Introduction
Cerebral injured and patients with severe stroke are at high risk for secondary ischemic brain damage, due to intracranial hypertension and cerebral vasospasm (CVS). Established methods for measurement of cerebral blood flow (CBF) are technically difficult or need a transport of the patient. Transports for perfusion magnet resonance imaging (Perfusion-MR), computer tomography (CT), positron emission tomography (PET) or single photon emission computed tomography (SPECT) are high risk situations for the patients. To avoid such situations of risk a bedside cerebral monitoring approach is necessary. Recently, conventional near infrared spectroscopy (NIRS) for oxymetry has been extended with an indocyanine green (ICG) dye dilution method. This non-invasive approach of NIRS used with ICG can be applied at the bedside to determine mean transit time (mtt), cerebral blood volume (CBV) and cerebral blood flow (CBF) of the patient based on the observed dye dilution curve of ICG. The modified NIRS method has been validated with perfusion-MR in a healthy volunteers study (Keller et al., Neuroimage, 2003, 20: 828–39).
Methods
Further validation of the NIRS ICG dye dilution technique is done by correlating the results with clinical events e. g. intracranial pressure (ICP) crisis or brain herniation. The patient status is observed using transcranial doppler (TCD) to measure the blood flow velocities, angiography and Perfusion-CT to estimate the occurrence of delayed ischemic neurological deficits (DIND). In parallel NIRS used with ICG is done. 4 NIRS optodes are placed bilaterally on the forehead (NIRS-system Oxymon, Nijmegen). Central venous injections of 0.5 mg/kg ICG are performed and the dye dilution curves are recorded to extract mtt, CBV and CBF. NIRS measurements were performed with the occurrence of CVS immediately before and after intraarterial spasmolysis.
Results
A case report will be presented of a 42 years old woman with subarachnoid hemorrhage (SAH) Hunt&Hess 2, Fisher 3, with ruptured left sided aneurysm of the middle cerebral artery (MCA). The mtt's in both hemispheres are detected with mttleft 7.2 sec and mttright 6.6 sec. Day 7 hemiplegia and aphasia occured. With the diagnosis of CVS, between day 7–14 triple h (hypertensive, hypervolemic hemodilution) therapy has been applied and three times spasmolysis with intraarterial papaverine instillation was performed. With persistent CVS, additionally, the patient was treated with hypothermia and barbiturate coma until day 14. Before papaverine instillation mtt over the left hemisphere (with CVS) has increased while the mtt over the right hemisphere remained (mttleft 8.8 sec to mttright 6.6 sec). After papaverine instillation into the left MCA mttleft decreased to 8sec, whereas the mtt values over the right hemisphere remained unchanged. Also the leftsided values for CBV and CBF decreased after spasmolysis (before CBVleft 1.5 ml/100 g and CBFleft 14 ml/100 g/min; after papaverine instillation CBVleft 2.5 ml/100 g and CBFleft 20 ml/100 g/min). Day 14, the rewarming was started based on the results of the perfusion-CT. The NIRS results correlated with the trend in the perfusion-CT (mttleft=mttright).
Conclusion
Mtt values may be the most important values to observe treatment effects of CVS with increasing brain edema. The new methodology could be a powerful tool in detection and treatment of CVS.