Randomised double blind study to investigate the effect of oxygen versus air driven nebulisers on partial pressure of arterial carbon dioxide in patients with an exacerbation of chronic obstructive pulmonary disease.

INTERVENTION: Oxygen driven nebuliser regimen (all administered on a single occasion): a. t=0‐15 min: 2.5 mg salbutamol by nebulisation, delivered by oxygen at a flow rate of 8L/min b. t=15‐20 min: Removal of nebuliser mask c. t=20‐35 min: 2.5 mg salbutamol by nebulisation, delivered by oxygen at a flow rate of 8L/min. CONDITION: Chronic Obstructive Pulmonary Disease (COPD) PRIMARY OUTCOME: PtCO2 (transcutaneous CO2) at t=35min*, adjusted for baseline. SECONDARY OUTCOME: Greatest PtCO2 change from baseline at any of the recorded time points between t=0 and t=35 minutes when the nebuliser is in place Heart rate at 5 minute intervals from t=0 to t=80 min. Measured via transcutaneous monitoring. Number of intervention terminations due to a rise in transcutaneous carbon dioxide level (PtCO2) greater than or equal to 10mmHg. PtCO2 is measured by transcutaneous monitor. PcapCO2 (fingertip or earlobe capillary gas sample) at completion of the second nebulisation (immediately prior to t=35min*), adjusted for baseline PcapCO2. Proportion of participants with greater than or equal to 4mmHg (physiologically significant) increase in PcapCO2 from baseline, measured by capillary blood gas. Proportion of participants with greater than or equal to 4mmHg (physiologically significant) increase in PtCO2 from baseline, measured by transcutaneous monitor. Proportion of participants with greater than or equal to 8mmHg (clinically significant) increase in PcapCO2 from baseline, measured by capillary blood gas. Proportion of participants with greater than or equal to 8mmHg (clinically significant) increase in PtCO2 from baseline, measured by transcutaneous monitor. Proportion of patients who required initiation of an increase in the flow of oxygen therapy during the regimen and observation periods. PtCO2 (transcutaneous carbon dioxide) at six minutes after the initiation of the first and second nebulisers (t=6 min and t=26 min). PtCO2 is measured through the skin via a transcutaneous monitor. PtCO2 at 5 minute intervals from t=0 to t=80 min. Measured via transcutaneous monitoring. SpO2 at 5 minute intervals from t=0 to t=80 min. Measured via pulse oximetry. The proportion of patients with a reduction in pH of greater than or equal to 0.06 from baseline. pH is measured using capillary blood gas. pH (Fingertip or earlobe capillary blood gas sample) immediately prior to t=35min, adjusted for baseline. INCLUSION CRITERIA: i. Ninety patients admitted to Hutt Valley or Wellington Regional Hospital medical inpatient wards with a primary admission diagnosis of an exacerbation of COPD. ii. Participants must have the mental capacity to allow them to provide written informed consent.