Liverpool Heart & Chest Hospital Shares their “O to U Approach” for capturing high quality diagnostic AP images
Mobile chest X-rays performed in the antero-posterior (AP) projection has always been considered an inferior examination to the more standard posterior-aneterior (PA) projection. However, for critically ill patients, at times an AP image is the only option.
By applying a structured technique – our O to U Approach – and with the aid of our four CARESTREAM DRX-Revolution mobile X-ray machines, we are able to achieve an optimum mobile chest image.
At Liverpool Heart & Chest Hospital (LHCH) we undertake approximately 45-50 mobile chest (and some abdominal) x-rays on a daily basis. Most of these mobile examinations are performed on acutely ill, post-operative patients in Intensive Care, Post Operative Critical Care, High Dependency Unit or Coronary Care 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.
Benefits of mobile chest X-rays in thoracic and cardiac care
The PA projection is considered to be the ‘gold standard’ examination. It reduces cardiac magnification, and the risk of producing a lordotic image as the patient is unlikely to lean backward. The PA projection 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 6 feet from the x-ray tube (2).
The inferiority of the AP projection lies in the magnification of the heart and widening of the mediastinum. If performed when the patient is supine, it will also lead to alteration of the pulmonary vasculature whilst the distance from the xray tube will also be considerably less than 6 feet, which will increase the effect of the beam divergence (ie magnification (3).)
As such, the AP examination (whether erect or supine) should only be performed on critically ill patients (4). 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 and 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 (5).
The LHCH technique to achieve an optimum mobile chest image
At LHCH, we have developed an “O to U” approach that, if followed by the radiographer, should result in an image of high diagnostic quality despite being a mobile Antero-Posterior image.
O – Observe the patient from the end of the bed space
Observation is often under-utilised and is, in my opinion, an essential clinical skill in producing a quality diagnostic image. The radiographer should observe:
- The patient’s position in the bed to establish if they are rotated. Hip and shoulder positions are vital to obtain a ‘straight’ (not rotated) patient. Can they be moved into the erect position?
- Any lines/devices/ECG leads – what is the patient attached to?
- The patient’s colour, state of mental awareness/conscious level (can they follow a command), what is their respiratory rate?
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 (6). If the patient is rotated, even if they are erect, the image will be sub-optimal, causing various anatomical structures to be projected laterally (7).
Move the bed mattress to horizontal, 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 co-operate 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 (8). 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 eg caudal, cranial, canted
It is essential that the x-ray beam is perpendicular to the detector. Observing the x-ray tube from the foot of the bed will prevent any lateral angulation that could result in a rotated image (9).
T – Test breathing; reposition as needed
Shallow inspiration is problematic in critical care patients, especially if they are conscious and in pain (10). Yet, an AP radiograph taken with minimal inspiratory effort can mimic atelectasis or infection (11). 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’
The preparation of depressing the exposure switch to commence anode rotation prior to the actual exposure will minimise breathhold. Radiographers should always use the ‘prep’ part of the X-ray exposure to watch the patient’s inspiration and to ensure that the actual exposure takes place at the optimal time. Following this technique should alleviate the need for repeat exposures and produce excellent diagnostic images.
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.
Mobility of DRX-Revolution enables PA exams in satellite room
In conjunction with our main thoracic ward, we have also established a satellite xray room that complies with IRR 99 and IR(ME)R 2000 regulations. The room is equipped with the CARESTREAM DRX-Revolution mobile machines, a portable detector stand, and stationary grid. This room is employed for use on a daily basis, yet does not inconvenience the ward as the Carestream DRX-Revolution 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 anesthesia (PCA) for example, can then be X-rayed in the ideal PA position regardless of chest drains and other devices. Without the advantage of the satellite room, these patients would be x-rayed at their bedsides in the sub-optimal AP position.
We have had a very positive response to this way of working. The patients especially appreciate not having to leave the ward and be wheeled through a potentially draughty corridor in full view 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 Carestream DRX-Revolution mobile xray units have been a successful and innovative addition for the effective diagnostic imaging of our critical care patients.
Learn more about our work in thoracic and cardiac imaging in the white paper mobile-thoracic-cardiac-white-paper
Diane Evans is a Radiology Education Specialist at Liverpool Heart and Chest Hospital NHS Foundation Trust in the United Kingdom. She has more than 25 years experience in cardiothoracic imaging.
1 Clark, K. (2005) Clark’s positioning in radiography (edited by S. Whiteley et al.) London: Hodder Arnold Chapter 12
2 G De Lacey et al. (2008)The Chest X-ray: A survival Guide. Saunders Elsevier Chapter 1
4 Grainger & Allison (2001) Diagnostic Radiology Vol 1. The post-operativecritically ill patient. Chapter 1
5 Interpreting the CXR (2010) Scion Publishing, Stephen Ellis Chapter 1
6 Ousey, K (2005) Pressure Area Care (Essential Clinical Skills for Nurses. Blackwell Chapter 7 G De Lacey et al. (2008)The Chest X-ray: A survival Guide. Saunders
Elsevier Chapter 1
8 Clark, K. (2005) Clark’s positioning in radiography (edited by S. Whiteley et al.) London: Hodder Arnold Chapter 12
9 G De Lacey et al. (2008)The Chest X-ray: A survival Guide. Saunders Elsevier Chapter 1
10 G De Lacey et al. (2008)The Chest X-ray: A survival Guide. Saunders Elsevier Chapter 1
11 Grainger & Allison (2001) Diagnostic Radiology Vol 1. The post-operative critically ill patient. Chapter 1