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S2 Lec 3 (1 of 2): Anesthesia by Dra. Alicia Bautista AAAuuuggguuusssttt 222333,,, 222000111000
ANESTHESIA
Physiological Changes during Pregnancy with Major Clinical
Anesthetic ImplicationA. Cardiovascular System
1. Increased Cardiac Output produces hyperdynamic state incworkloadpredisposes to functional murmur
Healthy female can tolerate the hyperdynamic state Gravid with heart disease inc workload precipitate
pulmonary congestion especially during labor toimmediately postpartum inc CO maximal
Provide effective analgesia continuous lumbar epiduralanalgesia
2. Increased blood volume Inc in plasma blood volume
40-50% inc plasma volume15-20% inc red cell volume
Physiologic anemiaDouble-edged sword Inc clotting factor protects patient from blood loss and
renders her hypercoagulable inc risk of thromboticevents
After delivery ask patient to ambulate
3. Aortocaval syndrome Supine position uterus is compressed against the
vertebral column impaired venous return bradycardia
and decrease BP SUPINE HYPOTENSIVE POSITION
Results from a drop in venous return for which CVScannot compensate
Sympathetic blockade due to spinal or epiduralanesthesia will interfere with the mechanism tocompensate for aortocaval compression profoundhypotension
At risk for aortocaval compression are those withlarge uterus (multiple gestation, polyhydramnios,DM)
B. Respiratory System1.
Upper airway
Generalized peripheral edema Increase vascularity of the respiratory tract mucosa Capillaries engorged In labor, airway is edematous with voluntary and
involuntary valsalva maneuver Preeclampsia
irway edematous + friable bleedingdifficulty intubation should be considered
2. Respiratory Mechanism Enlarging uterus produces upward displacement of diaphragm dec FRC 15% (thus induction of inhalation anesthesia is
faster) Dec inhalation anesthesia required Dec FRC + inc O2 consumption = predisposes the parturient to
limited o2 reserve rapid development of hypoxemia +hypercarbia during periods of apnea
C. Gastrointestinal Inc progesterone dec gastric motility, dec food absorption Inc gastrin level (of placental origin) more acidic gastric
content Enlarged uterus inc intragastric pressure dec normal
oblique angle in the gastroesophageal junction Pregnant patient should always be considered to have a full
stomach irrespective of time of last meal. Why? Gastric
emptying decreases so be very particular of last intake of yourpatient
General anesthesia should always be avoided when possibleas they are at risk for aspiration of gastric contents
Pain Mechanism in Labor
1. Pain during 1st stage laborArises from uterus and adnexae during contraction Mediated by T10-L1 spinal segment Visceral in nature Characteristics: dull, diffuse, periodic and build peaks
2. Pain during 2ndstage labor Results from distention of birth canal, vulva and perineum Mediated by afferent fibers of posterior roots ofS2-S4 nerve Somatic in character: well localized, sharp and definitive,
often constant*sabi ni docS.S.S. (Second stage, S2-S4)
Methods of Pain Relief
1. Non-pharmacologica. Childbirth education
i. Lamazeb. Mind-body intervention
i.
Hypnosisii. Biofeedbackiii. Music therapy
c. Bioelectromagneticsi. Transcutaneous nerve stimulation
d. Intracutaneous nerve stimulationi. Sterile water blocksii. Acupuncture
e. Manual healingi. Therapeutic pouchii. Massage therapyiii. Muscle tension release
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iv. Reflexologyv. Acupressure systemsvi. hydrotherapy
f. Herbal medicinei. Herbal cocktailsii. Aromatherapy
2. Pharmacologic methodsa.Systemic
i. Opioidsthe more lipid soluble is, the more freely it can
pass through and are associated with risk ofneonatal respiratory depression andneurobehavioral changes
ii. Sedative and/or tranquilizersPhenothiazinesBenzodiazepins
iii. Dissociative medications - ketamineiv. Barbituratesv. Propofolvi. Inhalational
causes dose-dependent relaxation of uterinesmooth muscle
high dose relaxes the uterus
b.RegionalPeripheral Blocks for Labor Analgesia
i. Perineal InfiltrationMost common local anesthetic technique
for vaginal delivery, mainly for episiotomyand repair
Lidocaine 5-10cc
ii. Pudendal nerve blockInvolves injection of total 7-10 mL each local
anesthetic into the right and left pudendalnerve as it passes medially to and posterior tothe ischial spine in each side of the pelvis
Goal: to block the pudendal nerve distal to itsformation by the anterior division of S2-S4 butproximal to its division into its terminalbranches
Adequate for spontaneous delivery and outletforceps delivery
Lidocaine
iii. Paracervical block
Blocks impulses from uterine body and cervixAim: block transmission through the
paracervical ganglion (FrankenhausersGanglion) which lies immediately lateral andposterior to the cervicouterine junction
Lidocaine injected to the cervix laterally 3 and9 oclock position
Complication: fetal bradycardia
iv. Neuraxial
SpinalEpiduralCombined spinal-epidural
Saddle blockModified spinal blockAffects only the sacral segmentIdeal for completion of 2nd stage labor
ANESTHESIA FOR CAESARIAN SECTION
Regional Anesthesia
Preferred technique because mother remains awake and is able tobond with her newborn upon delivery
2 most common regional techniques:
Spinal or Subarachnoid anesthesia More commonly used in the Philippines during CSdelivery
Simpler, more reliable with lesser chances of failure,faster onset of action, requires lesser drug dosagethus minimizing the risks of local anesthetic toxicityand drug transfer to the fetus
Hypotension: most common side effect(Tx: uterine displacement, IV hydration, ephedrine)
Other complications: spinal headache, high spinalblock and failed regional block
Epidural anesthesia Less severity and incidence of hypotension It avoids dural puncture which may diminish the
incidence of spinal headache With epidural catheter in place duration of anesthesia
can be prolong Requires high drug doses, delayed onset of action
prone to patchy or incomplete blockade Gold Standard: for pain relief during ALL stage of
labor
Absolute contraindications: Refractory maternal hypotension Maternal coagulopathy Treatment with once daily dose of low molecular weight
heparin within 12 hrs Untreated bacteremia
Skin infection over site of needle placement Increased in the intracranial pressure caused by masslesion
The Choice of Anesthetic Technique
- depends on three important factors:1. indication of pain relief2. condition of mother and baby3. skill of the anesthesiologist
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