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:

Parameter

Patient Value

Adult Normal Range

7.12*

7.35 - 7.45

PaO2

50 mmH 6.6 kPa

PaCO2

50 mmH 6.6 kPa *

35-45 4.6 -6.0

HCO3

16 mmol/L*

22 - 28

Chest X-ray shows bilateral pulmonary infiltrates.

  1. List the possible causes for his respiratory failure.    (20% marks)

The patient is intubated and mechanical ventilatory support is initiated.

  1. Describe the ventilator settings you will prescribe, giving the rationale for your decision.

(60% marks)

Following intubation, there is no immediate improvement in the patient's oxygenation.

  1. List the initial strategies that may be used to improve oxygenation. (20% marks)

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College answer

a)  

Differential diagnosis should include:

  • ARDS secondary to sepsis from any source or other inflammatory insult including the following
  • Pneumonia (hospital-acquired)
  • Aspiration
  • 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

b)  

  • 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

c)

  • High FiO2 (titrated to lowest possible level to limit toxicity)
  • Confirm ETT pos

     

    ition and patency
  • 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

 

Examiners Comments:

Answered well overall. Lack of detail and structure in some answers.

Discussion

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
    • Pancreatitis

b) Describe the ventilator settings you will prescribe, giving the rationale for your decision.

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:

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.

References

References

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