Ventilators

Usage

. When patient is incapable to adequte ventilation by the natural process:

 .Insure that sufficient O2  delivers to the organs & tissues(PO2 in the blood within normal range).

  .Excessive levels of CO2 are wasted (PCO2 in the blood within normal range).

                                                                       Principle

.Applying Positive  pressure during inspiration.

.Recoiling of the chest muscle during expiration.

                                                              Ventilators can be used to:

.Control the breathing process (Patient who are unable to control his breaths ).

.Assist in the breathing process (Patient who are able to control his breaths but couldn't inhale  a   sufficient a mount of air).

.Controller –assistance.

                       

                                                             Definitions (Figure)

.Tidal Volume (T.V): it is the volume of gas inspired or expired during each normal   breathing cycle.  

.Respiration rate ( frequency ):it is the number of breathing cycle in one minute.

.Minute Volume :it is the Tidal volume multiplied by respiration rate ( T.V* R.R).

.Flow: it is the change of volume during one breath cycle. 

.Pause :Time between the insp. time & exp. Time.

.FiO2 :Fractional concentration of O2 in the delivered mixture (air & O2).

.I:E ratio: Ratio between the inspiration time And expiration time.

.PO2:Partial pressure of  O2   in the blood.

.PCO2: Partial pressure of  CO2   in the blood

.Baseline Pressure (Pbase): the Minimum value of airway pressure refers to the dead space   pressure.

                                                         Ventilation Types

.Pressure Control:

The main Parameter to be control is the pressure of the airways.

.Volume Control :

The main parameter to be control is the Tidal volume.

.Volume Target Pressure Control:

 Trying to control the Airways Pressure &same time  Tidal Volume.

                                                          Modes of Ventilation

The mode is the way to deliver  a certain ventilation type.

There are a lot of modes.

The main modes are :

Control Mandatory ventilation (CMV).

Assist-control Ventilation (ACV)

Synchronized Intermittent mandatory ventilation (SIMV).

Spontaneous ventilation (support) (Spont.).

                             Control Mandatory Ventilation (CMV)

Patient Receive a full ventilator breath.

Machine control the patient breath &does not respond to his effort.

Patient does not trigger the machine.

                               Assist – Control Ventilation(ACV)

Patient Receive a full ventilator breath.

Machine controls the patient breath and responds to his effort.

Patient triggers the machine.

Machine start the breathing cycle when the patient is ready. 

This mode is safe for patient.

          Synchronized Intermittent Mandatory ventilation (SIMV).

Patient Receive Mandatory ventilator breaths& he can breath spontaneously (with its own T.V) between these breaths.

Machine deliver these Mandatory breaths intermittently.

After each Mandatory breath machine start  a timing window and waits for any patient’s spontaneous breath if there is not ,it start anther  mandatory one.

                         Spontaneous ventilation (support) (Spont.).

In this mode machine works as assistance only no mandatory breaths delivers to patient.

Machine support the patient’s own breaths by rising the air way pressure to certain set value.

                                                                      PEEP

PEEP is abbreviation of Positive End of  expiratory pressure.

Means keeping the airway pressure always positive at the end of the expiration.

Can be set with any mode. 

It is not a mode and used only to increase the diffusion of the O2 through the alveoli.

It is equal to Baseline Pressure of the lung (Dead Space Pressure).

                                                             CPAP

CPAP is abbreviation of continuous Positive airway pressure.

It is set in the spontaneous mode.

Rising the baseline pressure (PEEP) to 1.5 cmH2O above the set value. 

No air being pushed by the machine.

Ventilator are drivered either Pneumatically or Electrically or Both of them.

 

                                                       Pressure Transducer

Mechanical transducers ex. gauge(figure).

Gauge:

Burdan gauge 

                                                         Electrical transducers 

Strain gauge:

Change in pressure lead to change in shape  lead to change in resistance lead to change in voltage of the bridge .

                                                     Flow transducers

VENTURI METHOD:

By using the Pernoli’s equation:

Flow =velocity*area.

Velocity  related to the differential pressure in the VENTURI

                                                          Flow Transducer

Thermistors flow meter:

2 thermistor ,one in the airflow &other one in gas dead space.

O2 Concentration Transducer                                                 

                             

Chemical cell diffution of   increase the conductivity of the aqueous solution.

Simple diagram of the ventilator 

inspiration part

Expiration part

                                        Newport  Ventilator

American company has its name in the market.

Have many models :e500,e100,e150,HT50