Acid-Base Imbalance Metropolitan Community College Fall 2013

Acid Base Balance  Hydrogen ions - Low concentrations but highly reactive  Concentration affects physiological functions  Alters protein and enzyme functioning  Can cause cardiac, renal, pulmonary abnormalities  Alters blood clotting,  Metabolization of meds

Acid and Bases  Acids – compounds that form hydrogen ion in a solution  Proton donors  Strong acids give up their hydrogen ion easily  Weak acids hold on to their hydrogen ion more tightly  Bases – compounds that combine with hydrogen ion in a solution  Proton acceptors  Neutralizes  20:1 ratio (20 parts bicarbonate to one part carbonic acid)

What is pH?  pH is a measurement of the acidity or alkalinity of the blood.  It is inversely proportional to the number of hydrogen ions (H+) in the blood.  The more H+ present, the lower the pH will be.  The fewer H+ present, the higher the pH will be.  Homeostasis keeps pH in a very narrow range  for optimum functioning  compatible with life

Blood pH Blood pH < 7.40 acidosis Blood pH > 7.40 alkalosis

Body Acids  Respiratory Acid - CO 2 – eliminated by lungs (288 L/day)  Metabolic acids:  Lactic acids  Pyruvic acid  Ketoacids (DKA)  Acetoatic acids  Beta-hydrobutyric acids  Very little metabolic acid is produced on a daily basis  Metabolized by the liver or eliminated by the kidneys

Four Basic Categories of Abnormalities  Respiratory acidosis  Excess of carbon dioxide leading to an acid pH  Respiratory alkalosis  Lower than normal level of carbon dioxide leading to an alkaline pH  Metabolic acidosis  Excess of hydrogen ion or a deficiency in bicarbonate leading to an acid pH  Metabolic alkalosis  Excess of bicarbonate leading to an alkaline pH

Buffer Systems  Like a sponge  Soaks up extra ions  Squeezed when there’s not enough  Extracellular Buffers  Carbonic acid: controlled by respiration  Bicarbonate: controlled by excretion  Intracellular Buffers  Phosphate Buffer System  Dihydrogen phosphate (H 2 PO 4 ) – hydrogen donor or acid  Hydrogen phosphate (HPO 4 ) – hydrogen acceptor or base

Buffer Systems  Protein Buffers  In the blood  Plasma Proteins  Hemoglobin: deoxygenated is better than oxygenated at buffering  Bones  Carbonate and phosphate salts in bone provide a long term supply of buffer.  In acute metabolic acidosis bone takes up hydrogen in exchange for calcium, sodium, and potassium.

Role of the Lungs  Regulate plasma pH minute to minute by regulating the level of Carbon Dioxide (CO2)  Carbon Dioxide is measured as a partial pressure of carbon dioxide in arterial blood  PaCO mmHg  Lungs alter rate and depth of ventilations in order to retain or excrete CO2

Minute Volume – Tidal Volume  Ventilation is measured by how much air the lungs move in one minute (minute ventilation)  Minute Ventilation is the product of respiratory rate and depth and is referred to as the TIDAL VOLUME (Vt)  Normal depth tidal volume is about 500ml  Normal respiratory rate is 12 breaths per min 12 breaths x 500 ml = 6000 ml or 6 liters

Anatomic Dead Space  The volume of air that doesn’t reach the alveolar airspace  Trachea & Bronchi  Doesn’t take part in gas exchange  Estimated at 1ml/lb of ideal body weight  150lb of ideal body weight = 150ml of dead space  Tidal volume – dead space = alveolar volume  500ml – 150ml = 350ml  RR x alveolar volume = minute alveolar ventilation  12 x 350ml = 4200ml or 4.2 L/min

Hypercarbic Drive  Respiratory center in the medulla controls the rate and depth of ventilation  Responds to levels of arterial CO 2, denoted as PaCO 2  Chemoreceptors in the medulla come into contact with CSF  As PaCO 2 rises the arterial PaCO 2 reaches equilibrium with the CO 2 in the CSF  The CO 2 in the CSF dissociates into hydrogen ions  The hydrogen ions stimulate the chemoreceptors in the medulla which in turn stimulates the diaphragm and intercostal muscles  Respiratory rate and depth increase and CO 2 is blown off

Hypoxic Drive  There are also peripheral chemoreceptors  Carotid arteries  Bifurcation of the common carotid and arch of aorta  Respond to levels of  Oxygen in the blood or PaO 2  Hydrogen ions or pH  Carbon dioxide in the blood or PaCO 2  As PaO 2 falls below 60 mmHg the respiratory center is stimulated to increase rate and depth

The role of the Kidneys  Two main functions to maintain acid/base  Secrete hydrogen ions  Restore or reclaim bicarbonate (HCO 3 )  In high metabolic acidosis, the kidneys can excrete ammonia as a urinary buffer.  In alkalosis - the kidneys retain hydrogen ion and excrete bicarbonate to correct the pH.  In acidosis - the kidneys excrete hydrogen ions and conserve bicarbonate to correct the pH.  Very slow process

Assessment of ACID BASE  Arterial Blood Gases (ABG) most often and the most accurate to assess acid base balances.  Serum Electrolytes can help fine tune acid base analysis  NORMAL ABG VALUES:  pH = 7.35 to 7.45  PaCO 2 = 35 – 45 mEq/L  HCO 3 = 22 – 28 mEq/L

Steps to Interpret ABG’s 1. Assess the pH 2. Assess the respiratory component – PaCO2 3. Assess the metabolic component – HCO3, base excess 4. Evaluate compensation

Compensation  Once the primary cause is identified look at the other value  If the value is abnormal but moving in the right direction to bring pH back to normal compensation is occuring  If the pH value is normal than compensation is complete  Because renal compensation is slower you can infer whether respiratory abnormalities are acute or chronic  If kidneys have had time to compensate is chronic  If the kidneys have not had time to compensate its acute

Respiratory Acidosis  Respiratory system fails to keep up with the body’s CO 2 production  Causes (pg. 442)  Acute: drug overdose, head trauma, spinal cord injury, upper airway obstruction, pneumothorax  Chronic: obesity, MS, emphysema, spinal cord injury  Clinical Manifestations  Anxiety, irritability, confusion, lethargy, increased heart rate, warm flushed skin  Mainly seen with acute causes because chronic patients have compensated

Respiratory Acidosis  Medical treatment  Treat the underlying problem  Increase ventilation  BiPAP  Intubation  Supplemental oxygen (care must be taken with chronic pts)  Nursing care  Assess PaCO 2 levels and pH.  Observe for signs of respiratory distress: restlessness, anxiety, confusion, tachycardia  Encourage fluid intake  Position patients with head elevated 30 degrees  Administer oxygen with care

Respiratory Alkalosis  Most common cause is hyperventilation caused by anxiety, panic, or pain  Stroke  Meningitis  Head trauma  Clinical Manifestations  Anxious  Tachycardia  Tachypnea  Vertigo  Forgetfulness

Respiratory Alkalosis  Medical treatment  Treat underlying cause of condition  Sedation may be needed  Nursing care  Administer sedatives or pain medications  Provide emotional support  Encourage patient to breathe slowly, which will retain carbon dioxide in the body  Breath into a paper bag

Metabolic Acidosis  Increase in total body acid  Causes (pg. 442)  Starvation  Diarrhea  Renal failure  Diabetic ketoacidosis  Signs and symptoms  Kussmaul respirations  Altered LOC  Headache  V tach

Metabolic Acidosis  Medical treatment  Treat the underlying disorder  Nursing care  Monitor VS & ECG  Assess neurological status  Provide emotional support

Metabolic Alkalosis  An accumulation of base or a loss of acid in the ECF  Causes (pg. 442)  Prolonged nasogastric suctioning or excessive vomiting  Diuretics  Electrolyte disturbances  Large volume blood transfusions, increased citrate  Clinical Manifestations  Lethargy  Altered LOC  Tetany  ECG changes

Metabolic Alkalosis  Medical Treatment  Treat the underlying disorder  Nursing care  Monitor VS & ECG  Monitor labs  Accurate I&O including the amount of fluid removed by suction  Provide emotional support  Use isotonic saline solutions rather than water for irrigating NG tubes because the use of water can result in a loss of electrolytes

 A client’s blood gas results are pH 7.36, PaCO 2 50, HCO What do these results indicate to the nurse? A. Respiratory acidosis, compensated B. Metabolic acidosis, compensated C. Metabolic acidosis, uncompensated D. Respiratory acidosis, uncompensated

Reference  Osborn, Wraa, & Watson chapter 19