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Haemodynamic monitoring. Problems, pitfalls and practical solutions
L L Bossaert1, H E Demey, R De Jongh
1Department of Intensive Care, University of Antwerp-University Hospital, Edegem, Belgium.
Drugs
|June 1, 1991
Summary
Optimizing oxygen delivery (DO2) is crucial for cellular energy production. Key factors include cardiac output, hemoglobin levels, and oxygen saturation, which are vital for monitoring critically ill patients.
Area of Science:
- Cardiology
- Critical Care Medicine
- Physiology
Background:
- Cellular adenosine triphosphate (ATP) synthesis relies on oxygen delivery and glucose metabolism.
- Peripheral cells depend entirely on circulation for oxygen; shock signifies cellular oxygen deprivation.
- Traditional vital signs lack sensitivity for predicting mortality or guiding therapy in critically ill patients.
Purpose of the Study:
- To highlight the inadequacy of conventional monitoring variables in critically ill patients.
- To emphasize the importance of oxygen transport and consumption parameters for assessing circulatory and metabolic function.
- To discuss the multifactorial approach required for optimizing oxygen delivery (DO2).
Main Methods:
- Analysis of factors influencing oxygen delivery (DO2): cardiac output, hemoglobin concentration, hemoglobin oxygen saturation, and oxygen-hemoglobin binding affinity.
- Evaluation of the oxygen-hemoglobin dissociation curve (p50) and its modulators (temperature, pH, pCO2, phosphorous).
- Discussion of ventilation strategies (FiO2, PEEP) and their impact on hemodynamics.
- Exploration of cardiac output determinants (preload, afterload, contractility, heart rate) and therapeutic interventions.
Main Results:
- Optimal hemoglobin concentration for viscosity is 90-100 g/L, but 100-115 g/L (or 30-35% hematocrit) is better for oxygen transport.
- Maintaining arterial oxygen saturation (SaO2) >90% requires careful adaptation of ventilation and inspired oxygen fraction (FiO2).
- Cardiac output is the most manipulable factor, influenced by preload, afterload, contractility, and heart rate, with specific therapeutic targets and agents discussed.
Conclusions:
- Calculated oxygen transport and consumption parameters are superior for monitoring critically ill patients compared to traditional variables.
- Optimizing DO2 requires a comprehensive understanding and manipulation of cardiac output, hemoglobin dynamics, and oxygen saturation.
- Effective management of shock and cellular oxygen deprivation necessitates a tailored approach to hemodynamic and metabolic support.