Page 75 - JSOM Winter 2021

TABLE 1 Cont.
Modes of
Mechanical Ventilation Waveform Anesthesia Machine Gaps to Consider
Spontaneous Continuous NA SPN-CPAP provides continuous positive airway pressure throughout the duration of the respiratory
Positive Airway Pressure cycle. The patient breathes at the PEEP level. Compared with the atmospheric pressure, the airway
(SPN–CPAP) pressure is increased during the complete breathing cycle. Most anesthesia machines have this
capability.
Assist Control (AC) NA With AC – set rate, volume – breath will be the same. Most anesthesia machines have this
capability.
Intermittent Mandatory NA With IMV, the user can use AC or SIMV for most anesthesia machines. Most anesthesia machines
Ventilation IMV have replaced traditional IMV with SIMV, improving both patient comfort and patient-ventilator
synchrony.
Volume Control– As with PC-SIMV, VC-SIMV represents a support mode of ventilation with set mandatory breaths.
Synchronized Intermittent When a patient-triggered breath occurs within the given trigger window, the machine delivers a
Mandatory Ventilation prespecified volume control breath. With VC-SIMV, the mandatory breaths are synchronized with
(VC-SIMV) the patient‘s own breathing attempts if these generate enough negative pressure within a trigger
window. If no breathing attempt is detected during the trigger window, the machine-triggered
mandatory breath is applied. The minute volume (MV or V ) remains constant over time. The
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patient can breathe spontaneously at PEEP level during the expiratory phase, and these breaths can
be pressure-supported using PSV Outside the mandatory breathes; pressure support breaths are supplied
to augment the patient’s intrinsic ventilatory drive. This is a readily available function with most
anesthesia machines.
Volume Limited For VC and VC–AutoFlow (VC-AF), with most ICU ventilators the upper airway pressure alarm
limit “P -high” is not only used for generating the airway pressure high alarm but also for limiting
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the maximum pressure generated by the therapy device. For most anesthesia machines, the alarm
limit is used for generating the alarm but does not limit the pressure. For the pressure limitation, the
P max setting is used, which also has to be set specific to the patient and the clinical situation.
Tube Compensation NA Some ICU ventilators are able to provide variable pressure support dedicated at overcoming the
additional resistance from the endotracheal tube and associated breathing circuit. This is useful
when extubating a patient; an alternative would be to apply PEEP with pressure support. Although
most anesthesia machines do not have “tube compensation” capabilities, manual PEEP adjustments
can mimic this functionality.
Peak Expiratory Flow NA Most anesthesia machines have this capability.
Rate (PEFR)
Inverse Ratio Ventilation IRV represents a rescue mode of ventilation aimed at increasing mean airway pressure, and
(IRV), Pressure Control– subsequent alveolar recruitment via lengthening inspiratory time. IRV and PC-IRV Most anesthesia
Inverse Ratio Ventilation machines allow for a long inspiratory time—e.g., 5 seconds only. Patient comfort issues could occur.
(PC-IRV Pressure )
Adaptive Support NA ASV is Hamilton proprietary technology. This mode adjusts RR, V , and T continuously, depending
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Ventilation (ASV) on the patient’s lung mechanics and effort. It adapts ventilation breath-by-breath from intubation to
extubation. This capability is not available on most anesthesia machines.
Neurally Adjusted NA NAVA represents a support mode of ventilation whereby the ventilator provides variable inspiratory
Ventilatory Assist (NAVA) pressure support as a function of diaphragmatic electrical potential measured via an esophageal
probe. This is a Getinge proprietary technology. It is a form of partial ventilatory support wherein
the machine applies positive pressure to the airway opening throughout each inspiration. In contrast
to all other modes of ventilation, which adopt conventional pneumatic signals (flow, volume, and
airway pressure) to drive and control the ventilator operation, NAVA uses the electrical activity of
the diaphragm. This capability is not available on anesthesia machines.
Volume Limited - NA With VL-IRV, most anesthesia machines allow for a long inspiratory time, e.g., 5 seconds only.
Inverse Ratio Ventilation Patient comfort issues could occur. The user may use PCGV.
(VL-IRV)
Apnea Vent Back-Up Some anesthesia machines offer this functionality (e.g., PSV Pro; Aestiva) as an option. Alternative
methods such as applying PEEP and alarm settings may be used. Special care must be taken when
using an anesthesia ventilator in support modes of ventilation because many ventilators lack apneic
ventilatory backup. Careful attention to alarm settings and practitioner proximity to the patient is
integral in preventing dangerous complications. SIMV modes of ventilation can be considered to
ensure a dedicated backup rate while allowing for adequate pressure support.
Battery Back-Up NA Most anesthesia machines have only 30-min battery capabilities compared with 2-h capabilities with
most ICU ventilators.
AF, autoflow; APRV, airway pressure release ventilation; ARDS, acute respiratory distress syndrome; AC, assist control; ASV, adaptive support ventilation;
BIPAP, biphasic positive airway pressure; bpm, breaths per minute; CMV, continuous mandatory ventilation; CPAP, continuous airway pressure; ICU,
intensive care unit; IMV, intermittent mandatory ventilation; IRV, inverse ratio ventilation; NA, not applicable; LPM, liters per minute; NAVA, neurally
adjusted ventilatory assist; NIV, noninvasive ventilation; PC, pressure control; PEEP, peak end expiratory pressure; PEFR, peak expiratory flow rate; P high ,
upper pressure level; P insp , inspiratory pressure; P , lower pressure level; P max , maximum pressure limit; PS, pressured support; PSV, pressure support ven-
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tilation; RR, respiratory rate; RR , minimum frequency; SIMV, synchronized intermittent mandatory ventilation; SPN, spontaneous; T high , time at high
min
pressure; T, inspiratory time; T , time low; VC, volume control; VL, volume limited; V , tidal volume
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