MH and dantroline Flashcards Preview

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Flashcards in MH and dantroline Deck (54)
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1

What area of the brain regulates temperature?

Hypothalamus

most improtant area for temp regulation

Gain center: posterior hypothalamus

Loss center: anterior hypothalamus

2

For each 1 degree fahrenheit change, basal metabolic rate will change how much?

7%

3

Routes of heat loss - in %

Radiation 40%

Convection 30%

Evaporation (burn pt)

Conduction

4

MH incidence?

1:8,000 to 1:50,000 adults (depending on the source cited)

Higher in children

5

How does someone get MH?

Genetic susceptibility;

autosomal dominant RYR mutations are common in MH patients

6

MH pathophysiology (generalized)?

It is a syndrome

a chain of clinical responses to muscle hypermetabolism ("decoupling"; ATP needed for Ca release)

issue with innapropriate Ca++ release

7

4 earliest signs of MH and other s/s?

4 earliest:

  1. hypercarbia
  2. tachycardia
  3. tachypnea
  4. masseter spasm

Other:

  1. hyperthermia (inc 1-2°C every 5 min)
  2. hypertension
  3. dysrhythmias (r/t acid/base imbalance, hyperkalemia)
  4. metabolic acidosis
  5. hyperkalemia
  6. myoblobinuria
  7. hypoxemia
  8. elevated CPK with rhabdo
  9. coke-colored urine

**Most common to be noted 1st  in clinical practice - hyperthermia**

8

What are triggers of MH?

Inhalational agents (probably excluding nitrous oxide)

Succinylcholine

Mild MH triggers: exercise in hot conditions, neuroleptic drugs (haldol, dopamine), alcohol, infections

9

How does someone get tested for MH?

1 gram of muscle is tested with the halothane -caffeine contracture test

10

How does dantrolene work?

Reduces muscle tone and metabolism

Prevents ongoing release of Ca++ from muscle (SR)

Blocks external entry of Ca++ into sarcoplasm

**Stabilizes calcium induced calcium release and stabilizes the negative feedback**

11

dantrolene

Side effects

 

Significant muscle weakness

  • can last long → ICU for 36h

Phlebitis - especially through peripheral IV 

  • watch it

 

12

Dantrolene interaction?

CCB will cause life thretening hyperkalemia and myocardial depression

13

You want the place you work to have how much dantrolene?

36 vials

Also lots of sterile water to mix with

14

Sequence of events the second you realize your patient has MH

Call for help

get MH cart

D/C volatile agent, sux

Change circuit and soda, use highest flow possible of O2 through the machine or ideally change to new dedicated MH safe machine

hyperventilate 100% oxygen and switch to TIVA

Dantrolene

Tx acidosis with sodium bicarb

  • Monitor with capnography & q 15 minute ABG

Monitor core temperature & Cooling to 38°C

Maintain urine output with diuretics and fluids (NOT LR) 

  • U/O >2 ml/kg/hr 

Tx dysrhythmias

  • give lidocaine or procainamide 15mg/kg IV (NOT CCB)

Tx hyperkalemia

  • 1mL/kg D50 glucose and 0.15 units/kg regular insulin
  • calcium chloride 5-10 mg/kg IV

Continue dantrolene sodium for at least 72 hours after control of episode (≈1 mg/kg q 6 hours)

15

Dantrolene dose?

Bolus 2.5 mg/kg

Then maintenance dose 2 mg/kg IV q5min up to 10 mg/kg

Then 1 mg/kg q6h for 72h

Each vial of dantrole contains 20 mg dantrolene and 3g mannitol; needs to be diluted with 60 mL sterile water

16

What lab tests do you want to get for someone having an MH episode?

ABG           CK            myoglobin        Electrolytes        thyroid 

LDH        PT/PTT         fibrinogen             FSP                 CBC

lactic acid                              Urine for myoglobin/hemoglobin

17

What muscle diseases are definitely associated with MH (predispose MH reactions)

  • Central core disease
  • King-Denborough syndrome
  • Evan's myopathy

Direct association with muscle dystrophy is not likely

  • however, can still develop rhabdomylosis  & hyperkalemia without hypermetabolic issues so avoid triggering agents anyway

18

Neuroleptic malignant syndrome presentation?

Mimics MH

Presents with muscle rigidity, fever (cardinal sign), autonomic instability, delirium & cognitive changes, elevated CPK

relieved by NMB (as opposed to MH)

pt population at risk: those on antipsychotics (haldol, prolixin, thorazine)

19

What is the presentation of occult myopathy in young males having surgery?

Mimics MH

Sudden cardiac arrest, especially soon after use of sux,

muscle rigidity

hyperkalemia

20

How does basal metabolic rate (oxidative metabolic consumption) chnage in regards to change in °C?

1°C = 11.2% change in BMR

21

Radiation

Electromagnetic waves that directly transport ENERGY through space

50% of heat loss

22

Convection

Transfer of heat from one place to another by the actual movement of fluids (warmed matter, either liquids or gases)

Heat transfer in a gas or liquid by the circulation of currents from one region to another

30% heat loss

23

Evaporation

In a liquid the particles have a range of energies. At the surface of the liquid some particles will have enough energy to escape from the liquid and overcome the attraction of the other liquid particles. This leaves the less energetic particles still in the liquid and so the liquid is cooler.

H2O is transferred from the surface to the atmosphere, the process by which water changes from a liquid to a gas

24

How do burn patients lose most H2O?

Through evaporation

25

Conduction

Is the movement of thermal energy through a material without the particles in the material moving.

Transfer of energy through matter from particle to particle

26

MH

mutations

Ryanodine receptor 1 (RYR-1) - on chromosome 19

CACNA1S gene - provides instructions for making calcium channels - on chromosome 1

STAC3 gene - protein encoded by this gene is a component of the excitation-contraction coupling machinery of muscles- on chromosome 12

27

MH pathophysiology - cascade of events

  1. membrane depolarization
  2. Ca++ release
  3.  failure of negative feedback (that would otherwise decrease subsequant Ca++ release) 
  4. increased myoplasmic Ca++ release 
  5. hypoxemia and cell death and other events

Lots of ATP needed and used up for Ca++ release, reuptake into SR, and troponin “decoupling” (hypermetabolism)

Aerobic metabolism replaces ATP with heat and CO2 → lactic acidosis

Excess Ca++​ also signals cell death

Myoglobin released causes rhabdo, hyperkalemia

When ATP is depleted = CV collapse

 

28

what is the key event in MH pathophysiology

uncontrolled myoplasmic Ca++ release

29

how does Succinylcholine trigger MH?

succinylcholine acts indirectly by activating the nicotinergic acetylcholine receptor (nAChR), a nonspecific cation channel, resulting in continuous local depolarization

The depolarization can trigger propagated action potentials and will further activate the dihydropyridine receptors (DHPR, CaV1.1)

this leads to the gating of both Ca++ release from the SR via RyR1 and L-type Ca++ current from the extracellular space

30

how do inhalational agents trigger MH?

inhalational agents dirrectly on RYR1

they stimulate Ca++ release via RYR1