Quantitative assessment of cytochrome C oxidase patterns in muscle tissue by the use of near-infrared spectroscopy (NIRS) in healthy volunteers.

Cytochrome C oxidase (CCO) acts as final electron acceptor in the respiratory chain, possibly providing information concerning cellular oxygenation. CCO is a chromophore with a broad absorption peak in the near-infrared spectrum in its reduced state (835 nm). However, this peak overlaps with deoxygenated haemoglobin (HHb; 755 nm) which is present in much higher concentrations. NIRO-300 measures CCO signals, but did not receive FDA approval for this use due to presumed lack of independency of the measured CCO changes. However, there is no proven evidence for this assumption. We hypothesized that the NIRO-300 provides a HHb independent measurement of CCO concentration changes. In this single-center crossover randomized controlled trial in healthy volunteers, subjects were randomized to receive arterial occlusion to the left arm and venous stasis on the right arm (n = 5) or vice versa (n = 5) during 5 min. After a resting period, the second part of the cross over study was performed. We placed the NIRO-300 optodes bilateral at the level of the brachioradial muscle in order to collect NIRS data continuously. Data was analysed using a generalized additive mixed model. HHb and CCO follow a significant different trend over time during the intervention period for both arterial occlusion (F = 20.645, edf = 3.419, p < 0.001) and venous stasis (F = 9.309, edf = 4.931, p < 0.001). Our data indicate that CCO concentration changes were not affected by HHb changes, thereby proving independency.Clinical trial registration: B670201732023 on June 28, 2017.

Microvascular reactivity monitored with near-infrared spectroscopy is impaired after induction of anaesthesia in cardiac surgery patients: An observational study.

BACKGROUND: Induction of anaesthesia causes significant macrohaemodynamic changes, but little is known about its effects on the microcirculation. However, alterations in microvascular perfusion are known to be associated with impaired tissue oxygenation and organ dysfunction. Microvascular reactivity can be assessed with vascular occlusion testing, which evaluates the response of tissue oxygen saturation to transient ischaemia and reperfusion. OBJECTIVE: The aim of the current study was to evaluate the effects of an opioid-based anaesthesia induction on microvascular reactivity. We hypothesised that despite minimal blood pressure changes, microvascular function would be impaired. DESIGN: Prospective, observational study. SETTING: Single-centre, tertiary university teaching hospital, Belgium. PATIENTS: Thirty-five adult patients scheduled for elective coronary artery bypass grafting surgery. INTERVENTION: Microvascular reactivity was assessed before and 30 min after anaesthesia induction by means of vascular occlusion testing and near-infrared spectroscopy. MAIN OUTCOME MEASURES: Tissue oxygen saturations, desaturation rate, recovery time (time from release of cuff to the maximum value) and rate of recovery were determined. RESULTS: Data are expressed as median (minimum to maximum). Tissue oxygen saturation was higher after induction of anaesthesia [70 (54 to 78) vs. 73 (55 to 94)%, P = 0.015]. Oxygen consumption decreased after induction, appreciable by the higher minimum tissue oxygen saturation [45 (29 to 69) vs. 53 (28 to 81)%, P < 0.001] and the slower desaturation rate [11 (4 to 18) vs. 9 (5 to 16)% min, P < 0.001]. After induction of anaesthesia, recovery times were longer [40 (20 to 120) vs. 48 (24 to 356) s, P = 0.004] and the rate of recovery was lower [114 (12 to 497) vs. 80 (3 to 271)% min, P < 0.001]. CONCLUSION: After induction of anaesthesia, oxygen consumption was decreased. The longer recovery times and slower rates of recovery indicate impaired microvascular reactivity after induction of anaesthesia. TRIAL REGISTRATION: The research project was registered at ClinicalTrials.gov (NCT02034682).

Evaluation of different near-infrared spectroscopy technologies for assessment of tissue oxygen saturation during a vascular occlusion test.

An increasing number of NIRS devices are used to provide measurements of peripheral tissue oxygen saturation (StO2). The aim of the present study is to test the hypothesis that despite technological differences between devices, similar trend values will be obtained during a vascular occlusion test. The devices compared are NIRO-200NX, which measures StO2 and oxyhemoglobin by spatially resolved spectroscopy and the Beer-Lambert law, respectively, and INVOS 5100C and Foresight Elite, which both measure StO2 with the Beer-Lambert law, enhanced with the spatial resolution technique. Forty consenting adults scheduled for CABG surgery were recruited. The respective sensors of the three NIRS devices were applied over the brachioradial muscle. Before induction of anesthesia, 3 min of ischemia were induced by inflating a blood pressure cuff at the upper arm, whereafter cuff pressure was rapidly released. Tissue oxygenation measurements included baseline, minimum and maximum values, desaturation and resaturation slopes, and rise time. Comparisons between devices were performed with the Kruskal-Wallis test with post hoc Mann-Whitney pairwise comparisons. Agreement was evaluated using Bland-Altman plots. Oxyhemoglobin measured with NIRO responded faster than the other NIRS technologies to changes in peripheral tissue oxygenation (20 vs. 27-40 s, p ≤ 0.01). When comparing INVOS with Foresight, oxygenation changes were prompter (upslope 311 [92-523]%/min vs. 114[65-199]%/min, p ≤ 0.01) and more pronounced (minimum value 36 [21-48] vs. 45 [40-51]%, p ≤ 0.01) with INVOS. Significant differences in tissue oxygen saturation measurements were observed, both within the same device as between different devices using the same measurement technology.

The patient with hypertension undergoing surgery.

PURPOSE OF REVIEW: General recommendations for the perioperative management of patients with hypertensive disease have not evolved much over the past 20 years, yet new pathophysiological concepts have emerged and new monitoring techniques are available today. In this review, we will discuss their significance and potential role in the modern perioperative care of hypertensive patients. RECENT FINDINGS: For hypertensive patients, total cardiovascular risk rather than blood pressure (BP) alone should determine the preoperative strategy. Except for grade 3 hypertension, surgery should not be deferred on the basis of an elevated BP in the preoperative assessment.New data suggest that even brief hypotensive episodes during surgery may have significant impact on outcome. Isolated systolic hypertension is the predominant phenotype in elderly patients who may be particularly vulnerable to hypoperfusion in the perioperative setting.New monitoring techniques such as echocardiography and near-infrared spectroscopy may provide crucial information to optimize intraoperative control of BP based on an individual patient's pathophysiology. SUMMARY: Hypertension is highly prevalent in patients presenting for surgery yet its impact on surgical outcome is still debated. Guidelines on risk stratification and perioperative hemodynamic management of patients with hypertensive disease remain sparse and cannot rely much on solid new evidence. Target organ damage associated with hypertensive disease rather than high BP per se appears to determine perioperative risk. In the absence of new data, an individualized and pathophysiology-based approach to control BP may be the best option to guide these patients through the perioperative period.