Effects of ETT obstruction and suction pressure
| Open suction procedure (ETT disconnected) | Before suction | Moderate suction | Maximum suction | |
| PMEAN MA (cm H2O) | PMEAN MA (cm H2O) | PMEAN MA (cm H2O) | ||
| ETT 9 | Catheter 12 Fr | 0 | −0.5 | −1.5 |
| Catheter 14 Fr | 0 | −1 | −2 | |
| Catheter 16 Fr | 0 | −2 | −3 | |
| Br.scope 16 Fr | 0 | −1.5 | −2 | |
| ETT 8 | Catheter 12 Fr | 0 | −1 | −2 |
| Catheter 14 Fr | 0 | −2 | −4 | |
| Catheter 16 Fr | 0 | −3 | −7 | |
| Br.scope 16 Fr | 0 | −2 | −5 | |
| ETT 7 | Catheter 12 Fr | 0 | −2 | −5 |
| Catheter 14 Fr | 0 | −4 | −10 | |
| Catheter 16 Fr | 0 | −9 | −23 | |
| Br.scope 16 Fr | 0 | −8 | −18 | |
The effects of altered ETT diameter relative to suction devices and vacuum pressures during open suction procedure are shown. Pressures are measured distal to ETTs, with the ETT disconnected from the test model. Pressures did not change during 30 s of suctioning or when recording was repeated; pressure changes induced by moderate and maximum suction were significant for each permutation. 16 Fr catheters are normally not used clinically in ETT 7 mm ID, but the measurement is included for comparative reasons.
ETT, endotracheal tube.