A 51 -year-old male has just been transferred to the ICU from the surgical ward with worsening shortness of breath five days post-oesophagectomy, and a presumed anastomotic leak.
On arrival in ICU, he is tachypnoeic and extremely agitated.
Arterial blood gas analysis on FiO2 0.6 — 0.8 via reservoir (non-rebreathing) mask shows the following:
Adult Normal Range
7.35 - 7.45
50 mmH 6.6 kPa
50 mmH 6.6 kPa *
35-45 4.6 -6.0
22 - 28
Chest X-ray shows bilateral pulmonary infiltrates.
- List the possible causes for his respiratory failure. (20% marks)
The patient is intubated and mechanical ventilatory support is initiated.
- Describe the ventilator settings you will prescribe, giving the rationale for your decision.
Following intubation, there is no immediate improvement in the patient's oxygenation.
- List the initial strategies that may be used to improve oxygenation. (20% marks)
Differential diagnosis should include:
- ARDS secondary to sepsis from any source or other inflammatory insult including the following
- Pneumonia (hospital-acquired)
- Atelectasis/pleural effusions/empyema
- Fluid overload secondary to resuscitation, renal failure
- Exacerbation of pre-existing condition e.g. heart failure, valvular heart disease, post-op ischaemia/MI, arrhythmia
- Lung diseases e.g. lymphangitis carcinomatosis
- Use a mode with which one is familiar and aim to limit ventilator-associated lung injury, i.e. oxygen toxicity, barotrauma, volutrauma, shear stress and biotrauma
- Choice of mode (any appropriate answer acceptable e.g. APRV for recruitment benefit, or volume assist control as staff familiarity and no one mode shown to have benefit over another)
- Avoid over-distention of alveoli by keeping tidal volumes at 6-8 ml/kg (predicted body weight which in the ARDSnet studies was ~20% below actual body weight and calculated by a formula linking height and sex)
- Use PEEP to minimise alveolar collapse and derecruitment.
- Titrate PEEP to achieve a PaO2 of 60 mmHg with lowest FiO2 that is needed
- Permissive hypercapnea to avoid large minute volumes and alveolar injury through collapse and expansion of lung units
- High FiO2 (titrated to lowest possible level to limit toxicity)
- Confirm ETT pos
- Exclude readily reversible cause of hypoxia e.g. PTX, mucus plug, large effusion
- Increased inspiratory time
- Increased PEEP
- Prone positioning for at least 16/24 hours per day
- Ensure adequate cardiac output
Answered well overall. Lack of detail and structure in some answers.
a) List the possible causes for his respiratory failure.
Tandon et al (2001) mention that this happened to over 14% of their oesophagectomy patients, with a 50% mortality. Why is this post-oesophagectomy patient so hypoxic, and what are those infiltrates? One might classify this into two broad categories:
- Related to the oesophagectomy
- ARDS due to sepsis
- Aspiration, eg. even some sort of tracheo-oesophageal fistula
- Atelectasis/pleural effusions/empyema
- Massive blood transfusion
- Unrelated to the surgery
- Pulmonary haemorrhage
- Hospital-acquired pneumonia
- Lymphangitis carcinomatosis
- Drug-related (eg. eosinophilic) pneumonitis
- Autoimmune pulmonary vasculitis
- Pulmonary oedema due to MI, valve disease or fluid overload
b) Describe the ventilator settings you will prescribe, giving the rationale for your decision.
- Use a Pressure Control mode (it may be safer, though the evidence is not strong). The college recommend to "use a mode with which one is familiar", which is reasonable because none have been shown to be superior in terms of mortality, but which opens the possibility of using a familiar and truly useless mode.
- Lung-protective ventilation: use low tidal volumes (6-8ml/kg)
- Open-lung ventilation: avoid derecruitment by using a higher PEEP
- Determine the optimal PEEP using any number of strategies, including:
- As the ARDS severity increases, consider using a higher PEEP.
- Optimise the driving pressure (ΔP) -that means, using a higher PEEP and aiming for a lower plateau pressure (Amato et al, 2015.)
- Accept a level of "permissive hypercapnea"
c) List the initial strategies that may be used to improve oxygenation.
Let's assume you've excluded sophomoric errors like right bronchial intubation and sputum plugging. Other strategies may include:
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 haemodynamics permit. Again, these offer a transient improvement in oxygenation, but do not influence survival.
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.
- ECMO may improve survival (CESAR, 2009) but again there were problems with methodology, and in any case the upper GI surgeon may have a big problem with heparinising the circuit.
Tandon, S., et al. "Peri‐operative risk factors for acute lung injury after elective oesophagectomy." British journal of anaesthesia 86.5 (2001): 633-638.
ARDS Definition Task Force. "Acute Respiratory Distress Syndrome." Jama307.23 (2012): 2526-2533.
Marini, John J. "Point: is pressure assist-control preferred over volume assist-control mode for lung protective ventilation in patients with ARDS? Yes." CHEST Journal 140.2 (2011): 286-290.
Esteban, Andrés, et al. "Prospective randomized trial comparing pressure-controlled ventilation and volume-controlled ventilation in ARDS." CHEST Journal 117.6 (2000): 1690-1696.
Gainnier, Marc, et al. "Effect of neuromuscular blocking agents on gas exchange in patients presenting with acute respiratory distress syndrome*."Critical care medicine 32.1 (2004): 113-119.
Watling, Sharon M., and Joseph F. Dasta. "Prolonged paralysis in intensive care unit patients after the use of neuromuscular blocking agents: a review of the literature." Critical care medicine 22.5 (1994): 884-893.
Armstrong Jr, Bruce W., and Neil R. MacIntyre. "Pressure-controlled, inverse ratio ventilation that avoids air trapping in the adult respiratory distress syndrome." Critical care medicine 23.2 (1995): 279-285.
Hodgson, Carol, et al. "Recruitment manoeuvres for adults with acute lung injury receiving mechanical ventilation." Cochrane Database Syst Rev 2.2 (2009).
Zavala, Elizabeth et al.Effect of Inverse I: E Ratio Ventilation on Pulmonary Gas Exchange in Acute Respiratory Distress Syndrome Anesthesiology: January 1998 - Volume 88 - Issue 1 - p 35–42
Brower RG, Lanken PN, MacIntyre N, et al; National Heart, Lung, and Blood Institute ARDS Clinical Trials Network. Higher versus lower positive endexpiratory pressures in patients with the acute respiratory distress syndrome. N Engl J Med. 2004;351(4):327-336.
Meade MO, Cook DJ, Guyatt GH, et al; Lung Open Ventilation Study Investigators. Ventilation strategy using low tidal volumes, recruitment maneuvers, and high positive end-expiratory pressure for acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. JAMA. 2008;299(6):637-645.
Mercat A, Richard JC, Vielle B, et al; Expiratory Pressure (Express) Study Group. Positive end-expiratory pressure setting in adults with acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. JAMA. 2008;299(6):646- 655.
Briel, Matthias, et al. "Higher vs lower positive end-expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome." JAMA: the journal of the American Medical Association 303.9 (2010): 865-873.
De Campos, T. "Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. The Acute Respiratory Distress Syndrome Network." N Engl J Med342.18 (2000): 1302-130g.
Putensen, Christian, et al. "Meta-analysis: ventilation strategies and outcomes of the acute respiratory distress syndrome and acute lung injury." Annals of internal medicine 151.8 (2009): 566-576.
de Durante, Gabriella, et al. "ARDSNet lower tidal volume ventilatory strategy may generate intrinsic positive end-expiratory pressure in patients with acute respiratory distress syndrome." American journal of respiratory and critical care medicine 165.9 (2002): 1271-1274.
Kahn, Jeremy M., et al. "Low tidal volume ventilation does not increase sedation use in patients with acute lung injury*." Critical care medicine 33.4 (2005): 766-771.
Hodgson, Carol L., et al. "A randomised controlled trial of an open lung strategy with staircase recruitment, titrated PEEP and targeted low airway pressures in patients with acute respiratory distress syndrome." Crit Care 15.3 (2011): R133.
MANCINI, MARCO, et al. "Mechanisms of pulmonary gas exchange improvement during a protective ventilatory strategy in acute respiratory distress syndrome." American journal of respiratory and critical care medicine 164.8 (2012).
Amato, Marcelo Britto Passos, et al. "Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome." New England Journal of Medicine 338.6 (1998): 347-354.
Chu, Eric K., Tom Whitehead, and Arthur S. Slutsky. "Effects of cyclic opening and closing at low-and high-volume ventilation on bronchoalveolar lavage cytokines*." Critical care medicine 32.1 (2004): 168-174.
Amato, Marcelo BP, et al. "Driving pressure and survival in the acute respiratory distress syndrome." New England Journal of Medicine 372.8 (2015): 747-755.
Guérin, Claude, et al. "Prone positioning in severe acute respiratory distress syndrome." New England Journal of Medicine 368.23 (2013): 2159-2168.
Young D, et al. " High-frequency oscillation for ARDS". N Engl J Med 2013, 368:806-813
Ferguson, Niall D., et al. "High-frequency oscillation in early acute respiratory distress syndrome." New England Journal of Medicine 368.9 (2013): 795-805.
Pathmanathan, N., et al. "Five-year single-centre review of ARDS patients receiving high-frequency oscillatory ventilation." Critical Care 18.Suppl 1 (2014): P338.
Long, Yun, et al. "Positive end-expiratory pressure titration after alveolar recruitment directed by electrical impedance tomography." Chinese medical journal 128.11 (2015): 1421.