Postoperative mechanical ventilation Flashcards
Review time: Shunt vs deadspace:
Deadspace: ventilation without perfusion (PE, trachea)
Shunt: blood is not being ventilated! 100% O2 can not overcome it
Controlled mechanical ventilation: How does it work? What determines the respiratory rate? What's fixed about it? Works independently of \_\_\_ Can the patient breathe spontaneously? Best used in which patients?
CMV:
The ventilator cycles from expiration to inspiration after a fixed time interval
The interval determines the respiratory rate
Fixed tidal volume and fixed rate; therefore fixed minute ventilation
Works independently of patient’s effort
The patient can not breathe spontaneously
Best used in patients with no respiratory effort (sedated/paralyzed)
Assist Control ventilation (AC)
It’s ___ ____ ventilation
What things are pre-selected?
What happens if the patient breathes?
What happens if there’s no inspiratory effort?
What are adverse effects and in who do they usually occur?
AC:
Postive pressure ventilation/Volume cycled
Each machine breath delivered has a pre-selected inflation volume, this pre-selected volume is delivered if the breath is initiated by either the patient or the machine.
Both volume and rate are pre-selected
If the patient breathes, the pre-selected volume will be given, if not-it will continue in control mode. Adverse effects happen in patients who are spontaneously breathing rapidly. Increased frequency of machine breaths can lead to over ventilation, hyperventilation, and respiratory alkalosis (Auto PEEP)
Intermittent Mandatory Ventilation
How does it work?
Does it allow spontaneous ventilation? What happens if a patient spontaneously breathes? What would make this synchronized?
What are disadvantages of IMV?
IMV:
Delivers periodic volume cycled breaths at pre-selected rates. Allows spontaneous ventilation between machine breaths, but spontaneous breathing from the patient does NOT trigger a machine breath. If the spontaneous breath triggers the scheduled machine breath, it is called SIMV. (synchronized-because machine breaths are synchronized to coincide with spontaneous lung inflation)
Disadvantages: increases the work of breathing, spontaneous ventilation occurs against a high resistance circuit, Could lead to respiratory muscle fatigue. It can reduce cardiac output in patients with LV dysfunction
Pressure controlled ventilation (PCV)
What things are set?
Lower ____ compared to volume cycled ventilation?
Ventilation is completely controlled by who?
What happens to inspiratory flow rate during lung inflation?
Advantages/disadvantages of PCV:
PCV:
Peak airway pressure and mandatory rate
Lower peak airway pressure compared to volume cycled ventilation
Ventilation is completely controlled by the machine
Inspiratory flow rate decreases exponentially during lung inflation
Advantages: decreased risk of barotrauma and volutrauma, reduces peak airway pressures and may improve gas exchange and oxygenation
Disadvantages: inflation volumes vary, patient must be heavily sedated or paralyzed to tolerate this mode.
Pressure support ventilation:
How does it work?
What’s set?
Allows patient to determine ___ and _____
Used to augment ______ and to overcome ________
When would you use this mode?
You could also use it with which mode?
Pressure support ventilation:
Pressure augmented breathing-at the onset of each breath, negative pressure generated by patient opens a valve that delivers inspired gas at pre-selected pressure, when patient’s inspiratory flow rate falls below 25% of the peak inspiratory flow, the augmented breath is terminated.
Peak airway pressure is set
Allows patient to determine inflation volume and respiratory cycle duration
Used to augment tidal volume of spontaneously breathing patients and overcome any increased inspiratory resistance from the ETT, breathing circuit, and ventilator.
I would use this mode to augment inflation volumes during spontaneous respiration, or to overcome resistance of breathing through ventilator. It can be used with IMV to decrease work of breathing imposed by circuit and machine.
PEEP: How does it work? What does this improve? What physiologic effects does PEEP have? How can PEEP help with oxygen toxicity? PEEP is also good for which states? pros/cons of PEEP:
PEEP
A pressure limiting valve is placed in expiratory limb of ventilator circuit
Positive pressure is applied during expiration
Improves gas exchange (decreases shunt) and makes lungs more compliant.
Physiologic effects: cardiac filling and cardiac output are hampered due to pressure in thoracic cavity having a negative effect on venous return.
Addition of PEEP can increase arterial and systemic oxygenation and allow reduction of inhaled oxygen to less toxic levels.
Also good for low volume ventilation and obstructive lung disease.
Pro: increase in FRC, improved compliance, correction of vent/perf abnormalities
Cons: Barotrauma (PTX, penumomediatstinum), decreased venous return, decreased cardiac output.
CPAP: How does it work?
Does the patient have to generate a negative pressure?
What are indications for CPAP?
Spontaneous breathing in which positive pressure is maintained throughout respiratory cycle. Positive pressure is applied during inspiration and expiration during spontaneous breathing. Patient does NOT have to generate a negative pressure to receive the inhaled gas. Indications: OSA, acute respiratory failure (to postpone intubation ), Acute exacerbation of COPD
