**4.1 Abdominal aorta**

Ideally, the abdominal aorta is to be scanned along its full length from the diaphragm to its bifurcation in both transverse and longitudinal planes with the patient in the supine position. Doppler imaging is not necessary unless to differentiate from other surrounding structures. Bowel gas and obesity may impede imaging, which can be reduced by applying firm pressure with the transducer probe.

Aorta is scanned starting at the epigastrium in the midline and proceeds caudally along its length. In the transverse plane, the aorta is identified lying anterior and to the left of the hyperechoic line of the spine as a pulsatile and round to oval structure. Tracing caudally, branches of the aorta, including superior mesenteric artery, renal artery, and then its bifurcation, can be identified. Similarly, a longitudinal view in the midline and coronal view from the right side along the anterior axillary line can be used to visualize the aorta from different angles.

Contained rupture of the aorta may be seen as a hypoechoic mixed density area surrounding the aorta. Traumatic aortic dissection can also occur, which can be seen as a dissection flap within the lumen of the aorta (**Figure 11**).

#### **4.2 Inferior vena cava**

Inferior vena cava (IVC) is identified by its termination into the right atrium of the heart by placing the curvilinear transducer in the longitudinal plane at the epigastrium with the pointer facing the head end of the patient. It is seen as a tubular structure with thin walls, varying size with respiration, and can be compressed with pressure from the transducer (**Figure 12**).

*POCUS in Abdominal Trauma: Old Gadget, New Insights DOI: http://dx.doi.org/10.5772/intechopen.107049*

#### **Figure 12.**

*Inferior vena cava on longitudinal view with M-mode applied for measurement of diameter and its variation with respiration [23].*

Injuries to the IVC are uncommon. However, it has utility in trauma settings to assess the volume status of the patient. A cause of hypotension or any hemodynamic instability in a patient with trauma is due to blood loss unless proven otherwise. This is the reason ATLS guidelines stipulate every patient to receive one liter of pre-warmed lactated Ringer's solution and arrange blood products for transfusion.

IVC diameter and degree of collapse correlate with volume status in the setting of hemorrhagic shock. Diameter is less than 1 cm in hypovolemia and more than 50% collapsing. In patients with obstructive shock secondary to cardiac tamponade or tension pneumothorax, the IVC may be dilated more than 2 cm with less than 50% collapsing nature. Repeat measurements show the patient response to resuscitation.

In pediatric population, IVC/aorta ratio is used to allow assessment independent of patient size. IVC/aorta ratio less than or equal to 0.8 correlates well with hypovolemia.

#### **4.3 Retroperitoneal hemorrhage**

Retroperitoneal region is divided into three compartments – anterior, middle, and posterior. The anterior compartment houses the bowel, pancreas, and great vessels, middle is occupied by the kidneys, and posterior compartment contains muscles, such as psoas and quadratus lumborum. Bleeding into these compartments, due to trauma or vessel rupture, can sometimes be seen with POCUS.
