How APRV Prevents ARDS:A Preemptive Ventilation Strategy

Introduction To ARDS

Acute respiratory distress syndrome (ARDS) is a life-threatening condition characterized by poor oxygenation and non-compliant or "stiff" lungs. The disorder is associated with capillary endothelial injury and diffuse alveolar damage.

Berlin Definition

ARDS is an acute,diffuse,inflammatory llung injury increase a pulmonary vasculature, increase lung weight and loss of associated tissues.

Introduction Of APRV

What is airway pressure release ventilation (APRV)

APRV was described initially by Stock and Downs in 1987as a continuous positive airway pressure (CPAP) with an intermittent release phase. APRV applies CPAP (P high) for a prolonged time
(T high) to maintain adequate lung volume and alveolar recruitment, with a time-cycled release phase to a lower set of pressure (P low) for a short period of time (T low) or (release time) where most of ventilation and CO2 removal occurs.

APRV Initial Parameters

APRV Adjustments

APRV PROS & CONS

Advantage

• alveolar recruitment and improved oxygenation
• preservation of spontaneous breathing
• reduction of left ventricular transmural pressure and therefore reduction of left ventricular afterload
• potential lung-protective effect
• better ventilation of dependent areas
• lower sedation requirements to allow spontaneous breathing.

Disadvantage

• risks of volutrauma from increased transpulmonary pressure
• increased work of breathing due to spontaneous breathing
• increased energy expenditure due to spontaneous breathing
• worsening of air leaks (bronchopleural fistula)
• Increased right ventricular afterload, worsening of pulmonary hypertension
• Reduction of right ventricular venous return: may worsen intracranial hypertension, may worsen cardiac output in hypovolemia
• Risk of dynamic hyperinflation

APRV in Action – Lung Protection

Application of APRV in ARDS

ARDS is a severe condition with high mortality, marked by increased alveolar-capillary permeability. The goal of lung-protective ventilation is to “open the lung and keep it open” by:

• Recruitment maneuvers (RMs) to reopen collapsed alveoli.
• High PEEP to prevent repeated alveolar collapse and reopening.

This Open Lung Strategy (OLS) improves oxygenation and can shorten hospital stay, though it doesn’t reduce mortality.
APRV applies this concept differently by:

• Using a prolonged high-pressure phase (PHigh) to continuously recruit alveoli.
• Allowing collateral ventilation to stabilize and evenly distribute air in the lungs.
• Using a very short TLow (as low as 0.2 s) to maintain auto-PEEP, which prevents alveolar collapse by allowing only partial lung deflation.

This makes APRV an effective and potentially life-saving ventilation strategy for ARDS patients by maintaining stable, open lungs throughout the breathing cycle.

APRV in adults with ALI/ARDS

 

• During the initial years of its use APRV was not usually employed as a primary ventilation mode, but was considered an alternative approach for patients with ALI/ARDS refractory to conventional MV.
• According to some studies they comparing APRV to convential MV with the patient of ALI/APRV,Most were crossover studies i.e., switching from assist/control ventilation [A/CV] or synchronized intermittent mandatory ventilation [SIMV] to APRV and randomized controlled trials (RCTs) with a small sample size 22 to 138 patients.
• In different studies used different settings, which indicate the inconsistency and complexity of ARPV. Most of the studies reported that APRV could improve oxygenation compared to other modes.
• In APRV is showed
• Improve oxygenation
• Improve hemodynamics and respiratory system compliance
• Reduce PIP
• Reduce airway pressure,Pplat
• Need for sedation and paralysis
• No studies proved that APRV could improve the mortality of patients with ARDS,But it was associated with a reduction of the duration of intensive care unit (ICU) stays and incidence of progression to extracorporeal membrane oxygenation (ECMO).

APRV In Adults With Prone Position

 

• Research on combined APRV and PP has been limited to two case reports and one prospective RCT.
• These studies reported that combining the two modalities resulted in a greater improvement in oxygenation.
• Varpula et al he in first discover that APRV with combine of PP is fessiable in severe ARDS,and a prospective RCT conducted 2 years later confirmed these results,Lee et al reported five ARDS cases where APRV and PP were used and found that APRV could be safely used in the PP in a subtype of ARDS patients with improving oxygenation.
• Rozé et al reported eight cases of ARDS under ECMO, demonstrating that moderate SB with APRV was feasible while maintaining the tidal volume in an ultra-protective range without complications after ECMO.

The Preemptive Approch

Risk Factor

Sepsis
Pneumonia
Aspiration
Trauma
Shock

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High LIPS

   LIPS score is >4 is high senstivity patient get ARDS.

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Early APRV

Early APRV is a better choice to prevent ARDS with the preemptive APRV ventilator settings.

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Lung Protective Ventilation

These strategies aim to minimize lung injury by preventing overdistension, reducing alveolar collapse, and maintaining adequate oxygenation.

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APRV Prevented

Using these steps we can prevent the ARDS in patients.

LIPS Predicting ARDS Risk

The lung injury prediction score(LIPS) is a tool to predict the patient that who developing of acute respiratory distress syndrome (ARDS).
The LIPS model uses a combination of factors, including:

• Predisposing conditions: Sepsis, shock, trauma, etc.
• Other clinical data: Respiratory rate, oxygenation status, etc.
• Risk modifiers: Factors that can increase or decrease the risk of developing ARDS.

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Clinical Evidence Supporting APRV

Clinical Evidence By Yongfang Zhou

Source: West China Hospital, Sichuan University (2015–2016)

Purpose: Animal studies suggested that updated APRV settings may enhance lung recruitment and oxygenation while reducing lung injury—without harming circulation. This study tested whether early use of APRV in ARDS patients could reduce the need for mechanical ventilation compared to standard low tidal volume (LTV) ventilation.

Methods:

138 patients with ARDS (ventilated <48h)

• Randomized: APRV (n=71) vs. LTV (n=67)
• APRV Settings:
  • Phigh = last Pplat (max 30 cmH₂O)
  • Plow = 5 cmH₂O
  • Tlow = terminate at ≥50% peak expiratory flow
  • RR = 10–14 releases/min
• LTV Settings followed ARDSnet protocol (6 mL/kg TV, Pplat ≤30 cmH₂O, PEEP-FiO₂ table).

Key Results

• Ventilator-free days at 28 days:
  • APRV: 19 days (IQR 8–22)
  • LTV: 2 days (IQR 0–15)
  • P < 0.001
• ICU stay was shorter in the APRV group (P = 0.003)
• ICU mortality trended lower in APRV (19.7% vs. 34.3%, P = 0.053)
• APRV patients had:
  • Better oxygenation & compliance
  • Lower Pplat
  • Reduced sedation needs in the first week.

Conclusion

Early APRV in ARDS patients improved lung mechanics and outcomes versus LTV. It led to fewer days on the ventilator, better oxygenation, and shorter ICU stays—potentially redefining ARDS ventilation strategy.

 

Gross pathology: Representative specimens of gross lungs from LTV ventilation and APRV groups are shown. A, Airway pressure release ventilation whole lung: animals exhibited normal, pink, homogenously well-inflated lung tissue with no evidence of inflammation and no evidence of atelectasis and appeared to be inflated nearly to TLC. B, Airway pressure release ventilation cut surface: the cut surface of the representative APRV lung specimen shows neither bronchial nor septal edema. C, Low tidal volume ventilation whole lung: the lungs were predominantly atelectatic with heterogeneous parenchymal inflammation. D, Low tidal volume ventilation cut surface: the cut surface shows gel-like edema filling the interlobular septae of the lung in the LTV ventilation group and airway edema in the bronchial openings.image credits

Challenges Of APRV

• No standardized settings
• Risk of volutrauma/barotrauma
• Difficult tidal volume monitoring
• CO₂ retention (hypercapnia)
• Requires skilled management
• Potential hemodynamic effects
• Not suitable for all patients
• Limited high-level evidence

Endobronchial Stenting|A Lifesaving Intervention for Airway Management

Endobronchial Stenting: Restoring Airway Patency with Precision and Innovation

Introduction

Endobronchial stenting has emerged as a pivotal intervention in managing various airway pathologies, particularly those leading to central airway obstruction (CAO). This procedure involves the placement of a stent within the tracheobronchial tree to maintain airway patency, thereby alleviating symptoms and improving the quality of life for affected patients. This comprehensive overview delves into the indications, types, techniques, outcomes, and potential complications associated with endobronchial stenting, with a focus on literature from 2021 to 2025.

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Indications for Endobronchial Stenting

Endobronchial stenting is primarily indicated in scenarios where airway patency is compromised. The main indications include:

1. Malignant Airway Obstruction: Tumors originating from the trachea or bronchi, or metastatic lesions causing extrinsic compression, can lead to significant airway narrowing. Stenting serves as a palliative measure to relieve obstruction and improve ventilation.

2. Benign Airway Stenosis: Conditions such as post-intubation tracheal stenosis, inflammatory diseases, or congenital anomalies can result in benign strictures. While surgical resection remains the definitive treatment, stenting offers a less invasive alternative, especially in patients unfit for surgery.

3. Tracheoesophageal and Bronchopleural Fistulas: Abnormal communications between the trachea and esophagus or pleural space can lead to severe respiratory complications. Stent placement helps seal these fistulas, preventing aspiration and improving respiratory function.

4. Airway Collapse Due to Extrinsic Compression: Mediastinal masses or lymphadenopathy can exert pressure on the airway, leading to collapse. Stenting provides structural support, counteracting the external compressive forces. 

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Types of Endobronchial Stents

The selection of an appropriate stent is crucial and depends on the underlying pathology, anatomical considerations, and the desired duration of stenting. The primary types include:

1. Silicone Stents

Silicone stents have been widely used in the treatment of both benign and malignant airway obstructions. They are typically inserted using a rigid bronchoscope and provide a non-reactive, biocompatible solution for maintaining airway patency.

Advantages

✅ Biocompatibility: Made of medical-grade silicone, reducing inflammation and tissue reaction.
✅ Easy Removal: Unlike metallic stents, silicone stents can be safely removed, making them ideal for temporary airway management.
✅ Lower Risk of Granulation Tissue Formation: Since they do not embed into the airway wall, the risk of excessive tissue overgrowth is lower.
✅ Customizable: Available in various sizes and shapes; some can be trimmed to fit individual patient anatomy.

Disadvantages

❌ Migration Risk: More prone to displacement, especially in mobile airway regions like the trachea.
❌ Mucus Plugging: Their non-porous surface can accumulate secretions, leading to obstruction.
❌ Rigid Bronchoscopy Requirement: Placement often requires general anesthesia and specialized equipment.
❌ Limited Radial Force: Less effective for extrinsic airway compression compared to metallic stents.

Best Used For

• Benign airway stenosis (e.g., post-intubation tracheal stenosis).
• Airway fistula sealing (e.g., tracheoesophageal fistulas).
• Patients requiring temporary stenting with an option for removal.

 The original Dumon Stent (Tracheobronxane ®, Novatech, la Ciotat, France)
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2. Metallic Stents (Self-Expanding and Balloon-Expandable)

Metallic stents, also known as self-expanding metal stents (SEMS), are widely used for malignant airway obstructions due to their excellent radial force and ability to resist external compression. These stents are usually composed of nitinol (nickel-titanium alloy), stainless steel, or cobalt-chromium and are inserted via a flexible bronchoscope.

Types of Metallic Stents

1. Self-Expanding Metallic Stents (SEMS) – Expand upon deployment, commonly used in malignant obstructions.
2. Balloon-Expandable Stents – Require external balloon dilation for expansion, used in certain rigid airway obstructions.

Advantages

✅ Strong Radial Force: Ideal for relieving extrinsic compression from tumors or lymphadenopathy.
✅ Minimally Invasive: Can be placed using flexible bronchoscopy under sedation.
✅ Lower Migration Rate: Compared to silicone stents, they stay in place better.
✅ Thin-Walled Structure: Provides a larger airway lumen than silicone stents of the same outer diameter.

Disadvantages

❌ Difficult Removal: Tends to embed into the airway wall, making removal challenging and sometimes requiring surgery.
❌ Granulation Tissue Formation: Chronic irritation leads to tissue overgrowth, potentially causing re-obstruction.
❌ Fracture Risk: Over time, metal fatigue can lead to stent fracture.
❌ Foreign Body Reaction: Some patients may experience chronic inflammation.

Best Used For

• Malignant airway obstruction (e.g., lung cancer, tracheal tumors).
• Tracheobronchial collapse due to external compression (e.g., mediastinal masses).
• Patients with a poor prognosis where stent removal is not anticipated.

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3. Hybrid Stents (Metallic Framework with Silicone Covering)

Hybrid stents combine the benefits of both metallic and silicone stents. They have a metallic framework for radial strength but are coated with silicone to reduce tissue ingrowth and facilitate removal.

Advantages

✅ Lower Granulation Tissue Formation: The silicone covering reduces direct metal-to-tissue contact.
✅ Strong Radial Force: Offers better airway support than pure silicone stents.
✅ Reduced Migration Risk: More stable than traditional silicone stents.
✅ Easier Removal: Can be extracted more easily than bare metallic stents.

Disadvantages

❌ Potential Mucus Plugging: The silicone coating can lead to secretion accumulation.
❌ Limited Flexibility: May not conform as well to highly distorted airways.
❌ Higher Cost: More expensive than conventional silicone or metallic stents.

Best Used For

• Malignant or benign airway obstruction requiring long-term management.
• Patients needing a balance between structural support and removability.
• Cases where granulation tissue formation needs to be minimized.

Comparison Table: Stent Types at a Glance

Feature	Silicone Stents	Metallic Stents (SEMS)	Hybrid Stents
Material	Medical-grade silicone	Nitinol, stainless steel	Metal framework with silicone coating
Placement	Rigid bronchoscopy	Flexible bronchoscopy	Flexible or rigid bronchoscopy
Radial Force	Low	High	Moderate to high
Migration Risk	High	Low	Moderate
Granulation Tissue Formation	Low	High	Lower than metal stents
Secretion Accumulation	High	Low	Moderate
Ease of Removal	Easy	Difficult	Easier than metallic stents
Best For	Benign conditions, temporary airway support	Malignant obstruction, external compression	Long-term airway support with removability option

Emerging Trends and Future Developments

The field of airway stenting is evolving, with new technologies aimed at improving stent performance and minimizing complications:

1. 3D-Printed Stents

   • Custom-made stents tailored to patient-specific airway anatomy.
   • Expected to reduce migration risk and improve patient outcomes.

2. Biodegradable Stents

   • Designed to degrade over time, eliminating the need for removal.
   • Particularly useful for temporary airway support in benign conditions.

3. Drug-Eluting Stents

   • Coated with anti-inflammatory or antibiotic agents to reduce granulation tissue formation and infections.
   • May improve long-term outcomes in patients with chronic airway disease.

Techniques of Stent Placement

The placement of an endobronchial stent is a meticulous process that requires careful planning and execution:

1. Pre-procedural Assessment: Comprehensive evaluation includes imaging studies like computed tomography (CT) scans to delineate the anatomy and extent of obstruction. Pulmonary function tests may also be conducted to assess the baseline respiratory status.

2. Bronchoscopic Guidance: The procedure is typically performed under general anesthesia using flexible or rigid bronchoscopy. The choice depends on the stent type and the specific clinical scenario.

3. Fluoroscopic Assistance: Real-time fluoroscopy aids in accurate stent deployment, ensuring proper positioning and expansion.

4. Post-deployment Evaluation: After placement, bronchoscopy is repeated to confirm stent position and assess for any immediate complications such as bleeding or misplacement.

Outcomes and Efficacy

The success of endobronchial stenting is measured by symptom relief, improvement in airway patency, and quality of life enhancements:

1. Symptomatic Improvement: Patients often experience immediate relief from dyspnea and other respiratory symptoms post-stenting.

2. Enhanced Airway Patency: Imaging and bronchoscopic evaluations post-procedure typically show significant improvement in airway diameter.

3. Quality of Life: Studies have reported improved quality of life scores in patients undergoing stenting for malignant obstructions, with reduced need for additional interventions.ns and Management

While endobronchial stenting is generally safe, potential complications can arise:

1. Stent Migration: More common with silicone stents, migration can lead to recurrent obstruction or airway injury. Securing the stent adequately during placement and selecting the appropriate size can mitigate this risk.

2. Granulation Tissue Formation: Particularly associated with metallic stents, excessive tissue growth can re-occlude the airway. Regular bronchoscopic surveillance and, if necessary, interventions like laser therapy can manage this complication.

3. Infection: The presence of a foreign body can predispose to infections. Prophylactic antibiotics and ensuring optimal stent hygiene are preventive strategies.

4. Mucus Plugging: Stents can act as a nidus for mucus accumulation, leading to obstruction. Nebulized mucolytics and adequate hydration are recommended to prevent this issue.

Recent Advances and Future Directions

The field of endobronchial stenting is continually evolving:

1. 3D-Printed Stents: Custom-made stents tailored to individual patient anatomy using 3D printing technology are being explored, promising better fit and reduced complications.

2. Biodegradable Stents: Research is ongoing into stents that gradually degrade over time, potentially reducing the need for removal procedures and minimizing long-term complications.

3. Drug-Eluting Stents: Incorporating medications such as anti-inflammatory agents or antibiotics into the stent material aims to prevent complications like granulation tissue formation and infections.

Conclusion

Endobronchial stenting remains a vital tool in the management of various airway pathologies, offering significant symptomatic relief and improved quality of life for patients with airway obstructions. Ongoing research and technological advancements continue to refine stent designs and placement techniques, aiming to enhance efficacy and safety. As with any medical intervention, careful patient selection, meticulous procedural execution, and diligent post-procedural care are paramount to achieving optimal outcomes.