Page 30 - JSOM Spring 2018

TABLE 2 Stages of Hypothermia medevac times, including tail-to-tail handoffs, as well as iatro-
Measured Core Temperature Clinical Assessment genic interventions such as cold IV fluids and paralytics, and
Mild: 32°C–35°C (89.6°F–95°F) Stage 1: Conscious, shivering DKA are powerful contributors to hypothermia.
Moderate: 28°C–31.9°C Stage 2: Confused, shivering
(82.4°F–89.6°F) This patient exhibited multiple pathophysiologic manifesta-
Stage 3: Unconscious, not tions of hypothermia, including life-threatening arrhythmias,
shivering, vital signs present electrolyte abnormalities, and decreased oxygen delivery. Dur-
Severe: <28°C (82.4°F) ing the rewarming phase of resuscitation, the patient exhib-
Stage 4: Unconscious, vital signs
absent ited rewarming shock, hyperkalemia, and difficult-to-control
blood glucose levels.
a temperature probe in the distal esophagus or specialized
instruments placed in the nasopharyngeal space or snuggly The cardiopulmonary effects of hypothermia vary. Blood
against the tympanic membrane can achieve accurate core pressure can remain stable due to peripheral vasoconstriction
temperatures. In expeditionary settings, an initial intermedi- shunting intravascular volume to the core. However, hypoten-
ate measurement by forehead Tempa Dot thermometer (3M) sion can occur secondary to hypothermia-induced arrhyth-
or the sublingual route followed by core measurement by the mias. The most common arrhythmia in hypothermic patients
rectal or esophageal route are accepted methods. 1
is atrial fibrillation, followed by ventricular tachycardia (in-
cluding ventricular fibrillation). Bradycardia can be seen. The
In contrast to induced hypothermia in patients after cardiac ar- patient in this report had a combination of these arrhythmias.
rest or who are undergoing cardiac bypass, accidental and iat- Rewarming shock, a phrase coined to describe hypotension
rogenic hypothermia can be life threatening owing to multiple and hemodynamic instability due to acidosis from oxygen con-
pathophysiologic derangements. Hypothermia, not intended sumption (Vo ) and oxygen delivery (Do ) mismatch, was ex-
as medical therapy, can be caused by environmental and non- hibited by our patient. Vo /Do mismatch during reperfusion
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environmental factors. Table 3 lists causes of nonenvironmen- is worsened by shivering, which increases oxygen demand.
tal hypothermia. In Afghanistan in the winter, as demonstrated Reperfusion during rewarming also contributes to a systemic
in the case reported here, it is challenging to maintain the ther- inflammatory response syndrome–induced vasodilatory re-
mal neutral zone during care in prolonged field settings and en sponse. This combination of decreased cardiac output from
route. The outside temperature on the ground on the day of acidosis in the setting of vasoplegia leads to cardiogenic shock
admission of this patient was −5°C (23°F). Convective cooling combined with distributive shock.
was exacerbated during the almost 12-hour combined rotary
wing and ground transportation. His prolonged medevac, in- Hypothermia affects renal and metabolic systems, leading to
terrupted by heat-losing interventions such as intubations and electrolyte disturbances such as hypokalemia (hypothermia
medicine administration, ultimately brought his core tempera- shifts potassium into cells), hypocalcemia, hypomagnesemia,
ture to 31°C (87.8°F).
and hypophosphatemia. In addition, cold diuresis can worsen
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hypokalemia. Because our patient had concomitant DKA and
TABLE 3 Nonenvironmental Causes of Hypothermia acute kidney injury, he was hyperkalemic. Potassium stasis
Cold intravenous fluids was challenging during his rewarming and resuscitation, and
Paralytic medications vigilance for hypokalemia was required while he was undergo-
Endocrine ing insulin infusion therapy.
Hypothyroidism
Hypopituitarism
Hypoglycemia A left shift of the oxyhemoglobin dissociation curve is caused
Diabetic ketoacidosis by hypothermia, whereas a right shift occurs in acidosis from
Neurologic DKA and increased lactate (Figure 3). This discordance likely
Cerebrovascular accidents contributed to our patient’s survival. A left shift leads to de-
Infections creased oxygen delivery, which is deleterious in the setting of
Antipsychotic medications already-hypoxic tissues. Our patient’s pH was 6.681 as a re-
Alcohol sult of ketoacidosis, respiratory acidosis, and chloride-liberal
fluid resuscitation, which resulted in a right shift. Just as hypo-
Although the patient was normothermic initially at the Role thermia increases hemoglobin’s oxygen affinity (and decreases
1 facility, he was near the threshold for hypothermia, likely oxygen delivery), his acidosis decreased hemoglobin’s oxygen
as a result of his DKA. Furthermore, his ability to shiver was affinity (and increased oxygen delivery). This patient had
reduced from cold IV fluids and the use of paralytics. Before mildly increased lactate level (2.8mmol/L)), which also con-
paralysis, his core temperature likely dropped below the point tributed to his acidosis. His base deficit (−30mEq/L) was the
when shivering was possible: stage 3 hypothermia. In addi- lowest the authors have ever calculated. In large case series,
tion, the patient was subjected to nonenvironmental causes of when a discordance between initial measured lactic acid and
hypothermia. DKA is a known cause of nonenvironmental hy- base deficit exists in critical care patients, the base deficit does
pothermia and results from the inability of adenosine triphos- not predict mortality. 4
phate to use glucose in the patient with highly insulin-resistant
DKA. Impaired glucose use leads to a lack of substrate for heat Hypothermia deserves respect when considering use of para-
production. In one case series spanning 7 years, DKA was the lytics. In addition to the reduction in our patient’s ability to
most common cause of nonenvironmental hypothermia. Non- maintain core temperature through shivering, paralytics have
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environmental causes of hypothermia are important factors altered pharmacokinetics and pharmacodynamics in hypo-
to consider when transporting patients in expeditionary set- thermia. Depolarizing agents such as succinylcholine are more
tings. The winter environment in Afghanistan and prolonged potent and have prolonged duration in hypothermic patients

26 | JSOM Volume 18, Edition 1/Spring 2018