Intraoperative Echocardiography: Guide to Decision-Making.

PURPOSE OF REVIEW: This review aims to provide a concise overview of key recommendations, with a specific focus on common challenges faced by intraoperative echocardiographers when dealing with frequently encountered valvular pathologies and mechanical circulatory support. It offers valuable insights for medical practitioners in this field. RECENT FINDINGS: The American Society of Echocardiography (ASE) and the American College of Cardiology/American Heart Association (ACC/AHA) have released updated comprehensive guidelines for the use of transesophageal echocardiography (TEE) for the assessment of cardiac structures and implanted devices to help guide intraoperative decision-making. Transesophageal echocardiography (TEE) is a regularly employed intraoperative diagnostic and monitoring tool, offering various modalities for the rapid evaluation of valvular and aortic pathology, hemodynamic disturbances, and cardiac function. It is particularly valuable in assessing and placing mechanical circulatory support (MCS) devices, providing views often challenging to obtain through transthoracic echocardiography. Additionally, intraoperative TEE can be used for decision-making in patients with valvular disease allowing incorporation of patient-specific and situational factors. Echocardiographers can employ this information in real-time to help guide surgical treatment selection such as repair, replacement, or deferral of intervention.

Astrocyte HIF-2α supports learning in a passive avoidance paradigm under hypoxic stress.

BACKGROUND: The brain is extensively vascularized, uses20% of the body's oxygen, and is highly sensitive to changes in oxygen. While synaptic plasticity and memory are impaired in healthy individuals by exposure to mild hypoxia, aged individuals appear to be even more sensitive. Aging is associated with progressive failure in pulmonary and cardiovascular systems, exposing the aged to both chronic and superimposed acute hypoxia. The HIF proteins, the "master regulators" of the cellular response to hypoxia, are robustly expressed in neurons and astrocytes. Astrocytes support neurons and synaptic plasticity via complex metabolic and trophic mechanisms. The activity of HIF proteins in the brain is diminished with aging, and the increased exposure to chronic and acute hypoxia with aging combined with diminished HIF activity may impair synaptic plasticity. PURPOSE: Herein, we test the hypothesis that astrocyte HIF supports synaptic plasticity and learning upon hypoxia. MATERIALS AND METHODS: An Astrocyte-specific HIF loss-of-function model was employed, where knock-out of HIF-1α or HIF-2α in GFAP expressing cells was accomplished by cre-mediated recombination. Animals were tested for behavioral (open field and rotarod), learning (passive avoidance paradigm), and electrophysiological (long term potentiation) responses to mild hypoxic challenge. RESULTS: In an astrocyte-specific HIF loss-of-function model followed by mild hypoxia, we identified that the depletion of HIF-2α resulted in an impaired passive avoidance learning performance. This was accompanied by an attenuated response to induction in long-term potentiation (LTP), suggesting that the hippocampal circuitry was perturbed upon hypoxic exposure following HIF-2α loss in astrocytes, and not due to hippocampal cell death. We investigated HIF-regulated trophic and metabolic target genes and found that they were not regulated by HIF-2α, suggesting that these specific targets may not be involved in mediating the phenotypes observed. CONCLUSION: Together, these results point to a role for HIF-2α in the astrocyte's regulatory role in synaptic plasticity and learning under hypoxia and suggest that even mild, acute hypoxic challenges can impair cognitive performance in the aged population who harbor impaired HIF function.

Fiber-optic Monitoring of Spinal Cord Hemodynamics in Experimental Aortic Occlusion.

BACKGROUND: Spinal cord ischemia occurs frequently during thoracic aneurysm repair. Current methods based on electrophysiology techniques to detect ischemia are indirect, non-specific, and temporally slow. In this article, the authors report the testing of a spinal cord blood flow and oxygenation monitor, based on diffuse correlation and optical spectroscopies, during aortic occlusion in a sheep model. METHODS: Testing was carried out in 16 Dorset sheep. Sensitivity in detecting spinal cord blood flow and oxygenation changes during aortic occlusion, pharmacologically induced hypotension and hypertension, and physiologically induced hypoxia/hypercarbia was assessed. Accuracy of the diffuse correlation spectroscopy measurements was determined via comparison with microsphere blood flow measurements. Precision was assessed through repeated measurements in response to pharmacologic interventions. RESULTS: The fiber-optic probe can be placed percutaneously and is capable of continuously measuring spinal cord blood flow and oxygenation preoperatively, intraoperatively, and postoperatively. The device is sensitive to spinal cord blood flow and oxygenation changes associated with aortic occlusion, immediately detecting a decrease in blood flow (-65 ± 32%; n = 32) and blood oxygenation (-17 ± 13%, n = 11) in 100% of trials. Comparison of spinal cord blood flow measurements by the device with microsphere measurements led to a correlation of R = 0.49, P < 0.01, and the within-sheep coefficient of variation was 9.69%. Finally, diffuse correlation spectroscopy is temporally more sensitive to ischemic interventions than motor-evoked potentials. CONCLUSION: The first-generation spinal fiber-optic monitoring device offers a novel and potentially important step forward in the monitoring of spinal cord ischemia.