Gold Standards Hypothermic CA Flashcards
Define accidental hypothermia
Below 35 degrees
Primary vs Secondary CA
Primary - cardiac arrest due to severe hypothermia. Better outcome - esp if no asphyxia.
Secondary - hypothermic after arrest due to other cause
4 methods of environmental heat loss?
Radiation, conduction, convection and evaporation
Survival in 15 and 5 degrees water?
- 4.5 hours
2. Less than 2 hours
Temperature classifications for hypothermia
Mild: 35-32 (shivering, conscious)
Moderate: 32-28 (Reduced consciousness, not shivering)
Severe: 28-24 (LOC, present vital signs)
Cardiac arrest/low flow state: <24 (No or minimal vital signs)
Irreversible: <13.7
Cardiovascular effects of cold (haemodynamic)
Initial: sympathetic response, increased catecholamines -> ^CO
Cardiovascular effects of cold (electrical)
Moderate hypothermia: e.g. 28-32:
SA node spontaneously depolarises less frequently as neural conduction is decreased ->prolonged conduction intervals -> bradycardia -> Decreased CO
At 20 degrees what is CO at?
20% of normal
Why do cold conditions lead to arrhythmias?
Purkinje fibres and myocardium are sensitised and increasingly irritable, especially below 30 degrees.
(AF->VF->Asystole)
What ECG changes might see?
Osbourne/ J waves - positive reflection at the J point - proportional to hypothermic extent.
Seen below 32 degrees, not pathognomonic.
Where else see J/Osbourne waves?
Hypercalcaemia, raised ICP, SAH, iodpathic VF - Le syndrome d’haissaguerre
Respiratory system response?
Increased drive initially.
Reduced metabolism -> slowing of RR.
Also: increased secretions, decreased ciliary motility, impaired cough reflex - aspiration likely. Also when recovering - infection/ARDS
Resp in relation to degree of hypothermia?
Mild: increased RR, alkalosis
Moderate: Low RR, acidosis, cough loss/ciliary dysfn/bronchorrhea
Severe: reduced VO2, pulmonary oedema
On O2 delivery graph, what way does hypothermia shift the graph?
Left (reduced oxygen delivery)
Longest ‘no flow’ with no adverse neuro outcome?
6.5 hours
Temperature -> cerebral requirement drop?
Below 35, 6%/degree.
So - 28: 50%
22: 75% etc
Hypothermia categories and expect to see neuro-wise?
Mild: ataxia, apathy, amnesia
Moderate: pupillary dilatation, paradoxical undressing, LOC.
Severe: no corneal reflex, no pain response
Cold diuresis?
Impaired Na/K pump causes K retenion ->hyperkalaemia -> acidaemia (decreased rest drive/lactic acidosis)
Central functional hypervolaemia: due to peripheral vasoconstriction
Why would chronic alcohol use contribute to hypothermia?
Impaired shiver response, thermogenesis and hypothalmic degeneration
Alcohol and hypothermia - interactions?
Peripheral vasodilation: worsens hypothermia.
Decreased metabolic rate: decreased clearance
LOC/failure to seek shelter
Signs of futility in hypothermia?
Ice in pharynx, inability to compress the chest or if cause of arrest is: lethal injury, fatal illness or prolonged asphyxia.
Remote area - practicality of rewarming.
What can precipitate VF when in hypothermic cardiac arrest?
Rough handling, intubation, etc
Intubation in hypothermic c/a?
Early! Beware reduced compliance of soft tissues.
Why is hyperventilation a risk in CPR?
Cerebral hypoxia due to reduced cerebral blood flow.
What used to measure temperature?
Tympanic thermometers - accurate to 20 degrees.
Why are rectal temperatures not accurate?
Faecal loading.
Also - rectal temperature lags by several degrees which can escalate care with hyperthermia.
How is defibrillation adapted in hypothermia?
VF/VT: try three times, but not again until temp reaches 30 degrees (myocardial damage risk)
No pacing for bradycardia until normothermic (may be physiological)
How are drug doses/administration of adapted in hypothermia?
Less effective due to reduced BMR.
Toxic levels can arise with same dose.
Reasonable to withhold until 30 degrees.
Same doses in ALS, but doubled intervals until reach 35 degrees.
NB - Adrenaline increases CPP, but not survival
Prehospital re-warming procedure - mild?
Passive rewarming. Insulate with blankets/foil/cap and move to warm environment.
Prehospital re-warming procedure - moderate-severe?
Active rewarming - apply chemical heat packs to trunk.
If unconscious, and airway unsecure, arrange the insulation around the patient in a recovery position. Reheating with warm IV and warm humidified air will not be feasible.
Intensive active rewarming must not delay transport to hospital where advanced rewarming techniques and monitoring are available.
Signs of cardiac instability in Stage II-IV?
Action?
SBP <90, centricular arrhythmias, core temp <28 etc
Action: Transfer to ECLS centre
Difficult extrication rules?
Intermittent CPR if not possible for continuous.
Below 28 degrees: 5 mins with, 5 mins without.
Below 20 degrees: 5 mins with, 10 mins without.
Not dead until you’re?
Warm and dead
ECMO location?
Femoro-femoral: easier, reduces heat loss compared to aortic-right atrial.
Internal re-warming if no ECMO?
Bair Hugger
Warm IV fluids
Warm inspired O2
Lavage - use warmed hartmanns solution; gastric, bladder, peritoneal or pleural.
Warmed peritoneal dialysate (4L) via Peritoneal Catheter. Leave for 15 mins to exchange heat before draining.
Pleural requires apical and basal chest drain on each side. “L of warmed hartmanss is infused into each hemithorax via apical drain and removed after 15 mins.
High volume renal hemofilter
Define slow rewarming
Increases temp by 0.3-1.2 degrees/hour. (17-30 kcal/hour)
What temperature are IV solutions heated to?
45 degrees (17 kcal/hour)
What temperature are inspired o2?
0.7 degrees/hour (30 kcal/hr)
How quickly do warmed blankets rewarm?
0.9 degrees/hour
Define moderate rewarming
3 degrees/hour
Gastric lavage, 65 degree IV solutions and 45 degree peritoneal lavage
Define rapid rewarming
Levels higher than 100 kcal/hour
Thoracic lavage, cariodpulmonary bypass, ECMO and AV dialysis
How quick is endogenous rewarming?
300 kcal/hour
Problem with warm water baths?
Core temperature after drop and CV collapse - peripheral vasodilation
How quickly should we rewarm?
Aggressively: rapid rewarming
What do you do if you get ROSC?
Re-warm to mild hypothermia - avoid overshooting.
When CV stable - re-warm aggressively
How can you avoid rewarming shock?
Volume load to maximise CO
Criteria of futility if no ROSC at >32 degrees
- Potassium over 10mmol/l
- Severe trauma
- Prior cardiopulmonary, renal or neuro disorders
Gold standard for rewarming?
ECMO/bypass
Is defibrillation more or less effective in hypothermia?
Less
What is the gold standard for temp reading?
oesophageal - closest to core
