Respiratory Acidosis And Alkalosis : Respiratory Acidosis And Alkalosis Dr. Aalekh Raj Dahal
MBBS Respiratory Acidosis : Respiratory Acidosis Defination: Respiratory acidosis is a condition in which a build-up of carbon dioxide in the blood produces a shift in the body's pH balance and causes the body's system to become more acidic. This condition is brought about by a problem either involving the lungs and respiratory system or signals from the brain that control breathing. There is primary increase in Pco2 with compensatory increase in HCO3 −; pH usually low but may be near normal. (Ventilatory failure; Respiratory failure; Acidosis – respiratory) Slide 3: Carbon dioxide is produced constantly as the body burns energy, and this CO2 will accumulate rapidly if the lungs do not adequately dispel it through alveolar ventilation. Alveolar hypoventilation thus leads to an increased PaCO2 (called hypercapnia). The increase in PaCO2 in turn decreases the HCO3−/PaCO2 ratio and decreases pH resulting respiratory acidosis. Etiology: : Etiology: Hypoventilation
Diseases of the airways (such as asthma and chronic obstructive lung disease), which send air into and out of the lungs
Diseases of the chest (such as scoliosis), which make the lungs less efficient at filling and emptying
Diseases affecting the nerves and muscles that "signal" the lungs to inflate or deflate
Drugs that suppress breathing (including powerful pain medicines, such as narcotics, and "downers," such as benzodiazepines), especially when combined with alcohol
Severe obesity, which restricts how much the lungs can expand Signs and symptoms: : Signs and symptoms: Symptoms and signs depend on the rate and degree of Pco2 increase. CO2 rapidly diffuses across the blood-brain barrier. Symptoms and signs are a result of high CNS CO2 concentrations (low CNS pH) and any accompanying hypoxemia.
The most notable symptom will be slowed or difficult breathing. Headache, drowsiness, lethargy, anxiety, sleepiness, easy fatigue, memory loss, restlessness, tremor, and confusion may also occur. Some personality changes like gait disturbance, blunted deep tendon reflexes, myoclonic jerks, asterixis, and papilledema might be seen. A rapid heart rate, changes in blood pressure, and swelling of blood vessels in the eyes may be noted upon examination. This condition can trigger the body to respond with symptoms of metabolic alkalosis, which may include cyanosis, a bluish or purplish discoloration of the skin due to inadequate oxygen intake. Severe cases of respiratory acidosis can lead to coma and death. Types of Respiratory Acidosis: : Types of Respiratory Acidosis: Acute:
In acute respiratory acidosis, the PaCO2 is elevated above the upper limit of the reference range (over 6.3 kPa or 47 mm Hg) with an accompanying acidemia (pH <7.35). Acute respiratory acidosis occurs when an abrupt failure of ventilation occurs. 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), or airway obstruction related to asthma or chronic obstructive pulmonary disease (COPD) exacerbation. Slide 8: Chronic
In chronic respiratory acidosis, the PaCO2 is elevated above the upper limit of the reference range, with a normal blood pH (7.35 to 7.45) or near-normal pH secondary to renal compensation and an elevated serum bicarbonate (HCO3− >30 mm Hg). Chronic respiratory acidosis may be secondary to many disorders, including COPD. 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.
Chronic respiratory acidosis also may be secondary to obesity hypoventilation syndrome (i.e., Pickwickian syndrome), neuromuscular disorders such as amyotrophic lateral sclerosis, and severe restrictive ventilatory defects as observed in interstitial fibrosis and thoracic deformities. Compensation: : Compensation: Problem: Increase pCO2 and this results in a decrease blood pH (high H+)
[H+] stimulates kidney to generate and retain bicarbonate
respiratory acidosis.is compensated for by the development of a metabolic alkalosis
Compensation is complete ([HCO3] levels out) in 2-4 days
Final HCO3 can be calculated from the following equation:
HCO3 mmol/L = 0.44 X pCO2 mmHg + 7.6 (+/-2).
Limit of compensation is a HCO3 of 45 mmol/L Alteration of metabolism and function : Alteration of metabolism and function Respiratory acidosis is associated with a plasma pH decrease, arterial PaCO2 increase and often accompanied by hypoxemia. The signs and symptoms of respiratory acidosis also depend on the rapidity of onset of acidosis.
The hypercapnia has some additional impacts on central nervous system. On CNS, the manifestations of CNS in respiratory acidosis are often intermixed with those of oxygen deficit.
CO2 readily crosses the blood-brain barrier, and elevated levels of CO2 exert its effects by producing vasodialation of cerebral blood vessels and more acid brain fluids resulting in several complications associated with chronic and acute acidosis.
Because for HCO3-, to cross the blood brain barrier is not easy as CO2, the pH values of cerebrospinal fluid in respiratory acidosis are usually lower than those of plasma, which means that the respiratory acidosis usually has more profound impacts on CNS than the metabolic acidosis with the same plasma level of pH. Slide 11: Diagnosis
Respiratory acidosis may be suspected based on symptoms. A blood sample to test for pH and arterial blood gases can be used to confirm the diagnosis. In this type of acidosis, the pH will be below 7.35. The pressure of carbon dioxide in the blood will be high, usually over 45 mmHg. Arterial blood gas (measures levels of oxygen and carbon dioxide in the blood; in respiratory acidosis, the level of carbon dioxide is too high), Chest x-ray and Pulmonary function test can be used for the diagnosis.
Treatment is aimed at the underlying lung disease, and may include:
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 Slide 12: Outlook (Prognosis)
Prognosis depends upon the disease causing the respiratory acidosis. f the underlying condition that caused the respiratory acidosis is treated and corrected, there may be no long term effects. Respiratory acidosis may occur chronically along with the development of lung disease or respiratory failure. In these severe conditions, the patient may require the assistance of a respirator or ventilator. In extreme cases, the patient may experience coma and death.
Poor organ function
Do not smoke. Smoking leads to the development of many severe lung diseases that can cause respiratory acidosis.
Losing weight may help prevent respiratory acidosis due to obesity (obesity-hypoventilation syndrome).
Be careful about taking sedating medicines, and never combine these medicines with alcohol.
Patients with chronic lung diseases and those who receive sedatives and narcotics need to be monitored closely for development of respiratory acidosis. Respiratory Alkalosis : Respiratory Alkalosis Defination:
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 (basic). This condition is brought on by rapid, deep breathing called hyperventilation.
There is a primary decrease in Pco2 with or without compensatory decrease in HCO3 −; pH high or near normal. (Alkalosis – respiratory) Slide 16: Respiratory alkalosis generally occurs when some stimulus makes a person hyperventilate. The increased breathing produces increased alveolar respiration, expelling CO2 from the circulation. This alters the dynamic chemical equilibrium of carbon dioxide in the circulatory system, and the system reacts according to Le Chatelier's principle. Circulating hydrogen ions and bicarbonate are shifted through the carbonic acid (H2CO3) intermediate to make more CO2 via the enzyme carbonic anhydrase .The net result of this is decreased circulating hydrogen ion concentration, and thus increased pH (alkalosis). There is also a decrease in ionized blood calcium concentration. Etiology: : Etiology: Hyperventilation
Intracerebral hemorrhage, meningitis, stroke
Salicylate and Progesterone drug usage
Anxiety, hysteria, stress and pain
Cirrhosis of the liver
Elevated body temperature
sexual activity, which may induce excessive breathing due to excitation
Any lung disease that leads to shortness of breath can also cause respiratory alkalosis. Signs and Symptoms: : Signs and Symptoms: Symptoms and signs depend on the rate and degree of fall in Pco2.
Hyperventilation, the primary cause of respiratory alkalosis, is also the primary symptom. This symptom is accompanied by dizziness, light headedness, agitation, confusions, cramps and tingling or numbing around the mouth and in the fingers and hands. Muscle twitching, trachypnea, hyperpnea, chest pain, blurred vision, spasms, and weakness may be noted. Seizures, irregular heart beats, and tetany (muscle spasms so severe that the muscle locks in a rigid position) can also result. Chronic is usually asymptomatic and has no distinctive signs. Types of Respiratory Alkalosis : Types of Respiratory Alkalosis Acute:
It occurs rapidly. During acute respiratory alkalosis, the person may lose consciousness where the rate of ventilation will resume to normal.
It is a more long-standing condition. For every 10 mM drop in pCO2 in blood, there is a corresponding 5 mM of bicarbonate ion drop. The drop of 5 mM of bicarbonate ion is a compensation effect which reduces the alkalosis effect of the drop in pCO2 in blood. This is termed metabolic compensation. Compensation : Compensation Problem: decrease pCO2 causing increase blood pH (low H+)
Increase pH stimulates the kidney to excrete bicarbonate
respiratory alkalosis is compensated for by the development of a metabolic acidosis
If the condition has been present for 7 days or more full compensation may occur.
Compensation is complete ([HCO3] levels out) in 7-10 days.
The limit of compensation is a HCO3 of 12 mmol/L. Alteration of metabolism and function: : Alteration of metabolism and function: The decrease in CO2 content of the blood causes constriction of cerebral blood vessels. CO2 crosses the blood-brain barrier rather quickly; therefore, manifestations of acute respiratory alkalosis are of sudden onset. The constrictions of cerebral blood vessels can cause regional cerebral ischemia in patients with a pre-existing limitations of cerebral blood flow.
Alkemia shifts the hemoglobin O2 dissociation curve to the left, impairing O2 delivery to the tissue.
An increase in neuromuscular excitability may be due to decreased free Ca2+ availability, resulting from increased albumin binding.
Respiratory alkalosis has alteration in cardiovascular systems as well and also has frequent hypokalemic consequences. Slide 23: Diagnosis: 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. In this type of alkalosis, the pH will be elevated above 7.44. The pressure of carbon dioxide in the blood will be low, usually under 35 mmHg. Arterial blood gas (measures levels of oxygen and carbon dioxide in the blood; in respiratory alkalosis, the level of carbon dioxide is too low),
Chest x-ray, Pulmonary function test may be used.
Treatment: Treatment focuses on correcting the underlying condition that caused the alkalosis. 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. Antibiotics may be used to treat pneumonia or other infections. Other medications may be required to treat fever, seizures, or irregular heart beats. If the alkalosis is related to a drug overdose, the patient may require treatment for poisoning. Use of mechanical ventilation like a respirator may be necessary. 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. Slide 24: (Outlook) Prognosis:
It depends on the condition that is causing the respiratory alkalosis. If the underlying condition that caused the respiratory alkalosis is treated and corrected, there may be no long-term effects. In severe cases of respiratory alkalosis, the patient may experience seizures or heart beat irregularities that may be serious and life threatening.
Seizures may occur if the alkalosis is extremely severe. This is very rare.