Browsing by Author "Sacco, C"

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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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    Hemodilution does not alter the aortic-to-femoral arterial pressure difference in dogs
    (1999) Urzua, J; Nunez, G; Lema, G; Canessa, R; Sacco, C
    Introduction. Distal arterial pressure normally differs from aortic pressure. This difference is modified by changes of vascular resistance. Hemodilution, due to decreased viscosity, decreases vascular resistance. Therefore, the difference between aortic and distal arterial pressures could be altered as well. We investigated whether acute hemodilution affected this difference in dogs. Methods. Eleven mongrel dogs weighing 16.6 +/- 4.4 kg were anesthetized with pentobarbital and sufentanyl and mechanically ventilated. Arterial presssure was recorded using Millar catheter-tipped pressure transducers in the proximal aorta and in the distal femoral artery. An electromagnetic flowmeter probe was placed around the aorta. Effective downstream pressure was estimated by extrapolation of exponential arterial pressure decay during 3-second occlusion of the proximal aorta. Hemodilution was effected by removal of 30 ml/kg of blood and replacement with 60 ml/kg of warmed saline. In addition, the effects of 1 mu g/kg phenylephrine and 4 mu g/kg of sodium nitroprusside were measured before and after hemodilution. Results. Hemodilution decreased hematocrit from 39 +/- 11.2% to 25.6 +/- 4.95%. Systolic and mean pressures were unchanged but aortic diastolic pressure decreased significantly, from 86 +/- 17 to 79 +/- 15 mmHg (p < 0.005). Peak systolic pressure was 13.5 +/- 7.2 mmHg higher in the femoral artery than in the aorta before, and 16 +/- 8.7 mmHg after, hemodilution (p > 0.05). Nitroprusside decreased the femoral to aortic peak systolic pressure difference from 14.3 +/- 6.3 to 7.7 +/- 15.3 mmHg, p = 0.05 before hemodilution and from 14.3 +/- 8.8 to 2.5 +/- 11 mmHg, p < 0.005 afterwards. Hemodilution significantly decreased the effective downstream pressure, from 44 +/- 9 to 36 +/- 6.8 mmHg in the aorta (p < 0.05), and from 51 +/- 2 to 37 +/- 3.1 mmHg in the distal femoral artery (p < 0.05). Conclusion.Acute hemodilution did not alter the aortic-to-distal arterial pressure difference in dogs.