Suction catheter size: an assessment and comparison of 3 different calculation methods

Current American Association for Respiratory Care (AARC) clinical practice guidelines recommend a suction catheter to endotracheal tube ratio (SC/ETT) based on the external diameter of the SC and the internal diameter of the ETT. An SC/ETT ratio of < 50% is consistent with the current recommendation. We theorized that a more satisfactory assessment of SC/ETT ratio could be accomplished using volume or area formulas and expansion of diameter recommendations. Some respiratory care texts recommend an SC/ETT ratio that exceeds the clinical practice guideline standard.

We calculated the internal volume and cross-sectional area of various ETT sizes, the external volume and cross-sectional area of various SC sizes, and the SC/ETT ratios. We also measured negative pressures created by suction in a lung model, during multiple suction maneuvers.

Volume and area calculations provide an alternative method for determining the SC/ETT ratio. A volume or area ratio of 50% corresponds to a diameter ratio of 70%. Negative pressures during suctioning remain low at the new ratios, so a larger SC than current clinical practice guidelines still allows adequate air passage between the SC and ETT.

Our results support an alternative SC/ETT ratio when pairing SCs and ETTs.