1. Acute respiratory failure is defined as a severe form of respiratory insufficiency resulting in a PaO2 of less than 60 mmHg or a PaCO2 of more than 50 mmHg. 2. There are two main types - type 1 with low PaO2 and normal or low PaCO2, and type 2 with low PaO2 and high PaCO2. 3. Major causes include diffuse airway obstruction, central airway obstruction, restrictive lung disease, pulmonary vascular disease, pleural and chest wall diseases, and neuromuscular diseases.

1. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
ACUTE RESPIRATORY FAILURE
Respiratory insufficiency:
Is a broad term indicating inability of the respiratory system to maintain PaO2 or PaCO2 or
both within the normal shape.
Respiratory failure:
Is a sever form of respiratory insfficiency resulting in a PaO2 < 60 mmHg (( 8KPa)) or PaCO2
> 50 mmHg (( 6.6 KPa )) or both.
2 types:
TYPE I respiratory failure ---PaO2 < 60 mmHg , Pa CO2 normal or decrease
TYPE II respiratory failure—PaO2 < 60 mmHg , PaCO2 50 mmHg or more
Respiratory failure may be ACUTE or CHRONIC.
ACUTE CHRONIC
Raptd onset Develops slowly
No time for compensatory mechanism to work CO2 HCO3 normal PH
O2 2ry polycythemia , RBC DPG
Deserve prompt diagnosis Less of an emergency
Vigorous therapeutic intervention This may be harmful
MAJOR CAUSES OF RESPIRATORY FAILURE
1. DIFFUSE AIRWAY OBSTRUCTION:
COPD-----hypoxemia ,ventilator failure
Bronchial asthma ----hypoxemic failure
V. failure iss status sever form and it is an ominous sign.
2. CENTRAL AIRWAY OBSTRUCTION:
Foreign body in the larynx or trachea
Laryngeal tumour ,tracheal tumor ,cricoids tumors
Bilateral laryngeal nerve palsy
Tracheal strictures
Extrinsic compression of the trachea
DIAGNOSTIC CLUES:
Stridor
Hoarsness
Brassy cough
Failure to improve on bronchodilator
3. RESTRICTIVE LUNG DISEASE:
Hypoxic failure type with low CO2

2. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
Ventilator failure occurs exceptionally with sever cases.
Acute pulmonary odema whether cardiac or non cardiac
Non cardiac:
Shock , High attitude ,Heroin ,Sepsis ,Chemicals ,Neurologic diseases
Cardiac :
Acute myocardial infarction , mitral or aortic valve disease
Alveolar proteinosis
Fibrosing alveolitis
Pneumocytosis pneumonia
Shock lung
4. PULMONARY VASCULAR DISEASE:
Acute – pulmonary emboli –fat ,emboli -----hypoxemic failure
Preexisting lung disease
Pulmonary A/V fistula -----hypoxic failure
Chronic ----recurrent thromboembolism ,pulmonary vasculitis
5. PLEURAL AND CHEST WALL DISEASE:
ACUTE CHRONIC
Flial chest
pneumothorax
Kyphoscoliosis
Obesity
Massive pleural effusion
Chronic pleural effusion
Ankylosing spondylitis
6. NEUROMUSCULAR DISEASE: ventiltory failure
A. Muscle disease---polyomyelitis ,muscle dystrophies ,myotonies
B. neuromuscular junction –Tetanus ,Mysthenia G. ,Anticholinestrase over dose
C. Neurological disease –poliomyelitis ,peripheral neuropathies ,spinal cord
injuries ,phrenic nerve paralysis, Amylotrophic lateral sclerosis, Guillian barre
syndrome ,Polyneuritis
D. Brain disorders:
Sedative drugs ,Anesthesia ,Vascular disease ,infections ,Tumours.
CLUES:
 FRC , FEV1/ FVC === NORMAL
 I.C. ,VC ,ERV ===REDUCED
 The maximal inspiratory flow rates more depressed then maximal
expiratory flow rates more depressed.
 Central airway obstruction and neuromuscular diseases both lower
maximal flow rates but maximal inspireatory and expiratory airway
pressure will be normal in the central airway obstruction and
decreased in NMD.
7. DEPRESSION OF RESPIRATORY CENTER:
The automaticity of ventilation is a function of the respiratory centre in the
medulla.

3. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
RESPIRATORY CENTRE
CAROTID BODIES RESPIRATORY MUSCLES LUNG RC IN CEREBELLUM
RC IN PONS
The chemosensitive receptors in the medulla is sensitive to changes in the PH—PaCO2.
The peripheral receptors in the carotid and aortic bodies are sensitive to the hypoxic
and PH changes.
CAUSES OF DEPRESSION OF RESPIRATORY CENTRE:
1. Drugs ----commnest cause ---Sedatives ,Narcotics ,Tranquilizer
2. Chronic hypercapnia
3. Sever hypoxemia
4. Neurological disease :
Brain stem tumors/infarction ,Bulbopolio ,M.S., Cerebellar trauma ,Syringomelia
8. OBESITY –HYPOVENTILATION SYNDROME:
Many obese patient have arterial hypoxemia due to basilar microatelectasis.
Small number of morbidity obese patient manifest the pickwickian syndrome
(( Hypersomnia ,Hypoxemia ,Hypercapnia )).
9. SLEEP—APNEA SYNDROME:
Central ---obstructive--- mixed.
There is transient R.F. during the apnea episodes.
Some patient will have chronic day time hypercapnia and hypoxiemia if markedly
obese.
Most of them have respiratory insufficiency rather than respiratory failure.
10. RESPIRATORY MUSCLE FATIGUE:
Is a contributory rather than 1ry cause.
Seen in patient with COPD due to :
a. Increased work of breathing
b. Arterial hypoxemia
c. Flattened diaphragm
Diagnosis ----Respiatory paradox
Chest up & diaphragm down
Diagnostic studies in patient with respiratory failure:
1) History and physical examination:
Are of major importance
Symptoms and signs could be due to underlaying disease process or to blood
gases derangements.
Signs of hypoxia:
Hyperventilation
Cyanosis
Cerebral hypoxia –headache ,restlessness ,somnolence ,confusion ,coma
Pulmonary HTN
Cor pulmonale
Right side heart failure

4. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
Signs of hypercapnia:
Headache
Restlessness
Confusion and coma
Asteriaxis
Neurological disease
Papilloedema
Changes in COP , BP ,and cardiac arrhythmia.
Wheezing ---is not completely specific
Central airway obstruction
Pulmonary embolism
Pulmonary oedema
Type of breathing :
Rapid and shallow breathing in patient with intrapulmonary restrictive lung
disease.
 Absence of dyspnea—
Respiratory centre depression
Neuromuscular disease of the chest wall
 Paradoxical movement of the diaphragm
Respiratory muscle fatigue
Diaphragm paralysis
 Stridor
Extrathoracic trachea or laryngeal obstruction.
2) Standard laboratory test:
Is of limited value.
Diffuse airway obstruction and peripheral eosinophilia ----bronchila asthma
Neuromuscular dysfunction:
EMG-----enzyme levels -----serum phosphate
CSF examination may help the diagnosis
In patient with diffuse pulmonary restrictive disease , RF & ANF & precipitins to
organ antigen
Urine for fat globules ----serology for fungal disease
3) Chest imaging:
CXR will identify blood categories like diffuse histopulmonary
opacities---interstitial ,alveolar ,miliary pattern
Associated finding like:
hilar or mediastinal adenopathy
Egg shell calcification of lymph nodes
Pleural effusion
Cardiomegally
Skeletal lesion
Pulmonary cavity

5. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
Radioopaque foreign body
Localized narrowing of the trachea with shadow endo or paratracheal lesions.
Bronchogenic carcinoma with pnemothorax in COPD patient.
Pulmonary angiography is available –PE ,A.V .fistula
4) Pulmonary function test:
 Arterial blood gase , spirometry ,flow volume loops
 Persistent increased alveolar –arterial O2 gradient after 100% O2
Intracardiac or intrapulmonary ---RT to LT shunt
 Restrictive or obstructive lung disease
 Reversibility studies after bronchodilator
 PFT is an analysis of single forced expiration and most sensitive
measure of airway obstruction in obstructive lung disease.
PFT is the most sensitive in small airway obstruction assessment.
Obstructive lung disease---
FVC (( airway close increase the limit expiration before the patient has
breathed out fully ))
FEV 1 decreased
FEVI /FVC % ----decreased --- increase the airway resistance which slow the
rate of expiration.
FRC increased and RV increased
Restrictive lung disease----
FVC ((limit expansion of lung and chest ))
FEV I (( airway resistance normal ))
FEV /FVC = normal / increased
Decrease RV and decrease lung compliance
FEVI :
Useful in assessing the efficiency of bronchodilatation therapy and to follow
the prognosis of patient with COPD and asthma.
Impaired lung function is a frequent association with decreased FEVI
Used as apart for reversibility studies after bronchodilatation.
Central airway obstruction----
Decrease flow rate ((inspiratory or both ))
Relatives normal lung volumes
Normal diffusing capacity
Normal maximum inspiratory and expiratory airway pressures
5) Bronchoscopy: diagnostic and therapeutic
6) Right heart catheterization :
It is of value for diagnosing certain problems e.g,-
Teft to right intracardiac shunts
Right to left shunts
7) ECHO ,ECG ,contrast ECHO
8) Lung biopsy :
Open lung biopsy or trans bronchial lung biopsy

6. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
Conditions that can be diagnosed by lung biopsy and for which
effective treatment is available are:
CMV pneumonia
Pneumocystis pneumonia
Bacterial and fungal pneumonia
Military TB
Chronic eosinophilic pneumonia
Lupus pneumonitis
Pulmonary alveolar proteinosis
Diffuse intra-alveolar haemorrhage
Fat embolism
Lymphocytic fibrosing alveolitis
MANAGEMENT :
A. Establishing an airway
B. O2 adminstration
C. Maintain adequate ventilation
D. Identifying and treat the underlaying disease
E. Monitor SaO2 ,ECG and vital signs
INDICATIONS FOR ENDOTRACHEAL INTUBATION:'
Current inability to protect the airway
CNS dysfunction:
1. Stroke
2. Head trauma
3. Toxic ---- metabolic central respiratory depression
Actual or potential airway compromise:
1. Excessive secretions
2. Airway edema:
a. Epiglotitis
b. Anaphylaxis
c. Facial or neck trauma
d. Inhalational injury
INDICATIONS FOR VENTILATORY SUPPORT
Respiratory rate > 35 (10 – 20)b/min
Vital capacity < 15 (65 – 75)ml/kg BWT
FEVI < 10 (50 – 60)ml/kg BWT
MAX.INSPIRATORY FORCE > 25 ( 75 – 100) cmH2O
PaO2 < 50 ( > 500 mmHg )
PaCO2 > 55 ( 35 – 45 mmHg)
VD / VT > 0.06 ( 0.25 – 0.40 )
After 10 minutes of 100% O2 except in patients with chronic
hypercapnia.

7. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
The final decision remains clinical.
INDICATIONS OF CONTROLLED MECHANICAL VENTILATION:
1. Apnea or severe respiratory depression present
2. Patient is unable to maintain adequate spontaneous ventilator activity or
assisted ventilation
3. Spontaneous ventilator effort is deleterious –flial chest
4. Application of PEEP is necessary
5. Ventilator is operating near its pressure limit or at high rate ( >25/min)
and is unable to deliver T.V.
Setting of ventilator:
1. Tidal volume ----start by large tidal volume (( 12 – 15 ml/kg ))
2. Respiratory rate ---- slow R.R. (( 10 – 20 b/min))
Desired F = pressure F X previous PaCO2
Desired PaCO2
3. Inspiratory to expiratory rate I/E (( 1/2 --- 1///4 ))
4. Flow wave form
5. FiO2 ---aim for PaO2 60 – 80mmHg & FiO < 50%
6. Pressure limits 10cm H2O above the peak P. reacting during each cycle
7. PEEP / CPAP:
Bypassing the oropharynx by E.T. tube will decrease FRC . The application of PEEP 3 –
5 cmH2O reverse this effect ( physiological CPAP ) .
The usual indication of PEEP is the presence of R. hypoxiemia due to lung injury :
1. ARDS
2. Cardiogenic pulmonary oedema
3. Flial chest
Start at 5cmH2O and increase progressively every 15—30 min until a satisfactory
Oxygenation is reached for FiO2 ideally < 60%
Rarely necessary to exceed levels of 20 cmH2o
Best way to asses PEEP is by mixed venous SO2.
Reduce PEEP if :
a. Hypotension
b. Step decrement of more than 5% of SV O2
c. > 20 % decrease of C.O.
d. Appearance of new cardiac murmur
Clinical monitoring of mechanical ventilation:
1. Regular clinical examination of the patient
2. Inspect the ventilator and V. circuit
3. Chest expansion should be symmetrical
4. E.T. check and its pressure < 30 mmHg
5. The humidifier temperature & H2O level checked
6. Pulse oximeter check
7. Ventilator pressure gauge .Peak inspiratory pressure

8. ACUTE RESPIRATORY FAILURE DR MAGDI AWAD SASI 2015
8. Compare inspiratory and expiratory tidal volumes for leak in the v. circuit or E.T.
tube cuff.
Weaning of mechanical ventilation :
Negative inspiratory force > -25 cmH2O
V.C. > 10 ml/ kg B.W.
COMPLICATION OF MECHANICAL VENTILATION:
1. E.T. tube ---displacement and pressure necrosis
2. Nasocomial pneumonia
3. PEEP ventilation :
Decrease C.O.
Decrease renal perfusion
Salt and H2O retention
Interstitial lung damage
4. Pneumothorax and mediastinal ---subcutaneous emphysema/pericardial
Weaning of mechanical ventilation:
CMV SIMV IMV pressure support ventilation
PEEP decrease by 5 cmH2O every 10—20 min
ABG must be checked for every step of weaning.
HISTROY ACUTE HYPOXEMIA CLEAR LUNG FIELDS
PHYSICAL EXAMINATION RESPIRATORY (( BLACK LUNG ))
CXR FAILURE
ABG SHUNT COPD PE
DIFFUSE OPACIFICATION (( WHITE LUNG ))
INTERSTITIUM ALVEOLAR FILLING
VENTILATORY
CLEAR LUNG (( BLACK LUNG )) DIFFUSE OPACIFICATION ((WHITE LUNG))
COPD LATE STAGES NEUROGENIC HYPOVENTILATION
CHEST WALL RESTRICTION CENTRAL AIRWAY OBSTRUCTION
COPD + ADDED PARENCHYMAL DISEASE DIFFUSE PARENCHYMAL DISEASE IN TERMINAL