1

ACID BASE BALANCE IN CHILDREN

APPLYING PHYSIOLOGY TO NURSING PRACTICE

LINK SESSION

2

LEARNING OBJECTIVES

• 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.

3

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+]

4

• 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

Acidic Alkaline

71 14

5

Neutral

H+

HCO3-

Alkaline

Acidic

6

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

7

Effects of changing pH on hydrogen ion concentration

0

50

100

150

200

6.8 6.9 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

pH

8

pH Effects on Enzyme ActivitypH Effects on Enzyme ActivitypH Effects on Enzyme Activity

pH

Enz

yme

Act

ivit

y

activity activity

Peak ActivityPeak Activity

activity activity

9

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 CO2 in blood as bicarbonate releases H+

CO2 + H2O H2CO3 H+ + HCO3-

10

The importance of pH

Gastric Juice 1.2 – 3.0Urine 4.6 – 8.0Saliva 6.35 – 6.85Blood 7.35 – 7.45CSF 7.4Pancreatic Juice 7.1 – 8.2Bile 7.6 – 8.6

But why is the pH of these fluids important?

11

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

12

Respiratory Acidosis. 

An increase in carbon dioxide levels (CO2).

Causes Decrease in ventilation (Hypoventilation): Asthma

BronchiolitusApnoea Alcohol or drug overdoseCardiac failure

 Signs and SymptomsRespiratory distress Fall in O2 saturationsTachypnoea / Difficulty in exhalingAcidic urine.  Nursing ActionTreat causePosition to maximise respiratory effort Place in O2Make child nil by mouth to ease respiratory effort

13

Respiratory Alkalosis. 

A decrease in carbon dioxide levels (CO2). 

CausesIncrease in ventilation (hyperventilation): Anxiety

ShockFeverMechanical over ventilationDrug toxicity

 Signs and SymptomsFast, gasping breathingSpasms or convulsionsAlkaline urine 

 Nursing ActionAllow inhalation of CO2 via a paper bag.

14

Metabolic Acidosis. 

A decrease in bicarbonate levels or retention of hydrogen ions. CausesLoss of bicarbonate: Diarrhoea

Renal failureAccumulation of acid: Diabetic ketoacidosis

Endocrine disordersImpaired liver function Signs and SymptomsHyperventilationAltered conscious stateDehydration  Nursing ActionTreat causeReplace fluids with I.V infusionSend urine for metabolic screening. 

15

Metabolic Alkalosis. 

A rise in bicarbonate levels or loss of hydrogen ions. 

CauseLoss of acid: Vomiting

Gastric washoutsIngestion of bicarbonate or alkaline saltsHepatic failureIncreased renal excretion Signs and SymptomsHypoventilationSpasms/convulsions  Nursing ActionTreat causeCorrect electrolyte deficienciesAcidifying diuretics may be used coupled with sodium replacement. 

16

  Respiratory Metabolic

 

Acidosis

 

Decrease in ventilation:A…..MorphineA…..Bronchitis PneumoniaUpper a…... obstructionSurgical anesthesiaAlcohol or drug o……..Musculoskeletal diseaseNeuromuscular diseaseC…… …….

 

StarvationS…..Loss of bicarbonate:DiarrheaRenal f……Accumulation of acid:D……. k………..Endocrine disorders Congenial metabolic disordersImpaired liver functionViolent exercise or c……….Circulatory failureHypovolemia.

17

 

Alkalosis  

 Hyperventilation:A……ShockMechanical over ventilationF….Drug toxicityMaternal heroin a……..Hepatic insufficiencyGram negative bacteria.   

 Loss of acid:V……. due to pyloric stenosisGastric suctioningIngestion of b………. (indigestion remedies)Administration of alkaline saltsIncreased renal excretion Diuretics Potassium deficitLiver f……Extensive burns.  

18

pH balance regulated by:

1. Chemical buffer system (act immediately)

2. Respiratory centre in brain stem (1-3 minutes)

3. Renal mechanisms (hours / days)

19

KIDNEYS

Excrete / reabsorb H+ / HCO3

-

LIVER METABOLISM PRODUCES H+

BLOOD BUFFERS

Protein, Bicarbonate &

Phosphate

LUNGS

Eliminate CO2

METABOLISM

CO2

HCO3-

H+

Protein buffers synthesisedH+

H+

20

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.

21

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

CO2 + H2O H2CO3 H+ + HCO3-

Carbonic anhydrase

Carbonic acid

Bicarbonate ion

22

• 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+

23

PCO2 in

arterial blood

PCO2 in

CSF

PCO2 in

arterial blood

 

expiration of PCO2

H+ in CSF

stimulation ofcentral

chemoreceptors

frequency of impulses to medullary rhythm generator

rate and depth of ventilation

more CO2

crosses blood brain

barrier

  

RESPONSE TO HYPERCAPNIA

24

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 HCO3

-

25

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)

26

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.

27

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 7.15 Paco2 9.25 kPa BE -1 mmol  What is Anna’s acid base status?

28

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?

29

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 7.10Paco2 4.2 kPaBE -10 mmol What is Jessica’s acid base status?

30

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 7.75Paco2 5.8 kPaBE +8.7 mmolWhat is Andrew’s acid base status?

31

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?

32

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?