Respiratory Failure

By:

Dr.Samet.MYazd University

Respiratory Failure

Respiratory failure is a condition in which the respiratory system fails in one or both of its gas-exchanging functions:

oxygenation

carbon dioxide elimination

CLASSIFICATION

Acute & Chronic

Hypercapnic: PaCO2 >45 mmHg

Hypoxemic: PaO2 <55 mmHg when FIO2 ≥0.60

Distinctions between acute and chronic respiratory failure

Arterial blood gas values

Presence of markers of chronic hypoxemia

( polycythemia or cor pulmonale)

Abrupt changes in mental status

PATHOPHYSIOLOGY

Controller dysfunctionController dysfunction

Pump dysfunctionPump dysfunction

Airway system dysfunctionAirway system dysfunction

Alveolar compartment dysfunctionAlveolar compartment dysfunction

Pulmonary vascular dysfunctionPulmonary vascular dysfunction

Controller dysfunctionController dysfunction“central apnea“central apnea””

Structural: meningoencephalitis, localized tumors or vascular abnormalities of the medulla,strokes affecting medullary control centers

Pharmacologic: narcotic, sedative

Metabolic: severe myxedema,hepati failure,advanced uremia,hypothermia

Elevation of Pco2 in the CNS: chronic metabolic alkalosis (diuretic use)

Obesity-hypoventilation syndrome

COPD

Controller dysfunctionController dysfunction“central apnea“central apnea””

Determine rate & depth of breathingDetermine rate & depth of breathing

Determine pattern of breathingDetermine pattern of breathing

Determine amount of effort for breathingDetermine amount of effort for breathing

1.1. Awareness patient without sedative use can`t Awareness patient without sedative use can`t increase RR>12/min or make use of accessory increase RR>12/min or make use of accessory musclesmuscles

2.2. Hypoxemia,HypercapniaHypoxemia,Hypercapnia

3.3. PAo2-Pao2 was normalPAo2-Pao2 was normal

4.4. Type II respiratory failureType II respiratory failure

Pump DysfunctionPump DysfunctionDecreased respiratory muscle strength:

Muscle fatigue Recovery from acute respiratory failure, high respiratory rates, increased inspiratory time

Disuse atrophyProlonged mechanical ventilation, following phrenic nerve injury

Electrolyte abnormalities

Decreased motor neuron function:

Decreased phrenic nerve output Polyneuropathy, Guillain-Barr´e syndrome, phrenic nerve transection or injury,

Poliomyelitis

Decreased neuromuscular transmissionMyasthenia gravis, use of paralyzing agents

Pharmacologic:paralyzing agents, corticosteroids, cholinergic crisis, aminoglycosides

Structural abnormalities: Kyphoscoliosis,Obesity,Ascites,Distention,Flail chest,Thoracoplasty

Pump DysfunctionPump DysfunctionParadoxical movement of diaphragmParadoxical movement of diaphragm

Respiratory distressRespiratory distress

Vital capacity<10ml/kgVital capacity<10ml/kg

Inspiratory force<-20cmH2OInspiratory force<-20cmH2O

RSBI>105RSBI>105

Transdiaphragmatic pressureTransdiaphragmatic pressure

EMG & NCVEMG & NCVHypercapniaHypercapnia

Type II respiratory failureType II respiratory failure

Airways System DysfunctionAirways System Dysfunction

Upper airways:acute epiglottitis, aspirated foreign body, tracheal tumor

narrowing of the trachea or glottis by fibrotic tissue

Lower airways: COPD, asthma, advanced cystic fibrosis

Airways System DysfunctionAirways System Dysfunction

A greater transthoracic pressure gradient requirement

The resistive work of breathing is increased Vo2

Tidal volume falls and dead space ventilation increases

Respiratory muscle fatigue shallow breathing pattern

Air trapping hyperinflation diaphragm flattening

Stirdor,Bronchospasm(wheez,rhonchi) Raw>10 cmH2O/L/S Type II respiratory failureType II respiratory failure

Alveolar Compartment DysfunctionAlveolar Compartment Dysfunction

Cardiogenic and noncardiogenic pulmonary edema

Diffuse pneumonia

Extensive pulmonary hemorrhage

Aspiration of stomach contents

Neardrowning

Lung contusion

Hypoxemia,HypercapniaHypoxemia,HypercapniaType I respiratory failureType I respiratory failure

Alveolar Compartment DysfunctionAlveolar Compartment DysfunctionHypoxemia:

Diffuse alveolar filling large right-to-left shunt

Interstitial edema impair diffusion across the alveolar-capillary membrane

Hypercapnia: Increased ventilatory demand:

Hypoxemia

Vd / Vt,

Elastic work of breathing (reduced lung compliance)

Resistive work of breathing (airway narrowing and airway reactivity)

Neural drive to breathe (mediated by pulmonary parenchymal vagal fibers) Decreased ventilatory supply:

Alveolar flooding

Reduced lung elasticity

Respiratory muscle fatigue

Reduced blood supply to the diaphragm secondary to shock

Alveolar Compartment DysfunctionAlveolar Compartment Dysfunction

ConsolidationConsolidation

bronchial sound,egophonia,dullnessbronchial sound,egophonia,dullness

Static compliance<30 ml/cmH2OStatic compliance<30 ml/cmH2O

Type I respiratory failureType I respiratory failure

Pulmonary Vascular DysfunctionPulmonary Vascular Dysfunction

Symptoms & Signs of right HFSymptoms & Signs of right HF::

JVP,S3,RV heave,TR,S2JVP,S3,RV heave,TR,S2

EKG RBBB,RV strain patternEKG RBBB,RV strain pattern

CX-Ray Pulmonary artery enlargementCX-Ray Pulmonary artery enlargement

Type II respiratory failureType II respiratory failure

Respiratory FailureType I:Type I: Acute Hypoxemic Respiratory Failure Acute Hypoxemic Respiratory Failure

alveolar flooding and subsequent intrapulmonary shunt physiologyalveolar flooding and subsequent intrapulmonary shunt physiology

pulmonary edema, pneumonia, or alveolar hemorrhagepulmonary edema, pneumonia, or alveolar hemorrhage

Type II:Type II: Alveolar hypoventilationAlveolar hypoventilation impaired CNS drive to breathe, impaired strength with failure of impaired CNS drive to breathe, impaired strength with failure of

neuromuscular function in the respiratory system, increased load on neuromuscular function in the respiratory system, increased load on the respiratory system the respiratory system

Type III:Type III: Lung atelectasisLung atelectasis perioperative respiratory failureperioperative respiratory failure

Type IV:Type IV: Hypoperfusion of respiratory musclesHypoperfusion of respiratory muscles

shockshock

Hypoxemic Respiratory Failure

Alveolar hypoventilation

Ventilation-perfusion Mismatch

Shunt

Diffusion limitation

PAO2 = FIO2 x (PB – PH2O) – PaCO2/R PAO2 = 150 – 1.25 x PaCO2 PAO2 = 150 – 1.25 x PaCO2 PAo2 − Pao2 = [PIo2 − PaCo2/R] − Pao2

Hypoxemic Respiratory Failure

Although changes in minute and alveolar ventilation can change Paco2 considerably, this is not so for Pao2.

At a Pao2>55-60 mmHg,the effect of increasing ventilation on CaO2 is minimal,since the oxyhemoglobin dissociation curve is flat in this range.

In the absence of underlying pulmonary disease, the hypoxemia accompanying alveolar hypoventilation is characterized by a normal alveolar-arterial oxygen gradient.

Hypercapnic Respiratory Failure

Paco2 is determined:

Rate of CO2 production (˙Vco2 ) rate of CO2 production # rate of CO2 elimination

) CvCO2-CaCO2.(CO.10 # 90-130 L/min/M2

Level of alveolar ventilation VA = K . ˙Vco2/Paco2

VE = K . (˙Vo2 . RQ) / (Paco2 / [1 − Vd / Vt] )

˙ Vo2 = rate of O2 consumption

RQ = respiratory quotient