Near-infrared spectroscopy assessed cerebral oxygenation during open abdominal aortic aneurysm repair: relation to end-tidal CO2 tension

Cerebral Tissue Oxygen Saturation Is Enhanced in Patients following Transcatheter Aortic Valve Implantation: A Retrospective Study

Transcatheter aortic valve implantation (TAVI) has emerged as an alternative to surgical aortic valve replacement. The aim of this study was to evaluate whether a relevant alteration in cerebral tissue oxygen saturation (rSO2) could be detected following TAVI. Retrospective data analysis included 275 patients undergoing TAVI between October 2016 and December 2020. Overall, rSO2 significantly increased following TAVI (64.6 ± 10% vs. 68.1 ± 10%, p < 0.01). However, a significant rise was only observed in patients with a preoperative rSO2 < 60%. Of the hemodynamic confounders studied, hemoglobin, mean arterial pressure and blood pH were lowered, while central venous pressure and arterial partial pressure of carbon dioxide (PaCO2) were slightly elevated (PaCO2: 39 (36−43) mmHg vs. 42 (37−47) mmHg, p = 0.03; pH: 7.41 (7.3−7.4) vs. 7.36 (7.3−7.4), p < 0.01). Multivariate linear regression modeling identified only hemoglobin as a predictor of altered rSO2. Patients with a EuroScore II above 4% and an extended ICU stay were found to have lower rSO2, while no difference was observed in patients with postoperative delirium or between the implanted valve types. Further prospective studies that eliminate differences in potential confounding variables are necessary to confirm the rise in rSO2. Future research should provide more information on the value of cerebral oximetry for identifying high-risk patients who will require further clinical interventions in the setting of the TAVI procedure.

Low vs high hemoglobin trigger for transfusion in vascular surgery: a randomized clinical feasibility trial

Current guidelines advocate to limit red blood cell (RBC) transfusion during surgery, but the feasibility and safety of such a strategy remain unclear, as the majority of evidence is based on postoperatively stable patients. We assessed the effects of a protocol aiming to restrict RBC transfusion throughout hospitalization for vascular surgery. Fifty-eight patients scheduled for lower limb bypass or open abdominal aortic aneurysm repair were randomly assigned, on hemoglobin drop below 9.7 g/dL, to either a low-trigger (hemoglobin &lt; 8.0 g/dL) or a high-trigger (hemoglobin &lt; 9.7 g/dL) group for RBC transfusion. Near-infrared spectroscopy assessed intraoperative oxygen desaturation in brain and muscle. Explorative outcomes included nationwide registry data on death and major vascular complications. The primary outcome, mean hemoglobin within 15 days of surgery, was significantly lower in the low-trigger group, at 9.46 vs 10.33 g/dL in the high-trigger group (mean difference, −0.87 g/dL; P = .022), as were units of RBCs transfused (median [interquartile range (IQR)], 1 [0-2] vs 3 [2-6]; P = .0015). Although the duration and magnitude of cerebral oxygen desaturation increased in the low-trigger group (median [IQR], 421 [42-888] vs 127 [11-331] minutes × %; P = .0036), muscle oxygenation was unaffected. The low-trigger group associated to a higher rate of death or major vascular complications (19/29 vs 8/29; hazard ratio, 3.20; P = .006) and fewer days alive outside the hospital within 90 days (median [IQR], 76 [67-82] vs 82 [76-84] days; P = .049). In conclusion, a perioperative protocol restricting RBC transfusion successfully separated hemoglobin levels and RBC units transfused. Exploratory outcomes suggested potential harm with the low-trigger group and warrant further trials before such a strategy is universally adopted. This trial was registered at www.clinicaltrials.gov as #NCT02465125.

Elevated Renal Oxygen Extraction During Open Abdominal Aortic Aneurysm Repair Is Related to Postoperative Renal Dysfunction

BACKGROUND

Open abdominal aortic aneurysm repair is often followed by elevated plasma creatinine, likely due to impaired renal blood flow. We evaluated whether postoperative elevation in creatinine relates to renal oxygen extraction during surgery as an index of renal blood flow and also monitored frontal lobe oxygenation.

METHODS

For 19 patients (66 ± 10 years; mean ± SD) undergoing open infrarenal abdominal aortic aneurysm repair, renal oxygen extraction was determined by arterial and renal vein catheterization. Near-infrared spectroscopy determined frontal lobe oxygenation.

RESULTS

During surgery mean arterial pressure (from 102 ± 14 to 65 ± 11 mm Hg; P < .0001), arterial hemoglobin (from 7.7 ± 0.7 to 6.6 ± 0.8 mmol/L; P < 0.0001), and frontal lobe oxygenation (from 74 ± 6% to 70 ± 6%; P = .0414) decreased, while renal oxygen extraction increased (from 5.3% [4.3-8.1]; median [interquartile range] to 10.8% [5.8-17.5]; P = .0405). Plasma creatinine became significantly elevated on the second day after the operation (from 83 [73-101] to 105 µmol/L [79-143]; P = .0062) with a peak increase observed after 2 days (1-2). The peak increase in creatinine correlated to intraoperative renal oxygen extraction ( r = 0.51; P = .026).

CONCLUSION

Kidney function was affected after open abdominal aortic aneurysm repair likely related to limited renal blood flow. We take the increase in renal oxygen extraction and reduction in frontal lobe oxygenation to suggest that mean arterial pressure and hemoglobin were too low to maintain renal and cerebral circulation in vascular surgical patients.

Low vs. high haemoglobin trigger for transfusion in vascular surgery: protocol for a randomised trial

BACKGROUND

In patients with cardiovascular disease, guidelines for administration of red blood cells (RBC) are mainly based on studies outside the vascular surgical setting with the recommendation to use a haemoglobin (hb) trigger-level lower than by guidelines from The European Society for Vascular Surgery. Restricting RBC transfusion may affect blood O₂ transport with a risk for development of tissue ischaemia and postoperative complications.

METHODS

In a single-centre, open-label, assessor blinded trial, 58 vascular surgical patients (> 40 years of age) awaiting open surgery of the infrarenal aorta or infrainguinal arterial bypass surgery undergo a web-based randomisation to one of two groups: perioperative RBC transfusion triggered by hb < 8 g/dl or hb < 9.7 g/dl. Administration of fluid follows an individualised strategy by optimising cardiac stroke volume and near-infrared spectroscopy determines tissue oxygenation. Serious adverse event rates are: myocardial injury (troponin-I ≥ 45 ng/l or ischaemic electrocardiographic findings at day 30), acute kidney injury, death, stroke and severe transfusion reactions. A follow-up visit takes place 30 days after surgery and a follow-up of serious adverse events in the Danish National Patient Register within 90 days is pending.

DISCUSSION

This trial is expected to determine whether a RBC transfusion triggered by hb < 9.7 g/dl compared with hb < 8 g/dl results in adequate separation of postoperative hb levels, transfusion of more RBC units and maintains a higher tissue oxygenation. The results will inform the design of a multicentre trial for evaluation of important postoperative outcomes.

Journal of clinical monitoring and computing 2016 end of year summary: monitoring cerebral oxygenation and autoregulation

In the perioperative and critical care setting, monitoring of cerebral oxygenation (ScO₂) and cerebral autoregulation enjoy increasing popularity in recent years, particularly in patients undergoing cardiac surgery. Monitoring ScO₂ is based on near infrared spectroscopy, and attempts to early detect cerebral hypoperfusion and thereby prevent cerebral dysfunction and postoperative neurologic complications. Autoregulation of cerebral blood flow provides a steady flow of blood towards the brain despite variations in mean arterial blood pressure (MAP) and cerebral perfusion pressure, and is effective in a MAP range between approximately 50–150 mmHg. This range of intact autoregulation may, however, vary considerably between individuals, and shifts to higher thresholds have been observed in elderly and hypertensive patients. As a consequence, intraoperative hypotension will be poorly tolerated, and might cause ischemic events and postoperative neurological complications. This article summarizes research investigating technologies for the assessment of ScO₂ and cerebral autoregulation published in the Journal of Clinical Monitoring and Computing in 2016.