Baseline cerebral oximetry values depend on non-modifiable patient characteristics

Preoperative cerebral oxygenation in high-risk noncardiac surgical patients: an observational study on postoperative mortality and complications

Near Infrared Spectroscopy (NIRS) has become widely accepted to evaluate regional cerebral oxygen saturation (rScO2), potentially acting as a surrogate parameter of reduced cerebral oxygen delivery or increased consumption. Low preoperative rScO2 is associated with increased postoperative complications after cardiac surgery. However, its universal potential in pre-anesthesia risk assessment remains unclear. Therefore, we investigated whether low preoperative rScO2 is indicative of postoperative complications and associated with poor outcomes in noncardiac surgical patients. We prospectively enrolled 130 patients undergoing high-risk noncardiac surgery. During pre-anesthesia evaluation, baseline rScO2 was recorded with and without oxygen supplementation. The primary endpoint was 30-day mortality, while secondary endpoints were postoperative myocardial injury, respiratory complications, and renal failure. We further evaluated the impact of body position and preoperative hemoglobin (Hb) concentration on rScO2. Of the initially enrolled 130 patients, 126 remained for final analysis. Six (4.76%) patients died within 30 postoperative days. 95 (75.4%) patients were admitted to the ICU. 32 (25.4%) patients suffered from major postoperative complications. There was no significant association between rScO2 and 30-day mortality or secondary endpoints. Oxygen supplementation induced a significant increase of rScO2. Furthermore, Hb concentration correlated with rScO2 values and body position affected rScO2. No significant association between rScO2 values and NYHA, LVEF, or MET classes were observed. Preoperative rScO2 is not associated with postoperative complications in patients undergoing high-risk noncardiac surgery. We speculate that the discriminatory power of NIRS is insufficient due to individual variability of rScO2 values and confounding factors.

The Influence of Age on Cerebral Tissue Oxygenation in Vasovagal Syncope and Orthostatic Hypotension

Age-related physiological impairment increases susceptibility to syncope. We tested the hypotheses that cerebral oxygenation during orthostatic provocation, as well as the level at which syncope occurs, differs according to age. Non-invasive hemodynamic monitoring and cerebral oximetry were applied during a head-up tilt test in 139 patients with vasovagal syncope (mean (SD) 45, (17) years, 60%-female); 121 patients with orthostatic hypotension (61.4 (19.2) years, 49.6%-female); and 82 patients with a negative head-up tilt test (45 (18) years, 61%-female). Group differences in cerebral tissue oxygenation levels and systolic blood pressure were assessed in supine at 3 and 10 min of orthostatic provocation, 30 s before (i.e., presyncopal phase) and during syncope in age groups of <30, 30−60, and >60 years. During the head-up tilt test, cerebral tissue oxygenation at the presyncopal phase decreased with age, both in patients with vasovagal syncope (<30 years: 66.9 ± 6.2, 30−60: 64.5 ± 6.1, >60: 62.2 ± 5.8%; p = 0.009) and orthostatic hypotension (<30: 67.4 ± 4.4, 30−60: 61.6 ± 6.2, >60: 57.5 ± 3.9; p < 0.001). Mean systolic blood pressure at the presyncopal phase did not differ according to age. Cerebral oxygenation prior to syncope in older individuals with vasovagal syncope and orthostatic hypotension is lower compared with younger individuals independently of systolic blood pressure. This suggests that the level of cerebral oxygenation at which syncope is elected is lower in older individuals.

Association between the variability of cerebral oxygen saturation during cardiopulmonary bypass and delayed postoperative neurocognitive recovery in cardiac valve surgical patients: A pilot study

AIMS OF THE STUDY

The association between regional cerebral oxygen saturation (rSO2) and postoperative cognitive decline is controversial. In this study, we investigated the association between the real variability of regional cerebral oxygen saturation during cardiopulmonary bypass (CPB) and postoperative delayed neurocognitive recovery in patients undergoing heart valve surgery.

METHODS USED TO CONDUCT THE STUDY

A total of 71 patients who underwent cardiac valve surgery were enrolled in this study. Patients were assessed for cognitive function using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment Scale (MOCA) on the day before surgery and the 7th day after surgery. The real variability of regional cerebral oxygen saturation (rSO2), real variability of the brain bispectral index of EEG (BIS), real variability of mean arterial pressure (MAP) and body temperature were monitored during CPB. Patients were divided into two groups according to neural cognitive function scores to explore the relationship between postoperative delayed neurocognitive recovery and the real variability of cerebral oxygen saturation, BIS, MAP, and body temperature during CPB.

RESULTS OF THE STUDY

Twenty-seven patients were diagnosed with postoperative delayed neurocognitive recovery. The occurrence of postoperative delayed neurocognitive recovery after surgery was closely related to the large variability of rSO2 during the rewarming phase of CPB (P < .05). Logistic analysis showed that preoperative arrhythmia, a lower level of serum albumin after surgery and greater rSO2 variability during the rewarming phase were risk factors for postoperative delayed neurocognitive recovery (P < .05). In this study, there was no correlation between postoperative delayed neurocognitive recovery and BIS, MAP or body temperature variability (P > .05).

CONCLUSIONS DRAWN FROM THE STUDY AND CLINICAL IMPLICATIONS

The real variability of rSO2 during the CPB rewarming phase was related to postoperative delayed neurocognitive recovery in patients who underwent cardiac surgery.

Extended recording of LMA in rats: Effects of IV catheters, "comfort jackets" and chamber lids on arterial blood gas parameters

The standard infrared photobeam locomotor activity system has been used extensively in neurobiology and neuropharmacology to study the functional impact of direct manipulations of the nervous system. There is interest in using the activity monitors to assess the early stages of drug withdrawal in rodents. In a standard twice-daily dosing strategy animals would be dosed at 6:00 am and 5:00 pm for 15 to 30 days. There is interest in using the chambers to assess the early stages of the discontinuation syndrome. Placement of the rodents into the chambers following the scheduled sham or vehicle last dose of a 15- to 30-day subchronic dosing regimen (b.i.d., t.i.d., etc.) and monitoring overnight allows for a quantitative measure of the initial physiological homeostatic acclimation period during the lights-out period. By using the chambers there is no circadian dysrhythmia induced as an experimental confound and objectively verifiable data is generated during the period expected to correspond with the plasma drug levels approaching zero and the onset of discontinuation syndrome. We demonstrated that untreated "normal" rats showed a normal decelerating time-effect curve over the 12-hour monitoring period that was not compromised by restricted access to food and water. Arterial blood gas monitoring before and after 12 h of night-time activity chamber monitoring clearly demonstrated normal respiratory function with no clinical signs of any blood gas-based diagnosis of metabolic dysfunction.

Modern technology-derived normative values for cerebral tissue oxygen saturation in adults

Modern near-infrared spectroscopy technology is increasingly adopted to measure cerebral tissue oxygen saturation. However, the normal range of cerebral tissue oxygen saturation in adults with such technology is unknown. We sought to measure cerebral tissue oxygen saturation in healthy volunteers using the novel O3 Regional Oximetry® device (Masimo Corporation, Irvine, CA, USA) and assess its relationship with key physical and haemodynamic characteristics. For ≥5 minutes, we continuously recorded cerebral tissue oxygen saturation, pulse oximetry, cardiac index and mean arterial pressure. We assessed for differences in cerebral tissue oxygen saturation between hemispheres, sex, skin type, comorbidity or smoking status, and for associations between cerebral tissue oxygen saturation and age, height, weight, SpO₂and haemodynamic parameters. We recorded >32,000 observations in 98 volunteers aged 22 to 60 years, including 41 (42%) males. One-fifth had one or more co morbidities ( n=22, 22.5%), one-tenth were either current or former-smokers ( n=13, 13%), and most had a Fitzpatrick skin type of 3 or lower ( n=84, 86%). The mean combined average cerebral tissue oxygen saturation was 67.6% (95% confidence interval 66.8%-68.6%). We found statistically significant differences in cerebral tissue oxygen saturation according to hemisphere and an association between cerebral tissue oxygen saturation and mean arterial pressure and cardiac index. The combined average cerebral tissue oxygen saturation in 98 healthy volunteers was 67.6% with a narrow confidence interval and no combined average cerebral tissue oxygen saturation was below 56%. We also observed statistically significant yet quantitatively small cerebral tissue oxygen saturation differences between hemispheres, and an association between cerebral tissue oxygen saturation and mean arterial pressure and cardiac index.

Ultrasound-tagged near-infrared spectroscopy does not disclose absent cerebral circulation in brain-dead adults

BACKGROUND

Near-infrared spectroscopy, a non-invasive technique for monitoring cerebral oxygenation, is widely used, but its accuracy is questioned because of the possibility of extra-cranial contamination. Ultrasound-tagged near-infrared spectroscopy (UT-NIRS) has been proposed as an improvement over previous methods. We investigated UT-NIRS in healthy volunteers and in brain-dead patients.

METHODS

We studied 20 healthy volunteers and 20 brain-dead patients with two UT-NIRS devices, CerOx™ and c-FLOW™ (Ornim Medical, Kfar Saba, Israel), which measure cerebral flow index (CFI), a parameter related to changes in cerebral blood flow (CBF). Monitoring started after the patients had been declared brain dead for a median of 34 (range: 11-300) min. In 11 cases, we obtained further demonstration of absent CBF.

RESULTS

In healthy volunteers, CFI was markedly different in the two hemispheres in the same subject, with wide variability amongst subjects. In brain-dead patients (median age: 64 yr old, 45% female; 20% traumatic brain injury, 40% subarachnoid haemorrhage, and 40% intracranial haemorrhage), the median (inter-quartile range) CFI was 41 (36-47), significantly higher than in volunteers (33; 27-36).

CONCLUSIONS

In brain-dead patients, where CBF is absent, the UT-NIRS findings can indicate an apparently perfused brain. This might reflect an insufficient separation of signals from extra-cranial structures from a genuine appraisal of cerebral perfusion. For non-invasive assessment of CBF-related parameters, the near-infrared spectroscopy still needs substantial improvement.

Cerebral oxygenation for pain monitoring in adults is ineffective: A sequence-randomized, sham controlled study in volunteers

BACKGROUND

Pain assessment by Numeric Rating Scale (NRS) is considered to be good clinical practice, but objective pain assessment is still a challenge. Near infrared spectroscopy (NIRS) measures cerebral tissue oxygen saturation (SctO₂) that increases with cortical-neuronal activity and may provide point-of-care bedside pain monitoring. Analogous to promising studies in newborns, we hypothesize that different levels of SctO₂ can probably quantify pain intensity. SctO₂ may increase following painful in contrast to non-painful or sham stimuli and may correlate with pain intensity as assessed by NRS in volunteers.

METHODS

Twenty healthy male students (24.2±1.9 years), recruited via local advertising, were consecutively included in a sequence-randomized, sham-controlled, single-blinded study. SctO₂ was recorded continuously with two NIRS sensors on the forehead. After resting, four stimuli were applied in a random order on the right forearm (unexpected and expected electrical pain, expected non-painful and sham stimuli). Blinded subjects were asked to rate each stimulus on NRS.

STATISTICS

RM-ANOVA; Wilcoxon or paired Student t-test; Spearman's rank correlation; P<.05.

RESULTS

Resting volunteers showed SctO₂ of 72.65%±3.39. SctO₂ significantly increased for about 60 to 70s until a maximum after unexpected painful (74.62%±3.9; P=.022) and sham stimuli (74.07%±3.23; P=.014). Expected painful (P=.139) and non-painful stimuli (P=.455) resulted in no changes in SctO₂. NRS scores (median, IQR) were rated significantly higher after expected (5.25, 3.5 to 6.75) than after unexpected (4.5, 3 to 5; P=.008) pain. No strong correlation was found between NRS and SctO₂.

CONCLUSIONS AND IMPLICATIONS

Contrary to our expectations, measuring SctO₂ via a two-channel NIRS is not able to remediate the lack of objective bedside pain assessment under standardized experimental conditions in alert adults.

TRIAL REGISTRATION

DRKS 00011575 (retrospectively registered).