Correlation of oxygen uptake and cardiovascular dynamics during N2O-fentanyl and N2O-thiopental anesthesia in the dog

Accurate measurement of oxygen consumption in children undergoing cardiac catheterization

Oxygen consumption (VO(2) ) is an important part of hemodynamics using the direct Fick principle in children undergoing cardiac catheterization. Accurate measurement of VO(2) is vital. Obviously, any error in the measurement of VO(2) will translate directly into an equivalent percentage under- or overestimation of blood flows and vascular resistances. It remains common practice to estimate VO(2) values from published predictive equations. Among these, the LaFarge equation is the most commonly used equation and gives the closest estimation with the least bias and limits of agreement. However, considerable errors are introduced by the LaFarge equation, particularly in children younger than 3 years of age. Respiratory mass spectrometry remains the "state-of-the-art" method, allowing highly sensitive, rapid and simultaneous measurement of multiple gas fractions. The AMIS 2000 quadrupole respiratory mass spectrometer system has been adapted to measure VO(2) in children under mechanical ventilation with pediatric ventilators during cardiac catheterization. The small sampling rate, fast response time and long tubes make the equipment a unique and powerful tool for bedside continuous measurement of VO(2) in cardiac catheterization for both clinical and research purposes.

Vascular aging and hemodynamic stability in the intraoperative period

The proportion of elderly people in the population is steadily increasing, and the inevitable consequence is that this subpopulation is more frequently represented in common medical procedures and surgeries. Understanding the circulatory changes that accompany the aging process is therefore becoming increasingly timely and relevant. In this short review, we discuss aspects of vascular control in aging that are particularly relevant in the maintenance of intraoperative hemodynamic stability. We subsequently review the effects of certain notable anesthetic agents with respect to the aging vasculature.

The pharmacology of anesthetic drugs in elderly patients

Elderly patients are more sensitive to anesthetic drugs than younger patients. This increased sensitivity has a pharmacokinetic basis if the dose produces a higher drug concentration in an elderly patient than in a younger patient. The increased sensitivity has a pharmacodynamic basis if the same concentration produces a more profound drug effect in elderly patients. This article reviews the mechanisms of increased sensitivity of elderly patients to opioids, hypnotics, amnestica, and muscle relaxants.

Determination of cardiac output and other reference physiology parameters in lightly anesthetized dogs

1. Cardiac output; arterial, pulmonary artery, central venous and pulmonary wedge pressures; heart rate, hematocrit, and plasma sodium and potassium; arterial and mixed venous blood gases; and respiratory rates were measured in 45 mixed sex, non-pregnant, clinically normal mongrel dogs of 8-30 kilograms body weight following light anesthesia with halothane/50% N20-02. 2. Arithmetic means and standard deviations were calculated to develop tables of reference values. 3. Mean measured cardiac outputs were found to be 31-59% higher in these dogs than the values indicated by published standards; cardiac indices were 30-44% higher; heart rates were 16-30% lower; calculated stroke volumes were 60-112% greater; and total peripheral resistances were 35-57% less than the standard published values. 4. All other measured or calculated parameters fell within previously published canine or human reference limits.

The effect of dopamine, atropine, phenylephrine and cardiac pacing on oxygen consumption during fentanyl-nitrous oxide anaesthesia in the dog

In animals deeply anaesthetized with fentanyl and nitrous oxide the arterial blood pressure and heart rate were increased using dopamine, atropine, electrical pacing and phenylephrine in order to study the accompanying change in whole body oxygen consumption. Seven dogs (16-24 kg) were anaesthetized with fentanyl 1 microgram . kg-1 . min-1. After completing instrumentation a dopamine infusion was started at a rate of 39 micrograms . kg-1 .min-1. After the mean blood pressure reached 18.6 kPa the infusion was reduced to 10 micrograms . kg-1 . min-1 and maintained for 10 minutes. After waiting 45 minutes an infusion of atropine 20 micrograms . kg-1 . min-1 was started and when the heart rate reached 120 b/min the infusion was slowed to 1.25 micrograms . kg-1. min-1 and maintained for 10 minutes. Twenty-five minutes later the heart rate was increased to 150 beats/min and maintained at that level for 10 minutes using electrical pacing. The pacing was removed and an infusion of phenylephrine 5 micrograms . kg-1 . min-1 was started. When the blood pressure reached 21.3 kPa the infusion was reduced to 2.5 micrograms . kg-1 . min-1 and maintained for 10 minutes. The results show increases in oxygen consumption of 14 per cent with dopamine, 19 per cent with atropine, 16 per cent, and 14 per cent with phenylephrine. All changes were significantly different from the control values. The magnitude of change in whole body oxygen consumption was best predicted by either the cardiac output X blood pressure product or by the cardiac output alone.