Browsing by Author "Irarrazaval, M"

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    An expert system for monitor alarm integration
    (1999) Oberli, C; Urzua, J; Saez, C; Guarini, M; Cipriano, A; Garayar, B; Lema, G; Canessa, R; Sacco, C; Irarrazaval, M
    Objective. Intensive care and operating room monitors generate data that are not fully utilized. False alarms are so frequent that attending personnel tends to disconnect them. We developed an expert system that could select and validate alarms by integration of seven vital signs monitored on-line from cardiac surgical patients. Methods. The system uses fuzzy logic and is able to work under incomplete or noisy information conditions. Patient status is inferred every 2 seconds from the analysis and integration of the variables and a uni ed alarm message is displayed on the screen. The proposed structure was implemented on a personal computer for simultaneous automatic surveillance of up to 9 patients. The system was compared with standard monitors (Space-Labs (TM) PC2), using their default alarm settings. Twenty patients undergoing cardiac surgery were studied, while we ran our system and the standard monitor simultaneously. The number of alarms triggered by each system and their accuracy and relevance were compared. Two expert observers (one physician, one engineer) ascertained each alarm reported by each system as true or false. Results. Seventy-five percent of the alarms reported by the standard monitors were false, while less than 1% of those reported by the expert system were false. Sensitivity of the standard monitors was 79% and sensitivity of the expert system was 92%. Positive predictive value was 31% for the standard monitors and 97% for the expert system. Conclusions. Integration of information from several sources improved the reliability of alarms and markedly decreased the frequency of false alarms. Fuzzy logic may become a powerful tool for integration of physiological data.
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    Arterial pressure-flow relationship in patients undergoing cardiopulmonary bypass
    (WILLIAMS & WILKINS, 1997) Urzua, J; Meneses, G; Fajardo, C; Lema, G; Canessa, R; Sacco, CM; Medel, J; Vergara, ME; Irarrazaval, M; Moran, S
    We determined the arterial pressure-flow relationship experimentally by means of step changes of blood flow in 30 adult patients undergoing cardiopulmonary bypass (CPB). Anesthesia technique was uniform. CPB was nonpulsatile; hypothermia to 25-28 degrees C, and hemodilution to 18%-25% hematocrit were used. During stable bypass, mean arterial pressure was recorded first with blood flow 2.2 L.min(-1).min(-2). Flow was then increased to 2.9 L.min(-1).m(-2) for 10 s and reverted to baseline for 1 min. Then it was decreased to 1.45 L.min(-1).m(-2) for 10 s, and reverted to baseline for 1 min. Subsequently, it was decreased to 0.73 L.min(-1).m(-2) for 10 s and then reverted to baseline. line. Similar sets of measurements were repeated after 0.25 mg of phenylephrine and once the patient was rewarmed. The pressure-flow function was individually determined by regression, and the critical pressure estimated by extrapolation to zero flow. All patients had zero-flow critical pressure during hypothermia, with a mean value of 21.8 +/- 6.4 mm Hg (range 8.8-38.9). It increased after 0.25 mg phenylephrine to 25.4 +/- 7.2 mm Hg (range 12.2-43.9, P < 0.001). During normothermia, critical pressure was 21.2 +/- 5 mm Hg (range 13.4-30.9), not significantly different from hypothermia. During hypothermia, the slope of the pressure-flow function (i.e., resistance) was 14.9 +/- 3.5 mm Hg.L-1.min(-1).m(-2) (range 7.6-22.1). It increased significantly (P < 0.001) after phenylephrine, to 19.7 +/- 6.2 mm Hg.L-1.min(-1).m(-2) (range 11.4-40.5), and returned to 15.4 +/- 3.4 mm Hg.L-1.min(-1).m(-2) (range 10.1-24.2) during normothermic bypass. Systemic vascular resistance appeared to vary reciprocally with blood flow, although this finding may represent a mathematical artifact, which can be avoided by using zero-flow critical pressure in the vascular resistance equation.
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    Comparison of isoflurane, halothane and fentanyl in patients with decreased ejection fraction undergoing coronary surgery
    (AUSTRALIAN SOC ANAESTHETISTS, 1996) Urzua, J; Serra, M; Lema, G; Canessa, R; Gonzalez, R; Meneses, G; Irarrazaval, M; Moran, S
    The aim of the study was to compare three anaesthetic agents in patients with ejection fraction below 0.40 subjected to coronary revascularization surgery. Twenty-five elective coronary surgical patients with ejection fraction below 0.40 were prospectively studied. Premedication was pethidine 1 mg/kg and induction was fentanyl 0.03 mg/kg and pancuronium 0.1 mg/kg. The patients were randomized to one of three maintenance techniques (fentanyl, isoflurane or halothane).