Hanan Fathy

Pediatric Nephrology Unit

Gas exchange across the alveolar-capillary barrier can be described as either perfusion-limited

or diffusion-limited:

• PaO2

• Arterial Oxygen Pressure• Measured on an ABG machine• Oxygen dissolved in plasma

• 0.003 ml O2/mmHg/dl plasma

• SaO2

• Percent Oxygen Saturation• Measured by saturation monitor (pulse-Ox)• ~1.34ml O2/g Hb

Increased Hemoglobin Affinity for Increased Hemoglobin Affinity for OxygenOxygen--a --a leftleftshiftshift of the curve...easy to load of the curve...easy to load oxygen...difficult to unloadoxygen...difficult to unload

Decreased Hemoglobin Affinity for Decreased Hemoglobin Affinity for OxygenOxygen-- a -- a right shiftright shiftof the curve...difficult to load...easy to of the curve...difficult to load...easy to unloadunload

Causes of shifts to the right

↑PCO2, ↓pH, ↑

temperature, ↑[2,3-DPG]

Causes of shifts to the left

↓PCO2, ↑pH, ↓

temperature, ↓[2,3-DPG]

• Bluish discoloration of skin and mucous membranes

• Noticeable when the concentration of deoxy-hemoglobin is at least 5g/dl

(O2 sat < 85%)

• 5g/dL of reduced Hb clinical cyanosis

• Hb 15 cyanosis at 75-80%• Hb 20 cyanosis at 80-85%• Hb 6 cyanosis at 45-50%

•  patient whose hemoglobin content is 15 g/dL (hematocrit approximately 45%) would not generate 5 g/dL of reduced (ie, deoxygenated) hemoglobin in the capillaries until his/her SaO2 level reached about 85% (PaO2 50 mm Hg).

• When hemoglobin content is 9 g/dL (hematocrit approximately 27%), the threshold SaO2 level for manifesting cyanosis is lowered to about 73% (PaO2 38 mm Hg). At this level of hypoxemia, the patient would certainly have other manifestations of hypoxemia (eg, respiratory symptoms, mental status changes) apart from cyanosis.

• With a hemoglobin content of less than 9 g/dL, the patient would likely succumb from hypoxemia before cyanosis became evident.

Cyanosis has one of two causes, which may act together:

• Reduction of the arterial saturation (low S aO2)

• Or increase in the arterio-venous oxygen content difference. 

(A large oxygen extraction is seen in disorders with low bloodflow).

• Central cyanosis may be simulated by methaemoglobulinaemia and sulphaemoglobulinaemia.

Impaired pulmonary function1. Airway obstruction2. Pulmonary diseases

Right-to-left shunting of blood

Central Cyanosis

Cyanosis (central, in children)

• This is cyanosis that is caused by reduced oxygen saturation of the systemic arterial blood.

Etiology• Possible causes include:• cardiac shunt - where the venous

blood enters the left side of the heart without passing through the lungs, ie. a right to left shunt

• pulmonary shunt - where there is inadequate oxygenation of the blood as it passes through unventilated alveoli

Cyanosis (central, in children)

• Parenchymal lung disease• Right to left cardiac shunt - congenital

cyanotic heart disease

• Decreased PO2 of inspired air - high altitude

• Hypoventilation

Parenchymal lung disease

• Airway obstruction,pneumonia,massive pulmonary embolism, pulmonary edema,chronic airflow obstruction emphysema

• Seriously impaired pulmonary function, through perfusion of unventilated or poorly ventilated areas of the lung or alveolar hypoventilation, resulting in decreased alveolar PO2 and SaO2

• Congenital cardiac lesion : tetralogy of Fallot (the combination of

ventricular septal defect and pulmonary outflow tract obstruction ).

• Pulmonary arteriovenous fistulae :congenital or acquired, solitary or multiple,

microscopic or massive.

Shunting of systemic venous blood into the arterial circuit

Associated features• Possible clinical features include:

• The warm mucous membranes are blue, for example the tongue, the inside of the lips

• Central cyanosis increases immediately on exercise which is not the case for peripheral cyanosis

• Often there is polycythaemia with an abnormally high haemoglobin and haematocrit; this must not be confused with neonatal polycythaemia which may mimic cyanosis

• Clubbing is often seen in patients with central cyanosis

• Note that the absolute discriminating feature between central and peripheral cyanosis is obtained from testing the oxygen saturation of arterial blood.

Chronic cyanosis causes clubbing of the digits

Cyanosis (peripheral)

• This is due to poor peripheral circulation.

• Possible causes:• All causes of central cyanosis cause

peripheral cyanosis• Low cardiac output e.g. heart failure• Vasoconstriction e.g. due to low

ambient temperature, Raynaud's phenomenon

• Arterial obstruction e.g. atheroma• Venous obstruction

peripheral vs central

peripheral

• Sluggish blow flow in capillaries

• Involves extremities (acrocyanosis)

• Spares trunk & mucous membranes

central

• Abnl of lungs or heart that interferes w/ O2 transport

• Involves trunk & mucous membranes

Possible causes of mixed cyanosis

• all causes of central cyanosis may lead to peripheral cyanosis

• low cardiac output e.g. heart failure

Cyanosis due to abnormal Hb derivatives

Central cyanosis may be simulated by methaemoglobulinaemia and sulphaemoglobulinaemia.

Evaluation of cyanosis: 100% O2 testmeasure PaO2 in room air and 100% O2

Lung disease:1. Room air PaO2 30 mmHg O2

sat=60%

2. 100% O2 PaO2 110 mmHg O2 sat=100%

Cardiac disease:1. Room air PaO2 30 mmHg O2

sat=60%

2. 100% O2 PaO2 40 mmHg O2 sat=75%

PaO2 >100 mmHg suggests lung diseaseLittle or no change in PaO2 O2 suggests cyanotic heart disease

• Infant on Room Air, get ABG• Infant on 100% oxygen, get

ABG

• PaO2 unchanged = fixed shunt = CCHD

• Max PaO2 <100 = CCHD

• Max PaO2 >200 = No CCHD

• History (age, gender, family disease history)

• Clinical differentiation of central as opposed to peripheral cyanosis

• The presence or absence of clubbing of the digits

• Determination of PaO2 tension and SaO2

• Spectroscopic and other examinations of the blood for abnormal types of hemoglobin (critical in the differential diagnosis of cyanosis)

• particularly the onset (cyanosis present since birth is usually due to congenital heart disease)

• possible exposure to drugs or chemicals that may produce abnormal types of hemoglobin

• Determination of arterial

oxygen saturation • Oximetric studies

• physical or radiographic

examination ,

echocardiography, right heart

catherization and

angiocardiography• Spectroscope

• Cyanosis + Dyspnea

Disorders of respiratory or cardiovascular

system

• Cyanosis with mild or no dyspnea

Methemoglobinemia

Sulfhemoglobinemia: Spectroscopy

helpful

• Cyanosis + clubbing

Severe, long duration

• Classification of CHD:

Acyanotic versus cyanotic

Acyanotic

Mixedblood flow

Pulmonary blood flow

Obstruction to Blood flow

from ventricles

PulmonaryBlood flow

Cyanotic

•Atrial septal defect (ASD)•Ventricularr septal defect (VSD)

•Coarctation of Aorta•Aortic stenosis

•Tetrology of Fallot•Tricuspid atresia

•TranspositionOf great vessels•Truncus arteriosus

• Placenta is the source of oxygen for the fetus, it has 2 arteries and 1 vein.

• Fetal lungs receive less than 10% of the blood volume ; lung don’t exchange gas.

• Right atrium of fetal heart is the chamber with the highest oxygen concentration.

The three openings that close at birth are:

• Ductus Arteriosus connects the pulmonary artery to the aorta, bypassing the lungs

• Ductus Venosus connects the umbilical vein and the inferior vena cava bypassing the liver.

• Foramen Ovale is the opening between right and left atrias of the heart , bypassing the lungs.

TOF

Oligem ia

TGA + VSD

Plethora

RV

T AtresiaP Atresia no VSD

Oligem ia

AVSDEisenm enger VSD

Plethora

LV

CYANOTIC

•Severe Cyanosis PaO2 ≤ 40 mmHg

• Decreased pulmonary blood flow

• Tricuspid atresia, intact ventricular septum

• Pulmonary atresia (with or without other lesion)

• Critical pulmonary stenosis• Ebstein’s anomaly• Tetralogy of Fallot*

• Chest X-RayDecreased pulmonary vascular markings

Huge cardiac silhouette in Ebstein’s anomaly

“Boot-shaped heart” in Tetralogy of Fallot

•MIXING LESIONS PaO2 > 40 and ≤ 100 mmHg

•Clinical Characteristics

• Transposition/ VSD• Total anomalous

pulmonary venous return• Truncus arteriosus

•Arterial oxygen content depends upon the relative amounts of pulmonary and systemic blood flow

•Left sided obstruction

• Clinical Characteristics

• Can present during newborn period when ductus arteriosus closes if severe

• If left-sided obstruction coexists with a left-to-right shunt or mixing lesion, can cause earlier symptoms

• Can present due to murmur, pulse abnormality, blood pressure abnormality, or shock

• Too much oxygen can hurtsteals blood flow from systemic to pulmonaryHigh sats – low blood pressureLower sats – better blood pressure

• A polycythemic newborn with a hemoglobin of 20 g/dL requires an arterial oxygen saturation below 75–85% (a P O2 of 40–45 mm Hg) before appearing cyanotic.

This arterial desaturation may be a result of• (1) structural defects, such as transposition of the

great arteries, tetralogy of Fallot, total anomalous pulmonary venous return, tricuspid atresia, or truncus arteriosus;

• (2) intracardiac right-to-left shunting, which occurs at the foramen ovale and ductus arteriosus in newborns with persistence of the fetal circulation due to high pulmonary vascular resistance, but an otherwise structurally and functionally normal heart; or

• (3) left heart obstructive lesions, such as critical aortic stenosis or coarctation, due to associated pulmonary edema and pulmonary venous oxygen desaturation.

• primary lung disease, including parenchymal and airway or diaphragmatic abnormalities, must be differentiated from cardiovascular etiologies as a cause of cyanosis.

PPHN

Normal Arterial Number Decreased Arteries e.g. CDH

Normal muscularization Increased muscularization

Developmentalimmaturity

Maladaptation dueto acute injury (commonest) e.g.Sepsis, Meconiumaspiration synd., asphyxia

Chronic injurywith vascularremodeling

Malform-ation

Primary lung disease• RDS, pneumonia, hypoplasia, CCAM, lymphangectasia,

lobar• Emphysema

• Mechanical interference with lung function• Congenital diaphragmatic hernia, pneumothorax,

pneumomediastinum, chylothorax, choanal atresia, vascular ring, tracheal esophageal atresia, anomalies of the airway/larynx, Pierre-Robin/ micrognathia

• Pulmonary hypertension• Meconium aspiration, pneumothorax, RDS, sepsis,

pneumonia

CENTRAL NERVOUS SYSTEM

Seizure, meningitis, encephalitis, severe IVH, subdural or subarachnoid hemorrhage,

• Severe hypermagnesemia• Shock• Sepsis, hypovolemia, adrenal crisis• Severe hypoglycemia (IDM, SGA babies)• Congenital neuromuscular condition

(Werdnig-Hoffman)• - METHEMOGLOBINEMIA

Newborn Presentation of CHD

• Cyanosis- Usually minimal symptoms- First 24-72 hours of life- Duct-dependent pulmonary

blood flow• CHF/Circulatory Collapse/Shock

- First 2 weeks of life- Ductal-dependent systemic

blood flow• Secondary end-organ dysfunction

- Heart, Brain, Kidneys, GI

Evaluation of the Cyanotic Neonate

• Detecting cyanosis:• ambient lighting• skin color • hemoglobin

•if Hg is 20 gm/dl; 4 gm desaturated-visible cyanosis

•if Hg is 10 gm/dl; 2 gm desaturated-not cyanotic• Check Saturation

• Hyperoxia Test to Determine Intrapulmonary vs. Intracardiac Shunt

Hyperoxia Test

1. DANGERS: Pulmonary overcirculation

Closing the PDADeath

Pulse Oximetry

•easy to use, harmless when

done correctly

•accuracy of 2% in the range of

70 to 100%

•consider cyanotic when Sat

<94% at 24 hours of age

•should be obtained prior to

discharge from nursery

CHD in the Neonate -- Cyanosis

Chest Radiograph may be helpful:

• Decreased pulmonary vascular markings with intracardiac right to left shunting

• Normal/increased pulmonary vascular markings with intracardiac mixing of pulmonary and systemic venous return

• Narrow mediastinum due to anterior-posterior orientation of great arteries and small thymus

• Cardiomegaly is present w/ increased pulmonary vascular markings

d-TGA CXR: “egg on a string”

Tetralogy of Fallot - CXR

• Typical “boot-shaped” heart secondary to RVH and small main pulmonary artery segment

•Pulmonary vascular markings are decreased

Supracardiac TAPVC - CXR

“Snowman” appearance secondary to dilated vertical vein, innominate vein and right superior vena cava draining all the pulmonary venous blood

TAPVR - CXR Infracardiac = Obstructed = Surgical Emergency

Ebstein’s malformation of TV

• Massive RA dilation due to severe tricuspid regurgitation

• R to L shunt at atrial level causes cyanosis

• Degree of cyanosis related to size and compliance of functional RV

• Cyanosis usually decreases as PVR falls shortly after birth

Cyanosis CHF/Shock

Rt to Lt shunting:

Tricuspid atresia

TOF/ Pulm atresia

Ebstein’s anomaly

Lt Ventricular Outflow Tract Obstruction: HLHS

Coarctation of Aorta/ AS

Truncus arteriosus

TGA with VSD

TAPVR

Critical CHD: Initial Evaluation and

Management

• ABC’s• Oxygen (judicial) to saturations of 80-

85%• Place umbilical lines• PGE (0.025-0.1 micrograms/Kg/min)

• History• Complete physical with four extremity

BP’s• Pre and post-ductal oxygen saturations• Hyperoxia test• CXR• EKG• Echocardiogram

Suspected CHD: Initial Evaluation and

Management • Pre and post-ductal oxygen saturations

• If pre-ductal sat higher than post-ductal sat (differential cyanosis)• Left heart abnormalities (such as

aortic arch hypoplasia, critical aortic stenosis, interrupted aortic arch)

• Persistent pulmonary hypertension• If post-ductal sat higher than pre-

ductal (reverse differential cyanosis)• TGA with CoA or TGA with IAA• TGA with supersystemic

pulmonary vascular resistance

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