Mechanical Ventilation Flashcards
What are the main indications for mechanical ventilation?
- Airway Protection and Patency
- Impending or existing respiratory failure
- Minimizing oxygen consumption & optimizing oxygen delivery
- Neurological indications (unresponsiveness, secondary brain injury prevention)
- Severe temperature derangement (hypothermia, hyperthermia)
Each indication plays a crucial role in determining the necessity for mechanical ventilation.
Which respiratory conditions commonly require intubation?
- COPD (Chronic Obstructive Pulmonary Disease)
- Asthma (Status Asthmaticus) – Severe exacerbations
- Anaphylaxis – Airway obstruction
- Burns – Airway compromise due to inhalation injury
- Saddle Pulmonary Embolism (PE) – Large PE obstructing blood flow
- Pneumonia – Severe cases requiring ventilatory support
These conditions often lead to compromised airway or severe respiratory distress.
Why do septic and burn patients have high oxygen consumption?
- Septic patients: Increased metabolic demand due to systemic inflammation
- Burn patients: Increased metabolic rate and oxygen needs for tissue repair
Understanding the metabolic demands of these patients is essential for appropriate ventilation management.
How does mechanical ventilation prevent secondary brain injury?
- Ensures adequate oxygenation and ventilation
- Prevents hypoxia and hypercapnia, which can worsen brain damage
Adequate ventilation is critical in preventing further neurological damage.
What are the primary aims of Positive Pressure Ventilation (PPV)?
- Support respiration
- Reduce work of breathing (WOB)
- Restore acid-base balance
- Increase oxygen delivery to organs
- Prevent ventilator-induced lung injury
These aims guide the use of PPV in clinical settings.
How does PPV move air into the lungs?
By delivering positive pressure via a mask or endotracheal tube (ETT)
This method creates a pressure gradient that facilitates air movement into the lungs.
Define Baseline Pressure in mechanical ventilation.
Normally 0 cmH₂O (atmospheric pressure)
Baseline pressure is crucial for understanding other pressure measurements.
What is Peak Inspiratory Pressure (PIP)?
Maximum airway pressure at the end of inspiration
PIP is an important parameter to monitor for assessing ventilatory function.
What does Positive End-Expiratory Pressure (PEEP) refer to?
Pressure remaining in lungs at the end of expiration
PEEP helps maintain alveolar stability and prevents collapse.
What is Plateau Pressure?
Pressure within the alveoli at the end of inspiration, before expiration begins
Plateau pressure is indicative of lung compliance.
What are the three types of breaths in mechanical ventilation?
- Spontaneous: Patient-initiated, with own tidal volume and duration
- Mandatory: Ventilator controls breath timing or volume
- Assisted: Patient starts the breath, but ventilator helps complete it
Understanding these types is essential for tailoring ventilation strategies.
What are the four main control variables for mechanical ventilation?
- Volume-Controlled: Fixed tidal volume, variable pressure
- Pressure-Controlled: Fixed pressure, variable tidal volume
- Flow-Controlled: Inspiratory flow rate is set
- Time-Controlled: Inspiratory time is fixed
These control variables help determine how ventilation is delivered.
What determines when inspiration ends in different cycling mechanisms?
- Time-Cycled: When set inspiratory time is reached
- Flow-Cycled: When flow rate drops to a set level
- Volume-Cycled: When set tidal volume is delivered
- Pressure-Cycled: When set pressure is reached
Each cycling mechanism has distinct applications and effects on ventilation.
Describe Continuous Mandatory Ventilation (CMV).
All breaths are mandatory; no patient effort required
CMV is often used for unstable patients requiring full ventilatory support.
What is Volume Assist/Control (A/C) Mode?
Pre-set breaths per minute at a set tidal volume; patient can trigger additional breaths at the same volume
This mode allows for patient-initiated breaths while ensuring a minimum level of ventilation.
What is Synchronized Intermittent Mandatory Ventilation (SIMV)?
Pre-set mandatory breaths with spontaneous patient efforts; helps weaning from ventilation
SIMV is beneficial for preserving respiratory muscle strength.
What is the ideal starting fraction of inspired oxygen (FiO₂) in mechanical ventilation?
Start at 0.7 - 1.0 FiO₂, then reduce based on PaO₂; aim for FiO₂ <0.6 to prevent oxygen toxicity
Monitoring FiO₂ is essential to avoid complications related to oxygen toxicity.
How is tidal volume (VT) set in ventilated patients?
5-8 mL/kg of ideal body weight; prevents alveolar overdistension
Proper tidal volume settings are crucial for lung protection.
What is the role of PEEP in mechanical ventilation?
Prevents alveolar collapse and improves oxygenation; typically starts at 5 cmH₂O, increased if needed
PEEP is a vital setting for optimizing oxygenation.
What does a high-pressure alarm on a ventilator indicate?
Increased airway resistance or obstruction
Identifying the cause of high-pressure alarms is critical for patient safety.
How is minute ventilation (MV) calculated?
Minute ventilation (L/min) = Tidal Volume (VT) × Respiratory Rate (RR)
This calculation is essential for assessing overall ventilation status.
How do you adjust ventilation settings based on blood gases?
- pH < 7.35 (Acidosis) → Increase RR or tidal volume to blow off CO₂
- pH > 7.45 (Alkalosis) → Reduce RR to retain CO₂
- PaO₂ < 80 mmHg → Increase FiO₂ or PEEP
- PaO₂ > 100 mmHg → Reduce FiO₂ to prevent oxygen toxicity
Adjusting settings based on blood gas analysis is crucial for effective ventilation management.
What are the main complications of mechanical ventilation?
- Airway Damage → High cuff pressures, intubation trauma
- Barotrauma → Excessive pressure, leading to pneumothorax
- Ventilator-Induced Lung Injury (VILI) → Overdistension of alveoli
- Cardiovascular Effects → Decreased cardiac output from increased intrathoracic pressure
- Neurological Effects → Increased ICP, decreased cerebral perfusion pressure (CPP)
- Renal & GI Effects → Decreased perfusion, stress ulcers
Awareness of these complications is important for managing ventilated patients.
What are the primary goals when adjusting ventilator settings?
- Maintain oxygenation (SpO₂ 92-95%)
- Prevent hypercapnia or hypocapnia
- Reduce work of breathing (WOB)
- Avoid ventilator-induced lung injury (VILI)
These goals guide clinical decisions regarding ventilator management.
What are the key ventilator settings that must be adjusted for each patient?
Fraction of Inspired Oxygen (FiO₂)
Tidal Volume (VT)
Respiratory Rate (RR)
Positive End-Expiratory Pressure (PEEP)
Sensitivity (Trigger Settings)
Inspiratory Time & I:E Ratio
Flow Rate
Pressure Support
Peak Inspiratory Pressure (PIP)
What is the initial FiO₂ setting for a ventilated patient?
Typically starts at 100% (1.0) and is weaned down based on oxygenation.
Aim: Maintain SpO₂ between 92-95% to reduce oxygen toxicity risk.
When should FiO₂ be reduced?
When PaO₂ > 100 mmHg or SpO₂ > 95% on high FiO₂.
Goal: FiO₂ < 0.6 to minimize oxygen toxicity.
How is tidal volume (VT) set in mechanical ventilation?
5-8 mL/kg of ideal body weight (IBW).
Prevents alveolar overdistension and volutrauma.
What factors influence tidal volume selection?
Lung compliance (lower compliance → smaller VT).
Lung pathology (ARDS patients require lower VT to prevent lung injury).
Patient height (not actual weight) determines IBW.
What is the normal respiratory rate (RR) setting for a ventilated patient?
Typically set between 10-16 breaths per minute.
Adjusted based on PaCO₂ and pH levels.
How does RR adjustment affect blood gases?
Increasing RR → Decreases CO₂ (Corrects acidosis).
Decreasing RR → Increases CO₂ (Corrects alkalosis).
What is the function of PEEP in mechanical ventilation?
Prevents alveolar collapse at the end of expiration.
Improves oxygenation by keeping alveoli open.
What is the typical starting PEEP value?
5 cmH₂O, adjusted up to 10 cmH₂O if needed.
When should PEEP be increased?
When PaO₂ is low (<80 mmHg) despite high FiO₂.
In conditions like ARDS or severe atelectasis.
What are the risks of excessive PEEP?
Barotrauma (pneumothorax).
Reduced venous return → Hypotension.
Increased intrathoracic pressure → Decreased cardiac output.
What is the standard inspiratory time setting?
1 second (range: 0.8 - 1.2 sec)
What is the typical I:E ratio in mechanical ventilation?
1:2 (Inspiration is 33% of the respiratory cycle, expiration is 66%).
How should the I:E ratio be adjusted for obstructive lung diseases (COPD, asthma)?
Increase expiratory time (e.g., I:E ratio 1:3 or 1:4) to prevent air trapping
What is the role of sensitivity (trigger settings) in ventilator settings?
Determines how easily the patient can trigger a breath.
Prevents delayed patient-initiated breaths.
What are the two types of trigger settings?
Flow Trigger: 1-3 L/min below baseline (less WOB required).
Pressure Trigger: -1 to -3 cmH₂O (patient effort required to start breath).
What happens if the trigger setting is too sensitive?
The ventilator may auto-trigger breaths (not patient-initiated).
What happens if the trigger setting is not sensitive enough?
The patient may struggle to initiate breaths.
What is the purpose of flow rate in mechanical ventilation?
Determines how quickly tidal volume is delivered during inspiration.
What is the normal flow rate setting?
40 - 60 L/min.
How does changing the inspiratory time affect flow rate?
Decreasing inspiratory time → Increases flow rate.
Increasing inspiratory time → Decreases flow rate.
What is the purpose of pressure support in ventilation?
Assists spontaneous breaths by reducing work of breathing (WOB).
Used in SIMV mode.
What is the typical pressure support setting?
5-10 cmH₂O, adjusted as needed.
What is Peak Inspiratory Pressure (PIP)?
Maximum airway pressure reached during inhalation.
What is the normal PIP range?
20-30 cmH₂O.
What conditions cause high PIP?
Increased airway resistance (bronchospasm, secretions, biting the tube).
Decreased lung compliance (ARDS, pulmonary edema).
What does a high-pressure alarm indicate?
Increased airway resistance or obstruction.
What are possible causes of a high-pressure alarm?
Bronchospasm.
Secretions/mucus plug.
Coughing.
Tube obstruction.
What does a low tidal volume alarm indicate?
Possible circuit disconnection or air leaks.
What does a high-minute ventilation alarm indicate?
Hyperventilation (e.g., pain, anxiety, metabolic acidosis compensation).
How do you adjust ventilator settings for respiratory acidosis (pH < 7.35, high CO₂)?
Increase RR or tidal volume to blow off CO₂.
How do you adjust ventilator settings for respiratory alkalosis (pH > 7.45, low CO₂)?
Reduce RR to retain CO₂.
How do you adjust ventilator settings for hypoxia (PaO₂ < 80 mmHg)?
Increase FiO₂ or PEEP.
How do you adjust ventilator settings for hyperoxia (PaO₂ > 100 mmHg)?
Reduce FiO₂ to prevent oxygen toxicity.
