J.G.C. Lerou

Automated charting of physiological variables in anesthesia: A quantitative comparison of automated versus handwritten anesthesia records

Eight physiological variables—tidal volume, breathing rate, end-tidal carbon dioxide fraction, oxygen fraction in the anesthetic circuit, oxygen saturation by pulse oximetry, systolic and diastolic blood pressure, and heart rate—recorded on-line by a commercially available automated system were compared with the same variables recorded on handwritten anesthesia records. We quantified the differences between the automated and handwritten records generated from the same 30 patients (2,412 minutes of general anesthesia for elective eye surgical procedures). Considering the design of the study, we claim that the differences between both records were caused by the incompleteness or inaccuracy of the handwirtten records, except in two instances. The amounts of missing or erroneous data for these eight physiological variables were expressed as fraction (“error fractions”) of the time being recorded, designated EFm and EFe, respectively. For the first five variables the EFm on the handwritten records ranged between 0.23 and 0.31, and the EFc ranged between 0.01 and 0.06. For the last three variables the EFm range was 0.08 to 0.13, and the EFe range was 0.05 to 0.11. Most of these missing or erroneous data occurred during the period of induction (first 15 minutes) and at the end of the case (last 10 minutes). The EFm and EFe during induction had increased to 0.62 and 0.26, respectively, and to 0.76 and 0.06, respectively, at the end of the case. Erroneous data were observed on the automated records for the tidal volume during induction (EFe=0.0044) and for the oxygen fraction during maintenance (EFe=0.0024). The effect of averaging by the recordkeeper is discussed. The results of this study indicate the clinical relevance of automated record keeping.

Model-based administration of inhalation anaesthesia. 1. Developing a system model

This paper is the first of a series of reports on a system model for the administration of inhalation anaesthesia. We present the development and basic testing of the model. It is a multiple-gas model; it covers fresh-gas flow rates from basal to more than total ventilation and includes an actual, not an idealized, circle-absorber breathing system featuring a standing bellows ventilator. Kinetics of nitrogen, oxygen, carbon dioxide, nitrous oxide, inhaled anaesthetic agents and helium are described. Their partial pressures sum to the total pressure. Ventilation and cardiac output are treated as continuous, not cyclical. The model of the breathing system was empirically matched to the chosen one (a GMS absorber and 7850 ventilator (Datex-Ohmeda)). Predictions for the wash-in of isoflurane and the uptake of desflurane and isoflurane agree well with observed data. The results obtained by continuously checking total gas pressures, calculating mass balances and simulating the measurement of alveolar space by the closed-circuit helium dilution method support the mathematical credibility of the model. It thus merits further exploration.

A system model for closed-circuit inhalation anesthesia. I. Computer study.

Developing a custom computer program to simulate the uptake, distribution, and elimination of inhalational anesthetics allows the anesthesiologist to address specific problems, but extensive skills are required to translate the involved processes first into a set of mathematical equations and then into a satisfactory computer program. The first step is often facilitated by solutions offered in the literature. The second step demands computer proficiency that is often not available, but this problem can be obviated by means of a special-purpose simulation language (SPSL). We therefore constructed a model for closed-circuit inhalation anesthesia with the aid of the block-structured SPSL TUTSIM. Noticeable differences with previous models are that the linear, 14-compartment basic model does not assume a constant alveolar concentration and mimics circulation times through the use of blood pools. Advanced features of the SPSL were used to develop variants of the basic model to simulate feedback-controlled isoflurane administration, nitrous oxide uptake, and the impact of a nonlinearity by incorporating the effect of enflurane on cardiac output. Two variants were concatenated to form a multiple model showing the concentration and second-gas effects. The model was capable of reproducing the anesthetic uptake from previous experimental studies for nitrous oxide. After its validation for other anesthetic agents, the model can be used for clinical, teaching, and research purposes. The SPSL freed the authors from the problems associated with computer programming and allowed them to concentrate on the structure of the model.

A System Model for Closed-circuit Inhalation Anesthesia II. Clinical Validation

Recently, we described a basic model and its more elaborate variants to predict the uptake and distribution of inhalational anesthetics during closed-circuit anesthesia. As an initial clinical validation of the linear, continuous, 14-compartment basic model, the current study examined its predictive performance in 50 patients by comparing quantitatively the predicted and the measured alveolar concentration-time profiles after bolus injections of liquid isoflurane into the closed system during mechanical ventilation. The two versions of the model studied differed in the size of their peripheral shunt, as 0% (version A) and 16% (version B) of the cardiac output. A total of 15,744 alveolar concentrations of isoflurane (one per 10s period) were measured by mass spectrometry. For each measured concentration we used computer simulations of version A and version B to calculate a predicted concentration for both versions. For each patient we calculated the bias (indicating over- or underprediction) and the scatter of the prediction errors (indicating the typical error size). The bias and the scatter of the prediction errors, both given as mean (and standard deviation), were 2.25 (13.59) and 12.51 (5.84)% for version A and 12.00 (14.97) and 14.12 (6.54)% for B. Version A performed better than B: both the bias (P = 0.008) and the scatter (P less than 0.0001) were closer to zero for A. Logistic regression analysis showed for version A that scatter, but not bias, increased with age (P = 0.002). Gender, body mass index (weight x height-2), and number of injections per hour did not influence scatter or bias.(ABSTRACT TRUNCATED AT 250 WORDS)

Electromyographic assessment of blink and corneal reflexes during midazolam administration: useful methods for assessing depth of anesthesia?

Background: There are at least three components of the anesthetic state: loss of consciousness, amnesia and obtundation of reflex responses to noxious stimuli. To investigate the third component, we used a standard electrical stimulus to evoke a blink reflex, which was electromyographically recorded. These data may give information on the anesthetic state.

Ultrasound‐guided needle handling using a guidance positioning system in a phantom

The SonixGPS™ needle guidance positioning system provides navigation assistance to facilitate needle handling during ultrasound‐guided procedures. Each of 20 inexperienced nurse anaesthetists performed 12 different ultrasound‐guided tasks in a porcine phantom. Using both in‐plane and out‐of‐plane approaches, they inserted a needle and made contact with metal rods at depths of 2, 4 and 6 cm. We compared their performances without and with navigation as paired observations. Using the out‐of‐plane approach, navigation yielded shorter execution times (26 s vs 14 s, respectively; p = 0.01) and fewer needle repositionings (8 vs 3, respectively; p = 0.001). Using the in‐plane approach, the needle was more visible with navigation assistance: 24% vs 52% of execution time, respectively (95% CI: 44%–12%; p = 0.0025). Better needle visibility was associated with shorter execution times and fewer needle repositionings. Combining ultrasound‐guided techniques with the needle guidance positioning system may reduce tissue manipulation, thus improving patient comfort and safety.

The clinical use of the Ohmeda Automated Anesthesia Record Keeper integrated in the Modulus II Anesthesia System. A preliminary report.

While performing his complex array of tasks, the anesthesiologist is also responsible for maintaining an anesthetic record. Up to now, this has been done by hand. The clinical use of automated anesthesia record keeping is presently evaluated. The anesthesia records generated by the Ohmeda Automated Anesthesia Record Keeper integrated in the Modulus II Anesthesia System is compared to hand written records. The differences between the two records of identical patients are quantified as erroneous or missing data. With the criteria adapted, we found significant and clinically relevant differences which stress the importance of automated record keeping.

Electromyographic assessment of blink reflexes correlates with a clinical scale of depth of sedation/anaesthesia and BIS during propofol administration

Background:  General anaesthesia is characterized by loss of consciousness, amnesia and obtundation of reflex responses to noxious stimuli. Quantifying the blink reflex may reflect the depression of reflex arches induced by anaesthetics and thus being informative on the anaesthetic state.

Intrathecal somatostatin produces effects dependent on the interval between catheter implantation and drug injection

Intrathecal (i.t.) injection of somatostatin has been reported to depress nociceptive reflexes as well as to cause severe disturbance of somatomotor performance. The present study was designed to assess the dependence of these effects on the dose and the interval between implantation of the catheter and i.t. injection of somatostatin in rats. The effects produced by i.t. injection of somatostatin consisted of an increase in the response latencies of nociceptive responses to noxious heat, impairment of motor performance and grooming behavior, convulsions, and death. Except for grooming behavior, these were related in incidence and degree to the dose and the interval, the potency of somatostatin being highest at short intervals. Sham operations also affected the effectiveness of somatostatin.

A system model for halothane closed-circuit anesthesia : structure considerations and performance evaluation

Background Previously, the authors described a physiologic model for closed-circuit inhalational anesthesia. The basic version of this system model was clinically validated for isoflurane. An extended version adopted nonpulmonary elimination causing a constant fraction of anesthetic to be irreversibly lost. This version improved the accuracy of the model for enflurane. The models performance for other inhalational anesthetics that are not biochemically inert, such as halothane, remained to be evaluated.