Krzysztof M. Kuczkowski, M.D
Course : 4
Year : 2009
Language : English
Country : Moldova
City : Chisinau
Weight : 1351 kb
Related text : nohttp://www.euroviane.net
ANESTHESIA FOR
CESAREAN SECTION
Texas Tech University Health Sciences Center at El Paso, Paul L. Foster School of Medicine, El Paso, Texas, USA
Cesarean section
• Choice of anesthesia: spinal (SAB), epidural (CLE), combined spinal epidural (CSE), general endotracheal (GETA)
• When compared to regional techniques, general anesthesia can be administered with shorter induction-to-delivery time
• However, the literature suggests that a greater number of maternal deaths occur when general anesthesia is administered
Cesarean section
• The literature indicates that a larger proportion of
neonates in the GA groups, compared to those in
the RA groups, are assigned Apgar scores of less
than 7 at 1 and 5 min
• The decision to use a particular anesthetic
technique should be individualized
• Resources for the treatment of complications
should be available
Neuraxial blocks
Obstetric analgesia & anesthesia
Single dose spinal (SAB)
Obstetric analgesia & anesthesia
Epidural (CLE)
Obstetric analgesia & anesthesia
Combined spinal epidural (CSE)
The technique: CSE versus CLE
CSE: special needle design
Regional versus general anesthesia
General anesthesia
Monitoring
Monitoring
• The overall goal of anesthetic management of a pregnant woman undergoing Cesarean section is to maintain the mother and her fetus (until the umbilical cord is severed) in the best possible physiologic
condition J Clin Anesth 2006
• This requires that we effectively monitor the mother
and the fetus in the perioperative period J Clin Anesth 2006
Monitoring
1. Blood pressure (non-invasive & invasive)
2. Heart rate
3. Respiratory rate
4. Electrocardiogram
5. Oxygen saturation
6. End tidal carbon dioxide
7. Fetal heart rate
Monitoring
• The FHR monitoring is useful at identifying intraoperative conditions leading to impaired uteroplacental blood flow and fetal oxygenation prior to delivery
• A normal FHR is between 120 - 160 beats per minute with 3-7 beats variability
• Variability is decreased by hypoxia and by sedative
and other drugs of anesthesia
Premedication
Premedication
• The goals of “routine” preanesthetic medications
typically are as follows;
– first, to dry secretions
– second, to prevent vagal activity
– third, to provide anxiolysis
– fourth, to ensure analgesia for uncomfortable
anesthetic procedures (e.g., arterial line placement
prior to induction of anesthesia)
– and fifth, to provide a basal level of analgesia for
surgery
Premedication
• Sedative drugs are usually avoided in pregnancy, and
verbal reassurance may often suffice for the patient
undergoing Cesarean section under general
• In selected cases, it is not unreasonable to administer
an anticholinergic agent, which decreases secretions
and lessens the likelihood of bradycardia during
anesthesia
Premedication
• Atropine readily crosses the placenta and results in an
increased FHR, with decreased beat-to-beat
variability
• In contrast, glycopyrrolate does not readily cross the
placenta, and it is the anticholinergic agent of choice
• Unfortunately, the anticholinergic agents result in
decreased lower esophageal sphincter tone
Premedication
• When anticholinergic agent is indicated, glycopyrrolate
may be given intramuscularly 30-60 minutes before the
induction of anesthesia or intravenously just before the
administration of anesthesia
Premedication
• Metoclopramide is a procainamide derivative that is a cholinergic agonist peripherally and a dopamine receptor antagonist centrally
• A 10-mg intravenous dose of metoclopramide increases lower esophageal sphincter tone has an antiemetic effect and reduces gastric volume by increasing gastric peristalsis
Premedication
• Metoclopramide can have a significant effect on gastric volume in as little as 15 minutes
• Metoclopramide crosses the placenta, but studies have
reported no significant effects on the fetus Expert Opin Drug Saf 2006
Premedication
• The parturient should also receive 30 ml of sodium bicitrate orally prior to induction of general anesthesia for Cesarean section [to reduce gastric
acidity] Expert Opin Drug Saf 2006
Drugs of anesthesia
Drugs of anesthesia
• Although the overall use of general anesthesia has
been steadily declining in obstetric patients, in selected
cases [e.g., an emergent Cesarean section], it may still
be preferred, indicated and/or necessary Anesth Analg 1997/Expert
Opin Drug Saf 2006
• The following section reviews the drugs most
commonly employed for administration of general
anesthesia in pregnant women
Drugs of anesthesia
• Potent inhalational halogenated agents
• Nitrous oxide
• Opioid receptor agonists
• Intravenous induction agents
– Propofol
– Barbiturates
– Ketamine
– Etomidate
• Neuromuscular blocking drugs
– Succinylcholine
– Rocuronium
– Vecuronium
– Atracurium
Potent inhalational agents
• Potent inhalational halogenated agents in adults are
administered for the maintenance phase of general
anesthesia
• Those in use today include sevoflurane, isoflurane
and desflurane
• Potent inhalational halogenated agents affect the fetus
– indirectly by causing maternal hypotension and/or hypoxia
– directly by depressing the fetal CV or CNS Expert Opin Drug Saf 2006
Potent inhalational agents
• Studies in an animal model have shown minimal
maternal and fetal effects with administration of
moderate (e.g., 0.75-1.0 MAC) concentration of
volatile halogenated agents Expert Opin Drug Saf 2006
Nitrous oxide
• Uptake and elimination of nitrous oxide are rapid, as
a result of its low blood-gas partition coefficient
• It produces some analgesia, and in concentrations
greater than 60% may produce amnesia Expert Opin Drug Saf 2006
Nitrous oxide
• Because of its high solubility nitrous oxide may diffuse into the cuff of an endotracheal tube and lead to a marked increase in cuff pressure, which could result in significant airway management complications (e.g., high cuff pressure-related ischemia of the tracheal mucosa) Acta Anaesthesiol Scand 2004
• This may be particularly important in pregnant patients because of physiological changes of pregnancy, which include narrowing of the airway secondary to edema Expert Opin Drug Saf 2006
Opioid receptor agonists
• Fentanyl, sufentanil, alfentanil, remifentanil are the
most popular opioids used in the practice of obstetric
anesthesia when general anesthesia is necessary
• Their primary effect is analgesia Expert Opin Drug Saf 2006
• Opioids and induction agents decrease the FHR
variability and cause fetal depression; possibly to a
greater extent than the inhalational agents
Intravenous induction agents
• When choosing an induction agent for general
anesthesia, the primary goals are as follows:
– First, to preserve maternal BP, CO, and uterine blood flow;
– Second, to minimize fetal depression;
– Third, to ensure maternal hypnosis and amnesia Expert Opin Drug
Saf 2006
Intravenous induction agents
• Propofol
• Barbiturates
• Ketamine
• Etomidate
Propofol
• Propofol = rapid, smooth induction of anesthesia
• It has no analgesic properties
• The drug produces dose-dependent decreases in
cardiac output and arterial blood pressure
• Decreased BP results in decreased uteroplacental
perfusion Expert Opin Drug Saf 2006
Propofol
• Propofol is a lipophilic agent with a low
molecular weight, and it rapidly crosses the
placenta Expert Opin Drug Saf 2006
• Propofol blunts the hypertensive response to
laryngoscopy and intubation more effectively than
the other induction agents
Barbiturates
• Thiopental is the barbiturate commonly used for induction of anesthesia in obstetrics
• It is very short-acting and produces unconsciousness in one arm-to-brain circulation time (30 seconds)
• Thiopental decreases arterial BP and CO in a dose dependent manner Expert Opin Drug Saf 2006
Barbiturates
• Thiopental rapidly crosses the placenta, and it can
be detected in umbilical venous blood within 30
seconds of administration
• The umbilical venous blood concentration peaks
in 1 minute Expert Opin Drug Saf 2006
Ketamine
• Ketamine is a very useful induction agent in obstetric patients
• It produces unconsciousness in 30-60 seconds after intravenous induction dose, which may last for 15-20 minutes Expert Opin Drug Saf 2006
• Ketamine has a rapid onset of action, it provides both analgesia and hypnosis, and it reliably provides amnesia
Ketamine
• In addition, its sympathomimetic properties are
advantageous in patients with asthma or modest
hypovolemia Expert Opin Drug Saf 2006
• Ketamine rapidly crosses the placenta, and it
reaches a maximum concentration in the fetus
approximately 1-2 minutes after administration
Etomidate
• Etomidate is an intravenous induction agent that
has been used in obstetric anesthesia practice
since 1979
• Etomidate produces a rapid onset of anesthesia in
one arm-to-brain circulation time Expert Opin Drug Saf 2006
• It undergoes rapid hydrolysis, which results in a
rapid recovery period
Etomidate
• Etomidate causes little cardiovascular depression;
thus it is an excellent choice in patients with
hemodynamic instability
• Intravenous injection of etomidate may result in
pain and myoclonus Expert Opin Drug Saf 2006
Neuromuscular blocking drugs
• Succinylcholine
• Rocuronium
• Vecuronium
Neuromuscular blocking drugs
• A small dose of a nondepolarizing muscle relaxant may be given 3 to 5 minutes before induction of general anesthesia to prevent fasciculations after the administration of succinylcholine
• Alternatively, this small dose may serve as a priming dose if a nondepolarizing agent will be used to achieve muscle relaxation Expert Opin Drug Saf 2006
Succinylcholine
• The depolarizing agent succinylcholine remains
the muscle relaxant of choice for the obstetric
patient
• The standard intubating dose provides complete
muscle relaxation and optimal conditions for
laryngoscopy and intubation within approximately
45 seconds of i.v. administration Expert Opin Drug Saf 2006
Succinylcholine
• Succinylcholine is highly ionized and water
soluble and only small amounts cross the placenta
• Maternal administration of succinylcholine rarely
affects fetal neuromuscular function Expert Opin Drug Saf 2006
Rocuronium
• Rocuronium is a suitable alternative to
succinylcholine when a nondepolarizing agent is
preferred for rapid sequence induction of general
anesthesia
• What dose?
Rocuronium
• Only very small amounts of the nondepolarizing
muscle relaxants cross the placenta; thus the fetus
rarely is affected
Summary
Take home message
“The position of woman in any civilization is an index of the advancement of that civilization; the position of woman is gauged best by the care given her at the birth of her child.”
Haggard HW, New York, 1929.
Who wants to be an obstetric
anesthesiologist?
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