Test 2- GENERAL ANESTHESIA Flashcards
Balanced anesthesia
refers to the achievement of a combination of unconsciousness, analgesia and muscle relaxation. Although all three of these factors may be achievable by using a single drug, it often requires high doses and will have undesirable side effects. Using a combination of different drugs whose actions complement each other generally allows each drug to be used at lower dose which reduces negative effects.
anesthetic plan or anesthetic protocol
he selection of a variety of drugs to be used at different stages of anesthesia and recovery is referred to as the anesthetic plan or anesthetic protocol.
‘dose sparing
Using one drug to reduce the required dose of another is called ‘dose sparing’.
The anesthetic protocol typically consists of the following:
- Drugs for premedication (at this point you usually want sedation and analgesia).
- Drugs for induction of anesthesia, to take the patient from just being sedated to being fully
anesthetized, usually this is when endotracheal intubation will happen (injectable or inhalant
anesthetic protocols can be used). - Drugs for maintenance of anesthesia (usually an inhalant with oxygen, but can be injectable).
o Additional drugs may be needed for muscle relaxation, further analgesia, prophylactic therapy (antibiotics).
o If inhalant anesthetics are not used it is termed ‘Total Intravenous Anesthesia (TIVA)’. - Drugs for recovery
o Additional drugs may be needed to ‘smooth’ the process of waking up from general anesthesia), to provide additional analgesia and sometimes will include prophylactic therapy (antibiotics).
Induction of anesthesia goes through several stages:
I. Analgesia
II. Excitement phase (we try to minimize this with our drug selection).
III. Surgical anesthesia
a. Light plane – very light anesthesia, the patient may respond to painful stimulation.
b. Medium plane – deeper anesthesia than a light plane, patient will not respond to
mild stimuli but something very painful may cause a response.
c. Deep plane – even very strong stimuli (e.g. pain) will not cause a response.
IV. Medullary paralysis (severe inhibition of the medulla oblongata resulting in loss of autonomic functions of the respiratory and vasomotor centers). You don’t want to be at this stage, get the patient to a lower stage of anesthesia ASAP or else you may end up at the next stage….
V. Death (obviously we don’t want this to happen).
When it comes time to induce anesthesia (at which point your patient is either awake or sedated to varying degrees)
When it comes time to induce anesthesia (at which point your patient is either awake or sedated to varying degrees)
Induction can be achieved with
Induction can be achieved with inhalant anesthetics alone but that is generally less preferable (see that section of the notes).
The pros of injectable anesthetic drugs are:
- They cause an extremely rapid onset of anesthesia, and this allows you to get control of the
airway very quickly by intubating the patient (and controlling the airway and thus oxygenation
of your patient is of the highest importance). - With some injectable drugs IM injection is possible which may be useful in cases where
placement of a catheter ahead of time is not feasible (like a feral cat). - They require minimal equipment (compared to inhalational anesthetics)
However there are cons as well:
- These are often controlled substances that require close monitoring, have paperwork associated
with them and serve as a potential attractant for theft or substance abuse. - You may have minimal control over when your patient awakes (which is why these are often used just for induction and then the more rapid inhalant drugs are used for maintenance,
allowing the injectable drug to be metabolized before you need to wake the patient up).
Central nervous system:
o Since our goal is to make the animal sleep just enough (and not too much) this is
monitored constantly and the plane of anesthesia assessed to make sure the patient is
not ‘too light’ and at risk for waking up or ‘too deep’ and at risk of death.
o Additionally we may be concerned about the intracranial pressure (ICP). For some patients this will not be a major concern, but if a patient has a neurologic disease or injury then increases to intracranial pressure could be very detrimental and so it is
useful to know if your drugs will reduce or increase ICP.
Cardiovascular:
o Blood pressure (usually with a doppler or other blood pressure monitor).
o Heart rate and pulse rate (these are normally the same but can differ when there is a
problem).
Respiratory:
o Breathing rate and depth. o Oxygen (by way of a ‘pulse ox’ monitor that clips to an ear or lip and measures the percentage of oxygenation in the blood) and Carbon dioxide (by way of a capnograph which attaches to the endotracheal tube and measures the end-tidal (end of breathing cycle) CO2 levels).
Skeletal system (degree of muscle relaxation):
o For most surgeries it is necessary to have skeletal muscle relaxation, it also helps for
intubation of the patient and expressing their bladder (in advance of abdominal
surgery).
o In other situations you may not want too much skeletal relaxation, eye surgery is a great
example of this (because as the periocular muscles relax the eye will ‘roll down’ and
make work on the cornea difficult).
Other systems:
o Renal system: We are mostly concerned about whether and how much our drugs may cause risk of renal injury or a decrease in glomerular filtration (GFR). o Reproductive system: Most important if anesthetizing pregnant animals (effects on uterus and fetus). o Miscellaneous: Unique effects of clinical importance for any given drug or class of drugs.
The pros of inhalant anesthetic drugs are:
- You have control of the airway and ventilation
- You have close control over drug uptake and elimination
