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Biomedical sciences
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Acid-Base Disturbances
Lidia M. Guerrero, DMD
Acid-base homeostasis
! Regulation of the hydrogen ion concentration – Chemical buffers of the body
! Bicarbonate-carbonic acid buffer pair – H(+) + HCO3 ! " H2CO3 " CO2 + H2O
– Lungs ! Eliminates CO2 & H2O
– Kidneys ! Reabsorbs filtered bicarbonate and regenerates new
bicarbonate via the titration of urinary buffers and the excretion of ammonium
Approach to the analysis of Acid-base disorders
! Careful history ! Arterial blood gases ! Serum electrolytes ! Urine electrolytes ! Rules of compensation
Arterial blood gasses (ABG s)
! Normal values – Oxygen saturation = 93% - 98% – Arterial pH = 7.35 – 7.45 – P O2 = 80 – 95 mm Hg – P CO2 = 36 – 43 mm Hg – {HCO3!} = 20 – 30 meq/L
Acid-base disorders
! Type – Acidosis – Alkalosis
! Origin – Metabolic – Respiratory
! Compensation or mixed disorder
Primary Acid-base disorders
Type of disorder
pH P CO2 Plasma HCO3!
Respiratory acidosis
## $$ N ($)
Respiratory alkalosis
$$
## N (")
Metabolic acidosis
## N (") ##
Metabolic alkalosis
$$
N ($) $$
Respiratory acidosis
! Primary increase in P CO2 – Interference in pulmonary excretion of CO2
! Compensatory response – Increase in renal resorption & generation of
bicarbonate ! Leads to a rise in serum {HCO3!}
Respiratory acidosis
! Common causes – Depression of respiratory
center ! Drugs ! Infections ! CNS injury
– Neuromuscular disorders ! Myopathy ! Guillian-Barré Syndrome
– Pulmonary diseases ! COPD ! Asthma ! Kyphoskoliosis ! Pneumothorax
! Manifestations – Agitation – Asterixis – Papilledema – Headache – Somnolence – Hypertension – Tachycardia – Heart failure – Cardiac arrhythmias
Respiratory acidosis
! COPD patients – Particularly serious condition
! Post operative period may accentuate preexisting chronic respiratory acidosis
– Airway obstruction – Atelectasis – Pneumonia – Pleural effusion – Abdominal pain or distention
Respiratory acidosis
! Signs indicating inadequate ventilation with hypercapnia – Similar to those associated with post
operative pain ! Restlessness ! Hypertension ! Tachycardia
– Narcotics should be used cautiously or avoided
Respiratory acidosis
! Management – Prompt correction of pulmonary defect – Ensure adequate ventilation – Encourage deep breathing and coughing – Avoid over-sedation
Respiratory alkalosis
! Decrease in P CO2
– Primary hyperventilation
! Compensatory response – Increased renal bicarbonate excretion
! Fall in serum {HCO3!}
Respiratory alkalosis
! Very common in the surgical/dental patient ! Common causes
– Hyperventilation ! Apprehension ! Pain ! Hypoxia ! CNS injury (encephalitis) ! Assisted ventilation
Respiratory alkalosis
! Common causes – CSN disorders
! Anxiety ! Brainstem lesions ! Infection
– Pulmonary diseases ! Pneumonia ! Pulmonary emboli ! Pulmonary edema ! Interstitial lung disease
! Common causes – Drugs
! Salycilates ! Theophyline ! Catecholamines
– Gram-negative sepsis – Liver disease – Pregnancy – Excessive ventilation
from mechanical ventilators
Respiratory alkalosis
! Manifestations – Lightheadedness – Paresthesias – Tetany – Syncope – Seizures – Cardiac arrhythmias
Respiratory alkalosis
! Dangers – Poor prognosis – Related to potassium depletion
! Ventricular arrhythmias ! Fibrillation
– Shift of the oxy-hemoglobin dissociation curve to the left ! Limits the ability of hemoglobin to unload oxygen at the
tissue level
Oxyhemoglobin dissociation curve
Respiratory alkalosis
! Management – Paper bag ???
! Patient’s hands over mouth and nose – Proper use of mechanical ventilation – Correction of preexisting potassium deficits
Metabolic acidosis
! Reduction in {HCO3!} – Accumulation of fixed acids – Loss of alkali
! Compensatory response – Increased ventilation (rate & depth)
! Fall in P CO2
Metabolic acidosis
! Common causes – Diabetes – Alcohol withdrawal syndrome – Renal damage
! Azotemia or uremia – Lactic acid accumulation
! Reflection of tissue hypoxia – Starvation – Drug intoxication – Diarrhea – Small bowel fistulae
Metabolic acidosis
! Management – Correction of the underlying disorder – Restoration of adequate tissue perfusion by
proper volume replacement – Avoid bicarbonate replacement
Metabolic alkalosis
! Primary increase in {HCO3!} – Loss of acids – Gain of bicarbonate – Aggravated by any preexisting potassium depletion
! Compensatory response – Primarily renal mechanisms
! Urinary excretion of bicarbonate – Hypoventilation
! Rise in P CO2
Metabolic alkalosis
! Common causes – Vomiting – Gastric suction with
pyloric obstruction – Excessive intake of
bicarbonate – Diuretics
! Same dangers as in respiratory alkalosis
! Manifestations – Impaired mental status – Hypotension – Cardiac arrhythmias – Hypoventilation – Hypokalemia – Decreased ionized
calcium
Metabolic alkalosis
! Management – Replacement of extracellular fluid volume deficit – Replacement of potassium
Thank you!!!