Mechanical ventilation Flashcards
1
Q
What are the different types of ventilator breaths
A
- Mandatory breath = ventilator controls initiation and/or termination of breath
- Assisted breath = initiated by the patient
- Controlled = initiated by the machine - Spontaneous breath = patient controls initiation and termination of breath
- Supported = inspiration augmented by the machine with an inspiratory flow
- Spontaneous = no inspiratory flow give by the machine
2
Q
Equation of motion (include the units)
A
Pvent + Pmuscles (cmH2O) = elastance (cmH2O/L) * volume (L) + resistance (cmH2O/L/s) *flow (L/s) + PEEP (cmH2O)
OR
= (Vt/compliance) + (resistance x flow)
3
Q
What are the different categories of variables that can be set on a ventilator? Give examples for each
A
- Control variables
- Pressure
- Volume / flow - Cycle variable
- Time
- Change in flow / pressure - Trigger variable
- Time
- Change in flow / pressure - Limit variable
- Pressure - Baseline variable
- Pressure (PEEP)
4
Q
List the different phases of the respiratory cycle
A
- Initiation
- Inspiratory flow
- Pause / inspiratory hold
- Expiratory flow
- Expiratory pause / hold
5
Q
What are recommended initial ventilator settings (FiO2, Vt, RR, PEEP, pressure above PEEP, Insp flow rate, Tinsp, rise time, I:E ratio, inspiratory trigger) for a patient with healthy lungs / with lung disease
A
See picture
6
Q
What should alarm settings be for low pressure alarm, high pressure alarm, low PEEP, high PEEP, low Vt, apnea, low MV
A
- Low pressure: 5-10 cmH2O below PIP
- High pressure: 10 cmH2O above PIP
- Low PEEP: 2 cmH2O below PEEP
- Low Vt: 10-15% below desired Vt
- Apnea: 20 sec
- Low MV: 10-15% below desired MV
7
Q
What is the prognosis for successful weaning of mechanical ventilation / survival to discharge (overall and for some specific diseases)
A
- Pulmonary disease: 30% successful weaning, 20% survival to discharge
- Neuro / muscular diseases: 50% weaning, 40% discharge
- Aspiration pneumonia in dogs: 50% weaned
- ARDS: 8% weaned
- Tick paralysis: 60% survival
- CHF: 60% survival
8
Q
What are the levels of PEEP recommended by ARDSnet
A
- Table with lower PEEP / higher FiO2 and table with higher PEEP / lower FiO2
- No clear benefit of higher PEEP at this point (except possible for some sub phenotypes of ARDS)
Pplat should always be < 30 cmH2O
9
Q
Briefly explain methods of optimal PEEP determination
A
- ARDSnet PEEP tables
- Incremental / decremental PEEP trials and choosing PEEP highest compliance or best oxygenation or lowest dead space
- Stress index (increasing or decreasing PEEP to get a SI of 1)
- Use of PV loops to determine the lower inflection point
- Use of lung ultrasound or electrical impedance to assess best recruitment
10
Q
What are the characteristics of APRV (cycle, control, mode)
A
- Mode = intermittent mandatory ventilation
- Cycle = time cycled
- Control = pressure-controlled
11
Q
How should Tlow be set in APRV
A
So that end-expiratory flow rate = 75% of peak expiratory flow rate
12
Q
What are the 3 modes of ventilation
A
- Continuous mandatory ventilation
- Intermittent mandatory ventilation
- Continuous spontaneous ventilation
13
Q
Dynamic and static compliance formulas
A
Cdyn = Vt/(PIP-PEEP)
Cs = Vt/(Pplat-PEEP)
14
Q
What is pendelluft
A
It is the intra-pulmonary flow caused by air redistribution among alveoli due to some alveoli filling faster than others. It happens when bulk flow (gas delivery) is paused.
15
Q
Explain what quasistatic compliance means
A
Compliance calculated with a shorter inspiratory hold than required to obtain a true Pplat (~ 1.5 sec). It is calculated from a pressure equilibrated with no gas delivery (bulk flow) but while inter-alveolar redistribution (intra-pulmonary flow = pendelluft) has not happened yet.
16
Q
Where do you assess pulmonary compliance / airway resistance on a pressure scalar
A
- Compliance = difference between PEEP and Pplat
- Resistance = difference between PIP and Pplat
17
Q
How to assess auto-PEEP? What are consequences of auto-PEEP?
A
- Assessed with an expiratory hold (air trapping can also be seen on flow scalar and flow-volume loop)
- Consequences = ineffective triggering (increased difficulty for patient to initiate breath - more to overcome), alveolar overdistension, hypercapnia
18
Q
In what mode(s) of ventilation will the pressure scalar be a square
A
- Pressure control
- Volume control with decelerating flow pattern (but more “rounded” than pressure control)
19
Q
In volume control mode, what is the benefit of a decelerating flow pattern vs constant flow delivery
A
- Lower PIP
- Allows better adjustments of I-time for patient-ventilator synchrony
20
Q
You are setting the ventilator for a patient who needs:
- Vt 300 mL
- RR = 15 bpm
- I:E = 1:2
What is the inspiratory flow rate?
A
Respiratory cycle length = 60/15 = 4 sec
Inspiratory time = 4/3 = 1.3 sec (1/3 of respiratoy cycle length for inspiration, 2/3 for expiration)
Flow = Vt/time = (300/1.3)*60 = 13 800 mL/min = 13.8 L/min
21
Q
On which loops / scalars can a leak be identified
A
- Volume scalars: abrupt plunge to baseline during expiratory limb (can also be air trapping)
- PV loop: pressure goes back to 0 but volume does not
- Flow volume loop: volume does not get back to 0 but flow does (vs. air trapping: volume goes back to 0 but flow does not)
22
Q
How to identify compliance / resistance on a PV loop? What type of compliance is it?
A
- Compliance = slope (dynamic compliance)
- Resistance = bowing
23
Q
List causes of increased resistance for a ventilated patient
A
- Bronchoconstriction
- Mucus plug
- Secretions in circuit or tube
- Tube or circuit kinking
- HME obstruction
- One lung intubation
24
Q
List causes of decreased compliance for a ventilated patient
A
- Worsening pulmonary disease (pneumonia, edema, contusions)
- Pneumothorax
- Atelectasis
- Chest wall restriction
25
How will a change in airway resistance show on a flow volume loop
Decreased peak expiratory flow with "scooped out" appearance of the expiratory limb
26
What are the PV loop inflections points and what do they indicate
- Lower inflection point = pressure at which the alveoli start opening more (increase in compliance) -> PEEP should be set just above that to improve recruitment and avoid atelectrauma
- Upper inflection point = pressure at which alveoli start being over distended (beaking) -> PIP should be set below that to avoid volutrauma / barotrauma
(in small patients, volume readings can be difficult and the loop can have artifactual beaking that is very linear)
27
What are the phases of the respiratory cycle where patient-ventilatory dyssynchrony can happen? Give examples.
1. Initiation / trigger phase -> trigger asynchrony (ineffective triggering, auto-triggering, double triggering, reverse triggering)
2. Flow delivery phase -> flow asynchrony
3. Breath termination point -> cycle asynchrony
4. Expiratory phase -> expiratory asynchrony (auto-PEEP)
28
What are causes of ineffective triggering / auto triggering / double triggering
1. Ineffective triggering
- Auto-PEEP
- Improper triggering threshold
- Decreased respiratory drive / strength
2. Auto triggering
- Improper triggering threshold
- Leak
- Secretions
- Tube position / cardiac oscillations
3. Double triggering
- I-time too short
- Vt / inspiratory flow too low
- Flow-cycle threshold too high
29
How can flow dyssynchrony be identified
1. "Flow hunger"
- Pressure scalars in volume control: scooped out appearance of inspiratory limb (can also be seen in pressure control)
- Flow scalar in volume control: saw-tooth appearance of inspiratory limb
- PV loop: scooped out appearance of inspiratory limb (concave)
- Flow volume loop: saw tooth appearance of inspiratory limb
Easier to see when comparing controlled and assisted breaths (controlled breath will look normal since there is no patient effort
2. Excessive inspiratory flow
- Pressure control: early overshoot on inspiratory limb
30
What are the 2 types of cycling asynchrony and how are they best identified
1. Premature cycling
- Flow scalar in pressure control -> abrupt initial reversal of expiratory flow
- Pressure scalar -> negative pressure just after the end of inspiration
-> can cause double triggering
2. Delayed cycling
- Pressure scalar: pressure spike during mid- to late-inspiration
- Flow scalar: rapid decline in inspiratory flow near the end of inspiration
31
What are adverse effects of long-term propofol use for mechanical ventilation
- Lipemia
- Accumulation of benzyl alcohol (for formulation with benzyl alcohol)
- Vasodilation and myocardial depression
- Heinz body anemia in cats
- Propofol infusion syndrome in humans (rhabdomyolysis, acidosis, arrhythmias)
32
Can etomidate be used as a maintenance agent for ventilated patients?
No - it causes adrenocortical suppression
33
What is a risk with prolonged administration of diazepam for mechanical ventilation? What is an alternative option?
Propylene toxicosis (causing lactic acidosis, hyperosmolarity, hemolysis, seizures, arrhythmias)
Can use midazolam instead
34
What anesthetics agents should be discontinued early in prevision of weaning from mechanical ventilation
- Neuromuscular blockers
- Ketamine, benzodiazepines
35
What are possible causes of an increase in PaCO2-ETCO2
Increased alveolar dead space -> severe parenchymal disease, decreased CO, PTE, excessive PEEP
36
What are the major components of the concept of lung protective ventilation
- Low tidal volumes (ideally 4-6 mL/kg, in vet patients more like 6-8 mL/kg)
- Pplat < 30 cmH2O
- Driving pressure < 15 cmH2O
- Higher PEEP
- Permissive hypercapnia
- Permissive hypoxemia
37
What are patient-related and ventilator-related causes of ventilator dyssynchrony
1. Patient related
- Hypoxemia
- Hypercapnia
- Hyperthermia
- Pain
- Insufficient sedation
2. Ventilator related
- Settings
- Increased circuit resistance
- Circuit secretions
- Leak
38
What are the 2 options for airway humidification in mechanical ventilation? Give adverse effects of each
- Heat moisture exchanger (HME):
Can become obstructed, increases dead space and resistance
- Heated water humidifier:
Can lead to condensation of water in the inspiratory limb (which can promote bacterial growth)
39
What are the criteria for readiness for a spontaneous breathing trial
- Improvement in the primary disease process
- PaO2:FiO2 ratio > 150-200 with FiO2 < 0.5
- PEEP of 5 cmH2O or less (+/- PIP of 25 cmH2O or less)
- Adequate respiratory drive
- Hemodynamic stability
- Absence of major organ failure
40
What is the recommended duration of a spontaneous breathing trial
30-120 min
41
What are criteria for failure of a spontaneous breathing trial
- Tachypnea (RR>50 or depending on baseline)
- PaO2 < 60 mmHg or SpO2 < 90%
- PaCO2 > 55 mmHg
- Vt < 7 mL/kg
- Tachycardia
- Hypertension
- Hyperthermia (or increase in temperature >1°C)
- Anxiety
- Signs of respiratory effort / distress (rapid shallow breathing also not good)
- Clinical judgement
42
What are common factors contributing to weaning failure
- Lack of resolution of primary disease process
- Acquired respiratory muscle weakness
- Inadequate recovery from sedation / neuromuscular blockade
- Increased airway resistance
- Decreased lung compliance
- Decreased chest wall compliance
- Cardiovascular instability (myocardial dysfunction)
43
What are the mechanisms of ventilator -induced lung injury
- Barotrauma: excessive airway pressure causing accumulation of extra-alveolar air (pneumothorax, pneumomediastinum, SQ emphysema) ; increased risk when PIP > 40 cmH2O but below that no correlation with Pplat
- Volutrauma: stretch injury caused by alveolar distension
- Atelectrauma: trauma to epithelial cells from repetitive opening and closing (+ shear stress to adjacent alveoli)
- Biotrauma: Inflammatory response caused by cell damage -> worsened lung injury +/- distant organ damage
- Oxygen toxicity: atelectasis, reactive oxygen and nitrogen species, interstitial edema, hyaline membrane formation with damage to alveolar membrane, altered mucociliary function, fibroproliferation
- Mechanical power: includes Vt, driving pressure, RR, flow rate, PEEP normalized to the area of lung available for ventilation
- Spontaneous breathing: decrease in pleural pressure caused by spontaneous efforts increases transvascular pressure and distends pulmonary capillaries -> edema
(Alveolar distension and atelectrauma can also happen with spontaneous breathing)
44
What is the definition of ventilator associated pneumonia
Pneumonia that arises more than 48h after endotracheal intubation and mechanical ventilation, that wasn't present at the time of intubation
45
What are the most common sources of bacteria in ventilator associated pneumonia? What type of bacteria are they commonly?
- Exogenous bacteria (contaminated equipment, environment, hands)
- Oral cavity (switches to mostly Gram neg aerobic bacteria with lack of hygiene)
- GI
They are usually aerobic bacteria
46
What are the criteria to diagnose ventilator associated pneumonia in veterinary patients
1. Ventilatory associated condition: ≥ 2 days of worsening oxygenation (increase in FiO2 ≥ 0.2 over baseline or PEEP ≥ 3 over baseline) following ≥ 2 days of stable or improving FiO2 and PEEP
2. Infection-related ventilator-associated condition:
- Dogs: T>39.2 or <38.1 or WBC≤6000 or ≥16000
Cats: T>40.0 or <37.8 or WBC≤5000 or ≥19000
- AND new antimicrobial started and continued for ≥ 4 days
3. Possible ventilator associated pneumonia:
- Purulent airway secretions with neutrophils ≥ 4+ and squamous epithelial cells ≤ 2+
- OR positive culture of sputum / endotracheal aspirate / BAL excluding normal respiratory / oral flora, coagulase neg Staph and Enterococcus
- OR positive culture of any pathogen from lung tissue
3'. Probable ventilator associated pneumonia:
- Purulent secretions as defined in possible VAP AND positive culture ≥ 10^5 CFU/mL in endotracheal / ≥ 10^4 in BAL / ≥ 10^3 in protected specimen brush / ≥ 10^4 CFU/g in lung tissue
- OR positive pleural fluid culture not from indwelling chest tube
- OR lung histopathology indicating infection
4. Final diagnosis of VAP would also include new or progressive pulmonary infiltrates on thoracic imaging
47
List measures of prevention of ventilator associated pneumonia
1. Nonpharmacologic
- Strict alcohol-based hand hygiene
- Education to caregivers with monitoring of compliance
- Minimize time of intubation
- No change of ventilatory circuit unless soiled
- Aspiration of subglottic secretions
- ET tube cuff pressure maintained 25-30 cmH2O
- Minimize nurse:patient ratio
Pharmacologic:
- Oral care with dilute chlorhexidine (0.12-2%)
- Use antacids only if GI bleeding is documented
48
A patient is on the ventilator in volume control with Vt 250 mL, RR 20 sec, I:E 1:2, PEEP 5 cmH2O. His PIP is 12 cmH2O and his Pplat is 11 cmH2O. What is his resistance and compliance?
1. Resistance
R = (PIP-Pplat) / flow
Flow = Vt / Tinsp
Tinsp = (60/RR) / 3 = 1 sec
-> R = (12-11)/0.25 = 4 cmH2O/L/s
2. Compliance
C = Vt / (Pplat - PEEP)
-> C = 0.25/(11-5) = 0.042 L/cmH2O = 42 mL/cmH2O
49
List causes and potential troubleshooting responses on the ventilator for hypoxemia.
Causes:
- Loss of O2 supply
- Machine or circuit malfunction
- Deterioration of underlying disease
- New disease (pneumothorax, pneumonia, VILI, ARDS)
Troubleshooting
- Increase FiO2
- Sternal recumbency
- Thoracic auscultation
- Machine function?
- Increase PEEP
- Increase PIP/Vt
50
List causes and potential troubleshooting responses on the ventilator for hypercapnia.
Causes:
- Pneumothorax
- Bronchoconstriction
- ET tube/airway obstruction
- Circuit leak
- Increased apparatus or alveolar dead space (alveolar overdistention, pulmonary embolism)
- Vent settings
- Low Vt/ RR
Troubleshooting:
- Evaluate patient data
- Thoracic ausultation
- Assess ET tube
- Machine function?
- Adequate expiratory time?
- Increase Vt or RR
51
What is the target oxygenation using the least aggressive ventilator settings in patients with ARDS?
PaO2 55-80 mmHg
SpO2 88-95%
52
What are advantages and disadvantages of using PEEP?
Advantages:
- Recruitment and prevention of alveolar collapse --> reduced risk of atelectrauma
- Improve oxygenation
- Reduce intrapulmonary shunting
- Improve gas exchange
Disadvantages:
- Decrease venous return and cardiac output
- Volutrauma, barotrauma, overdistention of normal lung regions
53
What are benefits of APVR?
- Lung protective
- Improved hemodynamics
- Reduced need for sedation and neuromuscular blockade
54
True or false: Dynamic compliance is altered by resistance (i.e. if resistance increases, Cdyn decreases)
True - because flow is not allowed to cease entirely. Static compliance is not altered by resistance
55
Associate the right pressure to what it overcomes during a breath:
1. PIP
2. Driving pressure
3. Pplat
4. PEEP
5. Delta P (PIP - Pplat)
a. Resistance
b. Compliance
c. Resistance & compliance
1 - c
5 - a
2 -b
56
At what % of peak flow should a breath be terminated when considering flow as a cycle variable?
25%
57
Which mode of ventilation?
VC -CMV
58
Which mode of ventilation?
PC -CMV
59
Which mode of ventilation?
VC - SIMV
60
What is going on?
1- increased resistance
2 - decreased compliance
61
How would you address each of these issues?
a - prolong I-time
b - decrease I-time
62
What should you be concerned about in this volume scalar?
Circuit leak? Pneumothorax?
63
Describe this flow-volume loop and what could be going on?
Scooping with reduced peak inspiratory flow rate
--> Increases resistance - kinked/obstructed ETT, bronchospasme, HME occlusion, increased airway secretions
64
How would you describe and troubleshoot this issue?
Scooped-out concave appearance of the pressure solar (in VC mode) associated with inadequate inspiratory flow ("flow starvation")
--> increase insp flow or change flow pattern
65
Describe your approach to a spontaneous breathing trial once the patient has been assessed and is ready for weaning
1. Disconnect the patient from the machine allowing it to breathe an enriched and humidified O2 source with FiO2 similar to what it was receiving on the ventilator - breathing circuit or mask
OR
2. Leave the patient connected to the machine and switch to a low level of CPAP (2-5 cmH2O) +/- PSV (5-8 cmH2O)
66
True or false: Routine use of gastric antacids is recommended in patients on mechanical ventilation
false - only in cases of demonstrated gastric ulceration
