Control (aka cycle or limit)
Pressure-controlled: Breath determined by achieving a set peak inspiratory pressure (PIP)
- Pro: limits risk of barotrauma
- Con: if compliance of lung changes then hypo- or hyper ventilation may occur
Volume–controlled: Breath determined by delivering a set tidal volume
- Pro: better control of tidal volume
- Con: if compliance of lung is high then PIP may be high, risking barotrauma
Volume-Control Modes
Controlled Mechanical Ventilation:
- Ventilator delivers breaths at set rate, patient unable to breathe spontaneously
- For apnoeic, deeply sedated, muscle relaxed patients
Intermittent Mechanical Ventilation (IMV):
- Ventilator delivers breaths at set rate, but patient able to make unassisted breaths too
Assist/Control (A/C) Ventilation or Continuous Mechanical Ventilation (CMV):
- Ventilator has a back-up rate set, and delivers a breath if no patient-initiated breath in time period. Patients may breathe above the set rate, each breath will be assisted.
- Often used in ED patients
Synchronized Intermittent Mechanical Ventilation (SIMV):
- Similar to A/C mode, the ventilator has a back-up rate set, and delivers a breath if no patient initiated breath in time period. Patients may breathe above the set rate.
- However only the set rate of ventilator- or patient-initiated breaths are assisted to the full TV or PIP. Additional patient-initiated breaths above the set rate are not assisted.
- Often used in ED patients
Pressure-Control Modes
Positive End Expiratory Pressure (PEEP) & CPAP:
- Functionally similar
- PEEP is the term used in mechanical ventilation and CPAP during spontaneously breathing
- ↑FRC, maintains alveolar patency, ↑PO2, but may ↓CO at higher pressures
Pressure Support Ventilation (PSV):
- Spontaneous breathing by patient supported by attaining a set PIP on each breath
- PEEP may be added too, as well as a mandatory back up rate (usually via SIMV)
Indications
- Intubation – Failure of ventilation, oxygenation, loss of airway patency or protection.
- Failed NIV
Common Initial Settings
- Depends on underlying issues – Lung protection (most situations) or Obstructive lung dz
- Lung protection:
- Vol A/C or SIMV – VT 6-8ml/kg, Insp Flow 60-80ml/min, RR 12-20, I:E 1:2, FiO2 1.0 & PEEP 5cmH2O, Plateau Pressure<30cmH2O
- Obstructive lung dz:
- PSV mode – PIP<40cmH2O OR Vol A/C or SIMV – VT 8ml/Kg, Insp Flow 60-80ml/min. For both: RR 8-10, I:E 1:4-5, FiO2 1.0, PEEP 0-5cmH2O, Plateau pressure<30cmH2O
Complications
- Intubation trauma
- Barotrauma
- Air-trapping/intrinsic PEEP
- Nosocomial infections
- ↑WOB if asynchrony of breaths or poor trigger