03-01-2013, 10:25 AM
VENTILATOR
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Introduction:
In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows.
There are two main divisions of mechanical ventilation: invasive ventilation and non-invasive ventilation. There are two main modes of mechanical ventilation within the two divisions: positive pressure ventilation, where air (or another gas mix) is pushed into the trachea, and negative pressure ventilation, where air is essentially sucked into the lungs.
Types of Ventilators:
Ventilators come in many different styles and method of giving a breath to sustain life. There are manual ventilators such as Bag valve masks and anesthesia bags require the user to hold the ventilator to the face or to an artificial airway and maintain breaths with their hands.
Mechanical ventilators are ventilators not requiring operator effort and are typically computer controlled or pneumatic controlled.
• Transport ventilators — these ventilators are small, more rugged, and can be powered pneumatically or via AC or DC power sources.
• Intensive-care ventilators — these ventilators are larger and usually run on AC power (though virtually all contain a battery to facilitate intra-facility transport and as a back-up in the event of a power failure). This style of ventilator often provides greater control of a wide variety of ventilation parameters (such as inspiratory rise time). Many ICU ventilators also incorporate graphics to provide visual feedback of each breath.
• Neonatal ventilators — designed with the preterm neonate in mind, these are a specialized subset of ICU ventilators which are designed to deliver the smaller, more precise volumes and pressures required to ventilate these patients.
• Positive airway pressure ventilators (PAP) — these ventilators are specifically designed for non-invasive ventilation. This includes ventilators for use at home for treatment of chronic conditions such as sleep apnea or COPD.
Breathe delivery:
Trigger:
The trigger is what causes a breath to be delivered by a mechanical ventilator. Breaths may be triggered by a patient taking their own breath, a ventilator operator pressing a manual breath button, or by the ventilator based on the set breath rate and mode of ventilation.
Cycle:
The cycle is what causes the breath to transition from the inspiratory phase to the exhalation phase. Breaths may be cycled by a mechanical ventilator when a set time has been reached, or when a preset flow or percentage of the maximum flow delivered during a breath is reached depending on the breath type and the settings. Breaths can also be cycled when an alarm condition such as a high pressure limit has been reached, which is a primary strategy in pressure regulated volume control.
Limit:
Limit is how the breath is controlled. Breaths may be limited to a set maximum circuit pressure or a set maximum flow.
Function:
The ventilator forces a mixture of air and oxygen into the lungs periodically to enable and assist in the vital transfer of gases into and out of the blood via the lungs when the patient is unable to breathe correctly on their own. It mixes oxygen and air to required levels and then delivers it to the patient via special tubing called a “breathing circuit”. The gas from the ventilator is humidified and heated in the breathing circuit before it goes to the patient. The ventilator increases the pressure in the breathing circuit so that the air is pushed into the lungs for inspiration.
The ventilator reduces the pressure so that the air in the lungs can be expired and the expired air is vented to atmosphere. Numerous ventilator parameters are adjustable and are determined by the doctor prior to attachment and during operation on the patient. All ventilator settings are made by Rotary dial. Flow and pressure are continuously measured by transducers and controlled by a feedback system in the Patient unit. The information is compared with the user interface settings, and a difference between the actual measured value and the preset/calculated values will cause adjusted gas delivery according to the target Flow/Volume/Pressure. Ventilator has two gas modules, one for Air and one for Oxygen. Gas can be connected from Medical Pipeline system, a compressor or gas Cylinders. Air can be supplied by a Compressor.
Modes of Ventilator:
The ventilator provides the following ventilation breath types:
• Volume Control Ventilation (VCV) – invasive ventilation
• Pressure Control Ventilation (PCV) – invasive ventilation
• Non-Invasive Positive Pressure Ventilation (NPPV) – non-invasive ventilation
During mechanical ventilation, the operator selects one of the ventilation modes. The selected ventilation breath type, along with the selected mode, the patient breathing effort, and the ventilator settings determine the type of breath delivered. Each ventilation breath type has its own settings, alarms, and monitor screens.
Volume Control Ventilation (VCV):
In Volume Control Ventilation, breaths may be controlled by the ventilator (mandatory) or triggered by the patient (spontaneous). When controlled by the ventilator, breaths will be flow controlled and time cycled, thus delivering an operator (TIDAL VOLUME) set volume. In Volume Control Ventilation, the flow pattern can be selected between square and descending ramp waveforms.
Aim of this mode:
1. Provide some mandatory, volume controlled breaths according to reset values.
2. Give the patient inspiratory pressure support during spontaneous breaths.
3. Deliver mandatory breaths (SIMV breaths) with preset tidal/volume and a preset respiratory rate independent of changes in resistance / compliance.
4. Provide a constant flow for the mandatory breaths.