Acid-Base Balance : Acid-Base Balance By Sr. Beverly Raway
Fall 2001
Normal Acid-Base Balance : Normal Acid-Base Balance Normal pH 7.35-7.45
Narrow normal range
Compatible with life 6.8 - 8.0
___/______/___/______/___ 6.8 7.35 7.45 8.0
Acid Alkaline
Maintenance of Balance : Maintenance of Balance Balance maintained by:
Buffering systems
Lungs
Kidneys H2CO3…..HCO3
Buffer Systems : Buffer Systems Prevent major changes in pH
Act as sponges…
3 main systems
Bicarbonate-carbonic acid buffer
Phosphate buffer
Protein buffer H+ H+ H+
Buffer Systems : Buffer Systems Bicarbonate buffer - most important
Active in ECF and ICF
Phosphate buffer
Active in intracelluar (ICF) fluid
Protein buffer - Largest buffer store
Albumins and globulins (ECF)
Hemoglobin (ICF)
Bicarbonate-Carbonic Acid : Bicarbonate-Carbonic Acid Body’s major buffer
Carbonic acid - H2CO3 (Acid)
Bicarbonate - HCO3 (Base)
1 20
pH = 7.4 H2CO3 ……………… HCO3 24 mEq/L 1.2 mEq/L
Bicarbonate-Carbonic Acid : Bicarbonate-Carbonic Acid Ratio important
Not absolute values
Person with COPD (CAL)
1 20
7.4 H2CO3 ……………… HCO3 48 mEq/L 2.4 mEq/L
Regulation : Regulation Key concept
Carbonic anhydrase equation
CO2 +H2O H2CO3 H+ + HCO3
Carbon Carbonic Bicarbonate Dioxide Acid
(ACID) (BASE)
Slide 9: Acid
Substance that contains H+ ions that can be released (H2CO3)
Carbonic acid releases H+ ions
Base
Substance that can accept H+ ions
(HCO3)
Bicarbonate accepts H+ ions
Slide 10: As CO2 increases, carbonic acid increases, H+ ions increase
pH drops….. becomes more acidic
CO2 +H2O H2CO3 H+ + HCO3
Carbonic Bicarbonate
Acid
CO2 H2CO3 H+ HCO3
(pH Acidic <7.35)
Slide 11: As HCO3 increases, H+ decreases
pH rises, becomes more alkaline
CO2 +H2O H2CO3 H+ + HCO3
Carbonic Bicarbonate
Acid
CO2 H2CO3 H+ HCO3
(pH Basic >7.45)
Respiratory & Renal Regulation : Respiratory & Renal Regulation Lungs control CO2
Kidneys control HCO3
pH = kidneys (bicarbonate)
lungs (carbon dioxide)
Respiratory Regulation : Respiratory Regulation Mechanisms of control …
Hyperventilation -- blow off CO2
Hypoventilation -- retain CO2
Regulation rapid...
Seconds to minutes
Measured by PaCO2 - Normal
35-45 mm Hg
Renal Regulation : Renal Regulation Mechanism of control
Excretion or retention of
H+ or HCO3
Regulation….. Slow
Hours to days to change pH
Normal serum HCO3
22-26 mEq/L
Acid-Base Imbalances : Acid-Base Imbalances Ratio of 20 to 1 out of balance
Acidosis (acidemia)
pH falls below 7.35
Increase in blood carbonic acid or
Decrease in bicarbonate
Acid-Base Imbalances : Acid-Base Imbalances Alkalosis (alkalemia)
pH greater than 7.45
Increase in bicarbonate
or
Decrease in carbonic acid
Acid-Base Imbalances : Acid-Base Imbalances Primary cause or origin:
Metabolic
Changes brought about by systemic alterations (cellular level)
Respiratory
Changes brought about by respiratory alterations
Acid-Base Imbalances : Acid-Base Imbalances Compensation
Corrective response of kidneys and/or lungs
Compensated
Restoration of pH and 20 : 1 ratio
Uncompensated
Inability to adjust pH or 20 : 1 ratio
Four Basic Types of Imbalance : Four Basic Types of Imbalance Respiratory Acidosis
Respiratory Alkalosis
Metabolic Acidosis
Metabolic Alkalosis
Respiratory Acidosis : Respiratory Acidosis Carbonic acid excess
Exhaling of CO2
inhibited
Carbonic acid builds up
pH falls below 7.35
Cause = Hypoventilation (see chart) H2CO3
Acid-Base Imbalances : Acid-Base Imbalances Normal
1 20
7.4 H2CO3 ……………… HCO3 24 mEq/L 1.2 mEq/L
Respiratory Acidosis : Respiratory Acidosis 1 13
7.21 H2CO3 ……………… HCO3 24 mEq/L 1.84 mEq/L
Respiratory Acidosis : Respiratory Acidosis Compensation: How?
Opposite regulating mechanism
Problem = depressed breathing, build up of CO2 in blood
Response - Kidney retains HCO3
(Response ….. Slow)
Respiratory Alkalosis : Respiratory Alkalosis Carbonic acid deficit
Increased exhaling
of CO2
Carbonic acid decreases
pH rises above 7.45
Cause = hyperventilation (see chart) H2CO3
Acid-Base Imbalances : Acid-Base Imbalances Normal
1 20
7.4 H2CO3 ……………… HCO3 24 mEq/L 1.2 mEq/L
Respiratory Alkalosis : Respiratory Alkalosis 1 40
7.70 H2CO3 ……………… HCO3 24 mEq/L 0.6 mEq/L
Respiratory Alkalosis : Respiratory Alkalosis Compensation:
Problem = excess “blowing off” of CO2
Result = decrease in carbonic acid and increase in HCO3
Response: Kidney excretes excess bicarbonate
Metabolic Acidosis : Metabolic Acidosis Base-bicarbonate deficit
Low pH (< 7.35)
Low plasma bicarbonate (base)
Cause = relative gain in H+ (lactic acidosis, ketoacidosis)
or actual loss of HCO3
(renal failure, diarrhea)
Acid-Base Imbalances : Acid-Base Imbalances Normal
1 20
7.4 H2CO3 ……………… HCO3 24 mEq/L 1.2 mEq/L
Metabolic Acidosis : Metabolic Acidosis Kidney failure (decrease in bicarbonate)
1 10
7.10 H2CO3 ……………… HCO3 12 mEq/L 1.2 mEq/L
Metabolic Acidosis : Metabolic Acidosis Lactic acidosis, keto acidosis (increase acid… no change in bicarbonate)
1 10
7.10 H2CO3 ……………… HCO3 24 mEq/L 2.4 mEq/L
Metabolic Acidosis : Metabolic Acidosis Compensation:
Problem = low HCO3 (base) or high H+ ion (acid)
Response: Lungs hyperventilate
Get rid of CO2
(decrease PaCO2 and therefore raise level of HCO3)
Metabolic Alkalosis : Metabolic Alkalosis Bicarbonate excess
High pH (> 7.45)
Loss of H+ ion or gain of HCO3
Most common causes vomiting, gastric suctioning (NG tube)
Other: Abuse of antacids, K+ wasting diuretics
Acid-Base Imbalances : Acid-Base Imbalances Normal
1 20
7.4 H2CO3 ……………… HCO3 24 mEq/L 1.2 mEq/L
Metabolic Alkalosis : Metabolic Alkalosis 1 30 7.58 H2CO3 ……………… HCO3 36 mEq/L 1.2 mEq/L
Metabolic Alkalosis : Metabolic Alkalosis Compensation:
Problem = too much base
Response: Lungs compensate by hypoventilating
Retain CO2, increase PaCO2
Increase acid level in blood
Assessing ABGs : Assessing ABGs pH 7.35 - 7.45
PaCO2 35 - 45 mmHg
HCO3 22 - 26 mEq/L
Base Excess -2 - +2 mEq/L
PaO2 80 - 100 mm Hg
O2 saturation 95 - 100 %
Interpreting ABGs : Interpreting ABGs 1. Start with pH
Normal?
Acidosis?
Alkalosis?
___/______/___/______/___ 6.8 7.35 7.45 8.0
Acidosis Alkalosis
Interpreting ABGs : Interpreting ABGs 2. Assess PaCO2
(respiratory value)
_____/________/______
35 45
Respiratory Respiratory
Alkalosis Acidosis (Note reversal)
(See Chart)
Interpreting ABGs : Interpreting ABGs 3. Evaluate metabolic indicators
Bicarbonate (HCO3) 22-26
and
Base excess (-2 to +2)
Interpreting ABGs : Interpreting ABGs HCO3
_______/_______/________
22 26
BE ______/_______/_________
-2 +2
Metabolic Metabolic
acidosis alkalosis
Interpreting ABGs : Interpreting ABGs 4. Determine level of compensation
Has the body tried to readjust the pH?
Uncompensated
Partly compensated
Compensated
Interpreting ABGs : Interpreting ABGs Uncompensated
pH abnormal (high or low)
One component abnormal (high or low CO2 or HCO3)
The other component is normal
(The component not causing the acid-base imbalance is still normal)
Slide 44: Partly compensated
pH not normal (but moving toward normal)
Both CO2 and HCO3 are outside normal range
The component that was normal is changing in order to compensate
Interpreting ABGs : Interpreting ABGs Compensated
pH normal
Other values abnormal in opposite directions
One is acidotic the other alkaline
Interpreting ABGs : Interpreting ABGs Determine amount of hypoxemia present
Normal PaO2 (adults - room air)
< 70 years = 80-100 mm Hg
70-79 = 70-100 mm Hg
Drops 10 mm Hg for each decade
Interpreting ABGs : Interpreting ABGs Hypoxemia = < 70 mm Hg
(for adult < 70 years old)
Mild = 60-80 mm Hg
Moderate = 40-60 mm Hg
Severe = < 40 mm Hg
Interpreting ABGs : Interpreting ABGs Oxygen saturation (pulse oximetry)
95-100%
< 91% confusion
< 70% life threatening
Practice Problem : Practice Problem 80 year old female with severe pneumonia, fever
pH = 7.25
PaCO2 = 55 mm Hg
HCO3 = 24 mEq/L
PaO2 = 65 mm Hg
O2 sat = 80%
Practice Problems : Practice Problems What is the problem?
Acidosis or alkalosis?
Respiratory or metabolic?
Compensated or not?
Level of hypoxemia?
Diagnoses? Interventions?
Tic-Tac-Toe Method : Tic-Tac-Toe Method ACID NORMAL ALKALINE
_pH__________________________
_PaCO2_______________________
HCO3
Problem: _Respiratory acidosis___
Compensated? _Uncompensated_____
Slide 52: Level of hypoxemia?
mild to normal….
Diagnosis?
Impaired gas exchange
R/T lung congestion Dx pneumonia AMB CO2, acid pH, low PaO2, crackles, rapid resp rate and HR etc.
Nursing Management : Nursing Management Assessment of breath sounds and respiratory rate
Maintain patent airway
Oxygen support, ventilation
Positioning/turning q 2 hrs… good lung?
Pulmonary hygiene
POE’s, IV antibiotic
More Practice Problems : More Practice Problems Handout and Transparencies
Phipps, p. 441 Critical Thinking
Collaborative Management : Collaborative Management Identifying clients at risk:
Pulmonary, renal, CV disease
Fever, sepsis, burns
TPN, tube feedings
Mechanical ventilation
Diabetes (insulin dependent)
Slide 56: Vomiting, diarrhea, enteric drainage
Elderly (limited ability to compensate)
Assessment : Assessment Comprehensive physical assessment (Phipps, p. 437-441)
Fluid balance - often disturbed
CV function - HR, BP, ECG (decreased K+)
Ventilatory status - always changes
Slide 58: Breathing
Respiratory acidosis - variable,
usually shallow/rapid
Respiratory alkalosis - increased rate, depth
Metabolic acidosis - “air hunger”
deep/rapid (Kussmaul) resp
Assessment : Assessment CNS function -
Acidosis - depressed activity
Alkalosis - stimulated
Neuromuscular function -
Acidosis - weak, flaccid
Alkalosis - cramps, twitching
Assessment (cont.) : Assessment (cont.) Skin -
Respiratory acidosis -
pale to cyanotic
Metabolic acidosis -
warm, dry, pink
Assessment (cont.) : Assessment (cont.) Lab values
ABGs - interpretation critical, reported first to nursing staff then to doctor
Electrolytes - coexisting imbalance almost always present (Na, K+, Ca+)
BUN, Creatinine, serum lactate
Diagnoses : Diagnoses Ineffective breathing pattern
Impaired gas exchange
Altered tissue perfusion (cerebral)
Activity intolerance
Altered thought processes
Risk for injury
Goals/Outcomes : Goals/Outcomes Client experiences:
improved pulmonary ventilation
adequate gas exchange and oxygenation of tissues
Outcome Criteria : Outcome Criteria ...evidenced by absence of symptoms of respiratory distress
(R rate decreases to ____)
...evidenced by ABGs within normal limits (list specifics)
by ______ (specify time)
Goals/Outcomes : Goals/Outcomes Protection of client from injury:
Client experiences no physical injury
Confusion decreases….
Oriented x 3 (to person, place, time)
Interventions : Interventions Monitor /interpret ABGs
Correction of underlying problem
Administer O2 as appropriate
Positioning, pulmonary hygiene
Hydration, appropriate IV solutions, electrolytes (bicarbonate, KCl)
Medications (antibiotics, bronchodilators, mucolytics, diuretics)
Reorientation
Protection of client from injury
See Table 16-4 p. 437 and pp. 437-441
Evaluation : Evaluation Frequency depends on severity
Goals met:
ABGs - normal limits /compensation
Patent airway
Minimization of respiratory effort
Increased activity tolerance
Oriented x 3
Nursing ManagementRespiratory Acidosis : Nursing ManagementRespiratory Acidosis Assessment of breath sounds and respiratory rate
Maintain patent airway
Oxygen support, ventilation
Positioning/turning q 2 hrs
Pulmonary hygiene (postural drainage, chest clapping)
POE’s
Nursing ManagementRespiratory Alkalosis : Nursing ManagementRespiratory Alkalosis Teach how to relieve/ prevent anxiety
Calm environment
Positioning for comfort
Assist with relaxation techniques
Reorientation
Protection from injury
Education re: drug overdose, esp aspirin
Nursing ManagementMetabolic Acidosis : Nursing ManagementMetabolic Acidosis Frequent assessment of vital signs esp respiratory rate and rhythm (compensatory mechanisms)
Reorientation
Safety precautions for confusion
For ketoacidosis, sodium bicarbonate IV
Education about diabetes
Nursing ManagementMetabolic Alkalosis : Nursing ManagementMetabolic Alkalosis Monitoring LOC and confusion
Reorientation, protection from harm
Monitor serum electrolytes, ABG’s
Administer K and Cl replacement as ordered
Antiemetics to relieve vomiting
Seizure precautions
Teaching/monitoring of diuretic therapy
Referrals re: eating disorders
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