An 80-year-old man is admitted to hospital
from his nursing home for severe obtundation and possibly dehydration.
He is diabetic and on tube feeding. The day before admission, he
was found on the floor in his room, semicomatose. His urine volume
was 1.5L within the first 12 h. Some of his vitals and laboratory
findings are as follows:
| Blood pressure | 128/60 mmHg | Na+ | 170 meq/L | Cl | 130 meq/L | | Blood glucose | 410 mg/dL | | BUN | 100 mg/dL | | Creatinine | 1.5 mg/dL | | Serum osmolality | 396 mOsm/L | | Urine osmolality | 408 mOsm/L |
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Given that he weighs 80 kg, his estimated water deficit is