Cardiac Function During Induction and Early Anesthesia with Methoxyflurane. An Evaluation Using Systolic Time Intervals and Pressure Time Indices

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Abstract
In addition to the standard monitoring of heart rate and blood pressure, the Systolic Time Intervals were used to evaluate cardiac performance, and the Pressure Time Indices (tension time index = TTI; diastolic pressure time index = DPTI) were used to estimate myocardial oxygen balance. Twelve patients with known heart disease were studied during induction with thiopental, intubation, and early anesthesia with methoxyflurane. Cardiac performance diminished after thiopental; and during methoxyflurane it was reflected in increases in pre-ejection period (PEP) and the ratio PEP/LVET. Intubation resulted in a hyperactive state of the heart, as shown by maximal decreases in PEP and PEP/LVET. Myocardial oxygen balance--estimated from the supply/demand ratio (DPTI/TTI)--was impaired after thiopental. After intubation, DPTI/TTI decreased to its lowest value due to an excess of myocardial oxygen demand (TTI) over myocardial oxygen supply (DPTI), signifying a transitory underperfusion of the subendocardium. During methoxyflurane the oxygen balance was gradually restored towards control value. The Systolic Time Intervals and the Pressure Time Indices provided valuable information on cardiac function not available from standard monitoring alone.