Obstetrics Flashcards
How does pregnancy affect minute ventilation?
Progesterone is a respiratory stimulant. It increases minute ventilation up to 50%.
Vt increases by 40%
RR increases by 10%
How does pregnancy affect mother’s arterial blood gas?
Compensated respiratory alkalosis via renal elimination of bicarbonate to normalize blood pH. There is a small reduction in physiologic shunt which explains the mild increase in PaO2. This increases the driving pressure across the fetoplacental interface.
Arterial pH = no change
PaO2 = 104 - 108 mmHg
PaCO2 = 28 - 32 mmHg
HCO3- = 20 mmol/L
How does pregnancy affect lung volumes & capacities?
-FRC decreases as a function of a decrease in expiratory reserve volume and residual volume (ERV decreases more than RV)
How does cardiac output change during pregnancy & delivery?
CO increases by 40% (HR 15%, SV 30%)
-Uterus receives 10% of the CO.
-CO during labor (Stage 1 = 20%, 2 - 50%, 3 - 80%)
Returns to pre-labor values in 24 - 48 hours.
Pre-pregnancy values in 2 weeks.
Twins cause CO to increase 20% above a single fetus pregnancy.
How do blood pressure and SVR change during pregnancy?
-MAP & SBP have no change.
-DBP decreases by 15%
-Increased blood volume & decreased SVR = net effect on MAP
-SVR decreases by 15%
-PVR decreases by 30%
Progesterone causes increase in nitric oxide and a decreased response to AT and NE.
How does intravascular fluid volume change during pregnancy?
It increases by 35%
Plasma volume = 45%
Erythrocyte volume = 20%
What hematologic changes accompany pregnancy?
Clotting factors 1, 7, 8, 9, 10, 12 increase
Anticoagulants protein s decreases
Fibrin breakdown increases
Anti-fibrinolytic systems 11 & 13 decrease
How does MAC change during pregnancy?
It is decreased by 30 - 40% (likely d/t progesterone)
How does pregnancy affect gastric pH and volume?
It increases the volume and decreases the pH. This is due to increased gastrin.
How does pregnancy affect gastric emptying?
Before the onset of labor, there is no change. However, after the onset of labor, it is slowed.
How does pregnancy affect uterine blood flow?
Non-pregnant state = 100 mL/m
Pregnancy at term = 700 mL/m or 10% of the CO
What conditions can reduce uterine blood flow?
It does NOT autoregulate. It is dependent on MAP, CO, and uterine resistance.
Causes: decreased perfusion or increased resistance (HTN condition, contraction)
Which law determines which drugs will pass through the placenta?
Fick’s = diffusion coefficient x surface area x concentration gradient / membrane thickness
What drug characteristics favor placental transfer?
Low molecular weight (< 500 Daltons)
High lipid solubility
Nonionized = Nonpolar
Define the 3 stages of labor
Stage 1 = Beginning of regular contractions to full cervical dilation (10 cm)
Stage 2 = 10 cm –> delivery of fetus (Pain in perineum begins here)
Stage 3 = delivery of placenta
Uncontrolled labor pain may result in:
Increased maternal catecholamines = HTN = reduced uterine blood flow
Maternal hyperventilation = leftward shift of oxyHgb curve = reduced delivery of O2 to the fetus
Compare and contrast the pain that results from the first and second stages of labor
First stage = pain begins in the lower uterine segment and the cervix. The origin is T10 - L1 posterior nerve roots!
Second stage = pain impulses from vagina, perineum, pelvic floor. The origin is S2 - S4 posterior nerve roots.
Compare and contrast the regional anesthetic techniques that can be used for first and second-stage pain.
Uterus & Cervix: afferent pathway is the visceral C fibers (hypogastric plexus). Dull, diffuse, cramping.
-Neuraxial, paravertebral lumbar sympathetic block, paracervical block (high risk of fetal bradycardia)
Perineum: pudendal nerve. Sharp, well-localized pain.
-Neuraxial, pudendal nerve block
Compare and contrast bupivacaine and ropivacaine for labor.
Bupivacaine- racemic mixture.
-Minimal tachyphylaxis.
-Low placental transfer due to high protein binding and high ionization
-Greater sensory block relative to other LAs.
-Cardiac toxicity is more common with the R-enantiomer
-Cardiac toxicity occurs BEFORE seizures.
-0.75% contraindicated via epidural due to risk of toxicity via IV injection
Ropivacaine- S-enantiomer of bupivacaine + propyl group substitution
-Less CV toxicity, less potency, and less of a motor block
Discuss use of 2-chloroprocaine for labor
Useful for emergency c/s when epidural already in place
-metabolized by pseudocholinesterase in the plasma - minimal placental transfer
-antagonizes opioid receptors (mu & kappa) and reduces efficacy of epidural morphine
-risk of arachnoiditis when used for spinal anesthesia due to preservatives
-solutions w/o methylparaben and metabisulfite do NOT cause neurotoxicity
Discuss the consequences of an epidural that is placed in the subdural space
-The placement of the tip of the catheter between dura and arachnoid. Neither catheter aspiration nor a test dose will rule out subdural placement
-10 - 25 minutes after the epidural is dosed, the patient will experience symptoms of an excessive cephalad spread of LA. b/c the subdural space is a potential space, it holds very low volume. For this reason, the block height presents much higher.
What is the treatment for a total spinal?
vasopressors
IVF
LUD
elevation of legs
intubation if LOC
What can cause a total spinal?
Epidural dose in subarachnoid space.
Epidural dose in subdural space.
Single shot after a failed epidural block.
Discuss fetal HR
Surrogate measure of overall fetal wellbeing. Assesses fetal hypoxia and acidosis.
Fetal oxygenation is a function of uterine and placental blood flow. The fetus responds to stress with peripheral vasoconstriction, HTN, and a baroreceptor mediated reduction in HR.
Normal FHR
110 - 160
Bradycardia FHR
<110
-maternal cause = hypoxemia, drugs
-fetal cause = asphyxia, acidosis
Tachycardia FHR
> 160
-maternal cause = fever, chorio, atropine, ephedrine, terbutaline
-fetal cause= hypoxemia, arrythmia
VEAL CHOP
Variable decelerations = cord compression
Early deceleration = head compression
Accels = ok or give o2
Late decelerations = placental insufficiency
Premature delivery definition
< 37 weeks or < 259 days from LMP
@ higher risk of neonate < 1500 g
Corticosteroids
Betamethasone takes effect within 18 hours, peaks at 48 hours
Tocolytic agents
Stop labor for 24 - 48 hours
What are the side effects of beta2 agonists used for tocolysis
hypokalemia
increased FHR
hyperglycemia from glycogenolysis in the liver
Side effects of hypermagnesemia
Apnea, hypotension, sk. muscle weakness, CNS depression, reduced response to ephedrine/phenylephrine
Treatment for hypermagnesemia?
-supportive
-diuretics
-IV calcium (to antagonize Mg)
How can oxytocin be administered? What are the potential SE?
It is synthesized in the supraoptic and periventricular (primary) nuclei of the hypothalamus in the posterior pituitary gland.
You can give it IV (diluted) or the OB can inject it directly into the uterus.
SE: water retention, hyponatremia, hotn, reflex tachycardia, coronary vasoconstriction
Pros vs cons of GA for cesarean section
-Mortality 17x higher with GA
-failure to manage the airway
Benefits: speed, secure airway, greater HD stability
Deficits: DAW, difficult mask, aspiration, MH, neonatal respiratory & CNS depression
When is the pregnant patient who presents for non OB surgery at risk for aspiration?
18 - 20 weeks gestation pregnant patients are considered a FULL stomach. They require RSI.
Sodium citrate = 15 - 30 mL within 15 - 30 mins.
H2 antagonist (ranitidine) = 1 hour prior
Reglan = 1 hour prior
LUD in 2nd and 3rd trimester
When do you avoid NSAIDS in the pregnant population
after 1st trimester as they may close the ductus arteriosus
Discuss the balance of prostacyclin and thromboxane in the patient with preeclampsia
Healthy placenta produces thromboxane and prostacyclin in equal amounts. Pre-e patients produce SEVEN X MORE THROMBOXANE!
this favors vasoconstriction, platelet aggregation, reduced placental flow
Mild Pre-e SBP, DBP
<160 mmHg/<110
thromboxane vasoconstriction
Mild vs severe pre-e proteinuria, 24 hour urine total
MILD = < 5 g/24hr, < 3+ dipstick
>500 mL UO
Severe = > 5g/24 hour, >/= 3+ dipstick, < 500 UO
glomerular capillary endothelial destruction and renal edema.
Generalized edema & pulmonary edema
Generalized edema is present for both mild pree, and severe. this is due to decreased oncotic pressure and increased vascular permeability.
Pulmonary edema is not present for mild pre-e. It is present for severe pre-e.
What is present for severe pre-e but not mild pre-e
Pulmonary edema
Cyanosis
HA (cerebral edema)
Visual changes (vasoconstriction of ocular arteries)
Epigastric pain (liver subscapular hemorrhage, hypoxic liver)
HELLP (5- 10% of those with pre-e = epigastric pain)
Plt < 100,000 (consumption by endothelial damage)
Impaired fetal growth (uteroplacental hypoperfusion)
Discuss the use of magnesium for preeclampsia
Prophylaxis: load 4g over 10 minutes
Infusion: 1 - 2 g/hr
If toxicity occurs, give 10 mL of 10% calcium gluconate IV.
Discuss anesthetic management for the patient with preeclampsia
-Fluid management is a balance btw leaky vasculature and being dry.
-Neuraxial assists with BP control and provides better uteroplacental perfusion.
-Be sure to r/o thrombocytopenia prior to neuraxial block
-Exaggerated response to sympathomimetic & methergine
Discuss the anesthetic consideration for maternal cocaine abuse
Cocaine is an ester-type LA that inhibits NE reuptake in the presynaptic SNS synaptic cleft with NE increases in SNS tone.
CV risks = tachycardia, dysrythmias, MI
Spontaneous abortions, premature labor, abruption
HTN = treat with VASODILATORS b/c BB will cause HF if SVR is severely elevated.
HoTN = treat with neo (likely depleted w/ephedrine)
Thrombocytopenia
Accreta, increta, percreta
Accreta: uterus abnormally attaches to myometrium
Increta: invades the myometrium
Percreta: extends beyond uterus
Placenta previa
Occurs when the placenta attaches to the lower uterine segment. It partially or completely covers the cervical os. Associated with PAINLESS VAGINAL BLEEDING
hemorrhage potential
What conditions increase the risk of placenta previa
Previous cesarean section
Multiple births hx
RF for placental abruption? How does it present?
PIH, Pree, Chronic HTN, Cocaine, Smoking, ETOH
painful vaginal bleeding
What is the most common cause of PPH? What are the RF?
Uterine atony.
-multiparity
-multiple gestations
-polyhydramnios
-prolonged pit infusion
Retained placental fragments. What IV Medication can you give for help with extraction?
Nitroglycerin
Treatment options for uterine atony
Uterine massage
Pitocin
Ergot Alkaloids
Intrauterine balloon
APGAR SCORE
1 minute = correlates with fetal acid/base status
5 minute = predictive of neurologic outcome
nml = 8 - 10
mod. distress = 4 - 7
impending demise = 0 - 3
Epinephrine and fluid dosing during neonatal resuscitation
10 - 30 mcg/kg IV
0.1 mg/kg intratracheal
10 mL/kg IVF over 5 - 10 minutes
