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Acid-Base Homeostasis Overview for Infusion Nurses

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Acid-Base Homeostasis Overview for Infusion Nurses The Art and Science of Infusion Nursing Natalie A. Masco , DNP, RN, FNP-C Acid-Base Homeostasis Overview for Infusion Nurses He subsequently was placed on IV phenobarbital. ABSTRACT Despite management of the kidney injury and sei- Acid-base homeostasis is essential to normal zures, the patient continued to demonstrate hyper- function of the human body. Even slight altera- kalemia and muscle twitching. Arterial blood gases tions can significantly alter physiologic processes obtained throughout this time showed alteration in at the tissue and cellular levels. To optimally care acid-base balance. Acid-base homeostasis must be for patients, nurses must be able to recognize maintained in a narrow range for the body to function normally. Even slight changes can significantly alter signs and symptoms that indicate deviations from physiologic processes at the tissue and cellular levels, normal. Nurses who provide infusions to as well as the pharmacokinetics of infused products. patients—whether in acute care, home care, or Nurses must be able to recognize possible causes and infusion center settings—have a responsibility to signs of acid-base imbalance that can indicate devia- be able to recognize the laboratory value changes tions from normal. In this article, the physiology of that occur with the imbalance and appreciate the acid-base homeostasis will be addressed as well as the treatment options, including intravenous impact of acid-base imbalance related to patient care, infusions. including infusion therapy. Key words: acid-base imbalance , arterial blood gas , infusion nursing , metabolic acidosis , meta- FOUNDATIONAL CONCEPT OF pH bolic alkalosis , respiratory acidosis , respiratory alkalosis When discussing acid-base homeostasis, it is important to start with the definition of pH. pH is defined as the nega- .J., a 24-year-old male, presented to the tive logarithm of the hydrogen ion concentration; it reflects the degree of acidity or alkalinity of an environ- hospital following a serious motor vehi- 1 cle collision. He suffered a head injury ment. The normal hydrogen ion concentration of the and multiple internal injuries that blood is quite small, estimated at 0.0004 mEq/L. This measure is documented as a pH of 7.40. The normal range required admission to the intensive care 2 unit. D.J. developed acute kidney injury and received of blood pH for adults is 7.35 to 7.45. Normal cellular D rapid-volume resuscitation with 0.9% sodium metabolism continually releases acids to be excreted from chloride. In the following days, he experienced multi- the body to prevent the fluids from becoming too acidic. ple seizures requiring intubation for airway protec- When a change in hydrogen ion concentration occurs and tion and large doses of intravenous (IV) lorazepam. the body is unable to counteract the extreme using chemi- cal buffers, respiratory regulation, or renal regulation, the Author Affiliation: Wegmans School of Nursing, St. John Fisher pH of the body fluids becomes abnormal and cellular College, Rochester, New York. function is impaired. An increase in hydrogen ion concen- Natalie A. Masco, DNP, RN, FNP-C, has more than a decade of tration results in acidity within the body. Acidemia is clinical practice in the acute care setting. Dr. Masco is an assistant defined as a blood pH of less than 7.35. 3 A pH of 6.9 or professor at the Wegmans School of Nursing at St. John Fisher College in Rochester, New York, and is the coordinator of the less in the body is incompatible with life and may result in Family Nurse Practitioner Program. death. 4 Likewise, a decrease in hydrogen ion concentra- The author has no conflicts of interest to disclose. tion results in alkalinity. Alkalemia is defined as a blood Corresponding Author: Natalie A. Masco, DNP, RN, FNP-C, St. pH of 7.45 or greater. 3 A blood pH of 7.8 or greater is John Fisher College, Wegmans School of Nursing, 3690 East Ave, 4 Rochester, NY 14618 ( [email protected] ). incompatible with life and may result in death. Figure 1 DOI: 10.1097/NAN.0000000000000187 shows the acid-base continuum. 288 Copyright © 2016 Infusion Nurses Society Journal of Infusion Nursing Copyright © 2016 Infusion Nurses Society. Unauthorized reproduction of this article is prohibited. Figure 1 Acid-base continuum in the human body. FINDING THE BALANCE: anhydrase, the carbonic acid is broken down into car- HOMEOSTASIS bon dioxide and water, neutralizing the excess acid. 4 Conversely if the body is too alkaline, the carbonic Homeostasis refers to the automatic, self-regulating acid, in conjunction with the bicarbonate buffers, will processes necessary to maintain the normal state of the form bicarbonate and hydrogen ions. The body then intracellular/extracellular environments, despite will reabsorb the excess hydrogen ions to achieve a changes in the environment. 5 The body has 3 lines of normal pH. response to maintain pH homeostasis: chemical buff- ers, respiratory regulation, and renal regulation. The RESPIRATORY REGULATION: method by which the body attempts to achieve homeo- SECOND-LINE RESPONSE stasis is dependent on a number of factors: (1) the length of time of the imbalance, (2) the baseline func- tion of the organs involved in achieving homeostasis, The respiratory system is the body’s second defense 4 and (3) the underlying condition resulting in the against acid-base imbalance. All cells continually pro- imbalance. 5 duce carbon dioxide. Carbon dioxide combines with water molecules to form carbonic acid. The body alters the rate and depth of respiration to make needed adjust- CHEMICAL BUFFERS: FIRST-LINE ments in the acid-base regulation. The respiratory sys- RESPONSE tem responds within minutes of imbalance and reaches maximum effectiveness in hours. 4 Chemical buffers are elements that help maintain a near The body’s ability to use respiratory compensation is consistency of the pH of fluids by preventing an increase dependent on normal function of all components of the or decrease in the hydrogen ions. 5 Buffers act to change respiratory system. Chemoreceptors and respiratory strong acids into weaker acids or to bind to acids to neurons in the brainstem must be functioning optimally. neutralize their effects. 2 Buffers take action immediately It is important to recognize that this mechanism in the setting of imbalance, and potential changes in pH responds more slowly with aging. Respiratory regula- are adjusted. It is for this reason that chemical buffers tion also depends on the motor nerve innovation of the are the first line of defense against pH imbalance. respiratory muscles, including the diaphragm. In addi- Chemical buffers can be found in the extracellular fluid, tion, the chest wall, airways, lungs, and pulmonary the intracellular fluid, the urine, and within erythro- circulation must be functioning normally if respiratory cytes. There are 3 individual buffers in the body: (1) regulation is to work effectively. carbonate/carbonic acid buffers, (2) phosphate buffers, The rate and depth of respiration are influenced and (3) plasma protein buffers. Plasma protein buffers strongly by chemoreceptors that sense alteration in the are most plentiful in the body; however, the carbonic partial pressure of arterial carbon dioxide and hydrogen 6 acid buffers are considered to be most important in rela- in the blood. If too much carbonic acid accumulates in tion to the respiratory system. the blood of a healthy person, hyperventilation will Bicarbonate buffers are imperative to maintaining occur. The rate and depth of respiration increases and homeostasis. Bicarbonate ions and carbonic acid are excess carbonic acid is exhaled in an attempt to correct normally in chemical equilibrium in the extracellular the pH imbalance. If too little carbonic acid is present fluid. When significant amounts of both carbonic acid in the blood, the rate and depth of the respiration and bicarbonate are present, a buffer is formed. 4 Under decrease, and hypoventilation occurs. This will result in normal circumstances, there is much more bicarbonate retention of carbon dioxide until it is once more present present in the body than carbonic acid, with a ratio of in normal amounts in the body. 20 to 1. 4 This is consistent with the body’s needs as more acids are produced as part of cellular function. The blood with its high base concentration is able to RENAL REGULATION: THIRD-LINE neutralize the metabolic acids produced. If the body RESPONSE becomes too acidic, the bicarbonate buffers take up excess hydrogen ions released by the acid to form car- Cells continually produce metabolic acids during nor- bonic acid. Through the action of the enzyme carbonic mal metabolism. The function of the kidneys is to VOLUME 39 | NUMBER 5 | SEPTEMBER/OCTOBER 2016 Copyright © 2016 Infusion Nurses Society 289 Copyright © 2016 Infusion Nurses Society. Unauthorized reproduction of this article is prohibited. excrete all acids from the body, with the exception of WHAT HAPPENS WHEN carbonic acid, which can only be excreted by the lungs HOMEOSTASIS FAILS? through exhalation. If metabolic acids begin to accu- mulate in the blood, the kidneys compensate by If the body is unable to achieve or maintain homeostasis increasing acid excretion. If alkalemia occurs, the kid- for the amount of time and degree needed by the body, neys slow their excretion mechanism to allow acid to clinical decompensation occurs. The rate of decompen- accumulate in the blood to normal levels. Given the sation depends on the degree of reserve and one’s base- complex nature of this process, renal regulation takes line organ function. For the very young, the very old, 2 to 3 days to respond maximally to an acid-base and those with chronic disease, this decompensation imbalance; however, it can respond indefinitely for 4 can occur more quickly. On the other hand, normal, chronic imbalances. healthy adults can use their compensatory mechanisms The kidneys have several mechanisms to achieve acid for a period of time before failure ensues.
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