Anaesthetic complications Flashcards
What should the pressure of the ETT cuff be
20 - 30 cm H20
Use cuff manometer
Inflated just enough to prevent leak
Complications
Acute - postoperative stridor
Chronic - tracheal stenosis
What is the smallest ETT with a cuff and is this safe to use in kids
ETT 3.5 mm internal diameter
Safe to use if correctly used
What causes permanent postoperative visual loss (POVL) following non-ocular surgery
- Retinal artery occlusion
- Ischaemic optic neuropathy
- Cerebral vision loss
Blurring to blindness can occur
What can happen if the eyes are not taped during GA
Corneal abrasion ± vision loss
Check eyes are protected when lateral and prone
Pad eyes before taping before head and neck surgery
What anaesthetic complications can arise from improper positioning
Nerve injury
- Radial nerve (Saturday night palsy)
- Ulnar nerve
- Brachial plexus (hyperextend > 90 deg)
- lateral popliteal nerve (Lithotomy)
What are the complications of neuraxial anaesthesia
- Neural injury
- Epidural hematoma
- Epidural abscess
- Meningitis
- Post dural puncture headache (PDPH)
- use 25G Whitacre or Sprotte (PPNs) instead of 22G Quincke (cutting needle) - Sympathectomy, hypotension
- High/complete spinal: Low HR, Low BP, Apnoea
Classify and describe the complications of central venous cannulation
EARLY Technical - Pneumothorax - Haemothorax - Nerve damage
Dysrhythmias (guidewire)
Air embolism (put patient head down)
LATE
Infection
- Sepsis
- Endocarditis
Thrombosis
Tamponade
Classify and describe the risk factors for postoperative nausea and vomiting
PATIENT
- Children
- Females
- Hx motion sickness
- Previous PONV / Chemo NV
- Obesity
- Non - Smokers
ANAESTHETIC
- Prolonged pre-op starvation
- Hypotension with neuraxial anaesthesia
- Emetic drugs: Opioids, etomidate, ketamine, N2O, VA
- Longer duration anaesthesia
SURGICAL
- Ear and Eye surgery (esp. strabismus surgery)
- Intra-abdominal surgery
- Laparoscopic surgery
- Gynaecological / Orchidopexy
POST-OP
- Pain
- Opiates
- Hypotension
- Forcing oral fluids to soon
What are the patient factors associated with PONV
- Children
- Females
- Hx PONV / Hx chemo NV
- Non-smoker
- Hx motion sickness
- Obesity
What are the anaesthetic factors associated with PONV
- Prolonged preop starvation
- Hypotension with spinals/epidurals
- Emetic drugs: Opioids/Etomidate/Ketamine/N2O/VAs
- Prolonged duration of anaesthesia
What are the surgical factors associated with PONV
- Ear and eye surgery (esp. strabismus)
- Intra-abdominal surgery
- Laparoscopic surgery
- Gynae surgery / orchidopexy
What are the post-op factors associated with PONV
- Pain
- Opioids
- Hypotension
- Forcing oral fluids
Describe Risk Scores for PONV for Adults and Kids
Adults - Apfel’s simplified risk score
Female
Non-smoker
PONV before
Expected Opioids
0, 1, 2, 3, 4, of the above associated with 10, 20, 40,60,80 % risk respectively
Kids
Age > 3
Duration > 30 mins
POV before / relative with PONV /POV
Strabismus surgery
1,2,3,4 of these associated with 10,30,50,70 % risk respectively
Describe the approach to prevention of PONV in patients with different PONV risk
HIGH RISK for PONV
- Multimodal pain Rx
- Minimise opioids
- Regional instead of GA
- TIVA with propofol instead of VAs
- Antiemetics
- Dexamethasone 4 - 8 mg after induction
- Ondansetron (5HT3 antagonist) 4 - 8 mg end of surgery - Rescue antiemetics (in different class to the above)
- Prochlorperazine (Stemetil) 12.5 IM stat 10 PO TDS
- Droperidol (Inapsin) 2.5mg STAT IV/IM then 1.25mg prn
- Metoclopramide (Maxalon) 10mg IV/IM/PO 8hrly - Non-pharmacological
- IV fluids - maintain hydration
- Complementary/alternative therapies (acupuncture/bracelets/ginger)
MOD RISK PONV
- Multimodal pain Rx
- Minimise opioids
- Then choose to modify anaesthetic technique or antiemetics or non-pharmacological
LOW RISK PONV
Patient/anaesthetist preference
- Ondansetron at the end of surgery
What are the mechanisms of action of: dexamethasone, ondansetron, prochlorperazine, droperidol, metoclopramide and promethazine
DEXAMETHASONE
- Incompletely understood
- Decreased prostaglandins –> decreased endogenous opioids
ONDANSETRON
- 5HT3 (serotonin 3) receptor antagonist in the chemoreceptor trigger zone and in the vagus nerve
PROCHLORPERAZINE
- D1 and D2 postsynaptic receptor antagonist in the chemoreceptor trigger zone
DROPERIDOL
- Blockade of dopamine stimulation in the chemoreceptor trigger zone
METOCLOPRAMIDE
- Prokinetic (enhances peristaltic response to Ach)
- Blocks D and 5HT receptors in CTZ
Define awareness and describe the different types and how common the different types are
Awareness under anaesthesia is the ability to recall events occurring during general anaesthesia
1: 10 000 - awareness with pain
1: 1000 - some awareness without pain
What is the definition of hypothermia
Core Temperature < 25 deg C
When should the temperature be monitored
Any case longer than 15 minutes
What are the five mechanisms of heat loss during surgery and state the approximate contribution of each to heat loss by the patient in the operating theatre
- Radiation - 40%
- Convection - 30%
- Evaporation - 20%
- Respiration - 10% (8% evaporation, 2% heating of air)
- Conduction - (very low contribution)
What is the incidence of death in first world and third world hospitals attributable to anaesthesia
1st world - 1:40 000
Rural areas with poorly trained anaesthetists: 1 : 280
What is the eponymous name for chemical pneumonitis caused by peri-operative aspiration of gastric contents
Mendelson’s syndrome
Describe a system to determine which patients are at risk for Mendelson’s syndorme
- Full stomach
- Trauma
- Obesity
- Ileus
- Gastric outlet obstruction
- Intra-abdominal pathology (acute abdomen)
- Pregnancy
What three strategies can reduce the risk of aspiration
- Reduce gastric pH
- Sodium citrate 30 ml within 30 mins
- Ranitidine 300mg (Zantac)
- Omeprazole 40mg (Losec) - Increase gastric emptying and LES tone with
- Metoclopramide 10 mg (Maxalon) - Reduce gastric volume via suction with NGT
Give 5 causes of laryngospasm
- ETT/LMA/OPA during light anaesthesia
- Irritating volatile agents (iso/des/enf)
- Secretions on the vocal cords
- Surgical stimulus (dilation of Cx or anal sphincter)
- Surgical stimulus during light anaesthesia
Describe the management of laryngospasm
- Avoid manipulation of the airway whilst in light plane of anaesthesia
- Stop causative stimulus
- FiO2 1 + PPV
- Propofol: 10 - 50 mg
- If there’s time - Spray cords: 2% lidocaine
- If no time - Sux 1 mg/kg and intubate.
If laryngospasm occur during emergence - then give 1/4 of the usual dose of sux and support the airway or intubate if not able.
List the causes of bronchospasm
- All 5 causes of laryngospasm
- Carinal stimulation (ETT deep)
- Asthmatics/COPD/Pneumonia
- Histamine release (Sux/Roc/Atra/Morphine/Thio)
- Anaphylaxis
Describe the management of bronchospasm
PREVENTION
- Avoid elective surgery if underlying respiratory conditions are not optimised.
- Regional Anaesthesia in high risk patients
GENERIC Rx
- Stop the precipitant, declare and call for help
- FiO2 100%
SPECIFIC Rx
- Deepen with SEVO (non-irritating)
- SALBUTAMOL inhaled 5mg every 15 mins
- Salbutamol 0.25mg IVI then infuse at 5mcg/minute
- PROPOFOL( 10 - 50mg)
- MGSO4
- ADRENALIN 100 ug SC
- Adenalin 10ug boluses IVI
- KETAMINE 2mg/kg
- HYDROCORTISONE 200mg
- JENNY’s solution
- 100ug adrenalin (0.1 mL) + 5mL of 2% lido to 10 mls
- Use 1 ml per 10 kg body weight and bag it down the ETT - Ventilation: High pressures + slow rate (allow exhalation)
(Aminophylline 250mg slow IVI up to 5mg/kg - not to be paired with ketamine)
- narrow therapeutic index
What are the causes of postoperative respiratory depression and decreased ventilation
- Anaesthetic agent/opioid
- Muscle relaxant
- Partial airway obstruction
- Abdo surgery (pain)
- Abdo distension
- Hypoglycaemia
- Electrolytes
- High block (spinal/epidural)
- Central depression due to stroke/bleed
Describe the causes of intra-operative dysrhythmia
Common causes
- Drugs
- Halothane (sensitises cardiac conduction system to catecholamines) - Electrolyte imbalance: Hyper and hypokalaemia
- Autonomic stimulation: Intubation / peritoneal stretching
- Underlying heart disease
Classify the factors that increase the perioperative risk of myocardial infarction
PATIENT factors
1. Heart disease (Valvular/Ischaemic/Failure/dysrhythmia etc)
ANAESTHETIC factors
- Hypotension/Hypertension
- Tachydardia
- Hypoxia
SURGICAL factors
- Intrathoracic surgery
- Abdominal surgery
- Vascular surgery
- Emergency surgery
What type of hypersensitivity reaction is anaphylaxis and describe the pathophysiology
Type hypersensitivity reaction
IgE Ab on the surface of mast cells and basophils bind the allergen and become cross-linked leading to degranulation of mast cells or basophils and the release of histamine and newly formed arachidonic acid metabolites
What is the clinical presentation of anaphylaxis
TRIAD
Skin (wheal and flare / urticaria)
RSP (Angiodema/bronchospasm/hypoxia)
CVS (Hypotension + tachy cardia to CVS collapse and Cardiac arrest)
GIT effects of the anaphylactic reaction are not immediately apparent intraoperatively
Which drugs used in anaesthesia are most likely to cause anaphylaxis
- Antibiotics
- Muscle Relaxants
- Sux
- Benzylisoquinolinums (ATRA/CIS/MIV)
- Rocuronium (aminosteroid) - Others
- Opiates
- Local anaesthetics (esters>amides)
- Colloids (not crystalloids)
- Blood
- Latex
- Rarely induction agents (thio/propofol)
Which anaesthetic drugs do not cause anaphylaxis
volatile anaesthetic agents
Describe the treatment of anaphylaxis
- Declare, call for help, stop precipitant
- ABCDE
- IV ADRENALIN 1mg in 20 ml syringe
- titrate 1/2 to 1 ml (25 - 50 ug) to effect
IM adrenalin in patients with no iv line.
Second line:
- FLUID
- Hydrocortisone 100mg IV
- Salbutamol 5mg inhaled
- Ranitidine/Promethazine
- Glucagon 1mg (patients on beta blockers)
Airway oedema may be significant and might warrant prolonged ventilation
–> Consider ICU
Take blood for mast cell tryptase
Inform GP
Allergy clinic -> ? cause
Medic Alert Bracelet
Define pharmacogenetic disease
Genetic diseases that are unmasked by exposure to specific drugs
Which pharmacogenetic diseases have specific relevance to anaesthesia
- Malignant Hyperthermia
- Halothane Hepatitis
- Scoline Apnoea
- Porphyria
Define malignant hyperthermia
A rare inherited syndrome characterised by a life-threatening hypermetabolic state triggered by exposure to a triggering agent: all volatile agents or succinylcholine.
How do you recognize malignant hyperthermia
Unexplained: - tachycardia - hypercapnoea - hypoxia - trismus - elevated core temperature (late) Late: rhabdomyolysis, myoglobinuria, renal failure, DIC, multiorgan failure
Onset may be rapid and fulminant or slow and insidious
What is the defect responsible for malignant hyperthermia
Defective ryanodine receptor on the sarcoplasmic reticulum which is a calcium channel receptor. Once exposed to the trigger agent, the receptor stays open and floods the cell with calcium with a resultant persistent contractile state.
Differentiate malignant hyperthermia from the serotonin syndrome and neuroleptic malignant syndrome
Malignant Hyperthermia
- Onset: INTRAOPERATIVE
- Trigger: Sux | Volatiles
- Muscle rigidity: rigor mortis like
- Rx: Dantrolene
Serotonin syndrome
- Onset: over 24 hours
- Triggers: E.g. Citalopram/fluoxetine
- Muscle rigidity: Neuromuscular hyperactivity (tremor | hypereflexia | myoclonus)
- Rx: Benzo + cyproheptadine (serotonin antagonist)
Neuroleptic Malignant Syndrome
- Onset: 1-3 days
- Triggers: antipsychotics (haloperidol) and antiemetics (metoclopramide, droperidol, prochlorperazine, promethazine)
- Muscle rigidity: sluggish neuromuscular response (rigidity and bradyreflexia)
- Rx: Dantrolene
What is the differential diagnosis for malignant hyperthermia
EQUIPMENT MALFUNCTION
- Expiratory valve malfunction
- Insufficient ventilation (circuit leak)
- Exhausted soda lime
HYPERMETABOLIC STATE
- Phaeochromocytoma
- Thyroid storm
- Sepsis
NEUROMUSCULAR ABNORMALITY
- Neuromuscular disease
- Neuroleptic malignant syndrome
Outline the Initial Management of Malignant hyperthermia
- Declare, Help, FiO2
- Discontinue TRIGGER
- Convert to TIVA (Propofol/ketamine/midazolam) boluses or infusion - Rx MUSCLE contraction
Start Dantrolene
- Fridge
- Reconstitute with STERILE WATER ONLY
- Bolus 2.5 mg/kg then give 1mg/kg prn
- Call GSH for more dantrolene –> initial dose requires 9 x 20mg vials to be administered
- Thereafter: 1mg/kg every 4 hours or 0.25 mg/kg/hr x 24 hours - Rx TEMPERATURE
- Ice packs in groin and axillae
- Cold IV fluids
- Peritoneal lavage with cold fluid
- Target Temp < 38 deg C - Rx HYPERKALAEMIA
- NaHCO3 with hyperventilation and Insulin/glucose shift - Rx DYSRHYTHMIAS
- MgSO4 or Amiodarone
- NOT CCB (interfere with dantrolene) - Rx ACIDOSIS
- NaHCO3 8.5% 1 - 2 ml/kg with hyperventilation - Rx KIDNEYS
- Forced alkaline diuresis: UO 2ml/kg/hour with IV fluids and diuretics - Admit to ICU with IABP, CVP, Urinary Catheter, oesophageal temperature probe
Summarise the treatment of MH
- Declare, Help, FiO2
- Stop TRIGGER
- Rx ABCDE’s
- Rx MUSCLE TONE (DANTROLENE)
- Rx HYPERKALAEMIA
- Rx ACIDOSIS
- Rx DYSRHYTHMIAS (not with CCB)
- Rx TEMPERATURE
- Rx KIDNEYS
- ICU with invasive monitors
Describe the actual reconstitution and administration of Dantrolene
Initial dose: 2.5 mg/kg
Then 1mg/kg every 4 hours
9 vials required for 70 kg adult
1 vial has 20 mg
1 vial is reconstituted with 60 ml of STERILE WATER (Not NaCL and not D5W)
Shake until the solution is clear and ensure there is no precipitation present
Protect: from direct light Use: within 6 hours of reconstitution Store: at room temperature Do not transfer into glass bottles Do transfer into empty sterile plastic vacoliter bags if necessary
List 5 specific practical requirements after dantrolene has been reconstituted
- Protect from direct light
- Use within 6 hours
- Store at room temperature
- Do not transfer into glass container
- Do transfer into sterile plastic vacoliter bags if necessary
List 5 specific important aspects related to the reconstitution of dantrolene
- Reconstitute with sterile water NOT NaCl or D5W
- Each 20 mg amp reconstituted with 60 mL STERILE WATER to achieve a pH of ± 9.5
- Call GSH for more amps as it is likely more will be needed
- Add each reconstituted amp to a sterile plastic vacoliter and administer 2.5 mg/kg
- 3000mg of mannitol and NaOH present within the amp permit the pH of 9.5 when reconstituted with 60 mL sterile water.
How can a definitive diagnosis of MH be made?
IN VITRO CONTRACTURE TEST (IVCT)
- Muscle biopsy must be taken
- Performed rarely –> now done at the MH Center in Pretoria
Genetic testing
- Complex and a negative test cannot rule out MH susceptibility
So…
NO IVCT and positive Fam Hx / adverse reaction to GA suggestive of MH –> presumed diagnosis and MH safe anaesthetic is performed.
Describe an MH safe anaesthetic
- Avoid GA entirely: regional
- If GA required
- First on the list
- Remove vaporizers from machine - Flush machine with high flow O2 for 20 minutes prior to anaesthetic: to reduce vapour concentration in the FGF to less than 5 ppm
- Maintain FGF of 10 L/minute throughout anaesthetic even after lengthy purging
- Use Activated Carbon Filters (ACFs)
- TIVA with propofol
- Muscle relaxation: NDMR are safe (No sux)
- Know where the Dantrolene is kept (usually locked up)
Summarise an approach to an MH safe anaesthetic
- RA
- If GA then TIVA and NDMR
- Purge machine (20 mins) < 5 ppm + Replace breathing circuit.
- FGF > 10 L/minute throughout anaesthetic
- Activated Carbon Filters
- Know where dantrolene is kept.
What is the incidence of halothane hepatitis
1: 35 000 anaesthetics
What is the pathophysiology of halothane hepatitis
Metabolites of halothane (20% metabolized in the liver) –> type 2 hypersensitivity reaction in the liver –>fatal fulminant hepatitis
Under what circumstances is halothane hepatitis more likely to occur?
Repeat exposure to halothane within 6 months of initial halothane exposure
Existing liver disease
Fat, middle aged females
(Isoflurane and desflurane have been implicated with causing fulminant hepatitis but much less frequently - significantly lower liver metabolism)
What is scoline apnoea
Susceptible individuals have an abnormal or absent pseudocholinesterase (buturylcholinesterase) enzyme resulting in prolonged paralysis after a single dose of succinylcholine.
Homozygous patients for the condition
Rx - prolonged sedation and ventilation after sux
–> FFP does contain the enzyme but is associated with all the risks associated with blood transfusion.
–> Risk vs benefit (? ventilation facility available)
Why should recovery from succinylcholine be checked before administration of NDMR?
Return of breathing on vent or 4 strong twitches on PNS should be demonstrated.
If patient does not recover after the anaesthetic you will not know if it is due to sux or NDMR.
Define porphyria
A pharmacogenetic disease involving porphyrin metabolism in which certain drugs such as barbiturates (thiopentone) can precipitate an acute attack resulting in:
- Paralysis
- Acute abdominal pain
- Death
In which population in RSA does porphyria have a higher incidence
Dutch descent/Afrikaners
What should be done if a patient reports a history of porphyria
Consult one of the safe/use with caution/unsafe drug lists for porphyria and plan accordingly
