Intra-abdominal hypertension (IAH) and abdominal compartment syndrome are terms referring to the same condition, which only differs in its severity. This nomenclature is recommended by the World Society of the Abdominal Compartment Syndrome (WSACS)(1). Intra-abdominal hypertension specifically refers to IAH between 12 mmHg and 20 mmHg, whereas ACS refers to intra-abdominal pressure >20 mmHg with associated one new organ dysfunction.
Furthermore, four stages of IAH have been distinguished:
stage I, 12–15 mmHg;
stage II, 16–20 mmHg;
stage III, 21–24 mmHg;
stage IV, >25 mmHg.
This staging is associated with an increasing decrease in perfusion, mainly in the kidneys and the intestines, which leads to organ ischemia due to restricted venous outflow from important abdominal organs. ACS in critically ill patients is associated with high mortality rates. Untreated ACS leads to death in more than 90% of patients as compared to 25–75% for treated ACS and 16–37% after surgical decompression(2). Early detection is crucial in this situation. This type of pathology is mainly dealt with by surgeons and intensive care physicians. Other specialists, including imaging diagnosticians, usually have limited knowledge on this issue. According to WSACS, it is worth familiarizing with the following data:
normal intra-abdominal pressure (IAP) is 5–7 mmHg during critical illness;
increased IAP is defined as IAP >12 mmHg;
primary IAH or ACS is due to an injury or disease in the abdomino-pelvic region;
secondary IAH or ACS is a consequence of extra-abdominal pathology;
recurrent IAH or ACS refers to the condition which redevelops following previous IAP normalization;
abdominal perfusion pressure (APP) = mean arterial pressure – intra-abdominal pressure; APP is <60 mmHg in ACS;
polycompartment syndrome refers to hypertension in at least two abdominal compartments;
abdominal compliance is a measure of the ease of abdominal expansion (elasticity), which is determined by the elasticity of the abdominal wall and diaphragm; it is expressed as a change in intra-abdominal volume per change in IAP;
lateralization of the abdominal wall is the phenomenon where the abdominal wall (rectus abdominis muscles in particular) moves laterally away from the midline in cases of treatment using open abdomen techniques.
The World Society of the Abdominal Compartment Syndrome has distinguished the following pathogenetic factors:
Diminished abdominal compliance – abdominal surgeries, major injuries, major burns, prone positioning.
Increased intraluminal contents – gastroparesis, major gastric retention, bowel obstruction, colonic pseudo-obstruction, volvulus.
Increased intra-abdominal contents – acute pancreatitis, meteorism, ascites, pneumoperitoneum, hemoperitoneum, abdominal collections, abscess/extensive inflammation, intra- and extraperitoneal tumors, laparoscopy, liver failure or cirrhosis with ascites, peritoneal dialysis.
Capillary leak – massive fluid resuscitation, acidosis, damage due to follow-up laparotomy, hyperthermia, multiple blood transfusions.
Other: age, bacteremia, coagulopathy, increased pillow angle during sleep, surgical treatment of large abdominal hernias, mechanical ventilation, obesity or overweight, peritonitis, pneumonia, sepsis, shock, and hypotension. Some authors also mention ruptured abdominal aortic aneurysm and pregnancy(2).
Vesical intra-abdominal pressure measurement performed in a patient in the supine position is the gold standard. This parameter may be also measured in the stomach or large bowel. These methods are invasive and may cause complications. Therefore, different methods for the measurement of intra-abdominal pressure based on the assessment of abdominal wall tension have emerged(3–5). So far, these methods have not been approved by WSACS. According to these experts, vesical intra-abdominal pressure measurement remains the gold standard. IAP should be monitored at 4–6-hour intervals (or continuously in some cases) to monitor the efficacy of the treatment used and decide for surgical intervention in the case of persisting high IAP. Decompression, which involves creating the so-called open abdomen, may be performed. Pressure monitoring itself does not reflect the intra-abdominal situation or the etiology of IAH/ACS. Therefore, CT is performed in some cases(6–8). In this modality, the following symptoms are suggestive of this pathology: bell-shaped abdomen, the ratio of anteroposterior-to-transverse abdominal diameter >0.80, the ratio of anteroposterior-to-transverse peritoneum parietale diameter >0.52, slit-like inferior vena cava and renal veins, thickened and strongly contrast-enhancing bowel and gastric walls.
Patel
However, it should be stipulated that the measurement of the width of the IVC will always fail in obese patients who usually present with some degree of IVC compression. This symptom may be also misinterpreted as hypovolemia.
Looking at the above mentioned causes of IAH/ACS, it may be concluded that most of them are acute conditions requiring emergency specialist intervention. Candan
The presented data show that point-of-care ultrasonography (POCUS) deserves a wider application in the diagnosis and monitoring of critically ill patients with suspected IAH. This technique should be also used in paracentesis.