The following article was one of the references in the Podcast 191 – Cardiac Arrest Update
January 23, 2017 by Dr. Scott Weingart:
Resource (1) Cerebral tissue saturation, the next step in cardiopulmonary resuscitation management? [PubMed Abastract] [Full Text HTML] [Full Text PDF]. Crit Care. 2014 Nov 1;18(6):583. doi: 10.1186/s13054-014-0583-0.
What follows are excerpts from the above Resource (1):
By using two sensors on the forehead, near infrared spectroscopy (NIRS) [link is to PubMed list of publications on cerebral near infrared spectroscopy (NIRS)]measures the regional difference between oxygenated and deoxygenated hemoglobin, which expresses the difference in oxygen supply and demand. It determines cerebral tissue saturation non-invasively and independent of pulsatile flow. Müllner and colleagues  were the first to examine the use of cerebral oxygenation in (post-)cardiac arrest circumstances. They recorded cerebral saturation in six patients with ongoing CPR in the emergency department. Patients who achieved ROSC had higher cerebral saturation values compared with the single patient without ROSC. Cerebral NIRS was also studied during coronary artery bypass surgery. A correlation between desaturation and cognitive dysfunction , prolonged length of hospital stay , and perioperative cerebrovascular accident  was observed, and accordingly
two landmark studies [7,8] showed that a goal-directed
protocol preventing cerebral desaturation resulted in a decrease
in length of intensive care unit and hospital stay,
lower incidence of major organ morbidity and mortality,
and decreased risk of cognitive decline [4-8].
Recent published research measures cerebral saturation in patients with ongoing CPR at arrival to the emergency department, but different cerebral saturation devices and different methods for analysis of NIRS data are used. The latest research on NIRS in the CPR setting focuses on two main questions.
Firstly, can cerebral saturation values predict ROSC or neurological outcome? . . . .
The second question recently addressed is whether cerebral saturation values can guide CPR efforts. . . .
In conclusion, preliminary data suggest that monitoring of cerebral saturation during CPR seems a likely predictor of both ROSC and neurological outcome and that it might have a role guiding CPR interventions. Although the current knowledge, obtained from small observational studies, is limited, both the further development of NIRS devices and the likely execution of well-designed large blinded observational trials, particularly in the difficult environment of out-of-hospital CPR, bode well for the future. A real-time monitoring tool providing vital information on the neurological and physiological response to CPR efforts and with predictive value for neurological outcome seems close at hand.
The following are excerpts from the abstract of Resource (2) below:
Bystander cardiopulmonaryresuscitation (CPR) patients have significantly higher rSO2 compared with no bystander CPR patients. It is unclear how quickly rSO2 changes with hemodynamic instability. rSO2 during mechanical CPR varies between 44 and 55% and manual CPR varies between 20 and 40%, representing a significant relative rSO2 increase. Studies have found a relationship between rSO2 and restoration of spontaneouscirculation (ROSC) and rSO2 increase can be used as a sign of ROSC. rSO2 evaluation is effective for monitoring quality of resuscitation and neurological prognostication. It seems that cardiac arrest patients with good neurologic outcome have significantly higher rSO2 levels (CPC 1-2 median rSO2 68%, CPC 3-5 median rSO2 58%, P < 0.01) and good neurologic outcome (CPC 1-2) increased ‘in proportion to the patients’ rSO2 levels irrespective of their ROSC status at hospital arrival’. However, most of the studies are small and a prospective outcome study focusing on rSO2 values is needed.
The following are excerpts from the abstract of Reference (3):
. . . , cerebral near-infraredspectroscopy provides continuous, noninvasive, real-time information about brain oxygenation without the need for a pulsatile blood flow. It measures transcutaneous cerebral tissue oxygen saturation (rSO2). This information could supplement currently used monitors. Moreover, an evolution in rSO2 monitoring technology has made it easier to assess rSO2 in CA conditions.
rSO2 is feasible in the setting of CA and has the potential to measure the quality of CPR, predict ROSC and neurologic outcome, and monitor post-CA patients during transport.
The literature shows that rSO2 has the potential to serve multiple roles as a neuromonitoring tool during CPR and also to guide neuroprotective therapeutic strategies.
The following are excerpts from the abstract of Resource (4):
A total of nine studies with 315 patients (119 achieving ROSC, 37.7%) were included in the meta-analysis. The majority of those patients had an OHCA (n=225, 71.5%; IHCA: n=90, 28.5%). There was a significant association between higher values of rSO2 and ROSC, both in the overall calculation (standardized mean difference, SMD -1.03; 95%CI -1.39,-0.67; p<0.001), and in the subgroups analyses (rSO2 at the beginning of resuscitation: SMD -0.79; 95%CI -1.29,-0.30; p=0.002; averaged rSO2 value during resuscitation: SMD -1.28; 95%CI -1.74,-0.83; p<0.001).
Higher initial and average regional cerebral oxygen saturation values are both associated with greater chances of achieving ROSC in patients suffering of CA. A note of caution should be made in interpreting these results due to the small number of patients and the heterogeneity in study design: larger studies are needed to clinically validate cut-offs for guiding cardiopulmonary resuscitation.
An example of the devices discussed above is the Invos system [of cerebral oximetry] (This link provides a clear simple explanation of how the rSO2 technology works).
Another commercial example of cerebral NIRS is FORE-SIGHT ELITE Absolute Tissue Oximetry
(1) Cerebral tissue saturation, the next step in cardiopulmonary resuscitation management? [PubMed Abastract] [Full Text HTML] [Full Text PDF]. Crit Care. 2014 Nov 1;18(6):583. doi: 10.1186/s13054-014-0583-0.
(2) Near-infrared spectroscopy during cardiopulmonary resuscitation and after restoration of spontaneous circulation: a valid technology? [PubMed Abstract]. Curr Opin Crit Care. 2016 Jun;22(3):191-8. doi: 10.1097/MCC.0000000000000301.
(3) Regional Cerebral Oximetry During Cardiopulmonary Resuscitation: Useful or Useless? [Pubmed Abstract]. J Emerg Med. 2016 Jan;50(1):198-207. doi: 10.1016/j.jemermed.2015.03.043. Epub 2015 Sep 26.
(4) Cerebral oximetry and return of spontaneous circulation after cardiac arrest: A systematic review and meta-analysis [PubMed Abstract]. Resuscitation. 2015 Sep;94:67-72. doi: 10.1016/j.resuscitation.2015.06.023. Epub 2015 Jul 6.