Invasive Mechanical Ventilation

Definition and Indications

Definition

Invasive mechanical ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (IMV) is a form of advanced airway Airway ABCDE Assessment management used to deliver oxygen and/or to regulate ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing at the level of the trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy through 3 main routes:

• Oropharyngeal intubation Intubation Peritonsillar Abscess
• Nasopharyngeal intubation Intubation Peritonsillar Abscess
• Tracheostomy Tracheostomy Surgical formation of an opening into the trachea through the neck, or the opening so created. Laryngomalacia and Tracheomalacia

Common indications for IMV

• Hypoxemia Hypoxemia Neonatal Respiratory Distress Syndrome refractory to noninvasive oxygenation (e.g., ARDS)
• Hypercapnia Hypercapnia A clinical manifestation of abnormal increase in the amount of carbon dioxide in arterial blood. Neonatal Respiratory Distress Syndrome with altered mental status Altered Mental Status Sepsis in Children (e.g., chronic obstructive pulmonary disease Pulmonary disease Diseases involving the respiratory system. Blastomyces/Blastomycosis ( COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD)) exacerbation)
• GCS GCS A scale that assesses the response to stimuli in patients with craniocerebral injuries. The parameters are eye opening, motor response, and verbal response. Coma < 8 (e.g., cardiac arrest Cardiac arrest Cardiac arrest is the sudden, complete cessation of cardiac output with hemodynamic collapse. Patients present as pulseless, unresponsive, and apneic. Rhythms associated with cardiac arrest are ventricular fibrillation/tachycardia, asystole, or pulseless electrical activity. Cardiac Arrest)
• Inability to protect the airway Airway ABCDE Assessment (e.g., anaphylaxis Anaphylaxis An acute hypersensitivity reaction due to exposure to a previously encountered antigen. The reaction may include rapidly progressing urticaria, respiratory distress, vascular collapse, systemic shock, and death. Type I Hypersensitivity Reaction)
• Surgical procedures (e.g., neuromuscular blockade Neuromuscular Blockade The intentional interruption of transmission at the neuromuscular junction by external agents, usually neuromuscular blocking agents. It is distinguished from nerve block in which nerve conduction (neural conduction) is interrupted rather than neuromuscular transmission. Neuromuscular blockade is commonly used to produce muscle relaxation as an adjunct to anesthesia during surgery and other medical procedures. It is also often used as an experimental manipulation in basic research. It is not strictly speaking anesthesia but is grouped here with anesthetic techniques. The failure of neuromuscular transmission as a result of pathological processes is not included here. Aminoglycosides)
• Progressive neuromuscular disorders (e.g., amyotrophic lateral sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor ( ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis))

Considerations

There are several modes of IMV that are managed jointly based on:

• Preferences of the intensivist
• Preferences of the respiratory therapist
• The individual’s needs

Invasive mechanical ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing is not a benign Benign Fibroadenoma intervention:

• Ventilator-induced lung injury (VILI) is common.
• VILI may compound the specific etiology of respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure.

General Concepts

Background ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing physiology

Ventilator mode is described based on 3 characteristics, namely, trigger, cycle, and limit:

• Trigger is the type of signal that initiates the inspiratory phase by the ventilator:
  • Patient-triggered signal: The individual’s inspiratory effort triggers the inspiratory phase by the ventilator.
  • Time-triggered signal: A time interval set by the operator determines when the ventilator initiates the inspiratory phase.
• Cycle: the type of signal that ends the inspiratory phase delivered by the ventilator
  • Volume-cycled ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing: The inspiratory phase ends once a preset volume exits the ventilator.
  • Other types include:
    • Time-cycled ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing
    • Pressure-cycled ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing
• Limit: a value (e.g., pressure or time) that should not be exceeded and that is specified by the operator to protect the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy

Basic settings controlled by the operator

• PEEP:
  • Pressure remaining in the distal airways (i.e., the alveolus) of an individual at the end of expiration Expiration Ventilation: Mechanics of Breathing
  • Keeps the alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) open to participate in oxygenation
  • Can be increased to improve oxygenation (↑ PaO₂)
  • Can be lowered to decrease oxygenation (↓ PaO₂)
• FiO₂ is the percentage of O₂ delivered directly to the individual:
  • Increasing FiO₂ increases oxygenation and decreasing FiO₂ lowers oxygenation.
• Tidal volume Tidal volume The volume of air inspired or expired during each normal, quiet respiratory cycle. Common abbreviations are tv or V with subscript t. Ventilation: Mechanics of Breathing is the volume (in mL) delivered with each breath:
  • Can be increased to increase ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (↓ PaCO₂)
  • Can be lowered to reduce ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (↑ PaCO₂)
• Respiratory rate Respiratory rate The number of times an organism breathes with the lungs (respiration) per unit time, usually per minute. Pulmonary Examination ( RR RR Relative risk (RR) is the risk of a disease or condition occurring in a group or population with a particular exposure relative to a control (unexposed) group. Measures of Risk) is the value set for breaths/min:
  • Can be increased to increase ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (↓ PaCO₂)
  • Can be lowered to reduce ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (↑ PaCO₂)
• Flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure rate is the maximum flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure (in L/min) that a ventilator can deliver a set tidal volume Tidal volume The volume of air inspired or expired during each normal, quiet respiratory cycle. Common abbreviations are tv or V with subscript t. Ventilation: Mechanics of Breathing:
  • Can be increased with a possible increase in ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing effect (↓ PaCO₂)
  • Can be lowered with a possible reduction in ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing effect (↑ PaCO₂)

Common Modes

Controlled mode

• Commonly used in critically ill individuals who have a significantly suppressed or absent respiratory drive
• All spontaneous patient breaths sensed by the ventilator are assisted with a preset volume or pressure specified by the operator.
• Patient-/time-triggered and volume-/pressure-cycled modes
• The 2 most common modes are:
  • Assist-control (AC) volume-control (VC) ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing
  • AC pressure-control (PC) ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing

Spontaneous/supported mode

• Used after a significant improvement of the critical state of individuals who can breathe spontaneously and are being considered for weaning
• Patient-triggered and flow-cycled modes
• Pressure-support (PS) ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing is the most common: All spontaneous patient breaths sensed by the ventilator are supported with a preset pressure specified by the operator.

Combined (controlled + spontaneous/supported) mode

• Commonly used for individuals on maintenance ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing and for weaning
• A preset number (not all) of patient breaths are assisted by the ventilator, as described for controlled mode; the remaining spontaneous patient breaths are supported as described for spontaneous/supported mode PS ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing.
• Also known as synchronized intermittent mandatory ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (SIMV)

Assist-control volume-control ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing

• Most commonly used initial mode of ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing
• Assists every sensed inspiratory effort made by the individual, thereby reducing the work of breathing Work of breathing Respiratory muscle contraction during inhalation. The work is accomplished in three phases: lung compliance work, that required to expand the lungs against its elastic forces; tissue resistance work, that required to overcome the viscosity of the lung and chest wall structures; and airway resistance work, that required to overcome airway resistance during the movement of air into the lungs. Work of breathing does not refer to expiration, which is entirely a passive process caused by elastic recoil of the lung and chest cage. Pulmonary Examination
• Trigger:
  • Time triggered, if the individual’s inspiratory effort is not sensed: The ventilator delivers a preset number of mandatory breaths per minute.
  • Patient triggered, if the individual’s inspiratory effort is sensed: All inspiratory efforts are assisted by the ventilator.
• Volume-cycled ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing:
  • Inspiratory phase ends when a preset volume exits the ventilator.
  • Inspiratory volume is an independent variable Independent variable Types of Variables because it is set by the operator and does not vary between breaths.
  • Inspiratory pressure is a dependent variable Dependent variable Types of Variables because it is not set by the operator and varies between breaths.
• Pressure-limited ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing:
  • Preset by the ventilator to abort the inspiratory phase if dangerous levels of airway Airway ABCDE Assessment pressure are reached
  • Helps prevent VILI
• Examples:
  • In an individual on AC/VC ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing who has spontaneous breaths of 20/min and with RR RR Relative risk (RR) is the risk of a disease or condition occurring in a group or population with a particular exposure relative to a control (unexposed) group. Measures of Risk set at 20/min:
    • All breaths are efficient enough to be sensed by the ventilator.
    • All breaths are assisted immediately after patient initiation.
    • Thus, the ventilator frequency is 20/min.
  • If the individual’s spontaneous breaths increase to 30/min while on AC/VC:
    • The ventilator frequency becomes 30/min.
    • The additional 10 breaths are assisted by the ventilator.
  • An individual has 4 spontaneous breaths/minute on AC/VC while the RR RR Relative risk (RR) is the risk of a disease or condition occurring in a group or population with a particular exposure relative to a control (unexposed) group. Measures of Risk is set at 12/min:
    • The ventilator assists with 4 breaths of the individual.
    • The ventilator adds 8 breaths every minute to reach the minimum number set by the operator.
• Problems:
  • Respiratory alkalemia Alkalemia Respiratory Alkalosis in individuals with tachypnea Tachypnea Increased respiratory rate. Pulmonary Examination due to anxiety Anxiety Feelings or emotions of dread, apprehension, and impending disaster but not disabling as with anxiety disorders. Generalized Anxiety Disorder, pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, or airway Airway ABCDE Assessment irritation
  • Auto-PEEP: dynamic hyperinflation Hyperinflation Imaging of the Lungs and Pleura of lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy when air builds up due to insufficient expiratory time

Assist-control pressure-control ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing

• Appropriate when the control of peak airway Airway ABCDE Assessment pressures is important (i.e., consider for individuals with previous barotrauma or after thoracic surgery Thoracic Surgery Basic surgical intervention in the thoracic cavity has the primary goal of alleviating any malady that mechanically affects the function of the heart and lungs, which can be secondary to underlying pathologies or, most commonly, trauma. Interventions include tube thoracostomy, thoracentesis, and emergency thoracotomy. Thoracic Surgery)
• Time-triggered, time-cycled, and pressure-limited ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing
• Inspiratory pressure is an independent variable Independent variable Types of Variables because it is set by the operator and does not vary between breaths.
• Inspiratory volume is a dependent variable Dependent variable Types of Variables because it is not set by the operator and varies between breaths:
  • Increasing volume at constant settings reflects improved pulmonary compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology.
  • Decreasing volume at constant settings reflects worsening pulmonary compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology.

Synchronized intermittent mechanical ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing/VC ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing

• More commonly used in surgical ICUs as opposed to medical ICUs
• Previously thought to be best for weaning individuals off the ventilator
• Allows the individual to practice unassisted breathing between assisted synchronized mandatory breaths
• Trigger:
  • Patient-triggered process if the individual’s inspiratory effort is sensed:
    • Some of the sensed inspiratory efforts are assisted by the ventilator.
    • Number of assisted breaths/minute is determined by the operator.
    • Patient breaths in excess of the operator’s settings remain unassisted.
  • Time-triggered process if the individual’s inspiratory effort is not sensed: The ventilator delivers a preset number of mandatory breaths/minute.
• Volume-cycled ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing:
  • Inspiratory phase ends when a preset volume exits the ventilator.
  • Inspiratory volume is an independent variable Independent variable Types of Variables because it is set by the operator and does not vary between breaths.
  • Inspiratory pressure is a dependent variable Dependent variable Types of Variables because it is not set by the operator and varies between breaths.
• Pressure-limited ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing:
  • Preset by the ventilator to abort the inspiratory phase if dangerous levels of airway Airway ABCDE Assessment pressure are reached
  • Helps prevent VILI
• Example for SIMV mode:
  • An individual has 20 spontaneous breaths while intubated, and the ventilator frequency is set to 12/min.
  • The ventilator delivers each of the 12 mandatory breaths in a synchronized fashion when the individual initiates a spontaneous breath.
  • Of the individual’s total 20 spontaneous breaths/minute, 12 are assisted by the ventilator and 8 remain unassisted.
  • The total number of breaths remains 20/min.
• Problems:
  • Reduced minute ventilation Minute ventilation Ventilation: Mechanics of Breathing:
    • When tachypneic, the individual exhales during the ventilator inspiratory phase.
    • Causes a rapid rise in airway Airway ABCDE Assessment pressure beyond the pressure limits set by the operator
    • Will lead to premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis cessation of ventilator-delivered breaths
  • A switch to AC ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing mode would increase the number of assisted breaths and minute ventilation Minute ventilation Ventilation: Mechanics of Breathing.
  • SIMV is usually delivered in combination with PS ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing to support unassisted breaths with a preset pressure.

Pressure-support ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing

• Commonly used in combination with SIMV to ensure volume-cycled backup.
• Patient-triggered, flow-cycled, pressure-limited ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing
• Operator sets the pressure that must be reached during each inspiratory phase by the ventilator.
• PS ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing is always patient triggered: All sensed inspiratory efforts are supported by the ventilator to reach the pressure set by the operator.
• Once the flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure in the airway Airway ABCDE Assessment reaches a level below a minimum threshold Threshold Minimum voltage necessary to generate an action potential (an all-or-none response) Skeletal Muscle Contraction, the PS is terminated.

Complications

Ventilator-associated pneumonia Ventilator-Associated Pneumonia Multidrug-resistant Organisms and Nosocomial Infections (VAP)

• Requires a minimum of 3 days on mechanical ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing
• Risk factors:
  • Advanced age
  • Higher degree of comorbidities Comorbidities The presence of co-existing or additional diseases with reference to an initial diagnosis or with reference to the index condition that is the subject of study. Comorbidity may affect the ability of affected individuals to function and also their survival; it may be used as a prognostic indicator for length of hospital stay, cost factors, and outcome or survival. St. Louis Encephalitis Virus
  • Prolonged length of hospital/ ICU ICU Hospital units providing continuous surveillance and care to acutely ill patients. West Nile Virus stay
  • Prolonged length of IMV
  • Exposure to invasive procedures
• Typically diagnosed via imaging along with:
  • Increased respiratory secretions
  • Culture data ( bronchoalveolar lavage Bronchoalveolar lavage Washing out of the lungs with saline or mucolytic agents for diagnostic or therapeutic purposes. It is very useful in the diagnosis of diffuse pulmonary infiltrates in immunosuppressed patients. Pulmonary Fibrosis or tracheal aspirate)
  • Presence of sepsis Sepsis Systemic inflammatory response syndrome with a proven or suspected infectious etiology. When sepsis is associated with organ dysfunction distant from the site of infection, it is called severe sepsis. When sepsis is accompanied by hypotension despite adequate fluid infusion, it is called septic shock. Sepsis and Septic Shock (worsening or new)
• Most common organisms:
  • Staphylococcus aureus Staphylococcus aureus Potentially pathogenic bacteria found in nasal membranes, skin, hair follicles, and perineum of warm-blooded animals. They may cause a wide range of infections and intoxications. Brain Abscess
  • Pseudomonas aeruginosa Pseudomonas aeruginosa A species of gram-negative, aerobic, rod-shaped bacteria commonly isolated from clinical specimens (wound, burn, and urinary tract infections). It is also found widely distributed in soil and water. P. Aeruginosa is a major agent of nosocomial infection. Pseudomonas
  • Klebsiella pneumoniae Klebsiella Pneumoniae Gram-negative, non-motile, capsulated, gas-producing rods found widely in nature and associated with urinary and respiratory infections in humans. Aminoglycosides
  • Enterobacter Enterobacter Multidrug-resistant Organisms and Nosocomial Infections species
  • Actinobacter species
• Treatment is with antibiotics.

Subtypes of VILI

• Barotrauma:
  • High lung inflation pressure that results in:
    • High transpulmonary pressure Transpulmonary pressure Ventilation: Mechanics of Breathing
    • Lung overdistension
    • Air leakage
• Atelectrauma: high shear forces that open and close recruitable atelectatic lung units
• Volutrauma:
  • Alveolar overdistension causing epithelial strain and lipid mobilization
  • Lipid mobilization causes cellular detachment of vascular endothelial cells:
    • Alveolar epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology breaks down.
    • Results in alveolar and interstitial edema Interstitial Edema Increased Intracranial Pressure (ICP)
• Biotrauma: inflammatory response from mechanical injury via cytokines Cytokines Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Adaptive Immune Response and other inflammatory mediators
• Practices preventing VILI include:
  • Low tidal volumes
  • Moderate amount of PEEP
  • Prone positioning
  • Neuromuscular blocking agents to prevent patient/ventilator dyssynchrony

Oxygen toxicity Toxicity Dosage Calculation

• Results from reactive O₂ species that cause:
  • Cellular damage
  • Inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation
  • Genetic alterations
• To avoid toxicity Toxicity Dosage Calculation, it is recommended to use the lowest FiO₂ to achieve targeted oxygenation.

Auto-PEEP

• Results of persistent end-expiratory airflow that compounds after each breath, contributing to increasing pulmonary hyperinflation Hyperinflation Imaging of the Lungs and Pleura
• Also known as “air stacking” or “intrinsic PEEP”
• Most commonly seen in asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma, COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD), and ARDS
• Results in alveolar overdistension and reduced lung compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology (barotrauma)
• Increases intrathoracic pressure
• Increases in intrathoracic pressure can result in:
  • Decreased venous return
  • Reduced cardiac preload Preload Cardiac Mechanics
  • Increased left ventricular afterload Afterload Afterload is the resistance in the aorta that prevents blood from leaving the heart. Afterload represents the pressure the LV needs to overcome to eject blood into the aorta. Cardiac Mechanics
  • Reduced cardiac output Cardiac output The volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat). Cardiac Mechanics leading to hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
• Suspect when the individual has:
  • Patient/ventilator dyssynchrony
  • Pulsus paradoxus Pulsus paradoxus A drop in systolic blood pressure of > 10 mm hg during inspiration. Pericardial Effusion and Cardiac Tamponade
  • Hypoxia Hypoxia Sub-optimal oxygen levels in the ambient air of living organisms. Ischemic Cell Damage
  • High plateau Plateau Cardiac Physiology pressure
  • Hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
• Therapeutic interventions Therapeutic interventions Therapeutic interventions alleviate or prevent mortality (reduce case fatality rate) and morbidity of a disease once established, including the management of infectious disease, surgical and radiation treatment, diagnostics to guide therapy, and control of chronic diseases. Points of Intervention depend on the ventilator mode, but include:
  • Lowering PEEP
  • Reducing inspiratory time to allow more expiratory time
  • Reducing respiratory rate Respiratory rate The number of times an organism breathes with the lungs (respiration) per unit time, usually per minute. Pulmonary Examination
  • Disconnecting from the ventilator and pressing down on the chest briefly
  • Hemodynamic support for hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension, if needed

Peptic ulcers

• Common in mechanically ventilated individuals becasue of gastric colonization Colonization Bacteriology
• Can be associated with upper GI bleeding
• Prevention strategies (note: may increase the risk of VAP):
  • Histamine-2 receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors antagonist
  • Proton pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols inhibitors

Ventilator bundles

Commonly used to prevent ventilator-associated complications.

• 30–45 degrees head-of-bed elevation and semirecumbent position: reduces the risk of gastric reflux, aspiration, and VAP
• General infection-control measures (vary by hospital)
• Peptic ulcer Peptic ulcer Peptic ulcer disease (PUD) refers to the full-thickness ulcerations of duodenal or gastric mucosa. The ulcerations form when exposure to acid and digestive enzymes overcomes mucosal defense mechanisms. The most common etiologies include Helicobacter pylori (H. pylori) infection and prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs). Peptic Ulcer Disease prophylaxis Prophylaxis Cephalosporins
• Deep venous thrombosis Venous thrombosis The formation or presence of a blood clot (thrombus) within a vein. Budd-Chiari Syndrome prophylaxis Prophylaxis Cephalosporins
• Daily spontaneous breathing trials
• Spontaneous awakening trials/periodic interruption of sedation
• Maintenance of endotracheal cuff pressure between 20 and 30 cm H₂O
• Frequent subglottic suctions
• Oral care with chlorhexidine gluconate
• Pressure care for wound prevention
• Early mobilization

Weaning and Extubation

Approach to weaning

• Ventilator weaning should be approached based on the following metrics:
  • Has the underlying issue been addressed and improved?
  • Is the individual headed toward hemodynamic stability?
  • Is the O₂ saturation O₂ saturation Gas Exchange consistently improving?
  • Is the individual able to breathe comfortably on minimal ventilator settings?
• If all the above questions are answered affirmatively, it may be time to start a spontaneous breathing trial (SBT).

Spontaneous breathing trial

An SBT consists of minimal ventilator settings that can be used to predict the chances of successful extubation.

• PS ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing with:
  • PS of 8–5 cm H₂O
  • PEEP of 5–0 cm H₂O
  • FiO₂ < 40%
• T-piece trial:
  • Use of an adapter piece that disconnects the individual from the ventilator
  • Allows the endotracheal tube to remain in place
• Should be trialed from 30–120 minutes on these minimal settings
• Sedation should be weaned off or set at minimum prior to SBT (exception is during dexmedetomidine use, as it does not suppress respiratory drive).

When to consider extubation

• Improvement in original cause of respiratory distress or when limited airway Airway ABCDE Assessment protection is required
• No severe tachypnea Tachypnea Increased respiratory rate. Pulmonary Examination or apneic episodes
• SpO₂ > 92%
• Tidal volumes consistently > 325 mL
• No tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children
• Normotensive
• Mental status: capable of following 1-step commands
• Cuff leak (checks for subglottic edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema)
• Minimal secretions
• Plan for the day (consider waiting after procedures or imaging studies).
• Rapid shallow breathing index:
  • Respiratory rate Respiratory rate The number of times an organism breathes with the lungs (respiration) per unit time, usually per minute. Pulmonary Examination/ tidal volume Tidal volume The volume of air inspired or expired during each normal, quiet respiratory cycle. Common abbreviations are tv or V with subscript t. Ventilation: Mechanics of Breathing < 105
  • Most reliable predictor

Post-extubation considerations

When extubating, consider trialing higher levels of supplemental O₂:

• High-flow nasal cannula Nasal Cannula Respiratory Failure in individuals with hypoxic respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure (ARDS)
• BiPAP BiPAP Noninvasive Ventilation in hypertensive individuals with left heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR) or mitral regurgitation Regurgitation Gastroesophageal Reflux Disease (GERD)