Respiratory acidosis and alkalosis

What are the main causes of respiratory acidosis (5)?

1. Hypoventilation due to drugs that suppress breathing (e.g powerful pain medicines like morphine, and antidepressants such as benzodiazepines), especially when combined with alcohol. Codeine/morphine (and alcohol) cause hypoventilation as they may depress respiratory centres in brain 2. Diseases of the airways (such as asthma and chronic obstructive lung disease - obstruct airflow and restrictive conditions such as pneumonia and atelectasis) 3. Diseases of the chest (such as scoliosis), which make the lungs less efficient at filling and emptying 4. Diseases affecting the nerves and muscles that drive the lungs to inflate or deflate 5. Severe obesity, which restricts how much the lungs can expand OVERALL: decreased rate and depth of breathing, obstruction of air passages, decreased gas exchange

How is respiratory acidosis diagnosed and treated (5)?

ABG - pH below 7.35 and the paCO2 will be high, usually over 45 mmHg. Treatment aimed at the underlying lung condition 1. Bronchodilator drugs to reverse some types of airway obstruction 2. Noninvasive positive-pressure ventilation (sometimes called CPAP or BiPAP) 3. Mechanical ventilation (in extreme cases) 4. Oxygen if the blood oxygen level is low 5. STOP SMOKING (and try to lose weight)

How is respiratory alkalosis diagnosed and treated?

ABG: pH will be above 7.44 paCO2 in the blood = low, usually under 35 mmHg Treated: LOOK to treat underlying condition May be relieved by having the patient breath into a paper bag. Rebreathing the air that was exhaled - contains higher than normal levels of CO2. Helpful to stop hyperventilation (due to e.g. anxiety) from causing respiratory alkalosis Antimicrobials - treat pneumonia or other infections Medications may be required to treat fever, seizures, or irregular heart beats. If to a drug overdose, may require treatment for poisoning. Use of mechanical ventilation e.g. a respirator 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 are the features (arterial blood gas) of acute and chronic respiratory alkalosis? Why is acute self regulating? Describe the compensation in chronic cases

ACUTE: occurs rapidly - person may lose consciousness where rate of respiration will return to normal - SELF-REGULATING, esp. if cause = anxiety, stress etc. High pH, low PaCO2, slightly reduced/normal bicarbonate CHRONIC: long-standing - often symptomless - metabolic compensation via kidney. If condition has been present 7-10 days, full compensation will occur - serum bicarbonate will fall - up to a minimum of 12 mmol/L - the low plasma bicarbonate compensates for the low CO2 - brings [HCO3-]/paCO2 to normal levels and thus returns pH to normal - this is considered COMPENSATING METABOLIC ACIDOSIS Roughly normal pH,

What does the Davenport graph look like for respiratory acidosis?

Bicarbonate conc. (y) vs pH (x). Also shows pCO2 The line going horizontally shows bicarbonate conc. doesn't vary much - stays around 25mM. The curves represent CO2 partial pressure Normal breathing - arterial CO2 is around 40mmHg and bicarbonate is around 24mM gives pH 7.4 Respiratory acidosis means CO2 has gone up. Bicarbonate has also gone up a bit (but less than the CO2) pH around 7.2. SHIFTED LEFT THIS has huge effect on enzyme reactions and blood flow to brain - both v. pH sensitive

Define respiratory acidosis

Build up of CO2 in blood - causes blood to become more acidic Caused by HYPOVENTILATION e.g. due to breathing difficulties - leads to HYPERCAPNIA - which leads to respiratory acidosis (fall in blood pH) CO2 (constantly produced from metabolism) will accumulate if not dispelled by lungs quickly enough THUS have HIGH paCO2 and slightly raised [HCO3-] - not raised enough to counter the increase in paCO2 - thus the [HCO3-]/paCO2 decreases - hence pH decreases.

What are the signs (7) and symptoms (6) of respiratory acidosis - how does it affect the brain?

CO2 = lipid soluble - rapidly diffuses across BBB - CSF = UNBUFFERED (NO HCO3- and little protein) - thus pH changes fast Signs and symptoms mainly result of low CNS pH LOW blood pH INCREASES cerebral blood flow (high does the opposite) Symptoms: Headache, lethargy, anxiety, fatigue, memory loss, and muscle weakness. Increased K retention in kidneys can cause arrhythmias Signs: Slowed breathing, gait disturbance, blunted deep tendon reflexes, disorientation, tremor, papilledema, tachycardia etc.

What are the normal values for bicarbonate, paCO2, paO2, pACO2 (alveolar), pAO2, pvCO2 (venous) and pVO2?

From ABG, we can get: bicarbonate conc. = 22-26 mEq/L paCO2 = 35 - 45 mmHg (4.7-6.0 kPa) paO2 = 80 - 100 mmHg Alveolar: pACO2 = 36 mmHg pAO2 = 105 mmHg Venous: pvCO2 = 50 mmHg pvO2 = 30-40 mmHg NORMAL BLOOD pH = 7.35-7.45

What are the signs (4) and symptoms (3) of respiratory alkalosis?

Hyperventilation = primary cause and primary symptom. In acute cases: dizziness, light headedness, confusion etc. - because the increased pH REDUCES cerebral blood flow - causes vasoconstriction of cerebral vessels Can also lead to muscle twitching, chest pain blurred vision, and irregular heart-beat (chronic raised pH can interfere with SAN) Chronic cases tend to be asymptomatic as kidney is able to compensate (retains H+ and excretes more bicarbonate) - makes urine more alkaline GENERALLY NOT TOO BAD

What are the main causes (12) of respiratory alkalosis?

Intracerebral haemorrhage, meningitis, stroke - these may damage respiratory centres in the brainstem Salicylate and Progesterone drug usage Anxiety, stress and pain Cirrhosis of the liver Sepsis Elevated body temperature Hypoxia Any lung disease that leads to shortness of breath can also cause respiratory alkalosis.

What is the anion gap and what is indicated by a high anion gap?

PLASMA is NEUTRAL: has to have same number of anions and cations OR it would be charged - charges have to balance Anion gap = difference in conc. of main cation vs conc. main anions Sodium = main cation - we often ignore K Main anions = plasma Cl- and HCO3- THUS - difference in total Na conc. vs total major anion conc. There IS ALWAYS LESS of the main anions vs main cations but for plasma to remain neutral, the charges must balance, hence there must be unmeasured anions - thus anion gap measures unmeasured anions High anion gap suggests loss of plasma bicarbonate - likely due to elevated levels of unmeasured anions e.g. lactate, acetoacetate etc. HIGH ANION GAP INDICATES METABOLIC ACIDOSIS Low bicarbonate but high Cl, the anion gap may be normal BUT if bicarbonate is low relative to normal levels, there could still be underlying disturbance - indicates illness e.g. GI loss - vomit/diarrhoea or renal loss due to renal damahe

What are the features of acute respiratory acidosis - include the causes and ABG?

PaCO2 is elevated above 6.3 kPa (47 mm Hg) and acidosis (pH <7.35). Occurs with abrupt failure of ventilation - can be caused by depression of respiratory centre e.g. due to disease/drugs, airway obstruction (COPD/asthma), neuromuscular disease Bicarbonate increases slightly BUT not as much as CO2, thus [HCO3-]/PaCO2 ratio still decreases

What are the features of chronic respiratory acidosis?

PaCO2 is elevated above 6.3 kPa (47 mm Hg), BUT BLOOD pH is NORMAL OR NEAR NORMAL Due to renal compensation - kidney detects drop in blood pH and thus increases bicarbonate retention and increased H+ excretion. Leads to high plasma bicarbonate - returns [HCO3-]/paCO2 to nearly normal. Maximum plasma bicarbonate reached in this way = 45 mmol/L Commonly caused by COPD, obesity, neuromuscular disorders, restrictive respiratory disease. Attached is the graph showing metabolic compensation for respiratory acidosis

What are the 4 major metabolic alterations that occur due to respiratory acidosis?

The increase in paCO2 causes vasodilation of cerebral blood vessels Acidaemia shifts the O2 dissociation curve to right - increases O2 delivery to the tissue. Increase in neuromuscular excitability - may relate to changes in blood Ca2+ levels. Increased H+ (proton) excretion by the kidney leads to K+ retention - hence hyperkalaemia

What is the Henderson-Hasselbalch equation - what does it tell you controls pH?

pH = 6.1 + log([HCO3-]/0.03 x paCO2) Remember the square brackets refer to concentration THUS pH is controlled by the ratio of [HCO3-]/paCO2 HENCE you can't tell pH simply from paCO2 - must consider the balance with [HCO3-] Acid will donate H+ and base will accept H+ Acid (HA) will dissociate in water: HA <-> A- + H+. A- = the conjugate base of acid HA

What is respiratory alkalosis?

paCO2 drops below normal - shifts body pH to alkaline Generally occurs in hyperventilation - excess CO2 removed - thus reducing the paCO2 and increasing [HCO3-]/paCO2 ratio The H+ and HCO3- ions in the plasma react to make more CO2 - leads to further reduction in H+ ions