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.     

An anesthesia information system for monitoring and record keeping during surgical anesthesia

We have developed an anesthesia information system (AIS) that supports the anesthesiologist in monitoring and recording during a surgical operation. In development of the system, emphasis was placed on providing an anesthesiologist-computer interface that can be adapted to typical situations during anesthesia and to individual user behavior. One main feature of this interface is the integration of the input and output of information. The only device for interaction between the anesthesiologist and the AIS is a touch-sensitive, high-resolution color display screen. The anesthesiologist enters information by touching virtual function keys displayed on the screen. A data window displays all data generated over time, such as automatically recorded vital signs, including blood pressure, heart rate, and rectal and esophageal temperatures, and manually entered variables, such as administered drugs, and ventilator settings. The information gathered by the AIS is presented on the cathode ray tube in several pages. A main distributor page gives an overall view of the content of every work page. A one-page record of the anesthesia is automatically plotted on a multicolor digital plotter during the operation. An example of the use of the AIS is presented from a field test of the system during which it was evaluated in the operating room without interfering with the ongoing operation. Medical staff who used the AIS imitated the anesthesiologist’s recording and information search behavior but did not have responsibility for the conduct of the anesthetic.     

Computerized monitoring of the EMG and EEG during anesthesia

Summary An intraoperative evaluation was made of the electroencephalographic (EEG) and electromyographic (EMG) functions of the Anesthesia and Brain activity Monitor (ABM®). This device derives both these measures from a single electrode pair that is typically placed on the mid-forehead and mastoid process. The evaluation consisted of 1) quantifying the zero-crossing frequency (ZXF) of the EEG and mean integrated voltage of both measures (MIV_EEG and MIV_EMG) that occurred during induction and emergence from general anesthesia in 17 patients and 2) case reports sampled from an additional 41 patients.Alone or combined, variations in these parameters did not consistently accompany changes in the depth or adequacy of anesthesia as determined by standard clinical signs (e.g. heart rate, blood pressure, movement). Interpatient variability in the EEG measures during recovery from anesthesia was so large that neither the absolute value of ZXF nor that of MIV_EEG could discriminate between moderate (i.e., maintenance) and light (i.e., emergence) anesthesia. Although MIV_EMG uniformly decreased in anesthetized, unparalyzed patients (compared to the pre-operative awake state), noticeable increases during recovery often did not occur until limb movement was observed. Additionally, the common use of neuromuscular blockers made interpretation of low MIV_EMG values quite difficult during anesthesia maintenance.However, selected individual case reports illustrated the potential benefit of routine intraoperative, microprocessor-based EEG/EMG monitoring. The single channel EEG/EMG display of the ABM seems sufficient to warn the anesthesiologist of pathologic decreases in cerebral electrical activity. Marked depression of cerebral function is associated with accidental anesthetic overdose, hypoxia or global ischemia. Additionally, the device should be useful for monitoring burst-suppression or isoelectric EEG patterns intentionally produced during barbiturate or isoflurane coma for cerebral protection.     

Pediatric reference intervals for 19 biologic variables in healthy children

We defined age- and sex-specific reference intervals for 19 biologic variables in serum samples from healthy children, 1 to 22 years of age, using common laboratory equipment. Upper and lower reference intervals were defined as the estimated 2.5 and 97.5 percentiles of the distribution. For variables (y) that varied with age, the relationship of y to age was modeled with polynomial regression. Parametric percentile estimates specific to each age were then calculated as the predicted y value +/- 1.96 . SD, in which SD = the standard deviation of the residuals. For variables not associated with age, the nonparametric 2.5 and 97.5 sample percentiles were used to define the reference intervals. No significant age or sex differences were found for serum sodium, total protein, glucose, direct bilirubin, or albumin. Potassium, chloride, and urea showed constant values in children that were higher than adult values in the case of potassium and chloride and lower than adult values in the case of urea. No sex-related differences were seen for these analytes. Creatinine, uric acid, and bicarbonate showed an upward trend in values with increasing age, whereas aspartate aminotransferase, phosphorus, and total and ionized calcium showed a downward trend with increasing age. Sex-related differences were noted for these analytes. The immunoglobulins (IgG, IgA, and IgM) showed an upward trend with increasing age, with no sex-related differences except for IgM in children.     

Methohexital in total intravenous anesthesia during intraoperative neurophysiological monitoring

Total intravenous anesthesia (TIVA) is usually recommended during spinal surgery when transcranial motor evoked potentials (tcMEPs) are used to monitor. A shortage of propofol has prompted a search for an alternative sedative-hypnotic agent. We explored the use of methohexital as an alternative. TIVA was provided for two adult patients having spinal surgery using an infusion of methohexital. TcMEPs and somatosensory evoked potentials were acquired to monitor neurological function and electroencephalogram was used to titrate the methohexital dose. Two cases are presented in which the anesthesia and monitoring that was provided were successful. These cases indicate that methohexital can be a suitable alternative to propofol in some patients.     

Chronic methemoglobinemia: Improving hemoglobin saturation monitoring during anesthesia

Methemoglobin interferes with the accuracy of pulse oximetry data. Methemoglobinemia is caused by many factors, both congenital and acquired. However, the increasing usage of dapsone, which converts hemoglobin to methemoglobin, is increasing the number of patients with methemoglobinemia. We present the case of a patient with dapsone-induced methemoglobinemia who was successfully treated with methylene blue, which converts methemoglobin back to hemoglobin. Methemoglobin interferes with the accurate pulse oximetric monitoring of oxyhemoglobin saturation [1—5]. Generally, in the presence of methemoglobin levels greater than 1 g’dL^-1, pulse oximeter readings above 85% underestimate the saturation of functional hemoglobin (the hemoglobin functioning normally with respect to oxygen); readings below 85% overestimate the saturation [2]. These inaccuracies are exaggerated as methemoglobin levels increase or functional hemoglobin saturation decreases [2]. In addition to other causes of methemoglobinemia, the spread of the HIV epidemic and the increasing number of HIV patients receiving dapsone (diaminodiphenylsulfone) as prophylactic treatment forPneumocystis carinii will expand the population of patients with clinical methemoglobinemia who require anesthesia for surgery [6-8]. Virtually all patients treated with dapsone will have levels of methemoglobin sufficient to interfere with pulse oximetric monitoring [7]. We present a case that illustrates these problems and emphasizes the importance of treating methemoglobinemia before the induction of anesthesia to ensure accurate intraoperative monitoring of oxyhemoglobin saturation.     

Electromyographic monitoring of profound surgical muscle relaxation during cardiac anesthesia

Quantitative assessment of neuromuscular block produced by large doses of nondepolarizing neuromuscular blocking agents during cardiac surgery is not possible with conventional methods of monitoring. Various posttetanic responses can, however, be elicited, even when no twitch response is present. Posttetanic responses measured by electromyography were used in this study. Twenty-four male patients undergoing coronary bypass surgery were anesthetized with sufentanil plus diazepam. Neuromuscular block was provided either with pancuronium 0.1 mg/kg or with vecuronium 0.07 mg/kg initially and supplemented with small increments when indicated. Neuromuscular block was monitored from the hypothenar muscle. The ulnar nerve was stimulated by train-of-four, with supermposed periodic tetanic stimuli to evoke posttetanic responses, once every 7 to 15 minutes. The tetanically potentiated responses were detectable during 96% ± 3.6 (vecuronium) and during 97% ± 3.7 (pancuronium) of the entire intraoperative period, while the nonpotentiated electromyographic responses were present for less than 50% of the time. The sum (of the amplitudes) of 6 posttetanic responses is significantly (p<0.05) greater than the sum of 6 nonpotentiated responses and than the size of a single-peak posttetanic response when compared with the normal, nonpotentiated responses. Higher-frequency tetanic stimuli (100 or 200 Hz) produced greater posttetanic responses (p<0.05) than did the 50-Hz tetanic stimulus. There were only slight or no significant differences in the degree of posttetanic potentiation between pancuronium and vecuronium either before, during, or after cardiopulmonary bypass. With posttetanic responses, we could detect changes in the level of neuromuscular block that occur during cardiac surgery and that are related to cardiopulmonary bypass, cooling, rewarming, and large doses of corticosteroids and antibiotics. Furthermore, it was not necessary to extend the arm or to use an arm board (on which the hand is immobilized when using mechanical monitoring methods) during cardiac surgery.     

Microcomputer-assisted monitoring system for measuring and processing cardiorespiratory variables: preliminary results of clinical trials

A microcomputer-assisted monitoring system was developed for the continuous measuring and processing of cardiorespiratory variables, including: systemic and pulmonary arterial pressures, CVP, minute ventilation, inspired and expired O2 and CO2 concentrations, temperature, and heart rate. The primary data were converted to digital form, processed, displayed on a CRT monitor, and also stored for later evaluation. This system automatically calculated and displayed on-line and in real-time both primary measurements and derived cardiorespiratory variables, including: oxygen consumption, CO2 production, left and right ventricular stroke work, pulmonary venous admixture, and systemic and pulmonary vascular resistances. Printouts of the variables and trend graphs could be obtained for any desired time period. During its development, we tested this monitoring system in 30 critically ill patients, finding that the real-time calculation of cardiorespiratory variables was a great advantage during monitoring and treatment.     

脑电双频指数监测下全身麻醉用于合并高血压老年患者的临床观察

目的观察在脑电双频指数(BIS)监测下实施全身麻醉对合并高血压老年患者血流动力学和麻醉恢复的影响。方法 80例择期行腹腔镜下胆囊切除手术的老年高血压患者,随机分为BIS组和对照组,BIS组依据BIS监测值调整麻醉深度,对照组患者根据麻醉医生经验调整麻醉深度。记录两组患者麻醉期间血压和心率的变化以及麻醉恢复情况。结果在气管插管后1min,BIS组患者收缩压、舒张压和心率均低于对照组,差异均有统计学意义(t分别=-3.26、-3.41、-4.25,P均<0.05);BIS组患者麻醉恢复时间为(18.60±6.08)min,对照组为(26.22±7.37)min,两者比较,差异有统计学意义(t=-8.47,P<0.05)。结论 BIS监测使老年高血压患者全身麻醉期间血压和心率波动小,麻醉恢复快,并发症少。     

多参数模块系统对儿童麻醉深度的监测评价

收集仿真生理学信号,在计算机多参数模块系统条件下,探索多参数监测儿童麻醉深度的方法。构建心电、呼吸、血氧信号采集处理计算机模块,获取心电、呼吸、血氧信号,分析心率、心率变异性、呼吸末二氧化碳浓度、血氧饱和度等生理指标综合评估儿童麻醉深度。获得了相应的生理信号,心率变异性的敏感度与前期对自主神经系统测试结果吻合,较为准确地判断了儿童麻醉深度。提示采用心率、心率变异性、呼吸末二氧化碳浓度、血氧饱和度等生理指标综合评估儿童麻醉深度的方法能较准确地评估儿童麻醉深度。     

Journal of clinical monitoring and computing 2016 end of year summary: anesthesia

Clinical monitoring and computing are essential during general anesthesia. As a result it would be impossible to review all the articles published in the Journal of Clinical Monitoring and Computing that are relevant to anesthesia. We therefore will limit this summary to those articles that are uniquely related to anesthesia. The topics include: anesthesia machines; ensuring the airway; anesthetic depth; neuromuscular transmission monitoring; locoregional anesthesia; ultrasound; and pain.     

Sampling and analysis techniques for monitoring serum for trace elements

We describe techniques for controlling contamination in the sampling and analysis of human serum for trace metals. The relatively simple procedures do not require clean-room conditions. The atomic absorption and atomic emission methods used have been applied in studying zinc, copper, chromium, manganese, molybdenum, selenium, and aluminum concentrations. Values obtained for a group of 16 normal subjects agree with the most reliable values reported in the literature, obtained by much more elaborate techniques. All of these metals can be measured in 3 to 4 mL of serum. The methods may prove especially useful in monitoring concentrations of essential trace elements in blood of patients being maintained on total parenteral nutrition.     

Normal fluctuation of physiologic cardiovascular variables during anesthesia and the phenomenon of “smoothing”

With the advent of automated anesthesia record keeping devices, concern has arisen that “abnormal” values will appear in the record and possibly lead to medicolegal compromise. A retrospective review of automated records from a series of anesthesia cases was undertaken to determine if abnormal values do occur, how frequent they are, and whether they cause problems. A total of 14,826 (4,942 each) noninvasive heart rate, systolic, and diastolic blood pressure readings from 118 case printouts generated by a Diatek Arkive Patient Information Management System (63 cases) or a Data-scope Datatrac record keeper (55 cases) were recorded. The study sample covered a broad range of surgical operations, anesthetic procedures, and patient ages and medical histories. During these 118 anesthetics, the majority of readings of all three variables fell within normal ranges (defined for this study as 80 to 180 and 50 to 110 mm Hg for systolic and diastolic blood pressures, respectively, and 60 to 140 beats/min for heart rate). During the anesthetics, 3.6% of the systolic pressure readings, 13.25% of the diastolic readings, and 4.25% of the heart rate readings were recorded outside these ranges. No serious intraoperative or postoperative anesthesia complications were associated with these out-of-range readings, nor would they be expected in a sample of this size, since serious anesthetic complications are rare. This preliminary observation of one person's experience may help address the concern associated with allowing high and low blood pressure and heart rate readings to be automatically recorded “unsmoothed.” In medicolegal situations, it should also begin to demonstrate that such fluctuations are neither uncommon nor abnormal, and that a true record of these readings should be neither a cause for concern nor an opportunity for medicolegal exploitation.     

新生儿幽门梗阻腹腔镜手术麻醉的临床观察

目的 观察在新生儿腹腔镜幽门环肌切开术中使用不同的麻醉方法，CO2气腹对呼吸循环系统功能和拔管的影响。方法 全麻组（I组）和硬膜外加浅全麻组（Ⅱ组）各30例，在注气前、气腹中、注气毕记录各时点的呼吸循环动力学指标并加以比较。结果 两组病例气腹后，心率、MAP、PETCO2、最大吸气压（PIP）、PaCO2与注气前基础值相比均明显增高，pH值明显下降，SaO2值没有显著性变化。拔管前所有数值转为基础值；硬膜外麻醉组拔管时间明显缩短。结论 新生儿气腹可以引起呼吸循环功能的改变，两种麻醉方法均安全可行，使用硬膜外麻醉可以使镇痛镇静完全，肌松良好，苏醒及时。