Unit 11: Across the Lifespan Flashcards
How does pregnancy affect minute ventilation?
Progesterone is a respiratory stimulant – Increases minute ventilation up to 50%
-Vt increases by 40%
-RR increases by 10%
How does pregnancy affect the mother’s arterial blood gas?
Arterial pH = no change
PaO2 = Increased (104-108 mmHg)
PaCO2 = Decreased (28-32 mmHg)
HCO3 = Decreased (20 mmol/L)
-progesterone = respiratory stimulant –> minute ventilation increases 50% –> Mom’s PaCO2 falls and develops respiratory alkalosis
-renal compensation eliminates bicarb to normalize blood pH
-small reduction in physiologic shunt explains mild increase in PaO2 –> increases driving pressure of O2 across the fetoplacental interface and improves fetal gas exchange
How does pregnancy affect the oxyhemoglobin dissociation curve?
Right Shift (increases P50) –> Facilitates O2 unloading to the fetus
How does pregnancy affect the lung volumes and capacities?
FRC is reduced (decreased expiratory reserve volume and residual volume) – ERV decreases more than RV
*increased oxygen consumption paired with decreased FRC hastens the onset of hypoxemia
How does cardiac output change during pregnancy and delivery?
Cardiac Output - increases 40%
-heart rate increases 15%
-stroke volume increases 30%
-uterus receives 10% of the CO
-uterine contraction causes autotransfusion (increased preload)
Compared to pre-labor values, CO during labor:
-increases 20% in 1st stage
-increases 50% in 2nd stage
-increases 80% in 3rd stage
-CO returns to pre-labor values in 24-48hr
-CO returns to pre-pregnancy values in ~2 weeks
*twins cause CO to increase 20% above a single fetus pregnancy
How do blood pressure and systemic vascular resistance change during pregnancy?
MAP = no change
SBP= no change
DBP = decreases 15%
*increased blood volume + decreased SVR = net even effect on MAP
SVR = decreases 15%
PVR = decreases 30%
*progesterone causes increased nitric oxide (vasodilation) and decreased response to angiotensin and norepi
Who is at risk for aortocaval compression, how do you treat it?
In supine position – gravid uterus compresses both the vena cava and the aorta – decreases venous return to the heart as well as arterial flow to the uterus and lower extremities
-decreased CO compromises fetal perfusion and can also cause the mother to lose consciousness
Treatment: displacing uterus away from the vena cava and aorta can reduce the compressive effects – elevate mother’s right torso 15 degrees
*should be used for anyone in their 2nd and 3rd trimester
How does the intravascular fluid volume change during pregnancy?
Intravascular Fluid - increases 35%
Plasma volume - increases 45%
Erythrocyte volume - increases 20%
What hematologic coagulation changes accompany pregnancy?
-Clotting factors: 1, 7, 8, 9, 10, 12 increase
-Anticoagulants: Protein S decreases and no change in Protein C
-Fibrin breakdown increases
-Anto-fibrinolytic system: 11 & 13 decrease
How does MAC change during pregnancy?
Decreased by 30-40%
-probably due to increased progesterone
How does pregnancy affect gastric pH and volume?
Increases gastric volume
Decreases gastric pH
*due to increased gastrin
How does pregnancy affect gastric emptying?
Before onset of labor = no change
After onset of labor = slowed
How does pregnancy affect uterine blood flow?
What is the non-pregnant flow rate vs pregnancy at term flow rate?
Non-Pregnant State = 100 mL/min
Pregnancy at Term = up to 700 mL/min or 10% of CO
What is uterine blood flow dependent on? What conditions can reduce uterine blood flow?
Uterine blood flow does NOT autoregulate – dependent on MAP, CO, and uterine vascular resistance
-decreased perfusion: maternal hypotension (sympathectomy, hemorrhage, aortocaval compression)
-increased resistance: uterine contraction, hypertensive conditions that increase UVR
Which law determines which drugs will pass through the placenta?
Fick’s Principle
Rate of Diffusion = [Diffusion Coefficient x Surface Area x Concentration Gradient (between mom/fetus)] / [Membrane Thickness]
What drug characteristics favor placental transfer?
-Low molecular weight <500 Daltons (most anesthetic drugs are smaller than 500 Daltons)
-High lipid solubility
-Nonionized
-Nonpolar
What are the 3 stages of labor?
Stage 1: beginning of regular contractions to full cervical dilation (10cm)
Stage 2: full cervical dilation to delivery of the fetus (pain in the perineum begins during stage 2)
Stage 3: delivery of the placenta
How does uncontrolled labor pain affect the mother and the fetus?
Increased maternal catecholamines –> HTN –> Reduced uterine blood flow to fetus
Maternal hyperventilation –> Leftward shift of oxyhgb curve –> Reduced O2 delivery to fetus
What spinal levels does the pain that results from the first and second stages of labor originate? What is the quality of pain during each stage?
Stage 1:
- T10-L1 posterior nerve roots
- pain begins in the lower uterine segment and the cervix
- dull, diffuse, cramping
Stage 2:
- S2-S4 posterior nerve roots
- adds in pain impulses from the vagina, perineum, and pelvic floor
- sharp, well localized
What anesthetic techniques can be used for 1st and 2nd stage labor pain? What spinal levels are targets for each stage?
Stage 1 – target T10-L1
- neuraxial (spinal, epidural, CSE)
- paravertebral lumbar sympathetic block
- paracervical block (high risk of fetal bradycardia
*afferent pathway = visceral C fibers hypogastric plexus
Stage 2 – target S2-S4
- neuraxial (spinal, epidural, CSE)
- pudendal nerve block
*afferent pathway = pudendal nerve
Explain the “needle through the needle” technique for CSE
-Epidural space is identified with epidural needle
-Spinal needle is placed through the epidural needle
-Local anesthetic and/or opioid is injected into the intrathecal space
-Spinal needle is removed
-Epidural catheter is threaded through the epidural needle
*CSE provides dual benefit of a rapid onset of spinal anesthesia and the ability to prolong the duration of anesthesia with an indwelling epidural catheter
Compare and contrast bupivacaine and ropivacaine in labor
Bupivacaine = amide, long duration
- racemic mixture
- minimal tachyphylaxis
- low placental transfer d/t increased protein binding and increased ionization
- greater sensory block relative to other LAs
- cardiac toxicity more common with R-enantiomer
- cardiac toxicity occurs before seizures
- 0.75% contraindicated via epidural due to risk of toxicity w/ IV injection
Ropivacaine = amide, long duration
- S-enantiomer of bupivacaine + substitution of propyl group
- when compared to bupivacaine – less risk of CV toxicity, decreased potency, and decreased motor block
Discuss the use of 2-Chloroprocaine for labor
-Useful for emergency c-section when epidural is already in place (very fast onset)
-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 without methylparaben and metabisulfite do not cause neurotoxicity
What are the consequences if an epidural is placed in the subdural space?
Within 10-25 minutes after epidural is dosed – patient will experience symptoms of excessive cephalad spread of LA
-subdural space is a potential space (hold very low volume) –> block height for a given amount of LA will be much higher than if the same volume was administered in the epidural space
*neither test dose or aspiration will rule out subdural placement
What might a total spinal result from? What is the treatment?
-Epidural dose injected into subarachnoid space
-Epidural dose injected into subdural space
-Single shot spinal after failed epidural block
Initial Treatment: vasopressors, IVF, left uterine displacement, elevation of legs, and intubation if LOC
What might cause fetal bradycardia and tachycardia?
Fetal Bradycardia = <110
- fetal causes: asphyxia, acidosis
- maternal causes: hypoxemia, drugs that decrease uteroplacental perfusion
Fetal Tachycardia = >160
- fetal causes: hypoxemia, arrhythmias
- maternal causes: fever, chorioamnionitis, atropine, ephedrine, terbutaline
*fetal oxygenation is a function of uterine and placental blood flow – fetus responds to stress w/ peripheral vasoconstriction, HTN, and baroreceptor-mediated reduction in HR
What are the causes of each fetal deceleration? Which are unremarkable and which are cause for concern?
-Variable Decels = Cord Compression
-Early Decels = Head Compression
-Accelerations = Ok of Give Oxygen
-Late Decels = Placental Insufficiency
*Early decelerations do not present a risk of fetal hypoxemia
*Late and Variable decelerations require urgent assessment of fetal status
What is defined as premature delivery? What are potential complications from preterm delivery?
Premature Delivery = delivery before 37 weeks gestation or less than 259 days from last menstrual cycle
Complications:
-respiratory distress syndrome
-intraventricular hemorrhage
-NEC
-hypoglycemia
-hypocalcemia
-hyperbilirubinemia
How are steroids and tocolytic agents used in the prevention of premature delivery?
Corticosteroids (betamethasone) - hasten fetal lung maturity (begin to take effect within 18 hours and peak benefit at 48hrs)
Tocolytic Agents - stop labor ~24-48 hours (provide a bridge that allows the corticosteroids time to work)
*seldom given after 33 weeks gestation
What are the side effects of beta-2 agonists when used for tocolysis?
-Hypokalemia results from intracellular K+ shift
-Cross placenta and may increase FHR
-Hyperglycemia results from glycogenolysis in the liver
*newborn of hyperglycemic mother is at risk of post-delivery hypoglycemia (glucose supply is gone, but neonatal insulin remains)
*Terbutaline and Ritodrine = examples
What are the side effects of hypermagnesemia?
-Apnea
-Hypotension
-Skeletal muscle weakness (synergism w/ NDMRs)
-CNS depression
-Reduced responsiveness to ephedrine and phenylephrine
What is the treatment for hypermagnesemia?
Supportive measures
Diuretics (to facilitate excretion)
IV Calcium (to antagonize Mg)
How can oxytocin be administered? What are the potential side effects?
Can be given IV (diluted in IVF) or can be injected directly into the uterus
Side Effects:
-water retention
-hyponatremia
-hypotension
-reflex tachycardia
-coronary vasoconstriction
How can methergine be administered? What is the dose?
Methergine = Ergot Alkaloid
Can be given 0.2 mg IM (not IV)
*IV admin can cause significant vasoconstriction, HTN, and cerebral hemorrhage
What are the pros and cons of general anesthesia for c-section?
Benefits:
- speed of onset
- secured airway
- greater hemodynamic stability
Drawbacks:
- risk of difficult mask ventilation
- risk of difficult laryngoscopy
- risk of difficult intubation
- risk of aspiration
- potential MH
- absence of maternal awareness
- neonatal respiratory & CNS depression
*mortality is 17x higher w/ general anesthesia – failure to manage airway is most common cause of maternal death
What is the triple prophylaxis against aspiration for a c-section?
- Sodium Citrate 15-30 mL within 15-30 min of induction (neutralize gastric acid)
- H2 Receptor Antagonists (Ranitidine) 1 hour before induction (reduce gastric acid secretion)
- Gastrokinetic Agent (Metoclopramide) 1 hour before induction (hasten gastric emptying and increase LES tone)
When is the pregnant patient who presents for non-obstetric surgery at risk for aspiration?
18-20 weeks gestation – considered “full stomach”
-require RSI w/ aspiration prophylaxis
*also apply to the immediate postpartum period
What is the risk of NSAIDs when used in the pregnant patient?
NSAIDs may close the ductus arteriosus
*AVOID after 1st trimester
What is the diagnostic criteria for gestational hypertension, preeclampsia, and eclampsia?
Gestational HTN:
-onset = after 20 weeks gestation
-severity = mild
-proteinuria = no
-seizures = no
Preeclampsia:
-onset = after 20 weeks gestation
-severity = mild to severe
-proteinuria = usually present
-seizures = no
Eclampsia:
-onset = after 20 weeks gestation
-severity = severe
-proteinuria = usually present
-seizures = yes
What happens to the balance of prostacyclin and thromboxane in the patient with preeclampsia?
Healthy placenta produces thromboxane and prostacyclin in equal amounts – Patient with preeclampsia produces up to 7x more thromboxane than prostacyclin
*increased thromboxane favors vasoconstriction, platelet aggregation, and reduced placental blood flow
What is the difference between mild and severe preeclampsia?
Why is magnesium used in preeclampsia?
Seizure Prophylaxis w/ magnesium sulfate
-Load: 4g over 10 min
-Infusion: 1-2 g/hr
*treatment for Mg toxicity = 10mL of 10% calcium gluconate IV
What is the anesthetic management for the patient with preeclampsia?
-Fluid management is balanced between a volume contracted patient and a “leaky” vasculature from endothelial dysfunction
-Neuraxial anesthesia assists w/ blood pressure control and also provides better uteroplacental perfusion
-Be sure to rule out thrombocytopenia (<100,000) before performing a neuraxial block
-Due to airway swelling, these pts have higher incidence of difficult intubation
-Have an exaggerated response to sympathomimetics and methergine
-If receiving Mg therapy – exhibit increased sensitivity to neuromuscular blockers
-Mg relaxes the uterus and increases the risk of postpartum hemorrhage
What is HELLP syndrome? What is the definitive treatment?
HELLP = Hemolysis, Elevated Liver enzymes, and Low Platelet count
-develops in 5-10% of those with preeclampsia
-experience epigastric pain and upper abdominal tenderness
Definitive Treatment = delivery of the fetus
What are the anesthetic considerations for maternal cocaine abuse?
Cocaine = ester-type local anesthetic that inhibits NE reuptake in presynaptic SNS neuron.. flooding the synaptic cleft with NE increases SNS tone
-CV risks: tachycardia, dysrhythmias, and myocardial inschemia
-Acute intoxication increases MAC
-Chronic use decreases MAC
-OB risks: spontaneous abortion, premature labor, placental abruption, and low APGAR scores
-HTN is best treated with vasodilators
-Beta-blockers can cause heart failure if the SVR is significantly elevated
-Hypotension may not respond to ephedrine in chronic cocaine abusers (d/t catecholamine depletion)
-Chronic cocaine abuse is associated with thrombocytopenia – check platelet count before neuraxial anesthesia
What is the difference between placenta accreta, increta, and percreta? What is the major risk that these complications present?
Types of abnormal placental implantation:
Accreta = attachment to the surface of myometrium
Increta = invades myometrium
Percreta = extends beyond the uterus
*uterine contractility is impaired and potential for tremendous blood loss
What is placenta previa? How does it present?
Occurs when placenta attaches to the lower uterine segment
-partially or completely covers the cervical os
-associated with PAINLESS vaginal bleeding
-potential for hemorrhage
What conditions increase the risk of placenta previa?
Previous c-sections
History of multiple births
What are the risk factors for placental abruption? How does it present?
Placental Abruption = partial or complete separation of placenta from uterine wall prior to delivery – results in hemorrhage and fetal hypoxia
Risk Factors:
-PIH
-preeclampsia
-chronic HTN
-cocaine use
-smoking
-excessive alcohol use
Presents: PAINFUL vaginal bleeding (pain may be so severe as to cause breakthrough when epidural is in place
What is the most common cause of postpartum hemorrhage? What are the risk factors?
Uterine Atony
Risk Factors:
-multiparity
-multiple gestations
-polyhydramnios
-prolonged oxytocin infusion prior to surgery
What IV medication can you give to help with the extraction of retained placental fragments?
IV nitroglycerine
*provides uterine relaxation
What are the treatment options for uterine atony?
-Uterine massage
-Oxytocin
-Ergot alkaloids
-Intrauterine balloon
What is the Apgar score? What does each value represent?
-Used to assess newborn and guide resuscitative efforts
-Five parameters are evaluated at 1 and 5 minutes after delivery
-Score at 1 min correlates with fetal acid-base status
-Score at 5 min may be predictive of neurologic outcome
Normal = 8-10
Moderate Distress = 4-7
Impending Demise = 0-3
How do you calculate the Apgar score?
What is the best indicator of ventilation during neonatal resuscitation?
Resolution of bradycardia
How do you dose epinephrine and fluids during neonatal resuscitation?
Epi: 10-30 mcg/kg (IV) or 0.05-0.1 mg/kg (intratracheal) of 1:10,000 concentration
Fluids: 10 mL/kg over 5-10 min of PRBCs, NS, or LR
What are normal vital signs for a newborn, 1yr, 3yr, and 12yr old?
Newborn: BP 70/40, HR 140, RR 40-60
1 yr: BP 95/60, HR 120, RR 40
3 yr: BP 100/65, HR 100, RR 30
12 yr: BP 110/70, HR 80, RR 20
Why is the neonate’s minute ventilation higher than the adult?
Oxygen consumption and CO2 production are 2x those of the adult – neonate must increase alveolar ventilation accordingly
-metabolically more efficient to increase respiratory rate than it is to increase tidal volume
What is the primary determinant of blood pressure in the neonate?
Heart Rate = primary determinant of CO and SBP
-neonatal myocardium lacks the contractile elements to significantly adjust contractility or SV (ventricle is noncompliant)
-frank-starling relationship is underdeveloped
-heart rate must be maintained to ensure adequate tissue perfusion and oxygen delivery
Explain the autonomic influence on the newborns heart
Autonomic regulation of the heart is immature at birth – SNS being less mature than the PNS
-stressful situations (i.e. laryngoscopy or suctioning) may cause bradycardia
-atropine may be administered prior to induction to mitigate this response
*baroreceptor reflex is poorly developed – fails to increase HR in the setting of hypovolemia
What is the difference between the breathing patten in adults and infants?
Adult = Mouth or Nose
Infant = Preferential Nose breather up to 5 months of age
-most infants convert to oral breathing if the nasal passages are obstructed
-bilateral choanal atresia may require emergence airway management if the infant is unable to mouth breathe
What is the difference between the relative size of the tongue in adults and infants?
Adult = Small relative to oral volume
Infants = large relative to oral volume
-tongue is closer to soft palate (makes it easier to obstruct upper airway)
-more difficult to displace during laryngoscopy
What is the difference between the epiglottis shape in adults and infants?
Adult = Leaf (C shape), floppier, shorter
Infant = U (omega shape), stiffer, longer
-makes it more difficult to displace during laryngoscopy
What is the vocal cord position in adults and infants?
Adult = perpendicular to trachea
Infant = anterior slant
-visualization and passage of ETT may be more difficult
-ETT may get stuck in anterior commissure
What is the laryngeal position in adults and infants?
Adult = C5 - C6
Infant = C3 - C4
-larynx more superior/cephalad/rostral but NOT anterior
-same position as the adult at age 5-6 years old
Where is the narrowest point of the airway in the adult and infant?
Adult = Glottis (vocal cords)
Infant = Cricoid or Glottis
-resistance to ETT insertion beyond vocal cords is likely at the cricoid ring
-cricoid tissue is prone to inflammation and edema formation –> stridor or obstruction
-Poiseuille’s law (small changes in radius can significantly increase resistance to airflow
What is the difference between the orientation of the right mainstem bronchus in adults and infants?
Adult = more vertical
- right bronchus takes off at 25 degrees and left at 45 degrees
Infant = less vertical
- up to age 3 both bronchi take off at 55 degrees
What is the optimal intubation position for adults and infants?
Adult = Sniffing position
Infant = head on bed with shoulder roll
-large occiput
-sniffing position will place glottic opening in a more anterior position
How does oxygen consumption, alveolar ventilation, respiratory rate, and tidal volume in neonates compare to adults? What are the values for each?
Oxygen Consumption:
-neonate = 6 mL/kg/min
-adult = 3.5 mL/kg/min
Alveolar Ventilation:
-neonate = 130 mL/kg/min
-adult = 60 mL/kg/min
Respiratory Rate:
-neonate = 35 bpm
-adult = 15 bpm
Tidal Volume:
-neonate = 6 mL/kg
-adult = 6 mL/kg
*neonatal alveolar surface area is only 1/3 of the adult and O2 consumption is 2x that of the adult – neonate must increase alveolar ventilation in order to sustain normal arterial gas tensions
Why do neonates desaturate faster than adults?
Neonates Have:
-Increased O2 consumption to support metabolic demand
-Increased alveolar ventilation to increase O2 supply
-Slightly decreased FRC reflects a reduced O2 reserve
*Net Result = increased ratio of alveolar ventilation relative to size of its FRC –> faster gas turnover means O2 supply in FRC is quickly exhausted during apnea
Why is inhalation induction faster with a neonate than with an adult?
Due to the increased alveolar ventilation relative to size of the FRC
*faster turnover of the FRC allows speedier development of anesthetic partial pressure inside the alveoli and consequently a more rapid change in anesthetic partial pressure inside the brain and spinal cord
What is the difference between fast and slow twitch muscle fibers? How does this relate to neonatal pulmonary mechanics?
Diaphragm and intercostal muscles are composed of:
- type 1 = slow twitch muscle fibers (built for endurance) – resistant to fatigue
- type 2 = fast-twitch fibers (built for short bursts of heavy work) – tire easily
Smaller number of type 1 fibers within the diaphragm increases neonate’s risk for respiratory fatigue and developing respiratory failure
Compare and contrast the FRC, VC, TLC, RV, CC, and Vt of neonates to adults
How does the newborn’s ABG change from delivery to the first 24 hours of life?
How does hypoxemia affect ventilation in the newborn?
Respiratory control doesn’t mature until 42-44 weeks
-before maturation: hypoxemia depresses ventilation
-after maturation: hypoxemia stimulates ventilation
What is the P50 of fetal hemoglobin? Why is this important?
19 mmHg
-fetal hemoglobin shifts curve to the left (left = love)
-benefits the fetus by creating an oxygen partial pressure gradient across the uteroplacental membrane that facilitates the passage of O2 from the mother to fetus