Point of care ultrasonography(POCUS) is the term used when non-radiologist medical staff use a portable ultrasound at the bedside as an adjunct to their clinical examination. Point of care ultrasound use is well established in Emergency and Intensive Care Medicine where it is used to answer a wide variety of diagnostic questions such as determining if a pneumothorax is present or if there is evidence of severe right hear strain suggestive a pulmonary embolism. In palliative medicine, point of care ultrasonography is less well established although it is frequently used for confirming the diagnosis and aiding the drainage of ascites.
Principles of point of care ultrasound
Basic physics
An ultrasound works by sending out very high frequency sound waves that are inaudible to human ears and recording and displaying them as they rebound. When displaying this on a screen white is used to show when sound rebounds back and black is used to show when sound does not rebound.
Various factors influence what the way ultrasound travels and rebounds and therefore the way the image looks, including:
Sound waves travel at different speeds through different substances(e.g. sound travels at a different speed through fat than it does through muscle
Sound waves tend to reflect when they reach the interface between two different materials(e.g. most of the ultrasound wave gets reflected when it hits a calculus)
Basic terminology
Some of the terminology that is used to describe the ultrasound image displayed include:
Anechoic = black
Hypo-echoic = dark
Hyper-echoic = bright, white
Homogenous = uniform echo pattern
Heterogenous = mixed echo pattern
Some basic rules of thumb are:
Fluid(e.g. ascites) is anechoic
Air(e.g. bowel gas) is heterogenously hyperechoic
Calcium and bone is very hyperechoic but as sound does not pass through calcium everything deep to this remains black
Organs(e.g. liver) are relatively homogenous in their echotexture
Point of care ultrasound is useful for non-radiologists to be able to answer specific focussed questions at the bedside. It can be used as an adjunct to clinical examination. It is not a replacement for formal imaging in a radiology department. Common uses of point of care ultrasound in palliative medicine include:
Confirmation of ascites and aiding drainage of it
Confirmation of a pleural effusion and aiding drainage of it
Measuring the bladder volume where urinary retention is thought to be a problem
Additional uses of point of care ultrasound in emergency and critical medicine can be translated for use in the palliative medicine setting with suitable basic training including:
Identifying dilated, fluid-filled loops of small bowel consistent with small bowel obstruction
Identifying hydronephrosis in patients with an obstructive uropathy
Identifying pericardial fluid(suggesting a malignant effusion) or severe right heart strain(suggesting a massive pulmonary embolism) in a patient who suddenly deteriorates with hypotension or dyspnoea
Identifying features of pulmonary oedema in a dyspnoeic patient
Measuring the diameter of the optic nerve in patients with suspected raised intracranial pressure
Principles of point of care ultrasound