Patients who achieve return of spontaneous circulation (ROSC) after sudden cardiac arrest
and remain comatose are at high risk of secondary brain injury that may prevent or worsen
the quality of neurological recovery. Current treatments that attempt to mitigate the
extent of secondary brain injury include targeted temperature management (TTM),
maintenance of adequate blood pressure and gas exchange (oxygen and carbon dioxide), and
antiepileptic treatment of seizures and other hyperexcitable patterns detected on
electroencephalographic (EEG) monitoring. Multiple recent large-scale clinical trials
comparing different magnitudes of such therapies (mild hypothermia vs. controlled
normothermia or fever prevention, aggressive antiseizure treatment of rhythmic/periodic
patterns vs. no treatment) or resuscitation targets (oxygen, carbon dioxide, and blood
pressure goals) did not detect improvement in neurologic outcome with the hypothesized
superior interventions. Research from the investigators and others suggests that
between-patient heterogeneity in patterns and severity of hypoxic-ischemic brain injury
(HIBI) after cardiac arrest may explain the repeated failure to find a population-level
benefit of any particular one-size-fits-all therapy: individual patients exhibit
differing pathophysiology and may respond best to different neuroprotective
interventions.
To tailor potential neuroprotective treatments to individual patients, doctors must be
able to detect and characterize neurological pathophysiology and treatment responsiveness
in real time. This requires use of one or more prospective neuromonitoring modalities,
including measurement of jugular venous oxygen saturation (SjO2). Measurement of SjO2
involves inserting a catheter retrograde into the internal jugular vein and determining
the oxygen saturation of blood just after it leaves the skull. By comparing the SjO2 with
the saturation of arterial blood (SaO2) entering the brain, measured from a large artery,
the percentage of oxygen extracted by the brain can be determined (SaO2 - SjO2). This is
akin to measuring central venous oxygen saturation (ScvO2) in various types of
circulatory shock. Measurement of SjO2 early after cardiac arrest provides information on
the balance between brain-specific oxygen supply, utilization, and demand. Identification
of abnormal brain oxygen balance during this time period in which secondary brain injury
is most likely to occur can trigger and guide potentially corrective therapies.
The Post Cardiac Arrest Service (PCAS) at UPMC Presbyterian uses SjO2 monitoring in
comatose patients after cardiac arrest as part of routine prognostic and therapeutic
purposes for the first 72 hours of hospitalization. Prior research has shown a
significant association between elevated mean SjO2 (>75%) during the early post-arrest
period and poor outcomes. It is hypothesized that this represents either poor brain
oxygen extraction resulting from abnormalities in diffusion through peri-neuronal tissue
or impaired mitochondrial oxygen uptake and utilization, leading to elevated oxygen
saturation/content in venous blood leaving the injured brain. Preliminary case series by
the investigators and Hoiland et al. have shown that some patients with elevated SjO2
exhibit a decrease in SjO2, and concomitant increase in brain oxygen utilization, after
treatment with hypertonic saline (HTS), suggesting that abnormal oxygen diffusion due to
perivascular edema plays some part in the pathophysiology of post-arrest HIBI.
The ability to detect and act upon abnormal brain oxygen balance, particularly
oxygenation changes that may result from potential neuroprotective interventions, is
limited by current SjO2 measurement technology. Presently, SjO2 is measured by
withdrawing blood from a single lumen, 3-4 French, 10-15 cm-long catheter on an
intermittent basis every 4-6 hours and calculating venous oxygen saturation from the
blood sample on a blood gas analyzer in the hospital laboratory. As a result, SjO2 data
granularity is limited by the practical frequency of blood draws and lab result
turn-around time. However, vascular catheter technology allowing for continuous,
in-dwelling measurement of venous blood oxygen saturation via spectrophotometry exists
and is routinely used to monitor central venous oxygen saturation (ScvO2) and mixed
venous oxygen saturation (SvO2) in patients with cardiogenic shock. Specifically, an
FDA-cleared, continuous venous oximetry-enabled, central venous catheter [PediaSat™
Oximetry Catheter, Edwards Lifesciences Corp, Irvine, CA] [triple lumen, 5.5 French, 15
cm] is currently used for measurement of ScVO2 in pediatric patients with cardiogenic or
septic shock. This catheter also allows for intermittent blood sampling. The
investigators seek to translate this existing continuous venous oximetry technology for
use in the measurement of SjO2. To do so, the investigators plan to perform a
prospective, observational, case series study to determine the feasibility and accuracy
of continuous measurement of SjO2 with the PediaSat™ Oximetry Catheter , compared to the
standard technique of measurement via blood sampling analysis on a laboratory blood gas
machine, in comatose participants at risk of secondary brain injury after cardiac arrest.
The investigators also plan to demonstrate the feasibility of obtaining and storing
jugular blood samples using the continuous SjO2 catheter for future biomarker analysis.