Anesthetics are used to relieve people of the feeling of pain.
There are three types of anesthetics based on their site of action:
- Local anesthetic
- Regional anesthetic
- General anesthetic
Local anesthetic
Local anesthetics are applied when very specific parts of the patient are to be made numb.
Examples:
- Dentists giving anesthetic injection before performing a root canal operation
- Numbing out a toe before removing infected nail
- Applied in low doses around hip during delivery to numb off labor pain (the injections for this are generally given in the spinal discs located between vertebrae)
These can be of 2 kinds:
- Topical (applied externally as a cream, gel or spray)
- Injected (the anesthetic is injected with the use of a syringe for deeper effect)
Sometimes a topical anesthetic is applied before giving the injection (to avoid the pain of injection or of the drug itself) for deeper anesthetic so as to numb out the pain of injection also.
Local anesthetics bind with the neurotransmitters of that area thus blocking their receptors making them essentially unavailable for transporting pain signals.
These are very simple with ultra rare cases of any long-lasting effects and can thus be safely administered by a standard medical practitioner.
Example: Procaine, Lidocaine
One of the problem with these drugs is that they are vaso-dilators (they expanding blood vessels) and can sometimes cause excessive blood loss. This is easily counter-acted by epinephrine.
Regional anesthetic
Regional anesthetics are applied when a larger part of the body is to be numbed out.
Examples:
- Numbing a whole foot (applied at the hip of that particular foot so that the whole set of nerves transporting signals to and from that foot get blocked)
Sub-categories:
- Peripheral regional anesthesia
Administered to numb-out usually a limb - Central anesthesia (not same as general anesthesia)
It involves an injection into the cerebro-spinal fluid or the epidural space just outside spinal canal
Regional anesthetics are generally local anesthetics applied in larger quantity at strategic sites so that the whole bunch of nerves going to the targeted region get blocked.
These generally need more precautions than local anesthetics since it has higher chance of something going wrong.
Women who have given birth are probably very familiar with the central anesthetic technique known as an epidural. In this procedure, an anesthesiologist inserts a catheter into the epidural space, typically in the lower back area. This continuously feeds drugs such as lidocaine as well as fentanyl or clonidine to provide pain relief, resulting in a loss of sensation from the waist down.
Spinal blocks, which are injected into the cerebrospinal fluid, are often used for other procedures below the waist, such as Cesarean sections or hernia surgery. They tend to paralyze further than epidurals.
General anesthetic
General anesthetics are used when the patient needs to be “put under” or made completely unconscious.
Examples:
- Knee replacement
- Heart bypass
Much less is known about the exact functioning of general anesthetics, but so far it has been understood that these function in the fat-based medium of the cells.
The current accepted theory is that they affect the spinal cord (which is why you end up immobile), the brain stem reticular activating system (which explains the unconsciousness) and the cerebral cortex (which results in changes in electrical activity on an electroencephalogram).
A whole team of anesthetic specialists is needed when the patient is to be put under general anesthetic so that their condition can be constantly monitored and corrective procedures taken in case the patient’s condition gets worse.
- Nitrous-Oxide is a popular choice for use as general anesthetic, it is administered in the form of inhaled gas.
- Other types of general anesthetics(like Valium) can also be administered through an IV line.
- It is quick to start its effects and similarly quick to wear off.
Notes:
- You’ll most likely be instructed not to eat for several hours before surgery. It’s possible for someone under general anesthesia to aspirate, or breathe in, the contents of the stomach.
- When you’re under general anesthesia, you’ll be wearing a breathing mask or breathing tube, because the muscles become too relaxed to keep your airways open.
- Several different things are continuously monitored while you’re under – pulse oximetry (oxygen level in the blood), heart rate, blood pressure, respiratory rate, carbon dioxide exhalation levels, temperature, the concentration of the anesthetic and brain activity. There’s also an alarm that goes off if your oxygen level drops below a certain point.
- There are 4 stages of general anesthesia
- Induction: The patient is given the medication and may start to feel its effects but hasn’t yet fallen unconscious.
- Excitement: Twitching and irregular breathing patterns or heart rates. Patients don’t remember any of this as they are unconscious. Very short stage which progresses rapidly to next one.
- Relaxed/Anesthetized: The muscles relax and breathing becomes regular. This is the target stage.
- Overdose: This isn’t part of the regular process. This overdose can result in halting heart or breath which may lead to brain damage or death if swift action isn’t taken.
Procedural Sedation (Bonus category)
Procedural sedation is much like general sedation in terms of its area of effect (it also works on the whole body) but in way milder doses.
The patient is usually awake and can respond to questions, but is not necessarily aware of what’s happening to/around him. The patient is usually in a sleepy and relaxed state.
Due to low dosages, the side-effects observed with general anesthesia are usually not observed in case of procedural sedation.
Alternate names:
- Conscious sedation
- Twilight anesthesia
Care needs to be taken that the patient doesn’t slip into deeper sedation state.
Notes
- Normally anesthetics are administered with analgesics that also help in dulling-down the pain.
- While administering anesthetics, many-a-times some kind of vaso-constrictor is used to counter-act the vaso-dilator action of the anesthetic
- Local anesthetics are usually mixed with different diluents including (but not limited to)
- Sterile saline solution
- Sterile distilled water
- Spinal Fluid
- Sterile dextrose solution (for hyperbaric technique)
- Hyperbaric solutions in spinal anesthesia are solutions that have a density greater than that of spinal fluid.
- After surgery, the patient goes to a PACU (post-anesthesia care unit).
- Often the patient will be given warm IV fluids to counteract both the dehydration resulting from anesthesia as well as shivering from changes in body temperature.
- As analgesic effect wears off, the patient also receives some sort of pain-relief medication.
Questions
- Why do general anesthetic medicines only affect those part of brain related to conscious/non-autonomic functions?
- Can the patient who is put under general anesthetic still see dreams?
- Why are heart-beats and breathing not as affected as the sensory receptors?
- As we move from sea-level air pressure to lower air pressure areas at higher altitude, we adjust our breathing without us giving it even a single conscious thought, if a patient under general anesthetic were to face such change in pressure will their body handle that change itself or will it cause any complication?
Disclaimer
I am not a doctor and I don’t pose as one on the internet. This post is just a compilation of what I found while learning about this topic.