MECANICAL VENTILATORPresented by

sangeethasasidharan

INTRODUCTION TYPES OF MEDICAL VENTILATOR MODES OF MECHANICAL VENTILATION VENTILATOR ALARMS GUIDE LINES FOR VENTILATOR SETTING

Overview of topics

Helps patients breathe by assisting the inhalation of oxygen into the lungs and the exhalation of carbon dioxide. Depending on the patient’s condition, mechanical ventilation can help support or completely control breathing.

INTRODUCTION

The two main categories of ventilators include:

Noninvasive ventilators  These devices provide breathing support through an

external interface, such as a mask or nasal prongs.

Invasive ventilators  Patients on long-term ventilation may require ventilation

through an endotracheal tube inserted through the mouth or nose, or through a tracheostomy tube inserted into an incision in the in the neck.

VENTILATOR TYPES

RATE VOLUME SENSITIVITY FLOW LIMITS MEASURES OF BREATHING

VENTILATOR TERMS

VENTILATOR SETTINGS

FiO2RateTidal volumeSensitivityPeak flowInspiratory and expiratory timesCyclinglimit

ASSIST CONTROL (AC) Continuous positive airway pressure

ventilation(CPAP) Synchronized intermitted mandatory

ventilation(SIMV) Pressure control ventilation(PCV) Pressure support ventilation(PSV or PS) Positive end expiratory pressure(PEEP)

VENTILATOR MODES

All breaths delivered by the ventilator will control either volume or pressure. The ventilator delivers the same measured breath every time, whether the breath is patient initiated or ventilator initiated, based on the rate setting.

ASSIST CONTROL

This mode also allows the patient to breathe at a continuous, elevated airway pressure that can improve oxygenation

The ventilator can also apply positive pressure during spontaneous inspirations taken during CPAP mode to reduce the patient’s work to breathe.

CONTINUOUS POSITIVE AIRWAY PRESSURE VENTILATION

The ventilator synchronizes machine breath delivery with the patient’s spontaneous breath efforts. This mode is a combination of set mandatory machine breaths synchronized with the patient’s own spontaneous breaths.

SYNCHRONISED INTERMITTED MANDATORY VENTILATION

This is a type of mandatory breath that can be used in either A/C or SIMV modes and targets a specific pressure during inspiration. The delivered flow rate varies according to the patient’s demand and own lung characteristics, such as lung compliance and airway resistance.

PRESSURE CONTROL VENTILATION

This is a type of spontaneous breath that can be used in either CPAP or SIMV modes and targets a set inspiratory pressure, much like PC. But the PS inspiration ends as the lung gets full and the delivered flow decreases to a specific valve set by the clinician. The patient decides the respiratory rate and inspiratory time as well as the flow rate and tidal volume.

PRESSURE SUPPORT

Mechanical positive pressure is applied at the end of exhalation to prevent the lungs from emptying completely and returning to a “zero” reading. The benefit of positive pressure at the end of exhalation is increased lung volume for improved oxygenation.

POSITIVE END EXPIRATORY PRESSURE

High airway pressure alarms Low airway pressure alarms High and low rate alarms High and low volume alarms

VENTILATOR ALARMS

Mode of ventilation Tidal volume Respiratory rate Supplemented Oxygen therapy I:E ratio Inspiratory flow rate Peep sensitivity

GUIDE LINES FOR VENTILATOR SETTING

SIMV and A/C are versatile modes that can be used for initial settings. In patients with a good respiratory drive and mild-to-moderate respiratory failure, PSV is a good initial choice.

Mode of ventilation

An initial TV of 5-8 mL/kg of ideal body weight is generally indicated.

the lowest values recommended in the presence of obstructive airway disease and ARDS

Tidal volume

A respiratory rate (RR) of 8-12 breaths per minute is recommended for patients not requiring hyperventilation for the treatment of toxic or metabolic acidosis, or intracranial injury. High rates allow less time for exhalation, increase mean airway pressure, and cause air trapping in patients with obstructive airway disease. The initial rate may be as low as 5-6 breaths per minute in asthmatic patients when using a permissive hypercapnic technique.

Respiratory rate

The lowest FiO2 that produces an arterial oxygen saturation (SaO2) greater than 90% and a PaO2 greater than 60 mm Hg is recommended. No data indicate that prolonged use of an FiO2 less than 0.4 damages parenchymal cells.

Supplemental oxygen therapy

The normal inspiration/expiration (I/E) ratio to start is 1:2. This is reduced to 1:4 or 1:5 in the presence of obstructive airway disease in order to avoid air-trapping (breath stacking) and auto-PEEP or intrinsic PEEP (iPEEP). Use of inverse I/E may be appropriate in certain patients with complex compliance problems in the setting of ARDS.

I:E RATIO

Inspiratory flow rates are a function of the TV, I/E ratio, and RR and may be controlled internally by the ventilator via these other settings. If flow rates are set explicitly, 60 L/min is typically used. This may be increased to 100 L/min to deliver TVs quickly and allow for prolonged expiration in the presence of obstructive airway disease.

INSPIRATORY FLOW RATE

Applying physiologic PEEP of 3-5 cm H2 O is common to prevent decreases in functional residual capacity in those with normal lungs. The reasoning for increasing levels of PEEP in critically ill patients is to provide acceptable oxygenation and to reduce the FiO2 to nontoxic levels (FiO2 < 0.5). The level of PEEP must be balanced such that excessive intrathoracic pressure (with a resultant decrease in venous return and risk of barotrauma) does not occur.

PEEP

With assisted ventilation, the sensitivity typically is set at -1 to -2 cm H2 O. The development of iPEEP increases the difficulty in generating a negative inspiratory force sufficient to overcome iPEEP and the set sensitivity. Newer ventilators offer the ability to sense by inspiratory flow instead of negative force. Flow sensing, if available, may lower the work of breathing associated with ventilator triggering.

SENSITIVITY

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