We thank Reade and Corkeron for their comments related to our article [1]. We acknowledge that not all of our patients with an arterial line in place had data that allowed them to be included in our analysis. Unfortunately, not all our patients had recorded simultaneous blood pressure values for each method both on land at the specified point before departure and at the mid-point of the flight. In an attempt to maximise our data's accuracy, if the two pressure readings were not recorded within the same minute by the monitor, they were not included in our analysis. In addition, there were some cases where the monitor printout had been lost and some where NIBP was deliberately turned off to prolong battery life. It is important to note that these patients were not excluded due to monitoring failures but we accept this as a reflection of the retrospective nature of our study. We would expect a prospective study to have a higher inclusion rate.

With regard to modes of transport, 42 of the 56 patients in our study were moved in a Eurocopter 135, five in a military Sea King helicopter, eight in Beechcraft Kingair fixed wing aircraft and one in a road ambulance. The numbers in the study preclude analysis by transport mode. We would suggest that our original conclusions are valid for rotary wing transport and perhaps future work could look for similarities or differences in fixed wing aircraft.

Our service is reserved for level-2 or -3 patients, so by definition all of our patients are seriously unwell. The use of vasopressors is often used as a surrogate marker of illness or patient severity but we feel this can be an oversimplification. We would concur that the use of intotropes mandates intra-arterial monitoring.

In our study, the median APACHE score of patients was 19 (IQR 13–27). Of the 56 patients, 52 had a catheter sited in the radial artery, three in the femoral artery and one in the brachial artery. Fifteen patients were on a vasopressor and/or inotropic infusion at the time of transfer.

We accept our study has some limitations and that absolute blood pressure readings form only a part of any clinical decision making process. Without doubt a larger, prospective comparison of the monitoring techniques, perhaps with subgroup analysis for rotary versus fixed wing, controlled vs spontaneous ventilation and those receiving inotropes could provide further conclusions.


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