Measurement Of Tissue Oxygen Tension Research Articles

Recovery of organ-specific tissue oxygen delivery at restrictive transfusion thresholds after fluid treatment in ovine haemorrhagic shock

BackgroundFluid resuscitation is the standard treatment to restore circulating blood volume and pressure after massive haemorrhage and shock. Packed red blood cells (PRBC) are transfused to restore haemoglobin levels. Restoration of microcirculatory flow and tissue oxygen delivery is critical for organ and patient survival, but these parameters are infrequently measured. Patient Blood Management is a multidisciplinary approach to manage and conserve a patient’s own blood, directing treatment options based on broad clinical assessment beyond haemoglobin alone, for which tissue perfusion and oxygenation could be useful. Our aim was to assess utility of non-invasive tissue-specific measures to compare PRBC transfusion with novel crystalloid treatments for haemorrhagic shock.MethodsA model of severe haemorrhagic shock was developed in an intensive care setting, with controlled haemorrhage in sheep according to pressure (mean arterial pressure 30–40 mmHg) and oxygen debt (lactate > 4 mM) targets. We compared PRBC transfusion to fluid resuscitation with either PlasmaLyte or a novel crystalloid. Efficacy was assessed according to recovery of haemodynamic parameters and non-invasive measures of sublingual microcirculatory flow, regional tissue oxygen saturation, repayment of oxygen debt (arterial lactate), and a panel of inflammatory and organ function markers. Invasive measurements of tissue perfusion, oxygen tension and lactate levels were performed in brain, kidney, liver, and skeletal muscle. Outcomes were assessed during 4 h treatment and post-mortem, and analysed by one- and two-way ANOVA.ResultsEach treatment restored haemodynamic and tissue oxygen delivery parameters equivalently (p > 0.05), despite haemodilution after crystalloid infusion to haemoglobin concentrations below 70 g/L (p < 0.001). Recovery of vital organ-specific perfusion and oxygen tension commenced shortly before non-invasive measures improved. Lactate declined in all tissues and correlated with arterial lactate levels (p < 0.0001). The novel crystalloid supported rapid peripheral vasodilation (p = 0.014) and tended to achieve tissue oxygen delivery targets earlier. PRBC supported earlier renal oxygen delivery (p = 0.012) but delayed peripheral perfusion (p = 0.034).ConclusionsCrystalloids supported vital organ oxygen delivery after massive haemorrhage, despite haemodilution to < 70 g/L, confirming that restrictive transfusion thresholds are appropriate to support oxygen delivery. Non-invasive tissue perfusion and oximetry technologies merit further clinical appraisal to guide treatment for massive haemorrhage in the context of Patient Blood Management.

Individualized Brain Tissue Oxygen-Monitoring Probe Placement Helps to Guide Therapy and Optimizes Outcome in Neurocritical Care

Background/ObjectiveIn order to monitor tissue oxygenation in patients with acute neurological disorders, probes for measurement of brain tissue oxygen tension (ptO2) are often placed non-specifically in a right frontal lobe location. To improve the value of ptO2 monitoring, placement of the probe into a specific area of interest is desirable. We present a technique using CT-guidance to place the ptO2 probe in a particular area of interest based on the individual patient’s pathology.MethodsIn this retrospective cohort study, we analyzed imaging and clinical data from all patients who underwent CT-guided ptO2 probe placement at our institution between October 2017 and April 2019. Primary endpoint was successful placement of the probe in a particular area of interest rated by two independent reviewers. Secondary outcomes were complications from probe insertion, clinical consequences from ptO2 measurements, clinical outcome according to the modified Rankin Scale (mRS) as well as development of ischemia on follow-up imaging. A historical control group was selected from patients who underwent conventional ptO2 probe placement between January 2010 and October 2017.ResultsEleven patients had 16 CT-guided probes inserted. In 15 (93.75%) probes, both raters agreed on the correct placement in the area of interest. Each probe triggered on average 0.48 diagnostic or therapeutic adjustments per day. Only one infarction within the vascular territory of a probe was found on follow-up imaging. Eight out of eleven patients (72.73%) reached a good outcome (mRS ≤ 3). In comparison, conventionally placed probes triggered less diagnostic and therapeutic adjustment per day (p = 0.007). Outcome was worse in the control group (p = 0.024).ConclusionCT-guided probe insertion is a reliable and easy technique to place a ptO2 probe in a particular area of interest in patients with potentially reduced cerebral oxygen supply. By adjusting treatment aggressively according to this individualized monitoring data, clinical outcome may improve.

Renal tissue Po2 sensing during acute hemodilution is dependent on the diluent.

Sensing changes in blood oxygen content ([Formula: see text]) is an important physiological role of the kidney; however, the mechanism(s) by which the kidneys sense and respond to changes in [Formula: see text] are incompletely understood. Accurate measurements of kidney tissue oxygen tension ([Formula: see text]) may increase our understanding of renal oxygen-sensing mechanisms and could inform decisions regarding the optimal fluid for intravascular volume resuscitation to maintain renal perfusion. In some clinical settings, starch solution may be nephrotoxic, possibly due to inadequacy of tissue oxygen delivery. We hypothesized that hemodilution with starch colloid solutions would reduce [Formula: see text] to a more severe degree than other diluents. Anesthetized Sprague-Dawley rats (n = 77) were randomized to undergo hemodilution with either colloid (6% hydroxyethyl starch or 5% albumin), crystalloid (0.9% saline), or a sham procedure (control) (n = 13-18 rats/group). Data were analyzed by ANOVA with significance assigned at P < 0.05. After hemodilution, mean arterial pressure (MAP) decreased marginally in all groups, while hemoglobin (Hb) and [Formula: see text] decreased in proportion to the degree of hemodilution. Cardiac output was maintained in all groups after hemodilution. [Formula: see text] decreased in proportion to the reduction in Hb in all treatment groups. At comparably reduced Hb, and maintained arterial oxygen values, hemodilution with starch resulted in larger decreases in [Formula: see text] relative to animals hemodiluted with albumin or saline (P < 0.008). Renal medullary erythropoietin (EPO) mRNA levels increased more prominently, relative to other hypoxia-regulated molecules (GLUT-1, GAPDH, and VEGF). Our data demonstrate that the kidney acts as a biosensor of reduced [Formula: see text] following hemodilution and that [Formula: see text] may provide a quantitative signal for renal cellular responsiveness to acute anemia. Evidence of a more severe reduction in [Formula: see text] following hemodilution with starch colloid solution suggests that tissue hypoxia may contribute to starch induced renal toxicity.

More bullets for PISTOL: linear and cyclic siloxane reporter probes for quantitative 1H MR oximetry

Tissue oximetry can assist in diagnosis and prognosis of many diseases and enable personalized therapy. Previously, we reported the ability of hexamethyldisiloxane (HMDSO) for accurate measurements of tissue oxygen tension (pO2) using Proton Imaging of Siloxanes to map Tissue Oxygenation Levels (PISTOL) magnetic resonance imaging. Here we report the feasibility of several commercially available linear and cyclic siloxanes (molecular weight 162–410 g/mol) as PISTOL-based oxygen reporters by characterizing their calibration constants. Further, field and temperature dependence of pO2 calibration curves of HMDSO, octamethyltrisiloxane (OMTSO) and polydimethylsiloxane (PDMSO) were also studied. The spin-lattice relaxation rate R1 of all siloxanes studied here exhibited a linear relationship with oxygenation (R1 = A′ + B′*pO2) at all temperatures and field strengths evaluated here. The sensitivity index η( = B′/A′) decreased with increasing molecular weight with values ranged from 4.7 × 10−3–11.6 × 10−3 torr−1 at 4.7 T. No substantial change in the anoxic relaxation rate and a slight decrease in pO2 sensitivity was observed at higher magnetic fields of 7 T and 9.4 T for HMDSO and OMTSO. Temperature dependence of calibration curves for HMDSO, OMTSO and PDMSO was small and simulated errors in pO2 measurement were 1–2 torr/°C. In summary, we have demonstrated the feasibility of various linear and cyclic siloxanes as pO2-reporters for PISTOL-based oximetry.

Hypoxia Detection in Infiltrative Astrocytoma: Ferumoxytol-based Quantitative BOLD MRI with Intraoperative and Histologic Validation.

Purpose To validate ferumoxytol-based quantitative blood oxygenation level-dependent (BOLD) MRI for mapping oxygenation of human infiltrative astrocytomas by using intraoperative measurement of tissue oxygen tension and histologic staining. Materials and Methods Fifteen patients with infiltrative astrocytomas were recruited into this prospective multicenter study between July 2014 and December 2016. Prior to treatment, participants underwent preoperative quantitative BOLD MRI with ferumoxytol to generate tissue oxygen saturation (StO2) maps. Two intratumoral sites were identified, one with low StO2 and one with high StO2. Neuronavigation was used to locate sites intraoperatively for insertion of oxygen-sensing probes to measure local tissue oxygen tension (PtO2). Biopsies from both sites were taken and stained for markers of hypoxia (hypoxia-inducible factor 1α, carbonic anhydrase IX) and neoangiogenesis (vascular endothelial growth factor, endoglin [CD105]). Spearman correlation and nonparametric sign-rank tests were used to analyze data. Results Ten patients with median age of 58.5 years (interquartile range, 25 years; four men and six women) completed the study. Because there is no linear relationship between StO2 and PtO2, the ratios of low to high StO2 versus low to high PtO2 in each patient were compared and a significant correlation was found (r = 0.73; P = .01). Pathologic analyses revealed differences between carbonic anhydrase IX (P = .03) for sites of low StO2 versus high StO2. CD105 displayed a similar trend but was not significant (P = .09). Conclusion Ferumoxytol-based quantitative blood oxygenation level-dependent MRI can potentially be used as a noninvasive surrogate for oxygenation mapping in infiltrative astrocytomas. This technique can potentially be integrated in treatment planning for aggressive targeting of hypoxic areas in tumors.

Aspects on the Physiological and Biochemical Foundations of Neurocritical Care.

Neurocritical care (NCC) is a branch of intensive care medicine characterized by specific physiological and biochemical monitoring techniques necessary for identifying cerebral adverse events and for evaluating specific therapies. Information is primarily obtained from physiological variables related to intracranial pressure (ICP) and cerebral blood flow (CBF) and from physiological and biochemical variables related to cerebral energy metabolism. Non-surgical therapies developed for treating increased ICP are based on knowledge regarding transport of water across the intact and injured blood–brain barrier (BBB) and the regulation of CBF. Brain volume is strictly controlled as the BBB permeability to crystalloids is very low restricting net transport of water across the capillary wall. Cerebral pressure autoregulation prevents changes in intracranial blood volume and intracapillary hydrostatic pressure at variations in arterial blood pressure. Information regarding cerebral oxidative metabolism is obtained from measurements of brain tissue oxygen tension (PbtO2) and biochemical data obtained from intracerebral microdialysis. As interstitial lactate/pyruvate (LP) ratio instantaneously reflects shifts in intracellular cytoplasmatic redox state, it is an important indicator of compromised cerebral oxidative metabolism. The combined information obtained from PbtO2, LP ratio, and the pattern of biochemical variables reveals whether impaired oxidative metabolism is due to insufficient perfusion (ischemia) or mitochondrial dysfunction. Intracerebral microdialysis and PbtO2 give information from a very small volume of tissue. Accordingly, clinical interpretation of the data must be based on information of the probe location in relation to focal brain damage. Attempts to evaluate global cerebral energy state from microdialysis of intraventricular fluid and from the LP ratio of the draining venous blood have recently been presented. To be of clinical relevance, the information from all monitoring techniques should be presented bedside online. Accordingly, in the future, the chemical variables obtained from microdialysis will probably be analyzed by biochemical sensors.

Advanced monitoring in traumatic brain injury: microdialysis.

Here, we review the present state-of-the-art of microdialysis for monitoring patients with severe traumatic brain injury, highlighting the newest developments. Microdialysis has evolved in neurocritical care to become an established bedside monitoring modality that can reveal unique information on brain chemistry. A major advance is recent consensus guidelines for microdialysis use and interpretation. Other advances include insight obtained from microdialysis into the complex, interlinked traumatic brain injury disorders of electrophysiological changes, white matter injury, inflammation and metabolism. Microdialysis has matured into being a standard clinical monitoring modality that takes its place alongside intracranial pressure and brain tissue oxygen tension measurement in specialist neurocritical care centres, as well as being a research tool able to shed light on brain metabolism, inflammation, therapeutic approaches, blood-brain barrier transit and drug effects on downstream targets. Recent consensus on microdialysis monitoring is paving the way for improved neurocritical care protocols. Furthermore, there is scope for future improvements both in terms of the catheters and microdialysate analyser technology, which may further enhance its applicability.

Prolonged and Continuous Measurement of Kidney Oxygenation in Conscious Rats.

A relative deficiency in kidney oxygenation, i.e., renal hypoxia, may contribute to the initiation and progression of acute and chronic kidney disease. A critical barrier to investigate this is the lack of methods allowing measurement of the partial pressure of oxygen in kidney tissue for long periods in vivo. We have developed, validated, and tested a novel telemetric method that can do this. Here we provide details on the calibration, implantation, implementation for data recording, and reuse of this telemetry-based technology for measurement of medullary tissue oxygen tension in conscious, unrestrained rats. This technique provides an important additional tool for investigating the impact of renal hypoxia in biology and pathophysiology.

Impact of percutaneous dilatational tracheostomy in brain injured patients

ObjectiveTracheostomy is an established method in the airway management of critically ill patients with traumatic and non-traumatic brain injuries. High priority in the treatment of those patients is to protect vulnerable brain tissue. While bedside percutaneously dilatative tracheostomy (PDT) technique is increasingly used, there is disagreement about the harms of this intervention for the damaged brain. Therefore, discussions about the safety of tracheostomy in those patients must consider direct and indirect cerebral parameters. MethodsWe examined a series of 289 tracheostomies regarding vital signs, respiratory and intracranial parameters in a retrospective study. Complications were recorded and risk factors for a complicated scenario statistically determined. ResultsSevere complications were rare (1/289). Arterial hypotension occurred in 3 of 289 cases with a systolic blood pressure below 90mmHg. We had two patients (0.5%) with transient hypoxia, but 43 cases (15%) of severe hypercapnia during PDT. Invasive measurement of brain tissue oxygen tension (PBrO2) ruled out any cerebral hypoxia during the procedure in 39 available cases. Intracranial pressure (ICP) rose temporarily in 24% of the cases. Cerebral perfusion pressure (CPP) however remained unaffected. Surgery time and hypercapnia are capable risk factors for intraoperative ICP elevation. There is no significant difference in intraoperative ICP rises between disease entities. ConclusionPDT is a safe procedure for the most common neurosurgical diseases, even for patients with respiratory insufficiency. Shortening surgical time seems to be the most important factor to avoid ICP increase.

Quantitative assessment of brain microvascular and tissue oxygenation during cardiac arrest and resuscitation in pigs

Cardiac arrest is associated with a very high rate of mortality, in part due to inadequate tissue perfusion during attempts at resuscitation. Parameters such as mean arterial pressure and end-tidal carbon dioxide may not accurately reflect adequacy of tissue perfusion during cardiac resuscitation. We hypothesised that quantitative measurements of tissue oxygen tension would more accurately reflect adequacy of tissue perfusion during experimental cardiac arrest. Using oxygen-dependent quenching of phosphorescence, we made measurements of oxygen in the microcirculation and in the interstitial space of the brain and muscle in a porcine model of ventricular fibrillation and cardiopulmonary resuscitation. Measurements were performed at baseline, during untreated ventricular fibrillation, during resuscitation and after return of spontaneous circulation. After achieving stable baseline brain tissue oxygen tension, as measured using an Oxyphor G4-based phosphorescent microsensor, ventricular fibrillation resulted in an immediate reduction in all measured parameters. During cardiopulmonary resuscitation, brain oxygen tension remained unchanged. After the return of spontaneous circulation, all measured parameters including brain oxygen tension recovered to baseline levels. Muscle tissue oxygen tension followed a similar trend as the brain, but with slower response times. We conclude that measurements of brain tissue oxygen tension, which more accurately reflect adequacy of tissue perfusion during cardiac arrest and resuscitation, may contribute to the development of new strategies to optimise perfusion during cardiac resuscitation and improve patient outcomes after cardiac arrest.

Telemetry-based oxygen sensor for continuous monitoring of kidney oxygenation in conscious rats

The precise roles of hypoxia in the initiation and progression of kidney disease remain unresolved. A major technical limitation has been the absence of methods allowing long-term measurement of kidney tissue oxygen tension (Po₂) in unrestrained animals. We developed a telemetric method for the measurement of kidney tissue Po₂ in unrestrained rats, using carbon paste electrodes (CPEs). After acute implantation in anesthetized rats, tissue Po₂ measured by CPE-telemetry in the inner cortex and medulla was in close agreement with that provided by the "gold standard" Clark electrode. The CPE-telemetry system could detect small changes in renal tissue Po₂ evoked by mild hypoxemia. In unanesthetized rats, CPE-telemetry provided stable measurements of medullary tissue Po₂ over days 5-19 after implantation. It also provided reproducible responses to systemic hypoxia and hyperoxia over this time period. There was little evidence of fibrosis or scarring after 3 wk of electrode implantation. However, because medullary Po₂ measured by CPE-telemetry was greater than that documented from previous studies in anesthetized animals, this method is presently best suited for monitoring relative changes rather than absolute values. Nevertheless, this new technology provides, for the first time, the opportunity to examine the temporal relationships between tissue hypoxia and the progression of renal disease.

Microdialysis in Early Detection of Temporary Pancreatic Ischemia in a Porcine Model

Background: Ischemic injury to the pancreas occurs in various clinical conditions. A method for online monitoring of pathophysiological events in pancreatic parenchyma is missing. Aims: To assess the timing of microdialysis (MD) technique response on temporary changes in pancreatic perfusion, and to evaluate the relationship between MD data and systemic markers of anaerobic metabolism and inflammation. Methods: In anaesthetized normoventilated pigs, MD probes were placed in right (control) and left (ischemic) pancreatic lobes, respectively. Following the clamping of the vessels, ischemia was verified by tissue oxygen tension (P_tiO₂) measurements. Results: P_tiO₂ decreased within 20 min after the clamping of the vessels, already returning to baseline levels at the first sampling point after the removal of the clamp. MD lactate levels increased, whereas pyruvate and glucose levels decreased at 20 min after the induction of ischemia. These trends continued until the end of ischemia and returned to baseline following reperfusion. Serum lactate, amylase and tumor necrosis factor-alpha levels decreased throughout the protocol time. Conclusion: MD data were in concordance with changes in P_tiO₂, which is indicative of local anaerobic metabolism. MD allowed the detection of pathophysiological processes within the ischemic pancreas at a stage when no elevations of systemic markers of ischemia or inflammation were observed.

Multimodal monitoring and neurocritical care bioinformatics

Neurocritical care bioinformatics is a new field that focuses on the acquisition, storage and analysis of physiological and other data relevant to the bedside care of patients with acute neurological conditions such as traumatic brain injury or stroke. The main focus of neurocritical care for these conditions relates to prevention, detection and management of secondary brain injury, which relies heavily on monitoring of systemic and cerebral parameters (such as blood-pressure level and intracranial pressure). Advanced neuromonitoring tools also exist that enable measurement of brain tissue oxygen tension, cerebral oxygen utilization, and aerobic metabolism. The ability to analyze these advanced data for real-time clinical care, however, remains intuitive and primitive. Advanced statistical and mathematical tools are now being applied to the large volume of clinical physiological data routinely monitored in neurocritical care with the goal of identifying better markers of brain injury and providing clinicians with improved ability to target specific goals in the management of these patients. This Review provides an introduction to the concepts of multimodal monitoring for secondary brain injury in neurocritical care and outlines initial and future approaches using informatics tools for understanding and applying these data to clinical care.

Real-time measurement of brain tissue oxygen tension by fluorescence quenching

Medical Center of the Johannes-Gutenberg-University Mainz, Department of Anaesthesiology, Mainz, Germany

An implantable telemetry system for continuous chronic monitoring of kidney oxygenation in freely moving rats

We present a telemetry system for long-term monitoring of in-vivo kidney tissue oxygen. The transmitter contains an embedded potentiostat and has an attached carbon-paste electrode for amperometric detection of dissolved O2 (electrode diameter 200μm, transmitter wt 11 gm). Each electrode responds to physiological concentrations of O2 (50–80μM). The O</sub> concentration of the tissue is converted to an electrical current by the reduction of O2 on the carbon-paste. The total RMS noise of the telemetry system was 0.23μM. Inductive power transfer is utilised to recharge the telemeter transcutaneously, thus maintaining continuous recording for potentially the lifetime of the animal. In anesthetised rats the system was validated against a Clark-type electrode (50μm tip) and both electrodes were simultaneously inserted into the kidney. Rats were ventilated with different O2 concentrations to vary the kidney oxygen tension, and measurements were made at increasing depths in the tissue. The renal tissue oxygen tension measurements by these two methods were correlated (r2=0.466; p<0.001), with no fixed or proportional bias. Electrodes were also chronically implanted in the kidney. In conscious rats, the inspired O2 concentration was varied (10%, 21%, 100%). The observed renal oxygen tension agreed with changes in inspired O2 concentration. The implanted system was shown to be stable for >5 weeks.

Neuromonitoring for Traumatic Brain Injury in Neurosurgical Intensive Care

The primary aim of neuromonitoring in patients with traumatic brain injury is early detection of secondary brain insults so that timely interventions can be instituted to prevent or treat secondary brain injury. Intracranial pressure monitoring has been a stalwart in neuromonitoring and is still very much the main parameter to guide therapy in brain injured patients in many centres. Cerebral oxygenation is also established as an important parameter for monitoring: global cerebral oxygenation is reliably measured using jugular venous oxygen saturation while brain tissue oxygen tension measurement allows focal brain oxygenation to be monitored. Near-infrared spectroscopy allows a non-invasive option for monitoring of regional cerebral oxygenation. Cerebral microdialysis makes focal measurements of markers of cellular metabolism and cellular injury and death possible, and it is in transition from being a research tool to being an important clinical tool in neuromonitoring. Multimodal monitoring allows different parameters of brain physiology and function to be monitored and can improve identification and prediction of secondary cerebral insults. Multimodal monitoring can potentially improve outcomes in patients with traumatic brain injury by promoting customised treatment strategies for individual patients in place of the commonplace practice of strict adherence to achieving the same standard physiological targets for every patient.

Importance of real-time tissue oximetry: relationship to muscle oxygenation and tissue viability

Background: There is currently no efficient and reliable clinical means of assessing the degree of ischemia and reperfusion associated damage in tissue during extracorporeal perfusion. The objective was to study correlation of tissue oxygen tension measurements with tissue oxygen saturation, cytochrome oxidase redox state and tissue viability.

Brain Tissue Oxygen Monitoring in Children—A Review

Brain tissue oxygen monitoring is a relatively new technique for continuous measurement of focal brain tissue oxygen tension (PbtO2). There are several studies of PbtO2monitoring in adult patients but few in children. The goal is the prevention, or early detection and treatment, of secondary insults. Episodes of low PbtO2are associated with worse outcome, and treatment directed by PbtO2may benefit patients, but there is no Class I evidence as yet. What determines PbtO2is multifactorial and the underlying pathophysiological events affecting PbtO2may be complex. The clinician using this technology must understand the technical and physiological aspects, as well as the limitations, of PbtO2monitoring if there is to be any clinical benefit. However, whether PbtO2monitoring delivers overall benefit across centers of different expertise requires a randomised controlled trial. This review examines the current literature on PbtO2monitoring with a focus on children, the important technical and physiological factors, and an approach to using a PbtO2monitor.

Importance of Real-Time Tissue Oximetry: Relationship to Muscle Oxygenation and Tissue Viability

There is currently no efficient and reliable clinical means of assessing the degree of ischemia- and reperfusion-associated damage in microvascular transplants. The objective was to study correlation of tissue oxygen tension measurements with tissue oxygen saturation, cytochrome oxidase redox state, and tissue viability. Latissimus dorsi muscle was dissected and mobilized in New Zealand white rabbits (n = 30, 2.5 ± 0.5 kg). Muscles were exposed to warm ischemia in two groups with either 4 or 6 h, followed by reperfusion. Tissue PO(2) was measured with a miniature intramuscular oxygen sensor (Licox microprobe; Integra Neurosciences, Ratingen, Germany) all along with tissue hemoglobin saturation (rSO(2)) and cytochrome oxidase aa3 redox state (CytOx) by in vivo near-infrared spectroscopy. Linear correlation was performed between tissue PO(2) and rSO(2), CytOx and tissue viability. After ischemia and reperfusion, tissue PO(2) and CytOx recovery was significantly decreased in both groups compared with control (4 h: P < 0.05; 6 h: P < 0.01). Significant correlations between changes in tissue PO(2) and rSO(2) (r = 0.92; P < 0.01), CytOx (r = 0.90; P < 0.01), wet-to-dry ratio (r = -0.97; P < 0.01), and mitochondrial viability index (r = 0.97; P < 0.01) were found. Tissue oxygen tension measured with microprobes correlated closely with tissue oxygenation, cellular oxygen utilization, and the extent of ischemia reperfusion injury.

Advances in free flap monitoring: have we gone too far?

Timely recognition of vascular compromise of free flaps is crucial to salvaging failing flaps. This review summarizes the most recent available literature about free flap monitoring over the period of 2008-2009. Novel techniques are discussed. Several case series have been published that highlight interesting methods for free flap monitoring; however, concerns of impracticality abound. The implantable Doppler has been used in a large case series with good success. Externalization of a flap component has undergone refinement in technique with success. Measurement of tissue oxygen tension and blood flow with PET is possible. Microendoscopy has been proposed as a possible technique for accessible flaps to assess capillary blood flow. Several retrospective studies elucidated trends in free flap compromise in the postoperative period, which confirm prior findings. We provide an overview of recent techniques for free flap monitoring. No single technique provides an ideal method for free flap monitoring, but these methods may prove promising with future research and refinement. New techniques in free flap monitoring largely remain out of the scope of reasonable implementation.