based on patient comorbid conditions. For adults who require general anesthesia for MRI, the location of planned imaging may influence airway management choice. For example, a patient with a laryngeal mask airway may still have slight airway obstruction resulting in unacceptable motion artifact during brain MRI scan, which would not occur with an endotracheal tube.

Certain MRI image sequences (e.g., fluid-attenuated inversion recovery [FLAIR]) are influenced by the patient’s oxygenation, which is managed by the anesthesia provider. Hyperoxia can increase signal intensity in brain cerebrospinal fluid, so the radiologist may request a decrease in the inspired oxygen concentration and must interpret the MRI scan accordingly.