Respiratory complications are well recognised following cardiac surgery and have been shown to increase morbidity, mortality and length of stay. Previous studies suggest that delivery of positive airway pressure following extubation may be beneficial.
We hypothesised that the administration of prophylactic nasal high flow oxygen therapy (NHF) would improve pulmonary function after cardiac surgery.
A prospective randomised controlled trial was undertaken. Participants received either NHF (45L/min) or standard care from extubation to post-operative day 2. For both groups, oxygen concentration was controlled by the treating clinician to achieve a target oxygen saturation of? 93%. The primary outcome was SpO2/FiO2ratio? 445 on post-operative day 3. Sample size was calculated on a 15% absolute reduction in primary outcome -? = 0.05 and 90% power to detect treatment effect. Secondary outcomes included atelectasis score on chest x-ray; spirometry; readmission to ICU for respiratory causes; ICU and hospital length of stay; mortality and incidence of respiratory complications at day 28; oxygenation variables; use of adjunctive respiratory support therapies; escalation of respiratory support; adverse events and patient comfort during administration of oxygen therapy.
Over 14 months 340 patients were randomised. The number of patients with a SpO2/FiO2 ratio? 445 on day 3 was 78 (46.4%) in the NHF group vs 72 (42.4%) in the standard care group (p= 0.45; Odds Ratio 1.18 95%CI 0.77 to 1.81). PaCO2 was significantly reduced at both 4 hours post-extubation and at 0900 hours day 1 (NHF 39.7 vs standard care 41.3mmHg p=0.029 and NHF 38.2 vs standard care 39.7mmHg p=0.029 respectively). 47 patients (27.8%) allocated to NHF required an escalation in support compared to 77 (45%) standard care (p=0.001; Odds Ratio 0.47 95% CI 0.29 – 0.7). Subgroup analysis demonstrated that gender and BMI had no influence on the primary outcome.
The use of NHF was not associated with an increase in SpO2/FiO2 ratio on day 3 post-operative, although it was associated with a reduction in escalation of respiratory therapy and a significantly lower PaCO2.
Cardiothoracic and Vascular ICU, Auckland District Health Board
Auckland District Health Board
The University of Auckland