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)

pH

7.457.35AlkalosisAcidosis

8.06.8

Normal

DeathDea

th

H2CO3 HCO3–

24-5

Acid-Base BalanceFigure 24.12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

Figure 27.6

The Basic Relationship between PCO2 and Plasma pH

Respiratory Acidosis• Mechanism

– 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

• Buffer system consists of a weak acid and its anion• Three major buffering systems:

1. Protein buffer system• Amino acid• H+ are buffered by hemoglobin buffer system

2. Carbonic acid-bicarbonate• Buffer changes caused by organic and fixed

acids3. Phosphate

• Buffer pH in the ICF

Mechanisms of pH control

Figure 27.9a, b

The Carbonic Acid-Bicarbonate Buffer System

• Lungs help regulate pH through carbonic acid - bicarbonate buffer system– Changing respiratory rates changes PCO2

• Respiratory compensation

• Kidneys help regulate pH through renal compensation

Maintenance of acid-base balance

Kidney tubules and pH Regulation

Figure 27.10c

• Buffer systems• Respiration• Renal function

– Maintain tight control within range 7.35 – 7.45

Disturbances of Acid-base Balance

Figure 27.11a

The Central Role of the Carbonic Acid-Bicarbonate Buffer System in the

Regulation of Plasma pH

Figure 27.11b

The Central Role of the Carbonic Acid-Bicarbonate Buffer System in the

Regulation of Plasma pH

• 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

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 disorders

Respiratory Acid-Base Regulation

Figure 27.12a

Respiratory Acid-Base Regulation

Figure 27.12b

• 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

Metabolic acid-base disorders

Figure 27.13

The Response to Metabolic Acidosis

Figure 27.14

Metabolic Alkalosis

• Diagnostic blood tests– Blood pH– PCO2

– Bicarbonate levels• Distinguish between respiratory and metabolic

Detection of acidosis and alkalosis

Figure 27.15

A Diagnostic Chart for Acid-Base Disorders

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 Equalif 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

Acid-base disturbance Common cause Mode of compensation

Respiratory acidosisRespiratory 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 alkalosisHyperventilation (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 alkalosisSodium bicarbonate overdose, prolonged vomiting, nasogastric drainage

Lungs retain CO2 to lower pH

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

Normal Levels of Substances in the Arterial Blood:

pH 7.30

pCO2 50 mm Hg

pO2 55 mm Hg

Hemoglobin - O2 saturation

45 %

[HCO3-] 24 meq / liter

#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 7.50

pCO2 30 mm Hg

pO2 100 mm Hg

Hemoglobin - O2 saturation

98%

[HCO3-] 24 meq / liter

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:

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

:

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 7.5CO2 was 30mmHg HCO3 was 20meq / liter

What is your diagnosis

What caused this woman’s problems