From the Guidelines
The patient is at risk of hypercapnic respiratory failure and should be managed with a target saturation of 88-92% to avoid worsening hypercapnia, as per the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. The patient's repeat ABG shows a pH of 7.458, which is slightly alkalotic, but the pCO2 remains elevated at 60.3, indicating persistent hypercapnia. The bicarbonate level has increased from 37.6 to 43.3, suggesting ongoing renal compensation for chronic respiratory acidosis. The pO2 has decreased from 119 to 86.5, but the SpO2 remains adequate at 96.9%.
- Key considerations in managing this patient include:
- Continuing NIV support with possible adjustments to settings to further improve CO2 clearance, as the patient is already on NIV round the clock and rehab 1.
- Monitoring the patient's respiratory rate and heart rate, as tachypnoea and tachycardia are more common than a physical finding of cyanosis in hypoxaemic patients 1.
- Evaluating the patient for possible sleep apnea if not already done, as this could contribute to CO2 retention during sleep periods.
- Considering pulmonary consultation if CO2 retention persists despite NIV adjustments.
- Daily ABG monitoring is recommended to track progress and adjust oxygen therapy accordingly, aiming for a target saturation of 88-92% to avoid worsening hypercapnia 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.