What is the role of furosemide (Lasix) in the prehospital setting?

Furosemide in the Prehospital Setting

Furosemide should be used cautiously in the prehospital setting, primarily as adjunctive therapy combined with high-dose nitrates rather than as monotherapy, with an initial dose of 20-40 mg IV for patients with acute pulmonary edema and systolic blood pressure ≥90-100 mmHg. 1

Critical Pre-Administration Requirements

Before administering furosemide in the field, verify the following:

• Systolic blood pressure must be ≥90-100 mmHg - furosemide will worsen hypoperfusion and precipitate cardiogenic shock in hypotensive patients 1, 2
• Absence of marked hypovolemia - assess for decreased skin turgor, tachycardia, and signs of poor perfusion 1, 2
• Clinical evidence of pulmonary edema - rales on chest examination, respiratory distress with SpO2 <90% when sitting upright 1

Evidence-Based Dosing Strategy

Initial dose: 20-40 mg IV push over 1-2 minutes 1, 2

• For new-onset heart failure or patients not on chronic diuretics: 40 mg IV 1
• For patients on chronic oral furosemide: IV dose at least equivalent to their oral dose 1
• Administer slowly over 1-2 minutes to avoid ototoxicity 2

Why Combination Therapy is Superior to Furosemide Alone

The most compelling prehospital evidence demonstrates that high-dose nitrates with low-dose furosemide significantly outperform high-dose furosemide with low-dose nitrates. 1

In the landmark Cotter study of 104 prehospital acute heart failure patients:

• High-dose nitrate + low-dose furosemide group had 13% intubation rate 1
• High-dose furosemide + low-dose nitrate group had 40% intubation rate (P<0.005) 1
• Composite endpoint of death, MI, and intubation: 25% vs 46% (P<0.04) 1
• Myocardial infarction rates: 17% vs 37% (P<0.05) 1

The benefit was attributed primarily to the nitrate, not the furosemide. 1

Hemodynamic Concerns with Furosemide

Furosemide causes transient worsening of hemodynamics for 1-2 hours after administration: 1

• Increased systemic vascular resistance 1
• Increased left ventricular filling pressures 1
• Decreased stroke volume 1

This is why nitrates should be the primary agent, with furosemide as adjunctive therapy. 1

Optimal Prehospital Treatment Algorithm

For acute pulmonary edema with SBP ≥110 mmHg:

1. Start IV nitroglycerin immediately - titrate to highest hemodynamically tolerable dose 1, 2
2. Add furosemide 40 mg IV as adjunctive therapy 1, 2
3. Apply non-invasive ventilation (CPAP) if respiratory rate >20 and SBP >85 mmHg 1
4. Consider sublingual nitrates as alternative if IV access delayed 1

For acute pulmonary edema with SBP 90-110 mmHg:

1. Furosemide 20-40 mg IV cautiously 1, 2
2. Nitrates with extreme caution - monitor BP every 5-10 minutes 1
3. Prepare for circulatory support if BP drops further 1

For acute pulmonary edema with SBP <90 mmHg:

• Do NOT give furosemide - it will worsen shock 1, 2
• Circulatory support required first (inotropes, vasopressors) 1

Common Prehospital Pitfalls

Diagnostic accuracy is poor - more than one-third of patients receiving prehospital furosemide do not have heart failure on ED evaluation 3. The most frequent alternate diagnoses are pneumonia and COPD exacerbations 4.

Furosemide monotherapy is ineffective - loop diuretic monotherapy does not improve short-term outcomes (hemodynamic status, dyspnea, intubation rates) in moderate-to-severe acute pulmonary edema 1

Avoid in hypotensive patients - furosemide causes volume depletion and worsens tissue perfusion when BP is already compromised 1, 2

Morphine may be harmful - despite historical use, morphine is associated with higher rates of mechanical ventilation, ICU admission, and death in acute heart failure 1. Its routine use cannot be recommended 1

Monitoring During Transport

• Blood pressure every 5-15 minutes - watch for hypotension 2
• Respiratory rate and SpO2 continuously 1
• Urine output if catheter placed - expect diuresis within 30-60 minutes 5
• Clinical response - improvement in dyspnea, respiratory rate, oxygen saturation 1

Renal and Electrolyte Concerns

Furosemide is associated with worsening renal function, particularly at higher doses (>60 mg greater total dose associated with renal deterioration) 1. This matters because:

• Worsening renal function during hospitalization increases mortality nearly 3-fold 1
• Admission creatinine >2.7 mg/dL + BUN >43 mg/dL + SBP <115 mmHg = >20% in-hospital mortality 1

This reinforces the strategy of using the lowest effective furosemide dose combined with nitrates rather than aggressive diuretic monotherapy. 1

Evidence Quality and Limitations

There are no randomized controlled trials evaluating furosemide alone in acute heart failure syndromes. 1 The recommendation for combination therapy is based on:

• One Class III prehospital RCT (Cotter study, N=104) showing superiority of high-dose nitrates over high-dose furosemide 1
• One small Class III prehospital study (Hoffman & Reynolds, N=57) showing nitrate + furosemide combination had highest clinical improvement, benefit attributed to nitrate 1, 4
• Consensus guidelines from European Society of Cardiology and American College of Emergency Physicians 1

Transition to Hospital Care

Communicate to receiving ED:

• Exact dose and time of furosemide administration 1
• Pre-treatment blood pressure and response 1
• Urine output during transport 1
• Any concurrent medications given (nitrates, morphine) 1

Expect ED to:

• Place bladder catheter for accurate output monitoring 1, 2
• Check electrolytes and renal function within 6-24 hours 2
• Continue combination therapy rather than escalating furosemide alone 1, 2

Time-Sensitive Administration

Door-to-furosemide time ≤1 hour is independently associated with lower 30-day heart failure hospitalizations (OR 3.65,95% CI 1.22-10.9) and composite of HF hospitalizations or cardiovascular death (OR 3.15,95% CI 1.49-6.64) 6. This supports early prehospital administration when appropriate, but only in combination with nitrates and with adequate blood pressure. 1