introduction to obstetric anesthesia

1. Obstetric anaesthesia
Dr/Ismail Ahmed
Anesthesia consultant
MD al azhar university Egypt

2. OUTLINE
•Physiological changes of pregnancy
•Analgesia for labour
•Anesthesia for caesarean delivery
•Obstetric emergencies
•CPR in pregnant patients
•Fetal Monitoring
•Anesthesia in Pregnancy for Non-Obstetric Surgery

3. Physiological changes of pregnancy
Changes to anatomy & physiology
Most changes to physiology occur during the 1st trimester
Most changes to anatomy occur during the 2nd and 3rd trimester
 anesthetist you must have a good understanding of these changes
Respiratory and airway Changes
Cardiovascular Changes
GI/Hepatic/Renal /hematological Changes
Changes in CNS

4. Respiratory Changes
• Weight gain
• Breast enlargement
• Vascularity of the respiratory tract mucosa
• Possible edema of the oropharynx, nasopharyx, and vocal cords (**most prevalent in
preeclampsia Progesterone-beneficial
• Intra abdominal pressure increase
• oxygen consumption ~ 20% (100% in labor) due to increased
metabolic rate
* minute ventilation ~ 50% (due to increased tidal volume)
* arterial pCO2
* FRC causing a decrease in oxygen reserves

6. Airway changes
•*Venous engorgement of airway mucosa
•*Edema of airway mucosa
•*Worsening of Mallampati score in labor
*Trauma to upper airway with suctioning, intubation
*Increased incidence of difficult/failed intubation x10
*Require smaller ETT

7. Cardiovascular changes
• Almost all the changes seen are due to high levels of progesterone
•*35% Total Blood Volume
•* heart rate 15 beats/min
•*40% CO
•*30% SV
•*15% SVR
•*500ml/min blood flow to uterus
•* venous return from legs
•*AORTOCAVAL COMPRESSION (mechanical)

8. VARIABLE CHANGE AVG CHANGE
Blood Volume *Increase *+ 35%
Plasma Volume *Increase
*Modifies
Transfusion
Requirement
*+ 45%
Stroke Volume Increase + 20%
Heart Rate Increase + 40%
Femerol (Uterine) venous
pressure
Increase + 30%
Total Peripheral Resistance Decrease - 15%
Mean Arterial Pressure Decrease - 15 torr
Systolic Blood Pressure Decrease 0 to - 15 torr
Diastolic Blood Pressure Decrease - 10 to - 20 torr
Central Venous Pressure - - - - - - - - No Change

9. •*Patients with pre-existing cardiac disease may decompensate
either during labor or immediately post delivery. This corresponds to
the time of maximal CO
•*Approx. 400 – 600ml blood loss occurs at delivery
•*Supine hypotensive syndrome Aorto-Caval Syndrome
• Hypotension 20 weeks gestation Gravid Uterus Weight Can Decrease C.O
30%
Management Plan
Pre-induction hydration
Left Uterine Displacement (or RUD)
Ephedrine/Phenylephrine
Venal Caval Compression
Distention of epidural venous plexus
Decrease LA dose 1/3 (>14 wks)

10. Gastrointestinal Changes
• Stomach displaced upward and 45 to the right & displaces the intra-abdominal
segment of the esophagus into the thorax decreased tone of the lower esophagus
• Delayed gastric emptying
• *Increased gastric fluid volume
• *Increased gastric fluid acidity
• *Decreased competency of lower esophageal sphincter
• *Increased risk of aspiration
• *All parturients are “full stomach”
• *Aspiration prophylaxis recommended for C/S
• * Sodium citrate 30 mls po
• *Ranitidine 50mg iv
• *Metoclopramide 10mg iv

11. CNS CHANGES
•*Decrease in MAC by 25 – 40%
•*Decreased dose of Local Anesthetic requirement for
regional techniques
•*More rapid onset of neural blockade
• *Decreased inhalation anesthetic agent requirements
•*Decreased dose of local anesthetic for same effect
•*Increased risk of local anesthetic toxicity

12. Haematological changes

13. Analgesia for labour
*Where is the pain coming from?
*Is pain bad in labor?
Psychological stress cause increased levels of catecholamines
And hyperventilation These may result in decreased
uterine blood flow leading to hypoxia and acidosis in the fetus
*Analgesic options ?
• *Non-medication
• *Inhalational
• *Parenteral
• *Regional

14. • Breathing exercises ,Acupuncture, Music,Massage, Water bath
• *Nitronox: 50:50 mixture of oxygen and nitrous oxide *Low dose
desflurane(0.2%),Isoflurane(0.20.25%),Sevoflurane(0.8%) in oxygen
variable efficacy, nausea,drowsiness, loss of airway reflexes
Narcotics: meperidine, morphine ,fentanyl
nausea, vomiting, sedation,neonatal depression (max. 2 hours aftermeperidine dose), short
duration of action.
• Lumbar Epidural
• Spinal
• Combined Spinal Epidural (CSE)
• Continuous spinal analgesia
• Paracervical block
• Lumbar sympathetic block
• Pudendal block
• Perineal infiltration

15. Anesthesia for caesarean delivery
• GENERAL CONSIDERATIONS
Altered physiology as mentioned
Altered response to anesthesia
Intraoperative effects on uteroplacental blood flow
Effect of the disease process/therapies
SO
• Avoidance of hypoxemia
• Avoidance of hypotension
• Avoidance of acidosis
• Maintain PaCO2 in the normal range for the parturient
• Minimize effects of aortocaval compression

16. • * Preparation
Premeds: antacid (sodium citrate),IV access and fluid bolus(avoid glucose containing fluids),Left
lateral tilt with wedge under right pelvis.Routine Monitors: ECG, NIBP, pulse
oximeter,Additional monitors for GAs: ETCO2, nerve stimulator, temp probe
•*Preventing complications
Aspiration prophylaxis,Detailed airway assessment,Fluid resuscitation/left
lateral tilt to prevent hypotension,Safe practice for placement of neuraxial
blocks
•*Choice of Anesthetic technique
Regional anesthesia: spinal,epidural, combined spinal-epidural OR General anesthesia
•*Effects on the fetus
Avoid hypotension, hypoxia, acidosis,hyperventilation,Limit time between uterine incision
and delivery to less than 3 minutes,Infants exposed to GA have lower Apgar at one minute
but no difference at 5 mins

17. Obstetric emergencies
HIGH RISK PREGNANCY
Maternal Age < 15 & > 35,Parity Factors - 5 or more - great risk , PP hemorrhage if new
pregnancy within 3 months , Medical-Surgical Hx - hx of previous uterine surgery &/or uterine
rupture, DM, cardiac dis, lupus, HTN, PIH, HELLP, DIC etc
COMMON OBSTETRIC EMERGENCIES
• *Obstetric Hemorrhage Placenta Praevia, Placental Abruption, uterine
rupture Uterine Atony,Surgical Trauma,Retained Placenta
• *Hypertension/ Pre-Eclampsia
• *Embolism Venous Thromboembolism, Amniotic Fluid Embolism
• *Sepsis e.g. Chorioamnionitis
• *Trauma

18. CPR in pregnant patients
• Patient Positioning Left lateral tilt - 30degrees using wedge(hard) OR Manual left uterine
displacement, with the patient in supine, also relieves aortocaval compression .
• Active airway management is the initial consideration
Use small endotracheal tubes, Give 100 % oxygen
• Chest compressions performed slightly higher on the sternum than normally recommended
• Establish intravenous (IV) access above the diaphragm.
• Foetal monitoring
• Defibrillationno delay if use of defibrillation is indicated, same as ACLS protocol, REMOVE
FETAL MONITORING EQUIPMENTS
• Emergency cesarean section, Gestational age greater than 24 weeks, Perimortem
caesarean section to be performed within 4 mins of cardiac arrest and delivery of the
foetus within 5 mins.
• PREGANACY RELATED REVERSIBLE CAUSES bleeding,embolism,mgso4
toxcicty,rupure uterus

20. Fetal Monitoring
Fetal Heart Rate Baseline between 110-160/min
Small square = 10 secon Large square = 1 minute
FHR Accelerations normally remain steady
or accelerate with uterine contractions Typically
viewed as a reassuring phenomenon
• Early Decelerations Begins with onset of contraction
& ends at the conclusion of contraction Typically caused from
Head Compression not viewed as a sign of fetal distress
• Late Decelerations Decreases in FHR caused by
Utero-Placental deficiency ,Persistent Late
Decelerations are considered an ominous sign

21. • No reassuring patterns suggest decreasing fetal capacity to cope
with the stress of labor.
• Nonreassuring Patterns Decrease in baseline variability, Progressive
tachycardia (>160bpm),Decrease in baseline FHR,Intermittent late decelerations with
good variability
• Ominous patterns suggest possible fetal compromise
Persistent late decelerations , Variable decelerations , tachycardia, Absence of
variability , Severe Bradycardia
Treatment
Change position & apply oxygen
IV fluids
Decrease Oxytocin

22. Anesthesia in Pregnancy for Non-Obstetric Surgery
• pregnant woman should never be denied urgent surgery,regardless of trimester
• Elective surgery should be postponed
• non-urgent surgery should be performed in the second trimester when preterm
contractions and spontaneous abortion are least likely
Pregnancy related : Cervical cerclage , Ovarian Torsion , Foetal surgery
 Not related to pregnancy: Appendicitis, Cholecystitis , Bowel obstruction
Trauma Malignancies , Cardiac procedures Neurologic procedures
• Safe anaesthesia in pregnancy
1. understanding maternal and foetal physiology
2. understanding altered drug pharmacology
3. proper counseling to parturient

23. Objectives
1. Optimize or maintain normal maternal physiological function
2. Optimize or maintain utero-placental blood flow and oxygen
delivery
3. Avoid unwanted drug effects on the foetus
4. Avoid stimulating the myometrium (oxytocic effects) - uterine
contractions, abortion
5. To prevent hypotension, hypovolemia, hypoxia and hypothermia
6. Avoid awareness during general anaesthesia
7. Preferential use of regional anaesthesia

24. • REFERENCES
• *MILLERS ANAESTHESIA 7th EDITION
• *CURRENT STATUS OF OBSTETRIC ANAESTHESIA: IMPROVING
• SATISFACTION AND SAFETY-IJA 2009
• *ANAESTHESIA FOR LSCS:CHANGING PERSPECTIVES-IJA 2010
• *OBSTETRICS ANAESTHESIA:WIDENING HORIZONS-IJA 2010
• *COURTESY : UPDATE JUNE 2012 LITERATURE REVIEW
• *AHA : CIRCULATION 2010 – CARDIAC ARREST IN PREGNANCY
• *TINTINALLI 7TH EDITION