Mech Vent and Anesthesia Flashcards
Pleural pressure surrogate
Esophageal pressure
- target Pes < 25cm/H2O
- Calculate by subtracting Pes from inspiratory hold on LTV
Ways to improve oxygenation:
- Increase FiO2
- Increase PEEP
- Paralyze patient
- Pressure control (square waveform)
- Lengthen I-time (inverse ratio)
- Recruitment maneuver
- Prone positioning
- Don’t forget to consider a fluid bolus to improve West Zone physiology
Low Pressure Alarm
Not enough Pip was created to hit the low pressure limit (usually set 5cm/H2O above PEEP). Check for…
- Leak in the circuit/disconnect
- ETT cuff deflation
- ETT displacement
High Pressure Alarm
Could mean increased resistance or worsened compliance. Check for…
- ETT secretions/foreign body
- Patient biting on tube
- Bronchospasm/constriction
- Patient airway mal-alignment
- Decreased lung compliance (edema, fibrosis, pneumonia)
- Decreased thoracic compliance (burns, MSK trauma)
- Kinked circuit
- Patient dysynchrony
LTV weight ranges
- Neonates: 5-10kg
- Pediatric: 10-40kg
- Adult: 40kg +
Describe Lung Compliance…
- Change in pressure divided by change in volume
- If a lot of pressure is required for not a big change in volume, you have a non-compliant lung.
- Can relate to inner (lung) and outer (MSK, integuementry, abdomen)
Describe the resistance/compliance relationship…
Resistance is the force that needs to be overcome to get air into the alveoli. Once air gets into the alveoli, compliance is the force that needs to be overcome to inflate them.
What factors adjust the I:E ratio?
Resp rate
I-time
What is the ideal vCalc and what factors influence it?
50-60lpm
I-time and tidal volume
What contributes to autoPEEP?
- Increased RR (not enough time to exhale)
- Minute volumes are too high
- Bronchospasm
- ETT too small
- Mucus plug in ETT
What are the three breath types?
- Machine (control)
- Assisted (pressure support, BPAP, ACV, SIMV)
- Patient (SIMV, CPAP)
Ventilator dyssynchrony is associated with badness. What is it and how do you go about addressing it?
Dyssynchrony is associated with ALI, respiratory fatigue (increased VO2) and a longer duration of mechanical ventilation. Increasing sedation to make the patient more compliant will also possibly lead to ICU delirium. Look for what the patient needs and give it to them. That being said, if you have too much other shit going on, paralyze the patient and get things under control before you go about fine tuning the vent.
Discuss Pip
- Highest pressure measured during the respiratory cycle
- Is a function of both resistance and compliance of the respiratory system
Discuss Pplat…
- Measured during a no-flow state at the end of inspiration
- Reflects static compliance of the respiratory system including the lung parenchyma, chest wall and abdomen
What does an increased Pip with a wide delta P (Pip- Pplat) indicate?
- Increased airway resistance
- Check for secretions/mucus plug, kinked circuit, bronchospasm, biting, tube position
What does an increased Pip and increased Pplat with a normal or narrow delta P signify?
- Suggest a worsening respiratory system compliance
- Check for right main stem, pneumothorax, atelectasis, pneumonia, ACS, edema, DOPES…
What is bias flow?
Flow within the circuit (usually 10lpm) that senses a patient breath (usually at 2lpm) and triggers the ventilator.
Common complications of mechanical ventilation…
- Diminished cardiac output (IVC compression)
- Increased right sided afterload (pulmonary vasculature compression)
- Pulmonary barotrauma/volutrauma (pneumothorax)
- VALI/ARDS
- AutoPEEP
- Elevated ICP
- VAP
- Pressure ulcerations
Considerations for venting a TBI
- There will be reduced ICP drainage
- Don’t let the patient become hypercapnic (target paCO2 to 35-40mm/Hg)
Ways to reduce VAP
- HOB at 30 degrees
- Swap out HME filters
- Ensure proper ETT cuff inflation
Ventilation strategies for obstructive pulmonary disease…
- vCalc of 80-100lpm
- I:E of at least 1:3
- 10 to 14 frequency (monitor EtCO2 waveform)
- Keep tidal volumes below 8mL/kg
- Allow permissive hypercapnia; target pH instead
- Keep Pplat <30cm/H20
- Monitor autoPEEP carefully
- Suction, larger ETT, bronchodilators, take off vent, reduce demand)
Target PaCO2 for elevated ICP? For herniation?
Increased ICP: 35 to 40mm/Hg
Herniation: 30 to 35mm/Hg
Effects of ACS on lungs
- Compresses lung parenchyma, reduces surface area
- Increases intrapulmonary shunt fraction
- Increases alveolar deadspace
- Will require higher Pips, MAP and Pplat (consider permissive hypercapnia)
DOPES for acute MV decompensation:
- Displaced ETT
- Obstructed ETT
- Pneumothorax
- Equipment failure
- Stacked breaths
Correct autoPEEP
- Change vent settings (increase vCalc, decrease rate, decrease TV)
- Reduce ventilator demand (treat fever, pain, anxiety)
- Reduce airway resistance (suction ETT, bronchodilators, larger ETT)
- Take circuit off of patient and let them fully exhale over an uncomfortably long period of time.
Effects of PPV on hemodynamics
- Increased intrathoracic pressure decreases preload.
- Alveolar over-inflation compresses pulmonary vascular bed, increasing PVR and reducing RV output.
- Increased PVR causes intraventricular septal shift which impairs diastolic filling and reduces CO of LV.
- Reduced afterload due to improved pressure difference in LaPlace’s law. Decreased wall tension = decreased MVO2.
Effects of PPV on neurological system…
- Can cause hyperemia/increased ICP by inhibiting cerebral drainage
- pH affects vascularity and cerebral blood flow.
- Changes in cerebral pH could affect respiratory center in brainstem.
Effects of PPV on respiratory system…
- Trauma (barotrauma, volutrauma, biotrauma, sheer trauma)
- Over-inflation of alveoli will compress blood vessels and cause VQ mismatch/shunt
Effects of PPV of GI/GU…
- GI bleeding from stress ulcerations
- Impaired renal blood flow and possible AKI due to decreased CO (pre-renal failure)
- Gut ischemia causes translocation of bacteria
- Liver dysfunction (decreased oncotic pressure, decreased coagulation)
Effects of PPV on immune system…
- Induces pulmonary inflammation
- Translocation of tracheal bacteria into bloodstream