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HKU SPACE College of Life Science and Technology

Higher Certificate in Medical Laboratory Science (Year 2)

HS 20-101-05(31)

Project One

Disorder of acid-base & electrolyte metabolism

Ng Susanna Sui-sum

Date of submission: 22nd

January, 2014

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Introduction

In clinical settings, it is important for clinicians to know what tests should be ordered that

might facilitate the diagnosis of a disease and give respective treatment. When patient is

admitted into the hospital, especially at the A&E department, the life of the patient is at the

edge that a single mistake might be life-threatening, hence clinicians, as well as laboratory

technician are important personnel that play a role in saving life.

In this case study, the admitted patient has a medical history of asthma with increased

breathlessness or dyspnea, wheezing and non-productive cough (dry cough) over the past

one day. Treatment given upon admission includes IV hydrocortisone that this steroid is

often used to suppress the immune system as asthma onset will cause hyperactive airway.

Antibiotics is given as asthma attack is often triggered by infection. This patient used

Salbutamol inhaler as treatment to asthma. Salbutamol, often prescribed to asthma and

Chronic Obstructive Pulmonary Disease (COPD) patient, is a short-acting beta-adrenergic

receptor agonist. Due to the young age of the patient, it is unlikely the patient is suffering

from COPD, hence very likely having acute asthma exacerbation. Salbutamol when inhaled,

will act directly on bronchial smooth muscle. It acts on the beta-adrenergic receptor that

causes smooth muscle relaxation that results in dilation of the bronchial passage. From the

information given, the patients chest X-ray also showed hyperinflated lungs, this condition is

often associated with obstructions in airway that air is trapped in the passage that cause the

lung to over-inflate. Hyperinflated lungs is often observed in COPD patients, but asthma and

cystic fibrosis will also cause such condition.

In order to know what causes the illness, an arterial blood gas (ABG) picture was taken by

drawing arterial blood. ABG analysis is often performed in assessing ones ventilation,

acid-base status and oxygenation by giving information on concentration of hydrogen ions

(pH), partial pressure of carbon dioxide (PaCO2) and partial pressure of oxygen

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(PaO2). It is important to note that the arterial blood should be collected quickly and should

be transport on cold ice or analyzed immediately by a blood gas analyzer to minimize pH,

PaO2, PaCO2 changes as low temperature lowers cell metabolism. Blood cells although

taken out of the body, will also consume O2 and CO2 that might affect test results accuracy

if not determined immediately. Upon sampling, one should avoid bubbles will dissolve in the

sample and cause falsely high PaO2 and falsely low PaCO2. Sample should be unclotted and

well-mixed in heparin capillary tubes. One should be cautious on heparin content in the

sampling tubes as excess heparin will decrease pH and dilute the PaCO2.

In the blood gas analyzer, the Ion selective electrode (ISE) inside that is only sensitive to the

measurement of interest will measure the pH, PaO2 and PaCO2 and the bicarbonate ion will

be calculated using Henderson-Hasselbalch equation.

In a blood gas report, the pH reflects H+ concentration, the reference range is 7.35-7.45 and

low pH is known as academia and high pH known as alkalaemia. And PCO2 and HCO3-

reflects respiratory and metabolic component respectively. There are numerous condition

that can be reflected from the ABG picture such as diabetic ketoacidosis, lactic acidosis,

metabolic acidosis, respiratory acidosis, and respiratory alkalosis. Abnormal results might be

due to lung, kidney or metabolic diseases. Any injuries that affect ventilation will also affect

test results.

Arterial Blood Gas On Admission After treatment Reference Range

pH 7.3 [L] 7.5 [H] (7.35-7.45)

PaO2 8.0kPa [L] 17.1kPa [H] (10.6-14)

PaCO2 8.84kPa [H] 4.1kPa [L] (4.7-6.0)

HCO3- 25mmol/L 23mmol/L (22-26)

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Results

Answers to Questions

1a) From the arterial blood gas results on admission, the patients pH is slightly acidic, and

has a low PaO2 and high PaCO2 value, and normal HCO3-. PaCO2 indicates ones production

and elimination of CO2 by ventilation. From the high PaCO2, it can be explained from her

dyspnea and hyperinflated lungs, patients pulmonary is poorly ventilated, as it is obstructed

and trap the respired CO2 which is also shown by the low PaO2. With high PaCO2, the CO2

will form carbonic acid and cause blood pH to decrease and this results in respiratory

acidosis.

1b) Upon treatment, the patients pH rise from 7.3 to 7.5 and results in alkalosis. The patient

was on salbutamol nebulizer and given oxygen to inhale and is on ventilation support. These

will assist her to perform ventilation that eliminate the CO2 accumulated; with salbutamol, it

dilates the patients smooth muscle of the lung airway. Upon oxygen and ventilation support,

the patients ventilation will be passively controlled, to take in more O2 and remove CO2

which these effect are reflected from the ABG report. The PaO2 increases drastically from

8.0kPa to 17.1kPa, since patient is on oxygen inhaler, the value is expected to exceed the

reference range. PaCO2 decreases from 8.84kPa to 4.1kPa, which shows the patient is

hyperventilated. Under ventilation support, the patient can remove CO2 effectively and

leads to low PaCO2 and such drop in CO2 will lead to respiratory alkalosis.

1c) From the routine biochemistry tests, it is observed the patients potassium falls greatly

below the reference range. Potassium is an electrolyte that is critical in proper functioning of

nerve and muscle cells, slight deviation from normal value will be life threatening. The

patient has potassium value of 3.0mmol/L, which is hypokalemia and will lead to tachycardia

if not immediately treated and will cause irreversible damage to the heart. Salbutamol

nebulizer, the therapy the patient is on, has a potassium depleting property and will results

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in a transient reduction in potassium level. It mode of action is by reducing plasma

potassium level by increasing shift of extracellular potassium into intracellular space.

Question 2

At ICU Discharged Reference Range

Sodium 145mmol/L 140mmol/L (136-148)

Potassium 3.0mmol/L [L] >14mmol/L [H] (3.6-5.0)

Urea 5.0mmol/L 5.1mmol/L (3.0-8.8)

Creatinine 80mmol/L 85mmol/L (67-109)

Total protein 76mmol/L (67-87)

Albumin 45mmol/L (39-50)

Total bilirubin 15umol/L (4-23)

ALP

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(

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Regarding biochemical test, preanalytical errors often occurred that will affect test

parameters and might lead to incorrect diagnosis if error not spotted. To avoid such error

being missed, hemolytic and triglyceride index such as hemoglobin concentration should be

included in test reports. Sample has to be rejected and request resampling when analyte

under studied will be affected by these conditions. In this case, if magnesium and phosphate

are also measured, their values under hemolytic condition are expected to increase

drastically like potassium. Sample that contains large amount of protein and lipid will affect

measurement when sample require dilution. The analyte measured will have a falsely low

result when value from stock was derived from back calculation. Hence it is better to

perform with no dilution such as measuring electrolyte using Direct ISE instead of indirect

ISE.

References

http://www.sswahs.nsw.gov.au/rpa/neonatal/html/listview.asp?DrugID=61

http://www.elsevier.pt/en/revistas/revista-portuguesa-pneumologia-320/artigo/nebulized-s

albutamol-for-asthma-effects-on-serum-potassium-90226462

http://www.webmd.com/lung/copd/tc/chronic-obstructive-pulmonary-disease-copd-exams-

and-tests

http://www.avogel.co.uk/health/immune-system/cough/dry/

http://www.lung.org/stop-smoking/about-smoking/health-effects/smoking.html#2

http://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistr

y+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=cli

nical%20biochemistry%20acid%20base&f=false

http://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+ac

id+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical

%20biochemistry%20acid%20base&f=false

http://www.sswahs.nsw.gov.au/rpa/neonatal/html/listview.asp?DrugID=61http://www.sswahs.nsw.gov.au/rpa/neonatal/html/listview.asp?DrugID=61http://www.elsevier.pt/en/revistas/revista-portuguesa-pneumologia-320/artigo/nebulized-salbutamol-for-asthma-effects-on-serum-potassium-90226462http://www.elsevier.pt/en/revistas/revista-portuguesa-pneumologia-320/artigo/nebulized-salbutamol-for-asthma-effects-on-serum-potassium-90226462http://www.elsevier.pt/en/revistas/revista-portuguesa-pneumologia-320/artigo/nebulized-salbutamol-for-asthma-effects-on-serum-potassium-90226462http://www.webmd.com/lung/copd/tc/chronic-obstructive-pulmonary-disease-copd-exams-and-testshttp://www.webmd.com/lung/copd/tc/chronic-obstructive-pulmonary-disease-copd-exams-and-testshttp://www.webmd.com/lung/copd/tc/chronic-obstructive-pulmonary-disease-copd-exams-and-testshttp://www.avogel.co.uk/health/immune-system/cough/dry/http://www.avogel.co.uk/health/immune-system/cough/dry/http://www.lung.org/stop-smoking/about-smoking/health-effects/smoking.html#2http://www.lung.org/stop-smoking/about-smoking/health-effects/smoking.html#2http://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=Je_pJfb2r0cC&pg=PA75&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://books.google.com.hk/books?id=oV2cAQAAQBAJ&pg=PA139&dq=clinical+biochemistry+acid+base&hl=zh-TW&sa=X&ei=XzDdUsqAMImCiQfMuYFg&redir_esc=y#v=onepage&q=clinical%20biochemistry%20acid%20base&f=falsehttp://www.lung.org/stop-smoking/about-smoking/health-effects/smoking.html#2http://www.avogel.co.uk/health/immune-system/cough/dry/http://www.webmd.com/lung/copd/tc/chronic-obstructive-pulmonary-disease-copd-exams-and-testshttp://www.webmd.com/lung/copd/tc/chronic-obstructive-pulmonary-disease-copd-exams-and-testshttp://www.elsevier.pt/en/revistas/revista-portuguesa-pneumologia-320/artigo/nebulized-salbutamol-for-asthma-effects-on-serum-potassium-90226462http://www.elsevier.pt/en/revistas/revista-portuguesa-pneumologia-320/artigo/nebulized-salbutamol-for-asthma-effects-on-serum-potassium-90226462http://www.sswahs.nsw.gov.au/rpa/neonatal/html/listview.asp?DrugID=61

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http://www.ncbi.nlm.nih.gov/pubmed/22141211

http://www.ncbi.nlm.nih.gov/pubmed/22141211http://www.ncbi.nlm.nih.gov/pubmed/22141211http://www.ncbi.nlm.nih.gov/pubmed/22141211