Acid base balance

Key points For cells to function optimally, a steady balance between the acids and the bases is necessary. Acid-base balance represents homeostasis of hydrogen (H+) ion concentration in body fluids. Minor changes in hydrogen concentration have major effects on normal cellular function. Arterial pH is an indirect measurement of hydrogen ion concentration and is a result of respiratory and renal compensational function. Arterial blood gases (ABGs) are most commonly used to evaluate acid-base balance.

Key points The pH is the expression of the balance between carbon dioxide (CO2), which is regulated by the lungs, and bicarbonate (HCO3-), a base regulated by the kidneys. Acid-base balance is maintained by chemical, respiratory, and renal processes. Chemical and protein buffers: Are the first line of defense. Either bind or release hydrogen ions as needed. Respond quickly to changes in pH.

Key points Respiratory buffers: Are the second line of defense. Control the level of hydrogen ions in the blood through the control of CO2 levels. When chemoreceptors sense a change in the level of CO2, they signal the brain to alter the rate and depth of respirations. Hyperventilation = decrease in hydrogen ions Hypoventilation = increase in hydrogen ions

Key points Renal buffers: The kidneys are the third line of defense. This buffering system is much slower to respond, but it is the most effective buffering system with longest duration. The kidneys control the movement of bicarbonate in the urine. High hydrogen ions = bicarbonate reabsorption and production Low hydrogen ions = bicarbonate excretion Compensation refers to the process by which the body attempts to correct changes and imbalances in pH levels. Full compensation occurs when the pH level of the blood returns to normal If the pH is not able to normalize, then it is referred to as partial compensation.

Key factors Acid-base imbalances are a result of insufficient compensation. Respiratory and renal function play a large role in the body’s ability to effectively compensate for acid-base alterations. Organ dysfunction negatively affects acid- base compensation

To determine the type of imbalance, follow these steps: Step 1 Look at pH. If < 7.35, diagnose as acidosis. If > 7.45, diagnose as alkalosis. Step 2 Look at PaCO2 and HCO3 - simultaneously. Determine which one is in the normal range. Then, conclude that the other is the indicator of imbalance. Diagnose < 35 or > 45 PaCO2 as respiratory in origin. Diagnose < 22 or > 26 HCO3 - as metabolic in origin. Step 3 Combine diagnoses of Steps 1 and 2 to name the type of imbalance

Step 4 Evaluate the PaO2 and the SaO2. If the results are below the normal range, the client is hypoxic. Step 5 Determine compensation as follows: Uncompensated: The pH will be abnormal and either the HCO3 - or the PaCO2 will be abnormal. Partially compensated: The pH, HCO3-, and PaCO2 will be abnormal. Fully compensated: The pH will be normal, but the PaCO2 and HCO3-will both be abnormal. Then, looking back at the pH will provide a clue as to which system initiated the problem, respiratory or metabolic. If the pH is < 7.40, think “acidosis” and determine which system has the acidosis value. If the pH is > 7.40, think “alkalosis” and determine which system has the alkalosis value

NANDA Nursing Diagnoses Respiratory acidosis/alkalosis Impaired gas exchange Ineffective breathing pattern Metabolic acidosis/alkalosis Decreased cardiac output

Nursing Interventions For all acid-base imbalances, it is imperative to treat the underlying cause. Respiratory acidosis: Oxygen therapy, maintain patent airway, and Enhance gas exchange (positioning and breathing techniques, ventilatory support, bronchodilators, mucolytics). Respiratory alkalosis: anxiety reduction interventions, Rebreathing techniques.

Nursing Interventions Metabolic acidosis: Varies with causes. If DKA, administer insulin; If related to GI losses, administer antidiarrheals and provide rehydration; if serum bicarbonate is low, administer sodium bicarbonate (1 mEq/kg). Metabolic alkalosis: Varies with causes. If GI losses, administer antiemetics, fluids, and electrolyte replacements; if related to potassium depletion, discontinue causative agent or potassium-sparing diuretic.

Complications and Nursing Implications Convulsions, Coma, and Respiratory Arrest Seizure precautions and management Life-support interventions