Vent Modes Education and Explanation**Rule #1: Do not touch the vent.**Kindly ask your Respiratory Therapist to make the change for you.
IMV IMV stands for Intermittent Mandatory Ventilation – This mode of ventilation would deliver a breath based entirely on time. » If you set a rate of 12 a breath would be given every 5 seconds regardless of where the patient is in their breathing cycle – This is a mode of ventilation that is no longer used because it can cause over stretching and barotrauma.
IMV (continued) What can be set? – Rate – How often the patient receives a breath – Inspiratory Time/Flow – How quickly the patient receives the ventilator breath. Measured in Sec, or LPM – FiO2 – The Fractional inspired Oxygen from 21% - 100% – Pressure/Volume – The amount of pressure or the volume to be received. » Pressure measured in cmH2O – PEEP – Positive End Expiratory Pressure » Is used to distend the alveoli and thin the alveolar capillary (AC) membrane. » Improves the gas transfer for the oxygen into the capillary system. » Increases a patients functional residual capacity (FRC)
AC/VC Assist Control or Volume Control – Same mode of ventilation with a different name. – Every breath is the same, and a vent breath. – Takes all the work away from the patient. – May be a “first choice” mode of ventilation in other institutions. – Can predispose a patient to atelectasis due to no change in volume. – If: Patient is set at a rate of 12 and a Tidal Volume (Vt) of 500 but breathing 20 times per minute what is the patients Minute Ventilation (MV)?
AC/VC (continued) It would be 10 LPM because every triggered breath is a volume of 500 mL. The set rate is really a “back up” rate. If the patient is sedated the rate of 12 will kick in and the patient will receive a breath every 5 seconds at the desired I time or flow. Have to make sure the I time is adequate for their RR. Can easily become inversed if the patient is tachypneic.
AC/VC (continued) What can be set? – Rate – Inspiratory Time (I time) or Flow LPM – FiO2 – Volume – PEEP
PC Pressure Control – A pressure is set instead of a volume. – Every breath is still the same, and a “back up” rate is set. » Same: Pressure I time or Flow – Volume delivered is determined by the patients lung compliance. – Have to make sure the I time is adequate for their RR. Can easily become inversed if the patient is tachypneic.
So, what is lung compliance? Lung compliance is how easily a breath can be pushed into the lung. – Expressed as mL/cmH2O – Can be static or dynamic » Static is preferred What can decrease lung compliance – Bronchospasm – Inflammation – Pulmonary Edema – Mucus – Size of the endotube – Auto-PEEP – Pleural Effusion – Pneumonia – Pneomothorax – Anything that makes it more difficult to push a breath into a patient
SIMV SIMV stands for Synchronized Intermittent Mandatory Ventilation – This mode uses a microprocessor to determine where the patient is in their breathing cycle and will fit the breath at the beginning of inspiration or in-between spontaneous breaths – Much less likely to “stack breaths” and helps encourage comfort on the vent. – Patient will breath spontaneous volumes unassisted by the vent in-between the vent breaths.
SIMV VC What can be set? – Rate – Volume – I time or Flow – FiO2 – PEEP
SIMV PC What can be set? – Rate – Pressure – I time or Flow – FiO2 – PEEP
Now lets add PSV PSV or Pressure Support Ventilation – Is a pressure that augments a patients spontaneous breaths. – Is set as a pressure greater than the baseline PEEP. – Helps the patient overcome the resistance of the endotracheal tube. – Give the patient assistance for the work put in. – Volume of PS breath is completely determined by the patient effort. – Most all “modern” modes of ventilation can have PS. » Ie: SIMV VC + PSV, SIMV PC +PSV, SIMV PRVC + PSV
PRVC Pressure Regulated Volume Control – Combines the best of two modes of ventilation. » Allows the patient to breath in as much flow as they demand…..BUT Is delivered over a set I time. Set to a target volume. Pressure delivered will increase or decrease to lung compliance Is like having a therapist set the patient’s vent in PC and adjusting the pressure each breath to acheave the target volume. Every breath is a PRVC breath.
PRVC (continued) Not good for a patient who is breathing a lot spontaneously. – The vent has a difficult time reaching the target volume when the patient’s lung compliance is changing drastically due to spontaneous (negative pressure) breaths. – Works well when a patient’s overall respiratory rate is 20 or less, and their spontaneous volumes are about that of the set volume » Otherwise the patient could be under ventilated compared to set MV
PRVC (continued) At Sparrow hospital it is customary to place patients in SIMV PRVC+PSV. This allows the patients spontaneous breaths to be pressure supported while assuring a specific MV is achieved. – This mode of ventilation is only offered on the newest generation of vents (Servo I and Servo S), and is better than PRVC with assuring the set MV.
Normal Vent Settings Since the ARDS Net Study, hospitals around the country have been setting lower Vt to decrease mortality. – Normal: » Vt = 8-10 cc per Kg of Ideal Body Weight (IBW) » RR = 10-14 breaths per minute » FiO2 = Starts at 100% and weaned to pt tolerance » I time = Usually set by the RT at 1 sec Increased or decreased based off of graphics and pt comfort / respiratory cycle.
How To Change ABG’s With The Vent To increase PO2 – Increase FiO2 till it is 60% then consider increasing the PEEP. – Increase the PEEP » This will allow for recruitment of alveoli » This will thin the AC membrane » O2 exchange will become easier » Be Aware: Too high of PEEP can cause a decrease in venous return or tamponade the heart (decrease BP)
Changing ABG’s With The Vent (continued) Decrease PCO2 – Increase the rate » Increasing the rate increases the patients MV » Be Aware: Too high of a rate can cause air trapping especially in those with an obstructive lung disease. » Cuts into E time or the amount of time a patient has to exhale. – Increase the Vt. » This increases MV and is only recommended in patients with compliant lungs » Be Aware: Too high of a Vt will cause barotrauma and cytokine release.
HFOV (High Frequency Oscillation Ventilation) This is the simplest mode of ventilation, and it is placed on the sickest patients. Works like a speaker Is the only vent that works off of an active ventilation concept. – All other modes of ventilation we push the breath in and the patient passively exhales. – With the oscillator we push the breath in and pull the breath out with a piston.
HFOV (continued) Works well as an oxygenator, but not so well as a ventilator. Should be considered when a patients FiO2 is greater than 60% on a PEEP greater than 10cm H2O Only 4 things are set and control ventilation. – MAP (works like PEEP and is started 2-4cmH2O greater than that on the ventilator.
HFOV (continued)– FiO2 (amount of inspired O2. Normally set at 100% and weaned down)– The P or d P (this is where ventilation occurs) » Is initially set by increasing till there is jiggling in the mid thigh. (YES REALLY) This is called the Chest Wiggle Factor (CWF) » Please remember: Only about 20% of the actual pressure set makes it to the alveoli.– And finally the HZ. (1HZ = 60 cycles in a minute) » Is initially set between 3HZ and 6HZ » The Vt is determined by the amount of distance between peaks in the waves.
How To Change Your ABG With HFOV To increase PO2 – Increase the FiO2 – Increase the MAP » This will thin the alveolar wall and make it easier to move the O2 into the capillary system. » Be aware: Just like PEEP, the higher the setting the more likely for a decrease in venous return or tamponade of the heart to occur. (decrease BP)
Changing ABGs with HFOV (continued) To decrease PCO2 – Increase the P » This increases the venilatory pressure. – Decrease the rate » Wait a minute this goes against everything we know! » The oscillator is trapping gas in the lung, by decreasing the HZ we allow more time for CO2 to escape. (this increases the Vt) – As a last ditch the cuff can be deflated some to allow a leak and more CO2 to escape.
Good Luck Remember every patient is different – Just because a mode of ventilation works with most patients does not always make it a fit for all your patients. And lastly – If you have a question, please ask your Respiratory Therapist.