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| IMV one of the worst ventilator modes in regards to patient comfort. |
Many will argue the best mode of mechanical ventilation
and prefer the mode that is most commonly used in their patient populations.
Strict believers of the ARDS net protocol will favor VC-CMV to ensure lower
tidal volume delivery. Pediatric centers will insist on Pressure targeted modes
to limit high pressures, and trauma centers may favor biphasic modes of
ventilation to obtain higher mean airway pressures.
However, some institutions use the worst modes of
ventilation that directly impede on patient comfort. Promoting patient comfort
is one of the main goals of mechanical ventilation [1] and not providing
comfort may lead to over sedation, over ventilation, ventilator induced
diaphragmatic dysfunction, and increased length of stay.
So what are the worst modes of ventilation specifically
in regards to patient comfort?
The two worst modes of ventilation are:
1. Volume
Controlled-Intermittent Mandatory Ventilation (VC-IMV). This mode (as far as I
know) is on every ICU ventilator that is commercially available.
2. Synchronized
Intermittent Mandatory Ventilation with Pressure Limited Ventilation. This mode
is specific to Draeger ventilators (a.k.a. Pmax).
So why are they, the worst modes of ventilation in
regards to patient comfort?
First, let’s evaluate the modes in regards to patient
ventilator asynchrony.
There are 10 documented patient ventilator asynchronies [2,
3] and each of the two targeting schemes [4] is associated with all of the
classified asynchronies. No other modality is associated with this many
asynchronies [5].
Second, let’s evaluate the modes in relation to promoting
patient comfort [1]:
1. Maximize trigger/cycle synchrony-
both modes are associated with all trigger & cycle asynchronies.
Additionally, the operator has to adjust both of these target values.
2. Minimize auto-PEEP-
both modes are associated with auto-PEEP.
3. Maximize flow synchrony-
both modes are associated with flow asynchrony.
4. Coordinate mandatory & spontaneous
breaths- both modes are IMV and allow for both mandatory &
spontaneous breaths, however diaphragmatic monitoring has shown that the
diaphragm continues to contract during the mandatory breaths. This leading to
increased work and asynchrony.
5. Optimize work demand versus work
delivered- both modes targeting schemes do not allow for
this.
6. Minimize inappropriate shifting of work
from the ventilator to the patient- both modes targeting schemes
do not allow for this.
So when evaluating the modalities based on these
considerations the operator should never utilize these modes on a spontaneous
breathing patient. Better yet not use these modes on any patient.
No mode of ventilation is a panacea and it remains
arguable what the ideal mode of ventilation may be. Conversely, it is easy to
identify the worst modes of ventilation in regards to patient comfort and the
operator should refrain from using them.
1. Chatburn,
R. & Mireles-Cabodevila, E. (2011). Closed-LoopControl of Mechanical Ventilation: Descritpion & Classification of TargetingSchemes. Respiratory Care. 56
(1): 85-102.
2. 10 documented patient ventilator
asynchronies: Auto-triggering, trigger delay, ineffective
efforts, double triggering, flow mismatch, driving pressure, pressurization
rates, pre-mature cycle, delayed cycle, & PEEPi.
3. Richey,
S. (2011). Ventilator Graphics:Identifying Patient Ventilator Asynchrony & Optimizing Settings.
Chesapeake, VA.
4.
Targeting
Scheme: “feedback control system used by a mechanical ventilator
to deliver a specific ventilatory pattern: a key component of a ventilation
mode” [1].
5.
The next highest number of associated
patient ventilator asynchronies is eight (8) out of the ten.