Basic Modes of Mechanical Ventilation 
 
1. Controlled Mechanical Ventilation (CMV) 

– Ventilator delivers all breaths 
– Patient makes no respiratory effort 

Indications: 
– Apnoea 
– Severe respiratory failure 
– General anaesthesia 
– Neuromuscular paralysis 

Disadvantages: 
– Requires deep sedation or paralysis 
– Causes respiratory muscle weakness 
– Not suitable for conscious patients 
 
2. Assist-Control Ventilation (AC) 

– Patient can trigger breaths 
– Each breath receives full ventilator support 
Indications: 
– Most common initial ICU mode 
– ARDS 
– Severe pneumonia 
– Sepsis 

Disadvantages: 
– Risk of hyperventilation 
– Respiratory alkalosis 
– Often requires sedation 
 
3. Synchronized Intermittent Mandatory Ventilation (SIMV) 

– Set number of mandatory breaths 
– Patient can breathe spontaneously between breaths 
– can be volume controlled (VC) or Pressure controlled (PC) 

Indications: 
– short term ventilation
– Partial ventilatory support 
– easier weaning from ventilator 

Disadvantages: 
– Slower weaning compared to PSV 
 
4. Pressure Support Ventilation (PSV) 

– Patient initiates all breaths 
– Ventilator provides pressure assistance 

Indications: 
– Weaning trials 
– Mild respiratory failure 

Contraindications: 
– Apnoea 
– Poor respiratory drive 
 
5. Continuous Positive Airway Pressure (CPAP) 

– Constant pressure throughout the respiratory cycle 
– No mechanical breaths 

Indications: 
– Obstructive sleep apnoea 
– Cardiogenic pulmonary oedema 
– Weaning assessment 

Contraindications: 
– Apnoea 
– Hypotension 
– Inability to protect airway 
 
6. Bi-level Positive Airway Pressure (BiPAP) 
– Two pressure levels: IPAP (inspiratory) and EPAP (expiratory)
– Non-invasive ventilation 

Indications: 

– COPD exacerbation 
– Acute cardiogenic pulmonary oedema 
– Hypercapnic respiratory failure 

Contraindications: 
– Altered mental status 
– Vomiting / aspiration risk 
– Facial trauma 

In summary: 
CMV – No patient effort 
AC – Full support for every breath 
SIMV – Mandatory + spontaneous breaths 
PSV – Only spontaneous breaths