Objective: To assess and compare the effects of respiratory physiotherapy and suction on deadspace volumes, carbon dioxide elimination (VCO(2)), end tidal CO(2) (ETCO(2)), and arterial partial pressure of carbon dioxide (PaCO(2)) in ventilated infants and children.
Design: Randomised crossover study. Participants received both treatments with a washout interval of more than 90 min.
Setting: Intensive tertiary care units, Great Ormond Street Hospital, London.
Patients: Eighty-seven fully ventilated children, requiring physiotherapy, with arterial lines in situ. Paired measurements were obtained in 81 patients, of whom 6 were excluded because of tracheal tube leak greater than 20%.
Interventions: Respiratory physiotherapy and suction.
Measurements and results: Data were collected April 1998-March 2000. The "CO(2)SMO Plus" respiratory monitor was used to calculate parameters before and 30 min after both interventions. Physiotherapy lasted longer and required more saline and catheters per treatment ( p<0.005). There were significant increases in physiological deadspace (VD(phys))/kg ( p<0.0001), alveolar deadspace (VD(alv))/kg ( p<0.0001) and VD(phys)/tidal volume (V(T)) ( p<0.05) following physiotherapy that were not observed following suction. There were no significant changes following either treatment with respect to airway deadspace (VD(airway)), VCO(2) or PaCO(2). Comparison of the mean differences following treatments indicated significant differences between physiotherapy and suction in terms of VD(phys)/kg ( p<0.005), VD(alv)/kg ( p<0.005), expired tidal volumes (V(TE)) ( p<0.05), mixed expired CO(2) (PeCO(2)) ( p<0.04) and ETCO(2) ( p<0.03).
Conclusions: Differences between physiotherapy and suction techniques probably accounted for their statistically distinguishable effects on deadspace. VD(phys) and VD(alv) may be more sensitive indicators of subtle changes in gas exchange and regional ventilation than VCO(2) or PaCO(2). However, interpretation of these outcomes is dependent on concurrent examination of the parameters from which they are derived.