How to manage metabolic acidosis in heroin users?

Management of Metabolic Acidosis in Heroin Users

In heroin users presenting with metabolic acidosis, prioritize immediate respiratory support with bag-mask ventilation, naloxone administration (starting at 0.04-0.4 mg IV, escalating to 2 mg if needed), and treatment of the underlying cause—recognizing that severe acidosis (pH <7.20) often indicates concomitant complications requiring aggressive supportive care rather than routine bicarbonate therapy. 1

Immediate Assessment and Stabilization

Respiratory Management Takes Priority

• Heroin-induced respiratory depression is the primary driver of acidosis in most cases, creating both respiratory acidosis from CO2 retention and metabolic acidosis from tissue hypoperfusion 1
• Assist ventilation immediately with bag-mask device in any heroin user with respiratory depression who is not in cardiac arrest 1
• Administer naloxone 0.04-0.4 mg IV initially, with repeat dosing or escalation to 2 mg if inadequate response; some patients may require much higher doses for massive overdose 1
• Critical caveat: Naloxone's duration of action (45-70 minutes) is shorter than most opioids, particularly methadone, requiring prolonged observation and potential repeat dosing 1

Identify the Acidosis Pattern

• Obtain arterial blood gas to determine if acidosis is primarily respiratory (elevated PaCO2), metabolic (low bicarbonate with normal/low PaCO2), or mixed 1
• Calculate anion gap to differentiate causes: elevated anion gap suggests lactic acidosis from tissue hypoperfusion, while normal anion gap may indicate other complications 2
• Severe metabolic acidosis with pH <7.20 in heroin users, especially if the exposure involved smoke inhalation, strongly suggests concomitant cyanide poisoning and warrants consideration of hydroxocobalamin 1

Treatment Algorithm Based on Severity

Mild to Moderate Acidosis (pH 7.20-7.35)

• Focus on reversing respiratory depression with naloxone and ventilatory support—the acidosis will spontaneously correct once adequate ventilation and tissue perfusion are restored 1, 2
• Provide IV fluids (normal saline) to restore circulatory volume and tissue perfusion 3
• Monitor serial blood gases every 30-60 minutes to assess response 4
• Bicarbonate therapy is NOT indicated at this level of acidosis, as supportive care alone will correct the acid-base disturbance 3, 2

Severe Acidosis (pH <7.20)

• This degree of acidosis correlates with 30-50% short-term mortality and requires aggressive intervention 1
• If cardiac arrest occurs, administer rapid IV bolus of 44.6-100 mEq (one to two 50 mL vials) sodium bicarbonate initially, continuing at 44.6-50 mEq every 5-10 minutes as guided by arterial blood gas monitoring 5
• Outside of cardiac arrest, bicarbonate use remains controversial and should be reserved for pH <7.0-7.1 with severe symptoms, as bicarbonate may worsen intracellular acidosis and produce hyperosmolality 1, 3
• For non-arrest severe acidosis, if bicarbonate is used: infuse 2-5 mEq/kg over 4-8 hours, monitoring blood gases, plasma osmolarity, and hemodynamics closely 5
• Target initial correction to total CO2 of approximately 20 mEq/L, NOT full normalization, as overly rapid correction causes rebound alkalosis due to delayed ventilatory readjustment 5

Special Consideration: Mixed Acidosis with Shock

• Heroin overdose can present with biventricular heart failure, pulmonary edema, and profound lactic acidosis from low cardiac output 6
• Hemodynamic monitoring reveals either low-output failure with high filling pressures OR hyperdynamic state with pulmonary edema but normal capillary pressures—both patterns have been documented 6
• Therapy must be monitored by measuring blood gases, plasma osmolarity, arterial lactate, and hemodynamics 5
• Bicarbonate therapy should be stepwise and cautious, as the degree of response is unpredictable and risks include hypernatremia, hyperosmolality, and reduced ionized calcium 1, 5

Critical Monitoring and Complications

Assess for Coingestions

• 44% of intentional poisonings involve coingestion of other drugs or ethanol (66% of coingestions), which can cause disproportionate mental status changes 1
• Obtain toxicology screening and blood alcohol level if mental status seems inconsistent with reported heroin exposure 1
• Check serum lactate: levels ≥10 mmol/L suggest severe tissue hypoperfusion or cyanide toxicity if smoke inhalation occurred 1

Monitor for Renal Complications

• Heroin users may develop acute kidney injury from rhabdomyolysis, requiring alkalinization of urine to diminish nephrotoxicity of hemoglobin breakdown products 5
• Morphine-6-glucuronide (M-6-G), the active metabolite, accumulates in renal failure with elimination half-life extending to 82 hours, causing prolonged opioid effects requiring extended naloxone therapy 7
• If acute kidney injury develops with severe acidosis (bicarbonate <18 mmol/L), hemodialysis becomes the definitive treatment 3

Avoid Common Pitfalls

• Physical restraints are detrimental in agitated patients, as they exacerbate isometric muscle contractions, worsening hyperthermia and lactic acidosis 1
• Do not attempt full correction of low total CO2 within the first 24 hours—achieving total CO2 of about 20 mEq/L by end of day one is appropriate, with complete normalization occurring over subsequent days 5
• Never withhold ventilatory support while waiting for naloxone to work—bag-mask ventilation must be initiated immediately 1

Disposition and Follow-Up

Observation Requirements

• Patients with life-threatening respiratory depression reversed by naloxone require extended observation for resedation 1
• Brief observation may suffice for morphine/heroin, but long-acting opioids (methadone) or sustained-release formulations require prolonged monitoring 1
• Any patient requiring bicarbonate therapy needs ICU-level care with continuous monitoring 3

Post-Stabilization Management

• Once acidosis resolves and patient is stable, focus shifts to addiction treatment and harm reduction strategies
• Survivors of intentional poisoning have extremely high risk for premature death from subsequent suicide attempts, requiring psychiatric evaluation before discharge 1