Management

Ultrasonography in ICU

Today's intensivist should have a thorough knowledge of anatomy and instrumentation and adequate training in performing and interpreting ultrasound

"A generation of portable, battery operated, cheap and light weight easy-to-carry ultrasound devices are available, which make this modality most useful in ICU, emergency department and operation theatres" - Dr Swaraj Garg HOD, Department of Anaesthesia Pushpanjali Crosslay Hospital NCR

Critically-ill patients are subjected to a variety of diagnostic and therapeutic procedures. It is desirable to make these interventions as timely, safe and effective as possible. Ultrasonography has become an invaluable tool in the management of critically ill patients. Its safety and portability allows for its use at the bedside to provide rapid and detailed information regarding the cardiovascular system and the anatomy and function of certain internal organs. At times it provides more valuable information about cardiac function as that derived from invasive haemodynamic monitoring. It can also be used by the physician for assessment of the pleural and intra-abdominal spaces and for the safe performance of a number of invasive procedures. It is of great advantage to the critically ill patient as the portability of examination prevents many potential complications that are known to occur during transport of the patient out of critical care unit. Ultrasonography also prevents the patient from the risk of harmful radiations and potentially toxic contrast reactions.

A brief synopsis of various diagnostic and therapeutic interventions by ultrasonography in ICU is discussed here.

Useful Tool

Ultrasound guidance helps in placing central venous cannula especially in the internal jugular vein accurately and safely even in hypotensive patients. It reduces the risk of complications like haematoma, injury to neighbouring structures and pneumothorax. It improves the rate of successful placement on the first try, ultimately reducing the morbidity, infection, need of antibiotics, length of stay and ultimatly the cost. Ultrasound guided central line placement should be considered in patients in whom cannulation is expected to be difficult, like in patients with masked surface landmarks when there are limited access sites for attempts, previous history of difficult catheterisation or complications, uncontrolled coagulopathies or inability of the patient to lie supine. It also helps in identifying any abnormal anatomy of the vessel. Two dimensional ultrasound guidance has proved to be a useful adjunct to arterial catheter insertion as well.

Role of TTE

In an ICU set up, Trans-Thoracic Echocardiography (TTE) quickly and effectively identifies cardiac pathologies including mitral and aortic valve function and pericardial fluid. It helps in assessing left ventricular function in patients who have unexplained haemodynamic instability. Assessing right and left ventricular function is integral to the management as is assessment of the pericardial space to rule out presence of a tamponade. TTE helps in assessment of patient's volemic status by examining the biventricular dynamics and right atrial pressure.

Ultrasound helps in diagnosis of intra-thoracic and intra-abdominal fluid collections. It helps in guiding delicate procedures of thoraco-centasis and para-centasis which are done otherwise blindly in an ICU set up.

General indications for performance of an echocardiography examination i.e. TTE are haemodynamic instability, aortic dissection and rupture, unexplained hypoxemia, infective endocarditis and to find the source of emboli.

TEE vis-à-vis TTE

In morbid obesity, emphysema or mechanically ventilated patients or with surgical dressing and wounds, image clarity will be better with Trans-Esophegeal echocardiography (TEE) as compared to TTE. Other major indications for the performance of primary TEE study are to visualise thoracic aorta, left atrial appendage, prosthetic valves, to diagnose aortic dissection, for assessment of endocarditis or intracardiac thrombus.

Accuracy Defined

Accuracy of lung ultrasound for diagnosing pneumothorax, lung consolidation, alveolar interstitial syndrome and pleural effusion in critically ill patients is clearly established. The routine use of lung ultrasound appears as an attractive alternative to bed-side chest radiography as it is non-invasive, easily repeatable at the bed-side and provides an accurate evaluation of the respiratory status of patients with acute lung injury. In ICUs, where it is used as a routine monitoring tool, the indications of bed side chest X- ray can be restricted to the assessment of the intra-thoracic position of catheters and endotracheal tubes and to patients where lung ultrasound is not feasible. As a consequence, radiation exposure to physicians, nurses and patients as well as costs is drastically reduced. Lung ultrasound performed by physicians-in-charge of ICUs appears to be one of the most promising techniques for respiratory monitoring and should rapidly expand in the near future. Lung ultrasound also has intrinsic limitations which are patient dependent like obesity, presence of subcutaneous emphysema or large thoracic dressings.

'FAST' Results

Blunt Abdominal Trauma (BAT) is a common event that brings patients to emergency department. Unfortunately patient's history and physical examination often lack the necessary sensitivity and specificity to accurately diagnose acute traumatic pathology. Diagnostic Peritoneal Lavage (DPL) was historically used to determine which patient needed exploratory laprotomy but DPL is difficult to perform in pregnant patients and it cannot be used for serial assessment as it is too sensitive which leads to a high negative laprotomy rate. Abdominal CT is better than DPL for intrabdominal injury but is difficult to perform in haemodynamically unstable patient, is expensive, requires removing the patient from clinical area and may relatively be contraindicated in pregnant patients. The Focused Assessment with Sonography for Trauma (FAST) examination on the other hand is an important and valuable diagnostic alternative to DPL and CT that often can lead to a timely diagnosis for patients with BAT.

Benefits of FAST examination include the following:

• Reduces the time to diagnose acute abdominal injury in BAT.
• Helps accurately diagnose hemoperitoneum.
• Helps assess the degree of hemoperitoneum in BAT.
• Is non-invasive.
• Can be integrated into the primary or secondary survey and can be performed quickly. without removing patients from the clinical area.
• Can be repeated for serial examination.
• Is safer in pregnant patient and children, requires less radiation than CT.
• Leads to fewer DPL, in the proper clinical setting, can lead to fewer CT scans.

Besides, ultrasonography can also provide a measurement of urine volume in the bladder and thus avoids bladder distension and reduce the need for unnecessary catheterisation. Frequent catheterisation is a major risk factor for UTI and it reduces the incidence of nosocomial UTI.

Airway Sonography

Ultrasound is helpful to examine pretracheal anatomy before open surgical tracheostomy or percutancous tracheostomy. Ultrasound can assess the position of potentially dangerous vessels or vital structures. Accurate mid-line needle placement can also be assisted.

Ultrasound helps in diagnosis of maxillary sinusitis in nasally intubated patients. Ultrasound has been useful in identifying the position of ET tube by filling the cuff with water. Position of Laryngeal Mask Airway can also be seen after filling fluid in the LMA cuff.

Venous Ultrasound

It is a non-invasive, easily repeatable technique without any contraindication which has become the most widely acceptable and available test for the detection of DVT as compared to invasive contrast venography. Compression ultrasonography has proved to be a highly sensitive and specific modality for the recognition of lower extremity DVTs without the need for radiation or contrast exposure.

Cerebrovascular Ultrasonography

A best screening tool for the detection of carotid artery stenosis. Transcranial sonography is used in the evaluation of patients with suspected cerebrovascular disease, but a common problem is the attenuation of the ultrasound signal by the skull. Contrast enhanced ultrasound play a particularly important role in the visualisation of the intracranial vessels and thus improves the accuracy of transcranial doppler and increases the potential of this technique. The use of micro-bubbles is helpful for classification of stenosis and for plaque evaluation in patients with poor initial examination. Ultrasound contrast agent avoids misdiagnosing a subtotal stenosis which is a very important clinical issue.

Visceral Abscesses

Extrapulmonary intrabdominal visceral and retroperitoneal abscesses are sometimes difficult to diagnose. Patient presents as septicemia. Ultrasonography helps in diagnosing and treating these abscesses.

In Retrospection

As one can see, ultrasound has many applications that can help the bedside physician in taking better and timelier decisions and perform procedures with greater patient safety.

For that, today's intensivist should have a thorough knowledge of anatomy and instrumentation and adequate training in performing and interpreting ultrasound. For a good ultrasound study, an acoustic window is required through which sound waves are reflected and a two dimensional image is constructed which should be of adequate quality. From this image, machine integrated software will compute a data and integrate into clinical interpretation. Nowadays a generation of portable, battery operated, cheap and light weight easy-to-carry ultrasound devices are available which make this modality most useful in ICU, emergency department and operation theatres. The ultrasound machines and probes used in ICU should comply with repeated decontamination procedure because they serve multiple patients and can be vector for resistant pathogens that could be disseminated in the ICU. If ultrasound machine is available and several ultrasounds are performed on daily basis, the learning curve for acquiring skills may be shortened. However to be able to deliver the goods efficiently and professionally the need for a formal training of the physician aimed at acquiring the necessary knowledge and skills in ultrasonography can not be overlooked.

swarajgarg@gmail.com