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A discussion on mobile chest radiography and how to achieve optimum imaging is given
Diane Evans BA (Hons) Healthcare DCR (R) FAETC
Radiology Education Specialist/Manager
Liverpool Heart & Chest Hospital NHS Foundation Trust
As a Radiology Education Specialist with 25+ years experience in Cardiothoracic imaging, I have long realised how challenging mobile chest radiography can be. At Liverpool Heart & Chest Hospital (LHCH) we undertake approximately 45–50 mobile chest (and some abdominal) X-rays on a daily basis, which is a significant difference to the four to eight mobiles performed daily in a District General Hospital. Most of these mobile examinations are performed on acutely ill, postoperative patients in the Intensive Care, Postoperative Critical Care, High Dependency or Coronary Care units and often require significant adaptation of technique.1 However, it is vital that these images are of high diagnostic quality and adhere to IR(ME)R 2000 regulations.2
In this article I aim to discuss the indications and common problems for performing mobile chest radiography, the benefits of using digital mobile machines, and the importance of using the LHCH technique to achieve an optimum mobile chest image.
I also explore the hybrid examination currently utilised at LHCH in performing PA mobile chest radiographs on thoracic patients in the ward environment.
Mobile chest radiography
Mobile chest radiography performed in the antero-posterior (AP) projection has always been considered an inferior examination to the more standard PA projection which allows accurate evaluation of the cardiothoracic ratio, comparison between PA examinations, removal of the scapula shadows from the lung fields, and is performed in the erect position on full inspiration at a distance of approximately 6ft from the X-ray tube.3 The inferiority of the AP projection lies in the magnification of the heart and widening of the mediastinum, and if performed when the patient is supine, will also lead to alteration of the pulmonary vasculature. The distance from the X-ray tube will also be considerably less than 6ft, which will increase the effect of the beam divergence, that is, magnification.4 As such, the AP examination (whether erect or supine) should only be performed on critically ill patients.5
At LHCH, we employ the high kVp (125kV) technique for all PA and AP chest radiography: PA with the use of a grid and AP mainly without a grid. This deliberately lowers contrast, allows better penetration and shorter exposure times, which enables the clinician to envisage the structures of the mediastinum without losing the definition of the lung markings.6
Some of the acceptable indications for an AP mobile chest X-ray (CXR) on critical care patients at LHCH are as listed below:
Problems associated with examinations on acutely ill patients
Clearly from my experience, these patients often require considerable medical support as they may not be haemodynamically stable and have other comorbidities. These facts mean the radiographer is presented with difficulties around the safe movement of the patient and accurate detector/patient positioning in order to achieve an optimal diagnostic image.7
For example, haemodynamically unstable patients will become hypotensive when raised to an erect position; similarly, those with an IABP (Intra-Aortic Balloon Pump) in situ cannot be raised to an upright position of more than 30o due to the large sheath in the femoral artery. The sedation of these patients can also vary, leading to different levels of patient cooperation or occasional distress during the X-ray examination. Accordingly, I believe that communication and team work between the nursing, medical staff and radiographers on the Critical Care Unit is crucial in producing a diagnostic mobile CXR.
I recommend that a brief patient history should be discussed in order to ascertain what movement or position is possible for the patients and, if conscious, what movement the patient can achieve on their own. Lifting and moving protocols must be adhered to, ensuring staff and patient safety in addition to infection control protocols, which at LHCH involve the radiographers using separate personal protective equipment (PPE) for each patient and placing the detector in a disposable bag. Finally, if the radiographer follows the LHCH technique as detailed below, then the resultant image should be one of high diagnostic quality despite being a mobile AP image.
The LHCH technique: O to U approach
This is a technique that I developed over five years ago as an aid for inexperienced radiographers.
O – Observe the patient from the end of the bed space.
Observation is often underutilised and is, in my opinion, an essential clinical skill in producing a quality diagnostic image.
The radiographer should observe the following:
These questions allow the radiographer to analyse how acutely ill the patient is and whether additional help or positioning aids will be needed to perform the X-ray.
PQ – Position with Quality
Patients in critical care are often rolled onto their sides to prevent bedsores.8 If the patient is rotated in any way, even if they are erect, the image will be suboptimal, causing various anatomical structures to be projected laterally.9 Move the bed mattress to a horizontal position and the patient to a completely straight supine position. The back of the bed can then be raised to an almost erect position to allow the patient to be moved forward and the cassette/detector placed behind. If the patient is in a comfortable position, then they are more likely to remain still and cooperate during the examination.
R – Remove ECG leads/ lines/ NG tubes from chest area
Any artefact is a complete distraction to the pathology on the radiograph and all external lines/leads devices should be moved where possible.10 For example, ECG leads can be placed around the back of the patient’s neck rather than across the front of the chest.
S – Set X-ray tube (for example, caudal, cranial, canted)
It is essential that the X-ray beam is perpendicular to the patient with ideally a 5–10o caudal tilt. Observing the X-ray tube from the foot of the bed will prevent any lateral angulation, which could result in a rotated image.11
T – Test breathing, may need to reposition
Shallow inspiration is problematic in critical care patients, especially if they are conscious and in pain.12 Yet, an AP radiograph taken with minimal inspiratory effort can mimic atelectasis or infection.13 Encouraging a conscious patient to practice their inspiratory breath-hold can enable better inspiration on exposure, and allows the radiographer to assess the patient’s respiratory pattern.
U – Use timing and prep to expose to minimise breath-hold
Radiographers should always use the ‘prep’ part of the X-ray exposure to watch the patient’s inspiration and to ensure the actual exposure takes place at the optimal time.
Following this technique should alleviate the need for repeat exposures and produce excellent diagnostic images such as those below, thus also avoiding the “Sinful Six” reasons to reject a mobile AP chest image as in Figures 3–8.
Benefits of DR and the LHCH hybrid mobile technique
The benefits of DR imaging as opposed to conventional film have been well documented.14 At LHCH, we are fortunate to have procured four Carestream DRX mobile machines, with wireless detectors and wireless transfer to PACS. Images can be duplicated and windowed to visualise lines, giving two images for one radiation exposure (Figure 9).
Clinical staff appreciate this instant imaging, which enables further patient treatment or interventions to hasten the patients’ recovery. In conjunction with our main thoracic ward, we have also established a satellite X-ray room which complies with IRR 99 and IR(ME)R 2000 regulations, utilising the DRX mobile machines and a portable detector stand and stationary grid. This room is employed for this use on a daily basis, yet does not inconvenience the ward as the DRX is always removed leaving the room available for patient treatments. Our thoracic patients who are unable to leave the ward due to ECG monitoring, or patient-controlled anaesthesia (PCA) for example, can then be X-rayed in the ideal PA position regardless of chest drains and other devices (Figure 10).
We have had a very positive response since introducing this method of working, not least from the patients themselves, who appreciate not leaving the ward in order to be wheeled through a potentially draughty corridor in full sight of other clinical staff, visitors and patients. This has also released our patient transfer staff to concentrate on the CT/MRI patients to aid an efficient, but extremely busy cross-sectional service.
Indeed, for a hospital that has consistently been rated the premiere hospital for patient care over the last eight years, our DRX units have been a successful and innovative addition for the effective diagnostic imaging of our critical care patients.
It is imperative to utilise clinical skills, clear communication, correct radiographic technique and teamwork when considering mobile chest radiography on the critically ill patient. In doing so, we can achieve an optimal diagnostic bedside image for the benefit of the reporting clinician, surgeons, and ultimately for the clinical management of these acutely ill patients.