Near infrared spectroscopy (NIRS) to assess the effects of local ischemic preconditioning in the muscle of healthy volunteers and critically ill patients

Altered Microvascular Reactivity During a Skin Thermal Challenge Is Associated With Organ Dysfunction and Slow Recovery After Cardiac Surgery

OBJECTIVES

To assess microvascular reactivity during a skin thermal challenge early post-cardiac surgery and its association with outcomes.

DESIGN

Noninvasive physiological study.

SETTING

Thirty-five-bed department of intensive care.

PARTICIPANTS

Patients admitted to the intensive care unit post-cardiac surgery.

INTERVENTIONS

Thermal challenge.

MEASUREMENTS AND MAIN RESULTS

A total of 46 patients were included; 14 needed vasoactive or ventilatory support for at least 48 hours (slow recovery), and 32 had a more rapid recovery. Skin blood flow (SBF) was measured on the anterior proximal forearm using skin laser Doppler. A thermal challenge was performed by abruptly increasing local skin temperature from 37°C to 43°C while monitoring SBF. The ratio between SBFs at 43°C and 37°C was calculated to measure microvascular reactivity. SBF at 37°C was not significantly different in patients with a slow recovery and those with a rapid recovery, but SBF after 9 minutes at 43°C was lower (48.5 [17.3-69.0] v 85.1 [45.2-125.7], p < 0.01), resulting in a lower SBF ratio (2.8 [1.5-4.7] v 4.8 [3.7-7.8], p < 0.01). Patients with lower SBF ratios were more likely to have dysfunction of at least one organ (assessed using the sequential organ dysfunction score) 48 hours post-cardiac surgery than those with higher ratios: 88% versus 40% versus 27% (p < 0.01), respectively, for the lowest, middle, and highest tertiles of SBF ratio. In multivariable analysis, a lower SBF ratio was an independent risk factor for slow recovery.

CONCLUSIONS

Early alterations in microvascular reactivity, evaluated by a skin thermal challenge, are correlated with organ dysfunction. These observations may help in the development of new, simple, noninvasive monitoring systems in postoperative patients.

Transfusion increased skin blood flow when initially low in volume-resuscitated patients without acute bleeding

Background

Alterations in skin blood flow is a marker of inadequate tissue perfusion in critically ill patients after initial resuscitation. The effects of red blood cell transfusions (RBCT) on skin perfusion are not described in this setting. We evaluated the effects of red blood cell transfusions on skin tissue perfusion in critically ill patients without acute bleeding after initial resuscitation.

Methods

A prospective observational study included 175 non-bleeding adult patients after fluid resuscitation requiring red blood cell transfusions. Using laser Doppler, we measured finger skin blood flow (SBF) at skin basal temperature (SBFBT), together with mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb), central venous pressure (CVP), lactate, and central or mixed venous oxygen saturation before and 1 h after RBCT. SBF responders were those with a 20% increase in SBFBT after RBCT.

Results

Overall, SBFBT did not significantly change after RBCT [from 79.8 (4.3-479.4) to 83.4 (4.9-561.6); p = 0.67]. A relative increase equal to or more than 20% in SBFBT after RBCT (SBF responders) was observed in 77/175 of RBCT (44%). SBF responders had significantly lower SBFBT [41.3 (4.3-279.3) vs. 136.3 (6.5-479.4) perfusion units; p < 0.01], mixed or central venous oxygen saturation (62.5 ± 9.2 vs. 67.3% ± 12.0%; p < 0.01) and CVP (8.3 ± 5.1 vs. 10.3 ± 5.6 mmHg; p = 0.03) at baseline than non-responders. SBFBT increased in responders [from 41.3 (4.3-279.3) to 93.1 (9.8-561.6) perfusion units; p < 0.01], and decreased in the non-responders [from 136.3 (6.5-479.4) to 80.0 (4.9-540.8) perfusion units; p < 0.01] after RBCT. Pre-transfusion SBFBT was independently associated with a 20% increase in SBFBT after RBCT. Baseline SBFBT had an area under receiver operator characteristic of 0.73 (95% CI, 0.68-0.83) to predict SBFBT increase; A SBFBT of 73.0 perfusion units (PU) had a sensitivity of 71.4% and a specificity of 70.4% to predict SBFBT increase after RBCT. No significant differences in SBFBT were observed after RBCT in different subgroup analyses.

Conclusion

The skin blood flow is globally unaltered by red blood cell transfusions in non-bleeding critically ill patients after initial resuscitation. However, a lower SBFBT at baseline was associated with a relative increase in skin tissue perfusion after RBCT.

Ischemic Conditioning to Reduce Fatigue in Isometric Skeletal Muscle Contraction

Ischemic preconditioning (IPC) is a non-invasive protective maneuver that alternates short periods of occlusion and reperfusion of tissue blood flow. Given the heterogeneity in the magnitude and frequency of IPC-induced improvements in physical performance, here we aimed to investigate, in a well-controlled experimental set-up, the local effects of IPC in exposed muscles in terms of tissue oxygenation and muscle fatigue. Nineteen subjects were enrolled in one of the two groups, IPC (3 × 5/5 min right arm ischemia/reperfusion; cuff inflations 250 mmHg) and SHAM (3 × 5/5 min pseudo ischemia/reperfusion; 20 mmHg). The subjects performed a fatiguing contraction protocol before and 30 min after the IPC treatment, consisting of unilateral intermittent isometric elbow flexions (3 s ON/OFF, 80% of maximal voluntary contraction) until exhaustion. While muscle strength did not differ between groups, post- vs. pre-treatment endurance was significantly reduced in the SHAM group (4.1 ± 1.9 vs. 6.4 ± 3.1 repetitions until exhaustion, p < 0.05) but maintained in IPC (7.3 ± 2.0 vs. 7.1 ± 4.3, n.s.). The decrease in tissue oxygenation and the increase in deoxygenated hemoglobin were significantly reduced post- vs. pre-IPC (p < 0.05), but not post- vs. pre-SHAM. The results suggest that IPC delays the onset of fatigue likely through improved metabolic efficiency of muscles.

Microvascular effects of oxygen and carbon dioxide measured by vascular occlusion test in healthy volunteers

BACKGROUND

Changes in near-infrared spectroscopy-derived regional tissue oxygen saturation (StO₂) during a vascular occlusion test (VOT; ischemic provocation of microcirculation by rapid inflation and deflation of a tourniquet) allow estimating peripheral tissue O₂ consumption (desaturation slope; DS), vascular reactivity (recovery slope; RS) and post-ischemic hyperperfusion (AUC-H). The effects of isolated alterations in the inspiratory fraction of O₂ (FiO₂) and changes in expiratory CO₂ remain to be elucidated. Therefore, in this secondary analysis we determined the effects of standardized isolated instances of hypoxia, hyperoxia, hypocapnia and hypercapnia on the VOT-induced StO₂ changes in healthy volunteers (n = 20) to establish reference values for future physiological studies.

METHODS

StO₂ was measured on the thenar muscle. Multiple VOTs were performed in a standardized manner: i.e. at room air (baseline), during hyperoxia (FiO₂ 1.0), mild hypoxia (FiO₂ ≈ 0.11), and after a second baseline, during hypocapnia (end-tidal CO₂ (etCO₂) 2.5-3.0 vol%) and hypercapnia (etCO₂ 7.0-7.5 vol%) at room air. Differences in DS, RS, and AUC-H were tested using repeated-measures ANOVA.

RESULTS

DS and RS remained constant during all applied conditions. AUC-H after hypoxia was smaller compared to hyperoxia (963 %*sec vs hyperoxia 1702 %*sec, P = 0.005), while there was no difference in AUC-H duration between hypoxia and baseline. The StO₂ peak (after tourniquet deflation) during hypoxia was lower compared to baseline and hyperoxia (92 % vs 94 % and 98 %, P < 0.001).

CONCLUSION

We conclude that in healthy volunteers at rest, common situations observed during anesthesia and intensive care such as exposure to hypoxia, hyperoxia, hypocapnia, or hypercapnia, did not affect peripheral tissue O₂ consumption and vascular reactivity as assessed by VOT-induced changes in StO₂. These observations may serve as reference values for future physiological studies.

TRIAL REGISTRATION

This study represents a secondary analysis of an original study which has been registered at ClinicalTrials.gov nr: NCT02561052.

The Effects of Temperature Management on Brain Microcirculation, Oxygenation and Metabolism

Purpose: Target temperature management (TTM) is often used in patients after cardiac arrest, but the effects of cooling on cerebral microcirculation, oxygenation and metabolism are poorly understood. We studied the time course of these variables in a healthy swine model.Methods: Fifteen invasively monitored, mechanically ventilated pigs were allocated to sham procedure (normothermia, NT; n = 5), cooling (hypothermia, HT, n = 5) or cooling with controlled oxygenation (HT-Oxy, n = 5). Cooling was induced by cold intravenous saline infusion, ice packs and nasal cooling to achieve a body temperature of 33–35 °C. After 6 h, animals were rewarmed to baseline temperature (within 5 h). The cerebral microvascular network was evaluated (at baseline and 2, 7 and 12 h thereafter) using sidestream dark-field (SDF) video-microscopy. Cerebral blood flow (laser Doppler MNP100XP, Oxyflow, Oxford Optronix, Oxford, UK), oxygenation (PbtO₂, Licox catheter, Integra Lifesciences, USA) and lactate/pyruvate ratio (LPR) using brain microdialysis (CMA, Stockholm, Sweden) were measured hourly. Results: In HT animals, cerebral functional capillary density (FCD) and proportion of small-perfused vessels (PSPV) significantly decreased over time during the cooling phase; concomitantly, PbtO₂ increased and LPR decreased. After rewarming, all microcirculatory variables returned to normal values, except LPR, which increased during the rewarming phase in the two groups subjected to HT when compared to the group maintained at normothermia. Conclusions: In healthy animals, TTM can be associated with alterations in cerebral microcirculation during cooling and altered metabolism at rewarming.

Evaluation of Different Near-Infrared Spectroscopy Devices for Assessing Tissue Oxygenation with a Vascular Occlusion Test in Healthy Volunteers

Near-infrared spectroscopy devices can measure peripheral tissue oxygen saturation (StO2). This study aims to compare StO2 using INVOS® and different O3™ settings (O325:75 and O330:70). Twenty adults were recruited. INVOS® and O3™ probes were placed simultaneously on 1 side of forearm. After baseline measurement, the vascular occlusion test was initiated. The baseline value, rate of deoxygenation and reoxygenation, minimum and peak StO2, and time from cuff release to peak value were measured. The parameters were compared using ANOVA and Kruskal-Wallis tests. Bonferroni's correction and Mann-Whitney pairwise comparison were used for post hoc analysis. The agreement between StO2 of devices was evaluated using Bland-Altman plots. INVOS® baseline value was higher (79.7 ± 6.4%) than that of O325:75 and O330:70 (62.4 ± 6.0% and 63.7 ± 5.5%, respectively, p < 0.001). The deoxygenation rate was higher with INVOS® (10.6 ± 2.1%/min) than with O325:75 and O330:70 (8.4 ± 2.2%/min, p = 0.006 and 7.5 ± 2.1%/min, p < 0.001). The minimum and peak StO2 were higher with INVOS®. No significant difference in the reoxygenation rate was found between the devices and settings. The time to reach peak after cuff deflation was faster with INVOS® (both p < 0.001). Other parameters were similar. There were no differences between the different O3™ settings. There were differences in StO2 measurements between the devices, and these devices should not be interchanged. Differences were not observed between O3™ device settings.

Alterations in Skin Blood Flow at the Fingertip Are Related to Mortality in Patients With Circulatory Shock

OBJECTIVES

Skin blood flow is rapidly altered during circulatory shock and may remain altered despite apparent systemic hemodynamic stabilization. We evaluated whether changes in skin blood flow during circulatory shock were related to survival.

DESIGN

Prospective study.

SETTING

Thirty-five-bed medical-surgical university hospital department of intensive care.

SUBJECTS

Twenty healthy volunteers and 70 patients with circulatory shock (< 12 hr duration), defined as the need for vasopressors to maintain mean arterial pressure greater than or equal to 65 mm Hg and signs of altered tissue perfusion.

INTERVENTIONS

We assessed skin blood flow using skin laser Doppler on the fingertip for 3 minutes at basal temperature (SBFBT) and at 37°C (SBF37) (thermal challenge test) once in volunteers and at the time of inclusion and after 6, 24, 48, 72, and 96 hours in patients with shock. Capillary refill time and peripheral perfusion index were measured at the same time points on the contralateral hand.

MEASUREMENTS AND MAIN RESULTS

The thermal challenge response (ΔSBF/ΔT) was calculated using the following formula: (SBF37-SBFBT)/(37-basal temperature). Area under the receiver operating characteristic curves were calculated to evaluate variables predictive of ICU mortality. At inclusion, skin blood flow and ΔSBF/ΔT were lower in patients than in volunteers. Baseline skin blood flow (31 [17-113] vs 16 [9-32] arbitrary perfusion units; p = 0.01) and ΔSBF/ΔT (4.3 [1.7-10.9] vs 0.9 [0.4-2.9] arbitrary perfusion unit/s) were greater in survivors than in nonsurvivors. Capillary refill time was shorter in survivors than in nonsurvivors; peripheral perfusion index was similar in the two groups. ΔSBF/ΔT (area under the receiver operating characteristic curve 0.94 [0.88-0.99]) and SBFBT (area under the receiver operating characteristic curve 0.83 [0.73-0.93]) had the best predictive value for ICU mortality with cutoff values less than or equal to 1.25 arbitrary perfusion unit/°C (sensitivity 88%, specificity 89%) and less than or equal to 21 arbitrary perfusion unit (sensitivity 84%, specificity 81%), respectively.

CONCLUSIONS

Alterations in fingertip skin blood flow can be evaluated using a laser Doppler thermal challenge technique in patients with circulatory shock and are directly related to outcome. These novel monitoring techniques could potentially be used to guide resuscitation.

Near-Infrared Spectroscopy in Adult Circulatory Shock: A Systematic Review

BACKGROUND

Circulatory shock affects every third patient in intensive care units and is associated with high mortality. Near-infrared spectroscopy (NIRS) could serve as a means for monitoring tissue perfusion in circulatory shock.

PURPOSE

To assess the evidence of NIRS monitoring in circulatory shock, we conducted a systematic review of the literature.

METHODS

The study protocol was registered in International Prospective Register of Systematic Reviews (PROSPERO). We searched PubMed, Ovid MEDLINE, Scopus, and EBM Reviews databases. The reference lists of included articles, last volumes of key journals, and NIRS monitor manufacturers' webpages were searched manually. Two reviewers independently selected included studies. The quality of studies was assessed. The qualitative synthesis was guided by 3 questions: First, does NIRS monitoring improve patient-centered outcomes in adult circulatory shock patient? Second, do NIRS-derived parameters predict patient-centered outcomes, such as mortality and organ dysfunction, and third, does NIRS monitoring give additional information to guide treatment decisions?

MAIN RESULTS

Eighteen observational studies with 927 patients were included. Because of considerable clinical heterogeneity of the data, we were not able to perform a meta-analysis. Also, due to lack of randomized controlled trials, the first review question could not be answered. Based on the current review, baseline tissue oxygen saturation (StO2) however seems to predict mortality and identify patients with most severe forms of circulatory shock.

CONCLUSIONS

Near-infrared spectroscopy-derived StO2 can predict mortality in circulatory shock, but high-quality data on the impact of NIRS monitoring are lacking. Furthermore, the marked heterogeneity of the studies makes combining the results of individual studies difficult. Standardization of methodology and clinical randomized trials are needed before wider clinical use.

Peripheral Muscle Near-Infrared Spectroscopy Variables are Altered Early in Septic Shock

BACKGROUND

Noninvasive evaluation of muscle perfusion using near-infrared spectroscopy (NIRS) coupled with a vascular occlusion test (VOT) may provide an early and simple marker of altered perfusion and microcirculatory function in sepsis.

OBJECTIVE

The aim of the study was to compare the time-course of NIRS-derived variables with systemic measures of perfusion in an experimental model of peritonitis.

METHODS

Peritonitis was induced in eight anesthetized, mechanically ventilated, adult sheep (24-34 kg), by injecting autologous feces into the peritoneal cavity. Animals were followed until death or for a maximum of 30 h. Muscle tissue oxygen saturation (StO2) was determined using NIRS on the right posterior leg and arterial VOTs were performed by intermittent intra-aortic balloon inflation. Microdialysis was used to measure muscle lactate and pyruvate levels.

RESULTS

Muscle StO2 was significantly lower than baseline values from 8 h after sepsis induction, but with considerable intersubject variability. The NIRS VOT ascending (Asc) slope decreased to values <120%/min in most animals from 12 h after sepsis induction. Muscle lactate/pyruvate ratios were higher than baseline from 16 h after sepsis induction. Mixed venous oxygen saturation (SvO2) decreased to <70% and blood lactate levels increased to >2 mmol/L in most of the animals only 24 and 28 h after sepsis induction, respectively. Muscle NIRS StO2 correlated strongly with femoral venous oxygen saturation (r = 0.820) and moderately with SvO2 (r = 0.436).

CONCLUSIONS

The muscle NIRS Asc slope after a VOT is altered earlier than global markers of tissue hypoperfusion during sepsis. This simple noninvasive test can detect early changes in peripheral perfusion in sepsis.

Measurement of peripheral muscle oxygen saturation in conscious healthy horses using a near-infrared spectroscopy device

OBJECTIVE

Maintaining adequate muscle tissue oxygenation is of paramount importance during equine general anesthesia. The objectives of this study were to assess the feasibility, reliability and repeatability of near-infrared spectroscopy (NIRS) muscle oximetry using the Inspectra m650 in conscious healthy adult horses.

STUDY DESIGN

Prospective, observational study.

ANIMALS

A group of 30 healthy client-owned adult horses admitted to the equine hospital between July 2017 and July 2018.

METHODS

The probe of an Inspectra m650 NIRS tissue oximeter was placed on the hairless surface of five muscle sites (omotransversarius, triceps long head, extensor carpi ulnaris, vastus lateralis and lateral digital extensor) on the left side of the body of each standing, unsedated horse. Each site had muscle oxygenation (StO₂) recordings measured in triplicate and statistical modeling used to assess the reading reliability and repeatability within and between muscle sites.

RESULTS

The readings acquired at the vastus lateralis and extensor carpi ulnaris muscle sites had highly repeatable values [mean (90% confidence interval): StO₂, 95% (93.8%, 96.5%) and 93% (91.6%, 93.9%), respectively; intraclass correlation coefficients, 0.92 and 0.80, respectively]. These two sites also had high reliability (represented by the percentage of successful readings; 70% and 86%, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

The use of NIRS muscle oxygenation technology is a clinically feasible means to assess tissue oxygenation in horses. The vastus lateralis and extensor carpi ulnaris muscle sites provided the most reliable and repeatable readings when using the Inspectra m650 machine in horses.

Effects of ischaemic conditioning on tissue oxygen saturation and heart rate variability: an observational study

Objective

Ischaemic conditioning (IC) has organ-protective effects, but its clinical results have been inconsistent. Tissue oxygen saturation (StO₂) and heart rate variability (HRV) reflect peripheral microcirculation and autonomic nervous system activity, but their changes during IC have not been well documented. We assessed StO₂ and HRV during IC in patients undergoing cardiac surgery and healthy volunteers.

Methods

Ten patients undergoing cardiac surgery and 10 healthy male volunteers underwent remote IC (four 5-minute cycles of ischaemia/reperfusion) applied to the upper arm. Changes in StO₂ at the thenar eminence and HRV according to the R-R intervals were recorded during IC.

Results

The lowest StO₂ during ischaemia significantly decreased in patients and significantly increased in volunteers. Among the HRV parameters, the low-frequency domain, which corresponds to sympathetic activity, significantly increased after IC in volunteers but not in patients. Other variables were similar between the groups.

Conclusions

These results suggest that the minimum tissue oxygen content is depleted during ischaemia in patients and preserved in healthy volunteers. Sympathetic nervous activity seems to increase after IC in healthy volunteers but remains unaffected in patients. Thus, IC may act differently between patients undergoing cardiac surgery and healthy subjects.

Skin microcirculatory reactivity assessed using a thermal challenge is decreased in patients with circulatory shock and associated with outcome

Background

Shock states are characterized by impaired tissue perfusion and microcirculatory alterations, which are directly related to outcome. Skin perfusion can be noninvasively evaluated using skin laser Doppler (SLD), which, when coupled with a local thermal challenge, may provide a measure of microcirculatory reactivity. We hypothesized that this microvascular reactivity would be impaired in patients with circulatory shock and would be a marker of severity.

Methods

We first evaluated skin blood flow (SBF) using SLD on the forearm and on the palm in 18 healthy volunteers to select the site with maximal response. Measurements were taken at 37 °C (baseline) and repeated at 43 °C. The 43 °C/37 °C SBF ratio was calculated as a measure of microvascular reactivity. We then evaluated the SBF in 29 patients with circulatory shock admitted to a 35-bed department of intensive care and in a confirmatory cohort of 35 patients with circulatory shock.

Results

In the volunteers, baseline SBF was higher in the hand than in the forearm, but the SBF ratio was lower (11.2 [9.4–13.4] vs. 2.0 [1.7–2.6], p < 0.01) so we used the forearm for our patients. Baseline forearm SBF was similar in patients with shock and healthy volunteers, but the SBF ratio was markedly lower in the patients (2.6 [2.0–3.6] vs. 11.2 [9.4–13.4], p < 0.01). Shock survivors had a higher SBF ratio than non-survivors (3.2 [2.2–6.2] vs. 2.3 [1.7–2.8], p < 0.01). These results were confirmed in the second cohort of 35 patients. In multivariable analysis, the APACHE II score and the SBF ratio were independently associated with mortality.

Conclusions

Microcirculatory reactivity is decreased in patients with circulatory shock and has prognostic value. This simple, noninvasive test could help in monitoring the peripheral microcirculation in acutely ill patients.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0393-7) contains supplementary material, which is available to authorized users.

Assessment of the adequacy of oxygen delivery

PURPOSE OF REVIEW

This article reviews the recent literature pertaining to assessment of the adequacy of oxygen delivery in critically ill patients with circulatory shock.

RECENT FINDINGS

The assessment of the adequacy of oxygen delivery has traditionally involved measurement of lactate, central (or mixed) venous oxygen saturation (ScvO2), and global hemodynamic markers such as mean arterial pressure and cardiac index. The search for noninvasive, reliable, and sensitive methods to detect derangements in oxygen delivery and utilization continues. Recent studies focus on near-infrared spectroscopy (NIRS) to assess regional tissue oxygenation, as well as bedside ultrasound techniques to assess the macrovascular hemodynamic factors in oxygen delivery.

SUMMARY

In this article, we review physiologic principles of global oxygen delivery, and discuss the bedside approach to assessing the adequacy of oxygen delivery in critically ill patients. Although there have been technological advances in the assessment of oxygen delivery, we revisit and emphasize the importance of a 'tried and true' method - the physical examination. Also potentially important in the evaluation of oxygen delivery is the utilization of biomarkers (e.g., lactate, ScvO2, NIRS). In complementary fashion, bedside ultrasound for hemodynamic assessment may augment the physical examination and biomarkers, and represents a potentially important adjunct for assessing the adequacy of oxygen delivery.

Evaluation for occult sepsis incorporating NIRS and emergency sonography

PURPOSE

We aim to determine whether the combination of regional tissue oxygen saturation (StO₂) measurement using near-infrared spectroscopy (NIRS), inferior vena cava (IVC) collapsibility and ejection fraction (EF) is able to detect occult sepsis.

METHODS

We included adult patients in the emergency department with at least one of the following: fever; any one component of the quick sepsis-related organ function assessment (SOFA) score; heart rate≥100 beats per minute; or white cell count <4.0×10⁹/L or >12.0×10⁹/L. StO₂ parameters, IVC collapsibility and EF were assessed. Primary outcome was composite of admission to intensive care unit, hypotension requiring fluid resuscitation or vasopressor use, and antibiotic escalation.

RESULTS

We included 184 patients with mean age of 55.4years and slight male predominance (51.6%). Increase in temperature (adjusted odds ratio [aOR] 3.05; 95% confidence interval [CI] 1.16 to 8.02), higher white cell counts (aOR 1.10; 95% CI 1.03 to 1.19), increase in time taken to new StO₂ baseline (aOR 1.03; 95% CI 1.01 to 1.06) and reduced EF (aOR 33.9; 95% CI 2.19 to 523.64) had higher odds of achieving the primary outcome.

CONCLUSION

Change in StO₂ and time taken to reach new StO₂ baseline, combined with EF could potentially predict sepsis among patients with infection.

Microvascular reactivity is altered early in patients with acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is associated with vascular endothelial dysfunction. The resultant microvascular reactivity can be assessed non-invasively using near-infrared spectroscopy (NIRS) and a vascular occlusion test (VOT) and changes have been correlated with severity of organ dysfunction and mortality in other critically ill populations. We used NIRS to study the presence of microcirculatory alterations in patients with ARDS.

METHODS

We studied 27 healthy volunteers and 32 ARDS patients admitted to our intensive care department. NIRS measurements were performed within 24 h after diagnosis (Berlin definition). VOTs were performed by inflating an arm-cuff to a pressure greater than the systolic pressure for 3 min, followed by rapid deflation. The descending (Desc) and ascending (Asc) thenar muscle oxygen saturation (StO2) slopes were calculated. We compared data from volunteers with those from ARDS patients, from ARDS survivors and non-survivors, and from ARDS survivors who required <7 days ventilatory support (good evolution) with those who required >7 days support or died (poor evolution).

RESULTS

ARDS patients had lower StO2 values [75(67-80) vs 79(76-81) %, p = 0.04] and Asc slopes [185(115-233) vs 258(216-306) %/min, p < 0.01] than healthy volunteers, but Desc slopes were similar. The Asc slope was lower in the patients with a poor evolution than in the other patients [121(90-209) vs 222(170-293) %/min, p < 0.01], and in the non-survivors than in the survivors [95(73-120) vs 212(165-252) %/min, p < 0.01].

CONCLUSIONS

In ARDS patients, microvascular reactivity is altered early, and the changes are directly related to the severity of the disease. The ascending slope is the best determinant of outcome.