Initial Ventilator Settings Flashcards
Initial Ventilator Settings
-One of the primary goals of mechanical ventilation is tio support the minute ventilation (Ve) to meet the oxygen and carbon dioxide requirements for PTs who cannot do so themselves
-This goal is accomplished by appropriate setting of the ventilator parameters -The main parameter for accomplishing this goal are tidal volume (Vt) and respiratory rate (f), which combines to provide the Ve
Minute Ventilation
-Normal Ve is about 5-6l/min depending on body size and oxygen consumption
-Predicted Ve for individuals with normal lungs and normal metabolic rates can be closely estimated: -For men 4 X surface area -For Women: 3.5 X body surface area -Body surface area (BSA) is obtained from DuBois nomogram -Ex Male with BSA of 2.1 2.1 * 4 = 8.4
Estimated Minute Ventilation
-The estimated Ve must be increased by 9% for every degree Celsius above normal (37 degrees C) when a Pt is hyperthermic, for Fahrenheit, Every degree above 99, must add 5% for every degree
-The estimated Ve must decreased by 9% for every degree C below normal when a PT is hypothermic, for F, every degree below 99, must add 5% for every degree -In the presence of metabolic acidosis, the Ve should ne increased by 20% -For seriously ill PT requiring MV, an initial setting of 1.5-2.0 times estimated Ve is frequently used Example: -A Physician orders a Tidal Volume of 500ml and a rate of 12 bpm for a 25 year old woman with a body surface area of 2.0. What is the estimated Ve -2.0* 3.5= 7
Ideal Body Weight (IBW)
-Estimate using IBW
-Men: 50+2.3( Height in Inches-60) -Women: 45.5 +2.3 (height in inches -60) -Remember, adult lungs do NOT get larger as he or she gains weight -Example: 5’10 Male 50+2.3(70-60) 50+2.3(10) 50+23=73kg -To Convert to Lbs multiply kg by 2.2
Tidal Volume (Vt)
-An estimated tidal volume is 6.8 ml/Kg of ideal body weight, we will use 6-8 ml/kg but can go up to 10 ml/kg if necessary
-The tidal volume should not exceed 10 ml/kg, since a greater volume will generate higher thoracic pressure and may result in barotraumas and or reduced venous return -The tidal volume should not be below 4 ml/kg of IBW if this minimum, limit is used, consider using sigh or lung recruitment maneuver and high PEEp -Note: Specific pathologies may use tidal volume of 4 ml/kg up to 10-15 ml/kg while maintaining a PPlat< 30 cmH20 -Example 5’10 Male From previous example we know IBW is 73kg - 73*6= 438 and 73* 8= 584 so 438-584
Respiratory Rate (f)
-f= Minute ventilation/Vt
-Example: -Ve=6.0 LPM (6000 ml) -Vt= 500 ml
-FiO2
–An initially high FiO2 of .5-1.0 is used to help relieve tissue hypoxia and or calculate shut
-This can be lowered after the first blood gas results are available -If a blood gas is available prior to beginning mechanical ventilation, then can be used to determine the FiO2 -FiO2 required= Desired PaO2 * known Fio2/ Known PaO2 -Example: desire PaO2=80, known FiO2=Room Air, known PaO2=60 80*.21/60=.28 or 28%
-Rule of Thumb: Pt currently on Oxygen… Set at same level prior to ventilation
-Clinical Example with Initial Ventilator Setting
-A 20 year Old female requires mechanical ventilation following a drug overdose. Breath sounds and chest x ray are normal. She is 5’2 tall and has a body surface area of 1.5
-Complete the initial vent settings for the following
-Ve=
-Kg IBW=
-IBW=
-Vt Range
-f Range
FiO2 =
-Ve=5.25
-Kg IBW= 50.1
-IBW= 110.22lbs
-Vt Range 300.6-400.8
-f Range 13-17.5
FiO2 = 50-100%
Inspiratory to Expiratory Ratio (I:E Ratio)
-An acceptable initial I:E ratio setting is 1:2
-Manipulating I:E ratio is a function of -Peak Flow -Increasing peak flow (turn knob to higher number) will decrease inspiratory time and Increase expiratory time -Decreasing peak flow (turn knob to lower number will increase the inspiratory time and decrease the expiratory time -Rate -increase rate = Increase Inspiratory time = decreased expiratory time =Decreases I:E -Decreased rate= decreased inspiratory time= increased expiratory time= decreased I:E -Tidal volume -Increased Vt= Invcreased Inpiratory time= decreased expiratory time= increased I:E -Decreased Vt= decreased Inspiratory time= increased E time= decreased !:E
Sensitivity
-Set so that the PT can easily trigger a breath
-Flow triggering -Set a range from 1 to 10 L/min below the base flow -Has a slightly faster response time compared to pressure triggering -Exhalation valve does not close -Flow of gas in the circuit during exhalation -Pressure triggering -Set below -1 and -2 cm H2O -Exhalation valve must close -Rule of Thumb (with pressure) - higher number = decreased sensitivity (harder) and takes more effort to trigger a breath
Inspiratory Pause
-also known as inflation hold
-Maneuver that can be performed by preventing the expiratory valve from opening for a short time at the end of inspiration, when the inspiratory valve is also closed -The inspiratory pause maneuver is used to obtain measurements of plateau pressure (Pplat), which allows estimation of the alveolar pressure for the calculation of static compliance -Inspiratory pause with each breath is not commonly used in clinical practice because it may significantly increase airway pressure and reduce pulmonary blood flow
Initial Ventilator Setting for the Pressure Control
-Determining Vt in pressure ventilation
-Measure Pplat and baseline pressure after initial volume triggered breath -Check Vt and adjust after initiating pressure ventilation at low pressure -If Pplat is not available, the peak pressure from VC-CMV minus 5 cm H20 (PIP -5 cm H20) -If volume reading are not available, an initial pressure of 10-15 cmH20 with close monitoring of volume measurement and adjustment/ titrates as appropriate to achieve Vt -Goal is less than equal to 35 cmH20
-All other parameters (f, I:E, sensitivity , FiO2 , peak flow, ect0 are set in the same manner as volume control ventilation
Mechanical Ventilator Alarms
-Designed to alert the clinician of potential dangers related to the PT ventilator interaction
-Action during ventilator alarm situation -Ensure the PT is being ventilated -When in doubt, disconnect and manually ventilate PT
-Common Alarms
-Pressure limit
-Pressure limit
-Set 10m-15 above peak pressure -High pressure alarm can be activated when the PT coughs, if secretions increase, compliance drops, increased RAW, pneumothorax, or there are kinks in the ET or circuit tubing -Low pressure -Low pressure alarm are usually set about 5-10 cm H2O below PIP -These alarms are useful for detecting Pt disconnections and leaks in the system, not enough flow, and endotracheal cuff leak
Common Alarms
Low PEEP/CPAP
-Low Peep/ continuous positive airway pressure (CPAP) alarms are usually set about 2 to 5 cm H2O below the PEEP level
-Activation of these latter alarms usually indicates the presence of a leak in the PT vent circuit
Common Alarms
-Apnea ALarm
-Apnea alarms are used to monitor mandatory or spontaneous breaths
-An apnea period of 20 seconds is the highest accepted maximum
-Common Alarms
-Low exhaled volume
-10% to 15% below set VT
-Good rule of thumb: 100 ml below exhaled Vt -Equipment disconnected (vent circuit) -Low spontaneous tidal volume
-Common Alarms
-Low Exhaled Minute Volume
-10% to 15% below average minute volume
-Common Alarms
-FIO2
-FiO2: 5% above and below set O2 percentage
-Other alarms are available for detecting low battery levels, if the vent is inoperative, ventilator circuit malfunction, exhalation valve leaks, and inappropriately set parameters
-Example
-A Pt who is being mechanically ventilated has received an MDI treatment inline with the vent circuit. Following the treatment, the low exhaled volume alarm is sounding. Why would this occur and how would you correct the problem?
-Answer
-The low exhaled volume alarm is most likely sounding from a leak in the system causing the loss in volume -Commonly after an MDI treatment is given the connection in the ventilator tubing may not be properly reconnected after removing the MDI. to correct this, you should inspect the circuit for loose connections and make fire they are tight
