Utilization of indirect calorimetry to assist in determining undiagnosed hypothyroidism in a patient on mechanical ventilation

Abstract

Published predictive equations are required when indirect calorimetry (IC) is unavailable in the clinical setting. Several medical conditions that are not accounted for by published predictive equations can impact a patient's resting energy expenditure, such as adrenal changes or alterations in thyroid‐stimulating hormone (TSH). TSH levels significantly impact a patient's resting energy expenditure, with hypothyroidism decreasing and hyperthyroidism increasing energy requirements. Clinical hypothyroidism has been correlated with increased ventilator dependency in patients with critical illness and malnutrition. The following case study describes the utilization of IC to trigger a full evaluation for the diagnosis of hypothyroidism in an adult patient with multiple myeloma who was mechanically ventilated. IC results for this patient were 39% lower than estimated by predictive energy equations. TSH, thyroxine, and triiodothyronine serum assays were obtained to rule out hypothyroidism. Based on elevated TSH and low thyroxine, the patient was found to have undiagnosed hypothyroidism. Appropriate pharmaceutical and nutrition interventions were made based upon these results. This case demonstrates the impact hormonal changes can have on resting energy expenditure and how the utilization of IC can provide additional information other than energy requirements.