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20-Feb-16Respiratory failure3 Hypercapnic Respiratory Failure Pa CO2 > 45 mm Hg Upper limit of normal Pa CO2 Upper limit of normal Pa CO2
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May 5, 2023 Respiratory failure 1
Pathophysiology Pathophysiology of Respiratory of Respiratory
FailureFailure
May 5, 2023 Respiratory failure 2
Respiratory FailureRespiratory Failure Severe impairment of gas exchangeSevere impairment of gas exchange May be categorized May be categorized
HypercapnicHypercapnic HypoxaemicHypoxaemic
Either may ariseEither may arise Acutely or chronicallyAcutely or chronically
May 5, 2023 Respiratory failure 3
Hypercapnic Respiratory Hypercapnic Respiratory FailureFailure PaPaCO2CO2 > 45 mm Hg > 45 mm Hg
Upper limit of normal PaUpper limit of normal PaCO2CO2
May 5, 2023 Respiratory failure 4
Hypoxaemic Respiratory Hypoxaemic Respiratory FailureFailure Defined as clinically Defined as clinically
Significant hypoxaemiaSignificant hypoxaemia Despite therapy with high ODespite therapy with high O22
PaPaO2O2 < 55 mm Hg < 55 mm Hg
May 5, 2023 Respiratory failure 5
Components of Components of Respiratory SystemRespiratory System
The normal gas exchange The normal gas exchange depend ondepend on Integration of several Integration of several
componentscomponents CNSCNS Chest cavityChest cavity
NervesNerves MusclesMuscles Chest wallChest wall
The airwaysThe airways Alveolar gas-exchange Alveolar gas-exchange
unitunit
CNS
Chest cavity
Airways
Alveoli
May 5, 2023 Respiratory failure 6
Components of Components of Respiratory SystemRespiratory System
CNSCNS Monitor levels of PMonitor levels of PO2O2
& P& PCO2CO2
These determineThese determine Level & pattern of Level & pattern of
ventilationventilation
CNS
Chest cavity
Airways
Alveoli
May 5, 2023 Respiratory failure 7
Components of Components of Respiratory SystemRespiratory System
Lung inflation & Lung inflation & deflation causedeflation cause Gas flow in and out Gas flow in and out
of gas exchange unitof gas exchange unit Passive diffusion Passive diffusion
Of OOf O22 & CO & CO2 2 across across Alveolar-capillary Alveolar-capillary
membranemembrane
CNS
Chest cavity
Airways
Alveoli
May 5, 2023 Respiratory failure 8
Components of Components of Respiratory SystemRespiratory System
Pump failure refers Pump failure refers to to Dysfunction of Dysfunction of
CNSCNS Chest bellows or Chest bellows or
airwaysairways
CNS
Chest cavity
Airways
Alveoli
May 5, 2023 Respiratory failure 9
Components of Components of Respiratory SystemRespiratory System
Lung failure refers Lung failure refers to to Dysfunction of Dysfunction of
AlveoliAlveoli Pulmonary Pulmonary
capillariescapillaries Alveolar – capillary Alveolar – capillary
membranemembrane
CNS
Chest cavity
Airways
Alveoli
May 5, 2023 Respiratory failure 10
Ventilatory SupplyVentilatory Supply Factors that affect ventilatory Factors that affect ventilatory
supplysupply Abnormal respiratory mechanicsAbnormal respiratory mechanics
Airflow obstructionAirflow obstruction AsthmaAsthma Chronic obstructive pulmonary Chronic obstructive pulmonary
diseases (COPD)diseases (COPD)
May 5, 2023 Respiratory failure 11
Ventilatory SupplyVentilatory Supply Chest wall deformitiesChest wall deformities
KyphoscoliosisKyphoscoliosis Loss of lung volumeLoss of lung volume
PneumoniaPneumonia
May 5, 2023 Respiratory failure 12
Ventilatory SupplyVentilatory Supply Respiratory muscle strength & Respiratory muscle strength &
enduranceendurance Nerve lesionsNerve lesions NMJ abnormalitiesNMJ abnormalities Muscle abnormalitiesMuscle abnormalities
AtrophyAtrophy Weakness Weakness
May 5, 2023 Respiratory failure 13
Failure of CNSFailure of CNS Blood gas changesBlood gas changes
Respiratory acidosisRespiratory acidosis PaPaCO2CO2 In pHIn pH PaPaO2O2
May 5, 2023 Respiratory failure 14
Failure of CNSFailure of CNS Following can cause CNS depression Following can cause CNS depression
& respiratory failure& respiratory failure Overdose with sedativesOverdose with sedatives
BarbituratesBarbiturates OpiatesOpiates
Anesthetic agentAnesthetic agent Hypoxia, hypercapniaHypoxia, hypercapnia
May 5, 2023 Respiratory failure 15
Failure of CNSFailure of CNS Diseases of medullary respiratory Diseases of medullary respiratory
control centercontrol center Encephalitis Encephalitis Haemorrhage Haemorrhage TraumaTrauma TumoursTumours
May 5, 2023 Respiratory failure 16
Failure of Chest Failure of Chest BellowsBellows Disorders of motor nervesDisorders of motor nerves
UMN innervating respiratory UMN innervating respiratory musclesmuscles
Trauma above CTrauma above C3-43-4 Interfere with phrenic nerveInterfere with phrenic nerve
May 5, 2023 Respiratory failure 17
Failure of Chest BellowsFailure of Chest Bellows Fracture dislocation Fracture dislocation
Lower cervical vertebraLower cervical vertebraRespiratory muscle paralysisRespiratory muscle paralysis
Weakness of respiratory muscleWeakness of respiratory muscle
May 5, 2023 Respiratory failure 18
Failure of Chest Failure of Chest BellowsBellows The fall in respiratory muscle The fall in respiratory muscle
strengthstrength
May 5, 2023 Respiratory failure 19
Failure of Chest Failure of Chest BellowsBellows Changes in arterial blood gasesChanges in arterial blood gases
Similar to those in CNS failureSimilar to those in CNS failure Respiratory acidosisRespiratory acidosis
PaPaCO2CO2 In pHIn pH PaPaO2O2
May 5, 2023 Respiratory failure 20
Airway Diseases Airway Diseases Causing FailureCausing Failure Airways diseases imposeAirways diseases impose
Severe limitation in ventilatory Severe limitation in ventilatory supplysupply
ventilatory demandventilatory demand
May 5, 2023 Respiratory failure 21
Airway DiseasesAirway Diseases Limitation of ventilatory supplyLimitation of ventilatory supply
Arise from narrowing of airwaysArise from narrowing of airways Lead to diminishedLead to diminished
Expiratory rateExpiratory rate Inspiratory rateInspiratory rate Exhaled volume (FEVExhaled volume (FEV11))
May 5, 2023 Respiratory failure 22
Failure of Gas Failure of Gas ExchangeExchange Failure of alveolar gas exchangeFailure of alveolar gas exchange
Leads to hypoxaemic respiratory Leads to hypoxaemic respiratory failurefailure
May 5, 2023 Respiratory failure 23
Gas Exchange FailureGas Exchange Failure CausesCauses
Disorders which cause Disorders which cause Diffuse alveolar diseasesDiffuse alveolar diseases
EmphysemaEmphysema PneumoniaPneumonia
May 5, 2023 Respiratory failure 24
Gas Exchange FailureGas Exchange Failure In both casesIn both cases
Diffusing capacity of the lungDiffusing capacity of the lung Ability of the lung to Ability of the lung to
Oxygenate bloodOxygenate blood Remove CORemove CO22
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