Metabolic Acidosis


Background

Anion Gap (defined)

Anion Gap (AG acidosis)

Non Anion-Gap Acidosis

"Delta Gap"

Treatment

  1. Check urine pH before initializing therapy
  2. Correction of underlying cause
  3.  NaHCO3 therapy for pH < 7.1 - 7.2
  4. Overaggressive NaHCO3  "overshoot alkalosis"
  5. Patients with renal failure or CHF  watch for hypernatremia, fluid overload
     
  6. If you need to intubate, Follow these setting:


 

Acidemia
(pH <7.40)
Respiratory Acidosis
(↓ pH + ↑ PCO
2)
Metabolic Acidosis
( ↓pH [<7.35] + ↓ HCO3 [<20], ↓ PCO
2 )
Inadequate ventilation or increased dead space.

Causes include:
- Head or chest trauma
- Oversedation, obtundation, or coma
- Neuromuscular disorders
- Pickwickian syndrome (obesity-hypoventilation syndrome)
- COPD

Renal compensation occurs after 48 hrs of steady state.
Anion gap
Normal anion gap [Na − (K + Cl)] =  12
HIGH Normal
MUDPILES

- Methanol, Metformin
- Uremia (Pericarditis)
- Diabetic (or alcoholic) keoacidosis
- Paraldehyde
- INH/iron/inhalant (ie, CO) poisoning
- Lactic acidosis (sepsis, shock, hypoxia, seizures, cyanide, metformin, Rhabdo, Ischemia)
- Ethylene glycol (Tx: Fomepizole)
- Salicylates, Solvents
 

↓Cl
↓ K ↑K
- Renal losses:
  Renal tubular acidosis or acetazolamide

- GI losses:
  Diarrhea or malabsorption
   Laxative abuse
- Adrenal insufficiency
- Renal insufficiency
- Posthypocapnia
HARD-ASS:
Hyperalimentation
Addison disease
Renal tubular acidosis
Diarrhea
Acetazolamide
Spironolactone
Saline infusion
Tx:
  - Intubation, mechanical ventilation
  - RTA Type 1,  & 2 (
K) : Potassium Citrate (Urocit-K) 20-40 mEq PO qd +/- HCTZ 12.5-50mg PO qd.
  - RTA Type 4 (
 K) : Lasix 20-80mg po qd  OR bumetanide 0.5-2mg PO qd
  - Refractory Acidosis : Na HCO3 8.4% (1mEq/ml) @ 50 cc/hr.
MOA:
- Likely HypOventilating = Retaining CO2
 - Goal = Help pt blow off CO2
 
Tx:

- Ventilatory support
- O2 may be necessary to treat hypoxia, but may worsen hypercapnia in patients with COPD or in heavily sedated patients.

 

NOTE:
Minute Ventilation (VE) = RR x TV

VE = CO2 = pH = Cerabral Flow/ICP
VE = CO2 = pH

Tx:
- May need to be intubated
- Treating the underlying cause is the most important action.
- Sodium bicarbonate treatment is a controversial and potentially dangerous treatment because of the risk of electrolyte disturbances and paradoxical cerebral acidosis. The cerebral acidosis occurs 2° to the inability of HCO3 to quickly cross the blood-brain barrier. Bicarbonate for the treatment of acidosis should only be considered for extremely ill patients with severe acidosis.
- A brief reminder of some special treatments of underlying causes of metabolic acidosis includes:
  - Ethylene glycol and methanol: Fomepizole, Ethanol or 4-methylpyrazole and dialysis
  - Salicylate toxicity: HCO3 to keep serum pH between 7.3 and 7.5 with resultant urine alkalinization; dialysis
  - Iron overdose: Deferoxamine
  - Isoniazid: Pyridoxine (vitamin B6)

If you need to intubate, Follow these setting:

  • Get a BiPAP and Vent Machine (not BiPAP machine). Connect the two and use following settings
    • Mode: SIMV
    • Vt:  550
    • RR: 0 (ZERO)
    • PEEP: 5
    • FiO2: 100%
    • Flow Rate: 30 lpm
    • PSV: 5-10
    • Monitor ETCO2 (it should NOT rise)
  • Now give RSI (Etomidate + Succs) and wait 45 seconds and NOW intubate
    • Immediately change Vent Settings
      • RR = 30
      • Vt = 8 cc/kg predicted IBW
      • Flow rate = 60 lpm
  • Check ABG in 20 min.

Acidosis Management: (pH < 7.30)
  If pH 7.15-7.30:

  - Increase RR until pH > 7.30 or PaCO2 < 25  (Maximum set RR = 35).
  If pH < 7.15:
  -
Increase RR to 35.
  - If pH remains < 7.15, VT may be increased in 1 ml/kg steps until pH > 7.15 (Pplat target of 30 may be exceeded).
  - May give
NaHCO3 2-5 mEq/kg IV x1
Alkalosis Management: (pH > 7.45)
  - Decrease vent rate if possible




 




Acute Respiratory Acidosis:

 


Chronic Respiratory Acidosis: