CCP 208 Designing Ventilation Strategies Flashcards
CCP approach to establishing Mech Vent
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- Am I adequately oxygenating (PaO2)
- Am I ventilating appropriately (PaCO2)
- Am I on safe ground
- What is my current acid-base status
4 types of hypoxia
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- hypoxic
- hypemic
- stagnant
- histotoxic
5 causes of hypoxemia
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- V/Q mismatch
- Diffusion impairment
- Shunt (think right to left shunt)
- Hypoventilation
- Decreased partial pressure of inspired oxygen (think high altitude)
causes of hypoxemia with normal A-a
- Hypoventilation
2. Decreased partial pressure of inspired oxygen (think high altitude)
causes of hypoxemia with high/wide A-a
- V/Q mismatch
- Diffusion impairment
- Shunt (think right to left shunt)
The bicarbonate-carbonic acid buffering system equation
CO2 + H2O β H2CO3 β HCO3- + H+
Oxygen extraction ratio
O2ER = VO2 / DO2 = (SaO2-SvO2) / SaO2
Oxygen delivery equation (DO2)
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DO2 = CO x CaO2 (mL/min/m2)
CaO2 = (1.34 X Hgb X SaO2) + (0.003 X PaO2)
equation of motion for the respiratory system
muscle pressure (Pmusc) + ventilator pressure (Pvent) = (elastance x volume) + (resistance x flow)
causes of increased airway resistance
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- bronchospasm
- ETT problems (too small/kinked/bitten/flexed/obstructed)
- mucus plugging/secretions
- water in HME
- blocked exhalation valve
causes of decreased lung compliance
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- ARDS
- atelectasis
- abdominal distention (abdominal HTN)
- CHF
- consolidation
- fibrosis (pulmonary fibrosis)
- hyperinflation
- pneumothorax
- pleural effusion
Functional Residual Capacity (FRC)
what is it and why is it important
this is very esoteric π§
simply, FRC is the volume of air present in the lungs at the end of passive expiration
Why is FRC important ?
- At optimized FRC, the work to inflate the lungs is the lowest, as the inward and outward lung compliances are balanced
- compliance of lung depends on both elastic recoil of lung tissue and outward expansion of chest wall. β in either of these result in a β FRC
- The FRC results in an O2 reserve, the residual air volume in the lungs allows for O2 exchange. β FRC = β oxygenation βtime under the curveβ
- β lung volumes result in β FRC. Low lung volumes result in less alveolar tension pulling the lung airways open, and the airway narrowing results in β airway resistance
- A β FRC can result in shunts and atelectasis. This occurs when the FRC β below the closing capacity of the lung; the volume at which the respiratory bronchioles collapse
Transpulmonary pressure
the difference between the alveolar pressure and the intrapleural pressure in the pleural cavity
pulmonary shunt
the passage of deoxygenated blood from the right side of the heart to the left without participation in gas exchange in the pulmonary capillaries
Ventilation perfusion mismatch or βV/Q defectsβ
condition in which one or more areas of the lung receive oxygen but no blood flow, or they receive blood flow but no oxygen
Physiologic right to left shunt
exist when non-ventilated alveoli are perfused
- atelectasis
- pneumonia
- acute respiratory distress syndrome
as opposed to anatomic shunt which would be d/t something like a VSD
diffusion limitation
- movement of oxygen from alveolus β pulmonary capillary impaired
- usually d/t alveolar and/or interstitial inflammation and fibrosis (pulmonary fibrosis)
donβt get this confused with V/Q mismatch, it is a distinct clinical entity
right to left shunt
deoxygenated blood flowing from right side of the heart to left side of the heart without being oxygenated via the lungs
could be d/t an ASD/VSD, could be pulmonary
Goals of NIPPV
- Decrease WOB (unload respiratory muscles)
- Increase FRC
- Improve atelectatic recruitment
- Improve lung compliance
- Improve oxygenation
- Decrease LV preload, decrease LV afterload, improve cardiac output, improve forward flow
- PEEP matching for autoPEEP
Contraindications to NIPPV
- Cardiac arrest
- Respiratory arrest
- Unable to protect airway
- Upper airway obstruction with foreign bodies
- Untreated or loculated pneumothorax found on imaging
- Shock
- Post GI surgery is a caution
- Maxillofacial injury
- Intractable vomiting
Adverse effects of NIPPV
- Local skin damage around bridge of nose
- Mask leak
- Eye and mouth irritation from mask leak air flow
- Sinus pain and sinus congestion
- Claustrophobia
- Mild gastric distention
simplified equation of motion of the respiratory system
Ventilation Pressure = Elastic Pressure + Resistive Pressure
effects of PEEP on the RV
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- decreased RV venous return (decreased RV preload)
- increased pulmonary vascular resistance due to vascular compression (increased RV after load)
- increased RV dilation, leading to a leftward shift in the intraventricular septum
effects of PEEP on the LV
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- decreased LV preload from decreased RV output
- decreased LV SV d/t bulging of the ventricular septum from RV dilation
- decreased LV afterload
- decreased LV preload and decreased LV dilation
- decreased myocardial oxygen demand
- increased pressure gradient from thorax to periphery
- increased hydrostatic displacement of alveolar edema
Summary of effects of PEEP on the heart
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- Net effect of PEEP on CO depends on RV/LV function, preload, after load, and ventricular interdependence
- In RV failure/RV preload dependence, moderate to high PEEP (5-15 cmH2O) may decrease RV CO
- In after load-dependent states (such as LV failure) moderate-to-high PEEP (10 to 15 cmH2O) may improve CO
Triggering variable
initiates the delivery of a breath (e.g. flow or pressure)
Control variable
algorithm that determines the delivered pressure during mechanical inspiration (e.g. volume or pressure)
Cycling off variable
signal for terminating the pressure delivery (e.g. time, pressure, flow)
causes of Increased Airway Resistance
- Asthma (e.g. bronchospasm)
- Obstruction or kinking in ETT
- Excessive airway secretions
- Clogged HME filter
- Small-bore ETT
- High flow rate
causes of Decreased Compliance
- ARDS
- Pulmonary fibrosis
- Abdominal distention
- Pneumonia
- Pleural effusion (e.g. heart failure)
- Pneumothorax
- Atelectasis
- Bronchial intubation
decreased compliance (pip/plat)
Increased PIP
Increased Pplat
increased resistance (pip/plat)
Increased PIP
Normal/Unchanged Pplat
ARDS Berlin definition
- Acute, within 1 week of a known risk factor
- Bilateral opacities on CXR
- Respiratory failure not purely of cardiac origin
Berlin ARDS staging
- Mild. P/F ratio 200-300, PEEP >5 cmH2O
- Moderate. P/F ratio 100-200, PEEP >5 cmH2O
- Severe. P/F ratio <100, PEEP >5 cm H2O
ARDSnet lung protective protocol
Starting at 6 mL/kg PBW Reduced stepwise by 1 mL/kg PBW to maintain plateau pressure < 30 cmH 2 O
If Plateau pressure <25 cmH20, TV increased by
1 mL/kg PBW until plateau pressure > 25 cmH2O
Minimal tidal volume 4 mL/kg
Maximum tidal volume 8 mL/kg
Minimal arterial pH 7.15
respiratory effects of prone ventilation
- recruitment of dorsal lung β increased lung compliance
- stiffening of chest wall β decreased chest wall compliance
- overall respiratory system compliance varies case-by-case