Pathophysiology of Respiratory Pathophysiology of Respiratory Failure and Failure and

Use of Mechanical Ventilation Use of Mechanical Ventilation

Puneet Katyal, MBBS, MSHI Puneet Katyal, MBBS, MSHI Ognjen Gajic Ognjen Gajic, MD , MD

Mayo Clinic, Rochester, MN, USA Mayo Clinic, Rochester, MN, USA

Definition Definition

n n Chest wall (including Chest wall (including pleura and pleura and diaphragm) diaphragm)

n n Airways Airways n n Alveolar Alveolar– –capillary capillary

units units

n n Pulmonary circulation Pulmonary circulation n n Nerves Nerves n n CNS or Brain Stem CNS or Brain Stem

n n Respiratory failure is a syndrome of inadequate Respiratory failure is a syndrome of inadequate gas exchange due to dysfunction of one or more gas exchange due to dysfunction of one or more essential components of the respiratory system: essential components of the respiratory system:

Respiratory System Respiratory System

Lung: Alveolar Unit

Brain

Spinal cord

Nerves

Intercostal muscles

Chest wall Airway Pleura Diaphragm

Epidemiology Epidemiology

n n Incidence: about 360,000 cases per year in the Incidence: about 360,000 cases per year in the United States United States

n n 36% die during hospitalization 36% die during hospitalization n n Morbidity and mortality rates increase with age Morbidity and mortality rates increase with age

and presence of comorbidities and presence of comorbidities

Classification Classification n n Type I or Hypoxemic (PaO2 <60 at sea level): Type I or Hypoxemic (PaO2 <60 at sea level): Failure of Failure of

oxygen exchange oxygen exchange n n Increased shunt fraction (Q Increased shunt fraction (Q S S /Q /Q T T ) )

n n Due to alveolar flooding Due to alveolar flooding n n Hypoxemia refractory to supplemental oxygen Hypoxemia refractory to supplemental oxygen

n n Type II or Type II or Hypercapnic Hypercapnic (PaCO2 >45): (PaCO2 >45): Failure to Failure to exchange or remove carbon dioxide exchange or remove carbon dioxide n n Decreased alveolar minute ventilation (V Decreased alveolar minute ventilation (V A A ) ) n n Often accompanied by hypoxemia that corrects with Often accompanied by hypoxemia that corrects with

supplemental oxygen supplemental oxygen

Classification Classification

n n Type III Respiratory Failure: Type III Respiratory Failure: Perioperative Perioperative respiratory respiratory failure failure n n Increased Increased atelectasis atelectasis due to low functional residual capacity due to low functional residual capacity

( (FRC FRC) in the setting of abnormal abdominal wall mechanics ) in the setting of abnormal abdominal wall mechanics n n Often results in type I or type II respiratory failure Often results in type I or type II respiratory failure n n Can be ameliorated by anesthetic or operative technique, Can be ameliorated by anesthetic or operative technique, posture posture, ,

incentive incentive spirometry spirometry, post , post- -operative analgesia, attempts to lower operative analgesia, attempts to lower intra intra- -abdominal pressure abdominal pressure

n n Type IV Respiratory Failure: S Type IV Respiratory Failure: Shock hock n n Type IV describes patients who are Type IV describes patients who are intubated intubated and ventilated and ventilated

in the process of resuscitation for shock in the process of resuscitation for shock n n Goal of ventilation is to stabilize gas exchange and to unload t Goal of ventilation is to stabilize gas exchange and to unload the he

respiratory muscles, lowering their oxygen consumption respiratory muscles, lowering their oxygen consumption

Classification Classification

n n Respiratory failure may be Respiratory failure may be n n Acute Acute n n Chronic Chronic n n Acute on chronic Acute on chronic

n n E.g.: acute exacerbation of advanced COPD E.g.: acute exacerbation of advanced COPD

Pathophysiology: Pathophysiology: Mechanisms Mechanisms

n n Hypoxemic failure Hypoxemic failure n n Ventilation/Perfusion (V/Q) mismatch Ventilation/Perfusion (V/Q) mismatch n n Shunt Shunt n n Exacerbated by low mixed venous O2 (SvO2) Exacerbated by low mixed venous O2 (SvO2)

n n Hypercapnic Hypercapnic failure failure n n Decreased minute ventilation (MV) relative to Decreased minute ventilation (MV) relative to

demand demand n n Increased dead space ventilation Increased dead space ventilation

Pathophysiology: Pathophysiology: Etiologic Categories Etiologic Categories

n n Nervous system Nervous system failure (Type II) failure (Type II) n n Central Central

hypoventilation hypoventilation n n Neuropathies Neuropathies

n n Muscle (pump) Muscle (pump) failure (Type II) failure (Type II) n n Muscular dystrophies Muscular dystrophies n n Myopathies Myopathies

n n Neuromuscular Neuromuscular transmission failure transmission failure (Type II) (Type II) n n Myasthenia gravis Myasthenia gravis

n n Airway failure Airway failure (Type II) (Type II) n n Obstruction Obstruction n n Dysfunction Dysfunction

Pathophysiology: Pathophysiology: Etiologic Categories Etiologic Categories

n n Chest wall and pleural Chest wall and pleural space failure (Type II) space failure (Type II) n n Kyphoscoliosis Kyphoscoliosis n n Morbid obesity Morbid obesity n n Pneumothorax Pneumothorax n n Hydrothorax Hydrothorax n n Hemothorax Hemothorax

n n Alveolar unit failure Alveolar unit failure (Type I) (Type I) n n Collapse Collapse n n Flooding: edema, blood, Flooding: edema, blood,

pus, aspiration pus, aspiration n n Fibrosis Fibrosis

n nPulmonary vasculature failure (Type I) Pulmonary vasculature failure (Type I) n nPulmonary embolism Pulmonary embolism n nPulmonary hypertension Pulmonary hypertension

Causes Causes n n Type I respiratory failure Type I respiratory failure

n n Pneumonia Pneumonia n n Cardiogenic Cardiogenic pulmonary edema pulmonary edema

n n Pulmonary edema due to increased hydrostatic pressure Pulmonary edema due to increased hydrostatic pressure

n n Non Non- -cardiogenic pulmonary edema cardiogenic pulmonary edema n n Pulmonary edema due to increased permeability Pulmonary edema due to increased permeability

n n Acute lung injury (ALI) Acute lung injury (ALI) n n Acute respiratory distress syndrome (ARDS) Acute respiratory distress syndrome (ARDS)

n n Pulmonary embolism (see also type IV respiratory failure) Pulmonary embolism (see also type IV respiratory failure) n n Atelectasis (see also type III respiratory failure) Atelectasis (see also type III respiratory failure) n n Pulmonary fibrosis Pulmonary fibrosis

Causes Causes n n Type II respiratory failure Type II respiratory failure

n n Central hypoventilation Central hypoventilation n n Asthma Asthma n n Chronic obstructive pulmonary disease (COPD) Chronic obstructive pulmonary disease (COPD)

n n Hypoxemia and Hypoxemia and hypercapnia hypercapnia often occur together often occur together

*Neuromuscular and chest wall disorders Neuromuscular and chest wall disorders n n Myopathies Myopathies n n Neuropathies Neuropathies n n Kyphoscoliosis Kyphoscoliosis n n Myasthenia gravis Myasthenia gravis

n n Obesity Hypoventilation Syndrome Obesity Hypoventilation Syndrome

Causes Causes

n n Type III respiratory failure Type III respiratory failure n n Inadequate post Inadequate post- -operative analgesia, upper abdominal operative analgesia, upper abdominal

incision incision n n Obesity, Obesity, ascites ascites n n Pre Pre- -operative tobacco smoking operative tobacco smoking n n Excessive airway secretions Excessive airway secretions

n n Type IV respiratory failure Type IV respiratory failure n n Cardiogenic Cardiogenic shock shock n n Septic shock Septic shock n n Hypovolemic Hypovolemic shock shock

Diagnosis: History Diagnosis: History n n Sepsis suggested by fever, chills Sepsis suggested by fever, chills n n Pneumonia suggested by cough, sputum production, Pneumonia suggested by cough, sputum production,

chest pain chest pain n n Pulmonary embolus suggested by sudden onset of Pulmonary embolus suggested by sudden onset of

shortness of breath or chest pain shortness of breath or chest pain n n COPD exacerbation suggested by history of heavy COPD exacerbation suggested by history of heavy

smoking, cough, sputum production smoking, cough, sputum production n n Cardiogenic pulmonary edema suggested by chest pain, Cardiogenic pulmonary edema suggested by chest pain,

paroxysmal nocturnal dyspnea, and orthopnea paroxysmal nocturnal dyspnea, and orthopnea

Diagnosis: History Diagnosis: History n n Noncardiogenic edema suggested by the Noncardiogenic edema suggested by the

presence of risk factors including sepsis, presence of risk factors including sepsis, trauma, aspiration, and blood transfusions trauma, aspiration, and blood transfusions

n n Accompanying sensory abnormalities or Accompanying sensory abnormalities or symptoms of weakness may suggest symptoms of weakness may suggest neuromuscular respiratory failure; as would the neuromuscular respiratory failure; as would the history of an ingestion or administration of history of an ingestion or administration of drugs or toxins. drugs or toxins.

n n Additional exposure history may help diagnose Additional exposure history may help diagnose asthma, aspiration, inhalational injury and some asthma, aspiration, inhalational injury and some interstitial lung diseases interstitial lung diseases

Diagnosis: Physical Findings Diagnosis: Physical Findings n n Hypotension usually with signs of poor perfusion Hypotension usually with signs of poor perfusion

suggests severe sepsis or massive pulmonary embolus suggests severe sepsis or massive pulmonary embolus n n Hypertension usually with signs of poor perfusion Hypertension usually with signs of poor perfusion

suggests cardiogenic pulmonary edema suggests cardiogenic pulmonary edema n n Wheezing suggests airway obstruction: Wheezing suggests airway obstruction:

n n Bronchospasm Bronchospasm n n Fixed upper or lower airway pathology Fixed upper or lower airway pathology n n Secretions Secretions n n Pulmonary edema ( Pulmonary edema (“ “cardiac asthma cardiac asthma” ”) )

Diagnosis: Physical Findings Diagnosis: Physical Findings

n n Stridor suggests upper airway obstruction Stridor suggests upper airway obstruction n n Elevated jugular venous pressure suggests right Elevated jugular venous pressure suggests right

ventricular dysfunction due to accompanying ventricular dysfunction due to accompanying pulmonary hypertension pulmonary hypertension

n n Tachycardia and arrhythmias may be the cause Tachycardia and arrhythmias may be the cause of cardiogenic pulmonary edema of cardiogenic pulmonary edema

Diagnosis: Laboratory Workup Diagnosis: Laboratory Workup n n ABG ABG

n n Quantifies magnitude of gas exchange abnormality Quantifies magnitude of gas exchange abnormality n n Identifies type and chronicity of respiratory failure Identifies type and chronicity of respiratory failure

n n Complete blood count Complete blood count n n Anemia may cause cardiogenic pulmonary edema Anemia may cause cardiogenic pulmonary edema n n Polycythemia suggests may chronic hypoxemia Polycythemia suggests may chronic hypoxemia n n Leukocytosis, a left shift, or leukopenia suggestive of Leukocytosis, a left shift, or leukopenia suggestive of

infection infection n n Thrombocytopenia may suggest sepsis as a cause Thrombocytopenia may suggest sepsis as a cause

Diagnosis: Laboratory Workup Diagnosis: Laboratory Workup

n n Cardiac serologic markers Cardiac serologic markers n n Troponin, Creatine kinase Troponin, Creatine kinase- - MB fraction (CK MB fraction (CK- -MB) MB) n n B B- -type natriuretic peptide (BNP) type natriuretic peptide (BNP)

n n Microbiology Microbiology n n Respiratory cultures: sputum/tracheal Respiratory cultures: sputum/tracheal

aspirate/ aspirate/broncheoalveolar broncheoalveolar lavage (BAL) lavage (BAL) n n Blood, urine and body fluid (e.g. pleural) cultures Blood, urine and body fluid (e.g. pleural) cultures

Diagnostic Investigations Diagnostic Investigations n n Chest radiography Chest radiography n n Identify chest wall, pleural and lung parenchymal Identify chest wall, pleural and lung parenchymal

pathology; and distinguish disorders that cause pathology; and distinguish disorders that cause primarily V/Q mismatch (clear lungs) vs. Shunt primarily V/Q mismatch (clear lungs) vs. Shunt (intra (intra- -pulmonary shunt; with opacities present) pulmonary shunt; with opacities present)

n n Electrocardiogram Electrocardiogram n n Identify arrhythmias, ischemia, ventricular Identify arrhythmias, ischemia, ventricular

dysfunction dysfunction

n n Echocardiography Echocardiography n n Identify right and/or left ventricular dysfunction Identify right and/or left ventricular dysfunction

Diagnostic Investigations Diagnostic Investigations n n Pulmonary function tests/bedside spirometry Pulmonary function tests/bedside spirometry

n n Identify obstruction, restriction, gas diffusion abnormalities Identify obstruction, restriction, gas diffusion abnormalities n n May be difficult to perform if critically ill May be difficult to perform if critically ill

n n Bronchoscopy Bronchoscopy n n Obtain biopsies, brushings and BAL for histology, cytology Obtain biopsies, brushings and BAL for histology, cytology

and microbiology and microbiology n n Results may not be available quickly enough to avert Results may not be available quickly enough to avert

respiratory failure respiratory failure n n Bronchoscopy may not be safe in the Bronchoscopy may not be safe in the if critically ill if critically ill

Respiratory Failure: Respiratory Failure: Management Management

n n ABC ABC’ ’s s n n Ensure airway is adequate Ensure airway is adequate n n Ensure adequate supplemental oxygen and assisted Ensure adequate supplemental oxygen and assisted

ventilation, if indicated ventilation, if indicated n n Support circulation as needed Support circulation as needed

Respiratory Failure: Respiratory Failure: Management Management

n n Treatment of a specific cause when possible Treatment of a specific cause when possible n n Infection Infection

n n Antimicrobials, source control Antimicrobials, source control

n n Airway obstruction Airway obstruction n n Bronchodilators, glucocorticoids Bronchodilators, glucocorticoids

n n Improve cardiac function Improve cardiac function n n Positive airway pressure, diuretics, vasodilators, Positive airway pressure, diuretics, vasodilators,

morphine, morphine, inotropy inotropy, revascularization , revascularization

Respiratory Failure: Respiratory Failure: Management Management

n n Mechanical ventilation Mechanical ventilation n n Non Non- -invasive (if patient can protect airway and is invasive (if patient can protect airway and is

hemodynamically stable) hemodynamically stable) n n Mask: usually orofacial to start Mask: usually orofacial to start

n n Invasive Invasive n n Endotracheal tube (ETT) Endotracheal tube (ETT) n n Tracheostomy Tracheostomy – – if upper airway is obstructed if upper airway is obstructed

Respiratory Failure

Secure airway

Supplemental oxygen as needed

Treat underlying condition

Need for endotracheal intubation or tracheostomy?

Invasive mechanical ventilation

Non-invasive mechanical ventilation

Yes No

Fails

Indications for Mechanical Indications for Mechanical Ventilation Ventilation

n n Cardiac or respiratory arrest Cardiac or respiratory arrest n n Tachypnea or bradypnea with respiratory fatigue or Tachypnea or bradypnea with respiratory fatigue or

impending arrest impending arrest n n Acute respiratory acidosis Acute respiratory acidosis n n Refractory hypoxemia Refractory hypoxemia (when the P a O 2 could not be

maintained above 60 mm Hg with inspired O 2 fraction (F I O 2 )>1.0)

n n Inability to protect the airway associated with depressed levels Inability to protect the airway associated with depressed levels of consciousness of consciousness

Indications for Mechanical Indications for Mechanical Ventilation Ventilation

n n Shock associated with excessive respiratory work Shock associated with excessive respiratory work n n Inability to clear secretions with impaired gas exchange Inability to clear secretions with impaired gas exchange

or excessive respiratory work or excessive respiratory work n n Newly diagnosed neuromuscular disease with a vital Newly diagnosed neuromuscular disease with a vital

capacity <10 capacity <10- -15 mL/kg 15 mL/kg n n Short term adjunct in management of acutely increased Short term adjunct in management of acutely increased

intracranial pressure (ICP) intracranial pressure (ICP)

Invasive vs. Non Invasive vs. Non- -invasive invasive Ventilation Ventilation

n n Consider non Consider non- -invasive ventilation particularly invasive ventilation particularly in the following settings: in the following settings: n n COPD exacerbation COPD exacerbation n n Cardiogenic pulmonary edema Cardiogenic pulmonary edema n n Obesity hypoventilation syndrome Obesity hypoventilation syndrome n n Noninvasive ventilation may be tried in selected Noninvasive ventilation may be tried in selected

patients with asthma or non patients with asthma or non- -cardiogenic hypoxemic cardiogenic hypoxemic respiratory failure respiratory failure

Goals of Mechanical Goals of Mechanical Ventilation Ventilation

n n Improve ventilation by augmenting respiratory Improve ventilation by augmenting respiratory rate and tidal volume rate and tidal volume n n Assistance for neural or muscle dysfunction Assistance for neural or muscle dysfunction

n n Sedated, comatose or paralyzed patient Sedated, comatose or paralyzed patient n n Neuropathy, myopathy or muscular dystrophy Neuropathy, myopathy or muscular dystrophy n n Intra Intra- -operative ventilation operative ventilation

n n Correct respiratory acidosis, providing goals of lung Correct respiratory acidosis, providing goals of lung- - protective ventilation are met protective ventilation are met

n n Match metabolic demand Match metabolic demand n n Rest respiratory muscles Rest respiratory muscles

Goals of Mechanical Goals of Mechanical Ventilation Ventilation

n n Correct hypoxemia Correct hypoxemia n n High F High F I I O O 2 2 n n Positive end expiratory pressure (PEEP) Positive end expiratory pressure (PEEP)

n n Improve cardiac function Improve cardiac function n n Decreases preload Decreases preload n n Decreases afterload Decreases afterload n n Decreases metabolic demand Decreases metabolic demand

Permissive Hypercapnia Permissive Hypercapnia

n n Ventilation strategy that allows P Ventilation strategy that allows P a a CO CO 2 2 to rise to rise by accepting a lower alveolar minute ventilation by accepting a lower alveolar minute ventilation to avoid specific risks: to avoid specific risks: n n Dynamic hyperinflation ( Dynamic hyperinflation (“ “auto auto- -peep peep” ”) and ) and

barotrauma in patients with asthma barotrauma in patients with asthma n n Ventilator Ventilator- -associated lung injury, in patients with, or associated lung injury, in patients with, or

at risk for, ALI and ARDS at risk for, ALI and ARDS

n n Contraindicated in patients with increased Contraindicated in patients with increased intracranial pressure such as head trauma intracranial pressure such as head trauma

Mechanical Ventilation

Correct Hypoxemia Optimize cardiac function

Correct respiratory acidosis*

F I O 2 , P

EEP

RR, TV

Preload, Afterload,

Metabolic demand

Meet increased metabolic demand

* Avoid ventilator induced lung injury and dynamic hyperinflation

Hyperventilation may be used as a short term adjunct to treat acutely elevated ICP

Enhance Ventilation *

Assistance for neural and/or muscle dysfunction

Other Issues to Consider When Other Issues to Consider When Initiating Mechanical Ventilation Initiating Mechanical Ventilation

n n Do not wait for frank respiratory acidosis Do not wait for frank respiratory acidosis especially with evidence of: especially with evidence of: n n Inability to protect airway Inability to protect airway n n Persistent or worsening tachypnea (respiratory rate Persistent or worsening tachypnea (respiratory rate

>35/minute) >35/minute) n n Respiratory muscle fatigue Respiratory muscle fatigue

n n Always consider risks and benefits of initiation Always consider risks and benefits of initiation and continuation of mechanical ventilation and continuation of mechanical ventilation

Other Issues in Intubated & Other Issues in Intubated & Mechanically Ventilated Mechanically Ventilated Patients Patients n n Always elevate the head of the bed >30 Always elevate the head of the bed >30º º and use ulcer and use ulcer

and DVT prophylaxis, unless contraindicated and DVT prophylaxis, unless contraindicated n n Use lung protective ventilation strategy for patients Use lung protective ventilation strategy for patients

with Acute Lung Injury (TV ~ 6 ml/kg ideal body with Acute Lung Injury (TV ~ 6 ml/kg ideal body weight, Plat pressure < 30 cmH weight, Plat pressure < 30 cmH 2 2 O) O)

n n Modify ventilator settings primarily to achieve patient Modify ventilator settings primarily to achieve patient- - ventilator synchrony. If this fails, use the least amount ventilator synchrony. If this fails, use the least amount of sedation required to achieve comfort and avoid of sedation required to achieve comfort and avoid unnecessary neuromuscular blockade unnecessary neuromuscular blockade

Other Issues in Intubated & Other Issues in Intubated & Mechanically Ventilated Mechanically Ventilated Patients Patients n n Monitor patient comfort, gas exchange, Monitor patient comfort, gas exchange,

mechanics, and ventilator waveforms daily, or mechanics, and ventilator waveforms daily, or more frequently if indicated more frequently if indicated

n n When minimal settings are required for When minimal settings are required for oxygenation (F oxygenation (F I I O O 2 2 <55%, PEEP<8) and <55%, PEEP<8) and patient is hemodynamically stable, perform a patient is hemodynamically stable, perform a spontaneous breathing trial daily spontaneous breathing trial daily

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