ACID BASE BALANCE IN CHILDREN APPLYING PHYSIOLOGY TO NURSING PRACTICE LINK SESSION
LEARNING OBJECTIVES • 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.
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+]
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 1 7 14 Acidic Alkaline
H+ HCO3- Neutral Acidic Alkaline
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
Sources of H+ in the body • 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+ + HCO3-
The importance of pHGastric 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 – 8.6But why is the pH of these fluids important?
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
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
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.
Metabolic Acidosis. A decrease in bicarbonate levels or retention of hydrogen ions. Causes Loss of bicarbonate: Diarrhoea Renal failure Accumulation of acid: 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.
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.
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. Acidosis
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. Alkalosis
pH balance regulated by: • Chemical buffer system (act immediately) • Respiratory centre in brain stem (1-3 minutes) • Renal mechanisms (hours / days)
LIVER METABOLISM PRODUCES H+ Protein buffers synthesised H+ BLOOD BUFFERS Protein, Bicarbonate & Phosphate METABOLISM CO2 H+ HCO3- H+ KIDNEYS Excrete / reabsorb H+ / HCO3- LUNGS Eliminate CO2
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.
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 Bicarbonate ion Carbonic acid
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+
PCO2 in arterial blood more CO2 crosses blood brain barrier PCO2 in CSF RESPONSE TO HYPERCAPNIA PCO2 in arterial blood H+ in CSF stimulation of central chemoreceptors expiration of PCO2 frequency of impulses to medullary rhythm generator rate and depth of ventilation
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-
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)
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.
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?
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?
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 7.10 Paco2 4.2 kPa BE -10 mmol What is Jessica’s acid base status?
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?
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?
END OF SESSION EVALUATION • Please answer the following questions: • How has your ability to relate theory to practice changed as a result of this session? • What influence did the linked teaching team of practicing nurse and UCE lecturer have on your learning? • What was the most valuable aspect of this session? • What was the most unclear aspect of this session?