n325 acid-base

acid-base balance

• cells function with pH of 7.35-7.45

  • pH is concentration of H+ ions

  • pH impacts enzymes, muscle contraction, O2 delivery

  • buildup of acid → hemoglobin not as effective in carrying O2

sources of acids in the body

• acids are normal byproducts of metabolism

• body must buffer/eliminate acids to maintain normal pH

• excess acid = decreased pH

• acid = CO2 or metabolism byproduct

  • cellular metabolism → carbonic acid (H2CO3)

  • anaerobic metabolism → lactic acid

  • fat metabolism → ketoacids

  • stomach → hydrochloric acid (HCl)

  
  

regulation of acid-base balance

• kidneys + lungs are compensatory systems

• buffer systems

• carbonic acid-bicarbonate buffer systems

• respiratory system

• renal system

buffer systems

• primary, MOST EFFICIENT, and acts IMMEDIATELY

• change strong acids into weaker ones or bind acids to neutralize them until they can be excreted

• carbonic acid-bicarbonate → predominant buffer in the bloodstream

• hemoglobin → bind to H+ ions and get ready to excrete them

  • when pt is more acidic → more hypoxic

  • instead of RBCs binding O2 → bind H+ instead

  • not enough O2 carriers thru the bloodstream

carbonic acid-bicarbonate buffer system

• CO2 + H2O ←→ H2CO3 ←→ HCO3- + H+

• bicarb binds H+ → PREDOMINANT BUFFER

  • creates carbonic acid: H2CO3

  • carbonic acid breaks down into H2O + CO2 in the lungs

  • breathe out O2 and some water, the rest of water remains in bloodstream

• if buildup of CO2 → binds to water → turns into carbonic acid → turns into bicarb and H+ → get rid of bicarb thru kidneys

respiratory compensatory system

• RCC in brainstem senses changes in CO2 and H+ → adjusts rate and depth of respirations to restore balance

• acts within MINUTES

• fast but TEMPORARY → lungs can only breathe so fast/slow without having alternate complications

• pH low → exhale CO2 → breathe faster and deeper

• pH high → retain CO2 → breathe slower

renal compensatory system

• SLOWEST compensatory system

• acts within HOURS TO DAYS

• LONG-TERM REGULATION!!

• regulate bicarb and H+

• pH low → pee out more H+ and increase bicarb production

• pH high → retain more H+ and decrease bicarb production

ABG

• venipuncture into an artery (radial/femoral/brachial)

• tells overall oxygenation status, acid-base balance, underlying cause of imbalance, body’s ability to compensate/regulate pH

• measures:

  • pH

  • PaCO2

  • PaO2

  • HCO3-

  • SaO2

PaO2 vs SaO2

• PaO2:

  • measures O2 dissolved in your plasma

  • pressure measurement

  • ex) the crows if ppl waiting at the bus stop trying to push their way on

• SaO2:

  • measures how much O2 is actually on hemoglobin

  • percentage measurement

  • ex) % of seats on the bus that are occupied by O2 passengers

normal pH value

• 7.35 - 7.45

normal PaCO2 value

• 35-45 mmHg

normal PaO2 value

• 80-100 mmHg

normal HCO3- value

• 22-26 mEq/L

normal SaO2 value

• 94-100%

respiratory acidosis causes

• hypoventilation

  • COPD → can’t exhale all air fully

  • pneumonia → fluid in lungs → can’t get CO2 breathed out as much

  • pulmonary edema → CO2 not effectively get out

  • airway obstruction

  • opioids

  • sedatives

  • chest wall injury

  • neuromuscular weakness

  • abdominal/chest surgery

• anything that will cause retention of CO2 or decreased RR

respiratory acidosis compensation

• kidneys → create bicarb and pee out more H+

respiratory acidosis ABGs

• pH < 7.35

• paCO2 > 45 mmHg

• HCO3- = normal or increased if compensating

respiratory acidosis S/S

• hypoventilation → hypoxia

• rapid, shallow respirations

• decreased BP with vasodilation

• dyspnea

• headache

• hyperkalemia

• dysrhythmias (d/t incr k+)

• drowsiness, dizziness, disorientation

• muscle weakness, hyperreflexia

respiratory acidosis management

• monitor VS, neuro, respiratory assessment, ABGs, lytes

• improve ventilation & oxygenation:

  • elevate HOB

  • deep breathing & coughing exercises

  • IS

  • CPT

  • administer O2

  • suction

  • non-invasive (CPAP, biPAP) or mechanical ventilation

    • give O2 and positive pressure to push alveoli partially open for better gas exchange

• treat the cause

respiratory alkalosis causes

• hyperventilation

  • blowing off too much CO2

  • anxiety, fear, pain, fever, hypoxia, brain injury, mechanical over-ventilation

respiratory alkalosis compensation

• kidneys → make less bicarb and retain more H+

respiratory alkalosis ABGs

• pH > 7.45

• PaCO2 < 35 mmHg

• HCO3- = normal or decreased if compensating

respiratory alkalosis S/S

• hyperventilation (increased rate & depth)

• tachycardia

• decreased/normal BP

  • low CO2 causes blood vessels to dilate

• hypokalemia

  • al-ka-LOW-sis

  • high pH causes H+ to move out of cells, forcing K+ into cells, out of the bloodstream, to maintain electrical balance

• hypocalcemia

  • al-ca-LOW-sis

• numbness & tingling of extremities

• hyper-reflexes & muscle cramping

• seizures

• increased anxiety, increased irritability

respiratory alkalosis management

• monitor: VS, ABGs, neuro/muscular & respiratory assessment, lytes (K+ and Ca+2)

• treat the cause

• reduce hyperventilation:

  • coached slow breathing

  • rebreathing techniques - breathe into paper bag and supervise pt

  • sedation

  • reassurance

  • calm environment

metabolic acidosis causes

• anything that doesn’t change ventilation but causes increased acid/decreased base

• excess acid production:

  • diabetic ketoacidosis - body doesn’t produce insulin/resistant, fat metabolism, ketones produced, ketones are acidic

  • lactic acidosis - byproduct of anaerobic metabolism

  • septic shock - hypoperfusion → anaerobic metabolism → produces lactic acic

• loss of bicarb:

  • AKI & CKD - kidneys stop making bicarb and stop getting rid of H+ thru urine

  • diarrhea

metabolic acidosis compensation

• respiration → increases → get rid of excess CO2

metabolic acidosis ABGs

• pH < 7.35

• PaCO2 normal or decreased if compensating

• HCO3- < 22 mEq/L

metabolic acidosis S/S

• headache

• decreased BP

• hyperkalemia

• muscle twitching

• warm, flushed skin (d/t vasodilation)

• nausea, vomiting, diarrhea

• changes in LOC → confusion/drowsiness)

• kussmaul respirations → breathing fast and rly deep to compensate

metabolic acidosis management

• monitor: VS, ABGs, anion gap (difference between major positive and negative ions in the body → bigger gap d/t H+ build-up in the body), lytes, neuro & respiratory status, UOP, BUN/Cr

• treat the cause:

  • DKA → IV insulin & fluids

  • diarrhea → rehydration, antidiarrheals

  • sepsis → antibiotics & IV fluids

  • shock → IV fluids, vasopressors

  • renal failure → dialysis

• support ventilation & oxygenation

• administer sodium bicarb

metabolic alkalosis

• loss of acid or gain of base

• GI acid loss: vomiting, NG suctioning

• excess bicarb intake: antacids, IV sodium bicarb, calcium supplements

• diuretics

• hypokalemia

  • when K+ low in blood, H+ lost in blood and blood becomes more basic

metabolic alkalosis compensation

• lungs!

• respirations slow and shallow

• RR decreases

metabolic alkalosis ABGs

• pH > 7.45

• PaCO2 normal or increased if compensating

• HCO3- = >26 mEq/L

metabolic alkalosis S/S

• restless followed by lethargy

• dysrhythmias (tachycardia)

• compensatory hypoventilation

• confusion (decreased LOC, dizzy, irritable)

• nausea, vomiting, diarrhea

• tremors, muscle cramps, tingling of fingers & toes

• hypokalemia and hypocalcemia

metabolic alkalosis management

• monitor: VS, ABGs, lytes, neuro & resp status

• treat the cause:

  • vomiting → antiemetics

  • hypokalemia → K+ replacement, avoid K-wasting diuretics

  • excess bicarbonate → discontinue or reduce intake

• support ventilation & oxygenation

  • breathing slows → not taking in as much O2 → may need external O2 source

mixed acid-base disorders

• two or more acid-base disorders present at the same time

• pH depends on the type, severity, and compensatory mechanisms involved

• common in critically ill or complex medical patients

• compensation from one system cannot fully correct abnormalities

• pH may appear near normal, so interpretation must include ABGs and clinical context

ABG interpretation

• 1. acidosis or alkalosis

• 2. respiratory or metabolic?

• 3. compensated?

• ROME method

  • Respiratory, opposite → CO2 and pH will be opposite trends

  • Metabolic, equal → HCO3- and pH will be equal trends

• assess for compensation - what is needed to compensate? more CO2 or bicarb?

  • no compensation: compensating lab value remains within normal range

  • partial compensation: compensating lab value shifts to correct imbalance, but pH not normal yet

  • full compensation: compensating lab value shifts to correct imbalance, and pH returned to normal range

    • if pH returned to normal - look what side closer to - high or low?