Acute respiratory failure (ARF) is a condition characterized by the failure of the respiratory system to maintain adequate gas exchange, leading to hypoxemia (low oxygen) and/or hypercapnia (high carbon dioxide). It can be classified into acute or chronic types and categorized as hypoxemic or hypercapnic. Treatment involves addressing the underlying causes, providing oxygen therapy, and potentially mechanical ventilation to ensure sufficient oxygen delivery and ventilation.

1. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
Acute Respiratory Failure (ARF)
Normal values Abnormalities
pH 7.35-7.45 ↓pH: Acidosis
PaO2 >70 mmHg ↓ PaO2: Hypoxemia
PaCO2 35-45 mmHg ↑PaCO2: Hypercapnia
- A syndrome in which the respiratory system fails in one or both of its gas exchange functions:
(oxygenation and CO2 elimination).
- in which PaO2< 60 mmHg while breathing room air OR a PaCO2> 50 mmHg
- it may be classified as:
 Acute or chronic
 Type 1 “hypoxemic” or Type 2 “hypercapnic”
Acute RF Chronic RF
- Develops over minutes to hours - Develops over days
- ↓ pH quickly to <7.2 - ↓ pH slightly
- ↑ in HCO3
Type 1 Type 2
Name Hypoxemic RF Hypercapnic RF
ABG PaO2 < 60 mmHg
with normal or ↓ PaCO2 Rthen increased
PaCO2 > 50 mmHg
with normal or ↓ PaOR
2
Mechanism Poor arterial oxygenation Alveolar hypoventilation
C/P Respiratory distress and chest signs Shallow breathing, cyanosis,
coma or paralysis
Etiology - Pulmonary edema
(Cardiogenic, noncardiogenic e.g. ARDS)
- pneumonia, collapse
- pulmonary hemorrhage
- Drug overdose
- Neuromuscular disease
- Chest wall deformity
- Status asthmaticus
Treatment Oxygen therapy + Mechanical ventilation Mechanical ventilation + Oxygen therapy
Type 3 Type 4
Perioperative respiratory failure Shock
Definition:
Arterial Blood Gases (ABG)
Classification of ARF:

2. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
Respiratory
insufficiency
Lung Failure
Hypoxemia
V/Q mismatch Shunting
Diffusion
Impairment
Pump Failure
Hypercapnia
Hypoxemia
Mechanical
defect
Neuromuscular
dysfunction
Depressed
central
respiratory drive

3. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
1. Hypoventilation
2. V/Q mismatch
3. Shunt
4. Diffusion abnormality
1. Hypoventilation
- Occurs when ventilation 
- ↑ PaCO2 & ↓ PaO2
- Causes:
 Depression of CNS from drugs
 Neuromuscular disease of respiratory muscles
2. V/Q mismatch
- Most common cause of hypoxemia
- Low V/Q ratio, may occur either from
 Decrease of ventilation 2ry
to airway or interstitial lung disease
 Over perfusion in the presence of normal ventilation e.g. PE
- Administration of 100% O2 eliminate hypoxemia
3. Shunt
- Deoxygenated blood bypasses ventilated alveoli & mixes with oxygenated blood → hypoxemia
- Persistent hypoxemia despite 100% O2 inhalation
- Hypercapnia occur when shunt is excessive >60%
Intracardiac Pulmonary
- Right to left shunt
1. Fallot’s tetralogy
2. Eisenmenger’s syndrome
- A/V malformation
- Pneumonia
- Pulmonary edema
- Atelectasis/collapse
- Pulmonary Hemorrhage
- Pulmonary contusion
Causes of Shunt
Pathophysiologic Causes of Acute RF

4. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
4 - Diffusion abnormality
- Less common
- Due to
 abnormality of the alveolar membrane
 ↓ the number of the alveoli
- Causes
 ARDS
 Fibrotic lung disease
(Clinical – Causes – Investigations)
1 - Clinical (symptoms, signs)
Hypoxemia Hypercapnia
 CNS manifestations:
Confusion, somnolence, fits
 CVS manifestations “In chronic RF”
Pulmonary HTN, cor pulmonale, Rt. HF
- Tachycardia, arrhythmia
 Chest manifestations:
 Respiratory distress signs:
o Tachypnea (good sign)
o Nasal flaring
o Use of accessory muscles
o Recession of intercostal muscles
 Dyspnea, Cyanosis
 Secondary Polycythemia
“In long-standing hypoxemia”
 CNS manifestations:
- ↑ Cerebral blood flow, and CSF Pressure
- Headache
- Papilledema
 CVS manifestations
- Warm extremities, collapsing pulse
- Flapping tremor “Asterixis”
- ↓pH, ↑ lactic acid
- Acidosis (respiratory, and metabolic)
Diagnosis of ARF

5. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
2 - Causes
i. Central causes:
 Characterized by:
- Depression of neural drive to breath
- This may lead to Acute or chronic hypoventilation and hypercapnia
 Examples:
o Brain stem tumors or vascular abnormality
o Overdose of a narcotic or sedative
o Metabolic disorders e.g. Myxedema, chronic metabolic alkalosis
ii. Peripheral causes:
a) Disorders of peripheral nervous system, Respiratory muscles, and Chest wall
 Characterized by:
- Inability to maintain a level of minute ventilation appropriate for the rate of CO2
production
- Hypoxemia & hypercapnia
 Examples:
o Guillain-Barré syndrome
o Muscular dystrophy
o Myasthenia gravis
o Morbid obesity
b) Abnormities of the airways
- Severe airway obstruction is a common cause of Acute or chronic hypercapnia
 Examples:
o Upper-airway disorders: Acute epiglottitis & Tracheal tumors;
o Lower-airway disorders: Asthma & Cystic fibrosis
c) Abnormities of the alveoli
 Characterized by:
- Diffuse alveolar filling
- frequently resulting in hypoxemic respiratory failure.
- Associate with intrapulmonary shunt & ↑ work of breathing
 Examples:
o Cardiogenic & noncardiogenic pulmonary edema
o Aspiration pneumonia
o pulmonary hemorrhage

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3 - Investigations
Laboratory Studies:
- ABG
- CBC, Hb  (Anemia – Polycythemia)
- Urea, Creatinine
- LFT
- Electrolytes (K, Mg, Ph)
- CPK, Troponin 1
- TSH
Radiography
- Chest x ray
Pulmonary Function Tests (FEV1/ FVC ratio)
Echocardiography
ECG
Right-Sided Heart Catheterization:
- Measurement of pulmonary capillary wedge pressure (PCWP)
- help in distinguishing cardiogenic from non-cardiogenic edema (ARDS);
 Normal (<18 mmHg) → ARDS
 Increased (>18 mmHg) → cardiogenic pulmonary edema
Non-cardiogenic edema (ARDS) cardiogenic pulmonary edema
Tachypnea, dyspnea, crackles Tachypnea, dyspnea, crackles
Aspiration, sepsis Lt ventricular dysfunction, valvular disease
Normal heart size, systolic, diastolic function Cardiomegaly,
Vascular redistribution,
3 to 4 Quadrant of alveolar flooding
 compliance
pleural effusion,
perihilar Bat's wing distribution of infiltrate
Severe hypoxemia refractory to O2 therapy Hypoxemia improved on high flow O2
PCWP: Normal (<18 mmHg) PCWP: Increased (>18 mmHg)

7. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
 ICU admission
1. Airway management:
- Via Endotracheal intubation
 Importance:
 Precise O2 delivery to lungs
 Remove secretions
 Ensure adequate ventilation
2. Correction of hypoxemia
- O2 administration via nasal prongs, face mask, intubation and mechanical ventilation
 Goal:
 Adequate O2 delivery to tissues
 PaO2 > 60 mmHg
 Arterial O2 saturation >90%
3. Correction of hypercapnia
- Control the underlying cause
- Controlled O2 supply
- 1-3 L/min, titrate according O2 Saturation
- O2 supply to keep O2 saturation >90%
Management of ARF
 Indications for ICU admission: (mnemonic: ABCD – Need 2V)
a) Severe/worsening respiratory Acidosis (PH<7.25) despite supplemental oxygen and/or
Persistent or worsening hypoxemia (PaO2 <5.3 KPa, 40 mmHg)
b) Changes in mental status (Confusion, lethargy, Coma)
c) Severe dyspnea that responds inadequately to initial emergency therapy
d) Need for invasive mechanical Ventilation
e) Hemodynamic instability – Need to Vasopressors

8. Acute Respiratory Failure
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4. Ventilation
 Types:
A. Noninvasive Ventilation (NIV):
- Supports breathing without the need for intubation.
B. Invasive Ventilation (mechanical ventilation):
- Follows endotracheal intubation.
A. Noninvasive Ventilatory support (NIV)
(IPPV: Intermittent positive-pressure ventilation)
- Via: Nasal or full-face mask
 Improve oxygenation,
 Reduce work of breathing
 Increase cardiac output
- Patient should have
 Intact airway,
 Alert, normal airway protective reflexes
- Considered in: Mild to moderate ARF
 Indications: At least One of the followings:
- Respiratory Acidosis (arterial pH < 7.35 and/or PaCO2 > 6.0 kPa,45 mmHg)
- Severe dyspnea with clinical signs of respiratory muscle fatigue, ↑work of breathing, or
both, such as use of respiratory accessory muscles, paradoxical motion of abdomen,
retraction of intercostal spaces

9. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
B. Invasive (Mechanical) ventilation
- Via: endotracheal tube or tracheostomy tube
 Principles: Mechanical ventilation is used for these reasons;
1) to  PaO2
2) to  PaCO2.
3) Rests respiratory muscles & it’s an appropriate therapy for respiratory muscle fatigue.
 Indications:
- Persistent hypoxemia despite O2 supply
- Hypercapnia with severe acidosis (PH<7.2)
-  level of consciousness
- Adequate oxygenation
- Intact respiratory drive
- Stable underlying respiratory status
- Stable cardiovascular status
- Patient is a wake, has good nutrition, able to cough and breath
Weaning from mechanical ventilation
o Unable to tolerate NIV or NIV failure
o Life-threatening hypoxemia in patients unable to tolerate NIV
o Respiratory or cardiac arrest
o Respiratory pauses with loss of consciousness or gasping for air
o  consciousness, psychomotor agitation inadequately controlled by sedation
o Persistent inability to remove respiratory secretions
o Massive aspiration
o HR < 50 /min with loss of alertness
o Severe hemodynamic instability without response to fluids and vasoactive drugs
o Severe ventricular arrhythmias

10. Acute Respiratory Failure
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Emergency 2018
Kareem Alnakeeb
5. Treatment of the underlying causes
- After correction of hypoxemia & hemodynamic instability
Antibiotics - for Pneumonia - infections
Diuretics
e.g. furosemide
- for pulmonary edema
Bronchodilators
e.g. salbutamol
-  bronchospasm +  airway resistance
Anticholinergics
e.g. Ipratropium bromide
- for BA
- Inhibit vagal tone + Relax smooth muscles
Theophylline - for BA
- Improve Diaphragmatic contraction + Relax smooth muscles
Methyl prednisone - for BA
- Reverse bronchospasm & Inflammation
Fluids and electrolytes - Maintain fluid balance + avoid fluid overload
IV nutritional support
e.g. fat, CHO, protein
- Restore strength & Loss of muscle mass
Physiotherapy - Chest percussion to loosen secretion
- Suction of airways
- Help to drain secretion
- Maintain alveolar inflation
- Prevent atelectasis, help lung expansion
Pulmonary Cardiovascular
Pulmonary embolism Hypotension
barotrauma  COP
Pulmonary fibrosis (may follow acute lung injury
associated with ARDS)
Arrhythmia
Nosocomial pneumonia
GIT Infections
Hemorrhage Nosocomial infection
ileus UTI
diarrhea catheter related sepsis
Stress ulcer Nosocomial pneumonia
Renal Nutritional
ARF (due to hypoperfusion, nephrotoxic drugs)
Poor prognosis
Malnutrition
Nasogastric tubes  diarrhea
Parenteral nutrition  hypoglycemia & electrolyte
disturbances
Complications of ARF