Following on from my previous post here is Part II …….
Trauma
POCUS first gained traction with Emergency Medicine clinicians with the introduction of the Focused Assessment Sonography in Truama (FAST) scan in 1997 and then the extended version eFAST scan. The theory being that after traumatic injuries bleeding ensues and by scanning the right and left upper quadrants, the pelvis and subxiphoid views of the heart any free fluid would accumulate in these areas due to gravity. The extended views involve scans of the heart and lungs looking for cardiac tamponade, pneumothorax and free fluid in the lung bases. Problems with FAST scan have previously been discussed at St Emlyns here. Whilst commonly used in adult trauma patients and the fact that it can be reliably performed in 3-5 minutes eFAST scanning has not been widely adopted in paediatric emergency medicine. The reason for this is it’s historical low sensitivity of 45-55% (Emery et al., 2001) which is mostly explained by the fact that significant abdominal injuries can occur without free fluid being present in up to 37% of children which is the key diagnostic finding in eFAST scanning (Taylor and Sivit, 1995). Another problem with eFAST scanning is that even if free fluid is detected it cannot tell you where the bleeding is coming from and unless the child is haemodynamically unstable and needs an immediate laparotomy a CT scan is still required to determine the full extent of injuries.
In a 2007 meta-analysis including 3838 patients POCUS had a sensitivity of 80% and specificity of 96% for free fluid but there were methodological concerns with some of these papers and when these were excluded the sensitivity reduced to 66% although the specificity remained high at 95%. (Holmes, Gladman, Chang, 2007.) A randomised control trial of FAST scan vs standard examination in haemodynamically stable children with blunt abdominal trauma found no improvement in clinical care, length of stay or missed intrabdominal injuries (Holmes et al., 2017). A recent systematic review and meta-analysis including 8 papers and 2135 patients showed the diagnostic performance of FAST scanning still performs badly as a rule out test but better as a rule in test with a pooled sensitivity of 35% and specificity of 96%, (Liang et al., 2021). Although the evidence is variable the low to moderate sensitivities support the argument that in paediatric trauma eFAST scanning is of little value as a rule out test and if clinical suspicion is high a CT scan must be performed. If free fluid is seen on POCUS the specificity is sufficiently high to rule in an intrabdominal injury although the child will most likely still need a CT to make a full diagnosis or ascertain the extent of other injuries e.g brain or spinal in a multiply injured patient.
One area of future research for FAST scans could be in the subset of very low risk patients. The Pediatric Emergency Care Applied Research Network (PECARN) blunt abdominal trauma rules show that in the absence of seven clinical signs the risk of a significant abdominal injury is 0.1% and that CT scanning can be withheld. (Holmes et al., 2013)
- no evidence of abdominal wall trauma or seat belt sign
- Glasgow Coma Scale> 13
- no abdominal tenderness
- no evidence of thoracic wall trauma
- no complaints of abdominal pain
- no decreased breath sounds
- no vomiting
Of the six children who did have an intra-abdominal injury but had none of the above criteria all six had free fluid on FAST examination and so if POCUS is used in this very low risk subset of patients the addition of a negative eFAST scan could give further confidence to the decision-making process although this needs validating in future studies.
Shock
Shock is a life-threatening form of circulatory failure that results in a state of cellular and tissue hypoxia due to inadequate oxygen delivery or increased oxygen consumption.
Shock is classified into different types based on the pathophysiology
• Cardiogenic- when cardiac function impaired secondary to acute myocardial infarction, arrhythmia, myocarditis, endocarditis or acute on chronic heart failure
• Obstructive- where the heart is prevented from pumping effectively by compression or a physical blockage such as in a tension pneumothorax, cardiac tamponade or pulmonary embolism.
• Distributive- systemic vasodilation leads to decreased blood flow to the vital organs. This is seen in anaphylaxis, sepsis or the rarely seen neurogenic shock where spinal cord damage leads to loss of sympathetic vasomotor tone.
• Hypovolemic-This is commonly seen with acute blood loss after trauma but also fluid loss from diarrhoea and vomiting or diabetic ketoacidosis. (Standl et al 2018)
Shock is not a diagnosis in itself but the endpoint of numerous disease processes and the primary mechanism of worldwide paediatric mortality. When children show signs of shock the clinician needs to urgently find the cause and take steps to rectify that. In adult populations the RUSH (Rapid Ultrasound for Shock and Hypotension) protocol and other multisystem protocols have been developed to quickly find the cause of shock. A paediatric shock protocol has been developed based on adult practice (Hardwick and Griksaitis, 2021). The main differences between the adult and paediatric protocols is the addition of paediatric specific conditions such as hepatic haemangioma and cranial views in children with open fontanelles. Supporting evidence is lacking in paediatric patients but in adult studies POCUS has been shown to help diagnose the causes of shock (Keikha et al., 2018 and Stickles et al., 2019).
Intravenous access
One of the biggest challenges in paediatric emergency medicine is obtaining IV (intravenous) access for taking bloods and delivering medications. The combination of distressed parents and child, toddlers with excess body fat and small veins can make this commonly performed procedure extremely difficult. Evidence shows that ultrasound guided cannulation is more successful, takes less time and that the cannulas survive longer. (Doniger et al., 2009, Oakley and Wong 2010, and Desai et al., 2018). One paper however showed significantly lower success rates when ultrasound was used with a 65% success rate compared to 84% for traditional cannulation (p= 0.002). This paper recruited patients who had had one previous failed attempt and used a two-person technique where one person held the ultrasound probe and the other tried to get IV access. This is different from the one-person technique usually taught and could explain the less successful results (Otani et al., 2018). In general, the evidence supports the use of POCUS in gaining IV access and it’s application is recommended by international consensus guidelines. (Singh, Y. et al 2020)
Cardiac
Point of care echocardiography can be performed in many clinical circumstances such as trauma, cardiac arrest, breathless patients, shocked patients and tachycardic patients. Longjohn et al showed that in 70 paediatric patients POCUS assessment of left ventricular function, inferior vena cava collapsibility and pericardial effusion showed good agreement with a paediatric cardiologist with κ score of 0.87, 0.73 and 0.77 respectively. The overall sensitivity and specificity of POCUS compared with a formal echocardiogram was 95% and 83% respectively (Longjohn and Pershad 2011.) A more recent study showed of 456 paediatric emergency department patients showed the sensitivity and specificity of real-time POCUS to be 100% and 99.5% for diagnosing left ventricular systolic dysfunction and pericardial effusion (Miller et al., 2022)
Cardiac arrest
Evidence for the role of POCUS in paediatric cardiac arrest is severely lacking. Currently there are only two papers that look at the role of POCUS during cardiac arrest of which only eight patients are included. In a case series of 3 children aged 6 years, 16 months and a new born baby all three had cardiac standstill on POCUS and were put onto extracorporeal membranous oxygenation (ECMO) and regained cardiac output but eventually all three children died (Steffen, K., et al 2017).
https://www.thepocusatlas.com/pediatrics
The other case series was five patients who were admitted due to either confirmed or suspected pulmonary embolism. All five went into a pulseless electrical activity (PEA) cardiac arrest and four out of five had evidence of pulmonary embolism on POCUS. Three patients were thrombolysed with tissue plasminogen activator (tPA) during the cardiac arrest and the other two after the return of spontaneous circulation. Four out of the five patients survived to hospital discharge. It’s of note that all five patients were aged 15-17 years so not really true paediatric ages and all were suspected of having pulmonary emboli prior to the cardiac arrest and so it’s unlikely that the POCUS scanners would have been unaware of this information when making diagnoses. (Morgan et al., 2018).
We know from adult studies that POCUS can increase time taken in rhythm checks and can delay chest compressions which we know is one of the key things leading to a successful cardiac arrest outcome (In’t Veld et al., 2017). Due to these facts and the low numbers of patients it’s very difficult to draw any conclusions about the role of POCUS in paediatric cardiac arrest. The 2020 Paediatric Life Support recommendations also concluded that there was ‘insufficient evidence to recommend for or against the routine use of bedside ultrasound and echocardiography during a paediatric arrest.’ They also said POCUS could be considered but that needed to be weighed against the risks of interrupted chest compressions. (Maconochie et al., 2020).
Femoral nerve Blocks
Its certainly beyond the scope of this blog (and my expertise!) to discuss nerve blocks in children in much detail but femoral nerve fractures are fairly common in children and so a good knowledge of femoral nerve block can be incredibly useful to reduce pain and opiate use and also to facilitate Thomas splint application. The use of ultrasound has been shown to reduce failure rates and avoid complications such as vascular injury. The addition of ketamine can be considered on a case-by-case basis. The technique is further described here.
Foreign Bodies
I’m sure we’re all familiar with the child with a retained foreign body. Whilst x-rays are generally the first line investigation POCUS can be extremely useful for locating radiolucent foreign bodies such as wood. The key to their identification is visualizing bright (hyperechoic) structures with posterior shadowing artefact. With practice ultrasound can also aid in the removal of deep retained foreign bodies and can avoid removal under general anesthetic.
Cocktail stick foreign body in the forearm with posterior shadow artefact.
Thanks for reading!
P
See also
Nerve blocks
