Tromethamine, often abbreviated as THAM, is a medication administered to help regulate the body’s pH balance. It functions as a “buffer,” directly interacting with and neutralizing excess acids within the body. This medication is primarily used in hospital settings, specifically in care situations, where a patient’s acid-base balance has become severely disrupted.
Understanding Acidosis and THAM’s Role
Acidosis is a medical condition that occurs when the body’s fluids contain too much acid, leading to an abnormally low pH level in the blood. The pH scale measures acidity and alkalinity, with values below 7.0 being acidic and values above 7.0 being alkaline or basic; a healthy human blood pH ranges around 7.35 to 7.45.
Maintaining this precise pH balance is important for nearly all bodily functions, including oxygen delivery to tissues and the proper functioning of proteins and enzymes. The body naturally produces acids as a byproduct of metabolism, and the kidneys and lungs work together to eliminate these acids and maintain pH equilibrium. However, in various severe medical conditions, these organs can become overwhelmed, leading to an excess accumulation of acid. This imbalance can impair heart function, cause low blood pressure, and in severe cases, lead to coma.
How THAM Works in the Body
THAM, chemically known as tris-hydroxymethyl aminomethane, is an organic amine buffer that works by directly accepting protons (hydrogen ions) from the body’s acidic environment. Unlike some other buffering agents, THAM does not produce carbon dioxide during its buffering process; in fact, it helps to reduce the partial pressure of carbon dioxide in arterial blood.
The medication works by reacting with water and carbon dioxide to form bicarbonate and a protonated THAM complex. This complex is then excreted by the kidneys. THAM is considered a more effective buffer than bicarbonate in the physiological pH range because of its higher pK (7.8 compared to 6.1 for bicarbonate). This unique mechanism allows THAM to be effective even in “closed” or “semi-closed” systems, meaning it can still buffer acids even when carbon dioxide elimination is impaired. It distributes rapidly through the extracellular space and can slowly penetrate the intracellular space, neutralizing acidic ions within cells.
Conditions Where THAM is Used
THAM is administered in several conditions where severe acidosis, either metabolic or respiratory, threatens organ function. One primary use is in metabolic acidosis associated with cardiac bypass surgery, where it helps to correct the acidity that can occur during or immediately after these procedures. It can also be added directly to blood used to prime heart-lung machines to neutralize its inherent acidity, preventing an initial acid load on the patient.
Another indication for THAM is in metabolic acidosis linked to cardiac arrest. Acidosis is a frequent consequence of cardiac arrest, and prompt correction can improve the heart’s response to resuscitative efforts. It is also considered for patients with increased intracranial pressure, as it can rapidly decrease this pressure.
THAM may also be used in cases of severe acute respiratory distress syndrome (ARDS) that involve acidosis and permissive hypercapnia, a strategy where carbon dioxide levels are intentionally kept high to protect the lungs. In these situations, THAM helps to manage the accumulated carbon dioxide and associated acidosis. Other instances where THAM might be considered include severe acidemia from conditions like sepsis, or in specific cases of diabetic or renal acidosis.
Important Considerations and Potential Side Effects
THAM is administered intravenously as a slow infusion, and requires careful medical supervision due to its potency and potential side effects. It is given in a 0.3 M solution, adjusted to a pH of approximately 8.6. The dosage is estimated based on the patient’s body weight and their “base deficit,” which indicates the amount of acid that needs to be neutralized.
Close monitoring of the patient’s acid-base status, ventilation, and plasma electrolytes, including potassium and glucose levels, is performed frequently. One notable side effect of THAM, especially with large or rapid doses, is respiratory depression, which can slow breathing and may necessitate mechanical ventilation. This occurs because THAM increases blood pH and reduces carbon dioxide concentration, which can suppress the body’s natural drive to breathe.
Another concern is hypoglycemia, or low blood sugar, which can be prolonged and requires frequent blood glucose monitoring during and after THAM administration. Other potential issues include hyperkalemia, an elevation of potassium in the blood, particularly in patients with kidney impairment, and the risk of localized tissue damage if the infusion leaks outside the vein. THAM is reserved for short-term use in severe acidotic states.