A HOT DAY IN THE OFFICE DR. M HAINES. FANZCA

Transcription

1 A HOT DAY IN THE OFFICE DR. M HAINES. FANZCA

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4 DIFFERENTIAL DIAGNOSIS Inadequate anaesthesia Sepsis Thyrotoxicosis Phaechromocytoma Neuroleptic malignant syndrome Anti-dopaminergics Drug overdose Eg.Amphetamines

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6 TREATMENT Prompt recognition and declaration Discontinuation triggers and commence IV anaesthesia Oxygenation (100% at 15 lpm FGF) and 3-4 times normal MV Dantrolene Hyperkalaemia Aggressive cooling Acidosis arrythmias lignocaine and amiodarone al and CVL Transfer ICU Refer to MH Investigation unit

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8 MALIGNANT HYPERTHERMIA (MH) Malignant hyperthermia (MH) rare potentially fatal Pharmacogenetic Inherited disease of skeletal muscle Hypermetabolic crisis on exposure to: Halogenated volatile anaesthetic agents (HISDM) Depolarising NMB/sux Other environmental stressors Case fatality 1970 s was 70% now less than 6%

9 EPIDEMIOLOGY Affects all ethnic groups males 2x greater than female Less than 19yrs greater than 50% of cases. Incidence of MH reaction 1 in 10,000 to 1 in 250,000 Prevalence rates: 1 in 100,000 operations

10 PATHOPHYSIOLOGY Dysregulated excess Ca++ in skeletal muscle after exposure to triggers Aetiology unknown Increased function and proclivity of calcium homeostasis receptors Maintains Ca++ release from SR into the cytoplasm Impedes Ca++ reuptake Resultant : sustained excitation-contraction coupling Exhaustion of oxygen and ATP scores Conversion to anaerobic metabolic state Widespread muscle cell death (rhabdomyolysis) Loss of cell membrane integrity releasing K+ / CK

11 CLINICAL Variable: nil mild atypical Fulminant +/- MOF Clinical grading scale 1-6 (multi factor), typically within 30 minutes but can be delayed 4 hours Signs and Symptoms Tachycardia Hyperthermia Muscle rigidity Hypertension Hyper CK (>10,000 IU) Acidosis (mixed) Arrythmia Normoglycemic Death

12 SIGNS AND SYMPTOMS AGE DEPENDENT 12-18yrs common features Increased H2 73% Increased CO2 69% Increased Temperatures 48% Higher peak temperature Diaphoresis Increased sk+ 0-24/12 Greater metabolic acidosis Assure ski mortality Less likely muscle rigidity however peak CK No difference in outcome amongst the age group

13 GENETICS Genetics Heterogenic Autosomal dominant Variable expressivity/penitence Currently known MH associated mutations RYRI_CR19: encoding Ca release channel of SR (50-70%) CACNA1S <1% Almost 30% indeterminate discordant missense mutations Other potential Ca+ modulators under investigation: Calsequetrin, calmodulin and others

14 MANAGEMENT OF KNOWN MHS Already discussed with case presentation Pre-Op Trigger free anaesthetic First on list Flush minutes Disconnect vaporisers Remove from OR New breathing circuit Replaced CO2 absorber. FGF greater than 10L/min to avoid rebound phenomenon Can use charcoal filter Dedicated vapour free anaesthetic machine

15 INTRA/OP POST/OP Intra/OP Appropriate monitoring Safe drugs: LA.IVA.NDMR.N2O.Xenon.Helium Post/OP ICU/HDU

16 DIAGNOSIS Clinical IVCT 99% sensitive, 94% specific Genetic 60%

17 IVCT Not in children under 4 years of age Not advised <10 years of age or <30kg 4 x 3 x1 cm quadriceps muscle biopsy (VL or VM) Caffeine (mm/l) Halothane (mm/l) MHShc (2%) MHSh MHSc 2 > 0.44 MHN 3 > 0.44 Threshold: lowest conc. causing sustained increase of tension of at least 2mN (0.2g) from baseline.

18 CONCLUSION Rare Life threatening Management Early identification Removal of precipitants Dantrolene Supportive measures IVCT/Genetic Testing