Figure 2. Case 1. Ambulance (pre-hospital) and selected hospital observations and blood gas analyses. VBG on arrival in the ED was suggestive of the presence of an acute respiratory acidosis (VBG1). Acute type II respiratory failure was later confirmed by ABG analysis (ABG1). The patient was commenced on BPAP. Glasgow Coma Scale (GCS) fell to 8–15 in the hours after admission and remained at that level overnight. The fall in systolic blood pressure (24: 00) responded to IV fluid administration. Overnight, a reducing oxygen need, as determined by titration of the FiO2 to the SpO2, allowed a gradual reduction in FiO2. Seventeen hours after admission, hypercapnia had resolved (ABG3) and the GCS had returned to baseline. The reason for the initial fall in respiratory rate, coincident with the application of the NRB (15: 38) by the ambulance crew, is not clear. The patient had not received any sedative medication at that time. Airway pressures (cmH20) delivered on BPAP and CPAP are in parentheses. RA – room air; BE – base excess. Reference ranges: ABG, pH (7.35–7.45), PaCO2 (35–45 mmHg), PaO2 (70–100 mmHg), HCO3– (21.0–28.0 mmol/l), BE (–2 to 3 mEq/l), lactate (0.4–0.8 mmol/l). VBG, pH (7.35–7.45), HCO3–, lactate. PCO2, PO2, BE, and SO2 measured on a VBG have no defined reference range.