Mechanical Ventilation Modes and Settings

Posted on May 10, 2024 in Biology

Mechanical Ventilation Modes

Volume Assist/Control Ventilation (A/C)

  • Delivers a preset number of breaths at a preset tidal volume (VT).
  • When the patient initiates a spontaneous breath, the preset VT is delivered (VT does not vary).
  • The ventilator performs most of the work of breathing (WOB).
  • Useful in patients with normal respiratory drive but are weak or unable to exert adequate WOB.
  • Risk of hyperventilation and respiratory alkalosis.

Pressure Ventilation (P-A/C)

  • The ventilator delivers air until a preset pressure is reached (set respiratory rate).
  • Every breath is augmented by a set amount of inspiratory pressure.
  • If the patient triggers a breath, these breaths are enhanced with positive pressure. Only pressure stays the same – NOT the amount of volume.

Synchronized Intermittent Mandatory Ventilation (SIMV)

  • Delivers a preset number of breaths at a preset VT.
  • In between “mandatory” (preset) breaths, the patient may initiate spontaneous breaths; synchronized with the patient’s spontaneous breathing (allows the patient to breathe on their own).
  • Patient is able to breathe spontaneously between ventilator breaths, and the VT of spontaneous breaths varies.
  • Potential benefits:
    • Improved patient-ventilator synchrony
    • Lower mean airway pressure
    • Prevention of muscle atrophy
  • Same volume
  • (If a patient doesn’t reach a goal – the machine will help & give a breath!)

Volume Ventilation

  • Predetermined tidal volume (VT) delivered with each inspiration (amount of pressure needed to deliver each breath varies).
  • Tidal volume is the same with each breath – constant volume.

Pressure Ventilation

  • Patient takes breaths on their own or receives breaths from the machine.
  • Predetermined peak inspiratory pressure.
  • Tidal volume varies (allowing the patient to do more).
  • Must prevent hyper/hypoventilation.
  • Don’t have to breathe as deeply.
  • Not as sick.
  • Pressure support if tiring.

Ventilatory Support

  • Controlled ventilatory support → machine does all the work – ‘ventilator does all the WOB’
  • Assisted ventilatory support → machine + patient work together (if patient doesn’t do well on their own the machine kicks in) ‘ventilator & patient share WOB’

Mechanical Ventilation Settings

DOCUMENT always → all ventilators will have ‘these’ settings

  • RR (f) → usually 6-20 breaths/min
  • Tidal volume (VT) → usually 6-10 mL/kg “about 500 mL” → not based on weight but how tall the patient is. Taller patient = taller lungs (500-1000 mL).
  • FIO2 (fraction of inspired O2) → stays consistent & set between 21-100%.
  • PEEP (positive end-expiratory pressure) → end of expiration amount staying within lungs to keep alveoli open so they do not collapse.
  • Pressure support (PS) or pressure support ventilation (PSV)
  • I:E ratio (inverse I:E ratio → paralyze patient & inspiration will be longer than expiration – provide O2 as long as we can but chance build up increase CO2 because not expiring as long → “needs to be paralyzed”).
  • Inspiratory flow rate & time
  • Sensitivity
  • High-pressure limit
  • Expiration longer

PEEP

  • Usually setting 5 but may be set as high as 20 cm H2O (5-10 normal – if higher it is a lot of pressure to keep lungs open. HIGH # = stiffer lungs – we don’t want to see higher than 5-15).
  • Positive pressure applied at the end of expiration.
  • Keeps alveoli open & to facilitate O2 transport.
  • Recruits collapsed alveoli; prevents alveolar collapse (when alveoli & capillaries touch – if collapsed no oxygenation is happening).
  • Can cause reduced cardiac output if high & impedes venous return (goes to chest to get back to ♥). Works at the end of expiration.
  • Increase of PEEP may cause decreased BP – cut PEEP back down. Cardiac output may drop if PEEP is too high – blood return to the right side of the chest.

Data to Monitor During Mechanical Ventilation

Data to monitor during mechanical ventilation is not preprogrammed-

  • Exhaled tidal volume (EVT): should not be more than 50 mL difference from set VT.
  • Peak inspiratory pressure (PIP): amount of pressure it takes for the ventilator to deliver the tidal volume of breath (should be less than 40 mmHg) → want decreased pressure not increased – if increased lungs are stiff (may see in ARDS).
  • Total RR (important to look at): count total rate, which accounts for set rate & patient effort.
    • Everything will climb! Lungs blown = hemothorax.
    • Want exhaled & tidal to really be the same.
    • PIP increased? → talk to HCP & RT! = sign lungs aren’t compliant as they were.
  • I:E ratio: inspiration:expiration ratio. Normally 1:2. Longer = 1:4 in people with COPD to prevent breath stacking.
  • Minute ventilation: amount of gas moved in & out of lung per min (RR x TV = MV normal 5-8 L/min).
    • 12 bpm x .600 (or 600 TV) = 7.2 L/min

Alarms

 

HO – high = obstruction (biting tube, kinking, excessive secretions in tube, coughing, pulmonary edema) auscultation & assess situation 

LL – low = leak or loss of connection (cuff leak, ET tube displaced, disconnected) assess and fix situation if cannot call RT! 

High pressure patient agitated? Instruct client to calm down and allow ma CB one to breathe for them