Mechanical ventilation Flashcards
What happens to normal preload during PPV?
reduced through two mechanisms:
-pressure differential between the abdomen and thorax is decreased
-get decreased venous return
-transmural pressures across ventricular wall change
-decreased compliance and decreased filling
How is decreased compliance depicted graphically on a volume control setting?
higher airway pressure per set Tv
How is decreased compliance depicted graphically on a pressure control setting?
lower tidal volume for given set pressure
Which triggering method is typically the default for most ventilated patients?
flow triggering- ventilator senses changes in inspiratory flow to initiate delivered breaths
What is the normal I:E ratio of a non-ventilated patient?
1:2 or 1:3
-inspiration is an active process, exhalation is a passive one
-remember in COPD and asthma exacerbations this is prolonged and needs to be adjusted
Which patient groups should you avoid permissive hypercapnia?
TBI and obstructive lung pathology
What vent changes can you make to make the I:E longer?
-increasing inspiratory flow
-decrease RR
-decrease Tv
What are advantes to a longer I:E? A disadvanage?
-prevents alveolar collapse
-improves gas exchange
-increases PO2
-also increases PCO2
In most patients what flow rate delivers adequate gas exchange?
60L/min
What type of flow time curve is seen for patients on a volume control setting? For pressure control?
-square wave
-descending ramp (increases inspiratory time)
On a pressure-volume curve what does the slope of the line represent?
compliance
What does the lower inflection point on a pressure-volume curve represent? The upper inflection point?
point where resistance to the patient’s airway is overcome
-shifts to the right if resistance is high
-the critical opening pressure of alveoli
point of maximal alveoli distention
PEEP should be set between these two points
How can you estimate the amount of auto PEEP occuring in a mechanically ventilated patient?
expiratory pause at the end of expiration (only if pt not breathing spontaneously)
On a flow/time curve how is auto-PEEP detected?
the expiratory flow curve does not return to 0 before the next breath is delivered
In VC mode what determines the airway pressures?
lung compliance
What is the equation for predicted body weight (PBW)?
female = 45.5 + 2.3[height(inches) - 60]
male = 50 + 2.3[height(inches) - 60]
female = 45.5 + 0.91[height(centimeters) - 160]
male = 50 + 0.91[height(centimeters) - 160]
What determines a patient’s plateau pressure?
lung compliance
How is plateau pressure checked?
ventilator pause and pressure check at the end of inspiration
What is the ARDSNet goal for plateau pressure?
< 35cmH2O
Why is hypercapnia detrimental to TBI patients?
elevated PCO2 leads to cerebral vasodilation which causes an elevation in intracranial pressures
What does SIMV stand for?
synchronized intermittent mandatory ventilation
What should be the main strategy for correcting hypoxia in a ventilated patient?
increasing the FRC
-due through manipulation of mean airway pressure (via increasing PEEP or delta P on PC, or by lengthening inspiratory time on I:E)
What should be the main strategy for correcting low PCO2 in a ventilated patient?
decrease RR or decrease Tv
What should be the main strategy for correcting hypercapnia in a ventilated patient?
increase RR if not already tachypneic
What can the high mean airway pressure alarm mean?
issues w/ lung compliance or airway problems
What does an increase in peak inspiratory pressure relative to plateau pressure signify?
an issue with the airway itself
-ventilator tubing issue
-upper airway obstruction (bronchospasm or increased secretions)
What does an elevation in plateau pressure relative to peak inspiratory pressure reflect?
issue with compliance
What are some examples of causes of decreased compliance?
-PTX
-ACS
-ARDS
-PNA
-auto-PEEP dyssynchrony
What are some disadvantages to using propofol for sedation in a ventilated patient?
-respiratory depression
-hypotension
What are some disadvantages to using dexmedetomidine for sedation in a ventilated patient?
-bradycardia
-hypotension
What is the MOA of propofol?
GABA receptor binder
What is the MOA of dexmedetomidine?
alpha 2 receptor agonist
Above what value for minute ventilation is spontaneous respiration unlikely to meet the metabolic demand?
10L/min (to know for weaning/extubation)
What percent of patients who have intubated for >36hrs have laryngeal edema?
5-22%
What percent of patients requiring mechanical ventilation die before discharge?
30-40%
What is a Mallampati class 1 view?
uvula and soft palate are fully visible
What is a Mallampati class 2 view?
hard and soft palate and upper portion of the uvula are visible
What is a Mallampati class 3 view?
soft and hard palate and base of uvula are visible
What is a Mallampati class 4 view?
only the hard palate is visible
How is compliance measured?
delta V / delta P
What are some complications of oxygen toxicity d/t high FiO2 settings and hyperoxia?
-interstitial fibrosis
-atelectasis
-tracheobronchitis
What does APRV stand for?
airway pressure release ventilation
What are some of the physiologic benefits to APRV?
-increased cardiac return
-improved oxygenation
-decreased sedation requirements
-improved lung aeration
What is the basic method to wean APRV?
Lower Phigh and lengthen Thigh
Which of the SBT parameters is the most sensitive and specific predictor of extubation success?
RSBI
-sens 97%
-spec 78%
What are risk factors for reintubation after extubation?
-age > 65
-cardiac failure as a cause of resp failure
-APACHE score > 12 on day of extubation
What is the 3-3-2 rule for intubation?
-3 fingerbreadths between the upper and lower teeth of an open mouth
-3 fingerbreadths from anterior tip of mandible to anterior neck (hyoid-mental distance)
-2 fingerbreadths between floor of mandible to thyroid notch on anterior neck (hyoid-thyroid cartilage distance)
What is the calculation to determine ETT depth?
Chula formula
-ETT depth = 0.1(height in CM) +4
Which patients are poor candidates when considering inverse ration ventilation?
those w/ COPD
-have increased risk of auto-PEEP
-want to do the opposite and increase expiratory time
What is the function of adding PEEP to mechanical ventilation?
-increases alveolar surface area
-increases FRC
-increases PaO2
-decreases shunt fraction
-decreases hypoxic pulmonary vasoconstriction
-decreases cardiac output ( > 15)
-no change in PaCO2 or pH
What is APRV?
-airway pressure release ventilation
-inverse ratio, pressure-controlled, intermittent mandatory ventilation
-allows spontaneous breathing
What does phase 1 of capnogram (baseline) represent?
baseline inspired gas, normally devoid of CO2
What does phase 2 of capnogram (upslope) represent?
-expired air
-displays the transition from dead space air flow to alveolar air flow
What does phase 3 of capnogram (upper plateau of square wave) represent?
-partial pressure of CO2 exchanged at alveoli
-represents EtCO2
What does phase 4 of capnogram (down slope) represent?
-inspiratory point in the ventilation cycle
-displays the transition from alveolar air flow to fresh air flow
How do you calculate the airway resistance in a mechanically ventilated patient?
airway resistance = peak pressure - plateau pressure
What driving pressure is strongly correlated to VILI?
driving pressure > 15
(driving pressure = plateau pressure - PEEP)
