Respiratory Acidosis and Alkalosis Flashcards
what is the normal arterial range for Pao2 and PaCO2
PaO2 is 10-13.5kPa
PaCO2 is 4.7-6.0 kPa
what is the normal alveolar range for PaO2 and PaCO2
PaO2 - 14 kPa
PaCo2 - 4.8kPa
when is acidosis produced
- Acidosis is present when the cell and/or tissue pH is less than 7.35
what produces respiratory acidosis
- there is a build up of carbon dioxide in the blood and this produces a shift in the body pH balance
- the blood becomes more acidic and decreases in pH
what can cause hypercapnia
Alveolar hypoventilation leads to an increased PaCO2 (called hypercapnia). The increase in PaCO2 in turn causes a decrease in blood pH.
what can cause respiratory acidosis
- Hypoventilation due to drugs that suppress breathing (including powerful pain medicines, such as narcotics, and “downers,” such as benzodiazepines), especially when combined with alcohol, not breathing of enough CO2 off
- Diseases of the airways (such as asthma and chronic obstructive lung disease)
- Diseases of the chest (such as scoliosis), which make the lungs less efficient at filling and emptying
- Diseases affecting the nerves and muscles that drive the lungs to inflate or deflate
- Severe obesity, which restricts how much the lungs can expand
what is the ratio that controls pH
[HCO3-]/pCO2
what is the Henderson hasselbach equation
pH = 6.1 + log([HCO3-]/0.03xpCO2)
what has to be higher or lower to cause alkalosis
Thus: if HCO3- higher than reference and/or pCO2 lower than reference then pH high = alkalosis.
what has to be higher or lower to cause acidosis
Similarly if HCO3- lower than reference and/or pCO2 higher than reference then pH low = acidosis.
what will someone with respiratory acidosis have in terms of the Henderson hasselbach equation
- They will have a high Paco2 (E.G. greater than 5.3kPa) and slightly raised [HCO3-] (eg >26 mmol). This means the ratio of [HCO3-]/pCO2 decreases and thus pH also decreases.
what is the normal pH range
7.35-7.45
what raises to compensate respiratory acidosis
carbon dioxide is increased a lot and bicarbonate therefore rises a little in order to compensate
where do the signs for respiratory acidosis often appear in
- main signs are in the brain
- this is because CO2 is a a lipid soluble gas and rapidly diffuses across the blood-brain barrier.
- Also because the CSF has little protein it is much less buffered than blood and thus changes pH faster in response to elevated pCO2.
what are the symptoms and signs of respiratory acidosis primarily due to
- Symptoms and signs of respiratory acidosis are primarily a result of low CSF pH
what are the symptoms of respiratory acidosis
Headache drowsiness lethargy anxiety sleepiness fatigue memory loss restlessness muscle weakness
what are the signs of respiratory acidosis
Slowed breathing gait disturbance blunted deep tendon reflexes, disorientation, tremor, myoclonic jerks, papilledema, tachycardia , drop in blood pressure, swelling of blood vessels in the eyes may also be present.
why does a low CSF affect brain function
Normally the brain regulates its own local pH, shifting towards acid or alkali depending on local neuronal activity.
A global acidity of the blood disrupts this local control, and so areas of the brain may become relatively hypoxaemic or hyperoxic and this can affect local neuronal function
how do you diagnose respiratory acidosis
- blood test sample to test for pH
- ABG
- the key finding would be The pCO2 in the blood will be high, usually over 5.9 kPa (45 mm Hg).
how do you treat respiratory acidosis
- Bronchodilator drugs to reverse some types of airway obstruction
- Noninvasive positive-pressure ventilation (sometimes called CPAP or BiPAP) or mechanical ventilation if needed
- Oxygen if the blood oxygen level is low
- Treatment to stop smoking
the treatment is aimed at the underlying lung disease
what is hyperkalamia
loss of potassium from cells and low pH may effect the distribution of the potassium, can cause atrial flutter
what are the types of respiratory acidosis
acute
chronic
what is the PaCO2 and pH in acute respiratory acidosis
- In acute respiratory acidosis, the PaCO2 is elevated above 6.3 kPa (47 mm Hg) with an accompanying acidemia (blood pH <7.35).
when does acute respiratory acidosis occur
- Acute respiratory acidosis occurs when an abrupt failure of ventilation occurs
what can cause acute respiratory acidosis
- This failure in ventilation may be caused by depression of the central respiratory center by cerebral disease or drugs,
- inability to ventilate adequately due to neuromuscular disease (e.g., myasthenia gravis, amyotrophic lateral sclerosis, Guillain-Barré syndrome, muscular dystrophy),
- airway obstruction related to asthma or chronic obstructive pulmonary disease (COPD) exacerbation.
what is the PaCO2 and pH like in chronic respiratory acidosis
- In chronic respiratory acidosis, the PaCO2 is elevated above 6.3 kPa (47 mm Hg), But the blood pH is normal or near normal.
what is the pH near normal in chronic respiratory acidosis
- This is because renal (metabolic) compensation is occurring and has produced a highly elevated serum bicarbonate (HCO3− >30 mm Hg). The high bicarbonate restores the pH to near normal.
why does chronic respiratory acidosis occur
- Chronic respiratory acidosis may be secondary to many disorders, including COPD.
- Chronic respiratory acidosis also may be secondary to obesity hypoventilation syndrome, neuromuscular disorders such as amyotrophic lateral sclerosis, and severe restrictive ventilatory defects as observed in interstitial fibrosis and thoracic deformities.
how does COPD cause chronic respiratory acidosis
- Hypoventilation in COPD involves multiple mechanisms, including decreased responsiveness to hypoxia and hypercapnia, increased ventilation-perfusion mismatch leading to increased dead space ventilation, and decreased diaphragm function secondary to fatigue and hyperinflation.
how does metabolic compensation for respiratory acidosis work
- After a few days of respiratory acidosis the high blood [H+] stimulates the kidney to retain bicarbonate.
- A high plasma bicarbonate compensates for the high paCO2 and brings the ratio of bicarbonate to pCO2 back to near normal. This raises the pH back towards normal
what is the compensation of the metabolic system for respiratory acidosis called
- This increased bicarbonate retention is sometimes called a compensating metabolic alkalosis
what I the maximum level of bicarbonate plasma that can be reached for compensating metabolic alkalosis
- Maximum level of plasma HCO3 that can be reached in this way is 45 mmol/L
what is respiratory alkalosis
- Respiratory alkalosis is a condition where the amount of carbon dioxide found in the blood drops to a level below normal range. This condition produces a shift in the body’s pH balance and causes the body’s system to become more alkaline
what can cause respiratory alkalosis
hyperventilation
- hyperventiation can occur due to anxiety
- Intracerebral hemorrhage, meningitis, stroke (altered respiratory drive)
- Salicylate and Progesterone drug usage
- Anxiety, hysteria, stress and pain
- Cirrhosis of the liver
- Sepsis
- Elevated body temperature
- Hypoxia
why does hyperventilation cause respiratory alkalosis
- The increased breathing produces increased alveolar respiration, expelling CO2 from the circulation. This reduces the level of carbon dioxide in the circulatory system, and the system reacts according to the Law of mass action.
- Hydrogen ions and bicarbonate in the plasma react (via the enzyme carbonic anhydrase) to make more CO2 .The net result of this is decreased circulating hydrogen ion concentration, and thus increased pH (alkalosis
what are the signs and symptoms of respriatory alkalosis
- hyperventilation is the primary symptom
- dizziness,
- light headedness,
- agitation,
- confusions,
- cramps and tingling or numbing around the mouth and in the fingers and hands.
- Muscle twitching, hyperpnea, chest pain, blurred vision, spasms, and weakness may be noted. In extreme cases seizures, irregular heart beats, and tetany can also result.
what are acidosis symptoms mainly associated with
Acidosis symptoms mainly associated with fatigue: eg drowsiness, lethargy, anxiety, fatigue, etc
what are alkalosis symptoms mainly associated with
- Alkalosis symptoms mainly associated with overactivity : gait disturbance, altered deep tendon reflexes, disorientation, tremor, seizures, myoclonic jerks, etc
what is the metabolic effects of respiratory alkalosis
1) The decrease in CO2 content of the blood causes constriction of cerebral blood vessels
2) Alkalaemia shifts the haemoglobin O2 dissociation curve to the left, impairing O2 delivery to the tissue.
3) pH related changes in blood Ca2+ levels can lead to an increase in neuromuscular excitability – if more calcium goes into the synapse more neurotransmitter comes out
how does respiratory alkalosis lead to hypokalaemia
Respiratory alkalosis causes reduced hydrogen ion (proton) excretion by the kidney.
Some other cation has to take the place of the hydrogen
. This is often potassium, leading to increased potassium excretion and hypokalaemia.
what are the types of respiratory alkalosis
- Acute
- Chronic
describe actue respiratory alkalosis
Occurs rapidly. During acute respiratory alkalosis, the person may lose consciousness where the rate of ventilation will resume to normal.
describe chronic respiratory alkalosis
A more long-standing condition. Generally symptomless due to metabolic compensation.
describe how the kidney deals with chronic respiratory alkalosis
The kidney excretes increased bicarbonate to give a metabolic acidosis that compensates for the respiratory alkalosis. If the condition has been present for 7 days or more full compensation may occur
what Is the minimum plasma bicarbonate level achievable in compensation for respiratory alkalosis
The minimum plasma [HCO3-] achievable is about 12 mmol/L
how do you diagnose respiratory alkalosis
Respiratory alkalosis may be suspected based on symptoms.
A blood sample to test for pH and arterial blood gases can be used to confirm the diagnosis.
The pH will be elevated above 7.44. The paCO2 in the blood will be low, usually under 35 mmHg.
how do you treat respiratory alkalosis
- have to treat the underlying condition causing it
- Hyperventilation syndrome due to anxiety may be relieved by having the patient breath into a paper bag. By rebreathing the air that was exhaled, the patient will inhale a higher amount of carbon dioxide than he or she would normally.
- Atimicrobials 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 respiratory alkalosis has triggered the body to compensate by developing metabolic acidosis, symptoms of that condition may need to be treated, as well.
what is type one respiratory failure
Type 1 Hypoxic (Pa O2 <60 mm Hg/ 8kPa) with normal or low PCO2
what is type two respiratory failure
Type 2 Hypercapnic (PaCO2 >50 mm Hg 6.5 kpA) with or without hypoxia
what are the common causes of type 1 respiratory failure
Ventilation/Perfusion (V/Q) mismatch
Shunting of blood across lungs
Poor gas exchange (alveoli filled with fluid eg in pneumonia)
Decreased minute ventilation (MV) relative to demand
Increased dead space ventilation (less gas to alveoli)
what is the confusion question to do with type I respiratory failure
Surely If a patient is hypoventilating such that they become hypoxic , then they must be accumulating CO2 and simultaneously become hypercapnic?
how can type I respiratory failure occur due to (Surely If a patient is hypoventilating such that they become hypoxic , then they must be accumulating CO2 and simultaneously become hypercapnic? )
The answer is due to the difference in diffusion of oxygen and CO2 in the lungs. CO2 diffuses out more easily than O2 diffuses in
- so carbon dioxide excretion can be maintained at near normal levels despite greatly reduced ventilation and oxygen uptake
what is the most common cause of respiratory failure
type I
what respiratory pathology can occur with or without pH alteration
type I respiratory failure
name some examples of type I respiratory failure
pulmonary edema
pneumonia
pulmonary hemorrhage.
what is the ventilation perfusion ratio in the lungs
This refers to the match between ventilation of a lobe and the blood flow through it
describe how the ventilation perfusion ratio works
If a lobe becomes poorly ventilated, the capillaries and arterioles constrict, reducing blood flow.
This is a useful adaptive mechanism in a healthy lung, as it redirects blood away from poorly ventilated regions to better ventilated ones.
how does the ventilation perfusion ratio make type I respiratory failure worse
If for example all bronchioles are constricted due to asthma then the downstream alveoli will be hypoxic and thus all the local capillaries will constrict.
Thus even less oxygen uptake can occur in the affected region.
If large parts of the lungs are vasoconstricted due to hypoxia,
AV shunts can open to prevent pulmonary arterial hypertension and right heart damage, but this does not help the hypoxia.
what is the anion gap
The anion gap is thus the amount of unmeasured anions in plasma
- The anion gap is the difference between the concentrations of the main cation sodium* and the main anions chloride and bicarbonate in the plasma
how do you work out the anion gap
[Na+] - ([Cl-] + [HCO3-]) < 11 mEq/L
what does it mean if the anion gap is higher than normal
- A high anion gap normally indicates that there is a loss of plasma bicarbonate and this is due to elevated levels of anions like lactate, beta-hydroxybutyrate and acetoacetate.
- thus a high anion gap normally indicates metabolic acidosis.
what anions can replace bicarbonate
e.g. lactate, beta-hydroxybutyrate and acetoacetate
what can metabolic acidosis occur due to
gastrointestinal loss of bicarbonate due to vomiting/diarrhoea, or renal loss of bicarbonate due to renal damage
