We adhered to the Declaration of Helsinki. Following approval by the institutional review board of Osaka City General Hospital, we conducted a retrospective study in a cohort of patients aged above 18 years who were transferred directly from the emergency room (ER) to the operating room (OR) for emergent craniotomy between May 2009 and November 2014 at the Osaka City General Hospital. We surveyed all cases of emergent DC required dural opening due to traumatic acute subdural hematoma or intracerebral hemorrhage which were performed within 12 h from injury. We excluded patients with medical history of ischemic or cardiovascular disease, chronic renal disease, chronic respiratory disease, and cerebrovascular disorder and also excluded those with insufficient medical charts, unknown mechanism of injury, and insufficient preoperative screening date. We also excluded craniotomy not required dural opening such as epidural hematoma, burr hole evacuation procedures, and repeated craniotomy from this study.
The following data were obtained from the medical records and emergency department records: age, gender, hemodynamic data, body weight, blood pressure and heart rate on admission at ER, Glasgow Coma Scale (GCS) score, neurologic symptom (pupil asymmetry, loss of light reflex), body temperature on arrival at ER, mechanism of injury (traffic injury or not), Injury Severity Score [12], type of intracranial injury (acute subdural hematoma, intracerebral hemorrhage, acute subdural hematoma) by computed tomography (CT), laboratory values (abbreviation, normal range) first collected on arrival at ER; white blood cell (WBC 3.3~8.6 × 103/μL), hemoglobin (Hb 11.6~16.8 g/dL), platelet count (PC 15.8~34.8 × 104/μL), lactate (Lac 4.2~17.0 mg/dL), C-reactive protein (CRP < 0.14 mg/dL), fibrinogen (Fbg 150~400 mg/dL), fibrinogen degradation products (FDP < 5 μg/mL), prothrombin time international normalized ratio (PT-INR 0.85~1.15), activated partial thromboplastin time (aPTT 24.3~36.0 s), treatment in ER; mannitol use, vasodilator use (nicardipine, nitroglycerin), vasopressor (ephedrine, phenylephrine, norepinephrine, epinephrine) use, blood transfusion, endotracheal intubation on ER, and time from estimated injury to operation.
The following intraoperative variables were also obtained from electronic anesthetic record: intraoperative bleeding (ml/kg), vasopressor use before dural opening (ephedrine, phenylephrine, epinephrine, norepinephrine), mannitol use before dural opening, operation time, intraoperative use of inhalation anesthetic, use of remifentanil before dural opening, blood pressure and heart rate on arrival at OR, and before and after dural opening.
Our study was a retrospective survey; therefore, there was no standardized protocol for the anesthetic management of the patients undergoing DC during the study period, and the anesthetic regime was determined by the anesthesiologist in charge. General anesthesia was maintained by intravenous propofol or by inhalation of sevoflurane combined with continuous remifentanil or by intermittent boluses of fentanyl and rocuronium. The choice of a vasopressor (ephedrine, phenylephrine, norepinephrine, or epinephrine) depended on the anesthesiologist in charge. Mannitol was used to induce brain relaxation, if required by the neurosurgeon. In addition to standard monitors, arterial catheters were used for continuous blood pressure monitoring and for sampling blood gas. All patients were transferred to the intensive care unit of the emergency and critical care center after the surgery.
Definition of IH
We defined IH as systolic blood pressure (sBP) < 60 mmHg occurring within 15 min of dural opening in this study. Patients with sBP < 60 mmHg before dural opening were excluded from this study. Blood pressure was measured by using arterial blood pressure monitoring on the radial artery during operation and recorded in the electronic anesthetic record.
Statistical analysis
Statistical analysis was performed with Bell Curve for Excel (Social Survey Research Information Co., Ltd. Japan). All data are presented as medians (interquartile range, 25th–75th percentile) or number with percentages. Parameters in patients with and without IH were compared using Mann–Whitney U tests, Fisher’s exact tests, and chi-square tests as appropriate. Odds ratios are presented with 95% confidence intervals (CI). p values less than 0.05 were considered statistically significant.