Analgesia and Anesthesia

Analgesia and Anesthesia

Anesthesia : abolition of pain perception by interrupting the nerve impulses going to the brain. Loss os sensation may be partial or complete, sometimes with loss of consciousness.

Analgesia : state in which there is allevation of the sensation of pain with no loss of consciousness.

Systemic Analgesia

► Systemic analgesia is the major method of analgesia for women in labor when personnel trained in regional are not available.

► Systemic analgesic cross the blood-brain barrier (BBB) to provide central analgesic effects. They also cross the placental barrier. The effect on the fetus depend on the maternal dosage.

► Route of administration is IV and IM.

► Classes of analgesic drugs:

1. Narcotic Analgesic compound:

Such as Meperidine (Demerol) and Fentanyl (Sublimaze), are especially effective for the relief of severe, persistent, or recurrent pain.

● Meperidine is the most commonly used narcotic for women in labor.
After IV injection :
- onset is (30 seconds)
- Maximum effect is reached in 5 to 10 minutes.
After IM injection :
- Peak effect is reached in 40-50 minutes
- Duration about 3 hours



To minimize neonatal depression, birth should occur less than 1 or more than 4 hours after IM injection.
Tachycardia is a possible side effect.


2. Mixed Narcotic Agonist-Antagonist Compounds:

An agonist is an agent that activates something, an antagonist is an agent that blocks something from happening.

Mixed narcotic agonist-antagonist compounds such as butorphanol (Stadol) and nalbuphine (Nubain), in the doses used during labor provide analgesia without causing respiratory depression of the mother or neonate.

Note: if the women has a preexisting narcotic dependency, the antagonist effect of these compoundswill cause her to immediately exhibit symptoms of narcotic withdrawal.

3. Analgesic Potentiators (Ataractics):

These ataractics do not relieve pain but decrease anxiety apprehension, as well as potentiate narcotic effects.

This potentiation effect causes two drugs to work together more effectively so that the addition of an ataractic allows the narcotic dosage to be reduced.

Analgesic potentiators include: promethazine (phenergan), propiomazine (largon), hydroxyzine (vistaril), and promazine (sparine).

Fetal or neonatal problems rarely develop with these drugs.






Nerve Block Analgesia and Anesthesia (Local Anesthesia)

Most of loca anesthetic drugs are related chemically to cocaine and carry the suffix caine.

The principal pharmacologic effect of local anesthetics is the temporary interruption of the conduction of nerve impulses.

Examples of common agents given are lidocaine ,bupivacaine, chloroprocaine, tetracaine, mepivacaine.

Classes of local anesthesia:

1. Local Infiltration Anesthesia:

Local infiltration anesthesia of perineal tissue is commonly used when an episiotomy is to be done and when time or the fetal head position does not permit pundendal block to be administered.

Procedure: done by injecting an average of 10 to 20 ml of local anesthetic with 1% lidocaine into skin and then subcutaneously into the region to be anesthetized.
Epinephrine often is added to the solution to intensify the anesthesia in a limited region and to prevent excessive bleeding and systemic effects by constricting local blood vessels.







Pudendal Block:

Is useful for the second stage of labor, episiotomy, and birth.

Pudendal nerve block does not relieve pain from uterine contractions, it does relieve pain in clitoris, libia majora and minora, and the perineum.

Procedure: the pudendal nerve traverses the sacrosciatic notch just medial to the tip of the ischial spine on each side. Injection of an anesthetic solution at or near these points will anesthetize pudendal nerve.

Because of the anesthesia the bearing-down reflex is lessened or lost completely.

Pudendal block does not change maternal hemodynamic or respiratory functions, vital signs, or fetal heart rate (FHR).

2. Subarachnoid (Spinal) Anesthesia:

In subarachnoid anesthesia local anesthesia is injected through the third, fourth, fifth lumber interspace into the subarachnoid space, where the medication mixes with cerebrospinal fluid.

Procedure: The low spinal (saddle) block injection is made with the women in a sitting position, and her legs over the side of the delivery table. The nurse stand in front of her. The women rests her chin on her chest, arches her back, and leans on the nurse for support.

This position is assumed to widen the intervertebral space for ease in inserting the spinal neddle and to allow the heavy anesthetic solution to gravitate downward.

After anesthesia injection the women remains upright for a period of 30 seconds to 2 min to permit downward diffusion. Then the women is assisted to a supine position with head elevation slightly.

Onset of anesthesia usually occurs within 1 to 2 min after injection.

Because the mother is not able to sense her contractions, she must be instructed when to bear down.


Epidural Block:

Used for relief pain of uterine contractions.

The portal of entry into the epidural space is through either a lumber intervertebral space or through the sacral hiatus and sacral canal.

Complete lumber epidural block requires block from T10 to S5, but for cesarean birth a block is essential from at least T8 to S1.

The diffusion of epidural anesthesia depends on the volume of anesthetic agent used and on the women’s position.
For induction of lumber epidural anesthesia, the women is positioned as for a spinal injection (sitting). For modified lateral position the women is placed on her side, shoulders parallel, legs slightly flexed, and back arched.

The women is positioned preferably on her side to avoid weight of the uterus on ascending vena cava and descending aorta, which can impair venous return and decrease placental perfusion.

The laboring women will not be aware of changes in strength of uterine contractions or descent of the presenting part. Occasionally depression of contractions may result, necessitating augmentation of labor with oxytocin.




Contraindications to Subarachnoid and Epidural Blocks:

1. Patient refusal.
2. Antepartum hemorrhage.
3. Anticoagulant therapy or bleeding disorder
4. infection at the injection site
5. allergy to anesthetic drug
6. history of spinal injury, spinal surgury, or CNS disease.
7. marked hypotension.


General anesthesia :

General anesthesia is rarely indicated for uncomplicated vaginal birth and it may be necessary if there is contraindication (including patient refusal) to nerve block anesthesia.

The women is not awake with this method, and there is danger of respiratory depression and vomiting followed by aspiration. For women with hypovolemia, general anesthesia is safer than nerve block anesthesia

Thiopental sodium (Pentothal) is commonly used for general anesthesia. Administered IV (4 mg per kilogram of body weight), thiopental sodium produces rapid induction of anesthesia and does not depress the fetus in this dosage.

In general anesthesia the nurse gives the women nothing by mouth and sees that an IV infusion is established. If time allows, the nurse gives the women with oral antiacid such as sodium citrate (30 ml) to increase gastric PH to neutralize acid contents of the stomach.

Combination Anesthesia for Cesarean Birth:

Light general anestheisa, considered by many to be ideal for cesarean birth, is achieved with a combination of thiopental, nitrous oxide-oxygen, and succinylcholine.

The women is given 100% oxygen for 3 mintues, followed by almost simultaneous rapid administration of thiopental and succinylcholine.
During intubation cricoid pressure is maintained, often by nurse, to prevent aspiration of vomitus.




























Summary

We talked about:
1. Definition of analgesia (state in which there is allevation of the sensation of pain) and anesthesia (abolition of pain perception by interrupting the nerve impulses going to the brain).

2. system analgesics and its types (Narcotic Analgesic compounds, Mixed narcotic agonist-antagonist compounds, and analgesic potentiators).

3. local anesthesia and its types (local infiltration anesthesia, pudendal block, subarachnoid (spinal) anesthesia, and epidural block).

4. General anesthesia.

5. Combination anesthesia for cesarean birth.