Background and objective: The present study was designed to compare cerebral oxygenation measured with near infrared spectroscopy and local brain tissue oxygen partial pressure, respectively, in pigs during cardiopulmonary resuscitation. Since tissue overlying the brain may have an impact on near infrared spectroscopy readings, we tested whether optode placement on intact skin or on the skull yielded comparable results.
Methods: Twelve healthy pigs were anaesthetized and subjected to continuous haemodynamic, near infrared spectroscopy and brain tissue oxygen partial pressure monitoring. After 4 min of untreated ventricular fibrillation, cardiopulmonary resuscitation was started and arginine vasopressin was administered repeatedly three times. Near infrared spectroscopy values recorded were both the tissue oxygenation index and the tissue haemoglobin index as well as relative changes of chromophores (haemoglobin and cytochrome oxidase). Four animals served as control and were measured with both near infrared spectroscopy optodes mounted on the intact skin of the forehead, while in the remaining eight animals, one near infrared spectroscopy optode was implanted directly on the skull.
Results: Near infrared spectroscopy readings at the skin or at the skull differed consistently throughout the study period. After arginine vasopressin administration, near infrared spectroscopy values at the different locations showed a transient dissociation. In contrast to near infrared spectroscopy measured on intact skin, near infrared spectroscopy readings obtained from skull showed a significant correlation to brain tissue oxygen partial pressure values (r = 0.67, P < 0.001).
Conclusion: Near infrared spectroscopy readings obtained from skin and skull differed largely after vasopressor administration. Near infrared spectroscopy optode placement therefore may have an important influence on the tissue region investigated.