Charles W. Hogue

Cerebral near-infrared spectroscopy monitoring and neurologic outcomes in adult cardiac surgery patients: a systematic review.

BACKGROUND:Near-infrared spectroscopy is used during cardiac surgery to monitor the adequacy of cerebral perfusion. In this systematic review, we evaluated available data for adult patients to determine (1) whether decrements in cerebral oximetry during cardiac surgery are associated with stroke, postoperative cognitive dysfunction (POCD), or delirium; and (2) whether interventions aimed at correcting cerebral oximetry decrements improve neurologic outcomes. METHODS:We searched PubMed, Cochrane, and Embase databases from inception until January 31, 2012, without restriction on languages. Each article was examined for additional references. A publication was excluded if it did not include original data (e.g., review, commentary) or if it was not published as a full-length article in a peer-reviewed journal (e.g., abstract only). The identified abstracts were screened first, and full texts of eligible articles were reviewed independently by 2 investigators. For eligible publications, we recorded the number of subjects, type of surgery, and criteria for diagnosis of neurologic end points. RESULTS:We identified 13 case reports, 27 observational studies, and 2 prospectively randomized intervention trials that met our inclusion criteria. Case reports and 2 observational studies contained anecdotal evidence suggesting that regional cerebral O2 saturation (rScO2) monitoring could be used to identify cardiopulmonary bypass cannula malposition. Six of 9 observational studies reported an association between acute rScO2 desaturation and POCD based on the Mini-Mental State Examination (n = 3 studies) or more detailed cognitive testing (n = 6 studies). Two retrospective studies reported a relationship between rScO2 desaturation and stroke or type I and II neurologic injury after surgery. The observational studies had many limitations, including small sample size, assessments only during the immediate postoperative period, and failure to perform risk adjustments. Two randomized studies evaluated the efficacy of interventions for treating rScO2 desaturation during surgery, but adherence to the protocol was poor in one. In the other study, interventions for rScO2 desaturation were associated with less major organ injury and shorter intensive care unit hospitalization compared with nonintervention. CONCLUSIONS:Reductions in rScO2 during cardiac surgery may identify cardiopulmonary bypass cannula malposition, particularly during aortic surgery. Only low-level evidence links low rScO2 during cardiac surgery to postoperative neurologic complications, and data are insufficient to conclude that interventions to improve rScO2 desaturation prevent stroke or POCD.

Blood Pressure Excursions Below the Cerebral Autoregulation Threshold During Cardiac Surgery Are Associated With Acute Kidney Injury

Objectives:To determine whether mean arterial blood pressure excursions below the lower limit of cerebral blood flow autoregulation during cardiopulmonary bypass are associated with acute kidney injury after surgery. Setting:Tertiary care medical center. Patients:Four hundred ten patients undergoing cardiac surgery with cardiopulmonary bypass. Design:Prospective observational study. Interventions:None. Measurements and Main Results:Autoregulation was monitored during cardiopulmonary bypass by calculating a continuous, moving Pearson’s correlation coefficient between mean arterial blood pressure and processed near-infrared spectroscopy signals to generate the variable cerebral oximetry index. When mean arterial blood pressure is below the lower limit of autoregulation, cerebral oximetry index approaches 1, because cerebral blood flow is pressure passive. An identifiable lower limit of autoregulation was ascertained in 348 patients. Based on the RIFLE criteria (Risk, Injury, Failure, Loss of kidney function, End-stage renal disease), acute kidney injury developed within 7 days of surgery in 121 (34.8%) of these patients. Although the average mean arterial blood pressure during cardiopulmonary bypass did not differ, the mean arterial blood pressure at the limit of autoregulation and the duration and degree to which mean arterial blood pressure was below the autoregulation threshold (mm Hg × min/hr of cardiopulmonary bypass) were both higher in patients with acute kidney injury than in those without acute kidney injury. Excursions of mean arterial blood pressure below the lower limit of autoregulation (relative risk 1.02; 95% confidence interval 1.01 to 1.03; p < 0.0001) and diabetes (relative risk 1.78; 95% confidence interval 1.27 to 2.50; p = 0.001) were independently associated with for acute kidney injury. Conclusions:Excursions of mean arterial blood pressure below the limit of autoregulation and not absolute mean arterial blood pressure are independently associated with for acute kidney injury. Monitoring cerebral oximetry index may provide a novel method for precisely guiding mean arterial blood pressure targets during cardiopulmonary bypass.

Risks for impaired cerebral autoregulation during cardiopulmonary bypass and postoperative stroke

BACKGROUNDnImpaired cerebral autoregulation may predispose patients to cerebral hypoperfusion during cardiopulmonary bypass (CPB). The purpose of this study was to identify risk factors for impaired autoregulation during coronary artery bypass graft, valve surgery with CPB, or both and to evaluate whether near-infrared spectroscopy (NIRS) autoregulation monitoring could be used to identify this condition.nnnMETHODSnTwo hundred and thirty-four patients were monitored with transcranial Doppler and NIRS. A continuous, moving Pearsons correlation coefficient was calculated between mean arterial pressure (MAP) and cerebral blood flow (CBF) velocity, and between MAP and NIRS data, to generate the mean velocity index (Mx) and cerebral oximetry index (COx), respectively. Functional autoregulation is indicated by an Mx and COx that approach zero (no correlation between CBF and MAP); impaired autoregulation is indicated by an Mx and COx approaching 1. Impaired autoregulation was defined as an Mx ≥0.40 at all MAPs during CPB.nnnRESULTSnTwenty per cent of patients demonstrated impaired autoregulation during CPB. Based on multivariate logistic regression analysis, time-averaged COx during CPB, male gender, Pa(CO(2)), CBF velocity, and preoperative aspirin use were independently associated with impaired CBF autoregulation. Perioperative stroke occurred in six of 47 (12.8%) patients with impaired autoregulation compared with five of 187 (2.7%) patients with preserved autoregulation (P=0.011).nnnCONCLUSIONSnImpaired CBF autoregulation occurs in 20% of patients during CPB. Patients with impaired autoregulation are more likely than those with functional autoregulation to have perioperative stroke. Non-invasive monitoring autoregulation may provide an accurate means to predict impaired autoregulation. Clinical trials registration. www.clinicaltrials.gov (NCT00769691).

Duration and magnitude of blood pressure below cerebral autoregulation threshold during cardiopulmonary bypass is associated with major morbidity and operative mortality

OBJECTIVESnOptimizing blood pressure using near-infrared spectroscopy monitoring has been suggested to ensure organ perfusion during cardiac surgery. Near-infrared spectroscopy is a reliable surrogate for cerebral blood flow in clinical cerebral autoregulation monitoring and might provide an earlier warning of malperfusion than indicators of cerebral ischemia. We hypothesized that blood pressure below the limits of cerebral autoregulation during cardiopulmonary bypass would be associated with major morbidity and operative mortality after cardiac surgery.nnnMETHODSnAutoregulation was monitored during cardiopulmonary bypass in 450 patients undergoing coronary artery bypass grafting and/or valve surgery. A continuous, moving Pearsons correlation coefficient was calculated between the arterial pressure and low-frequency near-infrared spectroscopy signals and displayed continuously during surgery using a laptop computer. The area under the curve of the product of the duration and magnitude of blood pressure below the limits of autoregulation was compared between patients with andxa0without major morbidity (eg, stroke, renal failure, mechanical lung ventilation >48 hours, inotrope use >24 hours, or intra-aortic balloon pump insertion) or operative mortality.nnnRESULTSnOf the 450 patients, 83 experienced major morbidity or operative mortality. The area under the curve ofxa0the product of the duration and magnitude of blood pressure below the limits of autoregulation was independently associated with major morbidity or operative mortality after cardiac surgery (odds ratio, 1.36; 95% confidence interval, 1.08-1.71; Pxa0=xa0.008).nnnCONCLUSIONSnBlood pressure management during cardiopulmonary bypass using physiologic endpoints such as cerebral autoregulation monitoring might provide a method of optimizing organ perfusion and improving patient outcomes from cardiac surgery.

Decreased Erythrocyte Deformability After Transfusion and the Effects of Erythrocyte Storage Duration

BACKGROUND:Erythrocyte cell membranes undergo morphologic changes during storage, but it is unclear whether these changes are reversible. We assessed erythrocyte cell membrane deformability in patients before and after transfusion to determine the effects of storage duration and whether changes in deformability are reversible after transfusion. METHODS:Sixteen patients undergoing posterior spinal fusion surgery were studied. Erythrocyte deformability was compared between those who required moderate transfusion (≥5 units erythrocytes) and those who received minimal transfusion (0–4 units erythrocytes). Deformability was measured in samples drawn directly from the blood storage bags before transfusion and in samples drawn from patients before and after transfusion (over 3 postoperative days). In samples taken from the blood storage bags, we compared deformability of erythrocytes stored for a long duration (≥21 days), those stored for a shorter duration (<21 days), and cell-salvaged erythrocytes. Deformability was assessed quantitatively using the elongation index (EI) measured by ektacytometry, a method that determines the ability for the cell to elongate when exposed to shear stress. RESULTS:Erythrocyte deformability was significantly decreased from the preoperative baseline in patients after moderate transfusion (EI decreased by 12% ± 4% to 20% ± 6%; P = 0.03) but not after minimal transfusion (EI decreased by 3% ± 1% to 4% ± 1%; P = 0.68). These changes did not reverse over 3 postoperative days. Deformability was significantly less in erythrocytes stored for ≥21 days (EI = 0.28 ± 0.02) than in those stored for <21 days (EI = 0.33 ± 0.02; P = 0.001) or those drawn from patients preoperatively (EI = 0.33 ± 0.02; P = 0.001). Cell-salvaged erythrocytes had intermediate deformability (EI = 0.30 ± 0.03) that was greater than that of erythrocytes stored ≥21 days (P = 0.047), but less than that of erythrocytes stored <21 days (P = 0.03). CONCLUSIONS:The findings demonstrate that increased duration of erythrocyte storage is associated with decreased cell membrane deformability and that these changes are not readily reversible after transfusion.

Factors contributing to the lower mortality with ticagrelor compared with clopidogrel in patients undergoing coronary artery bypass surgery.

OBJECTIVESnThis study investigated the differences in specific causes of post-coronary artery bypass graft surgery (CABG) deaths in the PLATO (Platelet Inhibition and Patient Outcomes) trial.nnnBACKGROUNDnIn the PLATO trial, patients assigned to ticagrelor compared with clopidogrel and who underwent CABG had significantly lower total and cardiovascular mortality.nnnMETHODSnIn the 1,261 patients with CABG performed within 7 days after stopping study drug, reviewers blinded to treatment assignment classified causes of death into subcategories of vascular and nonvascular, and specifically identified bleeding or infection events that either caused or subsequently contributed to death.nnnRESULTSnNumerically more vascular deaths occurred in the clopidogrel versus the ticagrelor group related to myocardial infarction (14 vs. 10), heart failure (9 vs. 6), arrhythmia or sudden death (9 vs. 3), and bleeding, including hemorrhagic stroke (7 vs. 2). Clopidogrel was also associated with an excess of nonvascular deaths related to infection (8 vs. 2). Among factors directly causing or contributing to death, bleeding and infections were more common in the clopidogrel group compared with the ticagrelor group (infections: 16 vs. 6, p < 0.05, and bleeding: 27 vs. 9, p < 0.01, for clopidogrel and ticagrelor, respectively).nnnCONCLUSIONSnThe mortality reduction with ticagrelor versus clopidogrel following CABG in the PLATO trial was associated with fewer deaths from cardiovascular, bleeding, and infection complications. (Platelet Inhibition and Patient Outcomes [PLATO]; NCT00391872).

Arterial pressure above the upper cerebral autoregulation limit during cardiopulmonary bypass is associated with postoperative delirium

BACKGROUNDnMean arterial pressure (MAP) below the lower limit of cerebral autoregulation during cardiopulmonary bypass (CPB) is associated with complications after cardiac surgery. However, simply raising empiric MAP targets during CPB might result in MAP above the upper limit of autoregulation (ULA), causing cerebral hyperperfusion in some patients and predisposing them to cerebral dysfunction after surgery. We hypothesized that MAP above an ULA during CPB is associated with postoperative delirium.nnnMETHODSnAutoregulation during CPB was monitored continuously in 491 patients with the cerebral oximetry index (COx) in this prospective observational study. COx represents Pearsons correlation coefficient between low-frequency changes in regional cerebral oxygen saturation (measured with near-infrared spectroscopy) and MAP. Delirium was defined throughout the postoperative hospitalization based on clinical detection with prospectively defined methods.nnnRESULTSnDelirium was observed in 45 (9.2%) patients. Mechanical ventilation for >48 h [odds ratio (OR), 3.94; 95% confidence interval (CI), 1.72-9.03], preoperative antidepressant use (OR, 3.0; 95% CI, 1.29-6.96), prior stroke (OR, 2.79; 95% CI, 1.12-6.96), congestive heart failure (OR, 2.68; 95% CI, 1.28-5.62), the product of the magnitude and duration of MAP above an ULA (mm Hg h; OR, 1.09; 95% CI, 1.03-1.15), and age (per year of age; OR, 1.01; 95% CI, 1.01-1.07) were independently associated with postoperative delirium.nnnCONCLUSIONSnExcursions of MAP above the upper limit of cerebral autoregulation during CPB are associated with risk for delirium. Optimizing MAP during CPB to remain within the cerebral autoregulation range might reduce risk of delirium.nnnCLINICAL TRIAL REGISTRATIONnclinicaltrials.gov NCT00769691 and NCT00981474.

Intraoperative hypotension and patient outcome: Does "one size fit all?"

495 September 2013 P ATIENTS who are anesthetized or heavily sedated surrender their ability to convey signs and symptoms of low blood pressure, particularly those associated with cerebral hypoperfusion (i.e., light headedness, mental status changes, or syncope). Consequently, physicians have come to rely on empiric definitions of what constitutes the lowest tolerable blood pressure during surgery or, stated differently, the definition of intraoperative hypotension. There remains debate, although, on what value of blood pressure in relation to preoperative baseline should be considered as hypotension with much variability in definitions between investigations.1,2 The need for a precise definition of intraoperative hypotension is supported by observational studies in adults that have linked low blood pressure with adverse patient outcomes after cardiac and noncardiac surgery, including 30-day and 1-yr mortality.3–8 In this issue of ANESThESIology, Walsh et al.9 confirm and extend these growing data when they report that mean arterial pressure (MAP) less than 55 mmhg during noncardiac surgery is associated with risk for postoperative acute kidney injury (AKI) or myocardial infarction (MI). In their study, Walsh et al.9 analyzed prospectively collected data obtained from the electronic medical records of 33,330 patients who underwent noncardiac surgery at the Cleveland Clinic (Cleveland, ohio). They have assessed the association between MAP less than 55–75 mmhg and postoperative AKI (defined as increases in serum creatinine of greater than 1.5-fold or 0.3 mg/dl from baseline) or MI (defined as serum troponin T ≥0.04 μg/l or creatinine kinase-MB ≥8.8 ng/ml). of note, patients with chronic kidney disease and those who underwent urologic surgery, nephrectomy, or renal transplantation were excluded because they did not have postoperative creatinine measurements. Serum myocardial injury biomarkers were selectively measured only in high-risk patients and those with clinical evidence of myocardial ischemia. Patients without myocardial injury biomarker data were assumed not to have suffered an MI. Blood pressure was measured noninvasively every 2–5 min in most patients, but 44.5% of patients had invasive arterial pressure monitoring every 1–2 min. A MAP threshold of less than 55 mmhg was found to be associated with risk for AKI and MI, events that occurred in 7.4 and 2.3% of patients, respectively. They further report an incremental exposure– risk relationship whereby increased duration of MAP less than 55 mmhg (1–5, 6–10, 11–20, and >20 min) increased the risk for AKI and MI. Moreover, 30-day mortality was significantly associated with more than 20 min of MAP of less than 55 mmhg. The current study by Walsh et al.9 and data from others draw important attention to the fact that blood pressure management during surgery might be a factor that can be modified as a means for improving patient outcomes.3–8 As questioned in the title of the article by Walsh et al.,9 are physicians now able to derive an empiric definition of Intraoperative Hypotension and Patient Outcome

Shoulder surgery in the beach chair position is associated with diminished cerebral autoregulation but no differences in postoperative cognition or brain injury biomarker levels compared with supine positioning: The anesthesia patient safety foundation beach chair study

BACKGROUND:Although controversial, failing to consider the gravitational effects of head elevation on cerebral perfusion is speculated to increase susceptibility to rare, but devastating, neurologic complications after shoulder surgery in the beach chair position (BCP). We hypothesized that patients in the BCP have diminished cerebral blood flow autoregulation than those who undergo surgery in the lateral decubitus position (LDP). A secondary aim was to examine whether there is a relationship between patient positioning during surgery and postoperative cognition or serum brain injury biomarker levels. METHODS:Patients undergoing shoulder surgery in the BCP (n = 109) or LDP (n = 109) had mean arterial blood pressure (MAP) and regional cerebral oxygen saturation (rScO2) monitored with near-infrared spectroscopy. A continuous, moving Pearson correlation coefficient was calculated between MAP and rScO2, generating the variable cerebral oximetry index (COx). When MAP is in the autoregulated range, COx approaches zero because there is no correlation between cerebral blood flow and arterial blood pressure. In contrast, when MAP is below the limit of autoregulation, COx is higher because there is a direct relationship between lower arterial blood pressure and lower cerebral blood flow. Thus, diminished autoregulation would be manifest as higher COx. Psychometric testing was performed before surgery and then 7 to 10 days and 4 to 6 weeks after surgery. A composite cognitive outcome was determined as the Z-score. Serum S100&bgr;, neuron-specific enolase, and glial fibrillary acidic protein were measured at baseline, after surgery, and on postoperative day 1. RESULTS:After adjusting for age and history of hypertension, COx (P = 0.035) was higher and rScO2 lower (P < 0.0001) in the BCP group than in the LDP group. After adjusting for baseline composite cognitive outcome, there was no difference in Z-score 7 to 10 days (P = 0.530) or 4 to 6 weeks (P = 0.202) after surgery between the BCP and the LDP groups. There was no difference in serum biomarker levels between the 2 position groups CONCLUSIONS:Compared with patients in the LDP, patients undergoing shoulder surgery in the BCP are more likely to have higher COx indicating diminished cerebral autoregulation and lower rScO2. There were no differences in the composite cognitive outcome between the BCP and the LDP groups after surgery after accounting for baseline Z-score.

Cerebral and tissue oximetry

The use of near-infrared spectroscopy (NIRS) has been increasingly adopted in cardiac surgery to measure regional cerebral oxygen saturation. This method takes advantage of the fact that light in the near-infrared spectrum penetrates tissue, including bone and muscle. Sensors are placed at fixed distances from a light emitter, and algorithms subtract superficial light absorption from deep absorption to provide an index of tissue oxygenation. Although the popularity of NIRS monitoring is growing, definitive data that prove outcome benefits with its use remain sparse. Therefore, widespread, routine use of NIRS as a standard-of-care monitor cannot be recommended at present. Recent investigations have focused on the use of NIRS in subgroups that may benefit from NIRS monitoring, such as pediatric patients. Furthermore, a novel application of processed NIRS information for monitoring cerebral autoregulation and tissue oxygenation (e.g., kidneys and the gut) is promising.