Investigations
1st investigations to order
trans-bladder measurement of intra-abdominal pressure
Test
Performed by treating physician at bedside. Baseline measurements should be performed in patients with clinical signs of raised intra-abdominal pressure, or two or more risk factors for intra-abdominal hypertension.[1]
Should be monitored at least every 3 to 4 hours. More frequent monitoring required if pressure is elevated or clinical course is changing rapidly.
Intra-abdominal pressure (IAP) >12 mmHg indicates intra-abdominal hypertension, graded as follows: grade I (12 to 15 mmHg), grade II (16 to 20 mmHg), grade III (21 to 25 mmHg), grade IV (>25 mmHg).[1]
Abdominal perfusion pressure is the difference between mean arterial BP and IAP. Must be 60 mmHg or greater for organ perfusion to be adequately maintained.
IAP >20 mmHg with or without abdominal perfusion pressure <60 mmHg, with new-onset organ dysfunction or failure is diagnostic for ACS.
In paediatric patients, the exact IAP that signals the transition from intra-abdominal hypertension to ACS is not currently known, but an IAP >10 mmHg with new-onset organ dysfunction has been proposed for children.
Result
elevated
oxygen saturation
Test
Decreased pulmonary compliance or atelectasis can lead to hypoxia.
Result
normal or decreased
serum urea and creatinine
Test
Required to monitor renal function and associated electrolyte balance.
Ratio of urea to creatinine is usually >20:1, a classical indicator of impaired renal perfusion.
Renal failure, due to impaired renal perfusion, is very common.
Result
elevated
arterial blood gases
Test
Metabolic acidosis due to organ ischaemia is the most common abnormality.
Decreased pulmonary compliance or atelectasis can lead to a respiratory component with hypoxia and hypercapnia.
Result
metabolic acidosis or mixed metabolic and respiratory acidosis
Investigations to consider
peak airway pressure
Test
Direct measurement of peak airway pressure is possible in mechanically ventilated patients.
Increased peak airway pressure is a late sign.
Result
normal or elevated
abdominal CT scan
Test
Frequently used to identify underlying intra-abdominal pathological conditions.
Not used to assess intra-abdominal pressure, but a careful interpretation of CT study can reveal circularisation of the transverse abdominal contour due to increased pressure as an incidental finding.
If found, measurement of intra-abdominal pressure should be considered.[30][31][32]
Result
'circularisation' of transverse abdominal contour
abdominal ultrasound
Test
Used to identify underlying intra-abdominal pathological conditions and, in ICU, to assess intravascular volume.
May show intra-abdominal fluid, renal vein compression, or inferior vena cava compression.
If found, measurement of intra-abdominal pressure should be considered.[34]
Result
intra-abdominal fluid, compression of renal veins and/or inferior vena cava
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