2.4.1 Hypoxemic respiratory failure

     Recognize severe hypoxemic respiratory failure when a patient with respiratory distress is failing standard oxygen therapy.

• Patients may continue to have increased work of breathing or hypoxemia even when oxygen is delivered via a face mask with reservoir bag (flow rates of 10-15 L/min, which is typically the minimum flow required to maintain bag inflation; FiO₂ 0.60-0.95).
• Hypoxemic respiratory failure in ARDS commonly results from intrapulmonary ventilation-perfusion mismatch or shunt and usually requires mechanical ventilation.
• Patients with hypoxemic respiratory failure on non-invasive ventilation are at risk of clinical deterioration, therefore it should only be used in selected patients and be closely monitored

     The following recommendations in this section pertain to mechanically ventilated patients with ARDS. These focus on adults; consensus-based recommendations for children are available.

• Implement mechanical ventilation using lower tidal volumes (4–8 ml/kg predicted body weight, PBW) and lower inspiratory pressures (plateau pressure <30 cmH2O). This procedure is needed for patients with ARDS and sepsis-induced respiratory failure who do not meet ARDS criteria.
• The initial tidal volume is 6 ml/kg PBW; tidal volume up to 8 ml/kg PBW is allowed if undesirable side effects occur (e.g. desynchrony, pH <7.15).
• Hypercapnia is permitted if meeting the pH goal of 7.30-7.45. Ventilator protocols are available.
• The use of deep sedation may be required to control respiratory drive and achieve tidal volume targets. Although high driving pressure (plateau pressure−PEEP) may be more accurate to predict increased mortality in ARDS compared to high tidal volume or plateau pressure.
• In patients with severe ARDS, prone ventilation for >12 hours per day is recommended.
• Application of prone ventilation is strongly recommended for adult and paediatric patients with severe ARDS but requires sufficient human resources and expertise to be performed safely.
• Use a conservative fluid management strategy for ARDS patients without tissue hypo perfusion. This is a strong guideline recommendation; the main effect is to shorten the duration of ventilation.
• In patients with moderate or severe ARDS, higher PEEP instead of lower PEEP is suggested.
• PEEP titration requires consideration of benefits (reducing atelectrauma and improving alveolar recruitment) vs. risks (end-inspiratory over distension leading to lung injury and higher pulmonary vascular resistance). Tables are available to guide PEEP titration based on the FiO2 required to maintain SpO2. A related intervention of recruitment manoeuvres (RMs) is delivered as episodic periods of high continuous positive airway pressure [30–40 cm H 2 O], progressive incremental increases in PEEP with constant driving pressure, or high driving pressure; considerations of benefits vs. risks are similar. Higher PEEP and RMs were both conditionally recommended, and patients should be monitored. In patients with moderate to severe ARDS (PaO2 /FiO2 <150), neuromuscular blockade by continuous infusion should not be routinely used.
• Continuous neuromuscular blockade may still be considered in patients with ARDS in certain situations: ventilator desynchrony despite sedation, such that tidal volume limitation cannot be reliably achieved; or refractory hypoxemia or hypercapnia.
• Avoid disconnecting the patient from the ventilator, which results in loss of PEEP and atelectasis. Use in-line catheters for airway suctioning and clamp endotracheal tube when disconnection is required (for example, transfer to a transport ventilator).

     2.4.2 Septic shock

Recognizing septic shock in adults

• When the infection is suspected or confirmed AND vasopressors are needed to maintain mean arterial pressure (MAP) ≥65 mmHg AND lactate is ≥2 mmol/L, in absence of hypovolemia.

For children, septic shock is recognized

• With any hypotension (systolic blood pressure [SBP] <5th percentile or >2 SD below normal for age) or 2-3 of the following:
• Altered mental state;
• Tachycardia or bradycardia (HR <90 bpm or >160 bpm in infants and HR <70 bpm or >150 bpm in children);
• Prolonged capillary refill (>2 sec) or warm vasodilation with bounding pulses;
• Tachypnea;
• Mottled skin or petechial or purpuric rash;
• Increased lactate;
• Oliguria;
• Hyperthermia or hypothermia.

In the absence of a lactate measurement, use MAP and clinical signs of perfusion to define shock. Standard care includes early recognition and the following treatments within 1 hour of recognition:

Managing septic shock by;

• Antimicrobial therapy and fluid loading and vasopressors for hypotension. The use of central venous and arterial catheters should be based on resource availability and individual patient needs.
• In resuscitation from septic shock in adults, give at least 30 ml/kg of isotonic crystalloid in adults in the first 3 hours. Crystalloids include normal saline and Ringer’s lactate.
• In resuscitation from septic shock in children, in well-resourced settings, give 20 ml/kg as a rapid bolus and up to 40-60 ml/kg in the first 1 hr

Do not use hypotonic crystalloids, starches, or gelatins for resuscitation.

Fluid resuscitation may lead to volume overload, including respiratory failure. If there is no response to fluid loading and signs of volume overload appear (for example, jugular venous distension, crackles on lung auscultation, pulmonary edema on imaging, or hepatomegaly in children), then reduce or discontinue fluid administration.

Alternate fluid regimens are suggested when caring for children in resource-limited settings. Determine need for additional fluid boluses

• (250-1000 ml in adults or 10-20 ml/kg in children) based on clinical response and improvement of perfusion targets.
• Perfusion targets include MAP (>65 mmHg or age-appropriate targets in children), urine output (>0.5 ml/kg/hr in adults, 1 ml/kg/hr in children), and improvement of skin mottling, capillary refill, level of consciousness, and lactate.

Consider dynamic indices of volume responsiveness to guide volume administration beyond initial resuscitation based on local resources and experience. These indices include passive leg raises, fluid challenges with serial stroke volume measurements, or variations in systolic pressure, pulse pressure, inferior vena cava size, or stroke volume in response to changes in intrathoracic pressure during mechanical ventilation.

Administer vasopressors when shock persists during or after fluid resuscitation. The initial blood pressure target is MAP ≥65 mmHg (Mean Arterial Pressure) in adults and age-appropriate targets in children.

If central venous catheters are not available, vasopressors can be given through a peripheral IV, but use a large vein and closely monitor for signs of extravasation and local tissue necrosis. If extravasation occurs, stop the infusion. Vasopressors can also be administered through intraosseous needles. If signs of poor perfusion and cardiac dysfunction persist despite achieving MAP target with fluids and vasopressors, consider inotrope such as dobutamine.

Vasopressors (i.e. norepinephrine, epinephrine, vasopressin, and dopamine) are most safely given through a central venous catheter at a strictly controlled rate, but it is also possible to safely administer them via a peripheral vein and intraosseous needle. Monitor blood pressure frequently and titrate the vasopressor to the minimum dose necessary to maintain perfusion and prevent side effects.

• Norepinephrine is considered first-line in adult patients; epinephrine or vasopressin can be added to achieve the MAP target.
• Because of the risk of tachyarrhythmia, reserve dopamine for selected patients with low risk of tachyarrhythmia or those with bradycardia.
• In children with cold shock (more common), epinephrine is considered first-line, while norepinephrine is used in patients with warm shock (less common).