Chapter 17 – Radiology in the Austere or Disaster Environment

Abstract

Radiology in the austere environment is an evolving entity. The extent to which the anesthesiologist will have to be aware of issues related to radiology is highly dependent upon the environment in which he or she will work. Capabilities may be limited to a portable ultrasound (US) carried by the provider in a backpack with an imaging screen the size of a modern smartphone to full magnetic resonance imaging (MRI) capabilities that may be seen in higher echelons of care, typically in a military setting. Each modality has its uses and limitations for the anesthesiologist and awareness of the capabilities, safety issues, and limitations of each modality allows maximal extraction of imaging in providing quality care in the “disaster” or austere environment. This chapter will focus on issues related to radiation safety in plain radiography (X-ray) and fluoroscopy, radiation protection, US familiarization, and image quality, and some issues surrounding computed tomography (CT) and MRI.

Chapter 17 Radiology in the Austere or Disaster Environment

David Besachio and Daniel Sutton

Radiation Safety

In recent years, greater attention has been placed on the importance of radiation safety within the radiology community.¹ Ionizing radiation refers to radiation that is produced from displacement of an electron from the outer shell of an atom. In biological systems, this can result in the formation of free radicals, subsequent damage to deoxyribonucleic acid (DNA), and resultant disease. In the recent past, the greatest amount of ionizing radiation any typical individual received was due to natural background sources (e.g. radon, solar). In the United States, the population dose of ionizing radiation is approximately the same as that from background sources.² While radiation-related injuries are rare, they have been reported with both fluoroscopy and CT in recent years.³ Techniques that utilize ionizing radiation include X-ray, fluoroscopy, and CT. Radiation dose is often dependent on the use of proper technique with each of these modalities. The essence of radiation protection of which the anesthesiologist should be aware can be simplified to understanding three basic principles: time, distance, and shielding.

With any modality that utilizes ionizing radiation, the amount of time that the patient or anesthesiologist is exposed will be proportional to the total radiation dose received. While fluoroscopy time is rarely under control of the anesthesiologist, he or she can influence the total exposure time received by the entire team and the patient, especially in the trauma setting, through cooperation with the radiologic technician in ensuring appropriate patient positioning, which will ultimately minimize the need for repeat exposures due to poor positioning.

Radiation exposure decreases with the square of the distance from the ionizing radiation source (i.e. the inverse square law). Understanding this principle is one of the greatest single methods by which the anesthesiologist can minimize radiation dose to themselves or their team. While the anesthesiologist may not be able to completely leave their patient during radiation exposure, even a small amount of distance separating them from the radiation source will markedly decrease dose.

Shielding is a more obvious principle of which most anesthesiologists are aware. Wearing protective lead aprons is also a method by which radiation exposure may be minimized. Keep in mind that much of the dose received by health care providers around a patient being radiated is not from the main beam generated by the X-ray machine but rather by scatter radiation emanating from the patient. The greatest dose therefore occurs at the patient level indicating the best protection practice for the anesthesiologist is to shield the most radiosensitive organs: the thyroid and gonads. A thyroid shield and lead apron covering the anesthesiologist to the knee level is necessary .

Modalities

A full discussion on imaging interpretation for all modalities is beyond the scope of this text; however, some basic imaging safety, interpretation pearls, and techniques are discussed below.

Radiography

Radiography is one of the more readily available modalities seen in austere environments and disaster scenarios. Generator-powered portable radiographic units, while rudimentary, are nevertheless effective and widely available (Figure 17.1). These units are typically operated by a technician with working knowledge of appropriate positioning of the unit and patient for various exams to ensure the best radiographic image. Most modern radiographic units require little modification of technique due to systems-wide availability of automatic exposure settings. In general, if visualization is limited, increasing the kilovoltage potential and/or milliampere-seconds may improve image penetration and/or quality, albeit at the expense of increased patient dose and potential provider exposure .

Figure 17.1 Portable radiographic unit.

(image courtesy of Commander David Besachio, Medical Corps, US Navy)

The most common imaging modality used by the anesthesiologist will be the chest radiograph. Upright posterior-anterior and lateral (the ubiquitous “PA and Lat”) imaging is superior to supine chest imaging (the “portable AP”) for diagnostic purposes; however, portable imaging is typically adequate for evaluation of supportive tube and line placement (Figure 17.2). Many portable X-ray units will have a digital screen on the unit. Such screens allow the technician to determine the adequacy of their technique with respect to exposure and anatomy imaged; as these screens do not contain the resolution necessary to fully identify important abnormalities, they are not intended for use for full diagnostic interpretation. Entities such as small pneumothoraces may be missed when using these monitors for interpretation. The concern over aspiration pneumonitis during a procedure is often raised and typically demonstrates increased lung density in the mid to upper lungs on supine images as the triggering event typically occurs in the supine position leading to involvement of the superior segments of the lower lobes or inferior portions of the upper lobes.⁴