From the Guidelines
The patient should continue on NIV support with adjustments to improve CO2 clearance, as the current settings have led to some improvement in pH but persistent hypercapnia, and rehabilitation efforts should be continued to complement respiratory support. The patient's repeat ABG shows a compensated respiratory acidosis with improvement in pH from 7.384 to 7.458, indicating better compensation with elevated bicarbonate (43.3 from 37.6), but the pCO2 remains significantly elevated at 60.3 mmHg 1. The drop in pO2 from 119 to 86.5 and SpO2 from 99% to 96.9% suggests some reduction in oxygenation, though still adequate. According to the 2016 ESC guidelines, non-invasive positive pressure ventilation should be considered in patients with respiratory distress and started as soon as possible to decrease respiratory distress and reduce the rate of mechanical endotracheal intubation 1.
Some key points to consider in the management of this patient include:
- Monitoring of transcutaneous arterial oxygen saturation (SpO2) is recommended, and oxygen therapy should be used to maintain saturations between 85% and 90% 1
- Measurement of blood pH and carbon dioxide tension should be considered, especially in patients with acute pulmonary oedema or previous history of COPD 1
- Non-invasive positive pressure ventilation can reduce blood pressure and should be used with caution in hypotensive patients, with regular monitoring of blood pressure 1
- The goal is to gradually normalize pCO2 while maintaining adequate oxygenation and allowing the kidneys to slowly adjust bicarbonate levels to prevent post-hypercapnic alkalosis.
Reassess with repeat ABG in 24 hours to evaluate response to adjusted settings, and consider increasing inspiratory pressure by 2-4 cmH2O or increasing backup respiratory rate by 2-4 breaths/minute while monitoring patient comfort 1. Continue rehabilitation efforts as they complement respiratory support by improving respiratory muscle strength and overall functional capacity. Monitor for NIV-related complications such as skin breakdown, gastric distension, and eye irritation.
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.