Regarding the management of heatstroke, which ONE of the following is TRUE?
Answer: B: Cooling is the cornerstone of good outcomes in heat-injured patients and must be done in an appropriate manner. Studies show that the degree of organ damage correlates with the degree and duration of temperature elevation above 40°C, therefore a reasonable clinical goal is to rapidly reduce the temperature to below 40°C within 30 minutes to an hour after the start of therapy. Cooling techniques should be stopped when the temperature reaches 38–39°C to avoid overshoot hypothermia. Lowering the body temperature to <38°C with cooling techniques is not recommended as dropping of the central temperature continues even after the technique is discontinued. This is due to a delay in the establishment of an equilibrium between the cold skin and the core. The amount of ‘core afterdrop’ can exceed >2°C.
Evaporative cooling is an effective and safe external cooling technique. The temperature of the water used to moisten the skin must be tepid (15°C). Warm, forced air is essential for effective evaporation and crucial to maintaining good peripheral perfusion and preventing shivering by warming the skin. If the skin temperature is reduced below 30°C, shivering will result in more heat production, and peripheral vasoconstriction will impair evaporation. In addition to cooling procedures, it is imperative that the clinician institute the judicious use of sedation and/or muscle paralysis to control agitation, suppress shivering, reduce energy expenditures, and make the patient receptive to sometimes unpleasant therapies. In general, intravenous benzodiazepines are the easiest and safest first-line drugs used for sedation.
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Regarding heat-related illnesses, which ONE of the following is TRUE?
Answer: D: The main distinguishing feature between heatstroke and heat exhaustion is central nervous system involvement. Hyperthermia (>40–41°C) is another cardinal feature of heatstroke. Anhidrosis, due to thermoregulatory failure, was traditionally included in the definition of heatstroke; however, sweat is present in >50% of patients with heatstroke and therefore does not exclude the diagnosis of heatstroke. Patients with heat exhaustion do not manifest signs of central nervous system involvement. Additionally, their temperature may be normal or elevated but usually not >40°C. While multiorgan dysfunction with disseminated intravascular coagulation, acute renal failure, lactic acidosis, hypokalemia (followed by hyperkalemia later on) and rhabdomyolysis are common with heatstroke, it is unlikely to occur in heat exhaustion.
Currently, only physical methods of cooling are recommended in the management of heatstroke. There is no role for antipyretics, either salicylates or paracetamol, in the setting of heatstroke because their efficacy depends on a normally functioning hypothalamus. In addition, overzealous use of paracetamol could potentiate hepatic damage, and salicylates may promote bleeding tendencies.
Regarding Osborne or J waves on the electrocardiogram (ECG) of a patient with severe hypothermia, which ONE of the following is TRUE?
Answer: C: Osborn waves consist of an extra positive deflection, with a dome or hump configuration, at the end of the QRS complex at the R-ST junction (J point) on the ECG. They are best seen at the inferior and lateral precordial leads. These waves become more prominent as the body temperature drops and they regress gradually with rewarming. Osborn waves are characteristic of hypothermia; however, they are not pathognomonic of hypothermia as they are also seen in ‘normothermic’ patients. The differential diagnosis includes common electrocardiographic variants such as early repolarization as well as other pathological conditions such as hypercalcaemia, Brugada syndrome, brain injury, subarachnoid haemorrhage, cardiopulmonary arrest from oversedation, and vasospastic angina. Although Osborn waves may have some arrhythmogenic implications, its arrhythmogenic potential is still unclear and not fully understood. Further studies are needed to determine the true significance of the Osborn waves under various conditions in which they can be observed.
A 32-year-old male developed confusion and dizziness shortly after ascending from a scuba dive.
Which ONE of the following is TRUE?
Answer: B: Onset of any symptoms during or in the hours after diving should be regarded as decompression illness (AGE and DCS) until proven otherwise. Distinguishing AGE from decompression sickness is difficult but differentiation between these disorders before recompression is unnecessary since recompression in a hyperbaric chamber is indicated for both. ‘Nitrogen narcosis’ is due to the anaesthetic effect of nitrogen dissolved in lipid membranes; symptoms are similar to those of alcohol intoxication and occur at depth. It is immediately reversible on ascent.
The optimal position to manage an injured diver is not known but current consensus is for horizontal orientation in a position that helps care of the patient. Traditionally, the head-down position (Trendelenburg) has been advocated to reduce bubble embolization to the brain but is not effective and can promote cerebral oedema. The diver should be prevented from sitting or standing up, to avoid bubbles redistributing from the left ventricle to the brain. One hundred percent oxygen should be provided until recompression in a hyperbaric chamber can be performed. Recompression in a hyperbaric chamber is indicated even if the diver becomes asymptomatic with normobaric oxygen therapy, otherwise many will relapse. The relapse may be more severe than the original presentation.
Regarding decompression illness, which ONE of the following is FALSE?
Answer: D: Decompression illness is a clinical condition associated with barotrauma of ascent and caused by intravascular or extravascular bubbles that are formed as a result of reduction in environmental pressure (decompression). The term covers both AGE, in which alveolar gas or venous gas emboli (via cardiac shunts or via pulmonary vessels) are introduced into the arterial circulation, and DCS, which is caused by in-situ bubble formation from dissolved inert gas, mostly nitrogen. AGE usually occurs on ascent or soon after surfacing and is not related to depth, as it can arise after ascent from very shallow depths, nor time spent under water. DCS usually occurs after prolonged exposure at depth, when the dive is long enough to saturate tissues, and is uncommon at depths of <10 m.
Boyle’s law states that at a constant temperature, the pressure and volume of an ideal gas are inversely related. This pressure-volume relationship is important in the aetiology of injuries due to barotrauma and produces the volume change of bubbles in the tissues and circulation that are associated with recompression therapy. Dalton’s law states that the total pressure exerted by a mixture of gases is the sum of the partial pressures of each gas. Therefore, the partial pressure of a given component of a gas mixture will increase as the ambient pressure increases. Henry’s law states that at equilibrium, the quantity of a gas in a liquid is proportional to the partial pressure of the gas. These last two gas laws best explain the uptake of inert gas into tissues when breathing compressed air at depth.
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