Airway And Mechanical Ventilation

Question 1

What is the LEMON pneumonic?

Answer 1

Look
Evaluate - 3:3:2 rule - 3 fingers in mouth:3 fingers from mentum to hyoid bone:2 finger hyoid to thyroid
Mallampati score - eg class I will be Cormack-Lehan grade I 99-100%.
class IV will always be a class III or IV
Obstruction - anything that might get in the way. Smoke, burns, broken necks, trauma to face, FB, obesity.
Neck - mobility

Question 2

What are the mechanisms by which hypoxia may be addressed?

Answer 2

Increase FiO2
Increase tidal volume
Increase PEEP
Address mucous plugging and derecruitment
Neuromuscular blocking agent to improve patient ventilator interaction and reduce chest wall compliance
Tracheal gas insuflation - alters alveolar gas constituents by washing out CO2. 2-5L via tube to tracheal in expiration
Prone ventilation - improves V/Q matching
Inhaled nitric oxide - ventilated units vascular bed dilates
HFOV
partial liquid ventilation
ECMO

Question 3

Outline the potential mechanisms of ventilator associated lung injury in patients with Acute Respiratory Distress Syndrome and the steps that can be taken to minimise them.

Answer 3

Volutrauma - over inflation of normal lung units above 30cm
Barotrauma - over distension with transpulmonary pressures above 50cm h2O causing membrane disruption and classic barotrauma
Biotrauma - mechanotransduction and tissue disruption with recruitment of inflammatory mediators
Derecruitment/recruitment injury - the weight of the oedematous ARDs lung in dependent areas
Shearing injury - the junction of collapsed and open lung significant shearing forces occur
Oxygen toxicity - high oxygen concentrations overwhelm the cells capacity to cope with free radicals

Question 4

What are the indicators to be assessed regarding fitness for extubation?

Answer 4

1. Has the condition that necessitated intubation resolved
2. Spontaneously breathing 30-120min
3. Adequate Oxygenation
   A. FiO2 not greater than 40%
   B. PEEP not greater than 5-8cm H2O
   C. pH not less than 7.25
4. Haemodynamic stability
   A. Absence of active myocardial
   ischaemia
   B. Absence of clinically significant hypotension
5. Effective cough - flow >160L/min. Not excessive secretions. Cuff leak test adequate flow >110ml average of three.

Question 5

What are the risk factors for post extubation stridor?

Outline the management of post extubation stridor?

Answer 5

= inspiratory noise post extubation indicated narrowing of the airway (can be supraglottic, but usually glottic and infraglottic)
- ET causes ulceration and oedema at the cords and where cuff abuts trachal
- incidence = 20%
Risk Factors
- excessive airway manipulation
- traumatic intubation
- prolonged intubation attempt (>10min)
- high cuff pressures
- intubation > 36 hours
- female
- short neck
- trauma patients
- recurrent intubations
- oroendotracheal intubation
- larger tubes
- small height:internal diameter ETT ratio
- known airway pathology (tracheal stenosis, tracheomalacia)
Treatment
- high flow O2
- observation
- adrenaline - nebulised (1-2mL of 1:1000)
- steroid IV - dexamethasone 0.15mg/kg or methylprednisolone 20mg (ARCO French DCMCRCT)
- CPAP
- re-intubation if develops airway obstruction or respiratory failure

Question 6

What are the predictors of difficult bag mask ventilation?

Answer 6

Presence of a beard
Body mass index >26 kg/m²
Lack of teeth
Age >55
History of Snoring
(Langeron: Prediction of difficult mask ventilation, Anesthesiology. 92:1229, 2000)