Lithium is used to treat bipolar disorder and can cause toxicity and nephropathy, which presents with moderate to severe dehydration (dry mouth, tachycardia, orthostatic hypotension) and cardiotoxicity (flattened T wave on EKG). Tachypnea is not necessarily a symptom of the volume depletion associated with lithium nephrotoxicity but may occur in response to acidosis if the condition is not treated appropriately. Increased jugular venous distention is a sign of fluid volume overload, not deficit as is experienced by the patient with lithium toxicity.