Respiratory

Ventilation Terminology

Terminology

 

  1. Continuous positive airway pressure (CPAP) – the delivery of continuous level of positive airway pressure.
    • Functionally similar to positive end expiratory pressure (PEEP), the ventilator does not cycle during CPAP
    • No additional pressure above the level of CPAP is provided
    • Patients must initiate all their own breaths.
    • Most often used for obstructive sleep apnea.

 

  1. Bilevel positive airway pressure (BPAP/BiPAP)- bilevel positive airway pressure is a mode used during noninvasive positive pressure ventilation (NPPV).
  • BPAP delivers a preset inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP)
  • Tidal volume correlates with the difference between IPAP and EPAP.
  • BPAP offers several advantages compared to CPAP.
    • Notably it is an active ventilation rather than solely pneumatic splinting of the upper airway.
    • A lower mean airway pressure (which means it is often tolerated better)
    • Allows for rest of ventilator muscles
    • Quicker resolution of respiratory acidosis
    • However, it does have an issue with asynchrony

 

  1. Assist Control (A/C) – physician determines minimal minute ventilation by setting respiratory rate and tidal volume.
  • Patient can trigger additional breaths, which are delivered with the same tidal volume as the previous breaths. 

 

  1. Synchronized Increased Minute Ventilation (SIMV) –SIMV delivers a minimum number of fully assisted breaths per minute that are synchronized with the patient's respiratory effort
  • These breaths are patient- or time-triggered, flow-limited, and volume-cycled.
    • Any breaths taken between volume-cycled breaths are not assisted
    • The volumes of these breaths are determined by the patient's strength, effort, and lung mechanics
    • A key concept is that ventilator-assisted breaths are different than spontaneous breaths
    • Another important concept is that AC and SIMV are identical modes in patients who are not spontaneously breathing due to heavy sedation or paralysis.
  • SMV is seen as better because it increases patient work to preserve respiratory muscle function
  • SIMV allows for better titration of ventilator support

 

  1. Volume control (VC) breaths are ventilator-initiated breaths with a set inspiratory flow rate.
  • Inspiration is terminated once the set tidal volume has been delivered.

 

  1. Volume assist (VA) breaths are patient-initiated breaths with a set inspiratory flow rate.
  • Inspiration is terminated once the set tidal volume has been delivered.

 

  1. Pressure control (PC) breaths are ventilator-initiated breaths with a pressure limit.
  • Inspiration is terminated once the set inspiratory time has elapsed.
  • The tidal volume is variable and related to compliance, airway resistance, and tubing resistance.
  • A consequence of the variable tidal volume is that a specific minute ventilation cannot be guaranteed.

 

  1. Pressure support (PS) breaths are patient-initiated breaths with a pressure limit.
  • The ventilator provides the driving pressure for each breath, which determines the maximal airflow rate.
  • Inspiration is terminated once the inspiratory flow has decreased to a predetermined percentage of its maximal value.

 

  1. Extrinsic positive end-expiratory pressure (Applied PEEP) is generally added to mitigate end-expiratory alveolar collapse.
  • A typical initial applied PEEP is 5 cm H2O, and this is adjusted accordingly depending on if atelectasis persists.

 

  1. Flow rate — The peak flow rate is the maximum flow delivered by the ventilator during inspiration.
  • The need for a high peak flow rate is particularly common among patients who have obstructive airways disease with acute respiratory acidosis.
  • In such patients, a higher peak flow rate shortens inspiratory time and increases expiratory time (ie, decreases the inspiratory to expiratory [I:E] ratio).
  • These alterations:
    • Increase carbon dioxide elimination
    • Improve respiratory acidosis
    • Decrease the likelihood of dynamic hyperinflation (auto-PEEP)

 

  1. End Tidal CO2 (Capnography)- provides instantaneous information about:
  • Ventilation (how effectively CO2 is being eliminated by the pulmonary system)
  • Perfusion (how effectively CO2 is being transported through the vascular system)
  • Metabolism (how effectively CO2 is being produced by cellular metabolism)
    • Used frequently in kids with vents as an easy way of assessing ventilation status.
    • Can be used to trend acid/base states, especially in conjunction with VBGs.
    • Capnography can be useful in evaluating respiratory status and is much quicker than pulse oximetry.
    • Make sure to look at wave forms to make sure that ETCO2 readings are accurate (look for a smooth hump) or else capnography readings may be abnormally high or low due to physiologic dead space.

 

  capnogram_0.pnghttp://clinicalgate.com/confirmation-of-endotracheal-intubation/

The CO2 waveform: A, Expiratory pause begins; A–B, Clearance of anatomic dead space; B–C, Dead space air mixed with alveolar air; C–D, Alveolar plateau; D, End-tidal partial pressure of CO2 registered by capnograph (arrow) and beginning of inspiratory phase; D–E, Clearance of dead space air; E–A, Inspiratory gas devoid of CO2.

 

  1. Chest Physiotherapy (CPT)- involves hyperoxygenation by bagging (or vent) with 100% oxygen, deep endotracheal instillation of 0.25-0.5ml/kg sterile saline, bagging with momentary inspiratory hold, followed by release of the hold and simultaneous forced exhalation and vibration to stimulate cough, and endotracheal suctioning.
  • Commonly done in children with persistent atelectasis or cystic fibrosis

 

  1.  Cough Assist – patients with respiratory muscle weakness can’t generate the force necessary to produce an effective cough.
  • Mechanical insufflation-exsufflation can be delivered via  mechanical device to patients who are spontaneously breathing or mechanically ventilated (works best in patients with trachs).
  • Positive pressure is applied during inhalation, and rapid exsufflation quickly follows generating a negative pressure differential which leads to a simulated cough. 

 

 ventilation_0.png   Jim Beck, MD, Division of Pulmonary and Critical Care Medicine, University of Michigan 

 

References

  1. Mechanical Ventilation: Basic Review, University of Colorado School of Medicine, Department of Internal Medicine http://www.ucdenver.edu/academics/colleges/medicalschool/departments/medicine/intmed/imrp/CURRICULUM/Documents/Mechanical%20ventilation%20review.pdf
  2. Ventilator Management, Medscape, 2015 http://emedicine.medscape.com/article/810126-overview
  3. Management and Prognosis of patients requiring prolonged mechanical ventilation, Up To Date, 2015http://www.uptodate.com/contents/management-and-prognosis-of-patients-requiring-prolonged-mechanical-ventilation?source=search_result&search=ventilator+management&selectedTitle=3%7E150
  4. Overview of Mechanical Ventilation, Up To Date, 2015
  5. http://www.uptodate.com.proxy.uchicago.edu/contents/overview-of-mechanical-ventilation?source=search_result&search=mechanical+ventilation&selectedTitle=1%7E150
  6. Critical Care Medicine Tutorials : http://www.ccmtutorials.com/rs/mv/