Joachim S. Gravenstein

Predictors of Cognitive Dysfunction after Major Noncardiac Surgery

Background:The authors designed a prospective longitudinal study to investigate the hypothesis that advancing age is a risk factor for postoperative cognitive dysfunction (POCD) after major noncardiac surgery and the impact of POCD on mortality in the first year after surgery. Methods:One thousand sixty-four patients aged 18 yr or older completed neuropsychological tests before surgery, at hospital discharge, and 3 months after surgery. Patients were categorized as young (18–39 yr), middle-aged (40–59 yr), or elderly (60 yr or older). At 1 yr after surgery, patients were contacted to determine their survival status. Results:At hospital discharge, POCD was present in 117 (36.6%) young, 112 (30.4%) middle-aged, and 138 (41.4%) elderly patients. There was a significant difference between all age groups and the age-matched control subjects (P < 0.001). At 3 months after surgery, POCD was present in 16 (5.7%) young, 19 (5.6%) middle-aged, and 39 (12.7%) elderly patients. At this time point, the prevalence of cognitive dysfunction was similar between age-matched controls and young and middle-aged patients but significantly higher in elderly patients compared to elderly control subjects (P < 0.001). The independent risk factors for POCD at 3 months after surgery were increasing age, lower educational level, a history of previous cerebral vascular accident with no residual impairment, and POCD at hospital discharge. Patients with POCD at hospital discharge were more likely to die in the first 3 months after surgery (P = 0.02). Likewise, patients who had POCD at both hospital discharge and 3 months after surgery were more likely to die in the first year after surgery (P = 0.02). Conclusions:Cognitive dysfunction is common in adult patients of all ages at hospital discharge after major noncardiac surgery, but only the elderly (aged 60 yr or older) are at significant risk for long-term cognitive problems. Patients with POCD are at an increased risk of death in the first year after surgery.

Randomized evaluation of pulse oximetry in 20,802 patients. II: Perioperative events and postoperative complications

BackgroundThe authors describe the effect of pulse oximetry monitoring on the frequency of unanticipated perl-operative events, changes In patient care, and the rate of postoperative complications in a prospective randomized study. MethodsThe study Included 20,802 surgical patients in Denmark randomly assigned to be monitored or not with pulse oximetry In the operating room (OR) and postanesthesla care unit (PACU). ResultsDuring anesthesia and in the PACU, significantly more patients in the oximetry group had at least one respiratory event than did the control patients. This was the result of a 19-fold Increase in the incidence of diagnosed hypoxemia in the oximetry group than in the control group in both the OR and PACU (P < 0.00001). In the OR, cardiovascular events were observed In a similar number of patients in both groups, except myocardial ischemia (as denned by angina or ST-seg-ment depression), which was detected in 12 patients in the oximetry group and In 26 patients in the control group (P < 0.03). Several changes in PACU care were observed in association with the use of pulse oximetry. These Included higher flow rate of supplemental oxygen (P < 0.00001), Increased use of supplemental oxygen at discharge (P < 0.00001), and increased use of naloxone (P < 0.02). The rate of changes in patient care as a consequence of the oximetry monitoring Increased as the American Society of Anesthesiologists physical status worsened (P < 0.00001). One or more postoperative complications occurred in 10% of the patients in the oximetry group and in 9.4% in the control group (difference not significant). The two groups did not differ significantly in cardiovascular, respiratory, neurologic, or Infectious complications. The duration of hospital stay was a median of 5 days in both groups (difference not significant). An equal number of in-hospital deaths were registered in the two groups. Questionnaires, completed by the anesthesiologists at the five partlc

Randomized evaluation of pulse oximetry in 20,802 patients: I. Design, demography, pulse oximetry failure rate, and overall complication rate.

BackgroundAlthough pulse oximetry is currently In widespread use, there are few data documenting Improvement in patient outcome as a result of the use of oximetry. The authors describe the study design, patient demographic findings, data validation, pulse oximetry failure rate, and overall postoperative complication rates in the first large prospective randomized multicenter clinical trial on perloperative pulse oximetry monitoring. Methods;In five Danish hospitals, by random assignment, monitoring did or did not include pulse oximetry for patients 18 yr of age and older, whether scheduled for elective or emergency operations, or for regional or general anesthesia, except during cardiac and neurosurgical procedures. Operational definitions were established for perioperative events and postoperative complications. The data were collected preoperatively, during anesthesia, in the postanesthesia care unit, and until the day of discharge from the hospital or the seventh postoperative day. ResultsOf 20,802 patients, 10,312 were assigned to the oximetry group and 10,490, to the control group. In general, the demographic data, patient factors, and anesthetic agents used were distributed evenly. A slight intergroup difference was found in the distribution of age, duration of surgery, some types of surgery, and some types of anesthesia. The total failure rate of the oximetry was 2.5%, but it increased to 7.2% in patients with American Society of Anesthesiologists physical status 4 (P < 0.00001). In 14.9% of the patients, one or more events occurred in the operating room and 13.5% in the postanesthesia care unit. The overall postoperative complication rate was 9.7%. The total rates of cardiovascular and respiratory complications were 2.78% and 3.50%, respectively. Within the

The effect of fatigue on the performance of a simulated anesthetic monitoring task

In a simulated monitoring situation, 21 anesthesia residents were tested for their ability to detect significant changes in four critical variables in the presence of a concurrent distraction. Each resident was tested after a night without clinical responsibility, (rested) and after 24 hours of in-house call (fatigued). When fatigued, the residents scored significantly worse on the vigilance test than when rested (57.2 ±15.4 versus 65.9 ± 10.9,P < 0.02). Despite the small population size, the possibility of subject and investigator bias, and the artificial setting, these results support the intuitive proposition that a fatigued person is less likely than a rested person to detect important changes in monitored variables.

Work and Rest Cycles in Anesthesia Practice

A questionnaire inquiring about existing and desirable work and patterns appeared in a newsletter mailed to about 22,000 anesthesiologists and anesthesiology residents and 24,000 nurse anesthetists (CRNA). Almost 3,000 anonymous replies were received and analyzed. Respondents reported mean work weeks of 47.5 h (CRNA) to 69.8 h (residents), longest continuous period of administering anesthesia without a break of 6.6 h (CRNA) to 7.7 h (residents), and longest period of administering anesthesia with or without breaks of 14.1 h (CRNA) to 20 h (resident). However, the respondents considered it safe to administer anesthesia without a break for 4.2 (CRNA) to 5.2 h (anesthesiologists) and with break for 12.8 h (CRNA) to 15 h (residents). A substantial number of respondents believed that they work at least occasionally beyond their perceived self-limitations. The majority of respondents recalled having made errors in the administration of anesthesia that they attributed to fatigue. These results may not be representative of work patterns or attitudes among American anesthesia providers because of the small sample size and the resultant potential for bias. Yet, the subject deserves attention and further study because fatigue can affect professional performance, ability to learn, and family life.

Sampling intervals for clinical monitoring of variables during anesthesia

Although five minutes is the sampling interval mentioned by the American Society of Anesthesiologists for monitoring blood pressure and heart rate during anesthesia, most patients are monitored more closely by continuous auscultation and with the help of automated instruments. Yet this difference between the interval recommended and that actually used indicates that sampling intervals are not defined clearly enough. Therefore, we present three methods with which to determine sampling intervals during monitoring. To explore the feasibility of these methods we examined data gathered every 7.5 seconds during three typical, noncatastrophic physiologic perturbations induced in an anesthetized dog. We chose hypercapnia secondary to rebreathing, hypotension secondary to deep anesthesia, and hypoxemia secondary to a low concentration of inspired oxygen as realistic examples of what can occur during operation and anesthesia. We studied three variables: respired carbon dioxide, femoral arterial blood pressure, and oxygen saturation of hemoglobin (pulse oximeter). The data obtained during monitoring were subjected to three methods of analysis: (1) recording of sets of data, with various starting times, at five-minute intervals only (moving grid); (2) Fourier analysis; and (3) analysis of slopes. For the data of the experiment, the Fourier analysis yielded, on average, longer sampling intervals than did the analysis of slopes.

EXTRACORPOREAL CIRCULATION AND ENDOGENOUS EPINEPHRINE AND NOREPINEPHRINE IN PLASMA, ATRIUM, AND URINE IN MAN. A COMPARISON OF ETHER AND HALOTHANE ANESTHESIA.

In 25 patients epinephrine and norepinephrine concentrations were measured in urine preoperatively and postoperatively, in plasma and atrial tissue during thoracotomy before, during and after cardiopulmonary bypass. Ether or halothane anesthesia was used. Both epinephrine and norepinephrine plasma levels rose during thoracotomy with either anesthetic. During bypass the levels continued to rise under ether but failed to change significantly under halothane anesthesia. Induced hypothermia delayed the rise of plasma cotecholamine levels during bypass. Atrial catecholamines did not change. Catecholamine levels were increased in the urine postoperatively with much higher excretion occurring in patients under ether anesthesia than under halothane anesthesia.None of the patients required sympathomimetic drugs. The changes in catecholamine levels in plasma and urine are believed to reflect a normal response to anesthesia, surgical trauma, and extracorporeal circulation. Ether or halothane anesthesia may modify this normal response significantly.

Tissue hypoxia distal to a Peñaz finger blood pressure cuff

The Peñaz finger method to measure blood pressure uses a finger cuff in which the pressure level fluctuates in the vicinity of the mean arterial pressure level and thereby interferes with the circulation of blood to and from the fingertip. We measured capillary blood gases and saturation of hemoglobin in the finger during Peñaz finger blood pressure (PFBP) monitoring to assess the degree to which it impairs circulation in the fingertip. Within 2.5 minutes after initiating PFBP monitoring, capillary oxygen tension (Po2) had decreased significantly, from about 71 mm Hg to between 49 and 58 mm Hg for up to 50 minutes. These changes were quite different from those occurring when an occlusive tourniquet was applied around the finger. Within 10 minutes of tourniquet application, acidosis (pH 7.25), hypercapnia (carbon dioxide tension, 59.0 mm Hg), and hypoxemia (Po2, 29 mm Hg) resulted. Within 30 seconds of releasing the PFBP cuff, capillary blood gas values were back to normal. Interspersing 30-second rest periods every 5 minutes during 35 minutes of PFBP monitoring actually decreased capillary oxygen values compared with monitoring without such rest periods. A finger pulse oximeter distal to the PFBP cuff showed desaturation from an average of 97% to 93.7%, with much variability. However, desaturation was statistically significant within 1 minute of application of the PFBP cuff. Within 1 minute the finger volume increased an average of 0.05 ml. After 1 minute the volumes varied widely and, on the average, returned to normal despite continued PFBP monitoring.

Influence of Pulse Oximetry and Capnography on Time to Diagnosis of Critical Incidents in Anesthesia: A Pilot Study Using a Full-Scale Patient Simulator

Objective. Many studies (outcome, epidemiological) have tested the hypothesis that pulse oximetry and capnography affect the outcome of anesthetic care. Uncontrollable variables in clinical studies make it difficult to generate statistically conclusive data. In the present study, we eliminated the variability among patients and operative procedures by using a full-scale patient simulator. We tested the hypothesis that pulse oximetry and capnography shorten the time to diagnosis of critical incidents. Methods. A simulator was programmed to represent a patient undergoing medullary nailing of a fractured femur under general anesthesia and suffering either malignant hyperthermia, a pneumothorax, a pulmonary embolism or an anoxic oxygen supply. One hundred thirteen anesthesiologists were randomly assigned to one of two groups of equal size, one with access to pulse oximetry and capnography data and the other without. Each anesthesiologist was further randomized to one of the four critical incidents. Each anesthetic procedure was videotaped. The time to correct diagnosis was measured and analyzed. Results. Based on analysis of 91 of the subjects, time to diagnosis was significantly shorter (median of 432 s vs. >480 s) for the anoxic oxygen supply scenario (p = 0.019) with pulse oximetry and capnography than without. No statistical difference in time to diagnosis was obtained between groups for the other three critical incidents. Conclusions. Simulation may offer new approaches to the study of monitoring technology. However, the limitations of current simulators and the resources required to perform simulator-based research are impediments to wide-spread use of this tool.

Helium Retards Endotracheal Tube Fires from Carbon Dioxide Lasers

Polyvinyl chloride (PVC) endotracheal tube segments were exposed to a 5.0-W CO2 laser beam in the presence of different fractions of oxygen and either helium or nitrogen. Time from onset of exposure until ignition was recorded, and mean time to ignition (MTI) was calculated after 10 exposures with the same gas mixture. A second series was done with 40% oxygen in either nitrogen or helium and a laser intensity of 7.5, 10.0, or 12.5 W; a third with 40% oxygen, 60% helium, and 2% halothane and a 10.0-W laser beam; and a fourth with 40% oxygen and 60% helium and a 10.0-W laser beam directed at the radioopaque barium sulfate stripe on the tube. With 5.0-W and 20% oxygen in either nitrogen or helium, segments did not ignite. With concentrations of oxygen greater than 20% in nitrogen, segments ignited sooner than with comparable concentrations in helium: MTIHe = 55.6 s and MTIN2 = 27.6 s in 40% oxygen (P < 0.05). Sixty per cent helium remained protective at laser intensities up to 10.0 W (MTIHe = 42.6 s vs. MTIN2 = 14.3 s) (P < 0.05).However, at 12.5 W, MTIHe = 11.5 s and MTIN2 = 11.3 s. Two per cent halothane in 40% oxygen and 60% helium reduced MTIHe to 25.3 s compared with 42.3 s without halothane. With the laser directed at the barium stripe, MTIHe was 7.2 s and MTIN2 1.1 s. Adding helium in concentrations ≥ 60% to anesthetic gases delays laser-induced PVC endotracheal tube fires, if laser intensity is ≤10.0 W and laser bursts are ≤10 s. The barium sulfate stripe should be avoided when using this technique.