Showing papers in "Journal of Clinical Monitoring and Computing in 1990"
TL;DR: This discussion first comments on four aspects of physiologic modeling and control; it next raises general questions calculated to highlight further the differing perspectives of the panelists; and it summarizes each panelist's formal presentation and seeks expansion of material that may puzzle nonexperts.
Abstract: I take the three tasks of the anchor to be (1)to situate-for noncognoscenti--the panelists' contributions in context, (2) to provide or elicit clarification of difficult points, and (3) to raise general questions to spark discussion. Consistent with these tasks, this discussion first comments on four aspects of physiologic modeling and control; it next raises general questions calculated to highlight further the differing perspectives of the panelists; finally, it summarizes each panelist's formal presentation and seeks expansion of material that may puzzle nonexperts.
157 citations
TL;DR: Logical explanations are provided for the economic, technical, and physiologic benefits of a stochastic system identification technique for measuring cardiac output and the limitations of developing a technique to measure cardiac output continuously.
Abstract: The limitations of developing a technique to measure cardiac output continuously are given. Logical explanations are provided for the economic, technical, and physiologic benefits of a stochastic system identification technique for measuring cardiac output. Heat is supplied by a catheter-mounted filament driven according to a pseudorandom binary sequence. Volumetric fluid flow is derived by a cross-correlation algorithm written in the C language. In vitro validation is performed with water in a flow bench. The computed flow (y) compared with the in-line-measured flow (x) yields the linear regression y = 1.024x - 0.157 (r = 0.99). The average coefficient of variation is less than 2% over a volumetric fluid flow range of 2 to 10 L/min.
143 citations
TL;DR: A retrospective evaluation of simultaneous tests of oximeters of various manufacturers in volunteer subjects disclosed greater errors at low saturations in subjects with low hemoglobin (Hb) concentrations, including the greatest additional errors associated with anemia.
Abstract: A retrospective evaluation of simultaneous tests of oximeters of various manufacturers in volunteer subjects disclosed greater errors at low saturations in subjects with low hemoglobin (Hb) concentrations. Forty-three pulse oximcters of 12 manufacturers studied over a period of 10 months showed that, at a mean arterial oxygen saturation (SaO2) level of 54.5%, as Hb concentration fell, average pulse oximeter (SpO2) bias increased approximately linearly from 0 at Hb > 14 g/dl to about -14% at 8 < Hb < 9 g/dl. At SaO2 = 53.6%, the mean bias (SaO2-SpO2) of 13 oximcters of 5 manufacturers averaged -15.0% (n = 43) in a subject with Hb = 8 g/dl, but -6.4% (n = 390) in nonanemic subjects. The additional bias in the anemic subject increased with desaturation. It was 0.13% at SaO2 = 98.5% (n = 13), -1.31% at 87.5% (n = 38), -2.71% at 75.1% (n = 38), -5.18% at 61.3% (n = 26), and -9.95% at 53.6% (n = 41); n is the product of the number of oximeters and number of tests in each saturation range. The instruments that showed the greatest errors at low saturations in nonanemic subjects also showed the greatest additional errors associated with anemia (the range between manufacturers of anemic incremental error at about 53% being from -3.2 to -14.5%) and conformed well to the relationship bias (anemic) = 1.35 × bias (normal)-8.18% (r = 0.94; Sy·x = 3.3%). The error due to anemia was zero at 97% SaO2 and became evident when SaO2 fell below 75%.
99 citations
TL;DR: The data suggest that, using transcutaneous PCO2 monitors with inbuilt temperature correction of 4.5%/‡C, the skin metabolic offset should be set to 6 mm Hg, and within both groups errors were significantly greater above but not below 80mm Hg.
Abstract: A multicentcr study used 756 samples from 251 patients in 12 institutions to compare arterial (PaO2, PaCO2) with transcutaneous (PsO2, PsCO2) oxygen and carbon dioxide tensions, measured usually at 44°C. Of these samples, 336 were obtained from 116 neonates, 27 from 25 children with cystic fibrosis, and 140 from 40 patients under general anesthesia. Ninety-one patients were between 4 weeks and 18 years of age, 32 were between 18 and 60 years, and 12 were over 60. The ratio of transcutaneous to arterial P(s/a)CO2 was 1.01 ±0.11 with PaCO2 less than 30 mm Hg, increasing to 1.04 ±0.08 at PaCO2 greater than 40 mm Hg. Mean bias and its standard deviation (PsCO2 — PaCO2) were + 1.3 ± 3.9 mm Hg in the entire group, + 1.8 ± 4.2 mm Hg in neonates (NS). Bias was +0.2 ± 2.7 mm Hg when PaCO2 was less than 30 mm Hg (N = 175, NS), 1.0 ± 3.4 with 30 80, P(s/a)O2 fell to 0.88 ± 0.18 in neonates and 0.74 ± 0.21 in older patients. The errors were significantly greater (p < 0.001) in older patients than in neonates above but not below 80 mm Hg, and within both groups errors were significantly greater above than below 80 mm Hg.
74 citations
TL;DR: Heart rate alarms were more reliable than alarms of the other parameters monitored in the study and possibilities for improving the physiological monitoring and alarm system are discussed.
Abstract: Postoperative monitoring of cardiac operated patients requires appropriately functioning monitor alarms as well as intensive nursing activity. The limit alarms can be used for detection of life-threatening situations and monitoring of physiological changes in the patient's state. We studied the significance and the frequency of audible alarms during the postoperative intensive care of ten cardiac patients. Of 1307 occasions when such an alarm was activated during the study period of approximately 26 hours per patient, only 139 (10.6%) were significant. The highest proportion of significant audible limit alarms was found during the immediate postoperative period. Heart rate alarms were more reliable than alarms of the other parameters monitored in the study. Possibilities for improving the physiological monitoring and alarm system are discussed.
74 citations
TL;DR: The accuracy of the retracted probe was evaluated in 4 subjects who breathed varying fractions of inspired oxygen and carbon dioxide and the mean in vivo 90% response times for step changes in inspired gas were 2.64, 3.88, and 2.60 minutes, respectively, for pHi, PiCO2, and PiO2.
Abstract: In vitro and in vivo animal studies have shown accurate measurements of arterial blood pH (pHa), carbon dioxide tension (PaCO2), and oxygen tension (PaO2) with small intravascular fluorescent probes. Initial human clinical studies showed unexplained intermittent large drops in sensor oxygen tension (PiO2). Normal volunteers were studied to elucidate this problem. In the first part of this study, the probe and cannula were manipulated and the probe configuration and its position within the cannula were varied. The decreases in PiO2 were judged to be primarily due to the sensor touching the arterial wall. Retraction of the sensor tip within the cannula eliminated the problem. In the second part of this study, the accuracy of the retracted probe was evaluated in 4 subjects who breathed varying fractions of inspired oxygen and carbon dioxide. The arterial ranges achieved were 7.20 to 7.59 for pH, 22 to 70 mm Hg for PaCO2, and 46 to 633 mm Hg for PaO2. Linear regression of 48 paired sensor (i) versus arterial values showed pHi = 0.896 pHa + 0.773 (r = 0.98, SEE = 0.017); PiCO2 = 1.05 PaCO2-1.33 (r = 0.98, SEE = 2.4 mm Hg); and PiO2 = 1.09 PaO2-20.6 (r = 0.99, SEE = 21.2 mm Hg). Bias (defined as the mean differences between sensor and arterial values) and precision (SD of differences) were, respectively, -0.003 and 0.02 tor pHi, 0.77 and 2.44 mm Hg for PiCO2, and -2.9 and 25.4 mm Hg for PiO2. The mean in vivo 90% response times for step changes in inspired gas were 2.64, 3.88, and 2.60 minutes, respectively, for pHi, PiCO2, and PiO2.
56 citations
55 citations
TL;DR: The clinical significance of the carbon dioxide and oxygen waveforms, inspired to expired carbon dioxideand oxygen differences, alveolar-arterial gradients, and global supply-to-dcmand oxygen relationships measured by capnography, oxygraphy, and pulse oximetry are addressed in this essay.
Abstract: During the past 10 years, instrumentation has been developed that can continuously and noninvasively measure changes in carbon dioxide and oxygen. The information gencrated, which cannot be obtained through the human senses, provides vital clinical data regarding the effectiveness of intubation, ventilation, circulation, oxygenation, and the circuit. This instrumentation plays a major role in decision making both in the safe conduct of anesthesia and mechanical ventilation as well as in the detection and prevention of potentially catastrophic mishaps. For these reasons, a review of what has been learned regarding the instrumentation, collection, and interpretation of the clinical data, and the clinical value of the information is timely. The clinical significance of the carbon dioxide and oxygen waveforms, inspired to expired carbon dioxide and oxygen differences, alveolar-arterial gradients, and global supply-to-dcmand oxygen relationships measured by capnography, oxygraphy, and pulse oximetry are addressed in this essay.
52 citations
TL;DR: Several levels of decision support are outlined with examples to illustrate the many areas where decision support is useful in the many hospital applications.
Abstract: Use of hospital information systems (HIS) are no longer limited to administrative functions. The addition to these systems of decision support capability is now a necessity. Development of the decision support modules requires a different software architecture than that employed by most HIS systems today. This paper describes the generic uses of decision support throughout the many hospital applications. Several levels of decision support are outlined with examples to illustrate the many areas where decision support is useful. At LDS Hospital in Salt Lake City, Utah we have developed an HIS using a new software architecture which supports the creation of decision support applications. This system uses a frame structure to represent knowledge. Examples of the frames and their syntax is presented. Using the frame tools which are provided, an application developer can easily develop and test decision support modules which interact directly with the clinical user and the patient database.
51 citations
TL;DR: Through implementation of COMPAS, a computer-based ventilatory therapy advice system, the groundwork for standardization of ventilator management of arterial hypoxemia in critically ill ARDS patients is laid.
Abstract: A collection of computer-based respiratory care algorithms were implemented as a prototype computer-based patient advice system (COMPAS) within the existing HELP hospital information system. Detailed medical logic recommended ventilator adjustments for 5 different modes of ventilation: assist/control (A/C), intermittent mandatory ventilation (IMV), continuous positive airway pressure (CPAP), pressure controlled inverted ratio ventilation (PC-IRV), and extracorporeal carbon dioxide removal (ECCO2R). Suggestions for adjusting the mode of ventilation, fraction of inspired oxygen (FiO2), positive end-expiratory pressure (PEEP), peak inspiratory pressure, and several other therapeutic measures related to the treatment of severe arterial hypoxemia in adult respiratory distress syndrome (ARDS) patients were automatically presented to the clinical staff via bedside computer terminals. COMPAS was clinically evaluated for 624 hours of patient care on the first 5 ARDS patients in a randomized clinical trial. The clinical staff carried out 84% (320/379) of the computerized therapy suggestions. In response to a questionnaire distributed to clinical users of the system, 86% judged the system to be potentially valuable. Through implementation of COMPAS, a computer-based ventilatory therapy advice system, we have laid the groundwork for standardization of ventilator management of arterial hypoxemia in critically ill ARDS patients.
49 citations
TL;DR: The process by which clinicians recognize potentially dangerous laboratory data is difficult to computerize as mentioned in this paper, and although a significant percentage of ICU laboratory results are abnormal, most should generate no undue alarm.
Abstract: The process by which clinicians recognize potentially dangerous laboratory data is difficult to computerize. Normal value limits are useful reference points, but although a significant percentage of ICU laboratory results are abnormal, most should generate no undue alarm. Critical value limits such as K+<3.0 mmol/L or hemoglobin <7.0 g/dl are more relevant to critical care areas and are relatively easy to program into a data management computer system. However, simple limits are inadequate for more complex laboratory results, which must be correlated with other data to insure that true critical values are present. For example, hypocalcemia is a relatively common finding in surgical ICU patients in whom bowel disorders, abdominal surgery, stress, and sepsis may rapidly produce a hypoalbuminemic state. Because calcium is bound to albumin, in such a setting the hypocalcemia may be more apparent than real. Critical value limits will also fail to identify subtle but dangerous trends such as falling hemoglobin or hematocrit until the blood loss is quite severe and a critical value threshold is exceeded.
TL;DR: It is demonstrated that striking variability occurs in the relationship between indirect and arterial blood pressure measurements, and that the systemic hemodynamic state influences accuracy of indirectBlood pressure measurements.
Abstract: In 38 adults undergoing cardiac surgery, 4 indirect blood pressure techniques were compared with brachial arterial blood pressure at predetermined intervals before and after cardiopulmonary bypass. Indirect blood pressure measurement techniques included automated oscillometry, manual auscultation, visual onset of oscillation (flicker) and return-to-flow methods. Hemodynamic measurements or calculations included heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect and intraarterial blood pressure values were compared by simple linear regression by patient and measurement period. Measurement errors (arterial minus indirect blood pressure) were calculated, and stepwise regression assessed the relationship between measurement error and heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect to intraarterial blood pressure correlation coefficients varied over time, with the strongest correlations often occurring at the first and last measurement periods (preinduction and 60 minutes after cardiopulmonary bypass), particularly for systolic blood pressure. Within-patient correlations between indirect and arterial blood pressure varied widely--they were consistently high or low in some patients. In other patients, correlations were especially weak with a particular indirect blood pressure method for systolic, mean, or diastolic blood pressure; in some cases indirect blood pressure was inadequate for clinical diagnosis of acute blood pressure changes or trends. The mean correlations between indirect and direct blood pressure values were, for systolic blood pressure: 0.69 for oscillometry, 0.77 for auscultation, 0.73 for flicker, and 0.74 for return-to-flow; for mean blood pressure: 0.70 for oscillometry and 0.73 for auscultation; and for diastolic blood pressure: 0.73 for oscillometry and 0.69 for auscultation. The mean measurement errors (arterial minus indirect values) for the individual indirect blood pressure methods were, for systolic: 0 mm Hg for oscillometry, 9 mm Hg for auscultation, -5 mm Hg for flicker, 7 mm Hg for return-to-flow; for mean: -6 mm Hg for oscillometry, and -3 mm Hg for auscultation; and for diastolic: -9 mm Hg for oscillometry and -8 mm Hg for auscultation. Mean measurement error for systolic blood pressure was thus least with automated oscillometry and greatest with manual auscultation, while standard deviations ranging from 9 to 15 mm Hg confirmed the highly variable nature of single indirect blood pressure measurements. Except for oscillometric diastolic blood pressure, a combination of systemic hemodynamics (heart rate, stroke volume index, systemic vascular resistance index, and cardiac index) correlated with each indirect blood pressure measurement error, which suggests that particular numeric ranges of these variables minimize measurement error.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: It is concluded that the pulse oximeter method can be used intraoperatively to measure systolic blood pressure and correlated well with values obtained by other conventional methods.
Abstract: The pulse oximeter is commonly used in the operating room. We evaluated the use of a pulse oximeter to monitor systolic blood pressure in 20 healthy volunteers and 42 anesthetized patients. We compared the pulse oximeter method of measuring systolic blood pressure with the cuff methods using Korotkoff sounds and Doppler ultrasound as well as with direct pressure measurement through an intraarterial cannula. Systolic blood pressure values obtained by pulse oximeter correlated well with values obtained by other conventional methods. The best correlation was found with Doppler ultrasound (r = 0.996) and the worst with arterial cannulation (r = 0.880). We conclude that this method can be used intraoperatively to measure systolic blood pressure.
TL;DR: It was concluded that under the conditions of this study, peak ETCO2 values did correlate with PaCO2 values and were not significantly affected by oxygen flow rate.
Abstract: End-tidal carbon dioxide (ETCO2) values obtained from awake nonintubated patients may prove to be useful in estimating a patient’s ventilatory status. This study examined the relationship between arterial carbon dioxide tension (PaCO2) and ETCO2 during the preoperative period in 20 premedicated patients undergoing various surgical procedures. ETCO2 was sampled from a 16-gauge intravenous catheter pierced through one of the two nasal oxygen prongs and measured at various oxygen flow rates (2, 4, and 6 L/min) by an on-line ETCO2 monitor with analog display. Both peak and time-averaged values for ETCO2 were recorded. The results showed that the peak ETCO2 values (mean = 38.8 mm Hg) correlated more closely with the PaCO2 values (mean = 38.8 mm Hg; correlation coefficient r = 0.76) than did the average ETCO2 values irrespective of the oxygen flow rates. The time-averaged PaCO2-ETCO2 difference was significantly greater than the PaCO2-peak ETCO2 difference (P < 0.001). Values for subgroups within the patient population were also analyzed, and it was shown that patients with minute respiratory rates greater than 20 but less than 30 and patients age 65 years or older did not differ from the overall studied patient population with regard to PaCO2-ETCO2 difference. A small subset of patients with respiratory rates of 30/ min or greater (n = 30) did show a significant increase in the PaCO2-ETCO2 difference (P < 0.001). It was concluded that under the conditions of this study, peak ETCO2 values did correlate with PaCO2 values and were not significantly affected by oxygen flow rate. However, obtaining peak ETCO2 values is clinically more difficult, especially when partial air-way obstruction is present.
TL;DR: Bedside medical devices from 18 operating rooms and 16 beds in the Anesthesia Intensive Care Unit are connected to a baseband Ethernet system and the overall architecture of the automatic record system conforms to emerging standards for information exchange between bedside monitors and computer systems.
Abstract: Manual recording of physiological data in patients receiving anesthesia or intensive care infrequently meets medical requirements or legal documentation standards. Automated recording allows the generation of reliable data that can be integrated into the patient's medical record. Such a system is beginning to function at University Hospital at Stony Brook, New York. Bedside medical devices (pulse oximeters, non-invasive blood pressure monitors, capnographs, infusion pumps and physiological monitors) from 18 operating rooms and 16 beds in the Anesthesia Intensive Care Unit are connected to a baseband Ethernet system. Data from the above devices are stored in a MicroVAX computer system. Data compression and interpretation, computation of derived values, statistical analysis of data from two related parameters are done by the bedside graphical microcomputer workstation. The MicroVAX computer and the workstation are also connected to the Ethernet system. The overall architecture of the automatic record system conforms to emerging standards for information exchange between bedside monitors and computer systems. Health care recipients and providers are likely to reap the benefits.
TL;DR: In this article, the operating principles of a fast paramagnetic oxygen sensor are described in detail, and the advantages of clinical breath-by-breath oximetry are briefly discussed.
Abstract: The operating principles of a fast paramagnetic oxygen sensor are described in detail. Some historical background of the paramagnetic effect in oxygen measurement is given as well. This sensor measures the difference between oxygen partial pressures in two gases as an alternating pressure signal being generated by the interaction of oxygen molecules with a switched magnetic field. Factors affecting the ideal performance of the sensor are analyzed. The main sources of interference are external pressure and vibration, and asymmetry in the transfer of the pressure signal to the microphone. Finally, the advantages of clinical breath-by-breath oximetry are briefly discussed.
TL;DR: To the extent that a two-degree of freedom model consisting of rib cage and abdominal motion is able to assist in quantifying ventilation, the piezoelectric belts can monitor flow in a manner analogous to the monitoring of volume with two magnetometer pairs or two respiratory inductive plethysmograph belts.
Abstract: Piezoelectric film-based respiratory belts are described and tested. To the extent that a two-degree of freedom model consisting of rib cage and abdominal motion is able to assist in quantifying ventilation, the piezoelectric belts can monitor flow in a manner analogous to the monitoring of volume with two magnetometer pairs or two respiratory inductive plethysmograph belts. The piezoelectric belts are shown to measure flow linearly when compared with a screen pneumotachometer to a flow of at least 2.6 L/s. There is no phase shift between the peak flow of belts and the pneumotachometer up to a frequency of at least 9.2 Hz. During normal ventilation, 68 and 95% of the peak flows measured with the belts fall within ±10 and 20%, respectively, of the flows measured with a screen pneumotachometer.
TL;DR: A computerized data management system for intensive care was compared to conventional manual record keeping to assess the nurses’ acceptance, the reliability in recording haemodynamic trends and the ability of the physicians’ to recall patient data after being on duty for 24 hours.
Abstract: A computerized data management system for intensive care was compared to conventional manual record keeping. The criteria for the comparison were the nurses’ acceptance, the reliability in recording haemodynamic trends and the ability of the physicians’ to recall patient data after being on duty for 24 hours. At the time of the study the data management system had been in routine clinical use for 18 months. During the study the data management system was replaced by manual record keeping for three weeks.
TL;DR: Spontaneous brain electrical activity, somatosensory evoked potentials, and heart rate variability were not significantly affected during hyperbaric oxygénation, whereas the heart rate showed a significant decrease, according to pairedt test.
Abstract: The purpose of this study was to investigate brain bioelectrical activity during hyperbaric oxygenation by continuous and simultaneous monitoring of electroenccphalographic and bimodal (auditory, somatosensory) evoked potentials. Multivariable recordings (electroencephalogram, brainstem auditory evoked potentials, early somatosensory evoked potentials, heart rate, heart rate variability, and transcutaneous partial pressure of oxygen) were measured with a new technique in 12 healthy male volunteers 26 to 52 years old (mean ± SD, 35.9 ± 9.5 years). Recordings were obtained while the subjects breathed (1) air at normal atmospheric pressure, (2) 100% oxygen at normal atmospheric pressure, (3) air at 2 atm (10 meters sea water [msw]), and (4) 100% oxygen at 2 atm (10 msw). Spontaneous brain electrical activity, somatosensory evoked potentials, and heart rate variability were not significantly affected during hyperbaric oxygenation, whereas the heart rate showed a significant decrease (pairedt test,P < 0.05). Alterations in brainstem auditory evoked potentials were seen under hyperbaric conditions and did not reach statistical significance (increase of the I-V interpeak latency by pairedt test;P < 0.2). All subjects showed insignificant increases in dominant alpha frequency and decreases in delta frequency under hyperbaric situations.
TL;DR: It is concluded that about 90% of anesthetists can achieve usable recognition accuracy with the current voice-recognition system, even with no previous experience with the system.
Abstract: We tested on three occasions, with anesthetists as subjects, the accuracy of two voice-recognition systems designed for anesthetic record keeping. Initially, a prototype system was tested (10 subjects); several years later the resulting commercial system was tested in a quiet environment (11 subjects) and in noisy operating rooms (10 subjects). For each test an anesthetist first trained the system to recognize his or her voice by reading aloud a list of common anesthetic terms. To determine recognition accuracy, the percentage of words recognized correctly by the computer, each subject repeated the vocabulary words ten times. Although accuracy was similar during the three tests, it was slightly higher with the laboratory test (mean percent of words recognized correctly, 96.5%; range of accuracy for individual anesthetists, 91.6 to 98.8%) than with the prototype test (95.9%; range, 89.1 to 99.6%). Accuracy was lowest with the operating room test (95.3%; range, 87.8 to 98.4%). Twenty-four words caused particular difficulty during the laboratory test and were eliminated from the vocabulary of the subsequent operating room test. Omitting these 24 words from the laboratory vocabulary list allowed a more nearly direct comparison with the results from the operating room list; recognition accuracy improved in the former to 97.5% (range, 92.1 to 98.9%). Two anesthetists--one each from the laboratory and operating room tests--performed poorly, and eliminating their scores changed the respective overall scores to 98.2% (range, 96.7 to 98.9%) and 96.5% (range, 94.3 to 98.4%). Thus, the corrected difference between the laboratory accuracy and the operating room accuracy was 1.7%.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Comprehensive data on 6,755 consecutive SICU patients receiving 18,394 days of care have been accumulated by Cedars-Sinai Medical Center's PDMS, and trends for severity of illness, severity adjusted survival, census, bed utilization, nursing utilization and many other parameters have been constructed.
Abstract: Computers are beginning to be utilized extensively for direct patient care, assisting nursing and medical staff with data collection and review at the bedside. However, most clinical data management systems are optimized for bedside patient care and offer limited resources for multi-patient data analysis. At Cedars-Sinai Medical Center, a network of computer systems has been developed to provide linkages between clinical, administrative and outcome data for Surgical Intensive Care Unit (SICU) patients. Increasingly, such data is needed to evaluate the relationship between severity of illness and patient outcome and the utilization of expensive critical resources.
TL;DR: The proponents of automated anesthetic records list the ostensibly logical reasons for them and then claim that automated records will make everything better, but this logic fails on several counts, which are detailed in this essay.
Abstract: The proponents of automated anesthetic records list the ostensibly logical reasons for them and then claim that automated records will make everything better. The logic goes as follows: (1) It is good to have accurate records because accurate records (a) make clinical decision making more effective and improve patient safety, (b) provide better defense against frivolous lawsuits, and (c) enable more astute medical policy decisions based on improved retrospective case reviews; (2) automatic record-keeping systems will give more nearly accurate records; (3) therefore, quality of care will improve if we acquire automatic record-keeping systems. This logic fails on several counts, which are detailed in this essay. Having said all this, however, I do believe that automated record systems will be implemented and they will be extremely useful, both for the patient and for those who care for the patient. However, we must exercise great care in their design and implementation, lest they wind up doing more harm than good.
TL;DR: This study determined the effects on the accuracy of a single-wavelength infrared anesthetic monitor of (1) incorrect anesthetic agent setting, (2) mixtures of volatile anesthetics, and (3) ethanol vapor in the analyzed gas.
Abstract: Infrared analysis can determine exhaled concentrations of the three volatile anesthetics in common use because each absorbs infrared light. Many infrared analyzers use a single source of infrared light at a wavelength of 3.3 microns for measurements of all three agents but cannot identify which agent is in use. Organic gases such as ethanol also absorb infrared light. This study determined the effects on the accuracy of a single-wavelength infrared anesthetic monitor (Capnomac, Puritan-Bennett PB254) of (1) incorrect anesthetic agent setting, (2) mixtures of volatile anesthetics, and (3) ethanol vapor in the analyzed gas. Changing the agent setting on the monitor during steady-state delivery of an agent resulted in readings for the halothane setting five times higher than those for the enflurane setting, and six times higher than those for the isoflurane setting. These ratios reflect the monitor's fixed internal gain for each agent setting. Mixtures of anesthetics had a simple additive effect on the monitor's accuracy. With the monitor set for halothane, 0.2 vol% isoflurane mixed with halothane caused readings 1.2 vol% higher than the true halothane concentration. Conversely, with the monitor set for isoflurane, 1 vol% halothane mixed with isoflurane resulted in readings 0.2 vol% too high. In a model simulating alveolar gas, ethanol vapor corresponding to blood alcohol levels of 0.10, 0.30, and 0.50% had a slight but not clinically significant effect on readings for enflurane and isoflurane but increased readings with the halothane setting 3.5 times the corresponding level of blood alcohol. Clinicians can test for an interfering gas such as ethanol before induction by checking the reading in the halothane setting during preoxygenation.
TL;DR: The integration of routinely used equipment has made possible a frequently repcatable method for estimating cardiac output in patients, and it was demonstrated that this new monitoring system was clinically feasible and sufficiently accurate, under the limited circumstances of this study.
Abstract: A computer-based system was developed for monitoring cardiac output using the Fick principle during general anesthesia. The variables of the oxygen-consumption Fick equation were measured using the following system: oxygen uptake by an originally developed respiratory gas monitoring system, arteriovenous oxygen saturation difference by pulse and fiberoptic oximetry, and hemoglobin concentration by an in vitro oximeter. Fick cardiac output and systemic vascular resistance were calculated every 30 seconds. Fick cardiac output was compared with thermodilution cardiac output in 11 anesthetized patients. A total of 208 corresponding cardiac output measurements showed a range of 2 to 9 L · min-1. The correlation coefficient between the thermodilution and Fick cardiac outputs was 0.961, with a regression equation of Fick cardiac output = 1.058 thermodilution cardiac output 0.359. The difference between the thermodilution and Fick cardiac outputs was 0.103 ± 0.395. The Fick cardiac output was significantly lower than the thermodilution cardiac output, especially in the low flow range. We demonstrated that this new monitoring system was clinically feasible and sufficiently accurate, under the limited circumstances of our study. The integration of routinely used equipment has made possible a frequently repcatable method for estimating cardiac output in patients.
TL;DR: The MDDL provides a rich and extensible method for standardized host-device communications and an elegant method of specifying parameter attributes incorporates the inheritance and encapsulation qualities common to object-oriented languages.
Abstract: A new object-oriented Medical Device Data Language (MDDL) has been developed by the P1073 Medical Information Bus (MIB) Standard Committee, under the auspices of the Engineering in Biology and Medicine Society (EMBS) of the Institute of Electronic and Electrical Engineers (IEEE). The MDDL treats devices, host computers, persons and parameters as objects, and provides methods for describing and passing messages between objects. An elegant method of specifying parameter attributes incorporates theinheritance andencapsulation qualities common to object-oriented languages. Existing standards for device, parameter and attribute nomenclatures are used to represent MDDL components whenever possible. The MDDL provides a rich and extensible method for standardized host-device communications.
TL;DR: Pulmonary extravascular water volume, measured with this system, was 67% of the gravimetric value (r = 0.91), which was consistent with values obtained from the radioisotope methods.
Abstract: We evaluated a commercially available, double-indicator-dilution densitometric system for the estimation of pulmonary extravascular water volume in oleic acid-induced pulmonary edema. Indocyanine green and heavy water were used as the nondiffusible and diffusible tracers, respectively. Pulmonary extravascular water volume, measured with this system, was 67% of the gravimetric value (r = 0.91), which was consistent with values obtained from the radioisotope methods. The measured volume was not influenced by changes in cardiac index over a range of 1 to 4 L.min.m2. This system is less invasive than the thermal-dye technique and has potential for repeated clinical measurements of pulmonary extravascular lung water and cardiac output.
TL;DR: The esophageal stethoscope has some definite limitations as a continuous monitor and that other monitoring techniques, such as oximetry, capnography, and ventilator disconnect alarms, as well as visual/tactile inspection of the patient, should be used as well.
Abstract: The esophageal stethoscope is used often during anesthesia to monitor ventilation and cardiac function. Deficiencies in observer vigilance may limit the effectiveness of this monitoring instrument. The aim of this study was to determine how long it took for an observer to detect a surreptitiously occluded monaural esophageal stethoscope in the setting of clinical anesthesia. During routine anesthesia, where an esophageal stethoscope was in use, a computer-guided device would artificially, silently, and at random time intervals, occlude the stethoscope tubing. Personnel using the stethoscope noted when they perceived the absence of stethoscope sounds. We studied 320 stethoscope occlusions in 32 patients. The time between stethoscope occlusion and detection was 34 ±59 seconds (mean ±SD). Eighty-seven percent of detections were made in less than 60 seconds. However, 13% of detections were delayed for more than 60 seconds, and 2.3% for more than 240 seconds. While anesthesia personnel using an esophageal stethoscope could detect most stethoscope occlusions, failure to appreciate such episodes occurred in a small but significant number of cases. This suggests that the esophageal stethoscope has some definite limitations as a continuous monitor and that other monitoring techniques, such as oximetry, capnography, and ventilator disconnect alarms, as well as visual/tactile inspection of the patient, should be used as well.
TL;DR: The automated anesthetic record is inevitable for at least three reasons: First, much of the information is in electronic form, and all the necessary tools for transferring this information into a computer and hence onto a piece of paper are already available.
Abstract: The automated anesthetic record is inevitable for at least three reasons: First, much of the information is in electronic form. Second, all the necessary tools for transferring this information into a computer and hence onto a piece of paper are already available. Third, the need for an improvement over the current way of keeping records is widely recognized. Manual records are often inaccurate, biased, incomplete, and illegible, and they divert attention from more important tasks of the anesthetist. Although automated record keeping will not produce perfection, it will improve the situation enough to justify the effort.
TL;DR: A knowledge-based decision support system for respirator treatment, the KUSIVAR system, has been designed in cooperation between hospital, university and industry and is being extensively validated by an expert group in the ICU.
Abstract: A knowledge-based decision support system for respirator treatment, the KUSIVAR system, has been designed in cooperation between hospital, university and industry. Changes in patient data from respirator and monitoring equipment trigger a computer program that generates advice to the staff concerning e.g. therapy modes and respirator settings using expert systems and process control technology. A prototype has been built on an advanced development workstation, the Unisys Explorer, using the software Knowledge Engineering Environment (KEE). The clinical version is implemented on an Intel 80396-based microcomputer connected on-line via a data-acquisition processor to the respirator. The decision support software is implemented as a module under the Microsoft Windows multitasking environment and communicates with modules for data acquisition, database, handling and data presentation by means of message passing using the Windows Dynamic Data Exchange protocol. The modules present coherent user interfaces by conforming to Microsoft Windows standards. The knowledge base is being extensively validated by an expert group in the ICU and the system will be evaluated through animal experiments and clinical studies.