OBJECTIVE Intrahospital transport for CT scans is routinely performed for neurosurgical patients. Particularly in the sedated and mechanically ventilated patient, intracranial hypertension and blood pressure fluctuations that might impair cerebral perfusion are frequently observed during these interventions. This study quantifies the impact of intrahospital patient transport on multimodality monitoring measurements, with a particular focus on cerebral metabolism. METHODS Forty intrahospital transports in 20 consecutive patients suffering severe aneurysmal subarachnoid hemorrhage (SAH) under continuous intracranial pressure (ICP), brain tissue oxygen tension (pbtO2), and cerebral microdialysis monitoring were prospectively included. Changes in multimodality neuromonitoring data during intrahospital transport to the CT scanner and the subsequent 10 hours were evaluated using linear mixed models. Furthermore, the impact of risk factors at transportation, such as cerebral vasospasm, cerebral hypoxia (pbtO2 < 15 mm Hg), metabolic crisis (lactate-pyruvate ratio [LPR] > 40), and transport duration on cerebral metabolism, was analyzed. RESULTS During the transport, the mean ICP significantly increased from 7.1 ± 3.9 mm Hg to 13.5 ± 6.0 mm Hg (p < 0.001). The ICP exceeded 20 mm Hg in 92.5% of patients; pbtO2 showed a parallel rise from 23.1 ± 13.3 mm Hg to 28.5 ± 23.6 mm Hg (p = 0.02) due to an increase in the fraction of inspired oxygen during the transport. Both ICP and pbtO2 returned to baseline values thereafter. Cerebral glycerol significantly increased from 71.0 ± 54.9 µmol/L to 75.3 ± 56.0 µmol/L during the transport (p = 0.01) and remained elevated for the following 9 hours. In contrast, cerebral pyruvate and lactate levels were stable during the transport but showed a significant secondary increase 1–8 hours and 2–9 hours, respectively, thereafter (p < 0.05). However, the LPR remained stable over the entire observation period. Patients with extended transport duration (more than 25 minutes) were found to have significantly higher levels of cerebral pyruvate and lactate as well as lower glutamate concentrations in the posttransport period. CONCLUSIONS Intrahospital transport and horizontal positioning during CT scans induce immediate intracranial hypertension and an increase in cerebral glycerol, suggesting neuronal injury. Afterward, sustained impairment of neuronal metabolism for several hours could be observed, which might increase the risk of secondary ischemic events. Therefore, intrahospital transport for neuroradiological imaging should be strongly reconsidered and only indicated if the expected benefit of imaging results outweighs the risks of transportation.

Background: Early detection of cerebral ischemia and metabolic crisis is crucial in critically ill subarachnoid hemorrhage (SAH) patients. Variable increases in brain tissue oxygen tension (PbtO 2 ) are observed when the fraction of inspired oxygen (FiO 2 ) is increased to 1.0. The aim of this prospective study was to evaluate whether a 3-minute hyperoxic challenge can identify patients at risk for cerebral ischemia detected by cerebral microdialysis.Methods: Twenty consecutive severe SAH patients undergoing continuous cerebral PbtO 2 and microdialysis monitoring were included. FiO 2 was increased to 1.0 for 3 minutes (the FiO 2 challenge) twice a day and PbtO 2 responses during the FiO 2 challenges were related to cerebral microdialysis-measures, ie, lactate, the lactate-pyruvate ratio, and glycerol. Multivariable linear and logistic regression models were created for each outcome parameter.Results: After predefined exclusions, 274 of 400 FiO 2 challenges were included in the analysis. Lower absolute increases in PbtO 2 (ΔPbtO 2 ) during FiO 2 challenges were significantly associated with higher cerebral lactate concentration (P < 0.001), and patients were at higher risk for ischemic lactate levels > 4 mmol/L (odds ratio 0.947; P = 0.04). Median (interquartile range) ΔPbtO 2 was 7.1 (4.6 to 12.17) mm Hg when cerebral lactate was > 4 mmol/L and 10.2 (15.76 to 14.24) mm Hg at normal lactate values ( ≤ 4 mmol/L). Median ΔPbtO 2 was significantly lower during hypoxic than during hyperglycolytic lactate elevations (4.6 vs. 10.6 mm Hg, respectively; P < 0.001). Lactate-pyruvate ratio and glycerol levels were mainly determined by baseline characteristics.Conclusions: A 3-minute FiO 2 challenge is an easy to perform and feasible bedside diagnostic tool in SAH patients. The absolute increase in PbtO 2 during the FiO 2 challenge might be a useful surrogate marker to estimate cerebral lactate concentrations and might be used to identify patients at risk for impending ischemia.