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Correction of Respiratory Acidosis with BiPAP: Step-by-Step Guide

1. Understanding Respiratory Acidosis — ABG Criteria

• Acute (< 24 hrs): HCO₃⁻ rises by 1 mEq/L per 10 mmHg rise in PaCO₂
• Chronic (> 24 hrs): HCO₃⁻ rises by 4 mEq/L per 10 mmHg rise in PaCO₂ (renal adaptation); max HCO₃⁻ rarely exceeds 38 mEq/L

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2. Indications for BiPAP in Respiratory Acidosis

• pH < 7.25 and rapidly deteriorating
• GCS ≤ 8 / inability to protect airway
• Hemodynamic instability / respiratory arrest
• Copious secretions / facial trauma
• Tachypnea > 35 with GCS < 11 (predictors of NIV failure)

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3. Interface Selection

1. Full-face (oronasal) mask — first choice; better seal, lower leak rate, better patient-ventilator synchrony
2. Nasal mask — second choice; higher leak rate, patient comfort varies
3. Helmet interface — option in some centers for prolonged use

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4. Initial BiPAP Settings — Hypercapnic (Type II) Respiratory Failure

For pure hypoxemia (Type I): IPAP 12–14 / EPAP 8 cmH₂O, FiO₂ 1.0

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5. Titration Protocol (Step-by-Step)

Phase 1 — First 30–60 Minutes

Step 1: Apply mask, start IPAP 10 / EPAP 4–5 cmH₂O, FiO₂ 1.0
Step 2: Observe for 5–10 min — patient comfort, synchrony, RR, SpO₂
Step 3: Increase IPAP by 2 cmH₂O increments if:
         ✓ WOB still increased
         ✓ RR still > 25
         ✓ Tidal volume inadequate (target 6–8 mL/kg IBW)
Step 4: Increase EPAP by 1–2 cmH₂O if:
         ✓ SpO₂ still < 88–92% despite adequate IPAP
         ✓ Auto-PEEP suspected (note: also re-raise IPAP to maintain PS)
Step 5: Check ABG at 60–90 minutes

Titration Targets (ABG Goals at 1 hour)

IPAP Limits

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6. ABG Check Schedule

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7. Signs of Success vs. Failure

Success (continue BiPAP)

• pH improving toward > 7.35
• PaCO₂ decreasing (not precipitously)
• RR decreasing (< 25/min)
• SpO₂ 88–92%
• Decreased accessory muscle use
• Patient comfort and synchrony improving

Failure (escalate to intubation)

• pH < 7.25 despite 1–2 hours of optimized BiPAP
• GCS falling (worsening encephalopathy)
• RR > 35 with deteriorating mechanics
• Hemodynamic instability
• Inability to tolerate mask
• PaCO₂ not improving or rising
• Excessive secretions / aspiration risk

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8. Maintenance Phase (Hours 2–24+)

1. Continuous monitoring: SpO₂, RR, HR, ETCO₂ if available, mental status
2. Wean FiO₂ to target SpO₂ 88–92% (COPD) or 92–96% (other causes)
3. ABG every 4–6 hours while on BiPAP
4. Treat underlying cause simultaneously:
   • COPD: bronchodilators, systemic steroids, antibiotics (if infective exacerbation)
   • CHF: diuresis, afterload reduction
   • OHS/OSA: weight management, positional therapy
5. Minimum 4 hours of continuous BiPAP recommended for acute exacerbation — do not interrupt for meals until stable

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9. Weaning from BiPAP

Step 1: Reduce IPAP by 2 cmH₂O every 2–4 hours
Step 2: Reduce FiO₂ toward 0.21–0.35 as tolerated
Step 3: Trial breaks (1–2 hours off BiPAP with supplemental O₂ via nasal cannula)
Step 4: Check ABG 30–60 min after removal of BiPAP
Step 5: Wean EPAP last — reduce to 4 cmH₂O before discontinuing

• pH > 7.35 consistently
• PaCO₂ at or near patient's chronic baseline
• SpO₂ > 90% on ≤ 4 L/min nasal cannula
• RR < 24/min
• Patient awake, cooperative, able to manage secretions

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10. Home NIV (Long-Term / Post-Discharge)

• High-intensity BiPAP (PS = IPAP−EPAP ≥ 15 cmH₂O, often IPAP 20–30 cmH₂O) improves outcomes
• Use S/T mode with backup rate and short inspiratory time for COPD
• Consider AVAPS (Average Volume-Assured Pressure Support) mode to maintain consistent tidal volumes despite disease progression
• NNT = 6 to avoid one readmission when home NIV added to LTOT in post-exacerbation persistent hypercapnia
• Aim for ≥ 4–5 hours/night usage minimum; longer is better

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Quick Reference Card

BIPAP FOR RESPIRATORY ACIDOSIS — QUICK GUIDE

INDICATION: pH 7.25–7.35, PaCO₂ > 45, ↑WOB, RR > 25

START:        IPAP 10–12 / EPAP 4–5 / FiO₂ 1.0
              Mode: S/T, RR backup 12–16/min
              I:E 1:2–1:3 (COPD), Short Ti, Short rise time

TITRATE:      ↑ IPAP by 2 cmH₂O q5–10 min for ↑WOB / ↑RR / ↑PaCO₂
              ↑ EPAP by 1–2 cmH₂O for refractory hypoxemia
              Max IPAP: 20–25 cmH₂O (up to 30 with expert review)
              Target PS (IPAP-EPAP) > 10–15 cmH₂O

ABG GOAL:     pH > 7.35, PaCO₂ ↓ gradually (<10 mmHg/hr)
              PaO₂ 55–80 (SpO₂ 88–92% in COPD)

CHECK ABG:    1 hr, 4 hrs, then q4–6 hrs / after each change

FAILURE:      pH < 7.25 at 1 hr, ↓GCS, ↑RR → INTUBATE

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What's Inside the Protocol (12 Sections, ~30 KB, A4 Format)