General Anesthesia information

Pre-anesthetic considerations:

Sometimes drugs are given before anesthesia is given. There are conditions that must be considered, like anxiety, so a sedative such as valium, which also causes anterograde amnesia another desired effect, can be given. Some drugs are given as prophylaxis to suppress some potential adverse responses to general anesthesia, or to minimize secretions (not so common anymore), to prevent bradycardia, or to minimize aspiration. Some of these substances, such as sodium citrate, are given to increase stomach pH so that if someone did aspirate, they wouldn’t aspirate such acidic material. Drugs are sometimes given for postoperative nausea. An antiemetic can be given pre-op or during the surgery to minimize problems. Some examples are:

1. Benzodiazepines are used for amnesia.

2. Barbiturates or narcotics are used as sedatives to relieve anxiety.

3. Anti-cholinergics are used to reduce secretions and prevent bradycardia.

(Note: these are being used before anesthesia)

Intraoperative Anesthesia:

5 components used during anesthesia, (with drugs that best carry out that function next to it):

1) Amnesia -- Benzodiazepines

2. Analgesia -- narcotics

3. Anesthesia – barbiturates (sodium pentathal), amidazols (atomidate), phencyclidine (ketamine), phenolic compounds like propofol (diprivan)

4. Muscle relaxation – neuromuscular blocking agents

5. Hemodynamic stability

1)Benzodiazepines given IV can work as anesthetic. It can also be used as an antiseizure med, along with being a great amnestic, and good sedative.These drugs include diazepam (Valium), midazolam (Versed).and narcotics s as well, all with some effect on BP. Depending on the patient, you choose a drug that best suits your needs for the patient.

2) Narcotics classically bind opioid receptors. Morphine is the classical example. They are agonists to opioid receptors. There are several classes of opioid receptors, being mu1, mu2, kappa, delta, and sigma. Depending on relative binding, you may see variations in respiration depression, analgesia, nausea, vomiting, and other side effects associated with opioids.

Meperidine (Demerol), fentanyl, sufentanil, alfentanil, and remifentanil are all opioids. Remifentanil is a short acting opioid. The mainstays are still morphine and fentanyl. Sufentanil is newer. 100 mg of (Demerol) = 10 mg morphine. 10 mg of morphine = 100 g of fentanyl = 10 g sufentanil. As a narcotic agonist, fentanyl is about 10 times more potent than morphine. Sufentanil is probably about 100 times more potent than morphine.

While morphine induces histamine release, and affect blood pressure, these newer drugs are cardio-stable. Patients on cardiac anesthetic procedures probably have a narcotic like fentanyl or sufentanil. Respiratory function is not as important in these patients because we’re breathing for them with respirators

3) Barbiturates The newer drugs generally bring a patient rapidly to a level 3 or 4, because they essentially stop breathing, this is not a problem because when we use positive pressure on ventilation.

Examples include sodium thiopental and methohexital (brevital). They are rapid acting intravenous agents causing significant respiratory (and sometimes cardiac) depression. Sodium pentathal is unique in that it does not cause seizures. It raises seizure threshold. Methohexital will decrease seizure threshold. For these reasons, in a patient with status epilepticus or if there is a need to intubate a patient who is seizing, sodium pentathal is used.

All barbiturates are a derivative of barbituric acid, which is a 5 carbon ring structure. Depending on the orientation of the side groups, you can have thiobarbiturates (with sulfur containing), or oxybarbiturates, like methohexital

Neuromuscular blocking agents do not promote any sense of euphoria or well being or any other functions besides complete paralysis. They must be used in conjunction with drugs that cause amnesia or you will have a patient awake and paralyzed on the table.

4) Neuromuscular Blocking Agents. They’re also known as muscle relaxants, but that’s misleading because they cause paralysis. These aren’t the drugs you would receive if you went to see your family doc for back pain and he or she gave you something that made you drowsy and you wake up with your back feeling better. These drugs do not alter level of consciousness or perception of pain. You must support or control ventilation when using these drugs and monitor the anesthetic level because the patient can be lying there in pain and awake, just paralyzed (I personally ask that this be done to me when I’m undergoing surgery because I like to feel every cut of the knife.)They interrupt nerve impulses at the neuromuscular junction (NMJ).

Succinylcholine is the one depolarizing agent used. It causes a randomized firing of muscle fibrils before causing paralysis. Patients receiving succinylcholine may have fasciculations when they first receive the med.

Nondepolarizing agents go straight to flaccid (don’t you just love this word) paralysis. You will not see fasciculations. They are all basically curare type drugs. They differ slightly by onset of action, pharmacology, duration of action and the way in which they’re metabolized. There are two groups of nondepolarizers.

One group is like pancuronium. Pancuronium is an older drug that is still used that is steroid based. Vecuronium is also a steroid class drug. As an aside, Dr. Vitkun informed us that D-Cuvocurarium is the poisoned arrow drug that was used by aborigine’s to kill prey. They’d shoot an animal and chase it until it dropped from the poison causing paralysis.

Atracurium is a bis-isoquinolonium derivative. They have a very different type of metabolism. A newer drug called cis-atracurium undergoes Hoffman elimination, meaning that elimination is solely temperature and pH dependent. Therefore, this is the drug of choice for the patient in liver or kidney failure, or both. Dr. Vitkun then reminded us that inhaled anesthetics also do not need the kidneys or liver, as they are exhaled for elimination. Even though there is some metabolism, because of the time course, the majority of elimination is through exhalation.

5) Phencyclidines Ketamine, also known at parties as special K, is a very good amnestic and analgesic. It is a dissociative anesthetic agent. It maintains respiration. You can give an induction dose and maintain blood pressure and respiration to a large extent. It is termed a dissociative anesthetic and produces a fugue state, meaning that it separates mind from body (alright now were talking). These effects can occur because phencyclidines are more commonly known as PCP or “angel dust,” thereby facilitating those effects. Because of its near relatives, ketamine has now become a controlled drug in NY. It is also known as the “date rape drug.” It has veterinary use. Interestingly, animals are LESS sensitive to ketamine than us weakly humans. This is probably in relation to how it works in the brain. It is a good drug for trauma and for asthmatics.

Negatives are the abuse potential and “emergence delirium.” “Emergence delirium” is the “medicalized” term for a “bad trip” akin to that experienced from PCP. It is in 10 – 15% of patients under Ketamine.

These drugs are used for the induction of anesthesia. Ketamine was most commonly used in children. They’re also used in trauma and burn patients to maintain blood pressure and respiration because they’re generally hemodynamically stable.

Category: Anesthesia Notes