Weaning / Discontinuation  Partial Ventilation Support

     
       

 

         
       

Many intensive care units use different techniques of partial ventilatory support as part of the generalized weaning process.

The objective of partial ventilator support (PVS) is to allow the patient to interact with the ventilator as the neuro-mechanical cause of respiratory failure resolves. Unless the patient is being ventilated for post-operative care, in which case the lungs are usually normal, the disease process and the intensive care interventions (sedation), do not allow for immediate movement from full support to extubation.

 Although partial support modes are widely used, there is no evidence that they are superior to multiple daily T-piece trials. The most effective method of PVS is  targeted pressure support.

Patients are actively weaned from full to partial support, using an algorithm such as that below.

 

Prior to weaning, the patient will usually be on one of three modes of support: pressure (assist) control (PC), synchronized intermittent mandatory ventilation (SIMV) with pressure support (PS), or volume (assist) control (VC). All of these modes allow for spontaneous patient breathing, differing in the amount of control the patient has over the spontaneous breath. In all three modes the first priority is to reduce FiO2 to less than 60%, and to ensure that the patient is hemodynamically stable.

Weaning from  pressure control requires normalization of inspiratory times and reversal of neuromuscular blockade if present. The driving pressure is targeted to a tidal volume of 4 - 6ml/kg.

As oxygenation improves and lung compliance increases, in all modes of ventilation, the tidal volumes for any airway pressure will increase. Thus the peak airway pressure and the CPAP/PEEP level can be weaned. Most physicians will wean PEEP to 10cmH2O or less at this point. Pre-extubation, the PEEP level is usually 3-5cmH2O (unless the patient is obese). Remember, the mean airway pressure, the CPAP level and the FiO2 are the interventions which are targeted at oxygenation; the minute ventilation and, in particular, the rate, are targeted at ventilation. Thus as PaCO2 reduces, it is possible to reduce the control rate in each mode, until the patient is breathing spontaneously.

In SIMV + PS the control rate is reduced towards zero (the patient is on pressure support alone). Pressure assist control is  weaned to pressure support, the control rate is reduced towards zero (pressure assist) and then, if tolerated, the mode switched.

When weaning from a full support to a partial support mode it is important that you use a logical approach. For example, it makes no sense to wean from pressure assist-control to SIMV volume control with pressure support. If you are using pressure targeted ventilation, you should stay in pressure targeted ventilation.

The most popular partial support mode, worldwide, is SIMV (volume control) + Pressure Support. It is known that gradual reduction in control breaths in SIMV (without PS) is the poorest weaning method. It is my practice to use this mode only in post-operative patients, and as soon as the patient is breathing to switch to pressure support alone. The patient should have full ventilation assistance when on the mixed mode (the pressure support is set as the same as the driving pressure (plateau pressure minus PEEP) on the controlled breath.

CLICK HERE FOR WEANING & DISCONTINUATION ALGORITHM

         
                   
       

         
     

       
       

Please note: these tutorials are for personal study purposes only.  They are not currently peer reviewed, and no responsibility will be taken for mistakes or inaccuracies. Reproduction of information is forbidden. All material is copyrighted by the GasWorks Group.