Continuous (CW) and pulsed light were used for the noninvasive measurement of hemoglobin oxygenation in tissues. A dual wavelength method of continuous illumination spectroscopy used 760 nm (deoxyhemoglobin peak) and 800 nm (an oxyhemoglobin-deoxyhemoglobin isosbestic point) to measure the kinetics and extent of oxyhemoglobin deoxygenation in brains during mild ischemia/hypoxia. Absorption and scattering were modeled in an artificial milk/yeast blood system, which gave an exponential relationship between absorption and optical path length to a depth of 7 cm. Time-resolved spectroscopy (10-ps resolution) afforded a display of the times and distances of arrival of photons emitted by the cat brain in response to a 10-ps input pulse. The emitted photons rose to a peak in a fraction of a nanosecond and declined exponentially over a few nanoseconds. The half-time of exponential decay corresponds to photon migration over a distance of 4 cm. Exponential light emission continued for several more nanoseconds when the brain was encased by the skull, which plays a key role in prolonging light emission. The exponential decline of light intensity has a value [exp( -pL)], where L is the path length determined from the time/distance scale and ,u is the characteristic of the migration of light in the brain. The factor ,u is increased by increasing absorption, and 1z' = EC where E and C are the Beer-Lambert parameters of extinction coeffilcient (E) and concentration (C). Thus, deoxyhemoglobin can be quantified in brain tissues.The utility of optical methods in studying metabolism and oxidative processes in cells and tissues was significantly enhanced in the early 1950s when a time-sharing dualwavelength system was developed for the quantitation of small changes in absorption in a highly scattering medium such as cell suspensions or muscle tissues in the visible and near-infrared (NIR) regions (1,2). Fluorescence signals from mitochondrial NADH complemented the absorption method for studies of the surface of heart, brain, and skeletal tissue (3,4). NIR spectroscopy was used to detect the redox state of the copper component of cytochrome oxidase in mitochondria (2) and yeast cells (5), and Jobsis-VanderVliet and coworkers (6-8) pioneered the study of NIR absorption in tissues by transillumination. More recently, algorithms have been developed by vanderZee and Delpy (9) to compensate for the interference from hemoglobin and myoglobin with cytochrome copper, as the latter may constitute as little as 10% of the total signal at 830 nm (see also ref. 10).This paper compares the use of continuous (CW) and pulsed light. The CW method has been applied to both animal and model systems to determine: (i) the attenuation characteristic of the light in models containing localized deoxyhemoglobin (Hb) and (ii) the ability to observe hypoxia in the brains of human subjects.II However, CW systems fail to quantify concentrations because they do not measure the optical path.The pulsed-light system time-resolves the emergence of light pulses ...

Background Despite the significant healthcare impact of acute kidney injury, little is known regarding prevention. Single-center data have implicated hypotension in developing postoperative acute kidney injury. The generalizability of this finding and the interaction between hypotension and baseline patient disease burden remain unknown. The authors sought to determine whether the association between intraoperative hypotension and acute kidney injury varies by preoperative risk. Methods Major noncardiac surgical procedures performed on adult patients across eight hospitals between 2008 and 2015 were reviewed. Derivation and validation cohorts were used, and cases were stratified into preoperative risk quartiles based upon comorbidities and surgical procedure. After preoperative risk stratification, associations between intraoperative hypotension and acute kidney injury were analyzed. Hypotension was defined as the lowest mean arterial pressure range achieved for more than 10 min; ranges were defined as absolute (mmHg) or relative (percentage of decrease from baseline). Results Among 138,021 cases reviewed, 12,431 (9.0%) developed postoperative acute kidney injury. Major risk factors included anemia, estimated glomerular filtration rate, surgery type, American Society of Anesthesiologists Physical Status, and expected anesthesia duration. Using such factors and others for risk stratification, patients with low baseline risk demonstrated no associations between intraoperative hypotension and acute kidney injury. Patients with medium risk demonstrated associations between severe-range intraoperative hypotension (mean arterial pressure less than 50 mmHg) and acute kidney injury (adjusted odds ratio, 2.62; 95% CI, 1.65 to 4.16 in validation cohort). In patients with the highest risk, mild hypotension ranges (mean arterial pressure 55 to 59 mmHg) were associated with acute kidney injury (adjusted odds ratio, 1.34; 95% CI, 1.16 to 1.56). Compared with absolute hypotension, relative hypotension demonstrated weak associations with acute kidney injury not replicable in the validation cohort. Conclusions Adult patients undergoing noncardiac surgery demonstrate varying associations with distinct levels of hypotension when stratified by preoperative risk factors. Specific levels of absolute hypotension, but not relative hypotension, are an important independent risk factor for acute kidney injury. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Summary:Detection of cerebral hypoxia-ischemia remains problematic in neonates. Near-infrared spectroscopy, a noninvasive bedside technology has potential, although thresholds for cerebral hypoxia-ischemia have not been defined. This study determined hypoxic-ischemic thresholds for cerebral oxygen saturation (ScO 2 ) in terms of EEG, brain ATP, and lactate concentrations, and compared these values with CBF and sagittal sinus oxygen saturation (SvO 2 ). Sixty anesthetized piglets were equipped with near-infrared spectroscopy, EEG, laser-Doppler flowmetry, and a sagittal sinus catheter. After baseline, ScO 2 levels of less than 20%, 20% to 29%, 30% to 39%, 40% to 49%, 50% to 59%, 60% to 79%, or 80% or greater were recorded for 30 minutes of normoxic normocapnia, hypercapnic hyperoxia, or bilateral carotid occlusion with or without arterial hypoxia. Brain ATP and lactate concentrations were measured biochemically. Logistic and linear regression determined the ScO 2, , CBF, and SvO 2 thresholds for abnormal EEG, ATP, and lactate findings. Baseline ScO 2 was 68 + 5%. The ScO 2 thresholds for increased lactate, minor and major EEG change, and decreased ATP were 44 ± 1%, 42 ± 5%, 37 ± 1%, and 33 ± 1%. The ScO 2 correlated linearly with SvO 2 (r ‫ס‬ 0.98) and CBF (r ‫ס‬ 0.89), with corresponding SvO 2 thresholds of 23%, 20%, 13%, and 8%, and CBF thresholds (% baseline) of 56%, 52%, 42%, and 36%. Thus, cerebral hypoxia-ischemia near-infrared spectroscopy thresholds for functional impairment are ScO 2 33% to 44%, a range that is well below baseline ScO 2 of 68%, suggesting a buffer between normal and dysfunction that also exists for CBF and SvO 2 .

In this series, the 95% CI for the frequency of epidural hematoma requiring laminectomy after epidural catheter placement for perioperative anesthesia/analgesia was 1 event per 22,189 placements to 1 event per 4330 placements. Risk was significantly lower in obstetric epidurals.

Background The incidence and impact of clinical stroke and silent radiographic cerebral infarction complicating open surgical aortic valve replacement (AVR) are poorly characterized. Methods and Results We performed a prospective cohort study of subjects ≥ 65 years of age undergoing AVR for calcific aortic stenosis. Subjects were evaluated by neurologists pre-operatively and post-operatively, and underwent post-operative magnetic resonance imaging (MRI). Over a 4 year period, 196 subjects were enrolled at 2 sites. Mean age = 75.8 ± 6.2 years, 36% female, 6% non-white. Clinical strokes were detected in 17%, Transient Ischemic Attack in 2%, and in-hospital mortality was 5%. The frequency of stroke in the Society for Thoracic Surgery (STS) database in this cohort was 7%. Most strokes were mild; the median National Institutes of Health Stroke Scale (NIHSS) was 3 (interquartile range 1 – 9). Clinical stroke was associated with increased length of stay, median 12 vs 10 days, p = 0.02. Moderate or severe stroke (NIHSS ≥10) occurred in 8 (4%) and was strongly associated with in-hospital mortality, 38% vs 4%, p = 0.005. Of the 109 stroke-free subjects with post-operative MRI, silent infarct was identified in 59 (54%). Silent infarct was not associated with in-hospital mortality or increased length of stay. Conclusions Clinical stroke after AVR was more common than previously reported, more than double for this same cohort in the STS database, and silent cerebral infarctions were detected in over half of patients undergoing AVR. Clinical stroke complicating AVR is associated with increased length of stay and mortality.