ANAESTHESIA D (28)

Question 1

COMMONEST ANAPHYLAXIS TRIGGERS DURING ANAESTHESIA

Answer 1

• Muscle relaxants
• Antibiotics
• Chlorhexidine (in both preps and devices)
• Latex
• Colloids

Question 2

OPTIMISING PRE-OXYGENATION

Answer 2

• POSITIONING:
  
  • sit up as this improves ventilation, airway patency, laryngeal view and decreases basal collapse
• PRE-OXYGENATION:
  
  • pre-oxygenate for either 3m or 8 maximal breaths using either a well fitting anaesthesia circuit with peep (best) or NRB on VERY HIGH FLOW (30 LPM)
  • aim for SPO2 >95% and ETO2> 90%
• PERI-OXYGENATION :
  
  • give O2 via nasal specs at 15+ LPM during laryngoscopy

Question 3

2 things to remember when doing RSI

Answer 3

• use nasal specs @ 15lpm for ‘PERI-OXYGENATION’
• consider NGT/OGT

Question 4

WHATS HAEMOPHILLIA A

Answer 4

Haemophillia A aka Classic Haemophillia is a rare, severe, X linked recessive haemophillia due to deficiency of F8 activity.

Rx

• F8 replacement with FFP, CRYO & F8 concentrates
• F8 boosters like DDAVP
• Fibrinolysis inhibitors like TXA

Question 5

WHAT IS VON WILLEBRANDS DISEASE?

Answer 5

• VWD = a relatively common, mild, Autosomally inherited Haemophillia due to a deficiency of VON WILLEBRANDS FACTOR, a protein which prolongs the half-life of F8
• Being Autosomal, sex ratio should be equal, but its more commonly Dx in females due to menorrhagia
• Management parallels that for Classic Haemophillia, but less aggressively, with FFP, CRYO, DDAVP and TXA

Question 6

WHAT IS HAEMOPHILLIA B

Answer 6

• Haemophillia B, aka CHRISTMAS DISEASE, after the index patient, Trevor Christmas, is a relatively common, relatively mild, X linked recessive Haemophillia due to F9 deficiency

Question 7

WHAT IS AUTONOMIC DYSREFLEXIA?

Answer 7

• = exaggerated SNS responses to relatively benign stimuli (eg full bladder) in denervated parts of the body seen in patients with cord lesions at T6 and above.
• this is why even high quadriplegics need anaesthesia for surgery

Question 8

OPTIMAL TIDAL VOLUME IN LUNG INJURY PATIENTS?

Answer 8

• use low volumes, 5ml/kg, not 7-10, and accept some hypercapnoea

Question 9

WHAT IS THE P/F RATIO?

Answer 9

• = pO2/fiO2, a measure of lung function in ventilated patients
• N is > 400
• < 150 is v bad, eg in ARDS

Question 10

WHEN TO ANTI-COAGULATE TRAUMA PATIENTS?

Answer 10

• trauma patients are at high risk of DVTs (even high amputees), so should have Clexane started early, as soon as haemostasis is achieved, and any coagulopathy corrected.

Question 11

WHAT ARE THE ‘FRENCH’ AND THE ‘GAUGE’ SYSTEMS FOR SIZING MEDICAL DEVICES?

Answer 11

The OUTSIDE DIAMETER of medical tubes is generally denoted using one of 2 sizing systems:

• The FRENCH system, where 1 Fr = 1/3mm, so a 36Fr chest tube has an OD of 12mm
• The GAUGE system, which is an archaeic, non linear 19th century wire sizing system, with size increasing as gauge decreases… like shotguns

Question 12

SBE PROPHYLAXIS

Answer 12

Despite recent research suggesting that most cases are sporadic, and few, if any, are prevented by antibiotic prophylaxis, Australian TGs continue to recommend the following for perioperative patients with structural heart defects:

• for Dental procedures:
  
  • AMOXIL 2g IV 60m prior (Cephalexin if allergic)
• for Abdominal & Urinary procedures:
  
  • AMOXIL 2g
  • • FLAGYL 500mg
  • • GENTAMYCIN 2mg/kg, all 60m prior

Question 13

ADVANCED CARE DIRECTIVES

Answer 13

• the ACD has now replaced* the MEDICAL POWER OF ATTORNEY in documenting a persons wishes with respect to their future medical** care should they become incompetent
• the ACD may set out the patients wishes, and/or nominate a SUBSTITUTE DECISION MAKER (SDM) to make medical decisions for them
• Health care workers should comply unless they reasonably believe the patients wishes have changed, are illegal, or they conscientiously object***
• when the patient becomes incompetent, the Hierachy of consent becomes:
  
  1. SDM
  2. ACD
  3. a PERSON RESPONSIBLE, in order of
     
     1. a legal GUARDIAN
     2. a Spouse or Adult relative
     3. a close friend
     4. a daily carer, eg Nursing home DON
• in emergencies where all the above are impractical, the 2 Dr rule applies, but must not contravene the patients wishes stated in an ACD

• * these remain valid unless superceded by an ACD*
• ** the POWER OF ATTORNEY continues as a instrument for deegation of their financial powers*
• *** in which case, they must hand over care*

Question 14

CONSENT TO MEDICAL TREATMENT: CHILDREN

Answer 14

for patients under 16y of age, consent can be given by:

1. the childs parents, but must be in best interests of the child
2. the child themselves, provided
   
   • they understand the nature of the treatment
   • the treatment is in their best interests
   • a 2nd Dr has examined the child and documented agreement
3. a PERSON RESPONSIBLE
4. in emergencies, where all the above are not practical, the 2 Dr rule still applies, AND TREATMENT CAN BE PROVIDED DESPITE PARENTAL REFUSAL if in the best interests of the child

Question 15

VENTILATOR MODES: IMV, SIMV, PS

Answer 15

• IMV = Intermittent Mandatory Ventilation: the vent delivers regular volume or pressure cycled breaths, irrespective of patient effort.
• SIMV = Synchronised IMV: the vent delivers regular volume or pressure cycled breaths unless it detects a patient effort, which it supports, then pauses before delivering another breath, to help synchronise with pt effort.
• Pressure Support: the ventilator delivers no mandatory breaths, but provides a set level of pressure support to any patient breath.

Question 16

WHAT DOES PRESSURE CONTROLLED VENTILATION AT 20/5 cm H2O MEAN?

Answer 16

• it means an inspiratory pressure of 20cm of water is added to the baseline PEEP of 5, ie 25 in total

Question 17

5 POINTS REGARDING ANAESTHESIA FOR TRACHEOSTOMY CREATION

Answer 17

1. BEWARE!!: most trachys are done percutaneously in the ICU now: those coming to the OR are the hard ones
2. Tracheostomies are done lower in the neck than crikes, where the airway is deeper: ‘loss’ of the trachea during the procedure is a real risk
3. go on 100% O2 before entering the trachea, but remind the surgeon no diathermy & have water ready for airway fire
4. surgical entry into the trachea is usually preceded by a request to withdraw the cuff to just below the cords, but pushing it deeper instead (to carina) and inserting a bougie to aid emergency re-intubation from above increases safety.
5. difficulty ventilating/no CO2 immediately after insertion probably indicates you are not in trachea, but if you are SURE you are in, consider DISTAL TRACHEAL OBSTRUCTION due to either:
   
   • clot or mucus displaced from above: suction
   • distal tracheal collapse*: replace with ET over the pre-sited bougie

* trachy tubes are short and tracheal collapse can occur beyond them, particularly when PEEP is lost when the trachea is opened

Question 18

ANAESTHESIA IN A PATIENT WITH AN EXISTING TRACHY

Answer 18

Trachy patients can be divided into 2 groups

1. PERMANENT trachy patients: these are usually laryngectomy patients with no upper airway. They can be identified by the absence of any trachy tube in the stoma, and the presence of a neck bib. They can be anaesthetised by SV of gas via the stoma, or an ET placed in it.
2. TEMPORARY trachy patients: who will often still have a potentially patent upper airway. They can be anaesthetised by connecting to the trachy tube, and in an emergency are potentially re-intubatable from above.

Question 19

LIKELY CAUSES OF ACUTE UPPER AIRWAY OBSTRUCTION IN A TRACHY PT

Answer 19

1. Migration of the trachy tube out of the trachea
2. Obstruction of the tube with secretions or clot

Question 20

RATIONALE FOR SALBUTAMOL PREMEDICATION IN ASTHMATICS?

Answer 20

• Premedication with Salbutamol reduces reflex bronchospasm in response to intubation, so is of value in brittle asthmatics even if apparently well

Question 21

SPO2 TARGETS IN TYPE ONE VS TYPE 2 RESPIRATORY FAILURE

Answer 21

• TYPE 1 = HYPOXAEMIC resp failure: titrate O2 therapy to SpO2 of 94-98%
• TYPE 2 = HYPERCAPNIC* resp failure: titrate O2 therapy to Spo2 of 88-92%

*these need some hypoxia to drive respiration

Question 22

LONG QT SYNDROME & TORSADES

Answer 22

• the normal QT interval, measured from the start of the QRS to the end of the T is < 0.44 sec (at 60 BPM*)
• a variety of inherited or acquired conditions which delay cardiac repolarisation (drugs, ODs, low K+/Mg++) can lengthen the QT interval & increase myocardial irritability, producing a tendency to develop TORSADES DE POINTES**, a polymorphic VT which can degenerate into VF.
• MANAGEMENT INCLUDES:
  
  • prophylactic B Blockers and ICDs
  • general avoidance of myocardial stimulants, eg Adrenaline and B Agonists, but also a WIDE RANGE of other drugs
  • MgSO4, 5mls x 49%
  • treat hypotension in ODs with Aramine, not Adren/Norad
  • give PHENYTOIN for acute arrhythmias, 15-20mg/kg slow IV

• * QT interval is rate dependent, there are various formulae for correcting QT to HR (QTc)*
• **= ‘turning of the points’ relating to the changing axis of the VT*

Question 23

WHAT IS BRUGADA SYNDROME?

Answer 23

BRUGADA* SYNDROME is an inherited disorder of the myocardial sodium channels producing high rates of sudden death, especially in middle aged asian males.

DIAGNOSIS

• ‘Coved’ ST elevation followed by T inversion in V1-V3 (aka the BRUGADA SIGN): exaccerbated by fever, ischaemia, drugs

TREATMENT

• prophylactic ICD
• * after the Brugada brothers, the index cases*

Question 24

MANAGEMENT OF HYPOKALEMIA DURING CARDIAC ARREST

Answer 24

Give as bolus

• 1/2 amp of KCl
• 1 amp of MgSO4

Question 25

ANAESTHESIA FOR PULMONARY HT

Answer 25

• N PA Pressure is 25/10, and severe Pulmonary HT is 70/40.
• like Systemic HT, Pulmonary HT is caused by an increase in vascular resistance, and may be idiopathic, or due to lung disease or L heart failure
• Increased PVR causes R heart strain and it fails early

The cornerstones of Anaesthesia for pulmonary HT are:

1. avoid increases in PVR by avoiding hypoxia, hypercapnoea, acidosis and pain (all of which incr PVR)
2. defend R heart perfusion by defending Systemic arterial pressure

All the usual general anaesthetic techniques have been successfully used, but spinal blockade requires aggressive attention to hypotension with vasoconstrictors

Question 26

WHAT IS CYCLIZINE

Answer 26

• CYCLIZINE (aka VALOID) is an antihistamine with good anti-emetic properties
• DOSE in PONV
  
  • 50mg slow IV tds, but not in pregnancy
• S/E
  
  • sedn
  • dry mouth
  • urinary retention
  • glaucoma
  • dystonia

Question 27

WHEN TO DEFLATE GASTRIC BANDS PREOP

Answer 27

• Gastric Bands are no longer deflated routinely, but only those showing signs of being ‘tight’ (ongoing difficulty eating solids) or of having slipped (significant reflux)
• deflation can be done electively by the original surgeon, or in the FMC DOSA suite by the Upper GI team

Question 28

PONV AND GASTRIC BANDS

Answer 28

• whilst forceful vomiting is a risk factor for band slippage, deflation prior to surgery does not reduce this risk