20-feb-16respiratory failure1 pathophysiology of respiratory failure

May 5, 2023 Respiratory failure 1

Pathophysiology Pathophysiology of Respiratory of Respiratory

FailureFailure


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


Hypercapnic Respiratory Hypercapnic Respiratory FailureFailure PaPaCO2CO2 > 45 mm Hg > 45 mm Hg

Upper limit of normal PaUpper limit of normal PaCO2CO2


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


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



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



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



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



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


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)


Ventilatory SupplyVentilatory Supply Chest wall deformitiesChest wall deformities

KyphoscoliosisKyphoscoliosis Loss of lung volumeLoss of lung volume

PneumoniaPneumonia


Ventilatory SupplyVentilatory Supply Respiratory muscle strength & Respiratory muscle strength &

enduranceendurance Nerve lesionsNerve lesions NMJ abnormalitiesNMJ abnormalities Muscle abnormalitiesMuscle abnormalities

AtrophyAtrophy Weakness Weakness


Failure of CNSFailure of CNS Blood gas changesBlood gas changes

Respiratory acidosisRespiratory acidosis PaPaCO2CO2 In pHIn pH PaPaO2O2


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


Failure of CNSFailure of CNS Diseases of medullary respiratory Diseases of medullary respiratory

control centercontrol center Encephalitis Encephalitis Haemorrhage Haemorrhage TraumaTrauma TumoursTumours


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


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


Failure of Chest Failure of Chest BellowsBellows The fall in respiratory muscle The fall in respiratory muscle

strengthstrength


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


Airway Diseases Airway Diseases Causing FailureCausing Failure Airways diseases imposeAirways diseases impose

Severe limitation in ventilatory Severe limitation in ventilatory supplysupply

ventilatory demandventilatory demand


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))


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


Gas Exchange FailureGas Exchange Failure CausesCauses

Disorders which cause Disorders which cause Diffuse alveolar diseasesDiffuse alveolar diseases

EmphysemaEmphysema PneumoniaPneumonia


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

20-feb-16respiratory failure1 pathophysiology of respiratory failure

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