Question 26

College comments

Syllabus topic/section: 2.1.21 Applied Pharmacology in Intensive Care; Respiratory: Pulmonary vasodilators

Discussion: 

In general, most candidates had answers that were reasonable, but some lacked in-depth knowledge of the use of pulmonary vasodilators.

A discussion of a therapies should include rationale, pathophysiology, advantages and disadvantages as
outlined in the glossary of terms for “Discuss” SAQs.

Some candidates only discussed iNO; the question was about inhaled pulmonary vasodilators; candidates are reminded that Prostacyclin / analogues are also inhaled (nebulised) medications.

To attain a passing mark, candidates needed to describe key principles in hypoxemic respiratory failure and should have mentioned hypoxemic respiratory failure in ARDS AND 1-2 other appropriate indications. Discussion points that needed to be included: local action and minimal systemic effect for advantages; specialised equipment and cost in disadvantages; description of some limitations (e.g. limited mortality benefit; limited oxygenation response). Adding headings would aid in scoring more marks.

Higher marks were obtained if in addition, candidates expanded in more depth on disadvantages and limitations (e.g. rebound PHT on abrupt withdrawal; association of renal failure with iNO use).

The rubric is provided to aid the candidate's future study.

	Below standard	At standard	Above standard
Discuss the use of inhaled pulmonary vasodilators in critically ill adult patients. 10 marks	Does not attempt OR poor understanding of principles OR only mentions hypoxemic respiratory failure (ARDS) for indications OR provides minimal information (e.g. only mentions duration of action or cost for advantages or disadvantages) OR does not mention limitations/risks 0-4.5 marks	Must describe key principles in hypoxemic respiratory failure. Should mention hypoxemic resp failure in ARDS AND 1-2 other appropriate indications Discussion points include: – mentions local action and minimal systemic effect for advantages; specialised equipment and cost in disadvantages; describes some limitations (limited mortality benefit; limited oxygenation response) 5 - 7.5 marks	at STANDARD PLUS Describes all the underlying principles (respiratory AND cardiac) and lists most indications. Names ≥ 2 agents. expands in more depth on disadvantages and limitations (eg rebound PHT on abrupt withdrawal; association with renal failure and iNO use) 8 - 10 marks

Interpretation

Being sufficiently similar to several past paper questions, this one should be regarded as a gift to the tired brain of the exam candidate, struggling through the convulsive labour of the second paper. Question 4 from the second paper of 2019, Question 14 from the first  paper of 2006 and Question 2 from the first paper of 2004 had something very similar to ask.

Rationale

• Possible indications include:
  • to improve V/Q matching in heterogenous lung disease
  • to reduce RV afterload in RV dysfunction due to pulmonary hypertension
  • to reduce intracardiac shunt fraction

Advantages

• Most agents are close to ideal (minimal recirculation, mostly only local effects, few adverse effects)
• Can be administered via widely available circuit extensions
• Minimal nursing workload (as compared to, for example, proning)
• A consistent signal for oxygenation improvements in the literature

Disadvantages

• Inhaled agents have their own toxicities (eg methemoglobinaemia with NO, platelet dysfunction and hypotension with prostacycline, rebound hypoxia after abrupt withdrawal)
• Increased fluid delivery to the ventilator filters can produce high airway pressure
• Response is unpredictable (i.e. may have little effect)
• Rebound pulmonary hypertension can occur
• Titration is difficult without invasive monitors like PA catheter
• Considerably more expensive than other similar therapies
• Difficult to administer reliably to awake spontaneously breathing patients
• No consistent signal for mortality improvement in the data

Controversies/risks

• Patient selection is unclear, expecially in the era of familiarity with prone ventilation and ECMO
• Availability is limited to the kind of centres that would also have ECMO and experience with prone ventilation
• Minimal data beyond observational, RCTs are few