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Intra-abdominal hypertension (IAH) is increasingly recognized as an important parameter in critically ill (ICU) patients. IAH affects perfusion to all abdominal components including the abdominal wall (AW). Near infrared spectroscopy (NIRS) measures changes in three chromophores including oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (Hb), and cytochrome aa3 (Cyt), providing information concerning dysoxia. We sought to examine whether NIRS measurement of the AW was safe, and correlated with intra-abdominal pressure (IAP) in ICU patients.A NIU-Pro001 system recorded NIRS data over 24 hours from the AW of 9 ICU patients at risk for IAH. IAP was recorded from the bladder. Changes in chromophore values are interpolated from best-fit polynomial curves.Sixty-six paired IAP and NIRS readings were taken from 9 ICU (4–12 observations/patient) patients. No measurement related adverse reactions occurred. The mean (range) first values measured in these patients were; IAP 17.2 mm Hg (9–31); HbO2 0.41 μmol/L (−8.4 to 7.6); Hb 2.6 μmol/L (−3.1 to 12.2); and Cyt 0.65 μmol/L (−3.4 to 4.8). A significant, inverse (or negative) association was found between ΔNIRS HbO2 level and ΔIAP (coefficient, −0.1588; p = 0.008). No association was found between ΔNIRS Hb or ΔCyt and ΔIAP.NIRS of the AW appears safe. NIRS measurement of changes in HbO2 appears to be associated with ΔIAP, and warrant further study in greater numbers of ICU patients with more frequent IAP readings, over longer periods of critical illness.