General OB Anesthesia Flashcards
Respiratory effects of pregnancy and anesthetic
- Swelling of nasal and oral
- Increases in MV, TV, VO2, Not RR (returns 6 wks PP)
- PaCO2 to 30 by week 12, pH to 7.44 with metabolic compensation
- Decrease in FRC (returns by 2 weeks PP)
- Use smaller ETT, possible difficult intubation
- Preoxygenate 3-5 min or 4 VC breaths (reduced FRC and increased VO2)
- MAC decreased 40%
CV effects of pregnancy
- Increased CO (highest immediately PP)
- Increased SV, HR
- Decreased SVR, DBP
- No change in BP
- Aortocaval compression (left uterine displacement)
GI effects of pregnancy
- Decreased motility during labor
- Decreased LES tone
- Increased aspiration risk
Hematologic effects of pregnancy
- Increased fluid volume, plasma volume, RBC volume
- Anemia of pregnancy (11 g/dL)
- Increased coagulation factors with shortened PT and PTT
Labs for healthy cesarean
- CBC with platelets
- Type and cross with 4 units (if increased risk of bleeding)
Preoperative medications for healthy cesarean
- Nonparticulate antacid Sodium citrate 30 minutes prior to anesthesia (goal pH > 2.5)
- IV H2 antagonist (ranitidine)
- Fasting guidelines as per non-OB
Monitors, lines for healthy cesarean
Std ASA monitors
- EKG, BP, pulse ox, ETCO2, Foley
- Two large bore IV catheters
- Forced air warmer
- IV fluid warmer
- Intermittent pneumatic compression stockings
- Consider a-line
Anesthesia choice for Placenta previa, accreta, increta, percreta
- Regional is ok for previa, accreta and increta
- Single shot is probably not good idea
- May need to convert to GA if massive bleeding
- General for percreta
Absolute and Relative contraindications to neuraxial anesthesia
Absolute
- Pt refusal
- Hypovolemia
- Infection at needle site
- Coagulopathies
- Mass lesions causing increased ICP
Relative
- Systemic infection (OK if treated)
- Neurological disease (rare)
- Isolated coagulation abnormalities
Expected blood loss
Vaginal 500 ml
Cesarean 1000 ml
Cesarean Hysterectomy 1500 ml
Physical findings of blood loss
< 20%
None
20-30%
Tachycardia, tachypnea
Narrowed PP
Orthostatic hypotension
30-40%
Worsening tachycardia and tachypnea
Hypotension
Oliguria
> 40%
Shock
Altered consciousness
Anuria
Postpartum hemorrhage causes
- Early <24 hrs, and late up to 6 weeks
- Bleeding from placental implantation site
Myometrial hypotonia (uterine atony)
Placenta previa
Retained placental tissue (accreta) - Bleeding from genital tract trauma
Lacerations
Uterine rupture - Coagulation deficits worsen bleeding
Physiology of placental separation
- At term 600 mL per minute flows in placenta
- With placental separation, spiral vessels are avulsed
- Myometrium contracts and compresses large vessels
- Next clotting occurs
- Often it is the lower uterine segment that has less myometrium which contracts poorly
Drugs and maneuvers to enhance myometrial coagulation
- Manual uterine massage
- Uterotonic medications
Oxytocin (Pitocin is synthetic oxytocin)
Increase frequency and duration of contactions
20 units in 1L crystalloid
Can cause hypotension via decreased SVR
Ergot alkaloids
Methylergonovine (Methergine) IM
Tetanic contractions
Avoid in hypertensive
Risk of coronary artery spasm
Prostoglandins
15-methyl prostaglandin F2 (Hemabate, Carboprost)
Avoid in asthma (bronchoconstriction)
When to transfuse?
Never if Hgb > 10
Always if Hgb < 6
Usually if Hgb < 7
Otherwise if evidence of inadequate oxygen carrying capacity
Can you use intraoperative blood salvaging in OB?
Yes, in circumstances with massive hemorrhage and the blood bank is depleted or pt refuses blood bank. Anti-D immune globulin if mother is Rh -
Differential for oozing after 8 units pRBC
Dilution coaguopathy (platelets first) DIC (transfusion related, fetal demise, sepsis, AFE) Also Acidosis and hypothermia should be corrected
Pathway during major hemorrhage
Send labs: PT/INR, PTT, Fibrinogen, Hct/Hgb, Platelet, ABG. CMP if large resuscitation (hyperkalemia, hypocalcemia)
Replete 1:1:1.
Correct hypofibringenemia, thrombocytopenia, hypocalcemia, acidosis, hypothermia.
If all else fails, can try RFVII 90 mcg/kg x 2 Q20 minutes
If that fails, hysterectomy
AFE syndrome
Maternal collapse (hypotension, hypoxia, dyspnea, cardiopulmonary arrest, SZ, LOC), DIC Unknown cause
DIC in a pt with epidural
Treat coagulopathy. If no signs of spinal hemorrhage, then remove it. If it is bleeding, leave it to tamponade and get NS consult. If pt intubated, correct coagulopathy and remove it.
Sheehan syndrome
Pituitary infarction after pregnancy/hypotension
Watch for hypotension (ACTH), no lactation (PH), hypothyroid (TRH)
Death in OB: cause
Hemorrhage, HTN, Sepsis
Level of analgesia for epidural
First Stage T10-L1
Second Stage S2-S4
Treatment for hypotension after epidural associated with fetal distress
- Hydration
- Left uterine displacement
- Elevate legs
- O2 for Mom
- Ephedrine / Phenylephrine boluses
Mgmt of total spinal
- Heralded by agitation, difficulty speaking, dyspnea
- Airway support
- Monitors
- Epi if needed for hemodynamic support
Fetal lie, presentation, position
Lie: Oblique, Longitudinal, Transverse
Presentation: Breech, Cephalic, Shoulder
Position: how it lies compared to maternal pelvis
What to do about breech
External manipulation can be attempted
Vaginal or c/s depending on provider experience.
Usually c/s if other complications
Timing of CO changes
- Highest CO immediately PP
- Returns to prelabor within 1 HR
- 3 to 6 months for CV changes to revert
Determinants of fetal oxygenation
- Oxygen partial pressure
- Oxygen carrying capacity
- Uteroplacental blood flow
- Placental diffusion
- Placental oxygen utilization
Determinants of uterine blood flow and percent of CO
Uterine blood flow = (Uterine Artery Pressure - Uterine Venous Pressure) / Uterine Artery Resistance
Uterus gets 10% of CO, 80% of which goes to placenta
How to monitor the fetus
FHT invasive via scalp or non-invasive doppler
Uterine contractions invasive via transcervical catheter or noninvasive via abdomina muscular tone
Normal FHR vs Fetal Compromise
120-160, beat to beat variability from 5 to 25 bpm. Early decels are ok
Late and Variable are not ok.
Loss of beat to beat variability is bad sign
If concern for compromise, fetal pH is rarely used now
Decelerations
Early: Head compression
Late: Uteralplacental insufficiency
Variable: Cord compression, decrease 60 bpm and last 60 sec
Meconium stained amniotic fluid
Meconium aspiration syndrome
Often associated with low fetal pH, but chicken or egg?
Meconium inactivates surfactant. Leads to pneumonia.
Improves in 72 hours, but may lead to pulm htn and persistent fetal circulation.
Do not suction/intubate vigorous baby, but do if distressed
Uterus effects of volatile
if < 1.0 MAC no effect, at higher levels decreased contractility and increased blood loss
APGAR
Appearance Pulse Grimace Activity Respirations
Relate to mortality, not morbidity
When are fetal heart tones heard
16 weeks
Fetal tachycardia >160
Hypoxia, fever, thyrotoxicosis, tachydysrhymia, terbutaline
Fetal bradycardia
Hypoxia, heart block, continuous head compression, hypothermia
Fetal scalp pH
> 7.25 is reassuring
