Ventilation Modes Flashcards
Peak Inspiratory Pressure
PIP
Total pressure required to distend the lungs & airway
Pressure used to calculate dynamic compliance
Plateau Pressure
Pplat
Distending pressure to expand only the lungs
Measures air redistribution flow through lungs
Used to calculate static compliance (reflects intrinsic lungs)
Mechanical Ventilation Variables
RR - respiratory rate
Vt - tidal volume
Pressure - PIP/Pplat/PAW
I:E ratio - inspiration to expiration
Trigger Variable
Represents inspiration start
*Pressure, volume, flow, time
Limit Variable
Target variable
Controls how inspiratory breath maintained
Once threshold reached will not exceed set limit
*Pressure, volume, flow
Cycling Variable
Transition from inspiration to expiration
Once achieved set cycling variable → start expiration
*Volume, pressure, flow, time
Baseline Variable
Pressure maintained at end expiration
Peak end expiratory pressure
PEEP
Alveolar pressure above atmosphere
Individualized to patient
Prevents atelectasis
Intrinsic - 2nd to incomplete expiration (auto-PEEP)
Extrinsic - applied PEEP via mechanical ventilator
Volume Control Ventilation
Time = trigger Volume = limit Time = cycling
Airway pressure (upside down V) changes breath-by-breath based on changing respiratory compliance Flow remains constant (flat box)
Set appropriate PIP/pressure alarms
Pressure Control Ventilation
Time = trigger Pressure = limit Time = cycling
Airway pressure controlled (flat box)
Vt changes breath-by-breath based on changing respiratory compliance
Decelerating wave flow - homogenous gas flow through lungs (improves ventilation pattern ↓WOB)
Avoid barotrauma d/t excessive pressure
Set appropriate Vt alarms
Pressure Control Volume Guarantee
PCV-VG
Time = trigger
Pressure = limit
Time = cycling
Ventilator adjusts pressure delivered when current volume not at set #
- Adjustments take 3-5 breaths to complete
- Atelectasis development when ↓compliance & ventilator delayed in providing adequate pressure to distend lungs
Synchronized Intermittent Mandatory Ventilation
SIMV Delivers set Vt at set RR w/ patient initiated breaths Time OR patient = trigger Flow L/min = limit Volume = cycling
Patient breaths are not supported (unless SIMV-PSV)
Appropriate mode when weaning from ventilator - less desynchrony w/ patient initiated breaths
Hypoventilation when inadequate Vt & RR w/ patient ↓respiratory effort
Hyperventilation when ↑PS level
Pressure Support Ventilation
PSV Supported ventilation mode for spontaneously breathing patient Patient = trigger Pressure = limit Flow = cycling
Set Psupport & PEEP
Back-up mode Pinsp & RR
Oxygen Delivery Formula
DO2 = CO x CaO2 (arterial)
Oxygen Use Formula
VO2 = CO x O2a - O2v
Hypoxemia
O2 deficiency in the blood
Hypoxia
O2 delivery to the tissues not sufficient to meet metabolic demand
Anesthesia Goal
Maintain oxygenation & ventilation
Oxygen Therapy Goal
Prevent & correct hypoxemia & tissue hypoxia
Hypoxia S/S
Vasodilation Tachycardia Tachypnea Cyanosis Confusion Lactic acidosis
Nasal Cannula
Flow rates 1-6L/min
FiO2 ↑4% per L/min
Simple Face Masks
FiO2 40-60%
Minimum 6L flow required to prevent rebreathing
Face Masks w/ Reservoir
FiO2 60-100%
Venturi Masks
FiO2 24-50%
Set flow rate to ensure exact oxygen delivery
Bernouilli’s principle application
Oxygen Toxicity
↑FiO2 over long periods → harmful to lung tissue
↓ciliary movement (unable to expel mucus)
Alveolar epithelial damage
Interstitial fibrosis
Safe 100% O2 up to 10-20hr
Toxic 50-60% O2 >24-72hr
Absorption Atelectasis
Nitrogen replaced by oxygen
Under-ventilated alveoli ↓volume
↑pulmonary shunting
COPD
Chronic CO2 retention
Hypoxic drive - do not administer oxygen
Induced hypoventilation d/t ↑O2
*Theoretical only
What triggers peripheral chemoreceptors?
Hypoxemia
Fire Hazard
Extreme caution in head & neck cases Vigilance when administering O2 Notify surgeon when ↑O2 Risk w/ cautery instruments Chronic ICU patients receiving tracheostomy = high risk d/t ↑FiO2 requirements
Retinopathy
ROP
O2 therapy → vascular proliferation, fibrosis, retinal detachment, & blindness
Premature neonates <36wk (up to 44wk) gestation or weigh <1500gm
Safe O2 admin = PaO2 60-80mmHg
Hypercapnia Causes
↑alveolar dead-space
↓alveolar perfusion
Impaired pulmonary circulation
Lung disease
↓alveolar ventilation (central or peripheral)
Respiratory depression most common cause
Hypercapnia Considerations
- Ventilatory drive regulation
- Cerebral blood flow
- Smooth & cardiac muscle depression
- ↑catecholamine release
- Vasodilation vs. vasoconstriction
- ↑RR & PVR
Hypercapnia Treatment
Identify cause
↑minute ventilation
Hypocapnia
Cause typically iatrogenic
Clinical manifestations:
↓CBF
↓CO & coronary constriction
Hypoxemia d/t hypoventilation
Treatment ↓minute ventilation
Anesthesia & Surgical Impact on Lungs
Neuromuscular blockers ↓muscle tone Abdominal contents cephalad displacement Alveolar compression ↑intra-abdominal pressure ↑BMI Trendelenburg position ↓FRC (upright → supine + paralysis + induction agents)
Functional Residual Capacity
Decreases w/ age
↓1.2-1.5L or 30mL/kg
Recruitable vs. Non-Recruitable
Recruitable
- General anesthesia
- ↓FRC
- Atelectasis
Non-Recruitable
- ARDS
- Cellular debris
- Edema
Ventilation Induced Lung Injury
VILI
Ventilator SETTINGS cause injury
Ventilation Associated Lung Injury
VALI
Specific to OR setting
Volutrauma - damaged epithelium, ↓surfactant, ↑capillary leak
Barotrauma - damage from + pressure effects
Atelectrauma - repeated collapse & re-inflation (under-utilized PEEP alveoli closed)
Biotrauama - inflammatory mediator release
Factors that Contribute to Alveolar Collapse
Position ↓FRC
Induction loss muscle tone
FiO2 reabsorption → atelectasis
Maintenance ↓compliance → progressive airway closure
Emergence high FiO2 promotes postop atelectasis
Absence CPAP after extubation → continued lung collapse
Lung Protective Ventilation Settings
Vt 6-8mL/kg IBW FiO2 <30% PEEP 30% BMI I:E 1:1.5 Alveolar recruitment maneuvers
Induction Strategies
Initial FiO2 100%
Elevate HOB >30% or reverse Trendelenburg
Apply CPAP w/ bag-mask APL valve or vent mode
Oral or nasal airway as needed
LPV Goals
Restore lung volume w/ alveolar recruitment maneuver
Maintain lung volume & minimize atelectasis formation (individualized PEEP)
Maximize lung compliance
- Use lowest possible driving pressure ΔP
- Compliance = Vt / ΔP
Alveolar Recruitment Maneuvers
BMI <30 → 40cmH2O
30-40 → 40-50cmH2O
40-50 → 50-55cmH2O
>50 → 50-60cmH2O
Emergence FiO2
<80%
Reduce atelectasis formation
Pressure-Volume Loop
Assesses driving pressure
Maximize volume delivered at lowest pressure
*See OneNote graphs
Flow-Volume Loop
Represents expiratory flow
*See OneNote graphs
