• Ask the surgeons to stop. Gently re-inflate top lung and ventilate BOTH lungs with 100% O2*

THEN, to prevent recurrence:

• Deliver O2 to top lung: Low flow O2 catheter or CPAP circuit (see above)
• PEEP to bottom lung
• Propofol infusion
• Clamp the pulmonary artery

PS - *Sometimes the surgeon will be in the middle of something that cannot be stopped to allow re-inflation of the top lung. This is one of the reasons why it’s so important to communicate across the drapes in thoracics.

The trick here is to re-establish safe oxygenation first. Then you can fiddle around to try and prevent further episodes of hypoxia.

Don’t forget the usual system for working out the cause of hypoxia: It’s either the machine, the tube, or the patient. In thoracics it is usually the patient. Never the tube if you use a Robert Shaw, and always the tube if you use a Broncho-Cath

The reason to choose top lung CPAP before bottom lung PEEP is that PEEP on the bottom lung can actually worsen the shunt. PEEP on the bottom lung does 2 things: Increases FRC and raises PVR. The effect on PaO2 is variable and depends on the balance of the two variables. In diseased lung FRC is usually the predominant effect. In healthy lung it’s usually PVR. This is one of the reasons that good pre-op spirometry is a risk factor for hypoxia in one lung ventilation. 5cm CPAP rarely gets in the way of the surgical field.

Propofol does not inhibit hypoxic pulmonary vasoconstriction (HPV), so theoretically there may be some benefit in using propofol. But the evidence for this is not really there. Volatiles only inhibit HPV significantly over 1 MAC.

Thoracics is seriously the best fun to be had in the operating theatre!

Picture: CPAP circuit on top lung with pressure at about 5cmH2O. If you don’t have one of these, just use an airway suction catheter taped to oxygen tubing. You also have to tape over the proximal opening to stop the oxygen leaking out. Don’t pass the tip of the catheter beyond the lumen of the double lumen tube or you risk injuring the trachea/bronchus.

Unless you do a lot of paediatrics, you often don’t think about the dose of blood products by body weight, and they can sometimes be difficult to find.

• Red Cells: 4ml X kg X Hb g/dL rise required. (1 unit/bag ~ 300mL)  
• Fresh frozen plasma: 10 - 20 ml/kg (1 bag ~ 230mL) 
• Cryoprecipitate: 5-10 ml/kg (1 bag ~ 20mL) 
• Platelets: 10ml/kg (1 unit ~ 60mL. 1 pooled bag = 5 units)
• Tranexamic acid: 100mg/kg then 10mg/kg/hr
• Factor 7: 90mcg/kg
• Prothrombin (factor 9) complex: 1mL/kg (25units/kg)

In the exam and even in real life, if you don’t know, then ring someone! (ie: the haemotologist)

PS - To make it easier to remember: FFP, cryo and platelets are all about 10ml/kg.

• 100% oxygen
• Hyperventilate to low normal CO2
• Sedate and paralyse to drop metabolic demand
• Keep warm
• Noradrenaline to improve perfusion of right ventricle
• Nitric oxide

PS -The usual starting dose of nitric oxide is dose 20ppm, which is easy to remember as the usual starting dose of PGE1 is 20ng/kg/min. Neonates with pulmonary hypertension are often on both.

Features of a pulmonary hypertensive crisis:

• These are a nerve wracking emergency
• Patient looks terrible. Pale and blue
• High CVP
• PA pressures nearing systemic pressures
• Decreased lung compliance
• Systemic hypotension
• Hypoxia
• Hypercarbia. Note ET CO2 will be low due to reduced pulmonary blood flow. PaCO2 will be high due to reduced elimination via the lungs
• Acidosis: Metabolic and respiratory 

Other things you can do once the patient is a bit more stable:

• Introduce pulmonary vasodilators: sildenafil, bosantan, phenoxybenzamine, prostacyclin
• get a new echo to see if anything is changed or can be improved

Tranfuse blood products with a giving set that has a filter (170 to 230µm). This filters clot and aggregates.

Microaggregate filters (20-40 µm) were used at the bedside in the past to leukodeplete blood products. However, most Australian blood products are now pre-storage leukodepleted. 

• MEND
• Metabolic
• Endocrine
• Neurological
• Drugs

PS - I hate mnemonics. But during the exam, I hated being asked for failure to wake/unconscious differentials even more. It was always a jumble. Categorisation CAN make your life easier in the exam.

Metabolic = Hypoxia, hypercarbia, hyponatraemia, low glucose, hypotension

Endocrine = Hypothyroid, hypoadrenalism, encephalopathic

Neurological = Raised ICP, stroke

Drugs = Anaesthetic, analgesic, paralytic, antcholinergic

(Source: J Golshevsky)

• Blindness
• Hypotension - reduced venous return
• Access to airway
• Pressure sores and peripheral nerve injuries
• Difficulty performing CPR

PS - Incidence of blindness is about 1:1000! Way higher than I ever appreciated. And it’s a devastating complication.

Central retinal artery occlusion occurs with globe compression, which is preventable. Hence, check the eyes!

Ischaemic optic neuropathy is the tricky one. Etiology is unknown, but might have something to do with hypotension, anaemia or venous pressure. Some think it might be the globe ‘hanging’ with gravity by the optic nerve causing a neuropraxia. This last hypothesis actually sounds pretty good to me.

To minimise the risks:

• Avoid prone position in the first place
• Position the patient carefully - head in neutral position, with no flexion, extension or rotation of the neck.
• Make sure the eyes are free. I just tape with a transparent dressing to keep them closed
• Head higher than the heart and no neck ties
• Keep surgery short (95% cases of prone/blindness cases are >6 hours). Stage surgery if possible.
• Avoid blood loss and anaemia, and think twice about induced hypotension

• Difficult airway - swollen/contractures
• Avoid suxamethonium
• IV access and monitoring difficulties
• Hypovolaemia and electrolyte abnormalities
• Pain
• Blood loss
• Temperature loss

PS - Avoid sux in major burns 24 hours after the injury and until fully healed. Major burns: > 10% paed or 20% adult.

What are the requirements for doing a block? ACIMPLE (pronounced a-simple)

• A - Assistance
• C - Consent
• I - IV access
• M - Monitoring
• P - Position
• L - Landmarks
• E - Endpoint

What are the possible complications of doing a block?

• Failure
• Needle related - bleeding, infection, neuropraxia, pneumothorax etc.
• Local related - allergy, toxicity etc.

• Difficult airway and other associated abnormalities
• South RAE tube and throat pack
• Nasal airways post op - Repair can cause upper airway obstruction in patients who were breathing though the cleft. Plus tongue can swell with gag
• Arm splints and respiratory monitoring post op

PS - For cleft lip use infraorbital nerve blocks via the mouth: Approach at the intersection of the mucobuccal fold and the junction of premolars 1 and 2. Palpate infraorbital foramen with 2nd finger and use to guide needle. 0.5 to 1ml of local is usually enough. See non-anatomical digram below.

For neonates anatomy is different: Halfway between the midpoint of palpebral fissure and the angle of the mouth.  Bosenberg. BJA 1995; 74: 506-508.

• 100% O2
• Laryngospasm notch pressure
• CPAP or positive pressure ventilation
• Lignocaine on the cords
• Induction dose of propofol
• Suxamethonium IV (1 to 2mg/kg) or IM (4mg/kg)

PS - Laryngeal notch pressure: Firm pressure to the notch behind the earlobe, bounded by the mastoid process, base of skull and condyle of mandible. Pressure on both sides in a cephalad and medial direction can terminate laryngospasm. The jaw should move anteriorly. Mechanism unknown.

Larson C. Anesthesiology. 1998 Nov,(5):1293-4

• Occurs in about 10% of children
• Lasts about 20 minutes
• Characterised by crying, lack of eye contact, non purposeful actions/verbalisations
• Exclude other causes (pain, hypoxia, hypercarbia, hypotension, raised ICP, full bladder)
• Clonidine 1mcg/kg IV works well

PS - Getting parents in to calm a child with emergence agitation is not helpful, as the child is in a dissociated state and will not usually respond. You will just end up with distressed parents too.  

• Cardiac and respiratory function
• No suxamethonium or volatile (anaesthesia induced rhabdomyolysis)
• Reflux
• Obese
• Bleeding risk

PS - An easy way to think about the problems of Duchenne’s is to remember that all muscle types are affected: striated muscle, cardiac muscle and smooth muscle. 

The Not Always Top 5 posts are aimed at registrars sitting the ANZCA final exam. They list a few important points by topic. Sometimes they’re 5 points, sometimes more, sometimes less. They are definitely not all inclusive! I found them useful to remember when I was preparing for the final SAQs and the viva. I thought that if I could remember three or more specific points about a topic then I was on the way to a pass mark. I still find them useful to think about in day to day practice, and they are a good starting point for teaching in the operating theatre.