From the Guidelines
The patient is at risk of hypercapnic respiratory failure and should be managed with a target saturation of 88-92% while awaiting further blood gas results, as per the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. The patient's repeat ABG shows a compensated respiratory acidosis with metabolic alkalosis, as indicated by the improved pH from 7.384 to 7.458, elevated pCO2 at 60.3 mmHg, and increased bicarbonate level from 37.6 to 43.3 mEq/L. However, oxygenation has decreased with pO2 dropping from 119 to 86.5 mmHg and SpO2 from 99% to 96.9%.
Key Considerations
- The patient is already on NIV round the clock and rehab, which is appropriate given the risk of hypercapnic respiratory failure.
- The BTS guideline recommends targeting a saturation of 88-92% in patients at risk of hypercapnic respiratory failure, which is the case here given the patient's elevated pCO2 and history of NIV use.
- The patient's declining oxygenation, as indicated by the drop in pO2 and SpO2, should be addressed by optimizing NIV settings to improve ventilation and oxygenation.
Management Recommendations
- Continue NIV support and optimize settings to better address CO2 retention and declining oxygenation.
- Consider increasing inspiratory pressure by 2-4 cmH2O if the patient tolerates it, or adjusting respiratory rate settings to improve ventilation.
- Monitor the patient's saturation closely and adjust oxygen therapy as needed to maintain a target saturation of 88-92%.
- Daily ABGs should be obtained to track progress, and underlying causes of hypoventilation should be addressed.
- The elevated bicarbonate level suggests the kidneys are compensating for chronic respiratory acidosis, but the high value may indicate an additional metabolic alkalosis component that should be investigated for causes such as diuretic use, vomiting, or hypokalemia, as recommended by the BTS guideline 1.
From the Research
Patient's Current Condition
The patient is currently on Non-Invasive Ventilation (NIV) round the clock and is also undergoing rehabilitation. The latest Arterial Blood Gas (ABG) results show:
- pH: 7.458 (previous value: 7.384)
- pCO2: 60.3 (previous value: 62.2)
- pO2: 86.5 (previous value: 119)
- Hco3: 43.3 (previous value: 37.6)
- Spo2: 96.9 (previous value: 99)
NIV Therapy and Ventilator Settings
According to the study 2, NIV therapy is used to provide positive pressure ventilation for patients, and there are protocols describing what ventilator settings to use to initialize NIV. However, the guidelines for titrating ventilator settings are less specific. The study developed an advisory system to recommend NIV ventilator setting titration and recorded respiratory therapist agreement rates at the bedside.
Adjusting Ventilator Settings
The study 3 suggests that the overall goal of NIV treatment is a successful reduction in CO2, which can be achieved by changing the following variables of the ventilator settings: increase in IPAP ± increase in back up respiratory rate ± use of assisted pressure controlled ventilation mode (APCV). The study 4 also details the effect of each setting and how the settings should be adjusted according to the individual patient.
Auto-Titrating Noninvasive Ventilation
The study 5 evaluated whether NIV with auto-titrating mode will decrease more PaCO2 within a shorter time compared to volume-assured mode in hypercapnic intensive care unit (ICU) patients. The results showed that the decrease in PaCO2 had been achieved within a shorter time period in the auto-titrating mode group.
Key Points to Consider
- The patient's pCO2 level has decreased from 62.2 to 60.3, indicating some improvement in ventilation.
- The patient's pO2 level has decreased from 119 to 86.5, which may require adjustment of the FiO2 setting.
- The patient's Hco3 level has increased from 37.6 to 43.3, which may indicate some degree of metabolic alkalosis.
- The study 6 highlights the importance of emergency physicians being knowledgeable regarding the indications and contraindications for NIV in emergency department patients with acute respiratory failure.
Some possible considerations for the patient's NIV therapy include:
- Adjusting the IPAP and EPAP settings to optimize ventilation and oxygenation.
- Monitoring the patient's ABG results and adjusting the ventilator settings accordingly.
- Considering the use of auto-titrating noninvasive ventilation to improve the patient's CO2 clearance.