وصف
Ventilatory strategies in Acute Respiratory Distress Syndrome (ARDS) are crucial for optimizing oxygenation and minimizing further lung injury. Ventilating with low tidal volumes (6 mL/kg of predicted body weight or lower) reduces the risk of ventilator-induced lung injury (VILI). PEEP is used to maintain alveolar recruitment and improve oxygenation while preventing lung collapse during expiration. A lung-protective ventilation strategy combines low tidal volume and appropriate PEEP levels to minimize barotrauma and volutrauma. Prone positioning can be beneficial in ARDS patients by improving oxygenation and reducing ventilator-induced lung injury. Allowing for higher levels of carbon dioxide (permissive hypercapnia) may be necessary to avoid excessive ventilator pressures. Continuous monitoring of oxygenation, ventilation, and lung mechanics is essential to adjust ventilatory settings as needed. Individualized PEEP selection using techniques like the recruitment-to-inflation (R/I) ratio helps tailor ventilatory support to each patient's needs.
ملخص
- ARDS is a severe and under-recognized condition with high mortality. The Lung Safe study highlighted the lack of proper ARDS recognition and management, even in developed countries, with instances of missed diagnoses and inadequate use of low tidal volume ventilation, PEEP measurement, and prone positioning.
- The Berlin definition of ARDS relies on timing (within a week of insult), chest imaging (bilateral opacities not explained by other causes), edema (non-cardiogenic), and oxygenation (PAO2/FIO2 ratio categories for mild, moderate, and severe ARDS). Modifications, such as using SPO2/FIO2 or considering HFNC use, have been proposed to improve recognition in resource-limited settings.
- ARDS pathophysiology involves an initial exudative phase with inflammatory mediator release, neutrophil accumulation, and damage to the alveolar-capillary barrier, leading to alveolar flooding. This progresses to a proliferative phase with attempts at repair and possible fibrosis, hindering gas exchange. Ventilator-induced lung injury (VILI) mirrors ARDS pathophysiology, compounding the problem.
- Transpulmonary pressure, the difference between alveolar and pleural pressure, is a crucial concept. Excessive transpulmonary pressure can cause lung damage. VILI arises from atelectrauma (repeated alveolar collapse and reopening), volutrauma (overdistension and rupture), and biotrauma (inflammatory mediator release).
- The "baby lung" concept acknowledges the heterogeneous nature of ARDS, where only some lung regions are functional. Ventilation strategies should protect this "baby lung" by using low tidal volumes and positive pressure to gently recruit alveoli. Prone positioning can improve oxygenation and reduce VILI by distributing pressure more evenly.
- Ventilation strategies should prioritize lung protection. The ARDSNet's ARMA trial established the benefits of low tidal volume ventilation with plateau pressure limits. Guidelines recommend calculating predicted body weight, starting with low tidal volumes (6-8 ml/kg), and gradually decreasing them. Permissive hypercapnia is acceptable to a certain extent.
- Ideal PEEP balances oxygenation, alveolar recruitment, and avoidance of overdistension. Strategies for PEEP titration include empirical setting, ARDSNet tables, targeting maximum compliance, using pressure-volume curves, and transpulmonary pressure monitoring, although the latter has shown mixed results.
- Recruitment maneuvers involve transiently increasing airway pressure to open collapsed alveoli. Prone ventilation is a crucial recruitment maneuver, improving lung mechanics and oxygenation. The PROSEVA trial demonstrated its mortality benefit in severe ARDS.
- Neuromuscular blockade can improve ventilator synchrony, but its use has been questioned by studies using higher PEEP and lighter sedation. Rescue strategies like ECMO can provide lung rest, but patient selection and timing are crucial. Individualizing treatment plans is vital, with ventilator management guided by patient assessment and lung mechanics.
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الدكتور ريشاب كومار ميتال
Principal Consultant Critical Care Medicine and Incharge Gastro Liver & liver Transplant ICU Max Super specialty Hospital, Delhi
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