Question 5

A patient in ICU requires intubation and is known to have a previous Grade 1 view on laryngoscopy.

a. Outline the physiological factors that could increase the risk of adverse events during intubation (4 marks)

b. Outline your strategies for optimising a physiologically unstable patient to minimise the risk of adverse events during intubation (6 marks)

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Discussion

Syllabus topic/section: 2.1.19 Intensive Care Procedures; 2.1.4 Cardiovascular Intensive Care; 2.1.5 Respiratory Intensive Care

Candidates are again reminded to carefully read the question. The question explicitly rules out the anatomically difficult airway and asks for the physiological factors, and many candidates wrote extensively about anatomical and other factors that did not attract marks. Similarly in Part B. whilst the question asked for physiological factors, many candidates wrote extensively about Front of Neck Access (FONA) and other structural/anatomical issues.

Candidates who used the template of an ABCD format to answer the question were distracted by the template focusing on A and B (anatomical) while candidates who used a system based or problem-based approach were better able to target their answers to the question and gain more marks. A useful strategy in the perusal time is to determine which structure will give the most accurate response to the content required.

Candidates who scored better in the question addressed the physiological factors such as hypoxia/oxygenation, arrhythmias, haemodynamic supports and shock management etc. The above standard candidate included management of acidosis, tiered therapies of inotrope deployment including timing and anticipation of further instability during the rigor of intubation. As with all questions, a clear structure helped answers to gain more marks.

Interpretation

The question could be read a number of ways, predominantly because "adverse events" is sufficiently broad to encompass an enormous amount of material. Is aspiration an "adverse event" related to a physiologically difficult airway? The Delphi consensus group from Karamchandani et al (2024) didn't think so, but most hospital's Serious Incident Review Committee members would disagree. Moreover, though the examiner's comments about the effort wasted on discussing anatomical airway problems are valid, one must also admit that the anatomical difficulty factors into the number of attempts and total apnoea time, which is exactly the sort of thing that one cannot afford if the patient is also physiologically difficult. So it's all interconnected, innit.  

Anyway: for four marks, 80-100 words is all that could be reasonably expected from this "outline" answer, which the answer given below would exceed even if none of the parenthesised explanations were included. The only option in this situation is to give a less than comprehensive answer, focusing on the basics (eg. hypovolemia) at the cost of clever rare stuff (thyrotoxicosis, aortic dissection, etc). 

a. Outline the physiological factors that could increase the risk of adverse events during intubation:

  • Respiratory factors
    • Hypoxia (shortens the possible apnoea time)
    • Hypercapnia (increases the risk of cardiovascular collapse)
    • High airway resistance (calls for a longer expiratory time) 
    • Dynamic hyperinflation (increases risk of cardiovascular collapse)
    • Increased risk from BVM (pneumothorax, abdominal distension)
    • Increased oxygen demand, eg. obesity, sepsis, pregnancy, thyrotoxicosis  (shortens the available timeframe)
  • Cardiovascular factors
    • Hypovolemia
    • Vasodilated distributive shock states
    • Pro-arhrythmic tendency
    • Poor LV or RV contractility
    • High RV afterload, eg. pulmonary hypertension
    • Limited coronary artery flow reserve (eg. critical unrevascularised stenosis)
    • Dependence on positive pressure ventilation (eg. APO)
    • Sensitivity to afterload (eg. severe MR, AR) 
  • Neurological factors
    • Sensitivity to BP fluctuations (eg. raised ICP, aneurysmal aortic or cerebrovascular pathology)
    • Delirium, agitation (frustrates prepapration)
  • Electrolyte and acid-base factors
    • Severe acidosis (promotes cardiovascular collapse)
    • Severe electrolyte derangement that promotes arrhythmias
    • Hyperkalemia  (influences choice of muscle relaxant)

b) Strategies for optimising a physiologically unstable patient to minimise the risk of adverse events during intubation:

  • Preparation:
    • Identify the potential haemodynamic and respiratory problems with bedside TTE, CXR, ECG and ABG
    • Correct metabolic acidosis (mindful of sodium bicarbonate use in patients with critical ventilation failure)
    • Correct volume deficit
    • Commence pre-induction vasoactive support for distributive shock states
    • Commence inotropes if contactility is poor
    • Add pulmonary vasodilators if the RV is the dominant source of cardiogenioc shock
  • Preoxygenation
    • NIV seems to be better than HFNP
    • HFNP is probably better than BVM or normal oxyegn
  • Choice of induction agents
    • Ketamine, ideally,  for haemodynamically unstable patients
    • Concurent boluses/uptitration of haemodynamic support
    • Reduced doses of induction agents
    • Rapid onset NMJ blockers (eg. rocuronium 2mg/kg)
  • Apnoeic oxygenation
    • HFNP
  • Tailored post-intubation ventilator strategy (eg. in metabolic acidosis, the ventilation goals are to sustain the respiratory performance that was required to compensate for the acidosis while the patient was awake)

References

Mosier, Jarrod M., et al. "The physiologically difficult airway." Western Journal of Emergency Medicine 16.7 (2015): 1109.

Mosier, Jarrod M., and Franz Rischard. "The physiologically difficult airway: Hemodynamics." Manual of Airway Management in Critical Care: eBook Without Multimedia. Wolters Kluwer Health, 2024.

Kornas, Rebecca L., et al. "Evaluation and management of the physiologically difficult airway: consensus recommendations from Society for Airway Management." Anesthesia & Analgesia 132.2 (2021): 395-405.

Karamchandani, Kunal, et al. "Tracheal intubation in critically ill adults with a physiologically difficult airway. An international Delphi study." Intensive care medicine 50.10 (2024): 1563-1579.