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By Alicia, Kerrie, Adam, Gail

Acid Base Balance. By Alicia, Kerrie, Adam, Gail. Acid-Base Balance. Arterial blood pH is normally closely regulated to between 7.35 and 7.45. Maintaining the pH within these limits is achieved by bicarbonate, other buffers, the lungs and the kidneys. Changes in bicarbonate are metabolic.

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By Alicia, Kerrie, Adam, Gail

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  1. Acid Base Balance By Alicia, Kerrie, Adam, Gail

  2. Acid-Base Balance • Arterial blood pH is normally closely regulated to between 7.35 and 7.45. • Maintaining the pH within these limits is achieved by bicarbonate, other buffers, the lungs and the kidneys. • Changes in bicarbonate are metabolic. • Changes in carbon dioxide are respiratory. • In the absence of any significant respiratory disease or hyperventilation it can be assumed that the primary cause is metabolic. • In general the kidneys compensate for respiratory causes and the lungs compensate for metabolic causes. Therefore hyperventilation may be a cause of respiratory alkalosis or a compensatory mechanism for metabolic acidosis.

  3. Normal blood gas results • pH 7.36-7.44 • [H+] 35-45 mmol/L • Paco2 4.6-5.6 kPa (35-42mmHg) • Pao 211.3-14 kPa (90-105mmHg) • HCO3 23-31mmol/L

  4. Acidosis and Alkalosis • The terms acidosis and alkalosis refer to abnormal situations which lead to acidaemia and alkalaemia respectively if there is no compensatory mechanisms to reverse the situation. Both situations can be equally disruptive.

  5. Metabolic Acidosis • Acidosis occurs when there is a high hydrogen ion concentration and thus a low pH (< 7.36).

  6. Metabolic Acidosis cont.. • Pathopysiology • The lowered pH leads to a compensatory respiratory drive to hyperventilate, thus causing a transitory fall in the Pco2 (measure of carbon dioxide in the blood). • If this is successful the pH will return towards normal. However if the acidosis is severe cardiac output may drop with accompanying bradycardia (because acidosis impairs cardiac contractility). • Renal compensation is made through the excretion of extra hydrogen ions. • Hyperkalaemia (  potassium) may also be present depending upon the cause of the acidosis. • The features of the underlying acidotic state (ie: peripheral vasodilatation) will also be present.

  7. Metabolic Acidosis cont.. • Metabolic acidosis can arise through: • Metabolism of proteins producing sulphuric and phosphoric acids. • Anaerobic metabolism producing lactic acid. • Metabolism of fats producing acetoacetic acid and ketone bodies. • Excessive intake of acidic products orally or intravenously. • Excessive loss of bicarbonate from the body. (As in diabetes, starvation and high fat diet all of which lead to the production of ketones in the blood which bind & remove bicarbonate). • Hypoventilation with resulting retention of carbon dioxide.

  8. Metabolic Acidosis cont.. • Signs and symptoms There are no specific signs or symptoms for metabolic acidosis however the three most common causes are: • Renal failure • Ketoacidosis • Hypoxia

  9. Metabolic Acidosis cont.. • Some other causes are: • Severe diarrhoea • Starvation • Excess alcohol • High ECF potassium concentrations

  10. Metabolic Acidosis cont.. • Effects • The lowered pH leads to a compensatory respiratory drive which in turn causes the patient to hyperventilate.

  11. Metabolic Acidosis cont.. • Nursing management • Treatment may involve the administration of bicarbonates but it is important to recall that each mmol of sodium bicarbonate given contains 1 mmol of sodium ions.

  12. What is Respiratory Acidosis • Respiratory acidosis is a condition in which a build-up of carbon dioxide in the blood produces a shift in the body's pH balance and causes the body's system to become more acidic. This condition is brought about by a problem either involving the lungs and respiratory system or signals from the brain that control breathing • .

  13. Normal/Abnormal Values • When a person is acidotic the ph value will be  7.35 compared to the normal values of between 7.36 – 7.42 • If the Pco2 is  5.7 kpa the respiratory system is the cause of the problem and the condition is known as Respiratory acidosis.

  14. Causes of Respiratory Acidosis • Lung diseases..such as emphysema, asthma, bronchitis, pneumonia • Blockages to the airway…foreign object, vomit, swelling • Brain injuries or tumours • Certain drugs such as anasthetics, sedatives, narcotics

  15. Signs and Symptoms • There will be slowed or difficult breathing. Headache, drowsiness, restlessness, tremor, and confusion may also occur. A rapid heart rate, changes in blood pressure, and swelling of blood vessels in the eyes may be noted upon examination.

  16. Body maintaining balance • When the respiratory problem is not too severe..the kidneys will try and help raise the blood ph by increasing excretion of H+ and reabsorption of HCO3…..known as Renal Compensation

  17. Treatment • Will be to determine and treat the underlying cause of the acidosis • In lung disease…bronchodilators, steroid drugs and maybe supplemental oxygen therapy…but oversupply could possibly make the acidosis worse…..(as in COPD) • Antibiotics for infection

  18. Treatment cont. • In the case of a drug overdose or use of narcotics……a dose of naloxone may be used to block the respiratory depressing effects • Use of mechanical ventilation may be required

  19. Nursing • Nursing staff must maintain strict monitoring of patient observations…..BP, pulse, respiratory rate, fluid input/output, temp, breathing difficulties, mental condition etc • Must also be aware of normal/abnormal ranges in investigative results and call medics if abnormal results are noted.

  20. Metabolic Alkalosis • What is it? A decrease in hydrogen ions (H+) And / Or An increase in Bicarbonate ions (HCO3-) This condition is not a disease (it is a symptom)

  21. Metabolic Alkalosis (cont) • Typical Values for Metabolic Alkalosis. - HCO3- < 22 mmol/l ; pH <7.40

  22. Metabolic Alkalosis (cont) • 2 Types • Chloride Responsive • Chloride Resistant

  23. Metabolic Alkalosis (cont) • Pathophysiology • Loss of H+ ions in the system. • More than HCO3- than H+ • Decreases the ionisation of Ca2+ and K+ leading to hypocalcemia and hypokalemia. • Respiratory rate compensates for alkalinity by raising the CO2 levels. • Increasing bicarbonate ions utilize Na+ thus decreasing the ration between Na+ and Cl- • Renal Compensation to preserve Hydrogen ions.

  24. Metabolic Alkalosis (cont) • Signs and Symptoms There are no specific signs and symptoms but the main causes this are: - Gut loss. - Selected Diuretics - Ingestion of large amounts of Na2CO3 - Constipation

  25. Metabolic Alkalosis (cont) • Effects • Oxygen Delivery. • Cardiovascular Effects. • Neuromuscular Effects. • Ionized Calcium Concentrational effects. • Other Effects.

  26. Metabolic Alkalosis (cont) • Management • Sort out the underlying cause of the Alkalosis. • Management of hypokalemia. • Acidification of blood plasma.

  27. Alkalosis • Alkalosis occurs when there is a loss of hydrogen ions or a gain in bicarbonate ions and hence a corresponding high pH (greater than 7.44). Alkalosis can occur through: • Excessive loss of gastric juices, e.g. vomiting, gastric aspirations. • Excessive intake of alkaline products, e.g. overdoes of anti-acids. • Hyperventilation with resulting removal of carbon dioxide.

  28. Respiratory Alkalosis • What is it ? • Respiratory alkalosis is a condition where the amount of carbon dioxide found in the blood drops to a level below normal range (PCO2 <5.7 kPa) • This condition produces a shift in the body's pH balance and causes the body's system to become more alkaline. This condition is brought on by rapid, deep breathing called hyperventilation.

  29. Respiratory Alkalosis • Pathophysiology • In the lungs, oxygen from inhaled air is exchanged for carbon dioxide from the blood. • When a person hyperventilates, this exchange of oxygen for carbon dioxide is speeded up, and the person exhales too much carbon dioxide. • This lowered level of carbon dioxide causes the pH of the blood to increase, leading to alkalosis.

  30. Respiratory Alkalosis • Signs and Symptoms • Primary cause is hyperventilation • This rapid, deep breathing can be caused by conditions related to the lungs like pneumonia, lung disease, or asthma. • Hyperventilation is associated with anxiety, fever, drug overdose, carbon monoxide poisoning, or serious infections.

  31. Respiratory Alkalosis • Nursing Management - Hyperventilation due to anxiety may be relieved by having the patient breath into a paper bag. • Antibiotics may be used to treat pneumonia or other infections. • If the alkalosis is related to a drug overdose, the patient may require treatment for poisoning. • If the underlying condition that caused the respiratory alkalosis is treated and corrected, there may be no long-term effects.

  32. References • Edwards.S and Richards, A. (2003) A nurses survival guide to the ward. London, Churchill Livingstone. • Yessem, S. (2006) Metabolic Alkalosis [online]http://www.emedicine.com/MED/topic1459.htm [accessed 3/11/06] • Alexander et al (2003) Nursing Practice Hospital and Home. London: Churchill Livingstone.

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