Balanced Anesthesia Achieved by Combining Anesthesia Agents
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What is Balanced Anesthesia?
General anesthesia renders you unconscious and unable to feel or respond to the operation. In fact, that is the definition of general anesthesia. There are several major goals of general anesthesia. It goes without saying that the anesthesiologists' job is to provide these (or as many as possible) while keeping the patient alive and safe. During general anesthesia, several goals are accomplished by the induction of unconsciousness. Among the goals of an anesthetic are:
- Anesthesia- Inability to feel pain
- Amnesia- lack of memory of the events
- Immobility- no voluntary or involuntary movement (important for surgical precision)
Obviously, strong medications must be used to induce such a dramatic change in the human body. All medications have side effects, which are usually worse with increasing amounts of the drug.
In order to achieve all of the above goals of anesthesia AND minimize the side effects of using large doses of a medication, "balanced anesthesia" is given. This refers to the practice of using smaller doses of many different kinds of medication rather than higher doses of fewer medicines.
Balanced Anesthesia Medications
Anesthesia Induction - Example
Anesthesia Agents Used in Balanced Anesthesia
General anesthesia can be divided into 3 main phases, the induction, the maintenance and the emergence phase. Different medications may be used in these phases to achieve the desired goals, although there may be significant overlap.
The "going to sleep" phase is called induction. Medications that induce amnesia include midazolam (often given as a premedication), before even going to the operating room.
During induction, the goal is to achieve a state of unconsciousness, maintain hemodynamic (heart, blood pressure, etc) stability and allow the placement of a breathing tube (ETT) or other breathing device. This last task requires a state of 'sleep' deep enough (really, unconsciousness) that normal reflexes like cough and gag are suppressed. It takes very strong drugs to achieve this. A combination of a narcotic pain medicine, a hypnotic/sedative and muscle relaxants (paralytics) are used so that this can be done while maintaining adequate vital signs without the patient reacting (by reflex) to this procedure. Oxygen is a component of every phase of anesthesia.
There is significant variability in the induction sequence for general anesthesia. Which drugs are actually used changes from case to case and is determined by the procedure, the type of airway device used (endotracheal tube vs. laryngeal mask airway-LMA), the medical condition of the patient and the anesthesiologist's preference. If the goals of anesthesia are achieved, there is no right or wrong way to induce the anesthesia.
In the O.R., a common sequence of medicine given into the intravenous line (IV) might include any combination of the following (or others):
narcotic pain medication
adjunctive agent to prevent burning from propofol, but has some sedative and airway-calming action
fast-acting muscle relaxant to facilitate endotracheal tube placement
The goal of the maintenance phase is to keep the patient unconscious, pain-free, with good muscle relaxation (paralysis) while also ensuring that he or she is safe and stable.
The anesthesia gases provide unconsciousness and have pain-fighting properties. By themselves, however, they have the capacity to slow the heart rate and lower the blood-pressure too much. So, the concentration of the gas can be decreased and narcotic pain medications can be used during this phase to block pain receptors. If the narcotics were used alone, they are good pain blockers, but don't have reliable ability to ensure amnesia or unconsciousness. Neither of those classes of drugs can give enough muscle relaxation to provide good conditions for the surgeon to operate in some cases. A muscle relaxant only paralyzes the muscles and does not induce unconsciousness or provide pain relief.
So, a narcotic pain medicine, an anesthesia gas and muscle relaxant may be combined. In this way, the goals are met by balancing the best qualities of each medicine while minimizing the side effects of each. This is just one simplified example of how the anesthesia drugs may be combined to provide balanced anesthesia.
Type of Medication
Sevoflurane, Desflurane, Isoflurane
Fentanyl, Morphine, Diluadid, Demerol
Narcotic Pain Medication
Rocuronium, Vecuronium, Mivacurium
Immobility, Relaxation of muscles for better surgical conditions
Added to other gases to decrease amount of them used
During emergence, the anesthesia gas or other hypnotic agent is stopped so the patient can awaken. Some anesthesia agents have reversal agents that may or may not need to be used. Most just wear off with time, though. More pain medicine or anti-nausea medicine may be given at this time. Oxygen is supplied during the awakening phase, as well.
Each stage of anesthesia has specific goals. Balanced anesthesia can be used from the induction, through the maintenance and during emergence to make the anesthetic as safe and effective as possible.
Your anesthesia provider will be monitoring your vital signs continuously during your general anesthetic. Heart rate, heart rhythm, blood pressure, oxygen level, breathing and other indicators are used to decide what medications should be throughout your operation. The selection of medications during each phase is influenced by your particular needs and reactions to the medicines and even the surgical procedure. It is the years of training that an anesthesiologist goes through that gives him or her the experience to make these decisions.