Unit 11: Across the Lifespan

How does pregnancy affect minute ventilation?

Progesterone is a respiratory stimulant, it increases minute ventilation by up to 50%

-Vt increases by 40%

-RR increases by 10%

How does pregnancy affect the mother's ABG?

Progesterone = RR stimulant

- it ↑ minute ventilation up to 50% (tv > RR rate)

→ mom's PaCO2 falls = respiratory alkalosis

Renal compensation eliminates bicarb to normalize blood pH

A small ↓ in physiologic shunt explains the mild ↑ in PaO2

WHICH then ↑s the driving pressure of O2 across placenta = IMPROVES fetal gas exchange

Arterial pH = no change (or slight ↑)

-PaO2 = ↑ (104-108)- d/t HYPERVENT & slight ↓ in physiologic shunt

-PaCO2 = ↓ (28-32)

-HCO3 = ↓ (20)

How does pregnancy affect the oxyhemoglobin dissociation curve?

Right shift (↑ P50) → facilitates O2 unloading to the fetus

How does pregnancy affect the lung volumes + capacities?

↓ FRC 2/2 ↓ ERV + RV

↑ O2 consumption + ↓ FRC hastens onset of hypoxemia.

Failure to reverse hypoxemia → brain death of the mother + fetus

How does CO change during pregnancy + delivery?

Compared to pre-labor:

1st stage labor: CO ↑ 20%

2nd stage labor: CO ↑ 50%

3rd stage labor: CO ↑ 80%

-returns to pre-labor values in 24-48 hrs

-returns to pre-preg values in ~2 wks

-twins cause CO to ↑ 20% above a single fetus pregnancy

How do BP + SVR change during pregnancy?

↑ BV + ↓ SVR = net effect on MAP

Progesterone causes ↑ NO → vasodilation + ↓ response to angiotensin + NE

Who is at risk for aortocaval compression? How do you treat it?

Pregnant women

In supine, a gravid uterus compresses both the vena cava + the aorta. This ↓ venous return + arterial flow to the uterus + LE. ↓ CO compromises fetal perfusion + cause the mother to lose consciousness.

Tx: LUD: elevate mother's right torso 15º

How does the intravascular fluid volume change during pregnancy?

↑ 35%

-plasma volume ↑ 45%

-Erythrocyte volume ↑ 20%

What hematologic changes accompany pregnancy?

↑ clotting factors: 1, 7, 8, 9, 10, 12

Anticoagulants:

-Protein S ↓

-no △ Protein C

↑ fibrin breakdown

↓ 11 + 13 antifibrinolytic system

How does MAC △ during pregnancy?

↓ by 30-40%

probably 2/2 ↑ progesterone

How does pregnancy affect gastric pH + volume?

↑ V + ↓ pH

2/2 ↑ gastrin

How does pregnancy affect gastric emptying?

Before onset of labor: no change

After onset of labor: slowed

How does pregnancy affect uterine BF?

Non-pregnant: 100mL/min

Term: up to 700mL/min or 10% CO

-some texts say up to 800-900 mL/min

What conditions can reduce UBF

Uterine BF is NOT auto regulated.

Therefore, it is dependent on MAP, CO, + uterine vascular resistance

1. ↓ perfusion: maternal hypoTN

-sympathectomy

-hemorrhage

-aortocaval compression

2. ↑ resistance

-uterine contraction

-HTN conditions that ↑ UVR

Uterine BF equation

UBF = (uterine a. P - uterine v. P) / uterine vascular resistance

Discuss the use of phenylephrine + ephedrine in the laboring patient.

Classic: neo ↑ UVR + ↓ placental perfusion

More recent: Neo is as efficacious as ephedrine in maintaining placental perfusion + fetal pH in healthy mothers.

-mothers who received neo had higher fetal pH (less fetal acidosis)

Which law determines which drugs will pass through the placenta?

Fick's principle

Characteristics that factor transfer:

-Low molecular weight

-High lipid solubility

-Nonionized

-Nonpolar

Fick's equation

Rate of diffusion =

(Diffusion coefficient x SA x [ ] gradient b/t mom/fetus) / membrane thickness

Define the 3 stages of labor.

Stage 1: Beginning of regular contractions to full cervical dilation (10 cm)

Stage 2: Full cervical dilation to delivery of the fetus

Stage 3: Delivery of the placenta

How does uncontrolled labor pain affect the mother and fetus?

1. ↑ maternal catecholamines → HTN → ↓ UBF

2. Maternal hyperventilation → L shift of oxyhgb curve → ↓ deliver of O2 to fetus

Compare + contrast the pain that results from the first + second stage of labor.

First stage:

-Pain begins in the lower uterine segment + cervix

-T10-L1 posterior n roots

Second stage:

-Adds pain impulses from vagina, perineum, + pelvic floor

-S2-S4 posterior n roots

Compare + contrast the regional anesthetic techniques that can be used for 1st + 2nd stage labor pain.

Neuraxial techniques

T10-L1 level for stage 1

Extend to S2-S4 for stage 2

Describe the "needle through the needle" technique for CSE.

Epidural space ID w/epidural needle

Spinal needle is placed through epidural needle.

LA is injected into the intrathecal space

Epidural catheter is threaded through the epidural needle

Compare + contrast bupivicaine + ropivicaine for labor

Both long duration amides

Bupi:

-racemic mixture

-minimal tachyphylaxis

-low placental transfer

-↑ sensory blockade

-↑ cv tax w/R-enantiomer

-cv tox before seizures

-0.75% CI via epidural 2/2 risk of toxicity w/IV injection

Ropiv:

-S-enantiomer of bupi + sub of propyl group

-↓ risk cv tox v bupi

-↓ potency v bupi

-↓ motor block v bupi

Discuss the use of 2-chloroprocaine for labor.

-Useful for emergency C/S when epidural is already in place (very fast onset)

-Metabolized by pseudocholinesterase in the plasma - minimal placental transfer

-Antagonizes opioid receptors (mu & kappa) and ↓ the efficacy of epidural morphine

-Risk of arachnoiditis when used for spinal 2/2 preservatives

-Solutions w/o methylparaben + metabisulfite do not cause neurotoxicity

Discuss the consequences of an epidural that is placed in the subdural space.

w/in 10-25 min after the epidural is dosed, the pt will experience symptoms of an excessive cephalad spread of LA.

Subdural space is a potential space that holds a very low volume.

What is the treatment for a total spinal?

May result from:

-epidural dose injected into the subarachnoid space

-epidural dose injected into the subdural space

-a single shot spinal after a failed epidural

Treatment:

-vasopressors

-IVF

-LUD

-Elevate the legs

-intubation if LOC

Discuss the fetal heart rate

Surrogate measure of overall fetal wellbeing.

Provides indirect method to assess fetal hypoxia + acidosis

Fetus responds to stress w/peripheral vasoconstriction, HTN, + baroreceptor mediated ↓ HR

Which type of fetal decelerations are unremarkable? Which cause concern?

Unremarkable: early decel

Concern: late + variable decels

VEAL: CHOP

Variable: cord compression

Early: Head compression

Accelerations: OK, or give O2

Later: Placental insufficiency

Define premature delivery.

Before 37 weeks gestation or less than 259 days from the last menstrual cycle.

Leading cause of perinatal M+M

-↑ risk for newborns <1500g

↑ incidence w/multip + PROM

List potential complications from premature delivery.

Respiratory distress syndrome

Intraventricular hemorrhage

NEC

Hypoglycemia

Hypocalcemia

Hyperbilirubinemia

Discuss the use of steroids agents in the prevention of premature delivery.

Betamethasone hastens fetal lung maturity

-effect w.in 18 hrs

-peak benefit at 48 hrs

seldom given after 33 weeks gestation

Discuss the use of tocolytic agents in the prevention of premature delivery.

-stop labor ~24-48 hrs.

-provide bridge that allows the corticosteroids time to work.

ABX prophylaxis for chorioamnionitis

seldom given after 33 weeks gestation

What are the side effects of β2 agonists when used for tocolysis?

Terbutaline, Ritodrine

-Hypokalemia 2/2 intracellular shift

-cross placenta + may ↑ FHR

-↑BG 2/2 glycogenesis in the liver

-newborn of. a hyperglycemic mother is at risk of post-delivery hypoglycemia.

--mothers glucose is gone

--insulin in neonatal circulation remains

What are the side effects of hypermagnesemia?

Apnea

HypoTN

Skeletal m weakness (synergism w/NDNMB)

CNS depression

↓ responsiveness to ephedrine + phenylephrine

What is the treatment fro hypermagnesemia?

Supportive measures

Diuretics to facilitate excretion

IV Ca to antagonize Mg

How can oxytocin be administered?

synthesized in the supraoptic + paraventricular (primary) nuclei of the hypothalamus.

Released from the posterior pituitary gland

IV (diluted in IVF)

OB can inject directly into the uterus

What are the potential side effects of oxytocin?

Water retention

Hyponatremia

HypoTN

Reflec tachycardia

Coronary vasoconstriction

How can methergine be administered?

-It can be given 0.2 mg IM (not IV)

-IV administration can cause significant vasoconstriction, hypertension, and cerebral hemorrhage

What are the pros + cons of GA for C-section?

Mortality is 17x higher

Failure to successfully manage the a.w. is the most common cause of maternal death

Pros

-speed of onset

-secured a.w.

-↑ HD stability

Cons

-risk diff MV/DL/intubation

-risk of aspiration

-potential MH

-absence of maternal awareness

-neonatal respiratory + CNS depression

Describe aspiration prophylaxis for the pt scheduled for a C-section.

Sodium citrate to neutralize gastric acid

-w/in 15-30 min of induction

H2 antagonist (ranitidine) to ↓ gastric acid secretion

Gastrokinetic agent (metoclopramide) to hasten gastric emptying + ↑ LES tone

-1 hour before induction

When is the pregnant pt who present for non-OB Sx at risk for aspiration?

~18-20 weeks gestation = "full-stomach"

RSI + aspiration prophylaxis

-maybe earlier if pt has GERD

-also in immediate postpartum period

What is the risk of NSAIDs when used in the pregnant patient?

Avoid in the 1st trimester

may close the ductus arteriosus

Compare + contrast the diagnostic criteria for gestational HTN, preeclampsia, and eclampsia.

Gestational

-after 20 weeks

-mild

-no proteinuria

-no seizures

Preeclampsia

-after 20 weeks

-mild/severe

-proteinuria

-no seizures

Eclampsia

-after 20 weeks

-severe

-proteinuria

-seizures

Discuss the balance of prostacyclin + thromboxane in the pt w/preeclampsia.

Healthy placenta produces thromboxane + prostacyclin in equal amounts.

Preeclamptic pt produces up to 7x more thromboxane than prostacyclin

↑ Thromboxane favors:

-vasoconstriction

-Plt aggregation

-↓ placental BF

Compare + contrast mild + severe preeclampsia.

Discuss the use of Mg for preeclampsia

Seizure prophylaxis:

-Load 4g over 10 min

-Infusion 1-2g/hr

Mg Tox Tx: 10mL of 10% Ca gluconate IV

Detail the anesthetic management for the pt w/preeclampsia.

-Fluid management is balanced b/t a volume contracted Pt + a "leaky" vasculature from endothelial dysfxn

-Neuraxial anesthesia assists w/BP control + provides better uteroplacental perfusion

-Check Plt before placing neuraxial (>100,000)

-2/2 a.w. swelling, these pts have a higher incidence of diff intubation

-exaggerated response to sympathomimetics + methergine

-If Mg therapy, ↑ sensitivity to NMB

-Mg relaxes the uterus + ↑ risk of postpartum bleeding

What is HELLP syndrome? What is the definitive treatment?

Hemolysis

Elevated liver enzymes

Low Platelet count

Developing in 5-10% of those w/preeclampsia.

Experience epigastric pain + upper abd tenderness

Definitive Tx is delivery of fetus

Discuss the anesthetic considerations for maternal cocaine abuse.

Ester-type local that inhibits NE reuptake in pre-synaptic cleft w/ NE ↑ SNS tone.

-CV risks: ↑HR, dysthymia, MI

-Acute intox ↑ MAC

-Chronic use ↓ MAC

-OB risks: spont abortion, premature labor, placental abruption, low APGAR scores

-HTN is probably best treated w/casodilators

-BB can → HF if SVR is sig elevated

-HypoTN may not respond to ephedrine in chronic abusers (d/t catecholamine depletion)

-Chronic abuse is associated w/thrombocytopenia

What is the difference b/t placenta accrete, intreat, and percreta? What is the major risk that these complications present?

Normal implantation: decider of endometrium.

A: attaches to the surface of the myometrium

I: invades the myometrium

P: extends beyond the uterus

Uterine contractility is usually impaired

Potential for tremendous blood loss.

Neuraxial is safe, GA is preferred

What is placenta previa? How does it present?

Placenta attaches to the lower uterine segment

-partially or completely covers the cervical os

-associated w/painless vaginal bleeding

-Potential for hemorrhage

What conditions ↑ the risk of placenta previa?

Previous C-sections

Hx of multiple births

What are the risk factors for placental abruption? How does it present?

Partial or complete separation of the placenta from the uterine wall prior to delivery. Results in hemorrhage + fetal hypoxia.

Risk Factors:

-PIH

-Preeclampsia

-Chronic HTN

-Cocaine use

-Smoking

-Excessive alcohol use

Presents w/painful vaginal bleeding. Pain may be so severe to cause breakthrough pain when an 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 Sx

A Pt suffers from retained placental fragments. What IV medication can you give to help with the extraction?

IV nitroglycerine

-uterine relaxation

What are the treatment options for uterine atony?

-Uterine massage

-Oxytocin

-Ergot alkaloids

-Intrauterine ballon

What does the APGAR score mean?

-Used to assess the newborn and guide resuscitation efforts

-Parameters are evaluated at 1 and 5 minutes after delivery

-May be predictive of neurologic outcome

-Normal → 8-10

-Moderate distress → 4-7

-Impending demise → 0-3

Know how to calculate the APGAR score.

HR

absent = 0

<100 = 1

>100 = 2

Respiratory Effort

Absent = 0

Slow, irregular = 1

Normal, crying = 2

Muscle tone

Limp = 0

Some flexion of extremities = 1

Active motion = 2

Reflex irritability

Absent = 0

Grimace = 1

Cough, sneeze, or cry = 2

Color

Pale, blue = 0

Body pink, extremities blue = 1

Completely pink = 2

What is the best indicator of ventilation during neonatal resuscitation?

Resolution of bradycardia

How do you dose epinephrine + fluids during neonatal resuscitation?

1:10,000

10-30mcg/kg IV

0.05-0.1mg/kg intratracheal

Volume expander

PRBC, NS, LR

10mL/kg over 5-10 minutes

What are the normal vital signs for a newborn? How do they trend as the child ages?

SBP 70

DBP 40

HR 140

RR 40-60

Why is the neonate's minute ventilation higher than the adult?

O2 consumption + CO2 production are 2x the adult's

It is metabolically more efficient to ↑ RR that to ↑ Vt

What is the primary determinant of BP in the neonate?

Heart rate

BP = HR x SV x SVR

Describe the autonomic influence on the newborn's heart.

immature at birth (SNS > PSNS) laryngoscopy/suctioning can → Bradycardia

-admin atropine to mitigate

BaroR reflex is poorly developed.

Contrast the breathing pattern in adults + infants.

Adult: mouth or nose

Infant: preferential nose up to 5 mo

-most infants convert to oral if nasal is obstructed

-bilat choanal atresia may req emergency a.w. management if infant is unable to mouth breathe

Contrast the relative size of the tongue in adults + infants

Adult: small r/t oral volume

Infant: large r/t oral volume

-tongue closer to soft palate + more likely to obstruct upper a.w.

-more difficult to displace during laryngoscopy

Contrast the relative neck length in adults + infants.

Adult: longer

Infant: short

-more acute angle required to visualize glottis

Contrast the epiglottis shape in adults + infants.

Adult: C shape, floppier, shorter

Infant: U shape, stiffer, longer

-stiff epiglottis makes it more difficult to displace during DL

Contrast the VC position in adults + infants.

Adult: perpendicular to trachea

Infant: anterior slant

-visualization + passage of ETT may be more difficult

-ETT may get stuck in the anterior commissure

Contrast the laryngeal position in adults + infants.

Adult: C5-C6

Infant: C3-C4

-larynx more superior/cephalad/rostral, but NOT anterior.

-only more "anterior" during neck flexion

-Same position as the adult ~5-6 y/o

Contrast the narrowest point of the a.w. in adults + infants.

Adult: glottis (VC)

Infant: cricoid or glottis

-resistance to ETT beyond the VC is likely the cricoid ring

-cricoid tissue is prone to inflammation + edema formation → stridor or obstruction

-Pouiseuille's law - small △ in radio can sig ↑ resistance to airflow

Contrast the orientation of the R mainstem bronchus in adults + infants.

Adult: more vertical

Infant: less vertical

-up to 3 y/o, both bronchi 55º

-adult: R 25º, L 45º

Contrast the optimal intubation position for adults + infants.

Adult: sniffing

Infant: head on bed w/shoulder roll

-infant has lg occiput

-sniffing position will place glottic opening in a more anterior position

Contrast the O2 consumption, Alveolar ventilation, RR, Vt in neonates + adults.

neonatal SA is 1/3 of the adult + O2 consumption is 2x the adult. neonate must ↑ alveolar ventilation to sustain normal gas tensions.

Why do neonates desaturate faster than adults?

Neonates have a/an:

-Increased oxygen consumption to support metabolic demand

-Increased alveolar ventilation to increase oxygen supply

-Slightly decreased FRC reflects a reduced oxygen reserve

-The net result is that the neonate has an increased ratio of alveolar ventilation relative to the size of its FRC.

Why is an inhalation induction faster with a neonate than with an adult?

↑ ratio of alveolar ventilation r/t the size of FRC

Faster turnover of FRC

What is the difference b/t fast + slow twitch m fibers? How does this r/t neonatal pulmonary mechanics?

Diaphragm + intercostal m are composed of 2 types of m fibers:

Type 1: slow-twitch

-built for endurance - resistant to fatigue

Type 2: fast-twitch

-built for short bursts of heavy work - tire easily

Smaller # of Type 1/endurance fibers in the diaphragm ↑ neonate's risk for respiratory fatigue + failure

Compare + contrast neonates to adults in terms of FRC, VC, TLC, RV, CC, and Vt.

How does the newborn's ABG change from delivery to the 1st 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 hgb? Why is this important?

19 mmHg

Oxyhgb curve shifts L (L = love)

benefits fetus by creating O2 partial P gradient across the uteroplacental membrane that facilitates passage of O2 from the mother to the fetus.

Why does Hgb F have a higher affinity for O2?

Adult Hgb (HgbA) consists of 2 ⍺ + 2 β chains

Hgb F consists of 2 ⍺ + 2 gamma chains

2,3 DPG causes a R shift in oxyhgb curve, but only β chains have a binding site for 2,3 DPG

Hgb F does not bing 2,3 DPG

-shifts curve L (L = love)

What are the indications for the FFP transfusion in the neonate?

Emergency reversal of warfarin

Correction of coagulopathic bleeding w/↑ PT > 1.5 or ↑ PTT

Correction of coagulopathic bleeding if > 1 BV has been replaced + coagulation studies are not easily obtained.

What is the dose for FFP transfusion in the neonate?

10-20 mL/kg

When is Plt transfusion indicated in the neonate? What it the dose?

to maintain Plt > 50,000

5 mL/kg if from apheresis

1pk/10kg if pooled concentrate

Describe the physiologic changes that occur as a result of a massive transfusion.

Alkalosis: 2/2 citrate metabolism to bicarbonate in the liver

Hypothermia: 2/2 cold blood

Hyperglycemia: 2/2 dextrose additive to stored blood

Hypocalcemia: 2/2 binding of Ca by citrate

Hyperkalemia: 2/2 administration of older blood

What is normal H/H at birth, 3 months, + 6-12 months?

Newborn: 14-20/45-65

3 months: 10-14/31-41

6-12 months: 11-15/33-42

Adult F: 12-16/37-47

Adult M: 14-18/42-50

What is the estimated blood volume in the premature neonate, term neonate, infant, child >1 y/o?

Premie: 90-100 mL/kg

Term: 80-90 mL/kg

Infant: 75-80 mL/kg

>1 y/o: 70-75 mL/kg

A 3-kg neonate requires emergency exploratory laparotomy for necrotizing enterocolitis. Her pre-op Hct is 50%. What is the maximum allowable blood loss to maintain a Hct of 40%?

EBV x [(Hct start - Hct target) / Hct start]

3kg x 90 mL/kg = 270

50% - 40% = 10%

270 x [10/50]

= 54

When do GFR + renal tubular fxn achieve full maturation?

Normal GFR 8-24 months

-before maturation, poor job conserving water → intolerant of fluid restriction

-unable to excrete lg volumes of water → do not do well with fluid overload

Normal tubular fxn 2 yrs

-1st few days: obligate Na loser

-then better to retain than excrete

-tendency to lose glucose to urine

Compare + contrast the distribution of body water in the premie, neonate, child, and adult.

Premie

TBW 85

ECF 60

ICF 25

Neonate

TBW 75

ECF 40

ICF 35

Child

TBW 60

ECF 20

ICF 40

Adult

TBW 60

ECF 20

ICF 40

What signs suggest dehydration in the neonate?

-Sunken anterior fontanel

-Weight loss (a 10% reduction the first week is normal)

-Irritability or lethargy

-Dry mucus membranes

-Absence of tears

-Decreased skin turgor

-Increased hematocrit in the absence of transfusion

Describe the 4:2:1 rule of fluid management.

-Step 1: 0-10 kg → Begin with 4 mL/kg/hr

-Step 2: 10-20 kg → Add 2 mL/kg/hr to the previous total

-Step 3: > 20 kg → Add 1 mL/kg/hr to the previous total

-If the patient is > 20 kg → patient's weight in kg + 40

How should the NPO fluid deficit be replaced?

Multiply hourly maintenance rate by # of hours NPO time.

Replace over 3 hours

1st hr: 50%

2nd + 3rd hr: 25%

How should 3rd space losses be replaced?

Minimal surgical trauma: 3-4 mL/kg/hr

Moderate surgical trauma 5-6 mL/kg/hr

Major surgical trauma: 7-10 mL/kg/hr

Generally, 1st hour of anesthesia is not included

What ratio should be used to replace blood loss w/crystalloid, colloid, and blood?

Crystalloid: 3:1

Colloid: 1:1

Blood: 1:1

Which pediatric populations should receive an IVF that contains glucose?

Generally not recommended.

Reserved for @ risk of developing hypoglycemia:

-prematurity

-< 48 hrs of age

-small for gestational age

-newborns of diabetic mothers

-children w/DM who received insulin on day of Sx

-children who receive glucose-based parental nutrition

What is the CO in the newborn? How does this affect pharmacokinetics?

200mL/kg/min

Drugs are delivered + removed from the rest of the body faster than in an adult

Discuss plasma protein binding in the neonate.

-Before 6 months of age there are lower [ ] of albumin and alpha-1 acid glycoprotein

-Highly protein bound drugs will display higher free drug levels, which ↑ the risk of toxicity.