Ventilatory function in children with severe motor disorders



This commentary is on the original article by Dawson et al. on pages 751–757 of this issue.

Children with severe motor disorders (SMD) have many different impairments and need a great deal of assistance from health care teams. Chiefly it is their movement disabilities we notice and keep trying to treat. Many of these children cannot verbally tell us how they are feeling and they are asleep most of the time. Because of these children's impairments we may think that this sleepy condition is a natural one. However, the respiratory condition of the children is mostly untested, with no knowledge about their blood gas tensions. If the oxygen tension (PO2) and the carbon dioxide tension (PCO2) are investigated you may get results lower than −1.96 SD and higher than +1.96 SD respectively. A sleepy child with SMD may be more wakeful if the PO2 increases and/or the PCO2 decreases. In our study of children with SMD it was shown that 12 of 18 children at baseline had a transcutaneous (tc)PO2 value below −2 SD, but when the children were treated with a Positive Expiratory Pressure (PEP)-mask the tcPO2 increased 1.0 kPa immediately afterwards.[1] When the children then used the PEP-mask regularly two to three times a day they were more wakeful, and ate and slept better than before they had used the PEP-mask. It is very important to highlight the supervision of the respiratory capacity of children with SMD. If it shows to be impaired the children should be given individually decided treatment like oxygen therapy, a PEP-mask, continuous positive airway pressure (CPAP), or bilevel positive airway pressure (BilevelPAP).

Dawson et al.[2] have measured oxygen saturation (SO2) and tcPCO2 in the blood of children with SMD and have shown that these children have a less stable ventilation during the night compared to typically developing children.

They have also measured tcPC02 but conclude that this measurement contains errors and in general is overestimating actual arterial (a) PaCO2.[2] Due to metabolic CO2 production in the living cells of the epidermis and circulatory disturbances that permit the gas to accumulate in the tissue, tcPCO2 is higher than PaCO2.[3] Therefore the same reference values as for arterial blood gas tensions cannot be used. The measurement of transcutaneous blood gas tensions is an indirect method with some error but can be effective if correct reference values are used.[4] There is a linear relationship between tcPCO2 and PaCO2, and tcPCO2 reliably follows the arterial values.[3] It is therefore incorrect to say that the different values between the transcutaneous and the arterial blood gas values are due to error, when reliable connections between them have been shown.

Dawson et al. have paid attention to the respiratory difficulties that children with SMD may have and recommend that the ventilatory function should be routinely assessed, which I strongly agree with. It is very important that these children get help not only with their movement disabilities but also with their respiratory difficulties, trying to decrease the risk of pulmonary hypertension and give them a good quality of life.