Joyce A. Wahr

Near-Infrared Spectroscopy: Theory and Applications

In conclusion, NIRS appears to offer both a new monitoring modality and new information about cerebral oxygenation. Technical problems in the application of this technology persist, most notably determination of pathlength and the volume of tissue interrogated. Those familiar with the history of pulse oximetry will recall that although Millikan developed an ear oximeter in 1947, it was not until Aoyagi combined recognition of the pulse signal with spectroscopy in the 1970s that oximetry was transformed into a clinically applicable monitor. In much the same way, NIRS may find the same tremendous usefulness as a noninvasive monitor of cerebral oxygen utilization, pending resolution of the remaining technical problems.

The Use of Bovine Hemoglobin Glutamer-250 (hemopure®) in Surgical Patients: Results of a Multicenter, Randomized, Single-blinded Trial

Hemoglobin-based oxygen carrier-201 (HBOC-201, hemoglobin glutamer-250 [bovine], Hemopure®; Biopure Corporation, Cambridge, MA) is polymerized hemoglobin of bovine origin being developed as an oxygen therapeutic. In this study, we evaluated the tolerability of a single intraoperative dose of HBOC-201 in surgical patients. In a single-blinded, multicenter study, 81 patients were randomized to receive either a single infusion of HBOC-201 (55 patients) or an equivalent volume of lactated Ringer’s solution (26 patients). Forty-two patients originally assigned to the HBOC-201 group received the entire planned treatment of only one of the following doses: 0.6, 0.9, 1.2, 1.5, 2.0, or 2.5 g/kg of body weight. Thirteen of the 55 patients in the HBOC-201-assigned group did not reach the trigger point for transfusion administration, and they were not included in the analysis. We studied clinical outcomes and compared hematologic findings, blood chemistry values, and blood use in the two treatment groups. There were no patient deaths in this study. No pattern of clinically significant laboratory abnormalities could be attributed to exposure to HBOC-201. In the HBOC-201 group, 2 patients had a transient increased concentration of serum transaminases and 6 had transient skin discoloration. One patient in the HBOC-201 group had mast cell degranulation with hypotension. Postoperatively, methemoglobin plasma concentrations increased in the HBOC-201 group in a dose-dependent manner, reaching maximal values of 3.7% ± 3.2% (average of all doses given) on postoperative day 3. There was no difference in the mean number of allogeneic blood units transfused in the 2 groups (3.3 ± 1.8 and 3.7 ± 4.1 for the lactated Ringer’s solution and HBOC-201 groups, respectively) over the course of hospitalization. The intraoperative administration of HBOC-201, up to a maximum of 245 g, was generally well tolerated. There was no relationship between HBOC-201 use and the number of allogeneic blood units transfused over the entire hospitalization course. The administration of HBOC-201 was associated with a delayed (third postoperative day) dose-dependent increase in the plasma methemoglobin concentration. We conclude that the intraoperative use of HBOC-201 was generally well tolerated.

Patient Safety in the Cardiac Operating Room: Human Factors and Teamwork A Scientific Statement From the American Heart Association

The cardiac surgical operating room (OR) is a complex environment in which highly trained subspecialists interact with each other using sophisticated equipment to care for patients with severe cardiac disease and significant comorbidities. Thousands of patient lives have been saved or significantly improved with the advent of modern cardiac surgery. Indeed, both mortality and morbidity for coronary artery bypass surgery have decreased during the past decade (Figure 1).1 Nonetheless, the highly skilled and dedicated personnel in cardiac ORs are human and will make errors. In 1991, Leape and colleagues2,3 estimated that among the 2 million patients hospitalized in New York in 1984, there were 27 179 adverse events that involved negligence; other evidence suggests that up to 16% of hospital inpatients are harmed.4 Gawande and associates5 found that the incidence of surgical adverse events was 12% among cardiac surgery patients versus 3% in other surgical patients; 54% of the adverse events were considered preventable. Of the roughly 350 000 to 500 000 patients who undergo cardiac surgery each year, 28 000 will have an adverse event, and one third of deaths associated with coronary artery bypass graft (CABG) operations may be preventable.6 Figure 1. Change in mortality and stroke rates in patients undergoing isolated coronary artery bypass graft (CABG) surgery, 2000 to 2009. There was a 24.4% and 26.4% reduction in the unadjusted observed operative mortality (2.4% vs 1.9%) and stroke rates (1.6% vs 1.2%), respectively, during the course of the study period. Reprinted from ElBardissi et al1 with permission from Elsevier. Copyright

Clinical evaluation of a prototype motion artifact resistant pulse oximeter in the recovery room.

The frequency and nature of spurious pulse oximetry readings were compared using both a conventional pulse oximeter (CPO) and a prototype Masimo signal extraction technology pulse oximeter (Masimo SET Trademark).At a university hospital, 50 ASA physical status I-IV adult patients who underwent general or spinalepidural anesthesia were selected from a group of 250 patients on the basis of high-alarm generation with routine postoperative pulse oximetry. Pulse oximetry data were recorded simultaneously from both devices with a computer. Overall, the CPO alarm frequency (i.e., oxygen saturation < 90%, or complete signal loss) was once every 13 min, and 87% of these alarms were considered false. Alarms were considered false based on reference electrocardiographs (16 patients), arterial blood gases (7 patients), and clinical assessment. The prototype Masimo SET Trademark device alarm frequency was once every 30 min, and 59% of these were considered false. During arm motion with 15 patients, the CPO device produced spurious signals on 54 occasions compared with five for the prototype Masimo SET Trademark. The incidence of artifactual pulse oximetry events during patient motion appear to be substantially reduced with the prototype Masimo SET Trademark device, relative to a CPO device. (Anesth Analg 1996;83:269-72)

A pilot study of the effects of a perflubron emulsion, AF 0104, on mixed venous oxygen tension in anesthetized surgical patients.

A pilot study of a perfluorochemical (PFC) emulsion was undertaken to determine whether administration of a perflubron emulsion could result in measurable changes in mixed venous oxygen tension.Seven adult surgical patients received a 0.9-g PFC/kg intravenous dose of perflubron emulsion after acute normovolemic hemodilution (ANH). Hemodynamic and oxygen transport data were collected before and after ANH, immediately after PFC infusion, and at approximate 15-min intervals throughout the surgical period. There were no clinically significant hemodynamic changes associated with the administration of the PFC emulsion. There was a significant increase in mixed venous oxygen tension (PVO2) after the PFC infusion, while cardiac output and oxygen consumption were unchanged. As surgery progressed, the hemoglobin concentration decreased with ongoing blood loss while PVO2 values remained at or above predosing levels. Peak perflubron blood levels were 0.8 g/dL immediately postinfusion, and approximately 0.3 g/dL at 1 h. This pilot study demonstrates that administration of perflubron emulsion results in measurable changes in mixed venous oxygen tension during intraoperative ANH. (Anesth Analg 1996;82:103-7)

Effect of postoperative atrial fibrillation on length of stay after cardiac surgery (the postoperative atrial fibrillation in cardiac surgery study [PACS2])

Atrial fibrillation (AF) after cardiac surgery is thought to increase length of stay (LOS). A clinical pathway focused on the management of postoperative AF, including prophylaxis with beta blockers, was implemented to assess the effect of AF on LOS after cardiac surgery. Data were obtained on consecutive cardiac surgery patients in preoperative normal sinus rhythm, no prior history of AF, and no chronic antiarrhythmic therapy from January to May 1995 (control) and November 1996 to June 1997 (pathway). Statistical analysis was performed to assess the effect of postoperative AF on the LOS, clinical outcomes, and cost after cardiac surgery. Despite the clinical pathway, the LOS (7 days for both periods; p = 0.12) and incidence of AF (28.9% vs 28.4%; p = 0.92) remained unchanged. Unadjusted direct costs were 15% higher in the pathway period (p <0.001). Increased rates of beta-blocker therapy had a marginal effect on the incidence of postoperative AF, except in the group who only underwent primary coronary artery bypass graft surgery (31.2% vs 25.3%; p = 0.31). Multivariate analysis revealed that AF contributed only 1 to 1.5 days to the LOS. Thus, this investigation represents the most recent analysis of the effects of postoperative AF on LOS, clinical outcomes, and cost after cardiac surgery. Unlike prior studies, the impact of postoperative AF is less prominent in the current era of cardiac surgical care regardless of the presence of a clinical pathway addressing AF.

Cardiovascular responses during sedation after coronary revascularization: Incidence of myocardial ischemia and hemodynamic episodes with propofol versus midazolam

Background Propofol sedation offers advantages for titration and rapid emergence in the critically ill patient, but concern for adverse hemodynamic effects potentially limits its use in these patients. The current study compares the cardiovascular effects of sedation with propofol versus midazolam during the first 12 h after coronary revascularization. Methods Three hundred fifty‐one patients undergoing coronary revascularization were anesthetized using a standardized sufentanil/midazolam regimen, and assigned randomly to 12 h of sedation with either propofol or midazolam while tracheally intubated. The incidence and characteristics of hemodynamic episodes, defined as heart rate less than 60 or greater than 100 beats/min or systolic blood pressure greater than 140 or less than 90 mmHg, were determined using data electronically recorded at 1‐min intervals. The presence of myocardial ischemia was determined using continuous three‐channel Holter electrocardiography (ECG) and of myocardial infarctions (MI) using 12‐lead ECG (Q wave MI, Minnesota Code) or creatine kinase isoenzymes (CK‐MB) analysis (non‐Q wave MI, peak CK‐MB > 70 ng/ml, or CK‐MB > 70 IU/l). Results Ninety‐three percent of patients in both treatment groups had at least one hemodynamic episode during the period of postoperative sedation. Propofol sedation resulted in a 17% lower incidence of tachycardia (58% vs. 70%, propofol vs. midazolam; P = 0.04), a 28% lower incidence of hypertension (39% vs. 54%; P = 0.02), and a greater incidence of hypotension (68% vs. 51%; P = 0.01). Despite these hemodynamic effects, the incidence of myocardial ischemia did not differ between treatment groups (12% propofol vs. 13% midazolam; P = 0.66), nor did its severity, as measured by ischemic minutes per hour monitored (8.7+/‐5.8 vs. 6.2+/‐4.6 min/h, propofol vs. midazolam; P = 0.19) or ischemic area under the curve (6.8+/‐4.0 vs. 5.3+/‐4.2; P = 0.37). The incidence of cardiac death (one per group), Q wave MI (propofol, n = 7; midazolam, n = 3; P = 0.27), or non Q wave MI (propofol, n = 16; midazolam, n = 18; P = 0.81) did not differ between treatment groups. Conclusions Hemodynamic episodes occur frequently in the first 12 h after coronary revascularization. Compared with a standard sedation regimen (midazolam), propofol sedation appears to modulate postoperative hemodynamic responses by reducing the incidence and severity of tachycardia and hypertension and increasing the incidence of hypotension. Both sedation regimens appear similarly safe with respect to myocardial ischemia. These findings indicate that propofol infusion provides effective sedation without deleterious hemodynamic effects in patients recovering from cardiac surgery.

Reducing Unnecessary Cross-matching: A Patient-specific Blood Ordering System Is More Accurate in Predicting Who Will Receive a Blood Transfusion Than the Maximum Blood Ordering System

UNLABELLED Most blood transfusions are given in the operating room. Adoption of the Maximum Surgical Blood Ordering Schedule in the 1970s reduced the amount of blood unnecessarily cross-matched, but the national cross-match-to-transfusion ratio remains at approximately two-to-one. We tested the ability of a patient-specific blood ordering system (PSBOS) to more accurately predict potential operative transfusion. All adult patients who had blood cross-matched before surgery (February through June 1999) for elective operative procedures at the University of Michigan Hospital were identified. Complex surgeries were excluded. Surgeons estimated the expected blood loss for their surgeries, and the expected postoperative hematocrit was calculated using the patients blood volume, the surgeon-defined expected blood loss, and preoperative hematocrit. Lowest tolerated hematocrit was set at 21% except in patients with coronary artery disease or who were ASA physical status III or more (28%). Sensitivity, specificity, positive predictive value, and negative predictive value of the PSBOS were calculated. Our analysis included 178 cases in which blood was cross-matched before surgery, representing 69 different surgeries and 42 surgeons. Only 16% of patients received an intraoperative transfusion. Of the 156 patients that PSBOS predicted would not require an operating room transfusion, 139 were not transfused. Of the 21 patients PSBOS predicted would be transfused, 11 were. The sensitivity of the algorithm as tested was 41%, the specificity 93%, the positive predictive value was 55%, and the negative predictive value was 89%. We conclude that PSBOS, which includes patient and surgeon variables in transfusion prediction, is more accurate than the Maximum Surgical Blood Ordering Schedule, which uses only surgical procedure. IMPLICATIONS Currently, many units of blood set aside for surgery are never required, resulting in extra work and expense for blood banks. A formula that included patient weight and hematocrit and typical surgery blood loss was used to predict who would require transfusions. We reduced the predicted number of patients who had blood set aside from 178 to 21.

Effects of acadesine on the incidence of myocardial infarction and adverse cardiac outcomes after coronary artery bypass graft surgery

Background Acadesine (AICA riboside) (5-amino-1-[beta-D-ribofuranosy]imidazole-4-carboxamide) is a purine nucleoside analog belonging to a new class of agents generally termed adenosine regulating agents (ARAs) that increase the availability of adenosine locally in ischemic tissues. The effects of acadesine on the incidence of fatal and nonfatal myocardial infarction (MI) and on the incidence of all adverse cardiovascular outcomes (cardiac death, MI, congestive heart failure, life-threatening dysrhythmia, or cerebrovascular accident) was investigated in patients undergoing coronary artery bypass graft (CABG) surgery.

Anesthetic considerations in patients presenting with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome

W ’ ith the passage of time and the advent of modern technology, new disease entities are constantly being described. It is inevitable that surgical procedures will be performed on patients with these diseases. The anesthetic implications, therefore, need to be addressed. We describe the anesthetic course and raise some anesthetic considerations for a patient with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome.