A 42-year-old miner has been transferred to the unit after an industrial accident in a remote location. He was entrapped in a fire underground.
He arrives 30 hours after injury, weighs 70 kg and is 1.75m tall.
He is intubated and ventilated. His admission chest x-ray shows widespread bilateral pulmonary infiltrates.
His initial arterial blood gas shows the following:
|pH||6.93*||7.35 - 7.45|
|p02||55 mmHg (7.3 kPa)|
|pC02||78.0 mmHg (10.4 kPa)*||35.0 - 45.0 (4.6 - 6.0)|
|Bicarbonate||_||16.0 mmol/L*||22.0 - 26.0|
|Base Excess||-14.0 mmol/L*||-2.0 - +2.0|
His current ventilator settings are as follows:
Peak lnspiratory Pressure
a) List six possible causes for his hypoxaemia. (20% marks)
b) Outline your management strategies for the treatment of his hypoxaemia. (80% marks)
• Aspiration pneumonitis
• Blast Injury
• Smoke inhalation
• Misplaced ETT
• Fluid overload
• Pulmonary oedema
• Restrictive defect from circumferential burn
b) General ventilator strategies based on ARDS net criteria
• Check adequate placement of ETT (no R endobronchial intubation)
• ARDS net ventilation Vt 6mls/kg = 420mls best PEEP.
Use of recruitment maneuvers with derecruitment to assess best PEEP
CPAP 40/40 or step wise recruitment maneuvers
Use of flow loops
Aim Plateau <30cm H2O avoid baro trauma
Increase I:E ratio towards 1:1 and increase rate if tolerated
Check for autoPEEP and use of broncho dilators
Treat reversible causes like PTX
C- rule out cardiomyopathy and improve V:Q match as cardiac function can be depressed in the severe inflammatory state.
General adjunctive measures
• Physio. Suctioning. Consider bronchoscopy
• Sedation, heavy sedation will be required. In advanced Hypoxia may require paralysis.
• Treat factors increasing metabolic demand (removal of eschar, treatment of sepsis, high risk of pneumonia)
• Optimize Hb and oxygen carrying capacity.
• If patient has been over resuscitated may require diuresis
General Rescue therapies
• Prone positioning- may not be practical in a burns patient
• Alternative ventilation strategies - prolonged
• ECMO in severe cases
• Nitric oxide or inhaled prostacyclin
Burns specific measures
B2 agonists such as Adrenaline or Salbutamol
Adrenaline reduces blood flow to injured/obstructed airways improving V:Q mismatch
Muscarinic receptor antagonists – reduction of cytokines, reduction of mucus secretions
Inhaled fibrinolytics for reduction of fibrin casts in volume and plugging.
• bronchoscopy for cast removal and prevention and treatment of mechanical obstruction and plugging
***rule out toxidromes, cyanide, CO, may need or antidote.****
• Ensure chest expansion not impeded by eschar
• May require escharotomies for free chest movement
This is hypoxia in a miner pulled from an underground fire. His ABG result demonstrates a severe metabolic and respiratory acidosis. Specific elements which arouse concern in that setting are:
- He's a miner, and therefore possibly exposed to exotic substances. Who knows what he was mining in there?
- He was underground, which as an enclosed space has two major consequences:
- It amplifies blast waves
- It concentrates heat
- It limits the oxygen supply
The differentials therefore are:
- Inhalational burns injury
- Corrosive agent inhalation
- Asphyxiant agent exposure (eg. carbon monoxide or cyanide)
- "Blast lung" due to primary blast injury.
- Aspiration due to a decreased level of consciousness
- Pulmonary oedema due to primary myocardial damage
- Barotrauma due to profoundly stupid ventilator settings.
The ventilator settings are mildly inappropriate This guy is being ventilated like a elective theatre case. The college clearly wanted the candidates to discuss the standard approach to ARDS ventilation.
Initial ventilator strategy:
- Use a Pressure Control mode (it may be safer, though the evidence is not strong)
- Lung-protective ventilation: use low tidal volumes (6ml/kg)
- Open-lung ventilation: avoid derecruitment by using a high PEEP
- The ideal PEEP can be found either by finding the lower inflection point or the pressure-volume curve or by observing a stepwise decrease in PEEP after a recruitment manoeuvre.
- As the ARDS severity increases, consider using a higher PEEP.
- Use a lower driving pressure (ΔP) -Amato et al, 2015. That means, using a higher PEEP and aiming for a lower plateau pressure
- Accept a level of "permissive hypercapnea"
Additional ventilator manoeuvres to improve oxygenation:
- Use an I:E ratio of 1:1, even though manipulating the I:E ratio does not seem to improve survival, even though it may improve oxygenation.
- One might attempt some recruitment manoeuvres if hemodynamics permit. Again, these offer a transient improvement in oxygenation, but do not influence survival.
Non-ventilator adjunctive therapies for ARDS:
- Minimization of dead space ventilation - Remove as much tubing as you can.
- Low-carbohydrate high-fat nutrition - Keep them off the carbs, and don't overfeed.
- Neuromuscular blockade improves survival, not just gas exchange.
- Sedation decreases energy expenditure and improves ventilator synchrony
- Fluid management should have a goal of neutral balance (keep em dry)
Ventilator strategies to manage refractory hypoxia
- Prone ventilation, for at least 16 hours a day (PROSEVA, 2013)
- High frequency oscillatory ventilation may not improve mortality among all-comers (OSCAR,2013) or it may actually increase mortality (OSCILLATE, 2013) but some authors feel that there were problems with methodology.
Non-ventilator adjuncts to manage refractory hypoxia
- Nitric oxide was a cause for some excitement, but is no longer recommended.
- Prostacyclin is still a cause for excitement, and is still vaguely recommended.
- Neither agent improves mortality, but prostacyclin can improve oxygenation.
- ECMO may improve survival (CESAR, 2009) but again there were problems with methodology.
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Kimmel, Edgar C., and Kenneth R. Still. "Acute lung injury, acute respiratory distress syndrome and inhalation injury: an overview." Drug and chemical toxicology 22.1 (1999): 91-128.
Gorguner, Metin, and Metin Akgun. "Acute inhalation injury." The Eurasian journal of medicine 42.1 (2010): 28.