unit i. oxygenation (1)

8/7/2019 UNIT I. Oxygenation (1)

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University of the Cordilleras

College of Nursing

UNIT I. Oxygenation

I. Respiratory

A. Assessment of Respiratory Function

1. Review: Purpose, Structure, Functions

Structures of the Upper Respiratory Tract

a. Nose

y Serves as passageway for air to pass to and from the lungs. It filters impurities,

humidifies and warms the air as it is inhaled.

y Responsible for olfactionolfactory receptors are located in the nasal mucosa. This

function diminished with age.

b. Sinuses/ Paranasal

y Frontal, ethmoidal, sphenoidal, and maxillary

y Serves as resonating chamber in speech

y Common site of infection

c. Turbiunate Bones (Conchae)

y Shell like appearance- because of their curves, these bones increase the mucous

membrane surface of the nasal passages and slightly obstruct the air flowing through

them.

d. Pharynx, Tonsils and Adenoids

y The pharynx (throat) connects the nasal and oral cavities to the larynx: nasa, oral,

laryngeal

y Epiglottis- forms the entrance of the larynx

y The adenoids a paryngeal tonsils are important links in the chain of lymph nodes

guarding the body from invasion by organisms entering the nose and the throat.

e. Larynx

y For vocalization; protects the lower airway from foreign substances and facilitatescoughing. Also called the voicebox.

f. Trachea (Windpipe)

y Serves as the passageway between the larynx and the bronchi.

Structures of the Lower Respiratory Tract

a. Lungs

y Paired of elastic structures enclosed in the thoracic cage, which is an airtight chamber

with distensible walls.

y Ventilation requires movement of the walls of the thoracic cage and its floor, the

diaphragm to increase and decrease the capacity of the lungs.

b. Pleuray A serous membrane enclosing the lungs

y Divides into 2:

Parietal pleura- lines the chestwall or thorax

Visceral pleura- covers the lungs

y Together and the small amount of pleural fluid between this two membranes serves to

lubricate the lungs and thorax and permit smooth motion of the lungs within the

thoracic cavity with each breath.



c. Mediastinum

y Contains all the thoracic tissue outside the lungs.

d. Lobes

y Left: upper and lower lobe; Right: upper, middle and lower

y Each lobe is further subdivided into two to fine segments separated by fissures, which

extensions of the pleura.e. Bronchi and Bronchioles

y Trachea and Segmental Bronchi conducting airways

y Subsegmental bronchi (Bronchioles)- surrounded by connective tissue that contains

arteries, lymphatics and membranes

y Non-respiratory- contains 150 ml of air, physiologic space

y Respiratory unit:

y Respiratory and Alveolar ducts- transitional passageway between the conducting

airways and the gas exchange airways.

f. Alveoli

y In adult, lungs is made up of about 300 million alveoli which are arraged in clusters of 15

to 20. Would cover 70 square meters- the size of a tennis court.

y Three types of alveolar cells:

y Type I- epithelial cells that forms the alveolar walls

y Type II- metabocally active, secretes surfactant- s phospholipids that line the inner

surface and prevents alveolar collapse.

y Type III- large phagocytic cells that ingest foreign matter (mucus, bacteria) and act as

important defense mechanism.

Functions of Respiratory System

The respiratory system performs this function by facilitating life sustaining process such as oxygen

transport, respiration, ventilation and gas exchange.

CO2

Must be remove from

cells to prevent buildup of acid waste

products

Cells derives energy

they need

Oxidation

CO, Fats, CHON OXYGEN

(Needed for Oxidation)



1. Oxygen Transport

y Approximately 1000 ml (1L) of O2 is

transported to the cells each minute.

y 2 Forms: a.) small amounts dissolves in

plasma b.) Binds to hemoglobin molecules

y Without Hgb, O2 would not reach the cellsin amounts sufficient to maintain normal metabolic

function.

y O2 is supplied to and removed from cells

by the way of circulating blood.

2. Respiration

y Gas exchange between the athmospheric air and the blood and cells of the body.

Tissue capillary exchange

Blood enters systemic veins

(called venous blood)

Travels the pulmonary circulation

O2 diffuses from alveoli to the blood

Concentration gradient

to

Alveoli - Blood

O2

CO2 diffuses from the blood to the alveoli

Concentration gradient

to

Alveoli - Blood

CO2

Movement of air in and out of the airways (Ventilation)

continually replenish the O2 and removes

the CO2 from the airways in the lungs

3. Ventilation

y Movement of air in and out of the airways

y Inspiration: air flows from the environment into the trachea, bronchi, bronchioles, and

alveoli

y Expiration: alveolar gas travels the same routine in reverse



Increased compliance:

y Indicates that the lungs or chest wall is abnormally easy to inflate and has lost some

elastic recoil / thorax is overdistended (i.e., emphysema, normal in ageing)

Decreased compliance:

y Indicates that the lungs or chest wall is abnormally stiff or difficult to inflate (i.e., RDS,

pneumonia, pulmonary edema, atelectasis, pulmonary effusion, pneumothorax,

hemothorax)

Lung Volumes and Capacities

y Lung function which reflects the mechanics of ventilation, is viewed in terms of lung

volumes and lung capacities.

a. Lung Volume: categorized as a tidal volume, inspiratory reserve volume, expiratory

reserve volume, and residual volume

b. Lung Capacity : evaluated in terms of vital capacity, inspiratory capacity, functional

residual capacity, and total lung capacity.



Diffusion and Perfusion

a. Diffusion: process by which the oxygen and carbon dioxide are exchanged at the air-blood

interface

b. P ulmonary P erfusion: the actual blood flow through the pulmonary circulation.

y Alveolar capillary membrane ideal for diffusion due to its large surface area and thin

membrane.

y Pulmonary circulation is considered a low presssure system

y Systolic- 20 to 30 mmHg ; Diastolic- 5 to 15 mmHg: can vary its capacity to

accommodate the blood flow it receives.

Ex ample:

Upright position- pulmonary artery pressure is not great enough to supply blood

to the apex of the lungs against the gravity.

Lying down turns to one side- more blood passes to the dependent part

y Perfusion is influenced by alveolar pressure.

Increased pressure in the alveoli

Capillaries will be squezzed

Increased blood pressure in the capillaries

Collapse or narrowing of the capillaries

Ceases the flow of blood

Altered perfusion

Ventilation and Perfusion Balance and imbalance

Ventilation: flow of gas in and out of the lungs

Perfusion: the filling of pulmonary capillaries with blood



y Effective and adequate gas exchange depends on an approximately even distribution of

gas (ventilation) and blood (perfusion) in all portions of the lungs.

y Alterations in perfusion may occur with a change in:

a. Pulmonary artery pressure

b. Alveolar pressure

c. Gravity

y Alterations in ventilation may occur in :

a. Airway blockage

b. Local changes in compliance

c. Gravity

y Ventilation/Perfusion (V/Q) imbalance occurs from inadequate ventilation, inadequate

perfusion or both.

N ormal Ratio (A)

y In a healthy lung, a given amount of blood passes an alveolus and is matched with an

equal amount of gas. The ratio is 1:1 (ventilation matches perfusion).



Low Ventilation P erfusion Ratio: Shunts (B)

y Also called shunt-producing disorders. When perfusion exceeds ventilation, shunt exists.

y Blood bypasses the alveoli without gas exchange occuring.

y Seen in obstruction of the distal airway (i.e., pneumonia, atelectasis, tumor or mucus

plug).

H igh Ventilation P erfusion Ratio: Dead Space (C)

y Ventilation exceeds perfusion, dead space results. The alveoli do not have an adequate

blood supply for gas exchange to occur.

y Seen in a variety of disorders, including pulmonary emboli, pulmonary infarction, abd

cardiogenic shock.

Silent Unit ( D)

y In the absence of ventilation and perfusion or with limikted ventilation and perfusion,

silent unit occurs.

y Seen in pneumothorax and severe acute respiratory distress syndrom (ARDS)

Ventilation and perfusion imbalance causes shunting of blood, resulting in hypoxia (low cellular

level of oxygen).

Severe hypoxia results when the amount of shunting exceeds 20%.

Supplemental oxygen may eliminate hypoxia depending on the type of V/Q imbalance.

Gas Exchange

y The air we breathe is a gaseous mixture consisting of:

Nitrogen (78.62%)

Oxygen (20.84%)

Traces of CO2 (0.04%)

Water vapor (0.05%)

Helium and argony Atmospheric pressure at sea level is about 760 mmHg

Figure 7.



y Partial pressure- is the pressure exerted by each type of gas in a mixture of gases.

y Partial pressure of gas: concentration of that gas in a mixture of gases.

y The total pressure exerted by the gaseous mixture is equal to the sum of the partial pressures.

Partial Pressure of Gases

Calculation:

PN2 = 79% of 760 (0.79 x 760) or 600 mmHg

PO2 = 21% of 760 (0.21 x 760) or 160 mmHg

Air from the atmosphere enters the trachea

& saturated with water vapor

H2O vapor displaces some of the gas

(so air pressure within the lung remains equal

To the air pressure outside= 760 mmHg)

H2O vapor exerts a pressure of 47 mmHg when fully saturates

A mixture of gases at a body temp. 37°C

N and O2 are respopnsible for the remaining 713 mmHg

(760-47) pressure

Mixture is diluted by CO2

In the alveoli: water vapor continues to exert

Pressure of 47 mmHg. The remaining 713 mmHg is exerted

As follows:

Nitrogen = 569 mmHg (74.9%)

Oxygen = 104 mmHg (13.6%)

CO2 = 40 mmHg (5.3%)



Partial Pressure in Gas Exchange

y Gas is exposed to liquid and dissolves until equilibrium is reached and exerts partial pressure

y At equilibrium: Partial pressure of gas in the liquid = Partial pressure of gas in gaseous mixture.

Oxygenation of venous blood in the lung

y Oxygen diffuses across the membraneto dissolve in the blood until the partial pressure of O2

is the same that is in the alveoli (104 mmHg)

y In the blood: Oxidation CO2 is a byproduct increases CO2 at higher partial pressure in the

blood than that of the alveoli

y In the lungs: CO2 diffuses out of the venous blood into the alveolar gas

y At equilibrium: PCO2 in the blood = PCO2 in the alveoli (40 mmHg)

Effects of pressure in O2 transport

y Each 100 ml of normal arterial blood carries 0.3 ml of O2 physically dissolved in plasma; 20 ml of

O2 in combination with Hgb.

O2 + Hgb HgbO2



y The higher the PaO2 thegreater the amount of O2 dissolved.

Example:

PaO2 of 10 mmHg, 0.03 ml of O2 is dissolved in 100ml of plasma

y The amount of dissolved O2 is directly proportional to the partial pressure regardless of how

high the O2 pressure rises.

y The amount of O2 that combines with Hgb depends on the PaO2 but only up to a PaO2 of about

150 mmHg.

y If the PaO2 is less than 150 mmHg the percentage of Hgb saturated with O2 is lower

Example:

PaO2 of 100 mmHg (NV); saturation is 97%

PaO2 of 40 mmHg; saturation is 70%

Oxyhemoglobin Dissociation Curve

y The curve shows the relationship between the partial pressure of oxygen (PaO2) and the

percentage of saturation of oxygen (SaO2).

y The percentage of saturation can be affected by the following factors:

1. Carbon dioxide

2. Hydrogen ion concentration

3. 2,3- diphosphoglycerate



y A rise in these factors causes the curve shift to the right so that more O2 is then released to the

tissues at the same PaO2.

y A reduction causes the curve to shift to the left making the bond between O2 and Hgb stronger,

so that less O2 is given up to the tissue at the same PaO2

Clinical Significance:

Normal Value of PaO2 = 80 to 100 mmHg (95% to 98% saturation)

15% margin of excess O2 available to the tissue

Normal Hgb level of 15 mg/Dl; PaO2 level of 40 mmHg (O2 saturation 75%)

y There is adequate O2 available for the tissue but no reserve for physiologic

stresses that increase tissue O2 demand.

Cardiac Output (CO)- important consideration in O2 transport. It determines the amount of O2

delivered to the body and which affects the lungs and tissue perfusion.

P repared by:

Ma. Theresa Murao-Adi RN

06/12/10

unit i. oxygenation (1)

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