DYNAMIC NEAR-INFRARED SPECTROSCOPY MEASUREMENTS IN PATIENTS WITH SEVERE SEPSIS

Prospective Evaluation of the Peripheral Perfusion Index in Assessing the Organ Dysfunction and Prognosis of Adult Patients With Sepsis in the ICU

Background: The peripheral perfusion index (PI) reflects microcirculatory blood flow perfusion and indicates the severity and prognosis of sepsis. Method: The cohort comprised 208 patients admitted to the intensive care unit (ICU) with infection, among which 117 had sepsis. Demographics, medication history, ICU variables, and laboratory indexes were collected. Primary endpoints were in-hospital mortality and 28-day mortality. Secondary endpoints included organ function variables (coagulation function, liver function, renal function, and myocardial injury), lactate concentration, mechanical ventilation time, and length of ICU stay. Univariate and multivariate analyses were conducted to assess the associations between the PI and clinical outcomes. Sensitivity analyses were performed to explore the associations between the PI and organ functions in the sepsis and nonsepsis groups. Result: The PI was negatively associated with in-hospital mortality (odds ratio [OR] 0.29, 95% confidence interval [CI] 0.15 to 0.55), but was not associated with 28-day mortality. The PI was negatively associated with the coagulation markers prothrombin time (PT) (β -0.36, 95% CI -0.59 to 0.13) and activated partial thromboplastin time (APTT) (β -1.08, 95% CI -1.86 to 0.31), and the myocardial injury marker cardiac troponin I (cTnI) (β -2085.48, 95% CI -3892.35 to 278.61) in univariate analysis, and with the PT (β -0.36, 95% CI -0.60 to 0.13) in multivariate analysis. The PI was negatively associated with the lactate concentration (β -0.57, 95% CI -0.95 to 0.19), mechanical ventilation time (β -23.11, 95% CI -36.54 to 9.69), and length of ICU stay (β -1.28, 95% CI -2.01 to 0.55). Sensitivity analyses showed that the PI was significantly associated with coagulation markers (PT and APTT) and a myocardial injury marker (cTnI) in patients with sepsis, suggesting that the associations between the PI and organ function were stronger in the sepsis group than the nonsepsis group. Conclusion: The PI provides new insights for assessing the disease severity, short-term prognosis, and organ function damage in ICU patients with sepsis, laying a theoretical foundation for future research.

The role of the microcirculation and integrative cardiovascular physiology in the pathogenesis of ICU-acquired weakness

Skeletal muscle dysfunction after critical illness, defined as ICU-acquired weakness (ICU-AW), is a complex and multifactorial syndrome that contributes significantly to long-term morbidity and reduced quality of life for ICU survivors and caregivers. Historically, research in this field has focused on pathological changes within the muscle itself, without much consideration for their in vivo physiological environment. Skeletal muscle has the widest range of oxygen metabolism of any organ, and regulation of oxygen supply with tissue demand is a fundamental requirement for locomotion and muscle function. During exercise, this process is exquisitely controlled and coordinated by the cardiovascular, respiratory, and autonomic systems, and also within the skeletal muscle microcirculation and mitochondria as the terminal site of oxygen exchange and utilization. This review highlights the potential contribution of the microcirculation and integrative cardiovascular physiology to the pathogenesis of ICU-AW. An overview of skeletal muscle microvascular structure and function is provided, as well as our understanding of microvascular dysfunction during the acute phase of critical illness; whether microvascular dysfunction persists after ICU discharge is currently not known. Molecular mechanisms that regulate crosstalk between endothelial cells and myocytes are discussed, including the role of the microcirculation in skeletal muscle atrophy, oxidative stress, and satellite cell biology. The concept of integrated control of oxygen delivery and utilization during exercise is introduced, with evidence of physiological dysfunction throughout the oxygen delivery pathway - from mouth to mitochondria - causing reduced exercise capacity in patients with chronic disease (e.g., heart failure, COPD). We suggest that objective and perceived weakness after critical illness represents a physiological failure of oxygen supply-demand matching - both globally throughout the body and locally within skeletal muscle. Lastly, we highlight the value of standardized cardiopulmonary exercise testing protocols for evaluating fitness in ICU survivors, and the application of near-infrared spectroscopy for directly measuring skeletal muscle oxygenation, representing potential advancements in ICU-AW research and rehabilitation.

Agreement of somatic and renal near-infrared spectroscopy with reference blood samples during a controlled hypoxia sequence: a healthy volunteer study

Purpose: O3® Regional Oximetry (Masimo Corporation, California, USA) is validated for cerebral oximetry. We aimed to assess agreement of somatic and renal near-infrared spectroscopy with reference blood samples. Methods: O3 sensors were placed bilaterally on the quadriceps and flank of 26 healthy volunteers. A stepped, controlled hypoxia sequence was performed by adding a mixture of nitrogen and room air to the breathing circuit. O3-derived oxygen saturation values were obtained at baseline and at six decremental saturation levels (5% steps). Blood samples (radial artery, iliac vein (somatic reference) and renal vein) were obtained at each step. Reference values were calculated as: 0.7 × venous saturation + 0.3 × arterial saturation. The agreement between O3-derived values with blood reference values was assessed by calculating root-mean-square error accuracy and Bland-Altman plots. Results: The root-mean-square error accuracy was 6.0% between quadriceps oxygen saturation and somatic reference values. The mean bias was 0.8%, with limits of agreement from -7.7 to 9.3%. These were 5.1% and 0.6% (-8.3 to 9.5%) for flank oxygen saturation and somatic reference values, respectively, and 7.7% and -4.9% (-15.0 to 5.2%) for flank oxygen saturation and renal reference values. The kidney depth was 3.1 ± 0.9 cm below the skin. Conclusion: O3 regional oximetry can be used on the quadriceps and flank to monitor somatic saturation, yet has a saturation-level dependent bias. O3-derived values obtained at the flank underestimated renal reference values. Additionally, it is unlikely that the flank sensors did directly measure renal tissue. Trial registration: Clinicaltrials.gov (NCT04584788): registered October 6th, 2020.

Muscle Oxygenation of the Paretic and Nonparetic Legs During and After Arterial Occlusion in Chronic Stroke

Oxygen delivery and demand are reduced in the paretic leg post-stroke, reflecting decreased vascular function and reduced muscle quantity and quality. However, it is unknown how muscle oxygenation, the balance between muscle oxygen delivery and utilization, is altered in chronic stroke during and after occlusion-induced ischemia.

OBJECTIVES

The objective was to determine muscle oxygen consumption rate, microvascular responsiveness and reactive hyperemia in the paretic and nonparetic legs during and after arterial occlusion post-stroke.

MATERIALS AND METHODS

Muscle oxygen saturation was measured with near-infrared spectroscopy on the vastus lateralis of each leg during 3-minute arterial occlusion and recovery (3 min). Muscle oxygen consumption was derived from the desaturation slope during ischemia, microvascular responsiveness was derived from the resaturation slope after ischemia and reactive hyperemia was derived from the area under the curve above baseline after ischemia.

RESULTS

Eleven subjects (91% male; 32.2±6.1 months post-stroke; age 62.9±13.6 years) with a hemiparetic gait pattern participated. There was no significant between-leg muscle oxygenation difference at rest (paretic: 64.9±16.6%; nonparetic: 70.6±15.6%, p = 0.13). Muscle oxygen consumption in the paretic leg (-0.53±0.24%/s) was significantly reduced compared to the nonparetic leg (-0.70±0.36%/s; p = 0.03). Microvascular responsiveness was significantly reduced in the paretic leg compared to the nonparetic leg (paretic: 4.6±1.8%/s; nonparetic: 5.7±1.6%/s, p = 0.04). Reactive hyperemia was not significantly different between legs (paretic:4384±2341%·s; nonparetic: 3040±2216%·s, p = 0.07).

CONCLUSION

Muscle oxygen consumption and microvascular responsiveness are impaired in the paretic compared to the nonparetic leg, suggesting both reduced skeletal muscle aerobic function and reduced ability to maximally perfuse muscle tissue.

Incongruous effect of phenylephrine on changes in cerebral blood volume measured by near-infrared spectroscopy (NIRS) indicating extracranial contamination

We assessed extracranial contamination of the near-infrared spectroscopy (NIRS) signal during administration of phenylephrine. The study was performed with NIRO 200NX which employs both the Modified Beer-Lambert (MBL) method to measure total hemoglobin (tHb, expressed in µM), and Spatially Resolved Spectroscopy (SRS) to measure total hemoglobin content (nTHI, expressed in arbitrary units (a.u.)). SRS tends to not be affected by extracranial blood flow. As vasoconstriction with phenylephrine mainly occurs in the extracranial area, we hypothesized that if NIRS measurements are indeed prone to extracranial contamination, tHb will be more affected by the administration of phenylephrine than nTHI. After ethical committee approval, 20 consenting cardiac surgery patients were included. Phenylephrine was administered whenever clinically indicated and its effect on nTHI and tHb was evaluated. To adjust for the difference in raw scale units, Z-scores were calculated. Data were analyzed with Wilcoxon Signed Ranks Test and the Hodges-Lehmann method. A total of 191 data sets were obtained in 20 patients (10 male, 65 ± 15 years, 77 ± 16 kg, 166 ± 11 cm). The median difference before and after administration of phenylephrine was - 0.006 a.u. [95%CI - 0.010 to - 0.002] (p < 0.001) and - 0.415 µM [95%CI - 0.665 to - 0.205] (p < 0.001) for nTHI and tHb, respectively. The median difference between the Z-scores of nTHI and tHb was - 0.02 [95%CI - 0.04 to - 0.003] (p = 0.03), with a higher variability in the Z-scores of tHb. Phenylephrine induced significant larger changes in MBL values compared to SRS values, indicating that the MBL method might be more prone to extracranial contamination. Trial and clinical registry: Trial registration number: B670201939459, ethical committee number: 2019/0265, date of approval: March 19, 2019.

Advances in translational imaging of the microcirculation

The past few decades have seen an explosion in the development and use of methods for imaging the human microcirculation during health and disease. The confluence of innovative imaging technologies, affordable computing power, and economies of scale have ushered in a new era of "translational" imaging that permit us to peer into blood vessels of various organs in the human body. These imaging techniques include near-infrared spectroscopy (NIRS), positron emission tomography (PET), and magnetic resonance imaging (MRI) that are sensitive to microvascular-derived signals, as well as computed tomography (CT), optical imaging, and ultrasound (US) imaging that are capable of directly acquiring images at, or close to microvascular spatial resolution. Collectively, these imaging modalities enable us to characterize the morphological and functional changes in a tissue's microcirculation that are known to accompany the initiation and progression of numerous pathologies. Although there have been significant advances for imaging the microcirculation in preclinical models, this review focuses on developments in the assessment of the microcirculation in patients with optical imaging, NIRS, PET, US, MRI, and CT, to name a few. The goal of this review is to serve as a springboard for exploring the burgeoning role of translational imaging technologies for interrogating the structural and functional status of the microcirculation in humans, and highlight the breadth of current clinical applications. Making the human microcirculation "visible" in vivo to clinicians and researchers alike will facilitate bench-to-bedside discoveries and enhance the diagnosis and management of disease.

Assessment of tissue oxygenation to personalize mean arterial pressure target in patients with septic shock

OBJECTIVE

To investigate whether assessment of tissue oxygenation could help personalizing the mean arterial pressure (MAP) target in patients with septic shock.

METHODS

We prospectively measured near-infrared spectroscopy variables in 22 patients with septic shock receiving norepinephrine with a MAP>75 mmHg within the first six hours of intensive care unit (ICU) stay for patients with community-acquired septic shock and within the first six hours of resuscitation for patients with ICU-acquired septic shock. All measurements were performed at MAP>75 mmHg ("high-MAP") and at MAP 65-70 mmHg ("low-MAP") after decreasing the norepinephrine dose. Relative changes in StO₂ recovery slope (RS) >8% were considered clinically relevant.

RESULTS

After decreasing the norepinephrine dose by 45 ± 24%, MAP significantly decreased from 81[78;84] to 68[67;69]mmHg, whereas cardiac index did not change. On average, the StO₂-RS significantly decreased between high and low-MAP from 2.86[1.87;4.32] to 2.41[1.14;3.72]%/sec with a large interindividual variability: the StO₂-RS decreased by >8% in 14 patients, increased by >8% in 4 patients and changes were < 8% in 4 patients. These changes in StO₂-RS were correlated with the StO₂-RS at low-MAP (r = 0.57,p = 0.006). At high-MAP, there was no difference between patients exhibiting a relevant decrease or increase in StO₂-RS.

CONCLUSIONS

A unique MAP target may not be suitable for all patients with septic shock as its impact on peripheral oxygenation may widely differ among patients. It could make sense to personalize MAP target through a multimodal assessment including peripheral oxygenation.

Prognostic Value of Tissue Oxygen Saturation Using a Vascular Occlusion Test in Patients in the Early Phase of Multiorgan Dysfunction Syndrome

BACKGROUND

Multiple organ dysfunction syndrome (MODS) is a common disease pattern in intensive care units which is associated with an increased mortality. The aim of this study was to investigate whether a near-infrared spectroscopy (NIRS)-based noninvasive ischemia-reperfusion test (vascular occlusion test) using the parameter of tissue oxygen saturation (StO2) contains prognostic information for patients in the early phase of MODS.

METHODS

Within a period of 18 months between 2010 and 2012, 56 patients who newly developed MODS (≤24 h after diagnosis, Acute Physiology and Chronic Health Evaluation [APACHE] II score ≥20, subgroups: cardiogenic MODS [cMODS] and septic MODS [sMODS]) were included into the study. The StO2 was determined non-invasively in the area of the thenar muscles using a bedside NIRS device, InSpectra Tissue Spectrometer Model 650 (Hutchinson Technology Inc., Hutchinson, MN). The VOT was carried out by inflating a blood pressure cuff on the upper arm 30 mmHg above systolic blood pressure for 5 min. The parameters occlusion slope (OS) and recovery slope (RS) were recorded.

RESULTS

Fifteen patients with cMODS and 41 patients with sMODS were included in the study (age: 62.5 ± 14.4 years, 40 men and 16 women, APACHE II score: 34.6 ± 6.4). Twenty-eight-day-mortality was 55.4% (cMODS: 7 out of 15 patients, sMODS: 24 out of 41 patients). The measurement of StO2 while applying the VOT at baseline showed an OS of -11.7 ± 3.7%/min and an RS of 2.2 ± 1.5%/s. Survivors had significantly better values compared with non-survivors at baseline regarding OS (-12.8 ± 3.5%/min vs. -9.8 ± 3.4%/min; P = 0.016) and RS (2.6 ± 1.7%/s vs. 1.6 ± 1.0%/s; P = 0.022). Receiver-operating characteristic (ROC) curves show that the area under the curve (AUC) for OS was found to be significantly related to 28-day mortality (AUC: 0.7; 95% confidence interval [CI]: 0.56-0.85; P = 0.01). However, using both univariate and multivariate binary logistic regression models, RS was significantly associated with increased 28-day mortality (OR [univariate model]: 1.21 [95% CI: 1.1-1.8]; OR [multivariate model]: 1.23 [95% CI: 1.1-1.3]).

CONCLUSIONS

Impaired values of the VOT-parameters OS and RS are associated with an increased 28-day mortality in patients in the early phase of MODS.

Thenar oxygen saturation (StO2) alterations during a spontaneous breathing trial predict extubation failure

Background

Weaning from mechanical ventilation (MV) is a cardiovascular stress test. Monitoring the regional oxygenation status has shown promising results in predicting the tolerance to spontaneously breathe in the process of weaning from MV. Our aim was to determine whether changes in skeletal muscle oxygen saturation (StO₂) measured by near-infrared spectroscopy (NIRS) on the thenar eminence during a vascular occlusion test (VOT) can be used to predict extubation failure from mechanical ventilation.

Methods

We prospectively studied 206 adult patients with acute respiratory failure receiving MV for at least 48 h from a 30-bed mixed ICU, who were deemed ready to wean by their physicians. Patients underwent a 30-min spontaneous breathing trial (SBT), and were extubated according to the local protocol. Continuous StO₂ was measured non-invasively on the thenar eminence. A VOT was performed prior to and at 30 min of the SBT (SBT₃₀). The rate of StO₂ deoxygenation (DeO₂), StO₂ reoxygenation (ReO₂) rate and StO₂ hyperemic response to ischemia (H_AUC) were calculated.

Results

Thirty-six of the 206 patients (17%) failed their SBT. The remainder 170 patients (83%) were extubated. Twenty-three of these patients (13.5%) needed reinstitution of MV within 24 h. Reintubated patients displayed a lower H_AUC at baseline, and higher relative changes in their StO₂ deoxygenation rate between baseline and SBT₃₀ (DeO₂ Ratio). A logistic regression-derived StO₂ score, combining baseline StO₂, H_AUC and DeO₂ ratio, showed an AUC of 0.84 (95% CI 0.74–0.91) for prediction of extubation failure.

Conclusions

Extubation failure was associated to baseline and dynamic StO₂ alterations during the SBT. Monitoring StO₂-derived parameters might be useful in predicting extubation outcome.

No effect of fitness on brachial or forearm vascular function during acute inflammation in young adults

Acute inflammation is associated with increased risk of cardiovascular events and impaired vasodilatory capacity. Vasodilatory capacity can be measured in different segments of the arterial tree; however, it is unknown if the effects of acute inflammation are vascular segment-specific or if inflammation-induced dysfunction can be attenuated by factors that modulate cardiovascular risk, such as high cardiorespiratory fitness. The purpose of this study was to determine the effect of acute inflammation and fitness on conduit artery, resistance artery, and microvascular function in healthy, young adults. Vascular function was assessed at baseline and 24 h after a typhoid vaccination in 11 low-fit (5 male, 24 yr of age, 34.5 ± 2.9 ml·kg^-1·min^-1 peak O₂ uptake (V̇o_2peak)] and 12 high-fit (7 male, 27 yr of age, 56.4 ± 9.7 ml·kg^-1·min^-1 V̇o_2peak) young adults. Vascular assessments included flow-mediated dilation (FMD) of the brachial artery, forearm reactive hyperemia (RH) via venous occlusion plethysmography, and near-infrared spectroscopy (NIRS) during a 5-min arterial occlusion. Acute inflammation was evident with increases in IL-6 and C-reactive protein (P < 0.01), and mean arterial pressure did not change (P = 0.33). FMD was lower in the high-fit group, yet it was reduced in both groups at 24 h, even after controlling for shear (P < 0.05). No effect of acute inflammation was observed for RH or NIRS (P > 0.05). Acute inflammation had nonuniform effects on vascular function throughout the arterial tree in young adults, and fitness did not alter the vascular response. This suggests that cardiorespiratory fitness may not protect the vasculature during acute inflammation in young adults in the absence of age- or disease-related decline in vascular function.

Central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference (PcvaCO2/CavO2) reflects microcirculatory oxygenation alterations in early septic shock

PURPOSE

To explore the relationship between central venous-to-arterial carbon dioxide difference (P_cvaCO₂), P_cvaCO₂/arterial-venous oxygen content difference ratio (P_cvaCO₂/C_avO₂) and the microcirculatory status, evaluated by using near-infrared spectroscopy, in septic shock patients.

METHODS

Observational study in a 30-bed mixed ICU. Fifty septic shock patients within the first 24 h of ICU admission were studied. After restoration of mean arterial pressure, hemodynamic, metabolic and microcirculatory parameters were simultaneously evaluated. Local tissue oxygen saturation (StO₂), and local hemoglobin index (THI) were measured on the thenar eminence by means of near-infrared spectroscopy. A transient vascular occlusion test was performed in order to obtain StO₂ deoxygenation rate (DeO₂), local oxygen consumption (nirVO₂), and reoxgenation rate (ReO₂).

RESULTS

At inclusion, increased P_cvaCO₂ values were associated with lower StO₂ and THI, whereas increased P_cvaCO₂/C_avO₂ values were associated with lower DeO₂, nirVO₂, and ReO₂. Multiple regression models confirmed the association between P_cvaCO₂/C_avO₂ and nirVO₂, while P_cvaCO₂ was only related to CI, and not to microcirculatory parameters.

CONCLUSIONS

In a population of early septic shock patients, increases in P_cvaCO₂ and P_cvaCO₂/C_avO₂ reflected different alterations at the microcirculatory level. While P_cvaCO₂ was related to global flow, the P_cvaCO₂/C_avO₂ ratio was associated to impaired local oxygen utilization and diminished microvascular reactivity.

Application of laser speckle contrast imaging in laparoscopic surgery

Anastomotic leakage is a worldwide problem in gastrointestinal surgery which seems to be related to the state of microcirculation. Laser speckle contrast imaging (LSCI) could give surgeons insight in the state of microcirculation to attune the site of anastomosis. This work studies the feasibility of LSCI as a tool for this purpose. An experimental setup was developed using a commercially available laparoscopic video system. Laser speckle contrast imaging is capable of detecting ischemic areas on the large intestine. Further research and development are required before adaptation of this technique in the operating room.

Exploration de la perfusion tissulaire microcirculatoire au cours du choc septique

Au cours des infections graves, les travaux chez l’animal et chez l’homme ont mis en évidence une altération de la perfusion microcirculatoire à l’origine des défaillances viscérales et potentiellement du décès. La sévérité des anomalies microcirculatoires ainsi que leur persistance sont des facteurs prédictifs de mortalité indépendamment du débit cardiaque ou de la pression artérielle. Il est donc indispensable de développer des outils permettant d’évaluer la perfusion microcirculatoire au lit du malade. De nombreux travaux au cours du sepsis suggèrent que l’analyse de la perfusion cutanée au travers de sa température (et/ou du gradient), du temps de recoloration cutané, de l’étendue des marbrures et de l’indice de perfusion périphérique constitue un outil simple qui permet au réanimateur une évaluation rapide des anomalies microcirculatoires.

Movement artefact removal from NIRS signal using multi-channel IMU data

Background

The non-invasive nature of near-infrared spectroscopy (NIRS) makes it a widely accepted method for blood oxygenation measurement in various parts of the human body. One of the main challenges in this method lies in the successful removal of movement artefacts in the detected signal. In this respect, multi-channel inertia measurement unit (IMU) containing accelerometer, gyroscope and magnetometer can be used for better modelling of movement artefact than using accelerometer only, which as a result, movement artefact can be more accurately removed.

Methods

A wearable two-channel continuous wave NIRS system, incorporating an IMU sensor which contain accelerometer, gyroscope and magnetometer in it, was developed to record NIRS signal along with the simultaneous recording of movement artefacts related signal using the IMU. Four healthy subjects volunteered in the recording of the NIRS signals. During the recording from the first two subject, movement artefacts were simulated in one of the NIRS channels by tapping the photodiode sensor nearby. The corresponding IMU data for the simulated movement artefacts were used to estimate the artefacts in the corrupted signal by autoregressive with exogenous input method and subtracted from the corrupted signal to remove the artefacts in the NIRS signal. Signal-to-noise ratio (SNR) improvement was used to evaluate the performance of the movement artefacts removal process. The performance of the movement artefacts estimation and removal were compared using accelerometer only, accelerometer and gyroscope, and accelerometer, gyroscope and magnetometer data from IMU sensor to estimate the artefact in NIRS reading. For the remaining two subjects the NIRS signal was recorded by natural movement artefacts impact and the results of artefacts removal was compared using accelerometer only, accelerometer and gyroscope, and accelerometer, gyroscope and magnetometer data from IMU sensor to estimate the artefact in NIRS reading.

Results

The quantitative and qualitative results revealed that the SNR improvement increases with the number of IMU channels used in the artefacts estimation, and there were approximately 5–11 dB increase in SNR when nine channel IMU data were used rather than using only three channel accelerometer data only. The artefact removal from natural movements also demonstrated that the combination of gyroscope and magnetometer sensors with accelerometer provided better estimation and removal of the movement artefacts, which was revealed by the minimal change of the HbO₂ and Hb level before, during and after movement artefacts occurred in the NIRS signal.

Conclusion

The movement artefacts in NIRS can be more accurately estimated and removed by using accelerometer, gyroscope and magnetograph signals from an integrated IMU sensor than using accelerometer signal only.

Correlation between regional tissue perfusion saturation and lactate level during cardiopulmonary bypass

Background

Cardiopulmonary bypass (CPB) can cause systemic hypoperfusion, which remains undetected by routine monitoring of physiological parameters. Noninvasive tissue perfusion monitoring offers a clinical benefit by detecting low systemic perfusion. In this study, we tried to evaluate whether regional tissue perfusion saturation reflects systemic hypoperfusion during CPB.

Methods

This retrospective study included 29 patients with American Society of Anesthesiologists physical status II–III, who required cardiac surgery with CPB. We evaluated the correlations of serum lactate and delivery oxygen with organ perfusion values of peripheral tissue oxygen saturation and cerebral oxygen saturation. Data were recorded at different stages of CPB: T1 (pre-CPB), T2 (cooling), T3 (hypothermia), T4 (rewarming), and T5 (post-CPB).

Results

Lactate levels were elevated after CPB and up to weaning (P < 0.05). The levels of peripheral and tissue oxygen saturation decreased after the start of CPB (P < 0.05). Lactate levels were negatively correlated with peripheral tissue oxygen saturation levels at T4 (R = −0.384) and T5 (R = −0.370) and positively correlated with cerebral oxygen saturation at T3 (R = 0.445). Additionally, delivery oxygen was positively correlated with peripheral tissue oxygen saturation at T4 (R = 0.466).

Conclusions

In this study, we demonstrated that peripheral tissue oxygen saturation can be a reliable tool for monitoring systemic hypoperfusion during CPB period. We also believe that peripheral tissue oxygen saturation is a valuable marker for detecting early stages of hypoperfusion during cardiac surgery.

[Prognostic relevance of tissue oxygen saturation in patients in the early stage of multiple organ dysfunction syndrome]

BACKGROUND

Patients in circulatory shock exhibit insufficient peripheral perfusion to ensure adequate oxygenation of vital organs such as the heart and brain. Early detection of reduced tissue oxygen saturation (S_tO₂) could be used for rapid therapeutic intervention and thus improve the prognosis of patients in the early stage of multiple organ dysfunction syndrome (MODS).

MATERIALS AND METHODS

A total of 60 patients in the early stage of MODS (APACHE [Acute Physiology and Chronic Health Evaluation] II score ≥20) were investigated in a monocentric, prospective, randomized phase II study. S_tO₂ was measured using the InSpectraTM S_tO₂ system and compared with known indicators of hypoxia (peripheral oxygen saturation [S_pO₂], arterial oxygen saturation [S_aO₂], central venous oxygen saturation [S_cvO₂], pH, serum lactate). Clinical endpoints of the study were 28-day and 6‑month mortality as well as the need for invasive mechanical ventilation and renal replacement therapy during the hospital stay, respectively.

RESULTS

An increased 28-day and 6‑month mortality is found for patients with S_tO₂ <75% in contrast to patients with S_tO₂ ≥75%. Correlations of S_tO₂ with S_pO₂, S_cvO₂, and serum lactate are confirmed. Patients with reduced S_tO₂ tend to show a higher disease severity as measured by APACHE II score.

CONCLUSION

S_tO₂ shows prognostic relevance in patients at the early stage of MODS. Thus, the rapid and noninvasive assessment of S_tO₂ could be useful in risk stratification of these patients.

Assessment of hand superficial oxygenation during ischemia/reperfusion in healthy subjects versus systemic sclerosis patients by 2D near infrared spectroscopic imaging

BACKGROUND AND OBJECTIVE

Patients affected by systemic sclerosis (SSc) develop functional and structural microcirculatory dysfunction, which progressively evolves towards systemic tissue fibrosis (sclerosis). Disease initially affects distal extremities, which become preferential sites of diagnostic scrutiny. This pilot investigation tested the hypothesis that peripheral microcirculatory dysfunction in SSc could be non-invasively assessed by 2D Near Infrared Spectroscopic (NIRS) imaging of the hand associated with Vascular Occlusion Testing (VOT). NIRS allows measurement of hemoglobin oxygen saturation (StO₂) in the blood perfusing the volume tissue under scrutiny.

METHODS

In five normal volunteers and five SSc patients we applied a multispectral oximetry imaging device (Kent camera, Kent Imaging, Calgary, Canada) to acquire StO₂ 2D maps of the whole hand palm during baseline, ischemia and reperfusion phase.

RESULTS

We found significant differences between controls and SSc patients in basal StO₂ (82.80 ± 2.51 vs 65.44 ± 7.96%, p = 0.0016), minimum StO₂ (59.35 ± 4.29 vs 40.73 ± 6.47%, p = 0.0007), final StO₂ (83.83 ± 4.09 vs 68.84 ± 11.41%, p = 0.02) and time to maximum StO₂ (40 ± 12.25 vs 62 ± 4.47 s, p = 0.005).

CONCLUSIONS

This is, to our knowledge, the first application of 2D NIRS imaging of the whole hand to the investigation of microvascular dysfunction in systemic sclerosis. The image processing presented here considered the StO₂ in the entire hand allowing a comprehensive view of the spatial heterogeneity of microvascular dysfunction.

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.

Monitoring End Points of Burn Resuscitation

This article discusses commonly used methods of monitoring and determining the end points of resuscitation. Each end point of resuscitation is examined as it relates to use in critically ill burn patients. Published medical literature, clinical trials, consensus trials, and expert opinion regarding end points of resuscitation were gathered and reviewed. Specific goals were a detailed examination of each method in the critical care population and how this methodology can be used in the burn patient. Although burn resuscitation is monitored and administered using the methodology as seen in medical/surgical intensive care settings, special consideration for excessive edema formation, metabolic derangements, and frequent operative interventions must be considered.

Proof of concept non-invasive estimation of peripheral venous oxygen saturation

BACKGROUND

Pulse oximeters continuously monitor arterial oxygen saturation. Continuous monitoring of venous oxygen saturation (SvO₂) would enable real-time assessment of tissue oxygen extraction (O₂E) and perfusion changes leading to improved diagnosis of clinical conditions, such as sepsis.

METHODS

This study presents the proof of concept of a novel pulse oximeter method that utilises the compliance difference between arteries and veins to induce artificial respiration-like modulations to the peripheral vasculature. These modulations make the venous blood pulsatile, which are then detected by a pulse oximeter sensor. The resulting photoplethysmograph (PPG) signals from the pulse oximeter are processed and analysed to develop a calibration model to estimate regional venous oxygen saturation (SpvO₂), in parallel to arterial oxygen saturation estimation (SpaO₂). A clinical study with healthy adult volunteers (n = 8) was conducted to assess peripheral SvO₂ using this pulse oximeter method. A range of physiologically realistic SvO₂ values were induced using arm lift and vascular occlusion tests. Gold standard, arterial and venous blood gas measurements were used as reference measurements. Modulation ratios related to arterial and venous systems were determined using a frequency domain analysis of the PPG signals.

RESULTS

A strong, linear correlation (r ²  = 0.95) was found between estimated venous modulation ratio (R_Ven) and measured SvO₂, providing a calibration curve relating measured R_Ven to venous oxygen saturation. There is a significant difference in gradient between the SpvO₂ estimation model (SpvO₂ = 111 - 40.6*R) and the empirical SpaO₂ estimation model (SpaO₂ = 110 - 25*R), which yields the expected arterial-venous differences. Median venous and arterial oxygen saturation accuracies of paired measurements between pulse oximeter estimated and gold standard measurements were 0.29 and 0.65%, respectively, showing good accuracy of the pulse oximeter system.

CONCLUSIONS

The main outcome of this study is the proof of concept validation of a novel pulse oximeter sensor and calibration model to assess peripheral SvO₂, and thus O₂E, using the method used in this study. Further validation, improvement, and application of this model can aid in clinical diagnosis of microcirculation failures due to alterations in oxygen extraction.

Microvascular reactivity measured by vascular occlusion test is an independent predictor for postoperative bleeding in patients undergoing cardiac surgery

The purpose of the study is to investigate the relationship between microvascular reactivity and postoperative bleeding in cardiac surgery. The authors retrospectively analyzed a prospectively collected registry of cardiac surgery patients. Data from 154 patients enrolled in the registry were analyzed. A linear mixed model was performed to evaluate the association between the amount of postoperative chest tube output (CTO, milliliter, repeatedly measured at 0-8, 8-24, and 24-48 h) and tissue oxygen saturation (StO₂₎ recovery slope (%/s) measured by vascular occlusion test (VOT) at skin closure. A logistic regression was carried out to see the relationship between StO₂ recovery slope and packed red blood cell (PRBC) transfusion during the 48-h postoperative period. In the multivariable adjusted model, the effect of StO₂ recovery slope on postoperative CTO (log-transformed) was statistically significant, and the degree of StO₂ recovery slope was inversely related to the amount of CTO (exp(estimate) = 0.935; exp(95% CI) 0.881-0.992; p = 0.027). StO₂ recovery slope was also inversely associated with postoperative PRBC transfusion possibility (OR = 0.795; 95% CI 0.633-0.998; p = 0.048). Microvascular reactivity measured by VOT is independently and inversely associated with postoperative bleeding in patients undergoing cardiac surgery.

Microcirculatory monitoring in septic patients: Where do we stand?

Microcirculatory alterations play a pivotal role in sepsis-related morbidity and mortality. However, since the microcirculation has been a "black box", current hemodynamic management of septic patients is still guided by macrocirculatory parameters. In the last decades, the development of several technologies has shed some light on microcirculatory evaluation and monitoring, and the possibility of incorporating microcirculatory variables to clinical practice no longer seems to be beyond reach. The present review provides a brief summary of the current technologies for microcirculatory evaluation, and attempts to explore the potential role and benefits of their integration to the resuscitation process in critically ill septic patients.

Direct Measurement of Tissue Oxygenation in Neonates via Resonance Raman Spectroscopy: A Pilot Study

BACKGROUND

The ability to monitor tissue oxygenation in neonates remains a challenge due to limited blood supply and the reliance on invasive procedures. Resonance Raman spectroscopy noninvasively measures tissue oxygenation (RRS-StO2). Peripheral tissue oxygenation using this novel technology has not been described in neonates.

OBJECTIVES

To examine the relationship between short-term RRS-StO2 measurements and central venous saturation (ScvO2) and pulse oximetry (SpO2) in preterm and term neonates.

METHODS

Ninety-seven term neonates had buccal and plantar RRS-StO2 measurements performed. In 15 preterm neonates, similar measurements were obtained in conjunction with ScvO2 in the first week of life. Simultaneous SpO2 and heart rate were also recorded.

RESULTS

In healthy neonates, buccal RRS-StO2 values negatively correlated with the day of life. No correlation existed between buccal and plantar RRS-StO2 values and ScvO2 or SpO2. Greater intra-patient plantar RRS-StO2 variability was seen in preterm neonates with increasing respiratory support.

CONCLUSIONS

Neonatal RRS-StO2 measurements are feasible short term but do not correlate with ScvO2 and SpO2. Healthy neonates had greater differences and variability in RRS-StO2 values, illustrating an evolving microcirculation not detected with pulse oximetry. Greater RRS-StO2 variability in sick neonates requiring respiratory support may indicate microcirculatory instability despite being within target SpO2 ranges. Further study is needed to establish if RRS-StO2 monitoring is an accurate representation of tissue oxygenation.

The microcirculation and its measurement in sepsis

The microcirculation describes the smallest elements of the cardiovascular conducting system and is pivotal in the maintenance of homeostasis. Microcirculatory dysfunction is present early in the pathophysiology of sepsis, with the extent of microcirculatory derangement relating to disease severity and prognosis in ICU patients. However, at present microcirculatory function is not routinely monitored at the bedside. This article describes the pathophysiology of microcirculatory derangements in sepsis, methods of its measurement and evidence to support their clinical use.

Near-infrared spectroscopy for assessing tissue oxygenation and microvascular reactivity in critically ill patients: a prospective observational study

Background

Impaired microcirculatory perfusion and tissue oxygenation during critical illness are associated with adverse outcome. The aim of this study was to detect alterations in tissue oxygenation or microvascular reactivity and their ability to predict outcome in critically ill patients using thenar near-infrared spectroscopy (NIRS) with a vascular occlusion test (VOT).

Methods

Prospective observational study in critically ill adults admitted to a 12-bed intensive care unit (ICU) of a University Hospital. NIRS with a VOT (using a 40 % tissue oxygen saturation (StO₂) target) was applied daily until discharge from the ICU or death. A group of healthy volunteers were evaluated in a single session. During occlusion, StO₂ downslope was measured separately for the first (downslope 1) and last part (downslope 2) of the desaturation curve. The difference between downslope 2 and 1 was calculated (delta-downslope). The upslope and area of the hyperaemic phase (receive operating characteristic (ROC) area under the curve (AUC) of StO₂) were calculated, reflecting microvascular reactivity. Outcomes were ICU and 90-day mortality.

Results

Patients (n = 89) had altered downslopes and upslopes compared to healthy volunteers (n = 27). Mean delta-downslope was higher in ICU non-survivors (2.8 (0.4, 3.8) %/minute versus 0.4 (−0.8, 1.8) in survivors, p = 0.004) and discriminated 90-day mortality (ROC AUC 0.72 (95 % confidence interval 0.59, 0.84)). ICU non-survivors had lower mean upslope (141 (75, 193) %/minute versus 185 (143, 217) in survivors, p = 0.016) and AUC StO₂ (7.9 (4.3, 12.6) versus 14.5 (11.2, 21.3), p = 0.001). Upslope and AUC StO₂ on admission were significant although weak predictors of 90-day mortality (ROC AUC = 0.68 (0.54, 0.82) and 0.70 (0.58, 0.82), respectively). AUC StO₂ ≤ 6.65 (1st quartile) on admission was independently associated with higher 90-day mortality (hazard ratio 7.964 (95 % CI 2.211, 28.686)). The lowest upslope in the ICU was independently associated with survival after ICU discharge (odds ratio 0.970 (95 % CI 0.945, 0.996)).

Conclusions

In critically ill patients, NIRS with a VOT enables identification of alterations in tissue oxygen extraction capacity and microvascular reactivity that can predict mortality.

Trial registration

NCT02649088, www.clinicaltrials.gov, date of registration 23rd December 2015, retrospectively registered.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1500-5) contains supplementary material, which is available to authorized users.

Vascular responsiveness measured by tissue oxygen saturation reperfusion slope is sensitive to different occlusion durations and training status

What is the central question of this study? Is the near-infrared spectroscopy-derived measure of tissue oxygen saturation (StO2) reperfusion slope sensitive to a range of ischaemic conditions, and do differences exist between trained and untrained individuals? What is the main finding and its importance? The StO2 reperfusion rate is sensitive to different occlusion durations, and changes in the reperfusion slope in response to a variety of ischaemic challenges can be used to detect differences between two groups. These data indicate that near-infrared spectroscopy-derived measures of StO2, specifically the reperfusion slope following a vascular occlusion, can be used as a sensitive measure of vascular responsiveness. The reperfusion rate of near-infrared spectroscopy-derived measures of tissue oxygen saturation (StO2) represents vascular responsiveness. This study examined whether the reperfusion slope of StO2 is sensitive to different ischaemic conditions (i.e. a dose-response relationship) and whether differences exist between two groups of different fitness levels. Nine healthy trained (T; age 25 ± 3 years; maximal oxygen uptake 63.4 ± 6.7 ml kg^-1  min^-1 ) and nine healthy untrained men (UT; age 21 ± 1 years; maximal oxygen uptake 46.6 ± 2.5 ml kg^-1  min^-1 ) performed a series of vascular occlusion tests of different durations (30 s, 1, 2, 3 and 5 min), each separated by 30 min. The StO2 was measured over the tibialis anterior using near-infrared spectroscopy, with the StO2 reperfusion slope calculated as the upslope during 10 s following cuff release. The reperfusion slope was steeper in T compared with UT at all occlusion durations (P < 0.05). For the T group, the reperfusion slopes for 30 s and 1 min occlusions were less than for all longer durations (P < 0.05). The reperfusion slope following 2 min occlusion was similar to that for 3 min (P > 0.05), but both were less steep than for 5 min of occlusion. In UT, the reperfusion slope at 30 s was smaller than for all longer occlusion durations (P < 0.05), and 1 min occlusion resulted in a reperfusion slope that was less steep than following 2 and 3 min (P < 0.05), albeit not different from 5 min (P > 0.05). The present study demonstrated that the reperfusion rate of StO2 is sensitive to different occlusion durations, and that changes in the reperfusion rate in response to a variety of ischaemic challenges can be used to detect differences in vascular responsiveness between trained and untrained groups.

Blood pressure targets for vasopressor therapy: a systematic review

Physicians often prescribe vasopressors to correct pathological vasodilation and improve tissue perfusion in patients with septic shock, but the evidence to inform practice on vasopressor dosing is weak. We undertook a systematic review of clinical studies evaluating different blood pressure targets for the dosing of vasopressors in septic shock. We searched MEDLINE, EMBASE, CENTRAL (to November 2013), reference lists from included articles, and trial registries for randomized controlled trials (RCTs) and observational and crossover intervention studies comparing different blood pressure targets for vasopressor therapy in septic shock. Two reviewers independently selected eligible studies and extracted data on standardized forms. We identified 2 RCTs and 10 crossover trials but no observational studies meeting our criteria. Only one RCT measured clinical outcomes after comparing mean arterial pressure targets of 80 to 85 mmHg versus 65 to 70 mmHg. There was no effect on 28-day mortality, but confidence intervals were wide (hazard ratio, 95% confidence interval [95% CI] 0.84 - 1.38). In contrast, this intervention was associated with a greater risk of atrial fibrillation (relative risk, 2.36; 95% CI, 1.18 - 4.72) and a lower risk of renal replacement therapy in hypertensive patients (relative risk, 0.75; 95% CI, 0.57 - 1.0). Crossover trials suggest that achieving higher blood pressure targets by increasing vasopressor doses increases heart rate and cardiac index with no effect on serum lactate. Our findings underscore the paucity of clinical evidence to guide the administration of vasopressors in critically ill patients with septic shock. Further rigorous research is needed to establish an evidence base for vasopressor administration in this population.

Effects of prolonged ischemia on human skeletal muscle microcirculation as assessed by near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) has been used to detect in vivo microvascular alterations by means of a vascular occlusion test. We sought to analyse by NIRS the microcirculatory profile of patients undergoing prolonged tourniquet-induced bloodless condition for extremity surgery, and compare the results with time of ischemia and comorbidities. We conducted a prospective observational study on 42 patients undergoing upper limb surgery. Regional anaesthesia was achieved and ischemia was induced by a tourniquet cuffed at 250 mmHg. The probe of a NIRS monitor (InSpectra 325, Hutchiston, USA) was placed on the brachial muscle, and muscle oxygen saturation (StO₂) was recorded continuously before anaesthesia, during and after surgery. The following variables were recorded: baseline StO₂, StO₂ desaturation slope during occlusion (dSlope, units/s), resaturation rate following ischemia (RR, units/s), hyperaemic peak (peak, units), and duration of the hyperaemic period following ischemia (hyperaemic time, s). Values of dSlope were similar among all patients. RR and hyperaemic time were significantly correlated with the duration of ischemia, but not with comorbidities [p = 0.007 CI (-35.64 to -13.1), and p < 0.001 CI (0.049-0.159), respectively]. Grouping patients by duration of ischemia (30, 60, or 90 min), we found a significant decrease in RR after 60 and 90 min (p < 0.001 and p = 0.03, respectively). Hyperaemic peak was lower in the 90 min group (83.9 ± 6.8 vs. 91.2 ± 5.7 %, p = 0.02) whereas the hyperaemic time was significantly increased (595 ± 136 vs. 429 ± 107 min, p < 0.001). Alterations of skeletal muscle microcirculation were correlated with the duration of ischemia, but not with comorbidities. We observed an initial impairment of the microcirculatory recovery at 90 min of ischemia.

A systematic review of human and veterinary applications of noninvasive tissue oxygen monitoring

OBJECTIVE

To describe the methodology for and utilization of tissue oxygen monitoring by near infrared spectroscopy, and to review the current literature on the use of this monitoring modality in human and veterinary settings.

DATA SOURCES

Scientific reviews and original research found using the PubMed and CAB Abstract search engines with the following keywords: "tissue oxygen monitoring," "near-infrared tissue spectroscopy," and "tissue oxygen saturation (StO2 )."

HUMAN DATA SYNTHESIS

Tissue oxygen monitors have been evaluated in a wide variety of human clinical applications including trauma and triage, surgery, sepsis, and septic shock, and early goal-directed therapy. StO2 more rapidly identifies occult shock in human patients compared to traditional methods, which can lead to earlier intervention in these patients.

VETERINARY DATA SYNTHESIS

Veterinary studies involving tissue oxygen monitoring are limited, but the technology may have utility for identification of hemorrhagic shock earlier than changes in base excess, blood lactate concentration, or other traditional perfusion parameters.

CONCLUSION

Tissue oxygen monitoring is most commonly performed utilizing a noninvasive, portable monitor, which provides real-time, continuous, repeatable StO2 measurements. A decline in StO2 is an early indicator of shock in both human and veterinary patients. Low StO2 values in human patients are associated with increased morbidity, mortality, and length of hospitalization, as well as the development of multiple organ system dysfunction and surgical site infections.

Near infrared image processing to quantitate and visualize oxygen saturation during vascular occlusion

The assessment of microcirculation spatial heterogeneity on the hand skin is the main objective of this work. Near-infrared spectroscopy based 2D imaging is a non-invasive technique for the assessment of tissue oxygenation. The haemoglobin oxygen saturation images were acquired by a dedicated camera (Kent Imaging) during baseline, ischaemia (brachial artery cuff occlusion) and reperfusion. Acquired images underwent a preliminary restoration process aimed at removing degradations occurring during signal capturing. Then, wavelet transform based multiscale analysis was applied to identify edges by detecting local maxima and minima across successive scales. Segmentation of test areas during different conditions was obtained by thresholding-based region growing approach. The method identifies the differences in microcirculatory control of blood flow in different regions of the hand skin. The obtained results demonstrate the potential use of NIRS images for the clinical evaluation of skin disease and microcirculatory dysfunction.

Prognostic value of brachioradialis muscle oxygen saturation index and vascular occlusion test in septic shock patients

OBJECTIVES

To compare rSO2 (muscle oxygen saturation index) static and dynamic variables obtained by NIRS (Near Infrared Spectroscopy) in brachioradialis muscle of septic shock patients and its prognostic implications.

DESIGN

Prospective and observational study.

SETTING

Intensive care unit.

SUBJECTS

Septic shock patients and healthy volunteers.

INTERVENTIONS

The probe of a NIRS device (INVOS 5100) was placed on the brachioradialis muscle during a vascular occlusion test (VOT).

VARIABLES

Baseline, minimum and maximum rSO2 values, deoxygenation rate (DeOx), reoxygenation slope (ReOx) and delta value.

RESULTS

Septic shock patients (n=35) had lower baseline rSO2 (63.8±12.2 vs. 69.3±3.3%, p<0.05), slower DeOx (-0.54±0.31 vs. -0.91±0.35%/s, p=0.001), slower ReOx (2.67±2.17 vs. 9.46±3.5%/s, p<0.001) and lower delta (3.25±5.71 vs. 15.1±3.9%, p<0.001) when compared to healthy subjects (n=20). Among septic shock patients, non-survivors showed lower baseline rSO2 (57.0±9.6 vs. 69.8±11.3%, p=0.001), lower minimum rSO2 (36.0±12.8 vs. 51.3±14.8%, p<0.01) and lower maximum rSO2 values (60.6±10.6 vs. 73.3±11.2%, p<0.01). Baseline rSO2 was a good mortality predictor (AUC 0.79; 95%CI: 0.63-0.94, p<0.01). Dynamic parameters obtained with VOT did not improve the results.

CONCLUSION

Septic shock patients present an important alteration of microcirculation that can be evaluated by NIRS with prognostic implications. Monitoring microvascular reactivity in the brachioradialis muscle using VOT with our device does not seem to improve the prognostic value of baseline rSO2.

Microvascular reactivity and clinical outcomes in cardiac surgery

Introduction

Microvascular reactivity is decreased in patients with septic shock; this is associated with worse clinical outcomes. The objectives of the present study were to investigate microvascular reactivity in cardiac surgery patients and to assess any association with clinical outcomes.

Methods

We retrospectively analyzed a prospectively collected registry. In total, 254 consecutive adult patients undergoing cardiac and thoracic aortic surgeries from January 2013 through May 2014 were analyzed. We performed a vascular occlusion test (VOT) by using near-infrared spectroscopy to measure microvascular reactivity. VOT was performed three times per patient: prior to the induction of anesthesia, at the end of surgery, and on postoperative day 1. The primary endpoint was a composite of major adverse complications, including death, myocardial infarction, acute kidney injury, acute respiratory distress syndrome, and persistent cardiogenic shock.

Results

VOT recovery slope decreased during the surgery. VOT recovery slope on postoperative day 1 was significantly lower in patients with composite complications than those without (3.1 ± 1.6 versus 4.0 ± 1.5 %/s, P = 0.001), although conventional hemodynamic values, such as cardiac output and blood pressure, did not differ between the groups. On multivariable regression and linear analyses, low VOT recovery slope on postoperative day 1 was associated with increases of composite complications (odds ratio 0.742; 95 % confidence interval (CI) 0.584 to 0.943; P = 0.015) and hospital length of stay (regression coefficient (B) −1.276; 95 % CI −2.440 to −0.112; P = 0.032).

Conclusion

Microvascular reactivity largely recovered on postoperative day 1 in the patients without composite complications, but this restoration was attenuated in patients with composite complications.

Trial registration

ClinicalTrials.gov NCT01713192. Registered 22 October 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1025-3) contains supplementary material, which is available to authorized users.

Dynamic muscle O2 saturation response is impaired during major non-cardiac surgery despite goal-directed haemodynamic therapy

BACKGROUND

Near-infrared spectroscopy combined with a vascular occlusion test (VOT) could indicate an impairment of microvascular reactivity (MVR) in septic patients by detecting changes in dynamic variables of muscle O2 saturation (StO2). However, in the perioperative context the consequences of surgical trauma on dynamic variables of muscle StO2 as indicators of MVR are still unknown.

METHODS

This study is a sub-analysis of a randomised controlled trial in patients with metastatic primary ovarian cancer undergoing debulking surgery, during which a goal-directed haemodynamic algorithm was applied using oesophageal Doppler. During a 3 min VOT, near-infrared spectroscopy was used to assess dynamic variables arising from changes in muscle StO2.

RESULTS

At the beginning of surgery, values of desaturation and recovery slope were comparable to values obtained in healthy volunteers. During the course of surgery, both desaturation and recovery slope showed a gradual decrease. Concomitantly, the study population underwent a transition to a surgically induced systemic inflammatory response state shown by a gradual increase in norepinephrine administration, heart rate, and Interleukin-6, with a peak immediately after the end of surgery. Higher rates of norepinephrine and a higher heart rate were related to a faster decline in StO2 during vascular occlusion.

CONCLUSIONS

Using near-infrared spectroscopy combined with a VOT during surgery showed a gradual deterioration of MVR in patients treated with optimal haemodynamic care. The deterioration of MVR was accompanied by the transition to a surgically induced systemic inflammatory response state.

Near-Infrared Spectroscopy in the Monitoring of Adult Traumatic Brain Injury: A Review

Cerebral near-infrared spectroscopy (NIRS) has long represented an exciting prospect for the noninvasive monitoring of cerebral tissue oxygenation and perfusion in the context of traumatic brain injury (TBI), although uncertainty still exists regarding the reliability of this technology specifically within this field. We have undertaken a review of the existing literature relating to the application of NIRS within TBI. We discuss current "state-of-the-art" NIRS monitoring, provide a brief background of the technology, and discuss the evidence regarding the ability of NIRS to substitute for established invasive monitoring in TBI.

Skeletal muscle oxygenation in severe trauma patients during haemorrhagic shock resuscitation

Introduction

Early alterations in tissue oxygenation may worsen patient outcome following traumatic haemorrhagic shock. We hypothesized that muscle oxygenation measured using near-infrared spectroscopy (NIRS) on admission could be associated with subsequent change in the SOFA score after resuscitation.

Methods

The study was conducted in two Level I trauma centres and included 54 consecutive trauma patients with haemorrhagic shock, presenting within 6 hours of injury. Baseline tissue haemoglobin oxygen saturation (StO2) in the thenar eminence muscle and StO2 changes during a vascular occlusion test (VOT) were determined at 6 hours (H6) and 72 hours (H72) after the admission to the emergency room. Patients showing an improved SOFA score at H72 (SOFA improvers) were compared to those for whom it was unchanged or worse (SOFA non-improvers).

Results

Of the 54 patients, 34 patients were SOFA improvers and 20 SOFA non-improvers. They had comparable injury severity scores on admission. SOFA improvers had higher baseline StO2 values and a steeper StO2 desaturation slope at H6 compared to the SOFA non-improvers. These StO2 variables similarly correlated with the intra-hospital mortality. The StO2 reperfusion slope at H6 was similar between the two groups of patients.

Conclusions

Differences in StO2 parameters on admission of traumatic haemorrhagic shock were found between patients who had an improvement in organ failure in the first 72 hours and those who had unchanged or worse conditions. The use of NIRS to guide the initial management of trauma patients with haemorrhagic shock warrants further investigations.

Prospective evaluation of regional oxygen saturation to estimate central venous saturation in sepsis

Current treatment guidelines for sepsis claim an early goal-directed hemodynamic optimization including fluid resuscitation, use of vasopressors and inotropic agents. We investigated the correlation between the prominent treatment goal central venous saturation (ScvO2) and the frontal and the thenar regional oxygen saturation (rSO2) measured by near infrared spectroscopy. Secondary, we examined the value of ScvO2, lactate levels and rSO2 as surrogate markers of an impaired tissue oxygenation for outcome prediction in sepsis. This prospective, observational study was performed at the surgical intensive care unit of the University Hospital Giessen. A total of 50 patients with sepsis, severe sepsis or septic shock were included. ScvO2, rSO2 and lactate were measured at sepsis diagnosis (baseline), 24 and 48 h, thereafter. We investigated the predictive value of frontal and thenar rSO2 for a decreased SvcO2 under 70%. For survivor and non-survivors ScvO2, rSO2 and lactate were analysed. Patients with ScvO2 >70% showed a trend to higher levels of fontal rSO2 (62.81 ± 8.06 vs. 53.54 ± 15.48; p = 0.058). ROC-analysis revealed a minor prediction of a decreased ScvO2 by frontal rSO2 levels at baseline (AUC = 0.687; 95% CI 0.511-0.863; p = 0.047). Combined measurements of lactate and ScvO2 showed significantly elevated mortality for patients with ScvO2 ≥70% and lactate levels ≥2.5 mmol/l (log rank test p = 0.004). In the group with ScvO2 <70% and lactate levels <2.5 mmol/l no patients died during the observation period. Frontal rSO2 correlates with ScvO2 but both frontal and thenar rSO2 do not exactly discriminate between patients with high or low ScvO2 in sepsis. The combination of elevated lactate >2.5 mmol/l and ScvO2 >70 % is highly associated with poor outcome in ICU patients with sepsis, severe sepsis and septic shock.

Tissue microcirculation measured by vascular occlusion test during anesthesia induction

Tissue microcirculation measured by vascular occlusion test is impaired during septic shock. However, it has not been investigated extensively during anesthesia induction. The aim of the study is to evaluate tissue microcirculation during anesthesia induction. We hypothesized that during anesthesia induction, tissue microcirculation measured by vascular occlusion test might be enhanced with peripheral vasodilation during anesthesia induction. We conducted a prospective observational study of 50 adult patients undergoing cardiac surgery. During anesthesia induction, we measured and analyzed tissue oxygen saturation, vascular occlusion test, cerebral oximetry, forearm-minus-fingertip skin temperature gradients and hemodynamic data in order to evaluate microcirculation as related to alterations in peripheral vasodilation as reflected by increased Tforearm-finger thermal gradients. During anesthesia induction, recovery slope during vascular occlusion test and cerebral oxygen saturation increased from 4.0 (1.5) to 4.7 (1.3) % s(-1) (p = 0.02) and 64.0 (10.2) to 74.2 (9.2) % (p < 0.001), respectively. Forearm-minus-fingertip skin temperature gradients decreased from 1.9 (2.9) to -1.4 (2.2) °C (p < 0.001). There was an inverse correlation between changes in the skin temperature gradients and changes in cerebral oximetry (r = 0.33; p = 0.02). During anesthesia induction, blood pressure and forearm-minus-fingertip skin temperature gradients decrease while cerebral oximetry and vascular occlusion test recovery slope increase. These findings suggest that anesthesia induction increases tissue microcirculation with peripheral vasodilation.

Near-infrared spectroscopy-based microcirculatory assessment in acute atrial fibrillation

Near-infrared spectroscopy is a means of assessing microcirculatory function, but has not been studied in atrial fibrillation (AF). We evaluated the effect of acute AF on thenar eminence near-infrared spectroscopy-derived microcirculatory variables. Stable patients presenting to the emergency department with acute onset AF underwent dynamic near-infrared spectroscopy assessment with a three minute vascular occlusion test (VOT). This was repeated after cardioversion to sinus rhythm (SR). Each assessment included baseline tissue oxygen saturation (StO2), slope of StO2 decrease during VOT, slope of StO2 increase post VOT, minimum and maximum StO2, amplitude of StO2 response and post-ischaemic hyperperfusion. Pre and post cardioversion values were compared by Wilcoxon signed-rank test. Twelve participants (seven male, five female) with a median age of 63 years (interquartile range 52 to 70 years) were enrolled. Median baseline StO2 was 74% before and 77% after cardioversion (P=0.03). The median slope of StO2 decrease during VOT was -0.19%/second and -0.16%/second (P=0.018) and the median slope of StO2 increase post VOT was 3.03%/second and 2.56%/second (P=0.002), pre and post cardioversion, respectively. Minimum StO2 was lower (39% versus 52%, P=0.002) and the amplitude of StO2 response greater (49% versus 40%, P=0.005) in AF, but there was no significant difference in maximum StO2 or the degree of reperfusion hyperaemia. In summary, baseline and minimum StO2 were lower with a greater ischaemic decrease in StO2 during AF, reflecting reduced tissue perfusion, compared with sinus rhythm. Recovery after ischaemia was higher in AF, suggesting normalisation of capillary recruitment during ischaemia.

Endpoints of resuscitation

Despite the multiple causes of the shock state, all causes possess the common abnormality of oxygen supply not meeting tissue metabolic demands. Compensatory mechanisms may mask the severity of hypoxemia and hypoperfusion, since catecholamines and extracellular fluid shifts initially compensate for the physiologic derangements associated with patients in shock. Despite the achievement of normal physiologic parameters after resuscitation, significant metabolic acidosis may continue to be present in the tissues, as evidenced by increased lactate levels and metabolic acidosis. This review discusses the major endpoints of resuscitation in clinical use.

Early identification and management of patients with severe sepsis and septic shock in the emergency department

Severe sepsis and septic shock have great relevance to Emergency Medicine physicians because of their high prevalence, morbidity, and mortality. Treatment is time-sensitive, depends on early identification risk stratification, and has the potential to significantly improve patient outcomes. In this article, we review the pathophysiology of, and evidence basis for, the emergency department management of severe sepsis and septic shock.

Fluid resuscitation in sepsis: reexamining the paradigm

Sepsis results in widespread inflammatory responses altering homeostasis. Associated circulatory abnormalities (peripheral vasodilation, intravascular volume depletion, increased cellular metabolism, and myocardial depression) lead to an imbalance between oxygen delivery and demand, triggering end organ injury and failure. Fluid resuscitation is a key part of treatment, but there is little agreement on choice, amount, and end points for fluid resuscitation. Over the past few years, the safety of some fluid preparations has been questioned. Our paper highlights current concerns, reviews the science behind current practices, and aims to clarify some of the controversies surrounding fluid resuscitation in sepsis.

Bedside assessment of tissue oxygen saturation monitoring in critically ill adults: an integrative review of the literature

Objective. Tissue oxygen saturation (StO2) monitoring is a noninvasive technology with the purpose of alerting the clinician of peripheral hypoperfusion and the onset of tissue hypoxia. This integrative review examines the rigor and quality of studies focusing on StO2 monitoring in adult critically ill patients. Background. Clinicians must rapidly assess adverse changes in tissue perfusion while minimizing potential complications associated with invasive monitoring. The noninvasive measurement of tissue oxygen saturation is based on near-infrared spectroscopy (NIRS), an optical method of illuminating chemical compounds which absorb, reflect, and scatter light directed at that compound. Methods. An integrative review was conducted to develop a context of greater understanding about complex topics. An Integrative review draws on multiple experimental and nonexperimental research methodologies. Results. Fourteen studies were graded at the C category. None reported the use of probability sampling or demonstrated a cause-and-effect relationship between StO2 values and patient outcomes. Conclusions. Future research should be based on rigorous methods of sampling and design in order to enhance the internal and external validity of the findings.

Low StO2 measurements in surgical intensive care unit patients is associated with poor outcomes

BACKGROUND

Near-infrared spectroscopy-derived tissue hemoglobin saturation (StO2) is a noninvasive measurement that reflects changes in microcirculatory tissue perfusion. Previous studies in trauma patients have shown a correlation between low StO2 levels and mortality, organ failure, and severity of injury. The goals of this study were to identify the incidence of low StO2 in the critically ill patient population of a surgical intensive care unit (SICU) and evaluate the relationship of low StO2 and clinical outcomes.

METHODS

We conducted a prospective cohort study at the University of Minnesota Medical Center. After institutional review board approval, 620 patients admitted to the SICU between July 2010 and July 2011 were screened for enrollment. Patients with an expected ICU length of stay of less than 24 hours were excluded. In the 490 patients who met inclusion criteria, StO2 measurements were obtained from the thenar eminence one to three times daily for the length of the ICU stay, up to 14 days. Outcome data included 28-day hospital mortality; ICU readmission; ventilator-free, ICU-free, and hospital-free days; and the need for lifesaving interventions.

RESULTS

The overall incidence of low StO2 (<70%) was 11% of the patients per day. Patients with at least 1 day in the SICU with an StO2 measurement of less than 70% had higher rates of ICU readmission and fewer ventilator-free, ICU-free, and hospital-free days compared with those who did not. Mortality (28-day in-hospital) trended higher for these patients but was not statistically significant. An increase in the number of days with StO2 less than 70% was also associated with fewer ventilator-free, ICU-free, and hospital-free days.

CONCLUSION

Low StO2 (<70%) is common and associated with poor outcomes in SICU patients. Near-infrared spectroscopy represents a potentially useful, noninvasive adjunct to monitoring of critically ill patients.

LEVEL OF EVIDENCE

Prognostic study, level II.