How to manage hypovolemic shock with Acute Respiratory Distress Syndrome (ARDS)?

Management of Hypovolemic Shock with ARDS

In patients with hypovolemic shock and ARDS, initial resuscitation should focus on careful fluid administration to restore tissue perfusion while implementing lung-protective ventilation strategies to minimize further lung injury. 1, 2

Initial Assessment and Stabilization

Hemodynamic Management

• First priority: Restore adequate tissue perfusion while minimizing pulmonary edema
• Assess intravascular volume adequacy using:
  • Ultrasound evaluation of inferior vena cava dimension and filling dynamics
  • Pulse pressure variation observations
  • Central venous pressure monitoring in response to intervention
  • Urine output and metabolic acidosis as indicators of tissue perfusion 1

Volume Resuscitation

• Initial fluid resuscitation: Administer fluid boluses based on central venous pressure (CVP) and urine output:

  • If CVP <4 mmHg: Give fluid bolus and reassess in 1 hour
  • If CVP 4-8 mmHg with low urine output (<0.5 mL/kg/h): Give fluid bolus and reassess in 1 hour
  • If CVP >8 mmHg: Consider furosemide rather than additional fluids 1

• Fluid type considerations:

  • Isotonic crystalloids are first-line (e.g., balanced salt solutions)
  • Consider blood transfusion if hemoglobin <8 g/dL
  • Consider albumin in cases of sepsis-related ARDS or severely decreased serum albumin 1
  • Small volume hypertonic saline (250 mL of 7.5% NaCl) may rapidly expand plasma volume by approximately 24% in severe hypovolemia 3

Vasopressor Support

• Once adequate intravascular volume is ensured, initiate vasopressors if needed
• Norepinephrine is the vasopressor of choice as it improves right ventricular function by restoring mean arterial pressure and RV blood supply 1
• Target mean arterial pressure ≥60 mmHg 1

Ventilator Management

Initial Ventilation Settings

• Implement lung-protective ventilation:
  • Tidal volumes of 6 mL/kg predicted body weight
  • Plateau pressures ≤30 cmH₂O
  • Initial PEEP of 5-8 cmH₂O
  • FiO₂ titrated to maintain SpO₂ 92-95% 2

PEEP Titration Based on ARDS Severity

• Mild ARDS (PaO₂/FiO₂ 201-300 mmHg): Lower PEEP (5-10 cmH₂O)
• Moderate ARDS (PaO₂/FiO₂ 101-200 mmHg): Higher titrated PEEP
• Severe ARDS (PaO₂/FiO₂ ≤100 mmHg): Higher titrated PEEP with consideration of adjunctive therapies 2

Permissive Hypercapnia

• Accept elevated CO₂ levels as a consequence of lung-protective ventilation
• Target pH >7.20
• Target PCO₂ 35-45 mmHg (may allow higher if necessary to maintain lung-protective strategy) 2

Balancing Fluid Management After Initial Resuscitation

Transition to Conservative Fluid Strategy

• Once shock is resolved (MAP ≥60 mmHg and off vasopressors for ≥12 hours), implement a conservative fluid management strategy using the FACTT-lite protocol:
  • Target neutral-to-negative fluid balance
  • Use diuretics based on CVP and urine output
  • Discontinue maintenance fluids
  • Continue medications and nutrition 1, 2

Diuretic Management

• Begin with furosemide 20 mg bolus or 3 mg/h infusion
• Double each subsequent dose until goal achieved (oliguria reversal or target intravascular pressure)
• Maximum infusion rate: 24 mg/h or 160 mg bolus
• Do not exceed 620 mg/day
• Withhold diuretics in renal failure or within 12 hours of fluid bolus/vasopressor administration 1

Adjunctive Therapies for ARDS

For Moderate to Severe ARDS

• Prone positioning: Implement for patients with severe ARDS (PaO₂/FiO₂ <150 mmHg) for at least 16 hours per session 2
• Neuromuscular blocking agents: Consider for ≤48 hours in severe ARDS to improve patient-ventilator synchrony 2
• Corticosteroids: Consider for all ARDS patients to reduce inflammatory response and pulmonary edema 2
• Venovenous ECMO: Consider for selected patients with severe ARDS refractory to conventional therapy 2

Monitoring and Ongoing Care

Hemodynamic Monitoring

• Regular assessment of:
  • Mean arterial pressure (target ≥60 mmHg)
  • Central venous pressure
  • Urine output (target >0.5 mL/kg/h)
  • Echocardiography to detect acute cor pulmonale (present in 20-25% of ARDS patients) 1

Ventilator Monitoring

• Daily assessment of:
  • Plateau pressure (maintain ≤30 cmH₂O)
  • Driving pressure (limit to <18 cmH₂O)
  • PaO₂/FiO₂ ratio under standardized ventilator settings at 24 hours after ARDS onset 2

Prevention of Complications

• Elevate head of bed between 30-45 degrees to prevent ventilator-associated pneumonia
• Implement prophylaxis for stress ulcers and venous thromboembolism 2

Common Pitfalls and Caveats

1. Excessive fluid administration: Can worsen pulmonary edema, decrease oxygenation, and precipitate right ventricular failure. Once adequately volume resuscitated, further fluid expansion is usually useless and potentially harmful 1

2. Inadequate initial resuscitation: Failure to restore adequate tissue perfusion can lead to worsening organ dysfunction and increased mortality

3. Neglecting right ventricular function: Right ventricular failure is a main factor limiting efficacy of fluid administration in restoring perfusion 1

4. Inappropriate ventilator settings: High tidal volumes, high plateau pressures, and inadequate PEEP can worsen lung injury and impair right ventricular function

5. Delayed implementation of adjunctive therapies: Early consideration of prone positioning and neuromuscular blockade in severe ARDS can improve outcomes 2