1

•
By the end of the session, the student will be able to:
1.
Identify the causes of acid base imbalance in children.
2.
Understand the physiological compensatory mechanisms that are triggered by disturbances in a child’s acid base balance.
3.
Recognise the clinical manifestations that may be seen in a child with acid base imbalance.
4.
Understand how paediatric nurses will monitor children with acid base disturbances.
5.
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 = -log
10
[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.
1
Acidic
Neutral
7
Alkaline
14
4

H +
HCO
3
-
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

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
7


 activity pH

 activity
8

Sources of H + in the body
1.
Ingested
Acidic substances present in ingested foods (eg. citric and acetic acid, milk, tea, coffee)
2.
Cellular metabolism
- fat metabolism yields ketones
- anaerobic respiration produces lactic acid
-gastric secretions of the stomach contain hydrochloric acid.
- transport of CO
2
H +
CO
2 in blood as bicarbonate releases
+ H
2
O

H
2
CO
3

H + + HCO
3
-
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Gastric Juice
Urine
Saliva
Blood
1.2 – 3.0
4.6 – 8.0
6.35 – 6.85
7.35 – 7.45
CSF 7.4
Pancreatic Juice 7.1 – 8.2
Bile 7.6 – 8.6
But why is the pH of these fluids important?
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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):
Shock
Fever
Anxiety
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.
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Metabolic Acidosis .
A decrease in bicarbonate levels or retention of hydrogen ions.
Causes
Loss of bicarbonate:
Accumulation of acid:
Impaired liver function
Diarrhoea
Renal failure
Diabetic ketoacidosis
Endocrine disorders
Signs and Symptoms
Hyperventilation
Altered conscious state
Dehydration
Nursing Action
Treat cause
Replace fluids with I.V infusion
Send urine for metabolic screening.
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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.
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Acidosis
Respiratory Metabolic
Decrease in ventilation:
A…..
Morphine
A…..
Bronchitis
Pneumonia
Upper a…... obstruction
Surgical anesthesia
Alcohol or drug o……..
Musculoskeletal disease
Neuromuscular disease
C…… …….
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.
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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.
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pH balance regulated by:
1.
Chemical buffer system (act immediately)
2.
Respiratory centre in brain stem (1-3 minutes)
3.
Renal mechanisms (hours / days)
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LIVER
METABOLISM
PRODUCES H +
H +
HCO
3
-
KIDNEYS
Excrete / reabsorb
H + / HCO
3
-
H +
BLOOD
BUFFERS
Protein,
Bicarbonate &
Phosphate
Protein buffers synthesised
METABOLISM
CO
2
LUNGS
H +
Eliminate CO
2
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Bicarbonate buffer system
• Mixture of:
- carbonic acid (H
2
CO
3
) and
- sodium bicarbonate (NaHCO
3
)
• 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.
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Respiratory system regulation of pH
• Eliminates CO
2 of O
2 from blood whilst replenishing stores
• CO
2 generated by cellular respiration.
• Enters RBC and converted to bicarbonate for transport in plasma to lungs
CO
2
Carbonic
+ H
2
O anhydrase
H
2
CO
3
Carbonic acid
H + + HCO
3
-
Bicarbonate ion
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• 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 CO
2 from blood.
• Thus less carbonic acid is formed resulting in less H +
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P CO in
2 arterial blood
P CO in
2 arterial blood more CO
2 crosses blood brain barrier
RESPONSE TO
HYPERCAPNIA
P CO
2
CSF in
H + in CSF expiration of P CO
2 stimulation of central chemoreceptors rate and depth of ventilation frequency of impulses to medullary rhythm generator
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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 HCO
3
-
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PH
Interpretation of blood gas should include patient history, examination and treatment
.
Indicates acid base status 7.35 – 7.45
H+
Paco2
Hydrogen ion concentration 38 – 42 nmol/l
Pressure of CO2 in the blood 4.7 – 6.0 kPa
35 – 45 mmHg
Base Excess Status of bases in the blood
HCO3 Bicarbonate status in blood
-2 - +2
23 – 27mmol/l
( Halperin and Goldstein 1994 p4)
(Mackway-Jones et al 2001 p265)
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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.
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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?
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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?
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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?
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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
Paco2
7.75
5.8 kPa
BE +8.7 mmol
What is Andrew’s acid base status?
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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
Paco2
7.3
3.35 kPa
BE -5.9 mmol
What is Jessica’s acid base status?
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• 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?
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