Mechanical ventilation strategies in burns

Overview

Burn patients requiring mechanical ventilation face a distinct set of physiologic challenges that complicate standard ventilator management ^[2]. Inhalation injury causes airway cast formation and increased airway resistance. Massive fluid resuscitation produces pulmonary edema and reduced compliance. The hypermetabolic response generates elevated CO2 production and increased minute ventilation requirements. These factors collectively make burn patients among the most difficult to ventilate in critical care ^[1][2].

Despite these unique challenges, the evidence base for ventilation strategies specific to burn patients remains limited. A survey of 46 North American burn centers found wide variation in mechanical ventilation practices and no consensus on burn-specific ventilator guidelines ^[7]. Most practice is extrapolated from ARDS literature developed in nonburn populations, and the largest international prospective study of ventilation practices in burn patients (LAMiNAR, 160 patients from 28 ICUs across 16 countries) found that low tidal volume ventilation, while used in 74% of patients, was not associated with a reduction in ventilator-free days at day 28 ^[6].

Lung-Protective Ventilation

Low tidal volume ventilation (6 mL/kg predicted body weight) with limitation of plateau pressures below 30 cmH2O is the standard of care for all mechanically ventilated patients at risk for or with established ARDS. The foundational evidence comes from the ARDS Network ARMA trial, which randomized 861 patients to 6 mL/kg vs 12 mL/kg predicted body weight and demonstrated a 22% relative reduction in mortality (31% vs 39.8%, P=0.007) with lower tidal volumes ^[3]. In burn patients, specific considerations include:

Tidal Volume

A multicenter retrospective study found that tidal volumes in burn patients decreased significantly over a 10-year period (2005-2015), reflecting adoption of lung-protective practices ^[1]. Lower tidal volumes were associated with reduced rates of ventilator-induced lung injury. However, achieving 6 mL/kg targets can be difficult in burn patients with high CO2 production from hypermetabolism ^[1][2]. In the LAMiNAR cohort, median tidal volume was 7.3 mL/kg predicted body weight, with only 26% of patients receiving tidal volumes at or below 6 mL/kg, underscoring the gap between guideline targets and real-world burn practice ^[6].

PEEP

Positive end-expiratory pressure (PEEP) maintains alveolar recruitment and improves oxygenation. In burn patients with inhalation injury, PEEP must be balanced against the risk of air trapping from cast-obstructed airways and the hemodynamic effects of high intrathoracic pressure during aggressive fluid resuscitation ^[2][8]. The LAMiNAR study found that median PEEP levels were modest (8 cmH2O) even in patients meeting ARDS criteria, suggesting underutilization of higher PEEP strategies in burn populations ^[6]. The Chung survey found that for mild ARDS, ARDSNet PEEP titration was the preferred approach across burn centers, while no consensus existed for moderate or severe ARDS ^[7].

Permissive Hypercapnia

Permissive hypercapnia (tolerating PaCO2 above normal to allow lower tidal volumes and pressures) is an accepted strategy in burn patients. The threshold for tolerable hypercapnia in burn patients has not been defined, and elevated intracranial pressure from concurrent head injury is a contraindication. In practice, burn patients with high metabolic rates may produce CO2 at levels that make strict adherence to 6 mL/kg tidal volumes untenable without significant respiratory acidosis ^[1][2].

Adjunctive Ventilator Strategies

Airway Pressure Release Ventilation (APRV)

APRV is a pressure-limited, time-cycled mode that maintains a high continuous positive airway pressure with brief release phases. It may improve oxygenation and recruit atelectatic lung in inhalation injury patients. An international expert panel using RAND/UCLA methodology identified APRV as a potentially beneficial mode in inhalation injury but noted the absence of RCTs comparing it to conventional lung-protective ventilation in burn patients ^[9]. The Chung survey found that APRV was the most popular ventilator mode for severe ARDS across North American burn centers, despite a complete absence of comparative effectiveness data in this population ^[7]. No standardized APRV protocols for burn patients exist, and settings vary widely between institutions.

High-Frequency Oscillatory Ventilation (HFOV)

HFOV delivers small tidal volumes at high frequencies, theoretically minimizing ventilator-induced lung injury. Two large RCTs in general ARDS populations settled the question for most intensivists. The OSCAR trial (795 patients) found no difference in 30-day mortality between HFOV and conventional ventilation ^[4]. The OSCILLATE trial (548 patients) was stopped early for harm, with higher in-hospital mortality in the HFOV group (47% vs 35%, relative risk 1.33, P=0.005) ^[5]. These results effectively ended routine HFOV use in ARDS. Burn-specific HFOV data remain limited to small case series, and given the negative results in general ARDS, HFOV cannot be recommended as a standard approach in burn patients.

Prone Positioning

Prone positioning improves ventilation-perfusion matching and has mortality benefit in severe ARDS (PaO2/FiO2 less than 150). In burn patients, prone positioning is complicated by burns on the anterior trunk, the need for wound care access, and hemodynamic instability during repositioning ^[8]. Feasibility and outcomes data specific to burn patients are limited. Despite logistical challenges, prone positioning should be considered in burn patients with severe refractory hypoxemia who are not responding to conventional optimization, with coordinated surgical and nursing planning around wound care schedules.

Nebulized Therapies During Mechanical Ventilation

Nebulized adjuncts are commonly used in mechanically ventilated burn patients with inhalation injury ^[8][9]:

• Nebulized heparin (5,000-10,000 units every 4 hours): Targets fibrin cast formation in subglottic inhalation injury.
• Nebulized N-acetylcysteine (3 mL of 20% solution every 4 hours): Targets mucus plugging.
• Bronchodilators (albuterol): Addresses bronchospasm from airway irritation.

The RAND/UCLA expert panel rated nebulized heparin as appropriate for subglottic inhalation injury but noted the absence of large RCTs ^[9].

Ventilator-Associated Complications

Burn patients have prolonged ventilator courses (mean 11 days in one cohort) and high rates of ventilator-associated pneumonia (VAP) ^[2]. Strategies to reduce VALI and VAP include:

• Lung-protective tidal volumes and pressure limitation
• Head of bed elevation to 30-45 degrees
• Oral care protocols
• Subglottic secretion drainage
• Early tracheostomy when prolonged ventilation is anticipated (see [[tracheostomy-in-burn-patients]])
• Daily sedation interruption and spontaneous breathing trials when clinically appropriate

Prophylactic antibiotics and corticosteroids are not recommended for inhalation injury based on current evidence ^[9].

Controversies and Evidence Gaps

• No large RCT has compared ventilator modes (volume-controlled vs pressure-controlled vs APRV) specifically in burn patients with inhalation injury ^[7][9].
• The LAMiNAR study's negative finding for low tidal volume ventilation in burns leaves open whether the ARDSNet survival benefit extends to this population, or whether burn-specific physiology requires different tidal volume targets ^[6].
• The optimal PEEP strategy in burn patients with combined inhalation injury and large TBSA burns undergoing massive resuscitation is undefined ^[2][7].
• Whether the ARDSNet 6 mL/kg tidal volume target should be modified upward in burn patients with elevated CO2 production from hypermetabolism is debated ^[1][6].
• The role of ECMO as rescue therapy in burn patients with refractory respiratory failure is supported only by case reports and small series ^[8].
• The interaction between ventilator-induced lung injury and the systemic inflammatory response of burn injury is incompletely understood ^[2].

References

[1] Glas GJ et al. "Changes in ventilator settings and ventilation-induced lung injury in burn patients." Burns 2019;46(4):762-770. PMID: 31202528. [2] Salman A et al. "Strategies to reduce ventilator-associated lung injury (VALI)." Burns 2012;39(2):200-11. PMID: 23183376. [3] Acute Respiratory Distress Syndrome Network. "Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome." N Engl J Med 2000;342(18):1301-8. PMID: 10793162. [4] Young D et al. "High-frequency oscillation for acute respiratory distress syndrome." N Engl J Med 2013;368(9):806-13. PMID: 23339638. [5] Ferguson ND et al. "High-frequency oscillation in early acute respiratory distress syndrome." N Engl J Med 2013;368(9):795-805. PMID: 23339639. [6] Schultz MJ et al. "Ventilation practices in burn patients -- an international prospective observational cohort study (LAMiNAR)." Burns 2022;48(5):1044-1054. PMID: 34926707. [7] Chung KK et al. "A Survey of Mechanical Ventilator Practices Across Burn Centers in North America." J Burn Care Res 2016;37(2):e131-9. PMID: 26135527. [8] Velamuri SR et al. "Inhalation Injury, Respiratory Failure, and Ventilator Support in Acute Burn Care." Clin Plast Surg 2024;51(2):237-248. PMID: 38429045. [9] Milton-Jones KJ et al. "An international RAND/UCLA expert panel to determine the optimal diagnosis and management of inhalation injury." Crit Care 2023;27:459. PMID: 38012797.