Definition and Indications

Definition

Invasive mechanicalventilationVentilationThe 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 advancedairwayAirwayABCDE Assessment management used to deliver oxygen and/or to regulateventilationVentilationThe 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 thetracheaTracheaThe 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:

• OropharyngealintubationIntubationPeritonsillar Abscess
• NasopharyngealintubationIntubationPeritonsillar Abscess
• TracheostomyTracheostomySurgical formation of an opening into the trachea through the neck, or the opening so created.Laryngomalacia and Tracheomalacia

Common indications for IMV

• HypoxemiaHypoxemiaNeonatal Respiratory Distress Syndrome refractory to noninvasive oxygenation (e.g., ARDS)
• HypercapniaHypercapniaA clinical manifestation of abnormal increase in the amount of carbon dioxide in arterial blood.Neonatal Respiratory Distress Syndrome withaltered mental statusAltered Mental StatusSepsis in Children (e.g., chronic obstructivepulmonary diseasePulmonary diseaseDiseases involving the respiratory system.Blastomyces/Blastomycosis (COPDCOPDChronic 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)
• GCSGCSA 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 arrestCardiac arrestCardiac 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 theairwayAirwayABCDE Assessment (e.g.,anaphylaxisAnaphylaxisAn 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 blockadeNeuromuscular BlockadeThe 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 lateralsclerosisSclerosisA pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve.Wilms Tumor (ALSALSAmyotrophic 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 mechanicalventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing is not abenignBenignFibroadenoma intervention:

• Ventilator-induced lung injury (VILI) is common.
• VILI may compound the specific etiology ofrespiratory failureRespiratory failureRespiratory 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

BackgroundventilationVentilationThe 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-cycledventilationVentilationThe 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-cycledventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing
    • Pressure-cycledventilationVentilationThe 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 thelungsLungsLungs 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 ofexpirationExpirationVentilation: Mechanics of Breathing
  • Keeps thealveoliAlveoliSmall 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 volumeTidal volumeThe 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 increaseventilationVentilationThe 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 reduceventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing (↑ PaCO₂)
• Respiratory rateRespiratory rateThe number of times an organism breathes with the lungs (respiration) per unit time, usually per minute.Pulmonary Examination (RRRRRelative 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 increaseventilationVentilationThe 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 reduceventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing (↑ PaCO₂)
• FlowFlowBlood 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 isthe maximumflowFlowBlood 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 settidal volumeTidal volumeThe 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 inventilationVentilationThe 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 inventilationVentilationThe 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)ventilationVentilationThe 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)ventilationVentilationThe 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)ventilationVentilationThe 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 maintenanceventilationVentilationThe 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 PSventilationVentilationThe 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 mandatoryventilationVentilationThe 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-controlventilationVentilationThe 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 ofventilationVentilationThe 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 thework of breathingWork of breathingRespiratory 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-cycledventilationVentilationThe 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 anindependent variableIndependent variableTypes of Variables because it is set by the operator and does not vary between breaths.
  • Inspiratory pressure is adependent variableDependent variableTypes of Variables because it is not set by the operator and varies between breaths.
• Pressure-limitedventilationVentilationThe 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 ofairwayAirwayABCDE Assessment pressure are reached
  • Helps prevent VILI
• Examples:
  • In an individual on AC/VCventilationVentilationThe 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 withRRRRRelative 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 theRRRRRelative 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:
  • RespiratoryalkalemiaAlkalemiaRespiratory Alkalosis in individuals withtachypneaTachypneaIncreased respiratory rate.Pulmonary Examination due toanxietyAnxietyFeelings or emotions of dread, apprehension, and impending disaster but not disabling as with anxiety disorders.Generalized Anxiety Disorder,painPainAn unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons.Pain: Types and Pathways, orairwayAirwayABCDE Assessment irritation
  • Auto-PEEP: dynamichyperinflationHyperinflationImaging of the Lungs and Pleura oflungsLungsLungs 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-controlventilationVentilationThe 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 peakairwayAirwayABCDE Assessment pressures is important (i.e., consider for individuals with previous barotrauma or afterthoracic surgeryThoracic SurgeryBasic 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-limitedventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing
• Inspiratory pressure is anindependent variableIndependent variableTypes of Variables because it is set by the operator and does not vary between breaths.
• Inspiratory volume is adependent variableDependent variableTypes of Variables because it is not set by the operator and varies between breaths:
  • Increasing volume at constant settings reflects improved pulmonarycomplianceComplianceDistensibility 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 pulmonarycomplianceComplianceDistensibility 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 mechanicalventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing/VCventilationVentilationThe 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:
    • Someof 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-cycledventilationVentilationThe 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 anindependent variableIndependent variableTypes of Variables because it is set by the operator and does not vary between breaths.
  • Inspiratory pressure is adependent variableDependent variableTypes of Variables because it is not set by the operator and varies between breaths.
• Pressure-limitedventilationVentilationThe 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 ofairwayAirwayABCDE 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:
  • Reducedminute ventilationMinute ventilationVentilation: Mechanics of Breathing:
    • When tachypneic, the individual exhales during the ventilator inspiratory phase.
    • Causes a rapid rise inairwayAirwayABCDE Assessment pressure beyond the pressure limits set by the operator
    • Will lead toprematurePrematureChildbirth 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 ACventilationVentilationThe 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 andminute ventilationMinute ventilationVentilation: Mechanics of Breathing.
  • SIMV is usually delivered in combination with PSventilationVentilationThe 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-supportventilationVentilationThe 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-limitedventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing
• Operator sets the pressurethat must be reached during each inspiratory phase by the ventilator.
• PSventilationVentilationThe 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 theflowFlowBlood 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 theairwayAirwayABCDE Assessment reaches a level below a minimumthresholdThresholdMinimum voltage necessary to generate an action potential (an all-or-none response)Skeletal Muscle Contraction, the PS is terminated.

Complications

Ventilator-associated pneumoniaVentilator-Associated PneumoniaMultidrug-resistant Organisms and Nosocomial Infections (VAP)

• Requires a minimum of 3 days on mechanicalventilationVentilationThe 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 ofcomorbiditiesComorbiditiesThe 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/ICUICUHospital 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 lavageBronchoalveolar lavageWashing 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 ofsepsisSepsisSystemic 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 aureusStaphylococcus aureusPotentially 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 aeruginosaPseudomonas aeruginosaA 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 pneumoniaeKlebsiella PneumoniaeGram-negative, non-motile, capsulated, gas-producing rods found widely in nature and associated with urinary and respiratory infections in humans.Aminoglycosides
  • EnterobacterEnterobacterMultidrug-resistant Organisms and Nosocomial Infectionsspecies
  • Actinobacterspecies
• Treatment is with antibiotics.

Subtypes of VILI

• Barotrauma:
  • High lung inflation pressure that results in:
    • Hightranspulmonary pressureTranspulmonary pressureVentilation: 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:
    • AlveolarepitheliumEpitheliumThe 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 andinterstitial edemaInterstitial EdemaIncreased Intracranial Pressure (ICP)
• Biotrauma: inflammatory response from mechanical injury viacytokinesCytokinesNon-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

OxygentoxicityToxicityDosage Calculation

• Results from reactive O₂ species that cause:
  • Cellular damage
  • InflammationInflammationInflammation 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 avoidtoxicityToxicityDosage 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 pulmonaryhyperinflationHyperinflationImaging of the Lungs and Pleura
• Also known as “air stacking” or “intrinsic PEEP”
• Most commonly seen inasthmaAsthmaAsthma 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,COPDCOPDChronic 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 lungcomplianceComplianceDistensibility 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 cardiacpreloadPreloadCardiac Mechanics
  • Increased left ventricularafterloadAfterloadAfterload 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
  • Reducedcardiac outputCardiac outputThe 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 tohypotensionHypotensionHypotension 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 paradoxusPulsus paradoxusA drop in systolic blood pressure of > 10 mm hg during inspiration.Pericardial Effusion and Cardiac Tamponade
  • HypoxiaHypoxiaSub-optimal oxygen levels in the ambient air of living organisms.Ischemic Cell Damage
  • HighplateauPlateauCardiac Physiology pressure
  • HypotensionHypotensionHypotension 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 interventionsTherapeutic interventionsTherapeutic 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
  • Reducingrespiratory rateRespiratory rateThe 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 forhypotensionHypotensionHypotension 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 gastriccolonizationColonizationBacteriology
• Can be associated with upper GI bleeding
• Prevention strategies (note: may increase the risk of VAP):
  • Histamine-2receptorReceptorReceptors 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
  • ProtonpumpPumpACES 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 ulcerPeptic ulcerPeptic 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 DiseaseprophylaxisProphylaxisCephalosporins
• Deepvenous thrombosisVenous thrombosisThe formation or presence of a blood clot (thrombus) within a vein.Budd-Chiari SyndromeprophylaxisProphylaxisCephalosporins
• 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 theO₂ saturationO₂ saturationGas 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.

• PSventilationVentilationThe 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 limitedairwayAirwayABCDE Assessment protection is required
• No severetachypneaTachypneaIncreased respiratory rate.Pulmonary Examination or apneic episodes
• SpO₂ > 92%
• Tidal volumes consistently > 325 mL
• NotachycardiaTachycardiaAbnormally 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 subglotticedemaEdemaEdema 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 rateRespiratory rateThe number of times an organism breathes with the lungs (respiration) per unit time, usually per minute.Pulmonary Examination/tidal volumeTidal volumeThe 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-flownasal cannulaNasal CannulaRespiratory Failure in individuals with hypoxicrespiratory failureRespiratory failureRespiratory 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)
• BiPAPBiPAPNoninvasive Ventilation in hypertensive individuals with leftheart failureHeart FailureA 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 mitralregurgitationRegurgitationGastroesophageal Reflux Disease (GERD)

Frequently Asked Questions

What is mechanicalventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing? 

MechanicalventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing is a medical intervention used to support a patient’s natural breathing when they are unable to do so adequately on their own, using a ventilator device.

What isCPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation mode on a ventilator? 

The medical abbreviationCPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation stands for continuous positiveairwayAirwayABCDE Assessment pressure. InCPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation mode, a ventilator delivers a continuous and constant pressure of air (or oxygen-enriched air) to the patient’sairwayAirwayABCDE Assessment. This pressure prevents theairwayAirwayABCDE Assessment from collapsing during exhalation and promotes better oxygen exchange in thelungsLungsLungs 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.CPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation is commonly used in non-invasiveventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing to supportpatientsPatientsIndividuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures.Clinician–Patient Relationship with conditions like obstructivesleep apneaSleep apneaRepeated cessation of breathing for > 10 seconds during sleep and results in sleep interruption, fatigue, and daytime sleepiness.Obstructive Sleep Apnea.

What is AC/VCventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing? 

ACVC stands for assist-control volume controlventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing. In AC/VC mode, the ventilator assists the patient’s breathing by delivering a preset volume of air with each breath, ensuring a consistenttidal volumeTidal volumeThe 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. If the patient initiates a breath, the ventilator will assist by delivering the settidal volumeTidal volumeThe 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. If the patient does not initiate a breath within a certain time frame, the ventilator will deliver breaths at a preset rate to maintainventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing. AC/VC is commonly used in the intensive care unit (ICUICUHospital units providing continuous surveillance and care to acutely ill patients.West Nile Virus) forpatientsPatientsIndividuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures.Clinician–Patient Relationship with various respiratory conditions.

What is PS/CPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation? 

PS/CPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation refers to pressure support/continuous positiveairwayAirwayABCDE Assessment pressure. It is a combined mode ofventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing that provides bothCPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation and pressure support.CPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation maintains a continuous positiveairwayAirwayABCDE Assessment pressure to keep the airways open, while pressure support is an additional level of pressure delivered duringinspirationInspirationVentilation: Mechanics of Breathing to assist the patient’s effort to breathe. PS/CPAPCPAPA technique of respiratory therapy, in either spontaneously breathing or mechanically ventilated patients, in which airway pressure is maintained above atmospheric pressure throughout the respiratory cycle by pressurization of the ventilatory circuit.Noninvasive Ventilation is often used when a patient needs both maintenance ofairwayAirwayABCDE Assessment patency and pressure support to assist with respiratory effort, such as inpatientsPatientsIndividuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures.Clinician–Patient Relationship with neuromuscular diseases or during weaning from mechanicalventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing.

What is VCVventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing? 

VCV stands for volume-controlledventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing. In VCV (also known as AC/VC) mode, the ventilator controls and delivers a fixed volume of gas, and the patient’srespiratory rateRespiratory rateThe number of times an organism breathes with the lungs (respiration) per unit time, usually per minute.Pulmonary Examination and effort determine the frequency and timing of breaths. This mode is particularly useful forpatientsPatientsIndividuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures.Clinician–Patient Relationship with specifictidal volumeTidal volumeThe 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 requirements, such as those withacute respiratory distress syndromeAcute Respiratory Distress SyndromeAcute respiratory distress syndrome is characterized by the sudden onset of hypoxemia and bilateral pulmonary edema without cardiac failure. Sepsis is the most common cause of ARDS. The underlying mechanism and histologic correlate is diffuse alveolar damage (DAD).Acute Respiratory Distress Syndrome (ARDS) (ARDS) orpatientsPatientsIndividuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures.Clinician–Patient Relationship undergoing surgery. VCV allows precise control over the deliveredtidal volumeTidal volumeThe 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, helping to maintain consistentventilationVentilationThe total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Ventilation: Mechanics of Breathing.

References

1. ABA Keywords. OpenAnesthesia.https://www.openanesthesia.org/modes_of_mechanical_ventilation/
2. Stephen, C., Gillespie, S., Roberts, D., Magdy, Y. (1997). Effect of Inspiratory Flow Rate on Respiratory Rate in Intubated Ventilated Patients. American Journal of Respiratory and Critical Care Medicine, 156, 304–308.https://doi.org/10.1164/ajrccm.156.1.9607031
3. Nickson, C. (2020). Spontaneous Breathing Trial. Life in the Fastlane, LITFL.https://litfl.com/spontaneous-breathing-trial/
4. Hyzy, R. C., & Taha, A. R. (2024). Diagnosis, management, and prevention of pulmonary barotrauma during invasive mechanical ventilation in adults.UpToDate. Retrieved June 13, 2025, fromhttps://www.uptodate.com/contents/diagnosis-management-and-prevention-of-pulmonary-barotrauma-during-invasive-mechanical-ventilation-in-adults