Basics of Acid Base Balance
Drchetancreation
Case I
A 7-year-old boy was admitted unconscious to a casualty department. On examination he was found to be hyperventilating. He had inadvertently consumed ethylene glycol antifreeze, which he had found in his parents’ garage stored in a lemonade
bottle. Blood results were as follows:
Plasma
Sodium 134 mmol/L (135–145)
Potassium 6.0 mmol/L (3.5–5.0) ⬆️
Bicarbonate 10 mmol/L (24–32)⬇️⬇️
Chloride 93 mmol/L (95–105)⬇️
Glucose 5.3 mmol/L (3.5–6.0)✅
Arterial blood gases
Ph-7.2(7.35-7.45)⬇️
PaCO2-3.18kPa(4.6-6.0)⬇️
PaO2-13.1kPa(9.3-13.3)
Anion gap=
(Sodium + Potassium ) - (Bicarbonate +Chloride)
(134+6)-(10+93)=140-103=37
High Anion Gap Metabolic Acidosis
Anion Gap= 37 mmol/L
(Normal=10-12mmol/L)
Causes:Ethylene glycol poisoning)
Hyperkalemia (Acidosis)
Case-II
A 67-year-old retired printer presented to casualty because of increasing breathlessness. He had smoked 20 cigarettes a day for 50 years. On examination he was found to be centrally cyanosed and coughing copious green phlegm. His arterial blood results were as follows:
pH = 7.31 (7.35–7.45)⬇️
PaCO2 = 9.3 kPa (4.6–6.0)⬆️⬆️
PaO2 = 6.9 kPa (9.3–13.3)⬇️
Bicarbonate = 37 mmol/L (24–32)⬆️⬆️
Respiratory Acidosis [ Cause- Acute exacerbation of COPD , increased retention of CO2 exceeding all the compensatory mechanisms]
Hypercapnia
Hypoxia
Cyanosis
Bicarbonate Reclamation [ Long term regulation by Kidney]
The patient had chronic obstructive pulmonary disease, and the blood gases show a respiratory acidosis with hypercapnia and hypoxia. The latter has resulted in central cyanosis. Compensation is via the kidneys, with increased acid excretion and HCO3– reclamation. Chronic cases of respiratory acidosis are usually almost totally compensated as there is time for the kidneys and buffer systems to adapt. This is unlike an acute respiratory acidosis due to bilateral pneumothorax, in which the rapid acute changes do not give sufficient time for the compensatory mechanisms to take place. This patient had an acute exacerbation of his lung disease and the CO2 retention exceeded the compensatory mechanisms.
Case-III
A baby girl a few days old had had projectile vomiting since birth due to pyloric stenosis. Her blood results were as follows:
Plasma
Sodium = 137 mmol/L (135–145)✅
Potassium = 3.0 mmol/L (3.5–5.0)⬇️
Bicarbonate = 40 mmol/L (24–32)⬆️
Chloride = 82 mmol/L (95–105)⬇️
Arterial blood gases
pH = 7.52 (7.35–7.45)⬆️
PaCO2 = 6.2 kPa (4.6–6.0)⬆️
PaO2 = 12.9 kPa (9.3–13.3)✅
Anion Gap:28mmol/L⬆️
🔸Metabolic Alkalosis [Cause: Severe Vomiting]
🔸Low Plasma Chloride Concentration [ Loss of HCL in Vomit]
🔸Hypokalemia [Shift of K+ inside the cells in exchange of H+](alkalosis)
🔸Compensation: By Hypoventilation and retention of CO2
The results are suggestive of a metabolic alkalosis due to the severe vomiting. Note also the low plasma [Cl–] due to loss of hydrochloric acid in vomit, and Hypokalaemia resulting from K+ movement into cells due to the alkalosis. Compensation is by hypoventilation and retention of CO2.
Case-IV
A 20-year-old woman presented to casualty with a panic attack. She had noticed peri-oral paresthesia and was found on examination to be hyperventilating. Her arterial blood results were as follows:
pH = 7.61 (7.35–7.45) ⬆️
PaCO2 = 2.7 kPa (4.6–6.0)⬇️⬇️
PaO2 = 13.3 kPa (9.3–13.3) – Normal ✅
Bicarbonate = 18 mmol/L (24–32) ⬇️
🔸Respiratory Alkalosis
Illustration
🔸Panic Attack Hyperventilation
🔸Peri-oral paraesthesia Due to a lowering of plasma ionized calcium concentration as a result of the alkalosis
🔸Compensation is by the kidneys, which increase HCO3– excretion and reduce acid excretion
Case-V
During resuscitation of a 60-year-old man from a cardiorespiratory arrest, blood gas analysis revealed pH 7.00⬇️ (hydrogen ion concentration 100 nmol/L) and pCO2 7.5 kPa ⬆️(52 mmHg). His bicarbonate concentration was 11 mmol/L⬇️. Lactate concentration was 7 mmol/L⬆️⬆️. pO2 was 12.1 kPa (91 mmHg) during treatment with 48% oxygen.
Comment : This patient presents with a mixed disorder: a respiratory acidosis caused by lack of ventilation, and metabolic acidosis caused by the hypoxia that had occurred before oxygen treatment was instituted. The acidosis was caused by an accumulation of lactic acid: the measured lactate concentration was 7 mmol/L
(Reference range is 0.7–1.8 mmol/L (6–16 mg/dL))
The terms acidosis and alkalosis do not just describe blood pH changes: they relate to the processes that result in these changes. Therefore, in some instances, two independent processes may occur: for example, a patient may be admitted to hospital with diabetic ketoacidosis and coexisting emphysema causing respiratory acidosis. The final result could be a more severe change in pH than would have resulted from a simple disorder. Any combination of disorders can occur; the skills of an experienced physician are usually required to diagnose this.
"Life is a struggle, not against sin, not against the Money Power, not against malicious animal magnetism, but against hydrogen ions"
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