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ACID BASE BALANCE IN
CHILDREN
APPLYING PHYSIOLOGY TO
NURSING PRACTICE
LINK SESSION
1
LEARNING OBJECTIVES
•
1.
2.
3.
4.
5.
By the end of the session, the student will be able to:
Identify the causes of acid base imbalance in children.
Understand the physiological compensatory mechanisms
that are triggered by disturbances in a child’s acid base
balance.
Recognise the clinical manifestations that may be seen in
a child with acid base imbalance.
Understand how paediatric nurses will monitor children
with acid base disturbances.
Interpret blood gas analysis.
2
pH
- Is the acidity or alkalinity of a solution.
- From French pouvoir hydrogène, "hydrogen power"
- pH is the Hydrogen ion concentration [H+] of a
solution.
- It is a measure of the solution's acidity.
pH is defined as the negative logarithm of the
concentration of H+ ions:
pH = -log10[H+]
3
• The greater the concentration of H+, the more acidic a
solution is.
• The lower the concentration of H+, the more basic or
alkaline a solution becomes.
Neutral
7
1
Acidic
14
Alkaline
4
H+
HCO3-
Neutral
Acidic
Alkaline
5
Plasma pH
• Plasma pH is maintained by homeostasis in the range
7.35 – 7.45
• pH has a widespread effect on cell function
- most cell enzymes work best at physiological pH
• An abnormal pH can result in disturbances in a wide
range of body systems
- abnormal respiratory and cardiac function
- blood clotting
- drug metabolism
6
Effects of changing pH on hydrogen ion concentration
200
150
100
50
0
6.8 6.9 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8
pH
7
Enzyme Activity
pH
pH Effects
Effects on
on Enzyme
Enzyme Activity
Activity
Peak
PeakActivity
Activity
activity
activity
activity
activity
pH
8
Sources of H+ in the body
1.
2.
Ingested
Acidic substances present in ingested foods (eg. citric
and acetic acid, milk, tea, coffee)
Cellular metabolism
- fat metabolism yields ketones
- anaerobic respiration produces lactic acid
-gastric secretions of the stomach contain
hydrochloric acid.
- transport of CO2 in blood as bicarbonate releases
H+
CO2 + H2O  H2CO3  H+ + HCO39
The importance of pH
Gastric Juice
Urine
Saliva
Blood
CSF
Pancreatic Juice
Bile
1.2 – 3.0
4.6 – 8.0
6.35 – 6.85
7.35 – 7.45
7.4
7.1 – 8.2
7.6 – 8.6
But why is the pH of these fluids important?
10
Acidosis and Alkalosis
• Disturbances of pH balance result in:
- Acidosis; too many H+
(pH < 7.35)
- Alkalosis; too few H+
(pH > 7.45)
• May be due to respiratory or other metabolic
causes resulting in:
• Respiratory acidosis
• Respiratory alkalosis
• Metabolic acidosis
• Metabolic alkalosis
11
Respiratory Acidosis.
An increase in carbon dioxide levels (CO2).
Causes
Decrease in ventilation (Hypoventilation):
Asthma
Bronchiolitus
Apnoea
Alcohol or drug overdose
Cardiac failure
Signs and Symptoms
Respiratory distress
Fall in O2 saturations
Tachypnoea / Difficulty in exhaling
Acidic urine.
Nursing Action
Treat cause
Position to maximise respiratory effort
Place in O2
Make child nil by mouth to ease respiratory effort
12
Respiratory Alkalosis.
A decrease in carbon dioxide levels (CO2).
Causes
Increase in ventilation (hyperventilation):
Anxiety
Shock
Fever
Mechanical over ventilation
Drug toxicity
Signs and Symptoms
Fast, gasping breathing
Spasms or convulsions
Alkaline urine
Nursing Action
Allow inhalation of CO2 via a paper bag.
13
Metabolic Acidosis.
A decrease in bicarbonate levels or retention of hydrogen ions.
Causes
Loss of bicarbonate:
Accumulation of acid:
Diarrhoea
Renal failure
Diabetic ketoacidosis
Endocrine disorders
Impaired liver function
Signs and Symptoms
Hyperventilation
Altered conscious state
Dehydration
Nursing Action
Treat cause
Replace fluids with I.V infusion
Send urine for metabolic screening.
14
Metabolic Alkalosis.
A rise in bicarbonate levels or loss of hydrogen ions.
Cause
Loss of acid:
Vomiting
Gastric washouts
Ingestion of bicarbonate or alkaline salts
Hepatic failure
Increased renal excretion
Signs and Symptoms
Hypoventilation
Spasms/convulsions
Nursing Action
Treat cause
Correct electrolyte deficiencies
Acidifying diuretics may be used coupled with sodium replacement.
15
Respiratory
Acidosis
Decrease in
ventilation:
A…..
Morphine
A…..
Bronchitis
Pneumonia
Upper a…...
obstruction
Surgical anesthesia
Alcohol or drug
o……..
Musculoskeletal
disease
Neuromuscular
disease
C…… …….
Metabolic
Starvation
S…..
Loss of bicarbonate:
Diarrhea
Renal f……
Accumulation of acid:
D……. k………..
Endocrine disorders
Congenial metabolic
disorders
Impaired liver function
Violent exercise or
c……….
Circulatory failure
Hypovolemia.
16
Alkalosis
Hyperventilation:
A……
Shock
Mechanical over
ventilation
F….
Drug toxicity
Maternal heroin
a……..
Hepatic insufficiency
Gram negative
bacteria.
Loss of acid:
V……. due to pyloric
stenosis
Gastric suctioning
Ingestion of b……….
(indigestion
remedies)
Administration of
alkaline salts
Increased renal
excretion Diuretics
Potassium deficit
Liver f……
Extensive burns.
17
pH balance regulated by:
1.
Chemical buffer system (act immediately)
2.
Respiratory centre in brain stem (1-3 minutes)
3.
Renal mechanisms (hours / days)
18
LIVER
METABOLISM
PRODUCES H+
H+
BLOOD
BUFFERS
Protein,
Bicarbonate &
Phosphate
HCO3-
Protein buffers
synthesised
METABOLISM
CO2
H+
H+
KIDNEYS
Excrete / reabsorb
H+ / HCO3-
LUNGS
Eliminate CO2
19
Bicarbonate buffer system
• Mixture of:
- carbonic acid (H2CO3) and
- sodium bicarbonate (NaHCO3)
• When pH of solution rises (becomes more alkaline),
the carbonic acid dissociates releasing more H+ which
reduces pH
• When pH of a solution drops (becomes more acidic),
the sodium bicarbonate combines with extra H+
mopping them up which ensures that pH rises.
20
Respiratory system regulation of pH
• Eliminates CO2 from blood whilst replenishing stores
of O2
• CO2 generated by cellular respiration.
• Enters RBC and converted to bicarbonate for transport
in plasma to lungs
Carbonic
anhydrase
CO2 + H2O
H2CO3
Carbonic
acid
H+ + HCO3Bicarbonate
ion
21
• An fall in plasma pH (more H+ present) recognised by
Chemoreceptors in medulla (and carotid sinus / aortic
arch). (What is the main cause of this in plasma?)
• High concentrations of plasma H+ can be corrected by
stimulating respiration.
• Respiratory rate and depth increased.
• Results in to excretion of more CO2 from blood.
• Thus less carbonic acid is formed resulting in less H+
22
PCO2 in
more CO2
crosses
blood brain
barrier
arterial
blood
RESPONSE TO
HYPERCAPNIA
PCO2 in
arterial
blood
expiration
of PCO2
rate and
depth of
ventilation
PCO2 in
CSF
H+ in CSF
stimulation of
central
chemoreceptors
frequency of
impulses to
medullary
rhythm
generator
23
Renal mechanisms regulating pH
• Can remove from the body acids generated by
cellular metabolism:
• Kidneys involved in:
1.
Increasing or decreasing the
excretion H+
2.
Increasing or decreasing reabsorption
of HCO324
Blood gas analysis in children.
Interpretation of blood gas should include patient history,
examination and treatment.
PH
Indicates acid base status
7.35 – 7.45
H+
Hydrogen ion concentration
38 – 42 nmol/l
Paco2
Pressure of CO2 in the blood
4.7 – 6.0 kPa
35 – 45 mmHg
Base Excess
Status of bases in the blood
-2 - +2
HCO3
Bicarbonate status in blood
23 – 27mmol/l
(Halperin
and Goldstein 1994 p4)
(Mackway-Jones et al 2001 p265)
25
A Analysis
1. Assess pH. Decide whether patient is acidotic or alkalotic.
2 2. Assess CO2. If this is abnormal and provides a cause for abnormal pH, e.g.
low pH and high CO2 (acidosis) or high pH and low CO2 (alkalosis), then the
patient has a respiratory imbalance.
3 3. If CO2 does not give a cause for the pH imbalance it is a metabolic
disturbance.
4. Assess base excess. If the patient has a metabolic imbalance an abnormal
base excess will provide a cause for the abnormal pH. E.g. low pH with
negative base excess (acidosis) or high pH with positive base excess
(alkalosis).
5 5. If base excess does not give a cause for the pH imbalance it is a respiratory
acid base imbalance that the metabolic system may be compensating for, or a
metabolic acid base imbalance that the respiratory system may be
compensating for.
26
Blood Gas Case Studies.
1. Anna is a 3 month old baby who has been in hospital for
one week. She has been tested RSV +ve. She is having
severe
difficulty in breathing.
PH
Paco2
BE
7.15
9.25 kPa
-1 mmol
What is Anna’s acid base status?
27
2. Craig is a 15 year old who has been involved in a RTA. He
was driving a stolen car. He has been admitted to your ward
awaiting police investigation. He is very anxious. He begins
to
hyperventilate.
PH
7.6
Paco2 3.15 kPa
BE
+3 mmol
What is Craig’s acid base status?
28
3. Jessica is a 10 year old newly diagnosed diabetic. She
has presented to A & E. She has been acutely unwell since
this morning. It is now 2pm.
PH
Paco2
BE
7.10
4.2 kPa
-10 mmol
What is Jessica’s acid base status?
29
4. Andrew is a 4 week old baby. He has vomited post
feeds since 1 week old. This vomiting has worsened, he
has come to your ward for investigation into pyloric
stenosis.
PH
7.75
Paco2
5.8 kPa
BE
+8.7 mmol
What is Andrew’s acid base status?
30
5. Jessica is a 10 year old newly diagnosed
diabetic. She has presented to A & E. She has been
acutely unwell since Monday morning but her parents
felt she would get better today. It is now Tuesday
2pm.
PH
7.3
Paco2
3.35 kPa
BE
-5.9 mmol
What is Jessica’s acid base status?
31
END OF SESSION EVALUATION
• Please answer the following questions:
1. How has your ability to relate theory to practice
changed as a result of this session?
2. What influence did the linked teaching team of
practicing nurse and UCE lecturer have on your
learning?
3. What was the most valuable aspect of this
session?
4. What was the most unclear aspect of this
session?
32

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