Effectiveness of the hemoglobin index for screening of subarachnoid hemorrhage in out‐of‐hospital cardiopulmonary arrest patients: a retrospective observational study

AIM: The hemoglobin index (HbI) represents the amount of hemoglobin, which reflects regional tissue blood volume. The HbI is calculated in real time by a regional oxygen saturation (rSO (2)) monitor. For the hypothesis of our HbI project, we theorized that HbI could be a new method for the screening of subarachnoid hemorrhage (SAH) in overcrowded emergency departments. As a first step, this study aimed to clarify the effectiveness of HbI in screening SAH in out‐of‐hospital cardiopulmonary arrest (OHCA) patients using the rSO (2) data of our previous studies. METHODS: In this single‐center, retrospective, observational study, we examined HbI in patients with OHCA transferred to the Trauma and Acute Critical Care Center at Osaka University Hospital (Osaka, Japan) during the period between April 2013 and December 2015. A sensor attached to the patient's forehead monitored HbI continuously. RESULTS: Among 63 patients (40 men and 23 women; mean age, 76 [interquartile range (IQR), 66–85] years) with OHCA, five were diagnosed as having SAH (SAH group) and 58 were not (non‐SAH group). The HbI values were significantly higher in the SAH group than in the non‐SAH group (1.35 [IQR: 0.80–2.69] versus 0.41 [IQR: 0.32–0.61]), P = 0.0042). In the SAH group, with an HbI cut‐off value of 1.18, the specificity and sensitivity were 96% and 80%, respectively, and the area under the receiver operating characteristic curve of HbI was 0.89. CONCLUSIONS: The HbI might be useful for the screening of SAH in patients with OHCA. The application of HbI in the emergency department could be expected in the future.