Life‐threatening heat‐related illness with severe hyponatremia in an aluminum smelter worker

Abstract Heat stress is a recognized occupational hazard in aluminum smelter pot rooms. This is the report of an unusual and complex case of heat‐related illness in an aluminum smelter worker. The 34‐year‐old male US worker developed life‐threatening heat‐related illness in August 2018, on his first day back at work after a 7‐day absence. The worker initially presented with bilateral hand then all‐extremity cramping followed some hours later by a generalized seizure and acute mental status changes, including combativeness. Emergency room evaluation identified a serum sodium level of 114 mmol/L. Acute liver and kidney injury ensued along with profound rhabdomyolysis, with peak total creatinine phosphokinase level reaching over 125 000 units/L at 3 days post incident. Initial ventilatory support, careful fluid resuscitation, and electrolyte management were provided. Metabolic encephalopathy resolved. Complications included sepsis. After 5 days in the intensive care unit and eight additional days of inpatient management, observation, and the initiation of rehabilitation, the worker was discharged. Residual effects include polyneuropathy of upper and lower extremities and the postdischarge magnetic resonance imaging finding of a cerebellar lesion. Prevailing considerations in the differential diagnosis included exertional heat stroke and/or exertion‐associated hyponatremia with encephalopathy.

occupational HRI that resulted in at least 1 day of lost work, with 214 hospitalizations and 37 fatalities. 6 Epidemiologically, the majority (over 70%) of heat-related fatalities occur during the first week on the job, with nearly half (45%) occurring on the first day on the job or return to duty after an absence of a week or more. 6 Aluminum smelter operations entail employee work in proximity to "pots"-aligned in series within a pot room ( Figure 1)-in which an electrochemical process reduces alumina ore into molten aluminum metal. 7,8 The nature of this work subjects employees to significant radiant heat load which, even with mild outdoor ambient thermal conditions, can result in personal heat strain that overwhelms the body's usual compensating mechanisms. [9][10][11] Consequently, HRI is an acknowledged and not infrequent adverse health outcome of work in pot rooms, although bona fide exertional heat stroke is rare and unreported in the literature to date. [9][10][11][12] 2 | CASE REPORT Following a 7-day scheduled absence from the workplace, a 34-year old male aluminum smelter pot room process control operator (PCO) returned to work to commence a series of evening shifts from 6.00 PM to 6.00 AM. The first half of the shift involved vigorous and intense pot room control tasks. Following the lunch break (ie, during the second half of the shift), the worker was assigned to other routine, though less demanding, tasks with less heat stress potential.
Within 6 hours of starting his first shift, while performing routine tasks that involved the occasional presence on the "catwalk" between sequential pots (Figure 2), he began to experience hand-cramping.
Shift safety personnel were notified, and the worker was encouraged to access available fluids. The worker continued to perform his assigned job tasks, however, and near the end of his shift at approximately 6.00 AM, he experienced hand-cramping again, mentioning this to a coworker but not the crew leader or supervisor. He finished his shift and clocked out.
Forty-five minutes later the site plant protection office received a request to send an ambulance to the shower house for a worker with difficulty breathing. Upon arriving at the scene, the dispatched emergency medical technician (EMT) found the operator walking out of the building and describing body cramps but without concern regarding his breathing. He was noted to be diaphoretic. The worker entered the ambulance under his own power, a presumptive assessment of heat exhaustion was made, and first aid attention consisting of oral fluids and rehydration salts was provided in accordance with site protocol. Initial vital signs showed an oral temperature of only 36.5°C (97.7°F), blood pressure of 160/80 mm Hg, pulse rate of 91 beats per minute, respiratory rate of 18 breaths per minute, and pulse oximetry of 98% (SpO 2 -peripheral oxygen saturation). Recognizing the temperature as unexpectedly low, which was thought secondary to the ingestion of cool rehydration fluids, the EMT intended to repeat this measurement within a few minutes; however, ensuing acute medical events took precedence and a repeat temperature was never obtained in the field.
During transport to the site medical department, the worker experienced a generalized seizure with, as described by the EMT, decorticate posturing, following which he became agitated, combative, and pugnacious. Random blood glucose was 142 mg/dL (7.9 mmol/L). The community ambulance service was summoned, the worker was stabilized with haloperidol and midazolam, and transferred to the proximate regional hospital emergency department for further evaluation and care.
In the emergency department his initial measured oral temperature was 38  Airway protection via intubation was achieved. However, he aspirated during the difficult procedure and remained intubated for the first 48 hours of hospitalization. Day-of-admission computerized tomography scan of the head without contrast showed no intracranial mass, hemorrhage, hydrocephalus, or acute intracranial abnormality. An electrocardiogram (EKG) showed sinus tachycardia.
Past medical history was notable for essential hypertension, gastroesophageal reflux disease, and mild attention deficit hyperactivity disorder (ADHD), for which the worker had been prescribed losartan, lansoprazole, and amphetamine/dextroamphetamine, respectively. He was a former smoker and admitted to moderate alcohol ingestion several times per week. He had no known history of prior HRI. However, in the aftermath of this incident, he discovered through family medical history inquiry that he had a history of "cramping" in relation to sports activities and exertion in his youth.
There was no known history of hyponatremia or alcohol-use disorders. 13,14 Stabilization treatment included rehydration with normal saline solution per recommendation of the consulting nephrologist.
An electroencephalogram (EEG) on admission day 2 was indicative of moderate encephalopathy of nonspecific etiology, but without evidence for epileptiform activity. Enterococcus faecalis sepsis was diagnosed by blood culture on admission day 4. Hepatitis serologies were nonreactive, as were human immunodeficiency virus 1 and 2.
The worker spent a total of 13 days in the hospital, the first five being in the intensive care unit. Total CPK, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) values in units/L peaked at 125 000, 1478, and 552, respectively, on the fourth hospital day, with a progressive decline in values thereafter ( Table 2).
The hospital discharge summary listed "severe hyponatremia likely triggered by heat exposure" among the discharge diagnoses,  approximately 500 ml/h across the work shift, which is less than the potential maximum compensatory renal loss of 800 to 1000 ml/ h. 17 In addition, given the strenuous job in hot conditions, it is likely that the sweat rate would have been similar to his fluid intake.
Rhabdomyolysis has been reported in association with EAH, with CPK levels typically highest at time of presentation. 29 While a temperature in this range would have been high enough to corroborate a diagnosis of heat stroke, unfortunately, no accurate temperature was recorded in the field to confirm this possibility.
Had this worker undergone a more formal clinical assessment by the on-site medical department when his hand cramping first occurred, or reoccurred late into his shift, it is possible that additional signs, symptoms, vital signs, and corroborating laboratory data suggestive of serious HRI may have been identified.
In contrast, the symptoms were perceived to be minor and self-limited.
It is not yet clear what pathology is responsible for the abnormalities seen on MRI of the cerebellum in this case.
Importantly, increased MR signal intensity has been reported in the cerebellum of patients in the acute phase of heat stroke, with subsequent scans revealing cerebellar atrophy months later. [36][37][38] Pathological processes that can result in cerebellar injury during heat stroke include ischemia, hemorrhage, and direct thermal cytotoxicity. [36][37][38][39] Peripheral neuropathy has been reported before in heat stroke cases. 40,41 Although there is reference to encephalopathy in EAH, we found no reports of cerebellar pathology or peripheral neuropathy in association with this condition.
In sum, the exposure circumstances and clinical character-

Reinforcement of existing control measures and remediation
actions stemming from this incident include the following: • Evaluation for pot room modernization opportunities to reduce work rate and heat stress load.
• Ensuring adequate crew numbers are maintained to enable sufficient rest periods based on heat stress evaluations. 15 • Extending heat stress prevention plan focus dates to start before the traditional "hot months" and continuing into the early fall.
• Deploying selective use of preshift urine-specific gravity testing, particularly for high-risk tasks and workers. 42,43 • Increasing contact by line supervisors with workers performing high-risk tasks.

ACKNOWLEDGMENTS
We acknowledge the health and safety, medical and operations personnel at the affected Alcoa location who provided relevant information in support of the preparation of this manuscript. We commend the emergency medical response team members whose quick action during the acute phase of this incident helped to forestall a more catastrophic outcome. And we thank the affected worker who willingly consented to have his experience shared in the context of a scientific publication towards the goal of preventing serious heat-related illness among others at risk in the occupational setting. This study was funded by Alcoa Corporation.

ETHICS APPROVAL AND INFORMED CONSENT
There was no ethics review and approval, however, written informed consent was obtained from the worker described in this case report.
Relevant medical records were acquired and maintained in accordance with applicable disclosure laws and practice, and consistent with Alcoa's global data privacy standards.