Suctioning of artificial airways is a necessary procedure but is not without risk. Hypoxaemia is a recognised complication. Several small studies have suggested that closed suction catheters offer benefits over open suction because disconnection from the ventilator circuit is not required [1], thereby maintaining ventilation, F_IO₂ and PEEP. Other studies have sought to prove the maintenance of lung volume and cardiovascular stability with closed suction [2]. There is little evidence that closed suction systems offer clinical advantage over open suction in terms of arterial oxygenation. No published study had compared changes in PaO₂/F_IO₂ post suction. We performed a study in critically ill adults to identify any differences in PaO₂/F_IO₂ between closed and open suction for a given PEEP.

We obtained local ethical approval for a prospective, randomised, crossover study. Adult ventilated patients with 6.5 tracheal tubes or larger and arterial catheter were randomised by sealed envelope to receive closed or open suction first, then the converse. Head injured patients were excluded. The two standardised suction episodes were separated by 2 hours. Ventilatory parameters, PEEP and position were unchanged. After baseline ABGs, subjects received F_IO₂ 1.0 (hyperoxygenation) for 3 min prior to suctioning. The authors performed suctioning at 100 mmHg negative pressure. 14 F Ballard Trach-Care and Indoplas suction catheters were used. Two suction passes were made, timed to less than 30 s total. The patients were re-commenced on presuction ventilator settings and F_IO₂. ABGs were drawn at 3, 15 and 30 min post suction and analysed immediately.

Twenty-three patients were recruited. Thirteen subjects were receiving PEEP 10 cmH₂O or greater and 10 less than 10 cmH₂O. Arterial oxygenation data was expressed as PaO₂/F_IO₂ and compared using a paired t-test. One high PEEP subject was withdrawn from the study after developing hypoxaemia after open suctioning. No critical incidents were noted. In all patients sedation scores were the same for both episodes.

Hyperoxygenation produced an expected significant increase in PaO₂/F_IO₂ at time zero. At 3 min the sustained increase approached significance. At 15 and 30 min, in both high and low PEEP groups, there were no statistically significant differences from baseline with either closed or open suction (P = 0.140–0.763). No comparison is therefore possible between the two suction methods.

Three minutes of 100% oxygen prior to tracheal suction would seem to prevent hypoxaemia and provide increased oxygenation for up to 3 min after suctioning. This period of hyper-oxygenation is longer than that recommended by the AARC. After 3 min, oxygenation returned to baseline in both high and low PEEP patients and as there was no difference demonstrated, the two methods of suctioning cannot be compared. If hyperoxygenation is performed properly before suctioning, it is unlikely there would be any clinically significant differences between suction methods in terms of hypoxaemia.