Browsing by Author "Urzua, J"

Now showing 1 - 5 of 5
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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).
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    Estimation of cardiac function from computer analysis of the arterial pressure waveform
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 1998) Guarini, M; Urzua, J; Cipriano, A; Gonzalez, W
    This paper presents a method for estimating parameters of a cardiovascular model, including the left-ventricular function, using the sequential quadratic programming (SQP) and the least minimum square (LMS) algorithms. In a first stage, a radial arterial-pressure waveform with corresponding cardiac output are used to automatically seek the set of parameters of the diastolic model. Computer simulation of the model using these parameters generate a pressure waveform and a cardiac output very close to those used for the estimation. In a second stage, the estimated arterial load parameters are used to select the best left-ventricular model function, from four different possibilities, and to estimate its optimum parameter values. The method has been tested numerically and applied to real cases, using data obtained from cardiovascular patients. It has also been subjected to preliminary validation using data obtained from laboratory dogs, in which cardiovascular function was artificially altered.
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    Renal preservation in the perioperative period
    (LIPPINCOTT WILLIAMS & WILKINS, 1999) Urzua, J; Lema, G; Canessa, R; Sacco, CM
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    Renal protection in patients undergoing cardiopulmonary bypass with preoperative abnormal renal function
    (LIPPINCOTT WILLIAMS & WILKINS, 1998) Lema, G; Urzua, J; Jalil, R; Canessa, R; Moran, S; Sacco, C; Medel, J; Irarrazaval, M; Zalaquett, R; Fajardo, C; Meneses, G
    We prospectively studied the effects of renal protection intervention in 17 patients with preoperative abnormal renal function (plasma creatinine >1.5 mg/dL) scheduled for elective coronary surgery. Patients were randomized to either dopamine 2.0 ,mu g.kg(-1).min(-1) (Group 1, n = 10) or perfusion pressure >70 mm Hg during cardiopulmonary bypass (CPB) (Group 2, n = 7). Glomerular filtration rate and effective renal plasma flow were measured with inulin and I-125-hippuran clearances before the induction of anesthesia, after sternotomy and before CFB, during hypo-and normothermic CPB, after sternal closure, and 1 h postoperatively. Plasma and urine electrolytes were measured, and free water, osmolar, and creatinine clearances, as well as fractional excretion of sodium and potassium, were calculated ed before and after surgery. Significant differences between groups were found before CPB for glomerular filtration rate (higher in Group 1), urine output (2.0 vs 0.29 mL/min in Group 1 versus Group 2), urinary creatinine (66 vs 175 mg/dL), urinary osmolarity (370 vs 627 mOsm/L), osmolar clearance (2.1 vs 0.7 mL/min), and urinary potassium (33 vs 71 mEq/L). There were no differences between groups during hypo-and normothermic CPB. After CPB, the only difference was a slightly higher urinary creatinine in Group 2. Renal plasma flow was lower than normal in all patients before the induction of anesthesia. A nonsignificant trend toward increased flow was seen during hypothermic CPB. Filtration fraction was high before CPB, which suggests efferent arteriolar vasoconstriction, descending toward normal during and after CPB. The same pattern of changes was present in both groups. In conclusion, there were no clinically relevant differences between the two treatment modalities during and after CPB. However, significant differences were observed before CPB, when dopamine seemed to partially revert renal vasoconstriction. Implications: Two protective interventions were compared in patients undergoing heart surgery to prevent deterioration of renal function; these were dopamine infusion throughout the operation and phenylephrine infusion during cardiopulmonary bypass. We found clinically relevant differences only during surgery before cardiopulmonary bypass.