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
Initial Settings
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
ARDS
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