Drowning 7 th April, 2010 Amanda Diaz Intensive Care Unit John Hunter Hospital.
-
date post
19-Dec-2015 -
Category
Documents
-
view
217 -
download
1
Transcript of Drowning 7 th April, 2010 Amanda Diaz Intensive Care Unit John Hunter Hospital.
Drowning in Oz
• Royal Lifesaving Society Australia (08-09)– 302 drowning deaths• 32 (11%) age 0 – 4 yrs• 11 (4%) age 5 – 14 yrs• 84 (28%) age 15 – 34 yrs
– 66 (22%) Males
• 80 (26%) age 35 – 54 yrs• 94 (31%) age > 55 yrs
– 1.4 / 100,000 people (same as 1999 levels)
Definition of Drowning
• Confusing!• Dictionary definition regards drowning as dying as
a result of water filling the lungs preventing gas transfer and causing asphyxiation
• Sub-classifications based on dying (drowning) v not (near-); primary v secondary drowning (dying at the time or later); aspiration v non-aspiration
Definition of Drowning
• 2002 World Congress on Drowning (Amsterdam) – Published in Circulation 2003:
• A process resulting in primary respiratory impairment from submersion/ immersion in a liquid medium.
• Liquid/ air interface present at the entrance of the victim’s airway prevents them from breathing air.
• Survival is not considered in this definition
The Drowning Process: A Continuum
• Submersion → Airway below surface• Voluntary breath-holding– Healthy volunteers 87s (longer with hyperventilation)– Shorter (10-20 s) in water < 15°C
• Break-point results in involuntary ventilation– Breath-hold can be prolonged with swallowing /
active respiratory movement• Laryngospasm when water stimulates
epiglottis /oropharynx
The Drowning Process: A Continuum
• Respiratory movement against closed glottis• Forced expiration against column of fluid:
acute emphysema; alveolar septal rupture• Decrease in alveolar / arterial pO2 • Increase in alveolar / arterial pCO2– Hypoxaemia, acidosis, hypercarbia
• Critical hypoxia – release of laryngospasm• Aspiration
The Drowning Process: A Continuum
• Aspiration amount varies widely– Up to 10% at autopsy have no evidence of
aspiration– Average 7 ml/kg aspirated– 22ml/kg considered fatal aspiration• Electrolyte disturbance from increase blood volume
– Up to 70% of drownings aspirate foreign material• Algae• Mud• Vomitus
Why is drowning so complicated?
• Primary respiratory insult relatively easy to treat
• Major therapeutic challenge is the limitation of brain injury
• Identifying those with poor prognosis is extremely difficult– No 2 drownings are alike
Factors Affecting Survival from Drowning
• Patient Factors:– Age– Co-morbidities / Intoxication– Aspiration– Core Body Temp– Blood pH / Stress level during submersion
• Environmental Factors:– Water Temperature
• Rescue Factors:– Duration of submersion– Time to effective BLS– Time to return of spontaneous circulation
• No single clinical or lab value predicts morbidity or mortality
Age
• Older people tend to have more co-morbidities– Decreased physiological reserve
• Children have a high body surface area : mass ratio– Cool down faster
• Diving Response– Ophthalmic division CN5– Marked generalised vasoconstriction, apnoea, bradycardia– Hypometabolism
• Case Reports of children surviving submersion of up to 25 min (Nordic countries)
Aspiration
• 20% of drownings have normal CXR on admission– At risk of ALI progression
• Water aspiration:– As little as 2.2 ml/kg impairs O2 transfer
• Freshwater aspiration:– Affects surfactant phosphlipids leading to unstable alveoli, collapse,
atelectasis– Increases absolute shunt– Hypotonic fluids directly cytotoxic
• Interstitial & alveolar oedema
• Saltwater (hypertonic):– Direct acute alveolar oedema
Aspiration
• Bronchospasm– Increases relative shunt
• Overall effect:– Increase V/Q mismatch– Decreased lung compliance– Increased work of breathing
Hypoxia
• Lowers set-point to thermoneutral zone (normally 22-28°C)– Worsens hypothermia in pre- & post-resuscitation phase
• Severe acid-base disturbance– Increase anaerobic metabolism
• Increased catecholamine release– Myocardial arrhythmias
• Coagulopathy• DIC (endothelial cell activation)
Core Body Temperature
• Hypothermia: core temp < 35°C• Rate of change of core body temp dependent on:– Physical factors: water temp, movement of water against
skin, insulation, head protection (increased heat loss via evaporation / convection / conduction)
– Physiological factors: BSA:Mass ratio, metabolic rate (affected by alcohol), peripheral circulation
• Cooling the fully clothed adult to < 35°C– 1 hour in water at 5°C – 2 hours in water at 10°C– 3-6 hours in water at 15°C
Hypothermia: Cerebral Blood Flow
• Consciousness lost at 30°C• Neurological protection only occurs if cerebral
hypothermia induced before hypoxic damage occurs
• Studies done in anaesthetised humans– Cerebral blood flow decreases in proportion to O2
requirements (autoregulation)– 6-7% reduction in CMRO2 for each 1°C decrease in core
body temp– Cerebral activity abolished at < 22°C
BUT...
• If ventilating:– Shivering at < 34°C
• Increased O2 requirements
• Increased CO2 / lactate production
• If hypoxic:– Set-point of thermoneutral zone lowered
• Shivering impaired• Vasodilation of peripheries
• If hypercarbic:– Cerebral vasodilation
Hypothermia: CV Function
• Arrhythmias occur – any are possible• Core temp < 28°C– VF
• Core temp 24-26°C– Asystole
• Why?– At < 30°C Purkinje fibres lose conduction
advantage over other ventricular muscle fibres
Hypothermia: Muscle Function
• Muscle (not core) temp < 28°C– Impaired NMJ function– Weakness– Unable to swim
You’re Not Dead til You’re Warm & Dead
• Hypothermia has profound effects• A & B – if you’re thinking the above – ETT• C: Fluid resuscitation – in water, hydrostatic
pressure increases vascular volume → baroreceptor activation → natiuresis & diuresis – 2-3 L deficit on entering ED
You’re Not Dead til You’re Warm & Dead
• C: CPR - <28°C core body temp– Manual compression CPR must be continued until
core temp > 33°C• Case reports of 4.5hrs manual compression CPR with
successful neurological outcome• Case reports of 6hrs with ‘Thumper’ device
– Try defibrillation• If not immediately successful, do not retry til > 29°C
– If successful, bear in mind reversion to VF is common until > 30°C
You’re Not Dead Til You’re Warm & Dead
Warming: If core temp > 28°C, aim for 1°C/hr re-warming• Active Re-warming (1-2°C/hr)– Forced-air warming device (Bair hugger)– Warmed fluid– Warmed humidified gases
• Aggressive Re-warming (temp < 28°C)– Bladder irrigation– Gastric/pleural lavage– Peritoneal Dialysis– Haemofiltration
Re-warming
• Cardio-pulmonary bypass– Fem-fem (partial) most common• Shown to be beneficial with core temp < 25°C,
regardless of rhythm• Core temp 25-28°C is no benefit of CPB v conventional
re-warming
– Can perform aorto-caval CPB• Increases core body temp by 10°C/hr
When to stop
• Resuscitation considered futile when– If core body temp 35°C– Stable cardiovascular function cannot be achieved
Neurological Outcome
• Of those who arrive ‘comatose’– ⅓ survived intact– ⅓ survived with minor neurological deficit– ⅓ died or survived in a persistent vegetative state
• The only predictor proposed is regarding avalanche:– K > 10 mmol/l indicates asphyxial cardiac arrest• Not compatible with successful resuscitation
“Cerebral Resuscitation”
• Many modes tried– Cooling / ICP monitoring / CPP targets
• None have been shown to produce improved morbidity or mortality– Horse has already bolted
References
• 2009. Royal Life Saving Society – Australia. The National Drowning Report 2009. http://www.royallifesaving.com.au//resources/documents/2009_RLSSA_National_Drowning_Report_Web.pdf
• Layon, J et al. Drowning: Update 2009. Anesthesiol. 2009; 110:1390.
• Hasibeder, WR. Drowning. Curr Op Anaesthesiol. 2003; 16:139
• Golden, F St C et al. Immersion, near-drowning & drowning. BJA. 1997; 79:214