Chp 24 Acid-base balance

Acid-Base Balance Acid-Base balance is: the regulation of HYDROGEN ions. The more Hydrogen ions, the more acidic the solution and the LOWER the pH The lower Hydrogen concentration, the more alkaline the solution and the HIGHER the pH

pH The acidity or alkalinity of a solution is measured as pH. The more acidic a solution, the lower the pH. The more alkaline a solution , the higher the pH. Water has a pH of 7 and is neutral. The pH of arterial blood is normally 7.35 to 7.45

Buffer Systems Regulate pH by binding or releasing Hydrogen Most important buffer system: Bicarbonate-Carbonic Acid Buffer System (Blood Buffer systems act instantaneously and thus constitute the body’s first line of defense against acid-base imbalance)

Acid-Base Balance Figure 24.12 pH Normal Alkalosis Acidosis 7.35 7.45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 24.12 pH Normal Alkalosis Acidosis 7.35 7.45 8.0 6.8 Death Death H2CO3 HCO3–

Respiratory Regulation Lungs help regulated acid-base balance by eliminating or retaining carbon dioxide pH may be regulated by altering the rate and depth of respirations changes in pH are rapid, occurring within minutes normal CO2 level 35 to 45 mm Hg

Renal Regulation Kidneys the long-term regulator of acid-base balance slower to respond may take hours or days to correct pH kidneys maintain balance by excreting or conserving bicarbonate and hydrogen ions normal bicarbonate level 22 to 26 mEq/L.

Factors Affecting Balance Age especially infants and the elderly Gender and Body Size amount of fat Environmental Temperature Lifestyle stress

Chart

The Basic Relationship between PCO2 and Plasma pH Figure 27.6

Respiratory Acidosis Mechanism Etiology Hypoventilation or Excess CO2 Production Etiology COPD Neuromuscular Disease Respiratory Center Depression Late ARDS Inadequate mechanical ventilation Sepsis or Burns Excess carbohydrate intake

Respiratory Acidosis (cont) Symptoms Dyspnea, Disorientation or coma Dysrhythmias pH < 7.35, PaCO2 > 45mm Hg Hyperkalemia or Hypoxemia Treatment Treat underlying cause Support ventilation Correct electrolyte imbalance IV Sodium Bicarb

Metabolic Acidosis Risk Factors/Etiology Conditions that increase acids in the blood Renal Failure DKA Starvation Lactic acidosis Prolonged diarrhea Toxins (antifreeze or aspirin) Carbonic anhydrase inhibitors - Diamox

Metabolic Acidosis (cont) Symptoms Kussmaul’s respiration Lethargy, confusion, headache, weakness Nausea and Vomiting Lab: pH below 7.35 Bicarb less than 22 Treatment treat underlying cause monitor ABG, I&O, VS, LOC Sodium Bicarb?

Respiratory Alkalosis Risk Factors and etiology Hyperventilation due to extreme anxiety, stress, or pain elevated body temperature overventilation with ventilator hypoxia salicylate overdose hypoxemia (emphysema or pneumonia) CNS trauma or tumor

Respiratory Alkalosis (cont) Symptoms Tachypnea or Hyperpnea Complaints of SOB, chest pain Light-headedness, syncope, coma, seizures Numbness and tingling of extremities Difficult concentrating, tremors, blurred vision Weakness, paresthesias, tetany Lab findings pH above 7.45 CO2 less than 35

Respiratory Alkalosis (cont) Treatment Monitor VS and ABGs Treat underlying disease Assist client to breathe more slowly Help client breathe in a paper bag or apply rebreather mask Sedation

Metabolic Alkalosis Risk Factors/Etiology Acid loss due to vomiting gastric suction Loss of potassium due to steroids diuresis Antacids (overuse of)

Metabolic Alkalosis (cont) Symptoms Hypoventilation (compensatory) Dysrhythmias, dizziness Paresthesia, numbness, tingling of extremities Hypertonic muscles, tetany Lab: pH above 7.45, Bicarb above 26 CO2 normal or increased w/comp Hypokalmia, Hypocalcemia Treatment I&O, VS, LOC give potassium treat underlying cause

Mechanisms of pH control Buffer system consists of a weak acid and its anion Three major buffering systems: Protein buffer system Amino acid H+ are buffered by hemoglobin buffer system Carbonic acid-bicarbonate Buffer changes caused by organic and fixed acids Phosphate Buffer pH in the ICF

The Carbonic Acid-Bicarbonate Buffer System Figure 27.9a, b

Maintenance of acid-base balance Lungs help regulate pH through carbonic acid - bicarbonate buffer system Changing respiratory rates changes PCO2 Respiratory compensation Kidneys help regulate pH through renal compensation

Kidney tubules and pH Regulation Figure 27.10c

Disturbances of Acid-base Balance Buffer systems Respiration Renal function Maintain tight control within range 7.35 – 7.45

The Central Role of the Carbonic Acid-Bicarbonate Buffer System in the Regulation of Plasma pH Figure 27.11a

The Central Role of the Carbonic Acid-Bicarbonate Buffer System in the Regulation of Plasma pH Figure 27.11b

Acid-Base Disorders Respiratory acid-base disorders Result when abnormal respiratory function causes rise or fall in CO2 in ECF Metabolic acid-base disorders Generation of organic or fixed acids Anything affecting concentration of bicarbonate ions in ECF

Respiratory acid-base disorders Respiratory acidosis Results from excessive levels of CO2 in body fluids Respiratory alkalosis Relatively rare condition Associated with hyperventilation

Respiratory Acid-Base Regulation Figure 27.12a

Respiratory Acid-Base Regulation Figure 27.12b

Metabolic acid-base disorders Major causes of metabolic acidosis are: Depletion of bicarbonate reserve Inability to excrete hydrogen ions at kidneys Production of large numbers of fixed / organic acids Bicarbonate loss due to chronic diarrhea Metabolic alkalosis Occurs when HCO3- concentrations become elevated Caused by repeated vomiting

The Response to Metabolic Acidosis Figure 27.13

Metabolic Alkalosis Figure 27.14

Detection of acidosis and alkalosis Diagnostic blood tests Blood pH PCO2 Bicarbonate levels Distinguish between respiratory and metabolic

A Diagnostic Chart for Acid-Base Disorders Figure 27.15

Interpreting ABGs 1. Look at the pH is the primary problem acidosis (low) or alkalosis (high) 2. Check the CO2 (respiratory indicator) is it less than 35 (alkalosis) or more than 45 (acidosis) 3. Check the HCO3 (metabolic indicator) is it less than 22 (acidosis) or more than 26 (alkalosis) 4. Which is primary disorder (Resp. or Metabolic)? If the pH is low (acidosis), then look to see if CO2 or HCO3 is acidosis (which ever is acidosis will be primary). If the pH is high (alkalosis), then look to see if CO2 or HCO3 is alkalosis (which ever is alkalosis is the primary). The one that matches the pH (acidosis or alkalosis), is the primary disorder.

Compensation The Respiratory system and Renal systems compensate for each other attempt to return the pH to normal ABG’s show that compensation is present when the pH returns to normal or near normal If the nonprimary system is in the normal range (CO2 35 to 45) (HCO3 22-26), then that system is not compensating for the primary. For example: In respiratory acidosis (pH<7.35, CO2>45), if the HCO3 is >26, then the kidneys are compensating by retaining bicarbonate. If HCO3 is normal, then not compensating.

Normal range in plasma pH HCO3 PCO2 7.35-7.45 22-26 mEq/L 35-45mm Hg Respiratory acidosis down up if compensating up Respiratory alkalosis up down if compensating down Metabolic acidosis down down down if compensating Metabolic alkalosis up up up if compensating Remember: ROME Respiratory opposite Metabolic Equal if both HCO3 and pH are up = metabolic alkalosis if both HCO3 and pH are down = metabolic acidosis CO2 up and pH down = respiratory acidosis CO2 down and pH up = respiratory alkalosis Look at the CO2 and HCO3 norms which ever one is closer to normal is the compensating factor

Acid-base disturbances, causes, and compensatory mechanisms Common cause Mode of compensation Respiratory acidosis Respiratory depression (drugs, central nervous system trauma) Kidneys will retain increased amounts of HCO3– to increase pH Pulmonary disease (pneumonia, chronic obstructive pulmonary disease, respiratory hypoventilation) Respiratory alkalosis Hyperventilation (emotions, pain, respirator overventilation) Kidneys will excrete increased amounts of HCO3– to lower pH Metabolic acidosis Diabetes, shock, renal failure, intestinal fistula, Lungs "blow off" CO2 to raise pH Metabolic alkalosis Sodium bicarbonate overdose, prolonged vomiting, nasogastric drainage Lungs retain CO2 to lower pH

Normal Levels of Substances in the Arterial Blood: pH 7.40 + 0.05 pCO2 (partial pressure of carbon dioxide)       40 mm Hg pO2 (partial pressure of oxygen) 90 - 100 mm Hg Hemoglobin - O2 saturation 94 - 100 % [HCO3-] 24 meq / liter

of green sputum over the last week. #1:A 14-year-old girl with cystic fibrosis has complained of an increased cough productive of green sputum over the last week. She also complained of being increasingly short of breath, and she is noticeably wheezing on physical examination. Arterial blood was drawn and sampled, revealing the following values: pH 7.30 pCO2 50 mm Hg pO2 55 mm Hg Hemoglobin - O2 saturation 45 % [HCO3-] 24 meq / liter

2. An elderly gentleman is in a coma after suffering a severe troke 2. An elderly gentleman is in a coma after suffering a severe troke. He is in the intensive care unit and has been placed on a ventilator. Arterial blood gas measurements from the patient reveal the following: pH 7.50 pCO2 30 mm Hg pO2 100 mm Hg Hemoglobin - O2 saturation       98% [HCO3-] 24 meq / liter

3. A 28-year-old woman has been sick with the flu for the past week, vomiting several times every day. She is having a difficult time keeping solids and liquids down, and has become severely dehydrated. After fainting at work, she was taken to a walk-in clinic, where an IV was placed to help rehydrate her. Arterial blood was drawn first, revealing the following: pH 7.50 pCO2 40 mm Hg pO2 95 mm Hg Hemoglobin - O2 saturation       97% [HCO3-] 32 meq / liter :

What caused this woman’s problems 4. A young woman cramming for her A&P final exam, suddenly feels dizzy and loses consciousness briefly. Her friends notice that she had been breathing faster than normal prior to her passing out. Her friends took her to the emergency ward and on the way she had an episode of dizziness again. At the hospital, these were the results of her blood tests: pH 7.5 CO2 was 30mmHg HCO3 was 20meq / liter What is your diagnosis What caused this woman’s problems A young woman cramming for her A&P final exam, suddenly feels dizzy and loses consciousness briefly. Her friends notice that she had been breathing faster than normal prior to her passing out. Her friends took her to the emergency ward and on the way she had an episode of dizziness again. At the hospital, these were the results of her blood tests: pH 7.5, CO2 was 30mmHg