Malignant hyperthermia : advances in clinical management

and diagnosis

Nurliyana binti Ramli11-2014-192

Malignant hyperthermia

• 1960 – severe reaction under GA• Malignant – caused fatality• Hyperthermia – high body temperature(late feature, therefore early intervention is

important)Earliest clinical feature : ↑end tidal [Co2] and

tachycardia

Preoperative diagnosis

CAUSES.• Exposure of susceptible individual to

triggering drugs• Family history - Abnormal musculoskeletal associated with MHEg. Scoliosis , hernias , strabismus

Pt. with history of :1. Exertional heat stroke2. Exercise induced rhabdomyolisis • More than 1 episode investigated for MH - ‘routine’ Preoperative biochemical screen = ↑ serum C-kinase

Causes of increased serum [c-kinase]Identifiable hypothyroid (commonest)

, myopathies , exercise , denervation syndrome, MCI , rhabdomyolisis (trauma, drugs)

Idiopathic MH susceptibility , Duschenne dystrophy carriers, hemolytic sy. Previous neuroleptic malignant sy.

When common and uncommon causes from the table above excluded thus indicative of MH

Presentation during anesthesia • No spesific clinical feature.• It changes according to their timing of onset reaction

Timing Clinical signs Changes in monitors Biochemical changes

Early Masseter spasm after succinylcholineTachypnoe Rapid exhaustion of soda limeHot soda lime canister Irregular pulse

↑ ventilation/min

↑end tidal CO2

↑ PaCO2

Succeeding Patient hot to touchCyanosis Dark blood in woundIrregular pulse

TachycardiaPerked T waves on EcgRising body tempSPo2 ↓

↓ pH↓ Pao2↑ [K+]

Late Generalized muscle rigidity Prolonged bleedingDark urineOliguria(irregular pulse)

Peaked T waves on BCG ↑ c-kinase↑ myoglobinuria↑ [K+]

Soda lime

• CO2 absorber.

Postoperative presentation• Onset MH varies in speed• CASES : After potent inhalant administration metabolic

stimulation, clinical feature in 10 minutes or several hours• Speed of onset depends on types of drug used

• Speed onset >> intracellular [Ca2+] >> stimulates

sarcoplasmic reticulum Ca2+ activate mx. Ca induced-Ca

released sustain MH rx. so, even triggered already eliminated

(initial intervention) clinical sign reappear.

Pharmalogical triggers of MH• Potent inhalational anaesthethic drug- Halothane , - Isoflurane - Sevoflurane- Desflurane

• Neuromuscular blocking drugs- Succinylcholine cause increase intracellular [Ca2+]- Most affect masseter muscle because , masseter m. contains

↑proportion of type I fibres - Myofilament type I fibres : more sensitive to Ca2+ compared

to type II fibres.

• Phenothiazine - Anticholinergic actions – antidiaphoresis

(mostly children) –> heat loss ↓ , so high body temperature

- MH rx. If consumed before general anesthesia.• Other drugs- Anticholinergic drugs , exacerbate pyrexia

because anti-diaphoresis rx.

Laboratory diagnosis of MH

• IVCT ( in vitro contracture test)- Living skeletal muscle , expose to halothane

and caffeine• Ryanodine contracture test – distinguish MH-

susceptible from normal patients.• Chlorocresol

Molecular genetics of MH

• Studies : Chr 19q12.1-13.2 locus of RYR1 (ryanodine receptor gene), the gene encoding

Skeletal muscle sarcoplasmic reticulum ca2+ release channel.

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