Case 1:

A 78 year old woman is found with decreased LOC in her apartment by her daughter. She was last seen well 3 days ago. When EMS arrives, they find her temperature to be 30.2 degrees Celsius.

Questions:

1. Input from cutaneous cold receptors travels via afferent fibers to which area of the brain?

a. Pre-optic nucleus of the anterior hypothalamus

2. This area of the brain then initiates a number of physiologic responses. Please list three general categories of physiologic responses that either aim to increase heat production or decrease heat loss and give one example for each.

a. activation of autonomic nervous system (vasoconstriction) b. activation of endocrine system (increased cortisol) c. stimulation of extra-pyramidal skeletal muscle (shivering) d. adaptive behavioural responses (move to area of warmth)

3. Define mild, moderate and severe hypothermia.

a. mild 33-35 b. moderate 28-32 c. severe <28

4. List at least 10 clinical manifestations of moderate hypothermia

References: 1. Hanania NA et al. Accidental hypothermia. Crit Care Clin 1999;15:235-249. 2. Mallet ML. Pathophysiology of accidental hypothermia. Q J Med 2002; 95:775–785 Case 2

You are completing rounds in the ICU when a Code Orange is called. The operations leader runs into the ICU and quickly updates you. The G-7 summit is currently going on in town and terrorists have set off a “dirty-bomb” at one of the main venues. They fear that in addition to powerful explosives, this bomb contained radioactive material.

Questions:

1. Please draw the dose-response relationship for radiation exposure.

2. List four factors that determine the extent and severity of the radiation’s impact on that patient’s health:

• Total dose of radiation • Rate at which the dose is delivered • Kind of radiation • Radiosensitivity and volume of tissue irradiated • Age • State of health/co-morbidities

3. What is the risk to healthcare workers when managing patients who have had direct exposure to ionizing radiation (gamma and x-rays that have penetrated the body at the time of detonation)?

• Direct exposure does not render the body radioactive, and an exposed individual poses no threat to others. However, if a patient is contaminated with actual radioactive materials, they will continue to emit ionizing radiation that does pose significant potential for harm to themselves and others.

4. Describe the acute radiation syndrome

5. Describe the initial management of patients exposed to high levels of radiation.

• Ensure healthcare workers have protective gear • ABC • Primary survey • Triage • Resuscitation • Decontamination • Secondary survey (Be wary of combined injuries (radiation and trauma/burns if blast occurred)) • Early ORs given bone marrow failure will make it harder to manage in 24-48 hrs • For minor exposures, anti-emetics, pain control • If internal contamination a possibility, consider specific countermeasures (potassium iodide, chelating agents).

References:

1. Wolbarst AB, et al. Medical Response to a Major Radiologic Emergency: A Primer for Medical and Public Health Practitioners. Radiology 2010;254:660-677. 2. Bland SA. CHEMICAL, BIOLOGICAL AND RADIATION CASUALTIES: CRITICAL CARE CONSIDERATIONS. JR Army Med Corps 2009;155(2):160- 171.

Case 3:

You are called to the emergency room to help with the ongoing resuscitation of a 22 year old man who was pulled from a nearby lake after being underwater for approximately 3 minutes. When EMS arrived, he was pulseless and CPR was being performed. After intubation and 1 mg of IV epinephrine, return of spontaneous circulation was achieved within 2 minutes.

Questions:

1. For each of the following organ systems, please describe the impact that aspirating large amounts of fresh water would have and provide an explanation for why it would occur.

Organ system Impact Mechanism(s) Pulmonary Hypoxemia Hypoventilation, V/Q mismatch, shunt, surfactant washout Cardiovascular Increase intravascular blood Fresh water is hypotonic, so volume intravascular volume will increase due to osmotic gradients drawing fluid from the lungs Hematologic Hemolysis Hypotonicity and hypoxemia lead to lysis of RBCs Central nervous system Cerebral edema Anoxic injury Metabolic Hyperkalemia Cell lysis Hyponatremia Fluid shifts

References:

Layon AJ, Modell JH. Drowning. Anesthesiology 2009;110:1390-1401.

Case 4:

You are completing rounds in the ICU when a Code Orange is called. The operations leader runs into the ICU and quickly updates you. The G-7 summit is currently going on in town and people at the conference are suddenly becoming very ill. They suspect it is a result of terrorist actions. The patients are now arriving in the emergency department and are found to be confused or unconscious, with some seizing. They are hypertense, vomiting and have respiratory failure due to what appears to be copious amounts of clear secretions.

Questions:

1. What is the most likely substance released by the terrorists?

Organophosphates (cholinergic)

2. Describe its mechanism of action.

Organophosphates are acetylcholinesterase inhibitors and act primarily at muscarinic and nicotinic receptors by preventing the degradation of acetylcholine. Consequently, postsynaptic neuromuscular junction stimulation persists after activation due to the continued presence of the neurotransmitter. Symptoms result from the overstimulation of the autonomic and central nervous systems as well as skeletal muscle nicotinic receptors.

3. What is the treatment of choice?

Atropine intravenously. 1-2 mg q5 -15 min to effect. Atropine acts as a muscarinic receptor antagonist, thereby blocking the activity of the excess acetylcholine present in the synapse. No solid evidence to support further benefit from pralidoxime, but some still give it. Removes the inhibitory phosphate bond with acetylcholinesterase, thereby reactivating the enzyme.

References:

1. Chen TMB, et al. Toxic Inhalational Exposures. Journal of intensive care medicine 2012;(publish ahead of print). 2. Oximes for acute organophosphate pesticide poisoning. Cochrane Collaboration 2011. (http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD005085.pub2/abstract)

Case 5:

A 50 year old male from the Downtown Eastside was found unconscious in a construction site next to the building’s main electrical transformer. The workers suspected the man was trying to steal the copper from the wires, but suffered a severe electrical injury as a consequence.

1. List and describe the 4 main mechanisms by which electrical current causes injury.

• Direct effect: current’s direct impact on body tissues (dysrhythmias, apnea) • Blunt mechanical injury: muscle contraction, falling/thrown • Conversion of electrical to thermal energy: burns • Electroporation: creation of pores in cell membranes by means of electrical current. Unlike thermal burns, which cause tissue damage by protein denaturation and coagulation, electroporation disrupts cell membranes and leads to cell death without clinically significant heating.

2. List at least 5 factors which determine the amount of damage suffered from an electrical injury.

• amount of current (most important) • voltage • resistance • type of current (AC or DC) • current pathway • duration of contact with source

3. Which type of current is considered to be more dangerous in electrocution and why?

• Although AC is considered to be a far more efficient way of generating and distributing electricity, it is also more dangerous than DC (approximately three times) because it causes tetanic muscle contractions that prolong the contact of the victim with the source

4. Using Ohm’s Law as your basis, provide an explanation for why different parts of the body will suffer significantly different amounts of damage as a result of an electrical injury despite being exposed to the same amount of voltage.

• In general, the type and extent of an electrical injury depends on the intensity (amperage) of the electric current. According to Ohm’s law, the electric current is proportional to the voltage of the source and inversely proportional to the resistance of the conductor: current = voltage/resistance. Thus, exposure of different parts of the body to the same voltage will generate a different current (and by extension, a different degree of damage) because resistance varies significantly between various tissues. The least resistance is found in nerves, blood, mucous membranes, and muscles; the highest resistance is found in bones, fat, and tendons. Skin has intermediate resistance.

References:

1) Spies C, Trohman RG. Narrative Review: Electrocution and Life-Threatening Electrical Injuries. Ann Intern Med. 2006;145:531-537. 2) Koumbourlis AC. Electrical injuries. Crit Care Med 2002; 30[Suppl.]:S424 –S430.