Continuous Muscle Tissue Oxygenation in Critically Injured Patients: A Prospective Observational Study

Abstract

Background: 

Despite normalization of vital signs, critically injured patients may remain in a state of occult underresuscitation that sets the stage for sepsis, organ failure, and death. A continuous, sensitive, and accurate measure of resuscitation after injury remains elusive.

Methods: 

In this pilot study, we evaluated the ability of two continuous measures of peripheral tissue oxygenation in their ability to detect hypoperfusion: the Licox polarographic tissue oxygen monitor (PmO₂) and the InSpectra near-infrared spectrometer (StO₂). We hypothesized that deltoid muscle tissue oxygenation measurements could detect patients in “occult shock” who are at increased risk for post-injury complications. The study was designed to (1) define values for PmO₂ and StO₂ in patients who by all standard measures appeared to be clinically resuscitated; (2) evaluate the relationship between PmO₂, StO₂ and other physiologic variables including mean arterial pressure (MAP), lactate and base deficit (BD); and (3) examine the relationship between early low tissue oxygen values and the subsequent development of infections and organ dysfunction. Licox probes were inserted into the deltoid muscle of critically injured patients after initial surgical and radiologic interventions, and transcutaneous StO₂ monitors were applied over the same muscle bed. PmO₂, StO₂, and standard physiologic data were collected continuously using a multimodal bioinformatics system.

Results: 

Twenty-eight critically injured patients were enrolled in this study at admission to the intensive care unit (ICU). For patients who appeared to be well resuscitated (defined as MAP ≥70 mm Hg, heart rate [HR] ≤110 bpm, BD ≥−2, and partial pressure of arterial oxygen (PaO₂) = 80 and 150 mm Hg), the mean PmO₂ was 34 ± 11 mm Hg and StO₂ was 63 ± 27%. There was a strong relationship between PmO₂ and BD (p <0.001) but no significant relationship between StO₂ and BD. The relationship between PmO₂ and StO₂ was weak but statistically significant. Early low values of both PmO₂ and StO₂ identified patients at risk for infectious complications or multiple organ failure (MOF). In patients who were well resuscitated by standard continuous parameters (HR and MAP), low PmO₂ during the first 24 hours after admission (PmO₂ ≤25 for at least 2 hours) was strongly associated with the development of infectious complications (Odds Ratio = 16.5, 95% CI 1.49 to 183, p = 0.02).

Conclusions: 

PmO₂ is a responsive, reliable and continuous monitor of changes in base deficit. Initial low values for either PmO₂ or StO₂ were associated with post-injury complications. PmO₂ monitoring may be useful in identifying patients in the state of occult underresuscitation who remain at risk for developing infection and MOF.