Rationale:~Recent studies have shown the potential of a protoporphyrin IX-triple state lifetime technique to measure mitochondrial oxygen tension (mitoPO2) in vivo, which possibly is an early indicator of oxygen disbalance in the cell. With the advent of the COMET measurement system, steps have been made to determine the feasibility of this measurement method. The INOX ICU-2 study (parent study) aims to tailor transfusion therapies to individual intensive care unit (ICU) patients based on mitochondrial oxygen tension. In the pilot study of the INOX ICU-2 study, in which the COMET measurement system was used on critically ill patients receiving red blood cell transfusion, an increase in the between- and within-subject variability was observed over time. This deviation was not explored during the development of the COMET measurement system. Therefore, we aim to determine the between- and within-subject variability of this measurement in healthy subjects and in hemodynamically stable subjects at the intensive care unit.~Main objectives:~To describe the between- and within-subject variability of mitoPO2 measurements during a 24 hour period after 5- aminolevulinic acid (ALA)-induction among healthy volunteers and among neurosurgical patients admitted postoperatively to the ICU or MC. Healthy subjects allow for the exploration of the effect of time-since-application of ALA-patch and neurosurgical patients allow for the exploration of a possible effect of ICU-admittance.~Study design:~Prospective cohort study.~Study population:~Healthy volunteers and neurosurgical patients admitted at the ICU or Medium Care(MC) of LUMC after surgery.~Study procedure:~MitoPO2 measurements will be taken in healthy volunteers using two ALA-patches offset to each other by 3 hours, this has been done to observe possible differences in measurements at different time-points after ALA-induction while maintaining other variables stable. Following the healthy volunteers, neurosurgical patients will be included. Patients will undergo neurosurgery as planned and common practice is that no major interventions are needed in the postoperative phase on the ICU/MC. At multiple predefined moments after surgery, mitoPO2 measurements will take place, again using two ALA-patches with a 3 hour offset.~Nature and extent of the burden and risks associated with participation, benefit and group relatedness:~The risks are small in this study with no serious adverse events (SAE) known. The burden for participants is small since it involves a non-invasive measurement. We will perform this study first in health volunteers. Following the healthy volunteers, neurosurgical patients will be included. Patients will undergo neurosurgery as planned and common practice is that no major interventions are needed in the postoperative phase on the ICU. Normal clinical practice will continue and will not be altered. These patients will allow for the exploration of a possible effect of ICU admittance.
To determine the between- and within-subject variability of the mitochondrial oxygenation measurement with the COMET device over time in healthy subjects and in hemodynamically stable subjects admitted to the intensive care unit.