Balanced anesthesia is an anesthetic method for surgical patients during their operation, which was proposed by John Lundy in 1926. The purpose of balanced anesthesia is not only to be less dangerous than using only one drug for general anesthesia but also to minimise the potential adverse side effects which may be caused by the anesthetic agents. The concept of balanced anesthesia is that of applying two or more medications or techniques in order to ease pain, relax the muscles, and have autonomous reflexes suppressed in the patient. In other words, it is an anesthesia method to maintain stable vital signs. There are numerous factors that come into play when the anesthetist decides to use this method of anesthesia. These factors include, but are not limited to: patients' major organ functions, general condition and compensatory capacity. By making use of adequate types and appropriate amounts of agents and accurate anesthesia methods, the anesthetist will promote a successful, safe, and efficient surgery.
Principles of pharmacokinetics
The scope of pharmacodynamics is the effects caused on the body by a medicine. However, the distribution of medicine, clearance and the concentration of medicine in tissue, blood or plasma are part of the pharmacokinetic features of the medicine. Using the anesthetic injection medicine, which is a portion of balanced anesthetic techniques, can be made like a single intermittent dose or as a single injection. It should keep a constant rate infusion (CRI) during the time. Both the foreseeable pharmacodynamic effects and foreseeable concentration of plasma can be offered by the CRI of specific medicine. It has similarity on keeping the invariable concentration of end-tidal by using the vaporous precise device, which can provide the volatile anesthetic.
When the administration rate exceeds the clearance rate, a stable-state concentration has been achieved by delivering the medicine as a CRI. In addition, if the medicine has distributed fully at equilibrium in the body, which is called the volume of distribution at a stable state. In case the loading dose was administered after the CRI, the time period of which will keep the concentration at a stable state equals 3 time constants or 5 terminal half-lives of the specific medicine. The bolus dose can full with the volume of the medicine in an efficiently and effectively way in order that the medicine can be cleared and delivered. This also can promote to achieve the stable state in a prompter approach.
Administering a CRI has two important methods: targeting the infusion rate, and making the infusion rate constant. Make the infusion rate constant It is relatively simple to make the infusion rate stay stable and supposed that the stable-state concentration is gained on the basis of proper distribution. Whereas, due to the saturated state of tissues and the same rate of infusion, it has the possibility to exceed the clearance rate and cause a higher concentration in plasma than the expected concentration. Hence, for this modality, it is necessary to adjust the CRI as the time goes by. Target the infusion rate This type of infusion rate is changed based on the specific rate constants. These rate constants control the movements of medicine in the compartments on the basis of saturated state of the tissues, which is decided by the study population in prior pharmacokinetic studies. Because a large amount of knowledge about the specific pharmacokinetic constants and the target-controlled infusion system which is made up of the computer program and the syringe pump needs to be known, it is extremely difficult to set up the target infusions in clinical conditions. Therefore, making the infusion rate constant are applied more widely than targeting the infusion rate.
Frequently used anesthetic agents
The quantity of a single anesthetic which is used for balanced techniques has similarity with that which is used for standing sedation. However, compare to the doses used for TIVA (total intravenous anesthesia), which is always lower than using the single anesthetics. The doses of anesthetics required differ, and depend on the required duration of anesthesia, the requirements for anesthesia to volatile, expected pain of injection of anesthesia, the experience the anesthetist using various medicines, and other factors.