Mechanical Ventilation PDF

 As inspiration occurs the alveoli expands to allow the air in. Gas exchange can then take place as the blood supply moves past the wall of the alveoli.  During expiration the alveoli contracts down. It does not completely collapse, partly due to the presence of a substance ca...

 As inspiration occurs the alveoli expands to allow the air in. Gas exchange can then take place as the blood supply moves past the wall of the alveoli.  During expiration the alveoli contracts down. It does not completely collapse, partly due to the presence of a substance called surfactant. This decreases the surface tension within the alveoli ensuring that complete collapse cannot take place.  Unfortunately, ventilation of a patient tends to inactivate the pulmonary surfactant which then leads to collapse of the alveoli , making gas exchange more difficult as the surface area of the lung is now reduced.  The ventilator also causes an increase in alveolar capillary permeability and causes the activation of inflammatory cells and the release of cytokines  Normal ventilation Diaphragm contracts. Negative pressure in chest cavity draws in air.  Positive pressure ventilation Generated by a device. Forces air into the chest cavity from the external environment.  With positive pressure ventilation, more air is needed to achieve the same effects of normal breathing. 1. Increases overall intrathoracic pressure 2. Blood flow is decreased  Cardiac output is a function of stroke volume multiplied by the pulse rate.  Normally, when a person breathes, air enters the trachea. ◦ Ventilations that are too forceful can cause gastric distention.  Non-Invasive Ventilation (NIV) ▪ Non-invasive ventilation refers to the delivery of mechanical ventilation to the lungs using techniques that do not require an artificial airway  Invasive Ventilation (IV) ▪ Invasive ventilation refers to a life support system designed to replace or support normal ventilatory function utilizing an artificial airway  Patient who is not breathing needs artificial ventilation and 100% supplemental oxygen. ◦ Indications include signs of:  Altered mental status  Inadequate minute volume o Relieve symptoms. o Reduce work of breathing. o Improve or stabilize gas exchange. o Improve duration and quality of sleep. o Enhance the quality of life. o Prolong survival. o Provide cost effective care. o Improve or sustain physical and psychological function.  There are five categories of pulmonary problems which may progress to the need for mechanical ventilatory support. These are: 1. Central nervous system problems which depress the drive to breathe (e.g., cerebrovascular accident). 2. Neuromuscular problems which lead to the failure of the peripheral nerves and muscles that aid respirations (e.g., multiple sclerosis). 3. Musculoskeletal and pleural dysfunctions (e.g., flail chest). 4. Problems with the airways themselves (e.g., asthma). 5. Reduction in the ability to exchange gases (e.g., pneumonia). 1. Tidal Volume 2. PEEP 3. Mode (type of assist given by vent) 4. Rate (Breaths per minute.) (Adjusted based on patient’s own respiratory rate) 5. FiO2 (amount of O2 being delivered)  There are three primary types of ventilators currently in use. Each specific type adjusts the flow of air into the patient, based on one of three cycles.  Pressure cycled ◦ Flow is shut off when a preset amount of pressure in the lungs is reached.  Time cycled ◦ Flow is shut off when a preset time limit is reached.  Volume cycled ◦ Flow is shut off when a preset amount of volume is reached.  Ventilator Settings summary S.No. SETTING FUNCTION USUAL PARAMETERS Respiratory Rate (RR) Number of breaths delivered 1. Usually 4-20 breaths per minute by the ventilator per minute Tidal Volume (VT) Volume of gas delivered 2. Usually 5-15 cc/kg during each ventilator breath Fractional Inspired 21% to 100%; usually set to keep Amount of oxygen delivered 3. PaO2 > 60 mmHg or SaO2 > Oxygen (FiO2) by ventilator to patient 90% Inspiratory:Expiratory Length of inspiration Usually 1:2 or 1:1.5 unless 4. compared to length of inverse ratio ventilation is (I:E) Ratio expiration required Maximum amount of 10-20 cm H2O above peak 5. Pressure Limit pressure the ventilator can inspiratory pressure; maximum use to deliver breath is 35 cm H2O S.No. MODE FUNCTION CLINICAL USE Delivers preset volume or pressure Control Usually used for patients who are 1. regardless of patient’s own Ventilation (CV) apneic inspiratory efforts Delivers breath in response to Usually used for spontaneously Assist-Control 2. patient effort and if patient fails to breathing patients with weakened Ventilation (A/C) do so within preset amount of time respiratory muscles Synchronous Intermittent Ventilator breaths are synchronized Usually used to wean patients 3. Mandatory with patient’s respiratory effort from mechanical ventilation Ventilation (SIMV) Preset pressure that augments the Pressure Support Often used with SIMV during 4. patient’s inspiratory effort and Ventilation (PSV) weaning decreases the work of breathing Positive End Used with CV, A/C, and SIMV to Expiratory Positive pressure applied at the end 5. improve oxygenation by opening Pressure of expiration collapsed alveoli (PEEP) Constant Positive Maintains constant positive Similar to PEEP but used only with 6. Airway Pressure pressure in airways so resistance spontaneously breathing patients (CPAP) is decreased Ventilates each lung separately; Used for patients with unilateral Independent Lung 7. requires two ventilators and lung disease or different disease Ventilation (ILV) sedation/paralysis process in each lung Used for hemodynamic High Frequency Delivers small amounts of gas at a instability, during short-term 8. Ventilation rapid rate (60-100 breaths/minute); procedures, or if patient is at risk  Steps for using: ◦ Attach to wall-mounted oxygen source. ◦ Set tidal volume and ventilatory rate. ◦ Connect to fitting on ET tube or airway device. ◦ Auscultate breath sounds and observe chest rise. Courtesy of Impact Instrumentation, Inc.  Have bag-mask device available in case ATV malfunctions.  Most models have adjustments for respiratory rate and tidal volume. ◦ Deliver a preset volume at a preset rate.  Generally consumes 5 L/min of oxygen  Pressure-relief valve can lead to: 1. Hypoventilation 2. Increased airway resistance 3. Airway obstruction  Patients with spontaneous breathing and having dyspnea or respiratory compromise need assistance to improve airflow and oxygenation.  Methods to improve patient's arterial oxygenation 1. Continuous positive airway pressure (CPAP) 2. Biphasic positive airway pressure (BiPAP)   CPAP and BiPAP purpose 1. Improve oxygenation through positive pressure during ventilation. 2. Reduce work of breathing. 3. Prevent atelectasis. 4. Allow for drug administration. 5. May prevent need for intubation and risks and complications associated with invasive airway procedures. CPAP Machine  Composed of a flow generator that pushes positive pressure into a tube that connects to a mask.  The mask is placed on the patients nose and/or mouth, where the air enters and then continues to the throat keeping the upper airway open.  Mechanism: 1. Increases gas exchange 2º to increased alveolar ventilation. 2. Prevents alveolar collapse during exhalation by maintaining a positive intra-alveolar pressure. 3. ↑’s intrathoracic pressure, reducing preload/afterload and improving cardiac output.  Patient exhales against a resistance (positive end-expiratory pressure [PEEP]). ◦ Controlled manually or predetermined. ◦ 5 to 10 cm H2O is general therapeutic range.  Some units use a continuous flow of oxygen; others use oxygen on demand.  Some newer units allow you to adjust FIO2.  Continuously monitor available oxygen.   Facial trauma  Unable to follow verbal commands  Cardiogenic shock  Respiratory arrest or agonal respirations  Tracheostomy  Unable to speak  GI bleeding, nausea, or  Hypoventilation vomiting  Hypotension  Recent GI surgery  Pneumothorax or chest trauma  Unable to sit up  Closed head injury  Unable to fit CPAP system  Cannot tolerate mask  Patients may feel claustrophobic and resist.  High volume of pressure can cause a pneumothorax.  Increased pressure in the chest cavity can result in hypotension.  Air may enter the stomach.  Irritation to skin and eyes.  Nasal congestion.  Dry nose, epistaxis.  Sore throat.   General guidelines Explain procedure to patient. Anticipate and control anxiety (consider sedation with benzodiazepines, per protocol). Provide coaching as needed. Connect CPAP to O2 source; begin CPAP pressure at 5 to 7.5 cm H2O. Apply mask and check for air leaks; use head straps if needed and if tolerated by patient. Administer nebulized medications as indicated. Treatment should be given continuously throughout transport to emergency department.  In prehospital setting, ventilatory support with PEEP can be provided through PEEP valve. ✓ – Hollow cylinders that contain weight in their lumens. ✓ – Connected to expiratory port of a bag‐valve device. ✓ – Available in pressures of 5, 10, and 15 cm H2O. ✓ – Creates PEEP by forcing patient to exhale against weight of metal ball. ✓ – Some transport ventilators have built‐in PEEP controls.  Begin at about 5 cm of H2O & increase in steps of 2 cm H2O until optimal PEEP is achieved– i.e, 1. PaO2>60,FiO2