Modes., Clincal Application to Respiratory Disease

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Indications ., Basics and Modes of mechanical ventilation with clinical applications to respiratory diseases Dr. Hany Hussein :

Indications ., Basics and Modes of mechanical ventilation with clinical applications to respiratory diseases Dr. Hany Hussein

Indications for Mechanical ventilation:

Indications for Mechanical ventilation

Indications for Mechanical ventilation :

Indications for Mechanical ventilation Acute lung injury (including ARDS , or chest trauma, broken ribs) Apnea , cardiac or respiratory arrest, including cases from intoxication Acute respiratory failure whatever the causes ( PaCO2↑ 50 mmHg and pH ↓ 7.25) which may be due to paralysis of the diaphragm due to Guillain-Barré syndrome , Myasthenia Gravis , spinal cord injury, or the effect of anaesthetic and muscle relaxant drugs Impending respiratory failure PaCO2 rises & pH falls inspite of adequate ttt . Refractory Hypoxemia with PaO2 ↓ 60 mm Hg with FiO2 ↑ 50%

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Marked increased work of breathing with impending respiratory Ms Fatigue as evidenced by significant tachypnea , retractions, & other physical signs of respiratory distress, sever metabolic acidosis with poor response to ttt . Clinical signs of sever respiratory failure Unconsciousness Gasping Rapid shallow breathing Marked abdominal paradox Hypotension including sepsis , shock , congestive heart failure Fixation of flail chest , Neurological disease or head trauma

Disease – specific indications for common ICU admission and MV :

Disease – specific indications for common ICU admission and MV Asthma Difficulty talking because of breathlessness Altered level of consciousness FEV1 and / or PEFR ↓ 40% predicted Pulsus paradoxus ↑ 18 mmHg Pneumothorax or pneumomediastinum PaO2 ↓ 65 mmHg on FiO2 40% PaCO2↑ 40 mmHg

The generally accepted indications for mechanical ventilation in Asthma :

The generally accepted indications for mechanical ventilation in Asthma PaCO2 ↑50 mmHg & rising Pa O2↓ 50 mmHg & falling pH of 7.3 or less & falling Intolerable respiratory distress (paradoxical thoraco - abdominal movement) Exhaustion due to lack of response to ttt (especially if associated with systemic hypotension) Cardio- respiratory arrest. Previous history of mechanical ventilation in ICU

Pneumonia :

Pneumonia Confusion Presence of septic shock OR need for vasopressor to support BP. RR↑30 cycle/m. 30 < WBC < 4 x 109 /L or Platelet↓ 80.000 x 109 /L Presence of acute renal failure [Urine output ↓ 30cc/h. ] BUN ↑ 20 mg / dL PaO2 ↓ 60 mmHg (room air) Sever lung injury defined by PaO2/FiO2 ↓ 250 Chest radiography showing either 50 % ↑ in infiltrates over 48h or bilateral or multilobar involvement. If pt. has 2 of the following 3 ICU add. Is necessary: S.BP ↓ 90 mmHg. PaO2/FiO2 ↓ 250 Multilobar pneumonia.


AECOPD Indication of ICU admission sever dyspnea that responds inadequately to initial emergency therapy. Changes in mental status ( confusion., lethargy and coma). Persistent or worsening hypoxemia ( pao2 < 40mmHG ) and / or sever worsening hypercapnia (paco2 > 60mmHG) despite supplemental oxygen and non invasive ventilation. Need for invasive mechanical ventilation. Hemodynamic instability_ need for vasopressors

Indication of NIV :

Indication of NIV Moderate to sever dyspnea with use of accessory muscles of respiration and paradoxical abdominal motion Moderate to sever acidosis ( pH <7.3) and /or hypercapnia (paco2 > 45mmHG) . RR > 25 breath per minute.

Contraindication for NIV:

Contraindication for NIV Respiratory arrest Cardiovascular instability (hypotension., arrythmias ., myocardial infarction High aspiration risk Copious secretions Recent facial or gastrointestinal surgery Craniofacial trauma Fixed nasopharyngeal abnormalities., burns., extreme obesity

Indication for invasive mechanical ventilation:

Indication for invasive mechanical ventilation Respiratory arrest Unable to tolerate NIV or NIV failure RR > 35 breath per minute Life threatening hypoxemia Sever dyspnea with use of accessory muscles and paradoxical abdominal motion Sever acidosis ( pH < 7.25) and /or hypercapnia (paco2 >60 mmHG ) Somnolence., impaired mental status. Cardiovascular complications(hypotension, shock) Other complications(metabolic abnormalities, sepsis, pneumonia, pulmonary embolism., barotraumas., massive pleural effusion)

Principles of Mechanical Ventilation :

Principles of Mechanical Ventilation

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Origins of mechanical ventilation Negative-pressure ventilators (“iron lungs”) Non-invasive ventilation first used in Boston Children’s Hospital in 1928 Used extensively during polio outbreaks in 1940s – 1950s Positive-pressure ventilators Invasive ventilation first used at Massachusetts General Hospital in 1955 Now the modern standard of mechanical ventilation The era of intensive care medicine began with positive-pressure ventilation The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output. Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

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Patients are often (ideally) intubated before they reach the point of respiratory failure. Respiratory distress can be due to inadequate ventilation, oxygenation or a combination them. The process can be either intrinsic to the lungs (pneumonia, for example) or to the chest wall (“pump failure”, as in muscular dystrophies).

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Principles (1): Ventilation The goal of ventilation is to facilitate CO 2 release and maintain normal P a CO 2 Minute ventilation (V E ) Total amount of gas exhaled/min. VE = (RR) x (TV) VE comprised of 2 factors VA = alveolar ventilation VD = dead space ventilation VD/VT = 0.33 VE regulated by brain stem, responding to pH and PaCO2 Ventilation in context of ICU Increased CO2 production fever, sepsis, injury, overfeeding Increased VD atelectasis , lung injury, ARDS, pulmonary embolism Adjustments: RR and TV V/Q Matching. Zone 1 demonstrates dead-space ventilation (ventilation without perfusion). Zone 2 demonstrates normal perfusion. Zone 3 demonstrates shunting (perfusion without ventilation).

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Vent settings to improve ventilation Respiratory rate Normal to set 12-20 (mean 14) Max RR at 35 breaths/min Efficiency of ventilation decreases with increasing RR Decreased time for alveolar emptying Tv Goal of 10 – 12 ml/kg Risk of volutrauma Other means to decrease PaCO2 Reduce muscular activity/seizures Minimizing exogenous carb load Controlling hypermetabolic states Permissive hypercapnea Preferable to dangerously high RR and TV, as long as pH > 7.15 RR and T V are adjusted to maintain V E and P a CO 2 I:E ratio (IRV ) (n 1:2) Increasing inspiration time will increase TV, but may lead to auto-PEEP . T- insp N 1.7 sec PIP Elevated PIP suggests need for switch from volume-cycled to pressure-cycled mode Maintained at <45cm H2O to minimize barotrauma Plateau pressures Pressure measured at the end of inspiratory phase Maintained at <30-35cm H2O to minimize barotrauma

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Principles (2): Oxygenation The primary goal of oxygenation is to maximize O 2 delivery to blood (P a O 2 ) Alveolar-arterial O 2 gradient (P A O 2 – P a O 2 ) Equilibrium between oxygen in blood and oxygen in alveoli A-a gradient measures efficiency of oxygenation P a O 2 partially depends on ventilation but more on V/Q matching Oxygenation in context of ICU V/Q mismatching Airway pressure, pulmonary parenchymal disease, small-airway disease Adjustments: FiO2 and PEEP V/Q Matching. Zone 1 demonstrates dead-space ventilation (ventilation without perfusion). Zone 2 demonstrates normal perfusion. Zone 3 demonstrates shunting (perfusion without ventilation).

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Vent settings to improve oxygenation FIO2 Simplest maneuver to quickly increase PaO2 start by 100% then decrease. Long-term toxicity start at >60 % for more than 24% Caused by Free radical damage to the tissues. Inadequate oxygenation despite 100% FiO2 usually due to pulmonary shunting Collapse – Atelectasis Pus-filled alveoli – Pneumonia Water/Protein – ARDS Water – CHF Blood - Hemorrhage PEEP and FiO 2 are adjusted to improve oxygenation

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Vent settings to improve oxygenation PEEP Increases FRC Prevents progressive atelectasis and intrapulmonary shunting Prevents repetitive opening/closing (injury) Recruits collapsed alveoli and improves V/Q matching Resolves intrapulmonary shunting Improves compliance Enables maintenance of adequate PaO2 at a safe FiO2 level Disadvantages Increases intrathoracic pressure so Rupture: PTX. May lead to ARDS PEEP and FiO 2 are adjusted in tandem

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Three types of Positive Pressure Ventilators : Volume Cycled ventilator : used in acute problems ( ie , spinal cord injury or COPD. Inspiration occurs until a preset volume of air is delivered. Pressure Cycled Ventilator : Used in home with long term patients. Inspiration ends when preset pressure is reached. 20 – 50 cm of water pressure. Time Cycled Ventilator : How many breaths/minute used with kids and infants. Inspiration ends with a preset time of interval.

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Volume-cycled modes Control Assist Assist/Control Intermittent Mandatory Ventilation (IMV) Synchronous Intermittent Mandatory Ventilation (SIMV) Pressure-cycled modes Pressure Support Ventilation (PSV) Pressure Control Ventilation (PCV) CPAP BiPAP

PowerPoint Presentation:

Breath delivery Trigger The trigger is what causes a breath to be delivered by a mechanical ventilator. Or how does the ventilator know when to give the breath (Trigger) Patient effort: as change in the pressure or the flow in the circuit(negative deflation) Elapsed time: This occurs when a certain amount of time has elapsed (e.g., 5 seconds if the rate is 12 [60 sec/12 b/m = 5 sec]) Cycle The cycle is what causes the breath to transition from the inspiratory phase to the exhalation phase. Breaths may be cycled by a mechanical ventilator when perset time has been reached, or when a preset flow or percentage of the maximum flow. Limit Limit is how the breath is controlled. Breaths may be limited to a set maximum circuit pressure or a set maximum flow. Breath exhalation Exhalation in mechanical ventilation is almost always completely passive

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Assist/Control Mode Control Mode Pt receives a set number of breaths and cannot breathe between ventilator breaths.variable pressure and fixed perset Tv Studies have demonstrated that suppression of spontaneous breathing and complete dependence on CMV lead to rapid resp. Ms atrophy. Assist Mode Pt initiates all breaths, but ventilator cycles in at initiation to give a preset tidal volume Pt controls rate but always receives a full machine breath Assist/Control Mode Assist mode unless pt’s respiratory rate falls below preset value Ventilator then switches to control mode Rapidly breathing pts can over ventilate and induce severe respiratory alkalosis and hyperinflation (auto-PEEP) Ventilator delivers a fixed volume

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IMV and SIMV Volume-cycled modes typically augmented with Pressure Support IMV Pt receives a set number of ventilator breaths Different from Control: pt can initiate own (spontaneous) breaths Different from Assist: spontaneous breaths are not supported by machine with fixed TV Ventilator always delivers breath, even if pt exhaling ventilator dys -synchrony lung over distention IMV may potentiate resp. Ms fatigue. Respiratory center output may be insensitive for breath-to-breath changes in mechanical load. SIMV Most commonly used mode Spontaneous breaths and mandatory breaths If pt has respiratory drive, the mandatory breaths are synchronized with the pt’s inspiratory effort

Pressure Control Ventilation (PCV):

Pressure Control Ventilation (PCV) The practitioner sets the maximal pressure given by the ventilator (preset Pressure), frequency and time the pressure is fixed ( inspiratory time ). Parameters Triggered by time Limited by pressure Affects inspiration only Disadvantages Requires frequent adjustments to maintain adequate VE

Pressure Support Ventilation (PSV):

Pressure Support Ventilation (PSV) The ventilator delivers a predetermined level of positive pressure each time the patient initiates a breath. A plateau pressure is maintained until inspiratory flow rate decreases to a specified level (e.g. 25% of the peak flow value). Parameters Triggered by pt’s own breath Limited by pressure Affects inspiration only Uses Complement volume-cycled modes (i.e., SIMV) Does not augment TV but overcomes resistance created by ventilator tubing PSV alone Used alone for recovering intubated pts who are not quite ready for extubation Augments inflation volumes during spontaneous breaths BiPAP (CPAP plus PS)

Positive End Expiratory Pressure (PEEP):

Positive End Expiratory Pressure (PEEP ) PEEP is the application of positive pressure to change baseline variable during CMV, SIMV, IMV and PCV. PEEP is primarily used to improve oxygenation in patients with severe hypoxemia . Advantages Improves oxygenation by increasing FRC Decreases physiological shunting Parameters CPAP – PEEP set at 5-10 cm H2O BiPAP – CPAP with Pressure Support (5-20 cm H2O) Shown to reduce need for intubation and mortality in COPD pt Disadvantages Increased incidence of pulmonary brotrauma Potential decrease in venous return Increased work of breathing Increased intracranial pressure

Continuous Positive Airway pressure (CPAP):

Continuous Positive Airway pressure (CPAP) Continuous Positive Airway Pressure is simply a spontaneous breath mode, with the baseline pressure elevated above zero. Advantages Improves oxygenation by increasing FRC Decreases physiological shunting Improved oxygenation will allow the FIO2 to be lowered Increased lung compliance Disadvantages Increased incidence of pulmonary brotrauma Potential decrease in venous return Increased work of breathing Increased intracranial pressure

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Alternative Modes I:E inverse ratio ventilation (IRV) ARDS and severe hypoxemia Prolonged inspiratory time (3:1) leads to better gas distribution with lower PIP Elevated pressure improves alveolar recruitment No statistical advantage over PEEP, and does not prevent repetitive collapse and reinflation Prone positioning Addresses dependent atelectasis Improved recruitment and FRC, relief of diaphragmatic pressure from abdominal viscera, improved drainage of secretions Logistically difficult No mortality benefit demonstrated High-Frequency Oscillatory Ventilation (HFOV) High-frequency, low amplitude ventilation. Avoids repetitive alveolar open and closing that occur with low airway pressures Avoids over distension that occurs at high airway pressures Well tolerated, consistent improvements in oxygenation, but unclear mortality benefits Disadvantages Potential hemodynamic compromise Pneumothorax Neuromuscular blocking agents

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Choosing amongst ventilator modes Assist-control mode minimizes patient effort by providing full mechanical support with every breath. This is often the initial mode chosen for adults because it provides the greatest degree of support. In patients with less severe respiratory failure, other modes such as SIMV may be appropriate. Assist-control mode should not be used in those patients with a potential for respiratory alkalosis (usually occurs in patients with end-stage liver disease, hyperventilatory sepsis, and head trauma) . Respiratory alkalosis will be evident from the initial arterial blood gas obtained, and the mode of ventilation can then be changed if so desired. For fear of Auto-PEEP.

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Positive End Expiratory Pressure may or may not be employed to prevent atelectasis in adult patients. It is almost always used for pediatric and neonatal patients due to their increased tendency for atelectasis . High frequency oscillation is used most frequently in neonates, but is also used as an always alternative mode in adults with severe ARDS and Pressure regulated volume control is another option

Ventilator setting and strategies for respiratory diseases:

Ventilator setting and strategies for respiratory diseases Comments PEEP Target PAo2 SaO2 Target pH- PaCO2 Tv Mode OBJECTIVES Clinical setting NIV Tried at first 0 – 5 Normal - Permissive hypercapnia and acidemia - Avoid resp alk 5-8 ml /kg V / Pr - Unload ventilatory muscles - Prevent further hyperinflation - Maintain acid base balance appropriate for the patient COPD This lung protective ventilatory strategy requires appropriate sedation 8-10 At least sufficient to maintain PO2 target without ↓ ing cardiac out put or compliance Mild to moderate PaO2 50-60% SpO2 80-90% Permissive hypercapnia and acidemia 5-8 ml /kg V / Pr - Support oxygenation - Preserve circulatory function - Avoid worsening lung injury - Avoid clinical barotraumas ARDS

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Comments PEEP Target PAo2 SaO2 Target pH- PaCO2 Tv Mode OBJECTIVES Clinical setting This settings are appropriate for the majority of patients who require mech vent. 0 – 5 Normal Normal 10-12 ml /kg V - Prevent atelectasis - Maintain normal acid base balance - Avoid hypoxemia - Avoid oxygen toxicity Drug overdose and Post-operative Value of acute respiratory alkalosis disputed except for emergent short term reduction of very high intracranial tension Avoid Normal Normal Or mild respiratory alkalosis (PaCO25-30) 10-12 ml /kg V - Avoid compromising cerebral perfusion pressure - decrease intracranial pressure Head trauma Such patients usually prefer high inspiratory flow 0-5 unless required for oxygenation Normal (avoid mild hypoxemia) Normal Or mild respiratory Alkalosis (PaCO25-30) 12- 16 ml/kg V - Avoid atelectasis - minimize dyspnea Acute NMD Ventilatory support usually unnecessary unless ALI present 5 or as needed for support of oxygenation Normal Normal 10-12 ml /kg unless ALI V Maintain adequate lung inflation and gas exchange Flail chest

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Follow up of mechanically ventilated patients and protocol of weaning in another set in shaa allah .



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