cardiology with critical care

mechanical ventilation

Increasing oxygenation
- increase FiO2
- Increase PEEP, I:E ratio (increase alveolar recruitment)
- Decrease O2 consumption (increase sedation, analgesia, paralysis, synchrony)
Minute Ventilation = RR X tidal volume

AC: assist control. Specified volume or pressure for all breaths regardless whether patient or machine initiates breath
- default mode for most ICU
- volume control
- pressure control
- VC-CMV, continuous mandatory ventilation
- PC-CMV
- full respiratory support
- clinician control inspiratory pressure or volume
- tachypneic patient: air trapping or respiratory alkalosis, problem in asthma/copd
- 4th breath: deflection, triggered by patient
SIMV: synchronized intermittent mandatory ventilation. Device gives pre-specified volume or pressure for set RR. Patient then takes spontaneous breaths in between
- pro: takes over full work of breathing, allows more spontaneous breathing, may help with weaning
- cons: patient fatigue if RR or pressure support too low

avoid ventilator induced lung injury
- volutrauma: lung overdistention
- barotrauma: high pressure
- atelectrauma: repeat opening/closing alveoli
FiO2: 100% at first then reduce to 60% in 30 min to 1 hour if SpO2 > 88%
RR: usually 14-18, or match pre-intubation RR
Volutrauma: TV: 6-8 cc/kg for ideal body weight for height
Barotrauma: PEEP: 5-10 cm H2O
Atelectotrauma: maintain plateau pressure < 30 cm H2O
- plateau pressure surrogate for transpulmonary pressure as pleural pressure negligible

acute lung injury from parenchymal or systemic process
increased capillary permeability from damage to alveolar epithelium and capillary endothelium
protein in alveoli = pro inflammatory cytokines => fibrosis => low compliance => hypoxemia
Berlin definition
- acute onset injury
- CXR bilateral opacities
- non-hydrostatic pulm edema, not cardiogenic
- P:F ratio < 300
  - mild: 200-300
  - mod: 100-200
  - severe: <100
low plateau pressure
permissive hypercapnia, pH > 7.25, do not have to get back to 7.4 with 40 CO2. Due to the magnitude of benefits from LTVV, it is sometimes recommended that bicarbonate drips be started temporarily to maintain an acceptable pH if needed, rather than making ventilator changes that would violate LTVV parameters.
relative hypoxemia: spO2 88-94%, keep FiO2 < 60%
start with volume control
low tidal volume: 6cc/kg IBW
PEEP: usually start with 8
ABG 30-60 min after stabilization
Then titrate:
- lower RR to target pH near 7.25
- FiO2: decrease to target 92-96% or PaO2 60 - 80
- Pplat: < 30 cm H2O
  - if plateau > 30 and pH > 7.25: decrease TV
  - if plateau > 30 and pH < 7.25: cautious decrease in PEEP
PEEP

spontaneous inspiration
- increase venous return => increase preload
- decreases pulmonary resistance => decrease RV afterload
- increase LV afterload
positive pressure ventilation
- decrease venous return => decrease preload
- compress pulmonary vasculature => increase RV afterload
- LV afterload decreased
- PEEP can be bad for pt preload sensitive (RV dysfunction)
- PEEP decreases LV afterload: good for MR or dilated LV
- RV volume/pressure overload: pushes into LV, PEEP can cause less preload and less push into LV