**6. Discussion**

The American College of Surgeons have detailed the use of ultrasonography for FAST and extended FAST (eFAST) examination as an adjunct to a primary survey of all trauma patients [5]. eFAST application was then well studied over the years. Netherton et al. conducted a systematic review and meta-analysis on the diagnostic accuracy of eFAST in trauma, which included seventy-five studies with a total of more than 24,000 patients [6]. Pooled specificity for detection of pneumothorax, pericardial effusion, and intra-abdominal free fluid were 99%, 94%, and 98%, respectively; whereas the sensitivity ranged between 69 and 91%. They concluded that eFAST was capable of ruling in the above diagnoses, but not adequate to rule out the same when negative. Their subgroup analysis showed that eFAST was more specific in detecting intra-abdominal fluid in normotensive than in hypotensive patients.

A similar meta-analysis on the application of FAST in the pediatric age group was conducted by Liang et al., including eight studies and an aggregate of more than 2000 patients [24]. FAST had a pooled specificity of 96%, but a poor sensitivity of 35%.

Practical implications of FAST in terms of predicting the need for laparotomy, cost-effectiveness, and reducing time to operative intervention have also been studied. A study by Lane BH showed that FAST examination is clearly cost-effective in unstable patients [12]. Moylan et al. noted that even in normotensive patients with blunt trauma, the positive FAST examination had a strong association with therapeutic laparotomy, or 116 [8]. In the pediatric population of unstable blunt abdominal trauma, Long et al. observed that positive FAST examination at 2 hours after ED arrival had 100% specificity and positive predictive value for early surgical intervention [11].

Applications of ultrasonography beyond eFAST then began to be explored. Solid organ injury is easily identified by POCUS. Richards et al. studied over 2000 patients with blunt abdominal trauma who underwent POCUS for identifying the splenic injury [13]. They found that ultrasonography had an overall sensitivity of 69% for splenic injury, and this increased to 89% for grade 3 or higher injuries. Similarly, McGahan et al. noted that acute renal trauma can be detected by ultrasonography, especially with higher-grade injuries [14].

A newer technique was introduced that allowed better delineation of solid organ injury - contrast-enhanced ultrasonography (CEUS). Valentino et al. studied 133 patients with blunt abdominal trauma by performing standard ultrasonography and CEUS [16]. These were compared with injuries detected on CT scans. CEUS had a sensitivity and specificity of 96.4% and 98%, respectively, and was thus nearly as accurate as CT scans.

Other than solid organ trauma, hollow viscus and vascular structures can also be scanned with POCUS. Moriwaki et al. performed ultrasonography on 484 patients with severe abdominal pain with or without blunt trauma for detecting intra-peritoneal free air. It had a sensitivity of 85.7% and a specificity of 99.6% [25]. Ultrasound-guided suprapubic catheter placement into the urinary bladder has been studied to be safe as per Muhammad AS et al. even in resource-poor settings without incidence of any major complication [26]. Scanning of large blood vessels of the abdomen, such as aorta and inferior vena cava, is challenging due to the overlying bowel with gas content. Sefidbakht S et al. measured the diameter of inferior vena cava (IVC) and its variation with respiration in 88 patients of trauma, with or without hemodynamic instability. The average diameter of the vessel was smaller in those with shock (p < 0.0001) and the collapsibility index of IVC was significantly higher in the

unstable trauma patients (p < 0.001). Thus, IVC diameter can be a reliable indicator of shock [23].

This chapter has described the possible applications of POCUS in abdominal trauma, but it is not an exhaustive list. Research and development in this field are ever-growing and further utility of ultrasonography remains to be seen.
