ABG Analysis - Mrs. Panchavarnam, 60F

Step 1: Interpret the ABG

• pCO2 is grossly elevated (89.3) with pH 7.27 - this is NOT fully compensated (in pure chronic respiratory acidosis, pH would be near normal ~7.34-7.36 for a pCO2 this high)
• The elevated HCO3 suggests a chronic component with renal compensation, but the low pH indicates an acute decompensation on top

Step 2: Check Compensation

• Expected HCO3 = 24 + [(89.3-40)/10 × 3.5] = 24 + 17.2 = ~41 mEq/L
• If HCO3 is around 40, this is consistent with chronic compensation, meaning the acidemia is from acute worsening of ventilation

Step 3: Note the Electrolyte Abnormalities

What You Should Do

IMMEDIATE PRIORITIES

• First line: Non-Invasive Ventilation (NIV) - BiPAP - indicated for acute hypercapnic respiratory failure in awake, cooperative patients without hemodynamic instability. Start with IPAP 12-14 / EPAP 4-5 and titrate. BiPAP will drive down pCO2 and improve pH.
• If NIV fails or patient is drowsy/uncooperative: Endotracheal intubation + mechanical ventilation - protect the airway and take control of ventilation. Ventilate to bring pCO2 down gradually (see caution below).

Do NOT correct pCO2 too rapidly. In a patient with chronic compensation (high HCO3), sudden normalization of pCO2 to 40 will cause severe metabolic alkalosis, cerebral vasoconstriction, arrhythmias, and seizures. Target pCO2 correction toward the patient's baseline (likely ~55-65 mmHg), not 40 mmHg. - Harrison's Principles of Internal Medicine 22E

• pO2 is 136 (already on O2) and sO2 is 98%, so oxygenation is fine
• Target SpO2 88-92% in a COPD/chronic hypercapnia patient - high-flow O2 can suppress hypoxic drive and worsen CO2 retention
• Use a Venturi mask for controlled FiO2 delivery (24-28%)

• COPD exacerbation (most common cause of acute-on-chronic hypercapnic failure)
• Severe asthma
• Pneumonia
• Sedative/opioid overdose suppressing respiratory drive
• Neuromuscular weakness
• Obstructive sleep apnea decompensation

• Nebulized bronchodilators (salbutamol + ipratropium)
• Systemic corticosteroids (prednisolone 40 mg/day or IV methylprednisolone)
• Antibiotics if infective trigger (amoxicillin-clavulanate or doxycycline)

CORRECT THE ELECTROLYTES

• Dangerous in the context of acidosis (K+ may shift further)
• IV/oral potassium replacement (KCl 40-80 mEq/day, monitor levels)
• This also important: Harrison's notes that Cl- and K+ must be supplied to allow kidneys to excrete excess HCO3 once hypercapnia resolves

• Both uncorrected and pH-corrected ionized calcium are low
• Risk of tetany, seizures, arrhythmias
• IV calcium gluconate if symptomatic; oral calcium + Vitamin D for ongoing replacement

• Likely dilutional or from secretion of ADH in respiratory failure
• Fluid restrict; will usually correct with underlying treatment

MONITORING

• ABG repeat in 30-60 minutes after starting BiPAP/ventilation
• Continuous SpO2 and cardiac monitoring (arrhythmia risk with hypokalemia + acidosis)
• Electrolytes every 4-6 hours
• Urine output

Summary of Action Plan

Clinical note: This is a medical emergency. The pCO2 of 89.3 with a pH of 7.27 is life-threatening if not reversed promptly. BiPAP should be initiated without delay if the patient is awake and protecting their airway.

BiPAP Settings for This Patient

Mode

• Supports patient-triggered breaths AND delivers timed backup breaths if patient apneas
• This is the standard mode for acute hypercapnic failure

Initial Settings

How to Titrate After Starting

1. Start IPAP at 10-12 cmH2O, EPAP at 4-5 cmH2O
2. Every 5-10 minutes, increase IPAP by 2 cmH2O increments
3. Target IPAP of 18-25 cmH2O - this patient has pCO2 of 89.3 and needs high-intensity BiPAP
4. Stop increasing if patient is intolerant, has air leaks, or reaches max tolerance
5. Do NOT increase EPAP - raising EPAP worsens dynamic hyperinflation in COPD

Evidence from Fishman's Pulmonary Diseases shows that high-pressure NIV (IPAP-EPAP ≥ 15 cmH2O) is what drives CO2 clearance and improves outcomes in COPD hypercapnia. Starting low and titrating fast is the strategy.

Why These Numbers?

What to Check at 30-60 Minutes

• Repeat ABG - expect pH to rise toward 7.30+ and pCO2 to fall by 10-15 mmHg
• If no improvement after 1-2 hours - escalate to intubation
• Watch for: air leaks around mask, patient agitation, worsening drowsiness (sign of CO2 narcosis - intubate)

Mask Choice

• Full face mask (oronasal) preferred in acute setting - better seal, prevents mouth leak
• Nasal mask is second option if patient is claustrophobic

Type 1 vs Type 2 Respiratory Failure

The Core Definition

Your Patient's ABG - Type 2

• pO2 is 136 because she is already on supplemental oxygen
• Without oxygen, her pO2 would likely be low too (she may have a mixed picture)
• The dominant problem is CO2 retention = Type 2

Type 1 - Hypoxemic Respiratory Failure

Type 2 - Hypercapnic Respiratory Failure (YOUR PATIENT)

Simple Memory Aid

Type 1 = O2 problem - lungs can't absorb oxygen (shunt/V/Q mismatch) Type 2 = CO2 problem - lungs/pump can't expel CO2 (hypoventilation)

Why This Matters for BiPAP

• IPAP (inspiratory pressure) = pushes air in, increases tidal volume = washes out CO2
• EPAP (expiratory pressure) = keeps alveoli open = improves oxygenation
• The IPAP-EPAP difference (Pressure Support) is what drives CO2 clearance - this is why you need a high IPAP target of 20-25 cmH2O for a pCO2 of 89

Your Current Ventilator Settings (PC-BiPAP - Dräger Savina)

🚨 Two Active Alarms - Urgent Issues

1. APNEA alarm (Image 1)

• MV = 0.00 L/min - the patient is NOT breathing at all
• Machine has switched to Apnea ventilation backup (Apn. vent. = ON)
• Apnea backup settings: VTapn 470 mL, RRapn 12 bpm
• This means the patient is apneic - check patient immediately
• Causes: CO2 narcosis (pCO2 89 can cause sedation), sedatives, obstruction, mask leak

2. VT High alarm (Image 2)

• MV = 0.23 L/min - still very low, nearly apneic
• Tidal volume is exceeding the upper alarm limit
• This is the machine trying to deliver the apnea backup tidal volume

What You Should Do RIGHT NOW

• Is she conscious? Responding?
• Is the mask properly seated? Air leak = no chest rise = apnea alarm
• Check SpO2 and respiratory effort

• High FiO2 in a chronic CO2 retainer (COPD) suppresses hypoxic drive and worsens hypoventilation - this may be WHY she is apneic
• Reduce FiO2 to 28-35% and titrate to SpO2 88-92%

• Current Pinsp = 15 mbar, PEEP = 6 → Pressure Support = 9 mbar only
• For a pCO2 of 89, you need PS ≥ 15-20 mbar
• Increase Pinsp to 20-22 mbar (while keeping PEEP at 6)

• Consider CO2 narcosis - she may need intubation and invasive mechanical ventilation
• Check if any sedatives were given
• Prepare for intubation if she does not respond to stimulation

Summary of Recommended Settings Changes

The most likely reason for apnea here is the high FiO2 (60%) suppressing her respiratory drive in a chronic CO2 retainer. Bring it down immediately and reassess.

Dräger Savina Ventilator - Complete Overview

What Is It?

Key Features

All Available Ventilation Modes

Volume-Controlled Modes

Pressure-Controlled Modes

Spontaneous / Assisted Modes

Understanding PC-BiPAP (Your Current Mode)

High pressure phase (Pinsp) ──────────────┐
                                           │  Ti (1.3s)
PEEP level ────────────────────────────────┘──────────────
                          ↑                ↑
                    Patient can       Patient can
                    breathe here      breathe here

Key formula: Tidal Volume is determined by Pinsp - PEEP (called the driving pressure). The bigger this difference, the larger the breath and the more CO2 is cleared.

Special Safety Feature - Apnea Ventilation (what fired on your patient)

• If the patient stops breathing beyond a set apnea time, the machine automatically switches to volume-controlled backup ventilation
• Your settings: VTapn = 470 mL, RRapn = 12 bpm
• This fires the red "Apnea" alarm you saw
• It is a life-saving safety net, but it tells you the patient has stopped triggering the machine

The "Calibrate O2 Sensor Manually" Message

1. Go to Sensors menu (visible on right side of screen)
2. Follow the on-screen calibration steps with room air (21% O2)
3. This ensures FiO2 readings are accurate - important for your patient

Bottom Line for Your Patient

1. FiO2 too high (60%) - reduce to 28-35%
2. Pinsp too low (15) - increase to 20-22 mbar to clear pCO2 of 89