Blood Gases and Acid-Base Damage Flashcards
What are physiological roles of hydrogen?
- Influence Mitochondria
- Protein conformation and function
- metabolism
Hydrogen ion concentration needs to be tightly regulated - how is this acheived?
-production - excretion
- bufferng
What does buffering do?
takes up hydrogenionswhenthere’stoo many and releases them when there’s to few.
when would you get carbon dioxide?
Tissue respiration, lung exretion
When is lactic acid produced?
glycolysis, oxidation or gluconeogenisis
when do you produce ketoacids?
ketogenesis, oxidation
what does urea synthesis give you?
ureagenesis, oxidation of amino acids
What does carbon dioxide give you when it is dissolved in water?
A week acid
what does bicarbonate bind with hydrogen to give?
carbonic acid
What does carbonic acid give when it dissociates?
carbon dioxide and water
what can hydrogen bind to whihc acs as a buffer forcing bicarbonate to be left out of the cell?
haemoglobin
what enters the cell when bicarbonate leaves?
chlorine
hydrogen ion homeostasis -what is the pathway of carbon deoxide entering the cell?
CO enters RBC and dissociates to give a hydrogen ion which then binds to haemoglobin and leaves bicarbonate to exit the cell and a cloride comes in.
what does hydrogen ion homeostasis help regulate and the haemoglobin do?
hydrogen ion concentration and haemoglobin releases oxygen.
what are some other buffering mechanisms?
Phosphate
Other proteins
Exchange of intracellular potassium for hydrigen meaning an intracellular shift of H ions ad extracellular shift of potassium.
Hydrogen excretion - this happens through the lungs - what leaves
Carbon dioxide is exhaled through the lungs
What limits the excretion of carbondioxide?
Lung function and your body having enough bicarbonate
What other way can H ions be excreted?
Kidneys in urine
What is the aim of kidneys in getting rid of hydrogen ions?
Get rid of as much hydrogen ions as possible but keep bicarbonate
At what speed do people get rid of hydrogen ions depending on how they do it?
Buffers - rapid
Lungs - fast
Kidneys - slow
Acid based disorders - what is the relationship of hydrogen ions and ph?
pH is the log of hydrogen ions
What is acidosis?
High hydrogen ions
What is alkalosis?
Low hydrogen ions
What can cause either acidosis or alkalosis?
Respiratory and metabolic causes
Homeostatic mechanisms will try and compensate
What happens when your carbon dioxide rises?
You hydrogen ions rise and you get respiratory acidosis
What can happen if you get respiratory acidosis? What disease does this give you?
Kidneys sense this and start to get rid of hydrogen ions and re absorbing bicarbonate. This can give you compensated respiratory acidosis
What would happen if you have low levels of carbon dioxide?
H ions decrease and you get respiratory alkalosis
What happens if hydrogen ions rise in your blood?
You will get rid of carbon dioxide to try and stable these levels (therefore having low Co2 in the body) and develop metabolic acidosis
What would happen if you have a bicarbonate excess?
Hydrogen falls but co2 high so you get metabolic alkalosis
What are causes of respiratory acidosis?
Co2 retention leading to high Hydrogen levels caused by malfunction of excretory mechanisms or control
Examples of diseases which cause respiratory acidosis?
CNS depression or disease/neurological disease - narcotics, stroke, spinal cord lesions, motor neurone disease
Defects in respiratory function:
- Mechanical - myasthenia, thoracic trauma, pneumothorax
- pulmonary disease - restrictive - extensive fibrosis,
- obstructive - chronic bronchitis, severe asthma
- impaired perfusion - massive pulmonary embolism.
What are the compensatory response of respiratory acidosis?
Kidney retaining more bicarbonate buffer
Renal hydrogen ion excretion
Respiratory acidosis - what does this do to your body? Depends on cause (Hypoxi and hypercapnia)
Hypoxia - SOB, drowsy, cyanosis
Hypercanpnia - neurological - anxiety, coma, headache, extensor planters, myoclonus
Cardiovascular - systemic vasodilation
Respiratory acidosis - biochemistry
Increased CO2
High hydrogen ions
Bicarbonate normal or rising
Chronic Respiratory acidosis - biochemistry? - no acidosis as kidneys have helped
High co2
high hydrogen
Compensatory bicarbonate
Acute on chronic Respiratory acidosis - biochemistry? - happens when they no longer have acidosis because of kidney response but then they get Ill and so have it once more
High co2
High hydrogen ions
High bicarbonate
Respiratory alkalosis - causes?
Increased excretion of carbon dioxide
Examples of causes of Respiratory alkalosis?
Hyperventilation
Stimuli to the respitroh centre -
- Cortisol - pain, fever
- Local - trauma, tumours
- Drugs, toxins, - salicylate, liver failure
- Hypoxaemia - R to L shunts, pulm disease
Respiratory alkalosis - what are the compensatory response?
Buffering from the kidneys - reduce renal hydrogen ion excretion, lower carbon dioxide leads to reduced renal bicarbonate generation and reduced urinary acidification.
Effect of Respiratory alkalosis?
Acute hypo apnea
- cerebral vasoconstriction - lightheadedness, confusion, syncope, fits
- fall in ionised calcium - preioral, peripheral, paraesthesia
Cardiovascular
- increased heart rate, chest tightness, angina
Respiratory alkalosis - biochemistry - Acute
Low carbon dioxide, low hydrogen ions, small decrease in bicarbonate
Respiratory alkalosis - biochemistry - chronic?
Renal compensation leads to only slightly low hydrogen ions, lower bicarbonate
Metabolic acidosis causes?
Increased hydrogen ions, decreased hydrogen ions excreted, decreased bicarbonate in blood
Metabolic acidosis examples of causes?
Increased acid formation -
Ketoacidosis - diabetic
Lactic acidosis - hypoxia
Poisoning - salicylate, methanol
Reduced excretion
Renal failure
Renal tubular acidosis (type 1 and 4)
Loss of bicarbonate buffer
Gastrointestinal - diarrhoea, pancreatic fistula
Renal - renal tubular acidosis type 2
Metabolic acidosis - compensatory responses?
If kidneys rants an issue then buffering but this leads to a further fall in bicarbonate
Hyperventilation
- hydrogen ions will stimulate chemoreceptors
- kissmaul - deep, sighing
- Lowers carbon dioxide which lowers hydrogen
- limit to how far carbon dioxide can fall
Increased renal hydrogen excretion
As long as renal is okay
Metabolic acidosis - biochemistry
High Hydrogen ions
Low bicarbonate
Hyperventilation causes low carbon dioxide
High extracellular potassium
Other features depend on underlying cause
Anion gap
- measure positive ions (Na) and (K) and taking away negative ions (Cl) (HCO)
- gap due to proteins, some small anions
- in metabolic acidosis
Gap normal In bicarbonate loss
So raised in increased acid production
Metabolic acidosis - effects on body?
Cardiovascular - negative inotropic effect (heart issues)
Oxygen delivery -
- right shift of oxyhaemoglobin facilitates O2 delivery
- reduced 2,3-DPG- left shift to the curve impairs delivery
Nervous system - impaired consciousness
Potassium homeostasis
- redistribution of hydrogen ions into cells and makes potassi7m come out of cells.
- plasma potassium rises whist intracellular potassium and total body potassium is
depleted
Bone - chronic acidosis - buffering by bone phosphate leads to decalcification.
Metabolic Alkalosis - causes?
Excess loss of hydrogen ion, alkali administration
- characterised by increased bicarbonate levels
bicarbonate is filtered by the kidneys so for metabolic alkalosis to persist inappropriate renal re absorption of filtered bicarbonate must occur:
- extracellular volume contraction
- potassium deficiency
- Mineralocorticoid excess
Metabolic Alkalosis - example causes?
Saline responsive
- GI - vomiting, gastric drainage
- urinary - diuretics (esp in CCF), nephrotic syndrome
Saline unresponsive - associated with hypertension - primary hyperaldosteronism, Cushing
- not associated with hypertension - severe potassium depletion, bartters syndrome
Metabolic Alkalosis - compensatory mechanisms
Buffering - release hydrogen ions
Hypo ventilation- usually incomplete to try and keep carbon dioxide in
Renal bicarbonate excretion increased
Metabolic Alkalosis - effects on body?
Asymptomatic
Potassium depletion
Metabolic Alkalosis - biochemistry
Low hydrogen ions,
High bicarbonate
Low carbon dioxide
How do you assess acid-base status?
Ask history,
Examination (doesn’t give you much)
Near-patient tests - arterial blood gas analysis (blood from artery and put in a machine to measure carbon dioxide, hydrogen ions)
Assessment of acid-base - what are some practical aspects of this?
delay/temperature
- pCO2, hydrogen ions, bicarbonate may drop after 10 mins at 22C but stable for 60 mins at 0c - so put on ice.
Bubbles/froth
- you could just measure oxygen levels in bubbles not blood
How would you approach working out what the patients has once you have all the blood results? Questions to ask yourself
What is the pH or Hydrogen ions
What is the carbon dioxide
What is the bicarbonate
Is there any compensation
What is the anion gap
