Utility of the routine daily chest Xray

This chapter addresses some basic administrative and functional answers to questions raised by Section 2.1.20, "Radiology in Intensive Care",  from the CICM Second Part General Exam Syllabus (First Edition). Specifically, it deals with indications, advantages, disadvantages, complications, risks and the relevant guidelines and evidence for chest X-rays in the ICU. 

Though the practice is almost universally acknowledged as pointless, routine chest Xrays are still ordered for all ICU patients in many ICUs, largely because the most junior member of staff is left to do the ordering, and the issue is never fully discussed with them. Having once been the aforementioned junior member, the author recalls the experience as a mixture of confusion and terror; at no stage was the indication for any of the Xrays explained to him, and frequently the request form ended up being filled out with a caricatured picture of the chest, a question mark inscribed in each lung field. Anyway. Question 4 from the second paper of 2007 and Question 12 from the first paper of 2001 were both of the "critically evaluate" format, asking the candidates to review the advantages and disadvantages of daily radiotherapy for ICU patients. The LITFL entry on the subject is both brief and information-dense.

Rationale for routine CXRs:

• Critically ill patients may have rapidly evolving thoracic pathology
• This pathology may not be easily evaluated by clinical means
• Mechanically ventilated patients are especially prone to rapid changes
• Routine radiography may yield a management-influencing surveillance benefit

Advantages:

• Regular review of line and tube position
• Regular review of fluid balance as observed by pulmonary interstitial water
• Surveillance for VAP
• Assessment of the readiness for extubation
• Observation of changes in lung parenchyma in response to treatment (eg. resolution of pneumonia)

Arguments for safety

• The dose of radiation is very small: 0.1-0.15mSv, comparable to about 10 days of exposure to the natural background (Leppek et al, 1998)
• The risk from such a dose is minute. The additional individual cancer risk (even from multiple exposures) ranges between 0.01% and 0.07%.
• The risk from a missed misplaced tube or line is massive, as it could be a lifethreatening complication.

Disadvantages:

• Radiation exposure from one X-ray is minute. However:
  • Each patient is likely to get several Xrays
  • Each patient is every day  exposed to the scatter radiation from Xrays being performed on all the other patients in the unit
  • The total additional lifelong mortality risk from cancer is additive with the mortality risk from whatever has put the patient into the ICU. It is therefore a preventable influence on ICU-related mortality, and we should want to reduce that.
• Risk of tube/line dislodgement with positioning is non-zero.
• Lack of association between radiological appearance and physiological performance
• Counter-argument to safety: if the line or tube dislodgement were clinically relevant, you would have picked it up without the Xray (eg. a leak would be occurring). Certainly, there is a lot of tube and line adjustment which goes on in the ICU - pull it out 2cm, push it in 1cm - but is this clinically relevant? There is no evidence such obsessive manipulation is associated with any sort of survival advantage.

Evidence and recommendations:

• Only about 7% of CXRs result in a change in management
• In another study, only 2.3% of CXRs revealed new pathology
• 2012 meta-analysis: no harm associated with "restrictive" use of CXRs
• Americal College of Radiology recommends they are performed for clinical indications only. However, "it is appropriate to obtain a chest radiograph after placement of an endotracheal tube, central venous line, Swan-Ganz catheter, nasogastric tube, feeding tube, or chest tube".