# A patient on mechanical ventilation has bilateral infiltrates on chest x-ray, no signs of cardiogenic edema, FiO2 0.80, PEEP 12, and a PaO2 of 88 mm Hg (PaO2/FiO2 ratio 110). The provider has ordered prone positioning. Which is the nurse's best understanding of why prone positioning is being used?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=372717&lang=en  
> language: en  
> subject: Complications of Procedures  
> category: ROR

## Question

A patient on mechanical ventilation has bilateral infiltrates on chest x-ray, no signs of cardiogenic edema, FiO2 0.80, PEEP 12, and a PaO2 of 88 mm Hg (PaO2/FiO2 ratio 110). The provider has ordered prone positioning. Which is the nurse's best understanding of why prone positioning is being used?

## Option

1. It is primarily a comfort intervention used in sedated ICU patients to redistribute pressure and prevent sacral pressure injuries during prolonged immobilization.
2. It primarily works by dilating the pulmonary vasculature and reducing pulmonary artery pressure, which lowers right ventricular strain and improves cardiac output in ARDS.
3. It improves ventilation–perfusion matching and recruits dependent dorsal lung regions in moderate-to-severe ARDS, reducing mortality when applied for 12–16 hours per day. **✔ Correct answer**
4. It is typically reserved for patients who have not responded to a trial of extracorporeal membrane oxygenation and continue to have refractory hypoxemia.

**Correct answer: 3**

## Explanation

A PaO2/FiO2 ratio of 110 with bilateral infiltrates and no cardiogenic origin meets Berlin criteria for moderate ARDS (P/F 100–200) approaching severe (

## In-depth explanation

ARDS Berlin criteria require acute onset within one week, bilateral infiltrates on imaging, edema not fully explained by cardiac failure or volume overload, and a PaO2/FiO2 ratio defining severity — mild 200–300, moderate 100–200, severe

## Clinical scenario

A patient on mechanical ventilation has **bilateral infiltrates** on CXR, **no signs of cardiogenic edema**, **FiO2 0.80**, **PEEP 12**, and a **PaO2 88 mm Hg** (**PaO2/FiO2 110**). The provider orders **prone positioning**.

## Key concepts

- **ARDS Berlin Criteria** — Acute respiratory distress syndrome diagnosis: acute onset within 1 week, bilateral infiltrates on imaging, edema not fully explained by cardiac failure or volume overload, and a PaO2/FiO2 ratio that defines severity — mild 200–300, moderate 100–200, severe
- **Prone Positioning Mechanism** — Improves ventilation–perfusion matching by recruiting dorsal (dependent) lung regions, redistributing perfusion, reducing ventral overdistention, and lowering ventilator-induced lung injury. Recommended 12–16 hours per day for moderate-to-severe ARDS (P/F
- **Prone Positioning Nursing Care** — Pre-positioning checklist: secure ETT, lines, and tubes; pad pressure points; suction; maintain head/neck alignment; reverse Trendelenburg slightly; use a team for the maneuver. Monitor for facial edema, pressure injuries, tube displacement, hemodynamic changes, and feeding tolerance.

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