What's New in Emergencies Trauma and Shock? Point of Care Imaging in Out-of-Hospital Cardiac Arrest.

Nontraumatic out-of-hospital cardiac arrest (OHCA) victim without a known predisposing illness poses a diagnostic challenge for doctors as well as the family. Making a quick diagnosis in OHCA can be life-saving and it can be reassuring for the family members to know what exactly happened wrong leading to a sudden cardiac arrest. Point-of-care ultrasound (POCUS) can reveal diagnoses that are otherwise difficult to establish by clinical findings alone. Imaging can be done either after return of spontaneous circulation (ROSC), during the cardiopulmonary resuscitation (CPR) or before declaring the patient dead. The idea is to find potentially treatable conditions such as cardiac tamponade, tension pneumothorax, aortic dissection, hypovolemia, or pulmonary embolism. It can also reveal some conditions like ruptured aortic aneurysm that is mostly untreatable. Lung ultrasound in an intubated and ventilated patient with cardiac arrest and can also reveal B-lines suggestive of pulmonary edema or acute respiratory distress syndrome.

The exact role of POCUS in cardiac arrest is not yet clear, but it continues to be a handy tool provided it is done by experienced operators in a way that it does not hamper with the ongoing resuscitative efforts, especially the cardiac compressions. The best time window for the cardiac scan is between the compressions while breaths are being delivered. This window is short and requires experience to detect the cardiac activity and pericardial effusion >1 cm with certainty. It is better to record the images and then review them later while compressions are restarted.

The sequence of the organ scanning with POCUS during CPR is not uniform. The published literature suggests the following sequences:[1]

Cardiac arrest ultrasound examination (CAUSE): Cardiac-lung ultrasound

Focused echocardiographic evaluation in life support: Cardiac ultrasound only

Focused echocardiographic evaluation in resuscitation: Cardiac ultrasound only

Sequential emergency scanning assessment mechanism used in shock patients: Lung-Proximal deep vein thrombosis (DVT) – Abdomen–Heart

Parasternal-epigastric-abdomen: Lung – Heart – Abdomen – proximal DVT.

Since the sequence of organ scan is not uniform and there are no definite guidelines, the review of the literature shows that cardiac scan was done initially by most authors. Table 1 shows a proposed sequence of scans their time window, findings to be recorded and outcomes expected.

Table 1

Suggested sequence of scan, notable findings, and resultant actions during the cardiac arrest

Order	Organ	Notable findings	Phase	Implications
1	Heart	Cardiac motion	During pulse check pause	Presence of cardiac motion diagnostic of ROSC in PEA
		Pericardial fluid >1 cm	During pulse check pause	Possible cardiac tamponade - drainage
		Dilated right ventricle	During Pulse check pause	Possible pulmonary embolism - IV thrombolysis
2	Lungs	Barcode sign, absent lung sliding	During breath delivery	Diagnostic of pneumothorax - needle or tube drainage
		Diffuse B - lines seen bilaterally during 2 breaths	During breath delivery	Diagnostic of pulmonary edema, acute respiratory distress syndrome
3	Lower limbs	Compression ultrasound of femoral and popliteal veins	Compression phase	Suggestive of pulmonary embolism. IV thrombolysis may help
4	Abdomen	Free fluid, retroperitoneal hematoma	Compression phase	Suggestive of ruptures abdominal aortic aneurysm. Mostly fatal
		Collapsed inferior vena cava	Compression phase	Suggestive of hypovolemic shock - IV fluids

ROSC: Return of spontaneous circulation, PEA: Pulseless electrical activity

Use of ultrasound during cardiac arrest is not entirely harmless. It is suggested by some studies that POCUS done during CPR is responsible for an excessive pause between cardiac compressions well beyond recommended time limits.[2] Still looking at its potential, it is hard to abandon the use of this important diagnostic modality. The International Liaison Committee on Resuscitation in 2015 concluded that it is reasonable to use if qualified personnel are present to perform it and can do so without interfering with timely, high-quality chest compressions.[2]

A recent systematic review concluded that bedside ultrasound done in patients with pulseless electrical activity (PEA) is helpful in diagnosing ROSC. The presence of cardiac activity in PEA may encourage more aggressive resuscitation.[3]

Another imaging technique for diagnosing the cause of CA is computed tomography (CT) done either at ROSC or before declaring the patient dead. Utility of CT as an imaging modality for resuscitation of CA patients is not demonstrated. However, postmortem noncontrast CT to identify the cause of arrest has been evaluated as an alternative for autopsy in cases where autopsy is refused or not performed. It has been shown to significantly improve the diagnostic accuracy over the clinical diagnosis. The diagnostic accuracy of CT for identifying the cause of death was 74% compared to the clinical diagnosis of 46%.[4]

To conclude, imaging, especially POCUS has a definite role in diagnosing both common and uncommon conditions responsible for OHCA. Although the impact of POCUS on patient survival has not been convincingly demonstrated in any large study, it still remains an attractive option for research and practice. The sequence of organ scan and timing of scanning is an important consideration. The emergency departments need to devise and test their own best practices for the use of POCUS in OHCA.