Donald Mathews

Increases in electroencephalogram and electromyogram variability are associated with an increased incidence of intraoperative somatic response.

BACKGROUND: sBIS, the variability of the Bispectral Index (BIS), sEMG, the variability of facial electromyogram power (EMG), and the Composite Variability Index (CVI) are 3 new measures of electroencephalogram and EMG variability. CVI is a single measure of the combined variability in BIS and EMG. We investigated whether increases in these variables are associated with intraoperative somatic responses. METHODS: This multicenter study included 120 patients undergoing elective, noncardiac surgery from 4 different sites. General anesthesia was maintained using propofol and remifentanil at 2 of the sites and sevoflurane and remifentanil at the 2 other sites. Propofol or sevoflurane was adjusted to maintain BIS between 45 and 60. Clinicians were blinded to CVI (v2.0) at all times, and remifentanil infusions were adjusted at the discretion of the clinician. The times of all intraoperative somatic events, defined as movement, grimacing, or eye opening, were recorded. Offline, the maintenance phase of each case was divided into consecutive, nonoverlapping, 10-minute segments. Segments were identified as containing a somatic event or containing no events. For each segment, mean sBIS, sEMG, and CVI and the heart rate (HR) range and mean arterial blood pressure range were calculated. To quantify how effectively each variable discriminated between somatic event segments and nonevent segments, we computed the area under the receiver operating characteristic (ROC) curve for each variable. Finally, we observed the time course of sBIS, sEMG, CVI, and the HR range before each somatic event and characterized the earliest time before the somatic event at which each variable was able to discriminate between the somatic events and a specified set of nonevents. RESULTS: The analysis included 33 somatic event segments and 829 nonevent segments from 105 surgical cases. The areas under the ROC curve (±SE) for sBIS, sEMG, and CVI were 0.83 ± 0.04, 0.92 ± 0.02, and 0.89 ± 0.03, respectively. The areas under the ROC curve for HR range and mean arterial blood pressure range were 0.77 ± 0.03 and 0.68 ± 0.05, respectively. CVI, sBIS, and sEMG all demonstrated higher average values before upcoming somatic events when compared with nonevents. HR range only showed a difference within a few seconds before the somatic event. CONCLUSION: sBIS, sEMG, and CVI, measures of electroencephalogram and EMG variability, increased when intraoperative somatic events occurred. sBIS, sEMG, and CVI discriminated between 10-minute segments that contained a somatic event and those segments that did not contain an event better than changes in HR and mean arterial blood pressure. Furthermore, CVI increases before somatic events began earlier than HR changes and may provide caregivers with an early warning of potentially inadequate antinociception.

Pulse contour cardiac output in surgical intensive care unit patients

STUDY OBJECTIVE To evaluate the ability of arterial waveform contour analysis to measure cardiac output (CO) continuously in postoperative critically ill patients. DESIGN Thermodilution CO (TDCO) measurements were compared with simultaneous pulse contour CO (PCCO) measurements. SETTING University hospital surgical intensive care unit. PATIENTS 29 critically ill surgical patients with indwelling systemic arterial and pulmonary artery catheters. MEASUREMENTS AND MAIN RESULTS TDCO measurements were compared with PCCO at 1- to 2-hour intervals. Mean TDCO was 5.75 +/- 1.79 L/min, and mean PCCO was 5.76 +/- 1.83 L/min. Analysis of the difference between TDCO and PCCO showed a bias of 0.01 +/- 0.5 L/min. Comparison of the difference between pairs of sequential TDCO measurements and the initial TDCO and subsequent PCCO measurements resulted in a correlation coefficient of 0.64. CONCLUSIONS The PCCO method appears to be able to estimate changes in CO under the conditions tested, in which PCCO was recalibrated after each TDCO measurement. However, limitations of this method in the immediate postoperative period following aortic aneurysm surgery were identified.

Cognitive outcome after spinal anesthesia and surgery during infancy.

BACKGROUND:Observational studies on pediatric anesthesia neurotoxicity have been unable to distinguish long-term effects of general anesthesia (GA) from factors associated with the need for surgery. A recent study on elementary school children who had received a single GA during the first year of life demonstrated an association in otherwise healthy children between the duration of anesthesia and diminished test scores and also revealed a subgroup of children with “very poor academic achievement” (VPAA), scoring below the fifth percentile on standardized testing. Analysis of postoperative cognitive function in a similar cohort of children anesthetized with an alternative to GA may help to begin to separate the effects of anesthesia from other confounders. METHODS:We used a novel methodology to construct a combined medical and educational database to search for these effects in a similar cohort of children receiving spinal anesthesia (SA) for the same procedures. We compared former patients with a control population of students matched by grade, gender, year of testing, and socioeconomic status. RESULTS:Vermont Department of Education records were analyzed for 265 students who had a single exposure to SA during infancy for circumcision, pyloromyotomy, or inguinal hernia repair. Exposure to SA and surgery had no significant effect on the odds of children having VPAA. (mathematics: P = 0.18; odds ratio 1.50, confidence interval (CI), 0.83–2.68; reading: P = 0.55; odds ratio = 1.19, CI, 0.67–2.1). There was no relationship between duration of exposure to SA and surgery and performance on mathematics (P = 0.73) or reading (P = 0.57) standardized testing. There was a small but statistically significant decrease in reading and math scores in the exposed group (mathematics: P = 0.03; reading: P = 0.02). CONCLUSIONS:We found no link between duration of surgery with infant SA and scores on academic achievement testing in elementary school. We also found no relationship between infant SA and surgery with VPAA on elementary school testing, although the CIs were wide.

Can remifentanil replace nitrous oxide during anesthesia for ambulatory orthopedic surgery with desflurane and fentanyl

BACKGROUND:The administration of nitrous oxide (N2O) may be associated with side effects and toxicities. Remifentanil shares characteristics with N2O, including MAC-reducing and antinociceptive effects and a rapid decrease in clinical effect when discontinued. We compared the outcome after ambulatory orthopedic surgery with desflurane and fentanyl supplemented with clinically equivalent doses of either N2O or remifentanil. METHODS:Seventy patients undergoing ambulatory orthopedic surgery were studied. Thirty-five received 66% N2O and 35 received remifentanil 0.085 &mgr;g · kg−1 · min−1 in addition to desflurane, titrated to a bispectral index (BIS) value of 50, and a fentanyl infusion. The principle outcome measure was time to awakening to verbal stimulation. Secondary outcome measures included neuropsychological testing, time to orientation, hemodynamic values, pain and nausea visual analog scores, discharge times, and satisfaction scores. The average end-tidal desflurane concentration and fentanyl effect-site concentration were determined. RESULTS:The median time (interquartile range) to awakening to verbal stimulation, 3.0 min (3.0–5.0 min) in the remifentanil group and 4.6 min (3.0–8.1 min) in the N2O group was not significantly different. Median time to orientation was significantly faster in the remifentanil group: 6.0 min (5.0–8.5 min) compared with 8.0 min (5.0–12.8 min) for the N2O group. There was no difference between groups in desflurane or fentanyl administration, neuropsychological testing, or any other outcome measure. CONCLUSIONS:This study demonstrates that a remifentanil infusion of 0.085 &mgr;g · kg−1 · min−1 may be substituted for 66% N2O during desflurane/fentanyl anesthesia without any clinically significant change in outcome.

Patterns of Fuel Utilization During Parenteral Nutrition

Utilization of fuel in clinical conditions has become an important area of interest to the clinician. Injury and sepsis cause predictable changes in the metabolism of fuel, favoring a shift toward the oxidation of fat. Similar considerations apply to the tumor-bearing host.

Blood Rheology and Oxygen Transport

Donald Mathews, Patrick LaSala, and Shu Chien series of progressively smaller vessels-arteries, arterioles, Depts. of Physiology, Neurological Surgery, and Anesthesiology and capillaries. From a solitary aorta, the flow is partitioned Columbia University College of Physicians and Surgeons into more than a billion capillaries. It is in the capillaries that one of the most important functions of blood occurs, i.e., THE CIRCULATORY system is uniquely designed for sevoxygen transfer to the tissue cells. The blood flows from Teral functions, one of the most important being oxygen capillaries into a series of venules, veins, and the superior and transport. This is accomplished through the interaction of the inferior vena cavae, and the number of vessels decreases heart, lungs, blood vessels, and the blood. Blood is a complex with successive generations of converging flow. fluid consisting of plasma and cells, primarily red blood cells, suspended in it. The ability to deliver oxygen depends partly BASIC RHEOLOGICAL PRINCIPLES on the relative concentrations of these elements and the As blood flows from the aorta to the capillaries, most of the interactions between them. It also depends on the properties pressure head generated by the heart is dissipated, particuof the vessels through which the blood flows. Blood rheology larly in the arterioles, which are the primary resistance is the study of blood flow and the response of blood to vessels. The flow of blood across the circulatory system (0) deforming forces in the circulatory system. is directly proportional to the pressure drop from the arterial to the venous side of the circulatory system (PA Pv) and THE CIRCULATORY SYSTEM inversely proportional to the resistance to blood flow (R): The circulatory system can be thought of as a circuit through which the heart pumps blood, generating the presPA-PV sure head needed for flow to occur. The left ventricle pumps Q= R (1) with a higher pressure than the right. Normal mean systemic blood pressure in the aorta and large arteries is 90 to 100 The resistance to blood flow has two components: vascummHg. Blood flows into the aorta and then into a branching lar hindrance (Z) and blood viscosity (Na):