Week 4: Cardiovascular Flashcards
Fetal circulation
- The placenta provides the fetus with ______ oxygenated blood.
- PO2 in umbilical vein is _____mmHg.
- poorly
- ~30
Fetal circulation
- Fetal lungs receive _______% of cardiac output
- Oxygenated blood from the placenta returns via the UV to the portal venous system where 30-50% is shunted across the ________ to the _________.
- 10-15
- ductus venosus; IVC
Cardiovascular physiology
Blood from the IVC enters the RA and then the blood with greater oxygen content is directed across the _________ to the LA.
This blood mixes with pulmonary venous circulation and is ejected out to the ascending aorta to the growing heart and brain.
O2 saturation is ___ - ____% at this point.
- foramen ovale
- 65-70%
- Venous return from the SVC and _____% of IVC blood flow reaches the RV and is pumped into the PA.
- The high pressure in the pulmonary vasculature redirects blood flow across the _______ _______into the descending aorta.
- Blood O2 saturation is ___ - ____% at this point
- _______ of this blood is returned to the placenta, the rest perfuses the intestines, kidneys and lower parts of the body.
- 20%
- ductus arteriosus
- 55-60%
- 2/3
Cardiovascular Physiology
- Blood supplied to the heart and upper body has a greater oxygen content [SaO2 = _____%; pO2 = ___-____ mm Hg]
- than that supplied to the abdominal organs, lower limbs and placenta [SaO2 = _____%; pO2 = _____-_____ mm Hg].
- 65% ; 26 – 28
- 55%; 20 – 22
Cardiovascular Physiology
- In utero, the ______ ventricle pumps about 60% of the combined ventricular output, and the ______ ventricle pumps the remainder.
- Fetal circulation is reliant on a high _____ _______ state, greater ______ concentrations and alterations in oxygen binding (think 2,3 DPG) in order to properly oxygenate the fetus.
- right ; left
- cardiac output, hemoglobin
Fetal circulation consists of 3 shunts, which are holes or small passages, which moves, or allows movement of fluid, from one part of the body to another:
– Ductus arteriosus
– Foramen ovale
– Ductus venosus
Ductus arteriosus functions and is associated with:
– Protects the lungs against circulatory overload
– Allows the right ventricle to strengthen
– Associated with high pulmonary vascular resistance and
low pulmonary blood flow
like a “pop-off” valve
Foramen ovale function
- Shunts highly oxygenated blood from the right atrium to the left atrium
Ductus venosus
– Fetal blood vessel connecting the ____ to the _____ and bypassing the liver.
– Blood flow is regulated by a _____ (any ring-like muscle that normally maintains constriction of a body passage or orifice and that relaxes as required by normal physiological functioning)
– Carries _______ blood from the placenta
- umbilical vein; inferior vena cava
- sphincter
- oxygenated
Three dramatic events that change circulation occur immediately after birth:
and most importantly:
- Cessation of the umbilical-placental circulation shortly after the lungs expand (umbilical vessels are reactive to mechanical stimulation esp. stretch)
- Expansion of the lungs to a normal FRC and pulmonary vasculature
- Alveolar PCO2 falls, alveolar PO2 rises
PULMONARY VASCULAR RESISTANCE FALLS
The ductus arteriosus
- Functionally closes in 58% of full-term infants by _______ after birth and in 98% by ______.
- This is in response to ______ oxygen tension and the reduction in circulating ________ that occurs once the placenta separates.
- Within ___ - ___ weeks ductal fibrosis occurs and the ligamentum arteriosum forms.
- 2 days; day 4
- increased; prostaglandins
- 2-3
Closure of the foramen ovale
In the fetus, over half of inferior vena caval blood comes from umbilical venous return.
- Removal of the placental circulation markedly decreases the amount of inferior vena caval blood returning to the heart and causes a small drop in right atrial pressure, whereas the increase in ____________ increases pulmonary venous return and elevates left atrial pressure.
– This combination of pressure changes closes the valve- like flap of the foramen ovale.
- pulmonary blood flow
The foramen ovale functionally closes when the LA pressure exceeds the RA pressure. But, it remains anatomically patent in 50% of children less than ____ years of age and in 25-30% of _______.
This explains why a healthy child can desaturate under anesthesia when _______ to ______ shunting occurs despite ventilation with 100% oxygen.
- 5; adults.
- right to left
Up to 1/3 of patients will have an unclosed patent foramen ovale!!!!
Cardiovascular Physiology
As the umbilical vein is ligated, ________ pressure falls and the ductus venosus functionally closes.
This will take _____-____ and by ______ only fibrous tissue, the ligamentum venosum is left.
portal;
1-2 weeks; 3 months
Neonatal Cardiovascular System
- Neonates have ____ muscle cells and ______ connective tissue compared to the adult myocardium
- ________ contractile elements and _______ water content
- ________ myofibrils and they are less organized
- fewer; more
- Limited; increased
- Fewer;
Neonatal Cardiovascular System
- Contractile dysfunction when exposed to substances that decrease extracellular ionized calcium (ie _____ in blood products, ______)
- ________ sensitive to inhalational anesthetics and calcium channel blockers
- citrate; albumin
- More
Neonatal Cardiovascular System
- Mitochondrial development is immature and the primary energy sources are _______ and ________ (as opposed to free fatty acids for adults).
- May explain why they tolerate _______ and recover faster than adults.
- carbohydrates; lactate
- ischemia
Neonatal Cardiovascular System
- Less contractile tissue means they have a limited response to increased __________. Compliance increases in the _______ period.
- High metabolic rate (______) compared to the adult (________ oxygen consumption). The neonate meets the demand with a high HR.
- _______ dominates initially and explains why neonates are prone to have a vagal response to stimuli.
- Very sensitive to negative inotrope and chronotropes
- preload; postnatal
- 6-8ml/kg vs. 2-3ml/kg
- PNS
Pulmonary Vascular Physiology
- Pulmonary vasculature development is _________ at birth and matures during the first few years of life.
- _______ proliferate faster than ______.
- Smooth muscle ______ and extends _______ in the vascular tree.
- By __________ of age PVR approximates adult levels.
- Incomplete
- Arterioles; alveoli
- thins; distally
- 6 months
Pulmonary Vascular Physiology
Fetal pulmonary vasculature is reactive to:
- ______,
- ______,
- increased levels of ______, and
- __________.
These can cause significant and prolonged increases in PVR (e.g., reactive pulmonary hypertension).
- hypoxia
- acidosis
- leukotrienes (particularly LTD4)
- mechanical stimulation (e.g., coughing on an endotracheal tube)
Pulmonary Vascular Physiology
7 strong vasodilators of fetal pulmonary vasculature:
- Acetylcholine,
- Histamine,
- Bradykinin,
- Prostaglandins D2, E1, E2 (PGE2)
- Prostacyclin (PGI2)
- β- adrenergic catecholamines, and
- Nitric oxide (NO)
Pulmonary Vascular Physiology
- Persistent fetal circulation occurs when severe and sustained increases in ________ prevent extrauterine life.
- Increased load on the RV induces ______ dysfunction and promotes ______ to ______ shunting through the foramen ovale.
- When ____ > ____ the ductus arteriosus opens and right to left shunting causes hypoxemia (treated with ____, ____, or_____).
remember RV does not have that musculature to contract
- PVR
- diastolic; right to left
- PVR; SVR
- NO, sildenafil, or ECMO
Pulmonary vascular occlusive disease (PVOD):
- Describes structural changes that occur in the pulmonary vasculature after long standing exposure to abnormal _____ and _______ patterns in utero and after birth.
- ____________, as well as external factors influence the development of the pulmonary vasculature and play a role in PVR.
- pressures; flow
- Congenital heart disease
Lung biopsies for Pulmonary Vascular Occlusive Disease demonstrate:
- Thickened muscle layers in the small pulmonary arteries,
- Intimal hyperplasia,
- Scarring
- Thrombosis
- Decreased number of distal (intraacinar) arteries.
Cardiovascular Physiology
■ Resting fetal heart rate averages ______ to _____ beats per minute.
■ The newborn heart rate averages about _____ beats per minute during sleep and increases to _____ to _____ beats per minute while the infant is awake.
■ In premature infants the resting heart rate is higher, averaging _____ to _____ beats per minute.
The heart rate gradually decreases with advancing age.
- 160 - 180
- 120; 140 - 160
- 120 - 140
Cardiovascular Physiology
■ Systemic arterial blood pressure in the fetus at term is about _______ mm Hg, and referred to as _________ pressure.
■ Arterial pressure in the mature infant averages _____ mm Hg, but it is lower in the premature infant.
Arterial pressure gradually increases with age.
- 60/35; amniotic cavity
- 70/50
Cardiovascular Physiology
■ After birth there is an ______ in the total output of the heart during the first few days.
■ There is a ______ increase in right ventricular output but a _______ increase in left ventricular output.
■ The cardiac output per kilogram of body weight falls fairly rapidly over the first 8 to 10 weeks after birth to about ________ mL/kg/min and then falls more slowly to the adult level of about ______-_____ mL/kg/min.
- increase
- modest; considerable
- 150; 70 to 80
Cardiovascular Physiology
■ The ________ in cardiac output after birth can be explained partly by the increased ________ required to maintain body temperature.
■ Cardiac output ______ changes in oxygen consumption.
■ Variations in metabolic activity, such as deviation from the neutral ambient temperature, increase _____ and _____.
- increase; metabolism
- parallels
- oxygen consumption and cardiac output.
Cardiovascular Physiology
The high resting cardiac output in the early postnatal period and the rapid fall over the first _______ weeks are also related to replacement of fetal hemoglobin by adult hemoglobin in circulating erythrocytes.
8
Cardiovascular Physiology
- The oxygen equilibration curve of fetal blood is shifted to the _______ as compared with that for adult blood.
- Although this is advantageous during fetal life because it aids in uptake of oxygen by fetal blood in the placenta, it is disadvantageous postnatally because it interferes with ______ of oxygen in the tissues at the PO2 levels prevailing after birth.
- left;
- release
**Changes occur in pulmonary circulation:
– The ______ pulmonary blood flow in the fetus results from the high pulmonary vascular resistance. The small arteries in the fetal lungs have a ______ medial smooth muscle layer, and maintained _______ of these vessels causes the high pulmonary vascular resistance.
– The total pulmonary vascular resistance markedly ________ with advancing gestation as a result of a great increase in the number of __________ during growth, resulting in an increase in cross-sectional area of the vascular bed.
- low; thick; constriction
- decreases; vessels
Cardiovascular Physiology
- The pulmonary vessels are very reactive to several physiological and pharmacologic influences.
- A decrease in ________ or in the _______ of the blood perfusing the pulmonary vessels constricts them.
- The vasoconstrictor responses to hypoxia and acidemia are _______.
- oxygen tension; pH
- additive
Pulmonary circulation is normally relaxed to some extent by release from endothelium of
nitric oxide (NO).
Congenital Heart Disease (CHD)
■ Defined as “a gross structural abnormality of the _______ or ____________ that is actually or potentially of functional significance”.
■ Occurs in _________ of 1000 live births
- heart; intrathoracic great vessels
- 4-50
Congenital Heart Disease (CHD)
Consists of an almost endless array of anatomic and functional variants.
Initial approach is to define what the cardiac position is in the thorax followed by the position of the abdominal organs:
– Levocardia, dextrocardia, mesocardiac
– Visceral solitus, inversus, ambiguous
CHD
There are several systems of classification for these lesions. Conceptually, some defects are best described as ______, ______, and __________.
Shunting,
Intercirculatory mixing
Single ventricle physiology.
CHD
Mask induction can be accomplished safely in a subset of these children.
However, reduced pulmonary blood flow in ______ lesions (_____ to _______ shunt where blood bypasses the lungs) will prolong the length of induction.
cyanotic;
Right to Left
CHD
occurs when blood return from one circulatory system (systemic or pulmonary) is recirculated to the same system, completely bypassing the other circulation.
Shunting
- Anatomic shunts are communications between two __________.
They are divided into simple and complex shunts.
- Complex shunts involve outflow obstructions at various levels within the ______, _______, or______.
- Volume overload lesions are usually caused by _______ to _____ shunting at the level of the atria, ventricles or great arteries.
- circulatory systems
- ventricle, valves or great vessels
- left to right
Anatomic features of tetralogy of fallot:
- Right ventricular outflow tract obstruction
- Large ventricular septal defect (VSD)
- Aortic override
- Right ventricular hypertrophy (RVH)
*Right to left shunting
* Infundibular narrowing
* Hypoplastic pulmonary arteries
CHD
Volume overload lesions
Atrial septal defect (ASD)
Ventricular Septal defect (VSD)
Atrioventricular septal defect (AVSD)
Patent Ductus arteriousus (PDA)
Truncus arteriousus
CHD
Obstruction to systemic blood flow: (4)
Coarctation of the aorta
Hypoplastic left heart syndrome
Interrupted aortic arch
Aortic stenosis
CHD
Obstruction pulmonary blood flow
- Pulmonary stenosis
- Tetrallogy of Fallot
- Pulmonary atresia
CHD
Parallel circulation
D-transposition of the great arteries
CHD
Single ventricle lesions
Tricuspid atresia
Double-inlet left ventricle
Unbalanced atrioventricular septal defect
CHD
Intrinsic Myocardial Disorders
Cardiomyopathy
Myocarditis
CHD
- Some lesions result in obstruction to systemic blood flow (ie severe aortic coarctation in which maintaining a patent _____ ______ is critical)
- Other lesions obstruct pulmonary blood flow (ie pulmonary atresia)
- Therapies are aimed at maintaining an open ductus arteriosus with _____, ______, _____, manipulating systemic and pulmonary vascular resistance and surgery when appropriate.
- ductus arteriosus
- PGE, stenting the ductus, diuretics
- Intercirculatory mixing describes ______________. Unless there is mixing of blood via an ASD, VSD, or PDA there is a complete separation of the two systems and is incompatible with life.
- _________ _________, among other interventions is life saving in these cyanotic infants.
- Transposition of the Great Arteries (TGA)
- Atrial septostomy
- is characterized by complete mixing of systemic and pulmonary venous blood at either the atrial or ventricular level; blood is distributed along both systems in parallel.
- Aortic or pulmonary outflow tract obstruction is commonly found.
- Examples are:
- Single ventricle physiology
- Hypoplastic left heart syndrome, Tetralogy of Fallot with pulmonary atresia, interrupted aortic arch.
Single ventricle physiology
- Management goals are to optimize pulmonary and systemic circulations.
- Sometimes, the ________ is the only source of systemic or pulmonary blood flow and these lesions are called ______________.
- PDA
- duct dependent
Table 18.3
Increasing PVR (9)
– PEEP
– High airway pressure
– Atelectasis
– Low FiO2
– Respiratory and metabolic acidosis
– Increased hematocrit
– Sympathetic stimulation
– Direct surgical manipulation
– Vasoconstrictors: Neo
Table 18.3
Decreasing PVR
– No PEEP
– Low airway pressure
– Lung expansion to FRC
– High FiO2
– Respiratory and metabolic alkalosis
– Low hematocrit
– Deep anesthesia
– Nitric oxide
– Vasodilators: milrinone, prostacyclin, others
Trisomy 21 (Down syndrome): associated with
- Macroglossia,
- Short neck,
- Hypotonia,
- OSA,
- Cervical spine instability,
- Obesity,
- Subglottic stenosis,
- Duodenal atresia,
- AV septal defects (in 40- 50% of patients),
- Bradycardia under anesthesia,
- Pulmonary hypertension.
Smaller ET-Tube
CATCH 22 (_________ syndrome) associated:
- Cardiac defects,
- Abnormal facies,
- Thymic hypoplasia,
- Cleft palate,
- Hypocalcemia.
Di George
Marfan syndrome associtated w:
- Involves a mutation of a connective tissue protein.
- Cardiovascular (ie.,aortic dissection),
- Pulmonary (spontaneous pneumothorax is common),
- Skeletal and Ocular manifestations.
VACTERL associated with
Vertebral,
Anal,
Cardiovascular,
Tracheoesophageal,
Renal,
Limb defects
you cannot IV blind stick
Physiology of the transplanted heart
- increase in resting HR and a blunted response to stress and exercise.
- altered response to atropine and glycopyrrolate.
- Titrate use of direct acting adrenergic agents for a pressor response.
- The denervated heart is sensitive to adenosine, calcium channel blockers, beta blockers and direct acting vasodilators. There is a lack of reflex tachycardia.
- Over time, the sympathetic reinnervation may occur but is variable in extent.
Physiologic HR Ranges
Normal Resting Blood Pressure in Children
■ 0-3 mos
■ 3-6 mos
■ 6-12 mos
■ 1-3 yrs
■ 3-6 yrs
■ 6-12 yrs
■ >12 yrs
■ 65-85/45-55
■ 70-90/50-65
■ 80-100/55-65
■ 90-105/55-70
■ 95-110/60-75
■ 100-120/60-75
■ 110-135/65-85
Anatomic features of tetralogy of fallot
- Right ventricular outflow obstruction
- Large ventricular septal defect (VSD)
- Aortic override
- Right ventricular hypertrophy (RVH)
Others:
- Arterial desaturation from right to left shunting
- Infundibular narrowing
- Hypoplastic pulmonary arteries
Table 16.1
Volume overload lesions
- ASD
- VSD
- AVSD
- PDA
- Truncus arteriousus
Table 16.1
Obstruction to systemic blood flow
- Aortic stenosis
- Coarctation of the aorta
- Interrupted aortic arch
- Hypoplastic left heart syndrome
Table 16.1
Obstruction to pulmonary blood flow
Parallel circulation
- Pulmonary stenosis
- Tetralogy of fallot
- Pulmonary atresia
D-Transpostion of great arteries
Table 16.1
Single ventricle lesions
- Tricuspid atresia
- Double-inlet left ventricle
- Unbalanced AVSD
Table 16.1
Intrinsic Myocardial Disorders
- Cardiomyopathy
- Myocarditis
Blood volume
Varies considerably during the immediate postnatal period and during the first year of life.
Preterm infant
Full-term infant
Infant
School aged
Adult
- 100 ml/kg
- 90ml/kg
- 80ml/kg
- 70ml/kg
- 70ml/kg
Table 18.9 Doses
Propranolol
0.01-0.1mg/kg
- nonselective B-blockade
Table 18.9
Labetalol
0.1-0.4mg/kg per dose
0.25-1.0mg/kg/hour infusion
- nonselective B-blockade,
- 0.1 mg/kg doses can be repeated every 5-10 minutes until desired effect
Esmolol
100 - 500mcg/kg loading dose (over 5 min)
50 - 250 mcg/kg/min
- Relative selective B-blockade
- can repeat or double bolus dose
- Venous sclerosis >10mg/ml
Sodium nitroprusside
start at 0.3 - 1.0 mcg/kg/min per infusion
maximum 6-10 mcg/kg/min
- Potent direct smooth muscle relaxation
- dilates both venous and arterial vessels
- potential cyanide toxicity
- reflex tachycardia
- check cyanide and thiocyanate levels if >4mcg/kg/min is infused or drug is used longer than 2-3 days.
Nicardapine
start at 0.5 -1 mcg/kg/min infusion
maximum 4-5 mcg/kg/min
- Dihydroxypyridine CCB
- Primary effect on coronary and peripheral vessels
- minimal effect on contractility or HR
- potentiates NMBAs
Nitroglycerin
0.5 - 10 mcg/kg/min infusion
Mainly venous dilation
Direct smooth muscle relaxation
facilitates cooling and rewarming during bypass
Phentolamine
0.05 -0.1 mg/kg dose;
0.5 -5 mcg/kg/min infusion
Selective a-blocker
mainly arterial dilation
Enalaprilat
5-10 mcg/kg per dose
q8-24 hours
- Lond duration effect
- angioedema
- renal failure
- hyperkalemia
- hypotension
Hydralazine
0.1 - 0.2 mg/kg bolus q6 hours
Maximum dose 20mg/dose
direct-acting smooth muscle (*arterial)
tachyphylaxis
reflex tachycardia
lupus-like syndrome
drug fever
thrombocytopenia
Prostaglandin E1
0.05-0.1mcg/kg/min infusion
Direct smooth muscle relaxation
**for ductus arteriosus
Variable pulmonary and systemic vasodilation
Apnea in neonates
