P. Thorgaard

Using physiological models and decision theory for selecting appropriate ventilator settings.

ObjectiveTo present a decision support system for optimising mechanical ventilation in patients residing in the intensive care unit.MethodsMathematical models of oxygen transport, carbon dioxide transport and lung mechanics are combined with penalty functions describing clinical preference toward the goals and side-effects of mechanical ventilation in a decision theoretic approach. Penalties are quantified for risk of lung barotrauma, acidosis or alkalosis, oxygen toxicity or absorption atelectasis, and hypoxaemia.ResultsThe system is presented with an example of its use in a post-surgical patient. The mathematical models describe the patient’s data, and the system suggests an optimal ventilator strategy in line with clinical practice.ConclusionsThe system illustrates how mathematical models combined with decision theory can aid in the difficult compromises necessary when deciding on ventilator settings.

The automatic lung parameter estimator (ALPE) system: non-invasive estimation of pulmonary gas exchange parameters in 10-15 minutes.

Objective.Clinical measurements of pulmonary gas exchangeabnormalities might help prevent hypoxaemia and be useful in monitoringthe effects of therapy. In clinical practice single parameters are oftenused to describe the abnormality e.g., the “effectiveshunt.” A single parameter description is often insufficient,lumping the effects of several abnormalities. A more detailed picturecan be obtained from experiments where FIO2 is varied and twoparameters estimated. These experiments have previously taken30–40 minutes to complete, making them inappropriate for routineclinical use. However with automation of data collection and parameterestimation, the experimental time can be reduced to 10–15 minutes.Methods.A system has been built for non-invasive, Automatic,Lung Parameter Estimation (ALPE). This system consists of a ventilator,a gas analyser with pulse oximeter, and a computer. Computer programscontrol the experimental procedure, collect data from the ventilator andgas analyser, and estimate pulmonary gas exchange parameters. Use of theALPE system, i.e. in estimating gas exchange parameters and reducingexperimental time, has been tested on five normal subjects, two patientsbefore and during diuretic therapy, and on 50 occasions in patientsbefore and after surgical intervention. Results.The ALPE systemprovides estimation of pulmonary gas exchange parameters from a simple,clinical, non-invasive procedure, automatically and quickly. For normalsubjects and in patients receiving diuretic therapy, data collection byclinicians familiar with ALPE took (mean ± SD) 13 min 40 sec± 1 min 23 sec. For studies on patients before and after surgery,data collection by an intensive care nurse took (mean ± SD) 10min 47 sec ± 2 min 14 sec. Parameter estimates were: for normalsubjects, shunt = 4.95% ± 2.64% and fA2 = 0.89± 0.01; for patients with heart failure prior to diuretictherapy, patient 1, shunt = 11.50% fA2 = 0.41, patient 2 shunt =11.61% fA2 = 0.55; and during therapy: patient 1, shunt =11.51% fA2 = 0.71, patient 2, shunt = 11.22% fA2 = 0.49.Conclusions.The ALPE system provides quick, non-invasiveestimation of pulmonary gas exchange parameters and may have severalclinical applications. These include, monitoring pulmonary gas exchangeabnormalities in the ICU, assessing post-operative gas exchangeabnormalities, and titrating diuretic therapy in patients with heartfailure.

Modelling of hypoxaemia after gynaecological laparotomy

Background: Late postoperative arterial hypoxaemia is common after major surgery, and may contribute to cardiovascular, cerebral or wound complications. This study investigates the time course of hypoxaemia following gynaecological laparotomy, and estimates parameters of mathematical models of pulmonary gas exchange to describe hypoxaemia.

Hypoxaemia after cardiac surgery : clinical application of a model of pulmonary gas exchange

Background and objective: To investigate the clinical application of a mathematical model of pulmonary gas exchange, which ascribes hypoxaemia to shunt and ventilation/perfusion mismatch. Ventilation/perfusion mismatch is quantified by ΔPO2, which is the drop in oxygen pressure from alveoli to lung capillaries. Shunt and ΔPO2 were used to describe changes in oxygenation after coronary artery bypass grafting. Methods: Fourteen patients were studied 2-4 h after surgery and on postoperative days 2, 3 and 7. On each occasion inspired oxygen fraction was changed in four to six steps to obtain arterial oxygen saturation (SaO2) in the range of 90-100%, enabling construction of FEO2/SaO2 curves. Measurements of ventilation, circulation and oxygenation were entered in a previously described mathematical model of pulmonary gas exchange. Results: We found that oxygenation was most impaired 3 days after surgery. By fitting the mathematical model to the FEO2/SaO2 curve, we found that shunt remained constant throughout the study period. However, ΔPO2 increased from 0.5 kPa (median, range 0-3.8) 2-4 h after surgery, to 3.2 kPa (range 1.2-6.4, P < 0.05) on day 2, and to 4.0 kPa (range 1.2-8.3) on day 3. On day 7, ΔPO2 decreased to 2.2 kPa (range 0-3.5, P < 0.05). Conclusions: Ventilation/perfusion mismatch (ΔPO2), rather than shunt, explains the changes in postoperative oxygenation. The model of pulmonary gas exchange may serve as a useful and potentially non-invasive clinical tool for monitoring patients at risk of postoperative hypoxaemia.

Assessing pulmonary congestion in left sided heart failure using pulmonary gas exchange parameters

In clinical practice there is a need for a method to measure pulmonary congestion in left sided heart failure. Current methods, including auscultation and chest X-rays, are imprecise, semiquantitative, and assess fluid accumulation, not impairment of lung function. This paper evaluates the use of a mathematical model of pulmonary gas exchange as a measure of pulmonary congestion in left sided heart failure. Eleven patients with pulmonary congestion were investigated on admission and during anticongestive therapy. Inspired oxygen fraction was varied, and measurements of ventilation and blood gases were used to estimate model parameters i.e. pulmonary shunt and ventilation-perfusion (V/Q) mismatch (/spl Delta/PO2). On admission, patients parameters were: shunt, median 9.9 % (range 0.0 - 22.2 %), and /spl Delta/PO2, 4.3 kPa (range 1.8 - 6.1 kPa), values outside the range of normal subjects (shunt, median 1.2 % range 0.0 -11.1 %, /spl Delta/PO2, median 0.1 kPa range 0.0 - 2.0 kPa) (p<0.001). During therapy both shunt and V/Q mismatch were reduced (shunt, median 7.8 % range 3.7 -14.4 %, /spl Delta/PO2, median 2.8 kPa range 0.2 - 3.9 kPa). This study illustrates a possible role for gas exchange parameters to quantify pulmonary congestion in patients with left-sided heart failure, and to monitor the effect of therapy.

Diagnosing Patient State in Intensive Care Patients Using the Intelligent Ventilator (INVENT) System

A method is presented to estimate parameters describing ICU patients ventilatory, circulatory, and metabolic state from simultaneous solution of models of O2 and CO2 transport. This method is shown to provide a consistent and reasonable picture of data from 5 ICU patients even without a pulmonary arterial catheter.

The intelligent ventilator project: application of physiological models in decision support

This paper describes progress in a model-based approach to building a decision support system for mechanical ventilation. It highlights that the process of building models promotes generation of ideas and describes three systems resulting from this process, i.e. for assessing pulmonary gas exchange, calculating arterial acid-base status; and optimizing mechanical ventilation. Each system is presented and its current status and impact reviewed.

INVENT - a decision support system for managing inspired oxygen

SELECTED ABSTRACTS PRESENTED AT THE 20TH MEETING OF THE EUROPEAN SOCIETY FOR COMPUTING AND TECHNOLOGY IN ANAESTHESIA AND INTENSIVE CARE (ESCTAIC) Berlin, Germany, Technical University, 23–26 September, 2009 Edited by: I. Marsolek, A. Dellermalm, L. Krummreich, S. E. Rees, W. Friesdorf LIST OF ABSTRACTS Bibian, S & Zikov, T: Predictability of BIS, Entropy and NeuroSENSE Bornemann, M: Data – Information – Knolwedge: The Way Up in the ICU? Using Information Making Knowledge Available? Bunker, N & Handy, J: Current Clinical Problems in Interpreting Electrolytes, Acid–base & Metabolites Dai, CY; Chen, CY; Chang, YK; Lin, WT; Lin, CP & Sun, WZ: A Multifunctional Endoscopic Platform with Detachable Probe DeVience, S; Moretti, E & Shang, AB: A Retrofittable Anesthesia Agent Alarm Dollman, M; Thien, C; Ingenlath, M; Pappert, D & Friesdorf, W: Sustainable Information of ICU Patient Family Members Eden, A; Barak, Y & Pizov, R: The Impact of an Electronic Reminder on the Administration of Preoperative Prophylactic Antibiotics Fuchs, D; Marsolek I & Friesdorf, W: Analyzing the Requirements for a Computer Based Optimization of the Medication Process Gerber, D.; Eberle, B & Trachsel, S: A Web-based Knowledge Database (Wiki Platform) for Standard Operational Procedures (SOPs) in Cardiac Anesthesia Grottke, O; Ullrich, S; Fried, E; Deserno, T; Kuhlen, T & Rossaint R: Regional Anaesthesia in Virtual Environments Gurman, G: Prevention of Ventilator Associated Pneumonia: Where Are We Now? Heinlein, M: Structured Medical Documentation in the OR: MediColor Web and MediAnes Web: Web Based Solutions for Surgery and Anaestehsia Huh, J; Ahn, W; Ro, Y; Min, S & Kim, C: Comparison of Perfusion Index, T-wave Amplitude and Heart Rate as an Indicator for Intravascular Injection of Epinephrine-Containing Test Dose in Anaesthetized Adults Karbing, DS; Allerød, C; Thorgaard, P; Andreassen, S; Kjærgaard, S & Rees, SE: INVENT – A Decision Support System for Managing Inspired Oxygen – Prospective Evaluation in an Intensive Care Unit Kennedy, R; Minto, C; French, R & McKellow, M: Effect Site Sevoflurane Levels for Airway Manipulations During Rapid Wash-In Kofránek, J; Mateják, M; Tribula, M & Matoušek, S: Educational Application of Acid–base, Volume and Electrolyte Modelling Koller, W: Data – Information – Knowledge: The Way Up in the ICU? Everyday Clinical Challenges Journal of Clinical Monitoring and Computing (2010) 24:1–33 DOI: 10.1007/s10877-009-9211-y Springer 2010

INVENT - a decision support system for managing inspired oxygen: prospective evaluation in an intensive care unit

SELECTED ABSTRACTS PRESENTED AT THE 20TH MEETING OF THE EUROPEAN SOCIETY FOR COMPUTING AND TECHNOLOGY IN ANAESTHESIA AND INTENSIVE CARE (ESCTAIC) Berlin, Germany, Technical University, 23–26 September, 2009 Edited by: I. Marsolek, A. Dellermalm, L. Krummreich, S. E. Rees, W. Friesdorf LIST OF ABSTRACTS Bibian, S & Zikov, T: Predictability of BIS, Entropy and NeuroSENSE Bornemann, M: Data – Information – Knolwedge: The Way Up in the ICU? Using Information Making Knowledge Available? Bunker, N & Handy, J: Current Clinical Problems in Interpreting Electrolytes, Acid–base & Metabolites Dai, CY; Chen, CY; Chang, YK; Lin, WT; Lin, CP & Sun, WZ: A Multifunctional Endoscopic Platform with Detachable Probe DeVience, S; Moretti, E & Shang, AB: A Retrofittable Anesthesia Agent Alarm Dollman, M; Thien, C; Ingenlath, M; Pappert, D & Friesdorf, W: Sustainable Information of ICU Patient Family Members Eden, A; Barak, Y & Pizov, R: The Impact of an Electronic Reminder on the Administration of Preoperative Prophylactic Antibiotics Fuchs, D; Marsolek I & Friesdorf, W: Analyzing the Requirements for a Computer Based Optimization of the Medication Process Gerber, D.; Eberle, B & Trachsel, S: A Web-based Knowledge Database (Wiki Platform) for Standard Operational Procedures (SOPs) in Cardiac Anesthesia Grottke, O; Ullrich, S; Fried, E; Deserno, T; Kuhlen, T & Rossaint R: Regional Anaesthesia in Virtual Environments Gurman, G: Prevention of Ventilator Associated Pneumonia: Where Are We Now? Heinlein, M: Structured Medical Documentation in the OR: MediColor Web and MediAnes Web: Web Based Solutions for Surgery and Anaestehsia Huh, J; Ahn, W; Ro, Y; Min, S & Kim, C: Comparison of Perfusion Index, T-wave Amplitude and Heart Rate as an Indicator for Intravascular Injection of Epinephrine-Containing Test Dose in Anaesthetized Adults Karbing, DS; Allerød, C; Thorgaard, P; Andreassen, S; Kjærgaard, S & Rees, SE: INVENT – A Decision Support System for Managing Inspired Oxygen – Prospective Evaluation in an Intensive Care Unit Kennedy, R; Minto, C; French, R & McKellow, M: Effect Site Sevoflurane Levels for Airway Manipulations During Rapid Wash-In Kofránek, J; Mateják, M; Tribula, M & Matoušek, S: Educational Application of Acid–base, Volume and Electrolyte Modelling Koller, W: Data – Information – Knowledge: The Way Up in the ICU? Everyday Clinical Challenges Journal of Clinical Monitoring and Computing (2010) 24:1–33 DOI: 10.1007/s10877-009-9211-y Springer 2010