Aim: An increased thyroxine requirement has been described in hypothyroid patients who have chronic gastritis as well as in patients who are treated with drugs that modify the acidic environment of the stomach. Patients with acute critical illnesses are generally treated with calorically dense enteral solutions and antacids, both of which influence the gastric acidic environment. In this study, we evaluated levothyroxine (L-thyroxine) requirements in hypothyroid patients admitted to our ICU.
Methods: The medical records of nine patients with pre-existing hypothyroidism who did not have gastrointestinal diseases and who were admitted to our ICU between 2003 and 2008 were retrospectively reviewed. Serum TSH, FT4, and FT3 levels were measured at the time of admission and every four to eight days thereafter. After the second measurement of these parameters, patients' L-thyroxine doses were adjusted to maintain their TSH concentrations at baseline levels.
Results: At the time of ICU admission, the median [interquartile range] TSH, FT4, and FT3 values of the included patients were 1.52 [0.79-3.8] mU/L, 6.5 [4.9-9.3] pg/mL, and 1.0 [<1.0-1.25] pg/mL, respectively. After the first 4-8 days of their ICU stay, while their L-thyroxine doses were unchanged, the TSH levels of all included patients increased (5.69 [3.87-6.83] mU/L, P=0.012). Over the same period, their FT4 levels decreased significantly. To restore patients' TSH levels to those at the time of admission, the L-thyroxine dose was increased in 8/9 patients by an average of 54.4+/-31.6% (P=0.001). At the time of ICU discharge, patients' TSH and FT4 levels had returned to near their levels at the time of admission. All patients' serum FT3 levels remained low throughout the entire duration of their ICU stay.
Conclusion: To maintain TSH levels in the normal range, it may be necessary to increase the L-thyroxine dose of critically ill patients with hypothyroidism. Our findings also suggest that during the first several days of a critical illness, the hypothalamic-pituitary-thyroid axis is not suppressed in hypothyroid patients.