| Give history of mechanical ventilation. | Negative pressure ventilator (iron lung) non-invasive used first in boston 1928, imp for polio outbreak in 1950s
Positive pressure ventilator: first in Massachussets 1955, modern standard of mechanical ventilation |
| How is the physiology of ventilation? | Goal is facilitating CO2 release with normal PaO2
Delivery of breath occurs with every change in transpulmonary pressure (mouth: pleura gradient)
Spontaneous breathing chest wall expansion, diaphragm descent and muscle contraction create negative pressure within pleural space, which allows gas flow through conducting airways to respiratory units.
So, negative pressure ventilators (NPV) create subatmospheric pressure around the chest to expand thoracic cavity.
They lack diaphragm movement so alveolar ventilation is not as efficient
Positive pressure ventilators (PPV) favor flow of gases down conducting airways overcoming pleural pressure |
| How is the physiology of expiration? | Passive, elastic recoil of lungs and chest wall.
PEEP maintains alveolar patency in presence of destabilizing forces like edema, loss of surfactant.
It reverses atelectasis, improving oxygenation by improving V/Q matching |
| What are the indications of mechanical ventilation? | Hypoxemic failure (pneumonia/ hemorrhage/ shunt...)
Hypercarbic failure (decreased minute ventilation - neuromuscular diseases, increased work of breathing - COPD, asthma to get air moving to lungs) |
| How do we establish the airway? | Cuffed endotracheal tube (intubation) or tracheostomy tube inserted in trachea allows PPV
Intubation needs sedation, analgesia, muscle paralysis (opiates and benzo can cause hemodynamic instability so contraindicated in shock, depolarizing agents contraindicated in kidney disease as it raises K+, morphine can cause bronchospasms by histamine release) |
| How is the PPV model? | Settings of breath trigger, cycle, limit and target are changed.
Target: Volume or pressure regulated.
Breath can be triggered by inspiratory effort or time-based cycle (way of termination of breath - by limiting factors like pressure limits...) |
| What is the difference between mandatory and spontaneous ventilators? | Mandatory: guaranteed min number of breathes per min with predetermined volume/ pressure (cannot breathe less)
Spontaneous depends on pt effort intiation and duration, and ventilator only helps with pressure |
| How is ventilator breath triggerring? | Either by flow or pressure
Flow sensors more sensitive to pt efforts than pressure ones, more dead space will lead to less sensation of the ventilator causing asynchrony |
| How are volume-targeted breaths vs pressure-targeted? | Volume-targeted: choose tidal volume, breath enters by flow rate and pattern of delivery, greater flow -> shorter Ti, shorter inspiration:expiration, greater peak inspiratory pressure. (but should avoid hyperinflation from too short expiration)
Depends on lung compliance (monitor hypocapnia (alkalosis), too high TV (COPD) risk of breath-stacking decreasing ventilation)
Pressure-Targeted: doesn't guarantee specific Vt, inspiratory pressure, Ti and lung compliance determine its effect, can be mandatory or spontaneous (Ti) whereas Pi is set by clinician |
| What is difference between ventilation and oxygentation? | Acceptable oxygenation and ventilation are interrelated, easiest solution of hypoxemia is increase FiO2 (inspired O2 fraction)
PEEP at low levels can splint open alveoli recruiting them and retaining them to decrease collapse and increase exchange |
| What are the three main types of ventilators? | AC (assist control/ AKA CMV)
SIMV (synchronized intermittent mandatory ventilation)
PSV (pressure support ventilation) |
| Compare AC, SIMV and PSV: trigger, volume/pressure, advatanges and disadvantages. | . |
| How does AC and SIMV differ in terms of mandatory breaths? | AC: minimum frequency mandatory and pt trigger are also mandatory
SIMV: mandatory frequency, one by pt are spontaneous but not mandatory (supported only by pressure) |
| What is pressure support ventilation PSV? | Requires pt effort for inhalation in all breaths, termination as well is determined by the pt
PEEP applied as CPAP since airway always positive, higher pressure = increased pressure
Higher PEEP = hypotension (obstructive shock on right atrium - recommended for ARDS)
Use 5-25 cm H2O as pressure support
Most comfortable for alert pt |
| What is PCV? | Controlled mode, used to be for ARDS, allowed extended inspiratory phases in excess of expiratory phases/ PC-IRV
clinician sets Pi and Ti -> Vt variable
MAP increases so alveolar recruitment, no improved survival or short duration MV
needed for heavy sedation |
| What is non-invasive ventilation (NIV)? | delivery through full-face/ nasal mask, mainly pressure targeted (but maybe volume targeted in ICU
Clinician sets inspiratory and expiratory pressures, doesn't guarantee constant Vt
Used for acute hypercapnic failure in COPD, cardiogenic pulmonary edema, fever and pulmonary infiltrates in immunocompromised, post-extubation respiratory distress is possible
Poor indications: imminent intubation with respiratory distress, hemodynamic instability, poor metal status, facual trauma, inadquate clearance of respiratory secretions, profound hypoxemia
Should have monitoring (setting up, ABG...) |
| How do we monitor mechanical ventilation? | Modern ones are easy (show numbers - pressure/ volume/ flow...)
Set acceptable parameters limits: Low ventilation ->ventilator disconnection, apnea alarm, high airway pressure alarm [ PIP seen for resistance, it increases in case of parenchymal disease, pneumothorax, obesity, increased abdominal pressure]
Lung mechanics (measure Pplat (hold breath at end of expiration - same auto-PEEP)
Ventilatory Synchrony (ineffective triggering arrow, common cause is auto-PEEP , airwflow obstruction (bronchospasm) and high ventilation) |
| What are complications of mechanical ventilation? | Oxygen toxicity, barotrauma (air leak from alveolar rupture - least resistance bronchovascular bundles/hila/mediastinum ->causes subcutaneous emphysema , eventually causes pneumothorax), hyperinflation (PEEPi - pneumothorax or diaphragm flattening, hypotension), VALI (volutrauma- inflammation), tracheomalacia, trauma of vocal cords, lips, teeth, oral.., unplanned extubation, bronchial intubation, esophageal intubation, tracheostomy bleed, GI bleed (stress ulceration/ gastritis) |
| How is weaning of mechanical ventilation done? | Progressive reduction of support, WOB done by pt increases gradually acc to his ability to breath independently ->ET tube removed finally
Either progressive reduction of PS in PSV mode, or decreasing mandatory breaths in SIMV, or increasing duration of spontaneous breath in AC
Done after we see good oxygenation/ airway protection/ ventilation/ toileting and no obstruction or failure anymore |
| When do we perform tracheastomy? | For long term management of airway in ventilated people, more stable and confortable and needs less sedation, percutaneous dilatational tracheostomy is very usefull with least complications |
