Cerebral autoregulation describes a mechanism that maintains cerebral blood flow stable despite fluctuating perfusion pressure. Multiple nonperfusion pressure processes also regulate cerebral ...perfusion. These mechanisms are integrated. The effect of the interplay between carbon dioxide and perfusion pressure on cerebral circulation has not been specifically reviewed. On the basis of the published data and speculation on the aspects that are without supportive data, the authors offer a conceptualization delineating the regulation of cerebral autoregulation by carbon dioxide. The authors conclude that hypercapnia causes the plateau to progressively ascend, a rightward shift of the lower limit, and a leftward shift of the upper limit. Conversely, hypocapnia results in the plateau shifting to lower cerebral blood flows, unremarkable change of the lower limit, and unclear change of the upper limit. It is emphasized that a sound understanding of both the limitations and the dynamic and integrated nature of cerebral autoregulation fosters a safer clinical practice.
Tissue Oximetry and Clinical Outcomes Bickler, Philip; Feiner, John; Rollins, Mark ...
Anesthesia and analgesia,
01/2017, Letnik:
124, Številka:
1
Journal Article
Recenzirano
A number of different technologies have been developed to measure tissue oxygenation, with the goal of identifying tissue hypoxia and guiding therapy to prevent patient harm. In specific cases, ...tissue oximetry may provide clear indications of decreases in tissue oxygenation such as that occurring during acute brain ischemia. However, the causation between tissue hemoglobin-oxygen desaturation in one organ (eg, brain or muscle) and global outcomes such as mortality, intensive care unit length of stay, and remote organ dysfunction remains more speculative. In this review, we describe the current state of evidence for predicting clinical outcomes from tissue oximetry and identify several issues that need to be addressed to clarify the link between tissue oxygenation and outcomes. We focus primarily on the expanding use of near-infrared spectroscopy to assess a venous-weighted mixture of venous and arterial hemoglobin-oxygen saturation deep in tissues such as brain and muscle. Our analysis finds that more work is needed in several areas: establishing threshold prediction values for tissue desaturation-related injury in specific organs, defining the types of interventions required to correct changes in tissue oxygenation, and defining the effect of interventions on outcomes. Furthermore, well-designed prospective studies that test the hypothesis that monitoring oxygenation status in one organ predicts outcomes related to other organs need to be done. Finally, we call for more work that defines regional variations in tissue oxygenation and improves technology for measuring and even imaging oxygenation status in critical organs. Such studies will contribute to establishing that monitoring and imaging of tissue oxygenation will become routine in the care of high-risk patients because the monitors will provide outputs that direct therapy to improve clinical outcomes.
Arterial blood pressure is the driving force for organ perfusion. Although hypotension is common in acute care, there is a lack of accepted criteria for its definition. Most practitioners regard ...hypotension as undesirable even in situations that pose no immediate threat to life, but hypotension does not always lead to unfavourable outcomes based on experience and evidence. Thus efforts are needed to better understand the causes, consequences, and treatments of hypotension. This narrative review focuses on the heterogeneous underlying pathophysiological bases of hypotension and their impact on organ perfusion and patient outcomes. We propose the iso-pressure curve with hypotension and hypertension zones as a way to visualize changes in blood pressure. We also propose a haemodynamic pyramid and a pressure–output–resistance triangle to facilitate understanding of why hypotension can have different pathophysiological mechanisms and end-organ effects. We emphasise that hypotension does not always lead to organ hypoperfusion; to the contrary, hypotension may preserve or even increase organ perfusion depending on the relative changes in perfusion pressure and regional vascular resistance and the status of blood pressure autoregulation. Evidence from RCTs does not support the notion that a higher arterial blood pressure target always leads to improved outcomes. Management of blood pressure is not about maintaining a prespecified value, but rather involves ensuring organ perfusion without undue stress on the cardiovascular system.
Pressure autoregulation is an organ's intrinsic ability to maintain blood flow despite changes in perfusion pressure. The purpose of this review is to discuss autoregulation's heterogeneity among ...different organs and variability under different conditions, a very clinically relevant topic.
Systematic search of Ovid MEDLINE; nonsystematic search of PubMed, Google Scholar, and reference lists.
Animal or human studies investigating the potency or variation of pressure autoregulation of any organs or the association between autoregulation and outcomes.
Two authors screened the identified studies independently then collectively agreed upon articles to be used as the basis for this review.
Study details, including subjects, organ investigated, methods of blood pressure intervention and blood flow measurement, and values of the lower limit, upper limit, and plateau were examined. Comparative canine studies were used to demonstrate the heterogeneity of pressure autoregulation among different organs and validate the proposed scale for organ categorization by autoregulatory capacity. Autoregulatory variability is discussed per organ. The association between cerebral autoregulation and outcome is summarized.
The organs with robust autoregulation are the brain, spinal cord, heart, and kidney. Skeletal muscle has moderate autoregulation. Nearly all splanchnic organs including the stomach, small intestine, colon, liver, and pancreas possess weak autoregulation. Autoregulation can be readily affected by a variety of clinically relevant factors. Organs with weak or weakened autoregulation are at a greater risk of suboptimal perfusion when blood pressure fluctuates. Cerebral autoregulation and outcomes are closely related. These lessons learned over 100+ years are instructive in clinical care.
Awake craniotomy is currently a useful surgical approach to help identify and preserve functional areas during cortical and subcortical tumor resections. Methodologies have evolved over time to ...maximize patient safety and minimize morbidity using this technique. The goal of this study is to analyze a single surgeon's experience and the evolving methodology of awake language and sensorimotor mapping for glioma surgery.
The authors retrospectively studied patients undergoing awake brain tumor surgery between 1986 and 2014. Operations for the initial 248 patients (1986-1997) were completed at the University of Washington, and the subsequent surgeries in 611 patients (1997-2014) were completed at the University of California, San Francisco. Perioperative risk factors and complications were assessed using the latter 611 cases.
The median patient age was 42 years (range 13-84 years). Sixty percent of patients had Karnofsky Performance Status (KPS) scores of 90-100, and 40% had KPS scores less than 80. Fifty-five percent of patients underwent surgery for high-grade gliomas, 42% for low-grade gliomas, 1% for metastatic lesions, and 2% for other lesions (cortical dysplasia, encephalitis, necrosis, abscess, and hemangioma). The majority of patients were in American Society of Anesthesiologists (ASA) Class 1 or 2 (mild systemic disease); however, patients with severe systemic disease were not excluded from awake brain tumor surgery and represented 15% of study participants. Laryngeal mask airway was used in 8 patients (1%) and was most commonly used for large vascular tumors with more than 2 cm of mass effect. The most common sedation regimen was propofol plus remifentanil (54%); however, 42% of patients required an adjustment to the initial sedation regimen before skin incision due to patient intolerance. Mannitol was used in 54% of cases. Twelve percent of patients were active smokers at the time of surgery, which did not impact completion of the intraoperative mapping procedure. Stimulation-induced seizures occurred in 3% of patients and were rapidly terminated with ice-cold Ringer's solution. Preoperative seizure history and tumor location were associated with an increased incidence of stimulation-induced seizures. Mapping was aborted in 3 cases (0.5%) due to intraoperative seizures (2 cases) and patient emotional intolerance (1 case). The overall perioperative complication rate was 10%.
Based on the current best practice described here and developed from multiple regimens used over a 27-year period, it is concluded that awake brain tumor surgery can be safely performed with extremely low complication and failure rates regardless of ASA classification; body mass index; smoking status; psychiatric or emotional history; seizure frequency and duration; and tumor site, size, and pathology.
Current therapy for carotid stenosis mainly includes carotid endarterectomy and endovascular stenting,which may incur procedure-related cerebral ischemia.Several methods have been employed for ...monitoring cerebral ischemia during surgery,such as awake neurocognitive assessment,electroencephalography,evoked potentials,transcranial Doppler,carotid stump pressure,and near infrared spectroscopy.However,there is no consensus on the gold standard or the method that is superior to others at present.Keeping patient awake for real time neurocognitive assessment is effective and essential;however,not every surgeon adopts it.In patients under general anesthesia,cerebral ischemia monitoring has to rely on non-awake technologies.The advantageous and disadvantageous properties of each monitoring method are reviewed.
Awake craniotomy (AC), defined as the performance of at least part of an open cranial procedure with the patient awake, has been tied to beneficial outcomes compared with similar surgery under ...general anesthesia. Improved anesthetic techniques have made a major contribution to the increasing popularity of AC. However, the heterogeneity of practice among institutions doing large numbers of ACs raises questions (often among those who only occasionally perform AC – i.e., practitioners in low-volume AC institutions) as to the ideal anesthetic technique for AC. The procedure presents a variety of decision-making dilemmas, the origins of which are the varying institutional preferences, lack of quality evidence, and several practice controversies. Evidence-based data that support a single anesthetic algorithm for AC are sparse. In this narrative review, the technical nuances of 13 aspects of anesthetic care for AC are discussed based on institutional preferences and available evidence, and the various controversies and research priorities are discussed. The skills, experience, and commitment of both the surgeon and the anesthesiologist are large variables that are likely more important than what the literature suggests about “best” techniques for AC. Optimizing patient outcome is the fundamental goal of the anesthesiologist.
In the present work, seven Mg-Zn-Ag alloys with the nominal composition of Mg96-xZnxAg4 (x = 17, 20, 23, 26, 29, 32, 35 in at.%) were prepared by induction melting and single-roller melt-spinning. ...The X-ray diffraction (XRD) analyses indicate the metallic glasses with three composition of Mg73Zn23Ag4, Mg70Zn26Ag4, and Mg67Zn29Ag4 were obtained successfully. The differential scanning calorimetry (DSC) measurement was used to obtain the characteristic temperature of Mg-Zn-Ag metallic glasses for the glass-forming ability analysis. The maximum glass transition temperature (Trg) was found to be 0.525 with a composition close to Mg67Zn29Ag4, which results in the best glass-forming ability. Moreover, the immersion test in simulated body fluid (SBF) demonstrate the relative homogeneous corrosion behavior of the Mg-Zn-Ag metallic glasses. The corrosion rate of Mg-Zn-Ag metallic glasses in SBF solution decreases with the increase of Zn content. The sample Mg67Zn29Ag4 has the lowest corrosion rate of 0.19 mm/yr, which could meet the clinical application requirement well. The in vitro cell experiments show that the Madin-Darby canine kidney (MDCK) cells cultured in sample Mg67Zn29Ag4 and its extraction medium have higher activity. However, the Mg-Zn-Ag metallic glasses exhibit obvious inhibitory effect on human rhabdomyosarcoma (RD) tumor cells. The present investigations on the glass-forming ability, corrosion behavior, cytocompatibility and tumor inhibition function of the Mg-Zn-Ag based metallic glass could reveal their biomedical application possibility.
Cardiac output (CO) monitoring based on pulse contour analysis (Vigileo-FloTrac) has the potential to be used for goal-directed fluid therapy in the perioperative setting. However, factors such as ...vasopressor usage may impact Vigileo-FloTrac's reliability in tracking CO changes. We tested third-generation Vigileo-FloTrac system's ability to accurately measure the changes in CO induced by vasopressor administration and increased preload in comparison with esophageal Doppler measurements.
In 33 anesthetized patients, CO was monitored simultaneously by the third-generation Vigileo-FloTrac and esophageal Doppler. Hemodynamic challenges included phenylephrine (to increase vasomotor tone), ephedrine (to increase myocardial contractility and heart rate), and whole-body tilting (to increase preload). Measurements were performed before and after each intervention.
Overall, 176 pairs of CO measurements were obtained. The difference between paired pulse contour and Doppler measurements of CO was 0.14 ± 2.13 L/min (mean ± SD), and the percentage error (2 SD of the difference divided by the mean CO of the reference method) was 66%. The trending ability of pulse contour versus Doppler was 23% (concordance, the percentage of the total number of data points that are in 1 of the 2 quadrants of agreement) after phenylephrine treatment, 69% (concordance) after ephedrine treatment, and 96% (concordance) after whole-body tilting.
The pulse contour method of measuring CO, as implemented in the third-generation Vigileo-FloTrac device, accurately tracks changes in CO when preload changes. However, the pulse contour method does not accurately track changes in CO induced with phenylephrine and ephedrine.
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