Winters' formula, [1] named after Dr. R.W. Winters, [2] is a formula used to evaluate respiratory compensation when analyzing acid-base disorders in the presence of metabolic acidosis. [3] [4] It can be given as:
,
where HCO3 − is given in units of mEq/L and PCO2 will be in units of mmHg.
Dr. R. W. Winters was an American physician and graduate from Yale Medical School. He was a professor of pediatrics at Columbia University College of Physicians and Surgeons. In 1974 he was awarded the Borden Award gold medal by the American Academy of Pediatrics. [5]
Dr. R. W. Winters conducted an experiment in the 1960s on 60 patients with varying degrees of metabolic acidosis. He aimed to empirically determine a mathematical expression representing the effect of respiratory compensation during metabolic acidosis. He measured the blood pH, plasma PCO2, blood base excess, and plasma bicarbonate concentrations. He focused on the relationship between plasma PCO2 and plasma bicarbonate. Winter's Formula was derived from a linear regression of this relationship between plasma PCO2 and plasma bicarbonate. [6]
There are four primary acid-base derangements that can occur in the human body - metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis. These are characterized by a serum pH below 7.4 (acidosis) or above 7.4 (alkalosis), and whether the cause is from a metabolic process or respiratory process. If the body experiences one of these derangements, the body will try to compensate by inducing an opposite process (e.g. induced respiratory alkalosis for a primary metabolic acidosis). [7]
Respiratory compensation is one of three major processes the body uses to react to derangements in acid-base status (above or below pH 7.4). It is slower than the initial bicarbonate buffer system in the blood, but faster than renal compensation. Respiratory compensation usually begins within minutes to hours, but alone will not completely return arterial pH to a normal value (7.4). Winter's Formula quantifies the amount of respiratory compensation during metabolic acidosis. [8]
During metabolic acidosis, a decrease in pH stimulates chemoreceptors. Peripheral chemoreceptors are found in the aortic and carotid bodies and respond to changes in the PaCO2, the arterial partial pressure of carbon dioxide. Central chemoreceptors are found in the brainstem and respond primarily to decreased pH in the cerebrospinal fluid. In response to decreased pH, these chemoreceptors lead to an increase in minute ventilation and increased elimination of carbon dioxide. A decrease in carbon dioxide lowers PaCO2 and pushes arterial pH towards normal. [8]
One difficulty in evaluation acid-base derangements is the presence of multiple pathologies. A patient may present with a metabolic acidosis process alone, but they may also have a concomitant respiratory acidosis. Winters' formula gives an expected value for the patient's PCO2; the patient's actual (measured) PCO2 is then compared to this. Using this information, physicians may elucidate additional causes of the acid-base derangement and identify different treatment options which may not have otherwise been considered. [9]
If the two values correspond, respiratory compensation is considered to be adequate.
If the measured PCO2 is higher than the calculated value, there is also a primary respiratory acidosis.
If the measured PCO2 is lower than the calculated value, there is also a primary respiratory alkalosis.
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe and a thin needle, but sometimes the femoral artery in the groin or another site is used. The blood can also be drawn from an arterial catheter.
A blood gas test or blood gas analysis tests blood to measure blood gas tension values, it also measures blood pH, and the level and base excess of bicarbonate. The source of the blood is reflected in the name of each test; arterial blood gases come from arteries, venous blood gases come from veins and capillary blood gases come from capillaries. The blood gas tension levels of partial pressures can be used as indicators of ventilation, respiration and oxygenation. Analysis of paired arterial and venous specimens can give insights into the aetiology of acidosis in the newborn.
Acidosis is a process causing increased acidity in the blood and other body tissues. If not further qualified, it usually refers to acidity of the blood plasma.
Alkalosis is the result of a process reducing hydrogen ion concentration of arterial blood plasma (alkalemia). In contrast to acidemia, alkalemia occurs when the serum pH is higher than normal. Alkalosis is usually divided into the categories of respiratory alkalosis and metabolic alkalosis or a combined respiratory/metabolic alkalosis.
The control of ventilation is the physiological mechanisms involved in the control of breathing, which is the movement of air into and out of the lungs. Ventilation facilitates respiration. Respiration refers to the utilization of oxygen and balancing of carbon dioxide by the body as a whole, or by individual cells in cellular respiration.
The carotid body is a small cluster of chemoreceptor cells and supporting sustentacular cells situated at bifurcation of each common carotid artery in its adventitia.
Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys to excrete excess acids. Metabolic acidosis can lead to acidemia, which is defined as arterial blood pH that is lower than 7.35. Acidemia and acidosis are not mutually exclusive – pH and hydrogen ion concentrations also depend on the coexistence of other acid-base disorders; therefore, pH levels in people with metabolic acidosis can range from low to high.
Respiratory acidosis is a state in which decreased ventilation (hypoventilation) increases the concentration of carbon dioxide in the blood and decreases the blood's pH.
Respiratory alkalosis is a medical condition in which increased respiration elevates the blood pH beyond the normal range (7.35–7.45) with a concurrent reduction in arterial levels of carbon dioxide. This condition is one of the four primary disturbance of acid–base homeostasis.
The anion gap is a value calculated from the results of multiple individual medical lab tests. It may be reported with the results of an electrolyte panel, which is often performed as part of a comprehensive metabolic panel.
Metabolic alkalosis is a metabolic condition in which the pH of tissue is elevated beyond the normal range (7.35–7.45). This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations. The condition typically cannot last long if the kidneys are functioning properly.
In physiology, base excess and base deficit refer to an excess or deficit, respectively, in the amount of base present in the blood. The value is usually reported as a concentration in units of mEq/L (mmol/L), with positive numbers indicating an excess of base and negative a deficit. A typical reference range for base excess is −2 to +2 mEq/L.
Carbaminohemoglobin (carbaminohaemoglobin BrE) (CO2Hb, also known as carbhemoglobin and carbohemoglobin) is a compound of hemoglobin and carbon dioxide, and is one of the forms in which carbon dioxide exists in the blood. Twenty-three percent of carbon dioxide is carried in blood this way (70% is converted into bicarbonate by carbonic anhydrase and then carried in plasma, 7% carried as free CO2, dissolved in plasma).
Acid–base homeostasis is the homeostatic regulation of the pH of the body's extracellular fluid (ECF). The proper balance between the acids and bases in the ECF is crucial for the normal physiology of the body—and for cellular metabolism. The pH of the intracellular fluid and the extracellular fluid need to be maintained at a constant level.
The factors that determine the values for alveolar pO2 and pCO2 are:
In acid base physiology, the Davenport diagram is a graphical tool, developed by Horace W. Davenport, that allows a clinician or investigator to describe blood bicarbonate concentrations and blood pH following a respiratory and/or metabolic acid-base disturbance. The diagram depicts a three-dimensional surface describing all possible states of chemical equilibria between gaseous carbon dioxide, aqueous bicarbonate and aqueous protons at the physiologically complex interface of the alveoli of the lungs and the alveolar capillaries. Although the surface represented in the diagram is experimentally determined, the Davenport diagram is rarely used in the clinical setting, but allows the investigator to envision the effects of physiological changes on blood acid-base chemistry. For clinical use there are two recent innovations: an Acid-Base Diagram which provides Text Descriptions for the abnormalities and a High Altitude Version that provides text descriptions appropriate for the altitude.
Respiratory compensation is the modulation by the brainstem respiratory centers, which involves altering alveolar ventilation to try and bring the plasma pH back to its normal value (7.4) in order to keep the acid-base balance in the body. It usually occurs within minutes to hours and is much faster than renal compensation, but has less ability to restore normal values.
Acid–base imbalance is an abnormality of the human body's normal balance of acids and bases that causes the plasma pH to deviate out of the normal range. In the fetus, the normal range differs based on which umbilical vessel is sampled. It can exist in varying levels of severity, some life-threatening.
Salicylate poisoning, also known as aspirin poisoning, is the acute or chronic poisoning with a salicylate such as aspirin. The classic symptoms are ringing in the ears, nausea, abdominal pain, and a fast breathing rate. Early on, these may be subtle, while larger doses may result in fever. Complications can include swelling of the brain or lungs, seizures, low blood sugar, or cardiac arrest.
Delta ratio, or "delta-delta", is a formula that can be used to assess elevated anion gap metabolic acidosis and to evaluate whether a mixed acid–base disorder is present. The anion gap (AG) without potassium is calculated first and if a metabolic acidosis is present, results in either a high anion gap metabolic acidosis (HAGMA) or a normal anion gap acidosis (NAGMA). A low anion gap is usually an oddity of measurement, rather than a clinical concern.
