# Situation: A 52-year-old man is in the intensive care unit (ICU) with septic shock and acute kidney injury. He is intubated and receives mechanical ventilation. Because his platelet count is low, he is on continuous kidney replacement therapy (CRRT) with regional citrate anticoagulation. By day 6 his condition improves. The team switches him to a ventilator mode in which he triggers every breath himself, there is no mandatory rate, and the ventilator boosts each breath to a preset inspiratory level; the mode is commonly used for weaning. Which mode is this?

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> subject: Nursing Practice V — Care of Clients with Maladaptive Patterns of Behavior; Care of Clients with Life-Threatening Conditions, Acute Multi-Organ Problems, High Acuity and Emergency Situations

## 문제

Situation: A 52-year-old man is in the intensive care unit (ICU) with septic shock and acute kidney injury. He is intubated and receives mechanical ventilation. Because his platelet count is low, he is on continuous kidney replacement therapy (CRRT) with regional citrate anticoagulation.

By day 6 his condition improves. The team switches him to a ventilator mode in which he triggers every breath himself, there is no mandatory rate, and the ventilator boosts each breath to a preset inspiratory level; the mode is commonly used for weaning. Which mode is this?

## 보기

1. Synchronized intermittent mandatory ventilation (SIMV)
2. Pressure support ventilation (PSV) **✔ 정답**
3. Assist-control (AC) ventilation
4. Continuous positive airway pressure (CPAP)

**정답: 2**

## 해설

In pressure support ventilation every breath is triggered by the client, and the ventilator augments each one with a preset inspiratory pressure; there is no mandatory rate. It is commonly used during weaning as the client takes over the work of breathing.

## 심화 해설

Mode identification

The clinical cue is that the patient triggers every breath himself, there is no mandatory rate, and the ventilator boosts each breath to a preset inspiratory level. This combination is the defining signature of pressure support ventilation (PSV).

PSV is a patient-triggered, pressure-limited, and normally flow-cycled mode [2]. The patient must initiate each breath; when that effort is detected, the ventilator delivers a clinician-set inspiratory pressure to augment the tidal volume and reduce the patient’s work of breathing. Because there is no backup mandatory rate, apnea is not supported by the mode itself, which is why PSV is reserved for patients with a reliable respiratory drive and is most often used during weaning [1][2].

The other options differ in one critical way each. Assist-control (AC) ventilation is also patient-triggered, but it delivers a preset tidal volume or pressure on every triggered breath and includes a backup mandatory rate, so it is not a weaning mode with no mandatory rate. Synchronized intermittent mandatory ventilation (SIMV) combines mandatory breaths at a set rate with spontaneous breaths between them; the mandatory component distinguishes it from PSV. Continuous positive airway pressure (CPAP) provides a constant positive airway pressure throughout the respiratory cycle but does not augment each breath with an additional inspiratory pressure above that baseline, so it does not “boost” the breath in the way described.

| Mode | Trigger | Mandatory rate | Inspiratory augmentation | Typical use |
| --- | --- | --- | --- | --- |
| PSV | Patient only | None | Preset pressure support on every breath | Weaning |
| AC | Patient or time | Yes (backup) | Preset volume or pressure | Full support |
| SIMV | Patient or time | Yes (set rate) | Mandatory breaths augmented; spontaneous breaths not | Partial support / weaning |
| CPAP | Patient only | None | No inspiratory boost above baseline | Oxygenation / spontaneous breathing trial |

Key point! The phrase “no mandatory rate” is the discriminator that removes AC and SIMV from consideration. The phrase “boosts each breath to a preset inspiratory level” removes CPAP. Only PSV satisfies both conditions.

During PSV, the delivered flow and tidal volume are not fixed; they depend on the pressure support setting, the patient’s inspiratory effort, and respiratory system mechanics [2]. The breath ends when inspiratory flow decays to a preset percentage of peak flow, which is the flow-cycling criterion [2]. This makes PSV more comfortable for an awake patient because the patient retains control over inspiratory time and flow pattern.

Watch out! In PSV, tidal volume is variable. If the patient’s compliance worsens or effort weakens, tidal volume can fall despite the same pressure support level. Monitoring exhaled tidal volume and respiratory rate is therefore essential during weaning trials. Flow asynchrony can also occur when support is insufficient relative to the patient’s inspiratory effort, and visual waveform analysis helps identify this mismatch .

For the patient in this scenario, the transition to PSV on day 6 signals that the team is shifting from full ventilatory support toward spontaneous breathing. The absence of a mandatory rate means the patient’s own respiratory center is now driving ventilation, while the preset pressure support offsets the resistance of the endotracheal tube and the imposed work of the ventilator circuit [1][2].References (research sources)

- [1]Mechanical Ventilation: Modes, Settings, and Clinical Considerations.Research articleGallagher JJ, Adamski JL (2025) · DOI: 10.4037/aacnacc2025722

- [2]Ventilator waveforms and the physiology of pressure support ventilation.Research articleHess DR (2005)

## 임상 시나리오

PSV for WeaningPatient-triggered pressure support with no mandatory rate
In pressure support ventilation, the patient must trigger every breath. The ventilator then delivers a preset inspiratory pressure to augment tidal volume and reduce work of breathing. There is no mandatory rate, so apnea is not supported by the mode itself.

PSV is most appropriate for patients with a reliable respiratory drive and is commonly used during weaning as the patient progressively takes over the work of breathing.

CautionPSV provides no backup mandatory rate. Do not use it in patients with unstable respiratory drive, heavy sedation, or risk of apnea, as hypoventilation can occur without alarm-triggered backup ventilation.

## 핵심 개념

- **Pressure Support Ventilation** — A patient-triggered, pressure-limited, flow-cycled mode where the ventilator augments each spontaneous breath with a preset inspiratory pressure.
- **Synchronized Intermittent Mandatory Ventilation** — A mode that delivers mandatory breaths at a set rate synchronized with patient effort, with spontaneous breaths allowed between them.
- **Assist-Control Ventilation** — A mode where every breath is patient-triggered or machine-triggered and delivers a preset tidal volume or pressure, with a backup mandatory rate.
- **Continuous Positive Airway Pressure** — A mode that maintains constant positive airway pressure throughout the respiratory cycle without providing additional inspiratory pressure support.
- **Weaning** — The process of gradually reducing ventilator support as the patient resumes spontaneous breathing and takes over the work of breathing.

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