This document discusses respiratory disorders and the assessment of respiratory function through arterial blood gas analysis. It covers the basics of respiration including pulmonary ventilation, gas exchange, transport of oxygen and carbon dioxide in the blood, and cellular respiration. It then discusses various lung volumes and capacities, abnormalities in acid-base balance, interpretations of blood gas results, and select respiratory disorders like chronic bronchitis and respiratory distress syndrome. Arterial blood gases provide information about acid-base status, ventilation, oxygenation, and carbon monoxide levels to aid in diagnosis.

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Assessment of
Respiratory Disorders

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INTRODUCTION
Exchange between capillary and body cells.
RESPIRATION
(1) Pulmonary ventilation
(2) External respiration
Respiratory gas transport
(3)
Internal respiration
(4)
Breathing: means
movement of air In and
Out of the body
Oxygen loading and
carbon dioxide loading Transportation of gasesby bloodstream

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(1) BREATHING (PULMONARY VENTILATION)
(A) Inspiration: Diaphragm flattens creates a vacuum pulling air into the lungs
(B) Expiration: Muscles relax and push air out of the lungs

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RESPIRATORY VOLUMES AND CAPACITIES
Volume Definition
Tidal Volume (TV) Volume of air moved into and out of the lungs each
breath
Inspiratory reserve
volume (IRV)
Amount of air you can forcibly be taken in
Expiratory reserve volume
(ERV)
Amount of air that can be forcibly expelled
Residual Volume Air that cannot be expelled from the lungs
Vital capacity (VC) Total amount of exchangeable air TV + IRV + ERV
Dead Space volume The amount of air that doesn’t make it to the lungs in
a breath.
Minute volume (MV) The total amount of air exhaled per minute.

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Functional residual capacity
(FRC). The amount of air left in lungs after exhaling normally.
Total lung capacity The total volume of the lungs when filled with as much
air as possible.
Forced vital capacity (FVC). The amount of air exhaled forcefully and quickly after
inhaling as much as you can.
Forced expiratory volume
(FEV).
The amount of air expired during the first, second, and
third seconds of the FVC test.
Forced expiratory flow (FEF) The average rate of flow during the middle half of the
FVC test.
Peak expiratory flow rate
(PEFR). The fastest rate that you can force air out of your lungs.
(2) EXTERNAL RESPIRATION

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Gas exchange at the lungs Oxygen into blood
and CO2 removed from blood
(3) GAS TRANSPORT IN THE BLOOD

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Oxygen forms oxyhemoglobin with hemoglobin molecules.



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CO2 in transported via bicarbonate in plasma.

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(4) INTERNAL RESPIRATION
Exchange of gases between
blood and tissue cells. Oxygen
unloaded and CO2 loaded.

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SOME TERMS:
Terms Description
Hypoxia
Inadequate supply of oxygen to the body tissues
Causes skin to become cyanotic
Carbon Monoxide
Poisoning
CO binds to the binding site that oxygen binds to on hemoglobin
preventing gas transport of oxygen
Hyperventilation
Body’s reaction to increased levels of carbon dioxide or acids in
blood.

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Respiratory terms Eupnea: normal respiratory rate.
Hyperpnea: Increased respiratory rate
(exercising) Apnea: stopped breathing.
Dyspnea: difficult breathing.
Arterial blood gases (ABGs):
Collection and handling of arterial blood gases:
1) The specimen for blood gases and pH should be arterial or arterialized capillary
blood
2) All air bubbles should be removed.
3) Air contamination will reduce the CO2 and increases the O2 in the sample due to
the difference in the PO2 and PCO2 tension of these gases in the atmosphere.

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4) Use the correct amount of heparin (0.05 mg heparin/ml blood).
5) The specimen must be placed in ice water until analysis or examined
immediately.
Calculations in blood gas analysis:
Given arterial pH and PCO2, the formula to solve for bicarbonate is derived as follows:
pH = 6.1 + log HCO3 /(PCO2 x 0.0301)
For example, calculate HCO3 given pH 7.50 and PCO2 of 30 mm Hg.
7.50 = 6.1 + log [HCO3 /(30 x 0.0301)]

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7.50 = 6.1 + log (HCO3/0.9)
1.4 = log (HCO3 /0.9) inv. log
1.4 = (HCO3 /0.9)
25 = (HCO3 /0.9)
25 X 0.9 = HCO3 = 23 mmol/L
Venous Versus Arterial Samples:
There are five main evaluations we need to consider in interpreting ABGs in the
clinical setting:
1)Acid-base status
2)Alveolar ventilation
3)Oxygenation status
4)O2 transport
5)Carboxyhemoglobin

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ACID-BASE STATUS
(1) Metabolic Acid-Base Disturbances:
Metabolic acidosis Metabolic alkalosis

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Diabetic ketoacidosis Vomiting
Uremia Gastric suction
Renal tubular acidosis Low potassium or chloride level
Lactic acidosis Liver cirrhosis with ascites
GIT loss of HCO3 , fluids
potassium
and Corticoid excess (Mineralocorticoids)
Toxins Massive blood transfusion
Hypertension due to dehydration High doses of alkalis in acidosis
(2) Respiratory Acid-Base Disturbances:
Respiratory acidosis Respiratory alkalosis
Pneumonia Hyperventilation due to high altitudes
Emphysema Fever

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Asphyxia Salicylates poisoning
Bronchial asthma Encephalitis
Morphine poisoning Hysterical
APPROACH TO INTERPRETING ACID-BASE DISTURBANCE:
In order to interpret acid-base disturbances, the following five factors are considered:
1. pH
2. HCO3–

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3. PCO2
4. Anion gap
5. Assessment for compensation Ventilation and PCO2 relationship
oVentilation is inversely proportional to the resulting PCO2.
oVentilation increases in response to a drop in plasma and cerebrospinal fluid (CSF)
pH detected by the respiratory center in the medulla.
oLikewise, the kidneys compensate for a primary respiratory defect. The respiratory
systemcan never completely compensate for a metabolic defect, but renal
compensation can almost be complete.
Steps for determination of acid base disturbances:
Steps Interoperation

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1) Determine if the patient is acidemic
alkalemic, based on pH.
or Normal pH 7.4±0.03
2) The primary disorder is determined
evaluating HCO3– and PCO2
by 1. If HCO3– is elevated and pH is elevated,
there is metabolic alkalosis.
2. If both are decreased, thereis
metabolic acidosis.
3. If HCO3– is within the normal reference
range and PCO2 is elevated but the patient
is acidotic, the condition is respiratory
acidosis.
4. If bicarbonate is within the normal reference
range and PCO2 is decreased but the patient
is alkalotic, the condition is respiratory
alkalosis.
3) Determine the anion gap from the formula
Anion gap= (Na+K)-(Cl+HCO3) or (Na)-(Cl+HCO3)
So anion gap is the difference between cations and
anions in the blood Normal = 10-20 mmol/L and
without K = 6-15 mmol/L
In metabolic acidosis and mixed acid-base
disorders, the anion gap is significantly elevated.

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4) pH, HCO3–, and PCO2 are considered to
determine if compensation is as expected based
on the typical ratio of 20:1 for bicarbonate to
carbonic acid.
1. both decreased HCO3– and PCO2 should
produce a slightly decreased or nearly normal
pH if they are in metabolic acidosis
compensation.
Steps Interoperation

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4) pH, HCO3–, and PCO2 are considered to
determine if compensation is as expected based
on the typical ratio of 20:1 for bicarbonate to
carbonic acid. ...........(Continued)
2. To determine the actual ratio of bicarbonate to
carbonic acid, PCO2 is converted to H2CO3
using the relationship PCO2 X0.03 =H2CO3
3. Metabolic acidosis with a normal anion gap
is associated with:
A. renal diseases such as proximal or distal
renal tubular acidosis,
B. Renal insufficiency with HCO3– loss,
C. Hypoaldosteronism with potassium-
sparing diuretics.
D. Other causes include loss of alkali due to
diarrhea or ureterosigmoidostomy or
ingestion of carbonic anhydrase inhibitors,
such as the medications used to treat
glaucoma.
4. Metabolic acidosis with a high anion gap is
generally due to:
A. Addition of acid from ketoacidosis;
B. Lacticacidosis from hypoperfusion or
decreased circulation
C. Toxic ingestions of aspirin, ethylene glycol,
or methanol.
D. Renal insufficiency.

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Compensation for metabolic acidosis or alkalosis is achieved initially by the
respiratory system. How?!
RESPIRATORY DISORDERS
Disorders Diagnosis
Chronic bronchitis These patients have chronic hypoxia, as indicated
by low SO2 and PO2, and CO2 retention, as
indicated by increased bicarbonate and PCO2.
Fetal Lung Maturity 1. Immature fetal lung resulted from the decrease
in the lung surfactant (phosphatidyl choline,).
2. It occurs to premature babies (< 37 weeks) or
weight < 2500 g.
3. causing decreased oxygenation of the
collapsed alveoli and cyanosis and respiratory
distress in the neonate
Respiratory Distress Syndrome (RDS) The arterial blood gases initially indicate
1.Very low PO2,
2.Normal or low PCO2, and
3.Elevated pH causing respiratory alkalosis.

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