Normal Levels of Substances in the Arterial Blood ph 7.40 0.05 pCO_2 (partial pr

Question

Normal Levels of Substances in the Arterial Blood ph 7.40 0.05 pCO_2 (partial pressure of carbon dioxide) 40 mm Hg pO_2 (partial pressure of oxygen) 90 - 100 mm Hg Hemoglobin - O_2 saturation 94 - 100 [HCO_3] 24 meq/liter A 76-year old man complained to his wife of severe sub-sternal chest pains that radiated down the inside of his left arm. Shortly afterward, he collapsed on the living room floor. Paramedics arriving at his house just minutes later found him unresponsive, not breathing, and without a pulse. CPR and electroconvulsive shock were required to start his heart beating again. Upon arrival at the Emergency Room, the man started to regain consciousness, complaining of severe shortness of breath (dyspnea) and continued chest pain. On physical examination, his vital signs were as follows: Systemic blood pressure 85 mm Hg 50 mm Hg Heart rate 175 beats/minute Respiratory rate 32 breaths/minute Temperature 99.2 F His breathing was labored, his pulses were rapid and weak everywhere, and his skin was cold and An electrocardiogram (ECG) was done, revealing significant "Q" waves in most of the leads (abnormal). Blood testing revealed markedly elevated creatine phosphokinase (CPK) levels of cardiac muscle origin. Finding heart creatine phosphokinase enzyme in the circulating blood is a signal of heart damage. Arterial blood was sampled and revealed the following: pH 7.22 pCO_2 30 mm Hg pO_2 70 mm Hg Hemoglobin-O_2 saturation 88% [HCO_3] 2 meq/liter What is the diagnosis? What evidence supports your diagnosis? How would you classify his acid-base status? (metabolic acidosis, metabolic alkalosis, respiratory acidosis or respiratory alkalosis) What specifically caused this acid-base disturbance? How has his body started to compensate for this acid-base disturbance? Discuss both the respiratory and kidney compensation. List some other causes of this type of acid-base disturbance. This case study was adapted from McGraw-Hill case studies in Anatomy and Physiology.

Explanation / Answer

1. Diagnosis - the patient has suffered with his first acute myocardial infarction. The implications for this diagnosis is a sudden stoppage of heart, along with an elevated Q wave and abnormally high level of CPK in the cardiac muscles. The pO2 and pCO2 levels have reduced with a reduced haemoglobin to oxygen saturation.

2. The condition is called metabolic acidosis which has resulted due to a very low level of bicarbonate in the body. This occurs as a result of the acute myocardial infarction.

3. The body has started to compensate for metabolic acidosis by hyperventilation m that is observed in the form of decreased arterial pCO2. Kidneys compensate by conserving bicarbonate and eliminating hydrogen ions via urine.

4. Metabolic acidosis can also be caused by

- renal dysfunction

- loss of bicarbonate in case of diarrhoea or severe dehydration

- failure of the kidneys to remove H+ ions

- accumulation of acids in the form of lactic acids or ketones in the case of starvation or high fever

- poisoning by aspirin or methanol or ethylene glycol

- liver failure

- prolonged lack of oxygen from shock or severe anemia.

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