a) Describe your initial ventilator settings for a patient just intubated for acute severe asthma. Explain the rationale for each of your choices. (50% marks)
b) Hypotension commonly occurs after intubation in an asthmatic. What are the potential aetiologies and what steps would you take to prevent and/or treat them? (50% marks)
Either volume controlled or pressure controlled modes are acceptable.
Generally spontaneous modes are avoided early and when unstable, needs deep sedation +/- paralysis to facilitate non injurious mode of ventilation
FiO2 1.0 – newly intubated – titrate down asap as risk of O2 toxicity and Aa gradient not usually a
PEEP: – controversial – Conventional teaching advocates a PEEP 0 to minimise high Paw, but there will already be some dynamic hyperinflation with intrinsic PEEP – set PEEP in or around this. Acceptable to mention PEEP titration to pressure/volume curves, but not required.(a discussion around what PEEP would be set with a reasonable justification was required for marks)
VT 4-6ml per kg – limited by plateau pressure < 30 – note PIPs will be high and need to be tolerated,
e.g. up to 50 cmH2O), ventilator alarms will need to be adjusted
RR / T insp. to be minimised to avoid dynamic hyper-inflation (or prolong exp. time) Generally aim Pplat <30cm/H20 and PEEPi <10
Dehydration – unwell by days, inadequate PO intake and then positive intrathoracic pressure – decreasing preload further, minimised by IV fluids loading prior to intubation, and volume loading afterwards to treat.
Afterload reduction/obliteration of sympathetic stimulation – drugs (sedatives and bronchodilators), use vasoconstrictors (titrated metaraminol or noradrenaline), may alter induction drugs or doses used
Dynamic hyperinflation exacerbating the preload reduction. Prevention is with settings targeting lower RR, and shorter insp time, Pplat <30 cmH2O and PEEPi<10. Treat by disconnection of patient from the ventilator and transiently ceasing ventilation. Occasionally manual compression of chest required to aid expiration.
Tension pneumothorax. Prevention is by avoiding high tidal volumes/ mean airway pressures, and accepting high pCO2 if necessary. Paralysis to prevent coughing. Tension pneumothorax is treated with immediate decompression (e.g. with 14 G needle, then early intercostal chest drain).
*If dynamic hyperinflation as a cause of hypotension was not mentioned, a candidate could only score a maximum of 4/10)
Generally, well answered other than the justification for PEEP use.
The asthmatic patient, upon intubation, has the tendency to arrest. There are several possible reasons for this. They are presented here in the format of [problem]:[solution], though in all honesty a table would probably work better.
Rate and rhythm problems
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