(Ch 21) Local and General Anesthetics

Question 1

Anasthetic Agents / General Anesthetics

Cause what type of Physical Changes ?

Answer 1

General anesthesia involves the physiological changes:

1. Reversible loss of response to painful stimuli, loss of consciousness and loss of motor and autonomic reflexes.
2. Loss of consciousness is associated with inhibition of the activity of reticular formation.

Question 2

Type of effects Anesthetic agents have on the CNS?

Answer 2

Anesthetic agents depress the central nervous system, causing a loss of consciousness (except for local and regional anesthetic agents) and relieving pain.

Question 3

Anesthetic agents are classified as:

Answer 3

Anesthetic agents are classified as:

• 1. Local Anesthetic:* Block specific nerve pathways in a region and result in temporary analgesia and paralysis but no loss of consciousness.
• 2. General Anesthetic:* A general anesthetic used for surgery consists of one medication or a combination that causes a temporary loss of consciousness.

General Anesthetic: are classified into 2 based on their ROA as ” Inhilation and Itravenous anesthetics”

Question 4

Name the 2 Routes in which General anesthetics are administered:

Answer 4

1. inhalation or 2. intravenous routes.

They are classified into 2 on the basis of their route of administration as inhalation and intravenous anesthetics.

Question 5

General anesthetics ROA

Inhalation anestetics:

Name 4 main Agents

Answer 5

1. Halothane
2. Nitrous Oxide
3. Enflurane
4. Ether

Question 6

Halothane:

Answer 6

Halothane:

Is the most widely used agent, highly lipid soluble, potent. It causes arrhythmia, hangover and the risk of liver damage is high if used repeatedly.

Question 7

Nitrous oxide:

Answer 7

Nitrous oxide:

Oderless and colourless gas. It is rapid in action and also an effective analgesic agent. Its potency is low, hence must be combined with other agents. It is a relatively free of serious unwanted effects.

Question 8

Enflurane:

Answer 8

Enflurane:

Halogenated ether (similar to halothane). Poorly metabolized in the liver, thus less toxic than halothane. It is faster in its action, less liable to accumulate in the body fat compared to halothane. It causes seizure during induction and following recovery from anaesthesia.

Question 9

Ether:

Answer 9

Ether:

Has analgesic and muscle relaxant properties. It is highly explosive, causes respiratory tract irritation, postoperative nausea and vomiting. It is not widely used currently.

Question 10

Describe Intravenous anesthetics

Use:

Answer 10

Intravenous anesthetics act much more rapidly, producing unconsciousness in about 20 seconds, as soon as the drug reaches the brain from the site of its injection.

These agents used for induction of anaesthesia followed by inhalation agent.

The main induction agent in current use is: thiopentone, etomidate, propofol, ketamine and short acting benzodiazepine (midazolam).

Question 11

Agents used for induction of anaesthesia followed by inhalation agent.

The main induction agent in current use:

Name 5

Answer 11

1. thiopentone
2. etomidate
3. propofol
4. ketamine
5. short acting benzodiazepine (midazolam).

Question 12

Thiopentone: (IV)

Answer 12

Thiopentone:

• a barbiturate with very high lipid solubility.
• After intravenous administration the drug enters to tissues with a large blood flow (liver, kidneys, brain, etc) and more slowly to muscle.
• Uptake into body fat occurs slowly because of the low blood flow to this tissue, which may cause prolonged effect if given repeatedly.
• It causes cardiovascular depression.

Question 13

Etomidate: (IV)

Answer 13

Etomidate:

It is more quickly metabolized and the risk of cardiovascular depression is less compared to thiopentone.

Etomidate suppresses the adrenal cortex, which has been associated with an increase in mortality in severely ill patients.

Question 14

Propofol (Diprivan) (IV agent)

Answer 14

Propofol is a nonbarbiturate hypnotic agent and the most recently developed intravenous anesthetic.

• Its rapid induction and short duration of action are identical to thiopental, but recovery occurs more quickly and with much less nausea and vomiting.
• Rapidly metabolized in the liver and
• -Can be used for long durations of anesthesia, *unlike thiopental.
• Propofol is rapidly replacing thiopental as an anesthetic agent.

Question 15

Ketamine: (IV)

Answer 15

Ketamine:

- acts more slowly than thiopentone and produces a different effect, known as dissociative anaesthesia in which there is a marked sensory loss and analgesia, as well as amnesia and paralysis of movement, without actual loss of consciousness. -

Ketamine causes dysphoria, hallucinations during recovery.

Question 16

Benzodiazepines

Provide example

Use

Answer 16

Benzodiazepines

(diazepam, lorazepam, midazolam)

• are used in general anesthetic procedures.
• Compared with intravenous barbiturates, benzodiazepines produce a slower onset of central nervous system effects.
• Benzodiazepines prolong the postanesthetic recovery period but also cause a high incidence of amnesia for events occurring after the drug is administered.

The benzodiazepines are useful in anesthesia as premedication and intraoperative sedation

Question 17

Opioid analgesic anesthesia:

Answer 17

Opioid analgesic anesthesia:

Opioid analgesics can be used for general anesthesia, in patients undergoing cardiac surgery and fentanyl and its derivates are commonly used for these purposes.

Question 18

Preanesthetic medication:

Answer 18

Preanesthetic medication:

• It is the use of drugs prior to the administration of anaesthetic agent with the important objective of making anaesthesia safer and more agreable to the patient.
• The drugs commonly used are, opioid analgesics, barbiturates, anticholinergics, anti emetics and glucocorticoids

Question 19

Local anesthetic

Define:

Answer 19

Block specific nerve pathways in a region and result in temporary analgesia and paralysis but no loss of consciousness.

Question 20

General Anesthetic

Define:

Answer 20

A general anesthetic used for surgery consists of one medication or a combination that causes a temporary loss of consciousness.

Question 21

The combination of general anesthetic medication

is called?

Answer 21

A Balance

-based on the patient’s age, weight, medical history, health, and allergies.

Question 22

The balanced approach administers the general anesthetic in phases to:

Answer 22

1. Minimize cardiovascular adverse effects.
2. Decrease the amount of general anesthetic.
3. Reduce postanesthetic nausea and vomiting.
4. Minimize disturbance of organ function.
5. Increase recovery time.

Question 23

Administering General Anesthetic Agents

Provide examples:

• Night before surgery
• Hour before surgery
• Premedications

Answer 23

1. A sedative-hypnotic is administered the night before surgery to assist with sleep.
2. An hour before the surgery, premedications (anticholinergic (atropine) to decrease secretions and either a narcotic analgesic or benzodiazepine) administered to sedate and decrease anxiety.
3. In the OR, the patient is given a short-acting barbiturate (thiopental sodium; Pentothal) to induce anesthesia.

Then a general anesthetic agent is then given either by IV or combined with oxygen as an inhaled gas delivered through a mask or breathing tube.

4. A muscle relaxant may also be administered depending on the surgery.

Question 24

4 Four Stages of Anesthesia

Name and describe:

Answer 24

1. Analgesia: The patient is conscious and able to converse, but has lost the sense of pain.

2. Excitement: Breathing increases, blood pressure increases and become irregular. Delirium sets in and the patient may become violent. This stage is shortened by administering a barbiturate (sodium pentothal) before administering the anesthesia.

3. Surgical Anesthesia: Eye movement slows then stops as breathing becomes regular. Skeletal muscles relax and surgery begins.

4. Medullary Paralysis: The respiratory center (medulla oblongata) becomes paralyzed. Breathing and vital functions cease. Death occurs. However, the anesthetist adjusts the general anesthetic to prevent the patient from reaching this stage.

Question 25

INHALATION AND INTRAVENOUS ANESTHETICS

USE:

Answer 25

Depress the CNS, alleviate pain, and cause a loss of consciousness

Question 26

INHALATION AND INTRAVENOUS ANESTHETICS

Example:

Pharmacokinetic:

Answer 26

Inhalation:

Volatile liquids: halothane (Fluothane)

Pharmacokinetic:

Metabolized in liver; eliminated via respiratory methoxyflurane within 24 hours as exhaled gas

Question 27

INHALATION AND INTRAVENOUS ANESTHETICS

Adult Dose:

Answer 27

• Response to anesthesia may differ based on age, current health problems, pregnancy, history of heavy smoking, obesity, and frequent use of alcohol and drugs. The dose of anesthesia is based on all of these factors.

Question 28

INHALATION AND INTRAVENOUS ANESTHETICS

Before Admininstration:

Answer 28

• Assess patient’s medical and drug history.
• Assess use of drugs, alcohol, and other such medications (such as antihistamines, sedatives, tranquilizers, sleep aids, certain pain relievers, muscle relaxants, and antiseizure medication) for at least 24 hours, except as prescribed by the patient’s healthcare provider.
• Notify anesthesiologist/anesthetist if any of the above medications were taken or if the patient has any respiratory difficulties, fever, or other acute medical conditions.
• Determine if the patient has any allergies or has had any hypersensitivities to barbiturates or benzodiazepine in the past.
• Determine if the patient has any blood relatives who have had reactions to anesthesia such as malignant hyperthermia.
• Obtain a pregnancy test.
• Determine if the patient has any dentures, dental bridges, or loose teeth. • Complete any other preoperative procedures required by the agency.

Question 29

INHALATION AND INTRAVENOUS ANESTHETICS

Side effects / adverse reactions

Answer 29

• Patients may feel drowsy, weak, or tired and experience fuzzy thinking, blurred vision, and coordination problems for as long as a few days after having general anesthesia.
• Headache, shivering or trembling, muscle pain, dizziness, lightheadedness or faintness, mood or mental changes, nausea or vomiting, sore throat, and nightmares or unusual dreams.

Question 30

What is the benefit of using a Topical anesthetic agent? Ex…

Answer 30

Topical anesthetic agents decrease the sensitivity of nerve endings on skin surfaces.

Question 31

Forms of Topical anesthetic agents ?

Answer 31

Topical anesthetic agents are in the form of :

• solutions,*
• liquid spray,*
• ointment,*
• creams,*
• gels.*

Question 32

• Commonly used topical anesthetic agents are:*
• Name 3*

Answer 32

Commonly used topical anesthetic agents are:

1. LET: LET is a combination of lidocaine, epinephrine, and tetracaine.

2. EMLA: EMLA anesthetizes skin before IM injections, venipuncture curettage, and biopsy. EMLA is administered 90 minutes before the procedure.

3. ELA-Max: ELA-Max is an OTC medication that anesthetizes skin faster than EMLA. ELA-Max uses the liposomal delivery system where tiny lipid balls provide moisture to the skin and penetrate the cell wall.

Question 33

TAC

Topical Anesthtic agent consists of WHAT?

Admin/Onset/Duration

Answer 33

TAC (0.5% tetracaine, 1:2000 epinephrine, and 11.8% cocaine)

2–5 ml (1 ml per cm of laceration) applied to wound with cotton or gauze for 10–30 minutes;

Onset: effective 10–30 minutes after application; Duration: not established;

May be as effective as lidocaine for lacerations on face and scalp.

Rare severe toxicity, including seizures and sudden cardiac death.

Question 34

LET

Topical Agent consisting of WHAT?

Onset/Duration/

Answer 34

LET

(4% lidocaine, 1:2000 and 0.5% tetracaine)

• 1–3 ml directly applied to wound for 15–30 minutes -Onset: 20–30 minutes
• Duration: not epinephrine, established;
• Similar to TAC for face and scalp lacerations;
• less effective on extremities;
• no severe adverse effects reported

Question 35

EMLA

Consists of WHAT?

Admin/Onset/Duration

Answer 35

EMLA

(2. 5% lidocaine and 2.5% prilocaine)
- Thick layer (1–2 g per 10 cm2) applied to intact skin with covering patch of Tegaderm;
- Onset: must be left on for 1–2 hours.
- Duration: 0.5 to 2 hours;
- Variable, depending on duration of application;
- Contact dermatitis, methemoglobinemia (very rare)

Question 36

(TAC) Topical Anesthtic Agents

Iontophoresis

Answer 36

• Small current applied to lidocaine-soaked sponges on intact skin;
• Onset: 10 minutes
• Duration: 10–20 minutes.
• Good for small procedures, depth of anesthesia greater than EMLA; Stinging sensation; may burn skin if high current

Question 37

What are Local Anesthetic agents used for?

Answer 37

A local anesthetic agent blocks pain at the site where the medication is administered.

It is used for:

Suturing lacerations

Short-term localized surgery

Spinal anesthesia

Diagnostic producers

Question 38

There are 2 groups of local anesthetics:

Name:

Answer 38

1. Esters: A chemical compound formed from the reaction between an acid and an alcohol

2. Amides: An organic chemical compound formed by reaction of an acid chloride, acid anhydride, or ester with an amine; are hypoallergenic

Question 39

LOCAL ANESTHETICS:

USE:

Answer 39

• For nerve block, infiltration, epidural (also called saddle block) and spinal anesthesias.
• Also used to treat cardiac dysthymias

Question 40

LOCAL ANESTHETICS:

Example:

ROA:

Answer 40

Lidocaine (Xylocaine): Moderate-acting amide (1–3 hours)

ROA: Route: IM/SC/I V Topical

Question 41

LOCAL ANESTHETICS:

How it works:

Answer 41

• Most local anesthetics are vasodilators therefore they increase blood flow to the area of administration and increase their own absorption.

• To decrease absorption, epinephrine (1:200,000 to 1:50,000) or other vasoconstrictors are often added to local anesthetic solutions.
• Block action by blocking Na channels

Question 42

LOCAL ANESTHETICS:

Adult Dose:

Answer 42

• Local anesthetic: Injectable dose dependent on procedure; maximum dose: 4.5 mg/kg. Do not repeat within 2 hours

• • IM:* 300 mg (or 4.3 mg/kd). May repeat in 60–90 min
• • IV:* Initially 50–100 mg (1 mg/kg) IV bolus at rate of 25–50 mg/min. May repeat in 5 min.

Give no more than 200–300 mg in 1 hr. Maintenance: 20–50 mcg/kg/min (1–4 mcg/min) as IV infusion

• • Topical:* Apply to affected areas as needed
• • Dermal patch:* Apply to intact skin over most painful area (up to three patches once for up to 12 hours in a 24-hour period)

Question 43

Local Anasthetic:

Name Contraindications

Answer 43

• Do not use a vasoconstrictor on appendages such as fingers, toes, earlobes, and penis.
• Use with caution with cardiac patients.
• Hypersensitivity to amide-type local anesthetics, Adams-Stoke syndrome, supraventricular arrhythmias, Wolf-Parkinson-White syndrome.

Spinal anesthesia contraindicated in septicemia.

Question 44

Local Anasthetic:

Side effects/ adverse reactions

Answer 44

• Anxiety, insomnia, apprehension, blurred vision, loss of hearing acuity, and nausea
• CNS depression, convulsion and respiratory depression
• Cardiovascular effects. Main toxic actions are in the heart. These may cause arrhythmias, decreased contraction, hypotension, cardiovascular collapse.

Question 45

• Spinal Anesthesia*
• 1. Define Spinal Anesthesia:*
• 2. Injection site:*
• 3. Common Side Effects:*

Answer 45

1. Spinal anesthesia is a local anesthetic injected into the spinal column to produce a regional neural block.
2. The injection is in the third or fourth lumbar space.
3. Headaches and hypotension are common side effects of spinal anesthesia because of changes in cerebrospinal fluid pressure caused by the injection.

Side effects are reduced by reaming in the supine position and increasing fluids

Question 46

Spinal Anesthesia

There are 4 types of spinal anesthesia:

Answer 46

1. Subarachnoid block: The injection is into the subarachnoid space in the third or fourth lumbar space.

2. Epidural block: The injection is into the outer covering (dura mater) of the spinal cord near the sacrum.

3. Saddle block: The injection is given into the lower end of the spinal column to block the perineal area.

4. Caudal block: The injection is near the sacrum.