To the Editor:—

We read with interest the case report and the study of Sanchez-Guijo et al. , 1which describes the failure of patient-controlled analgesia pumps in a hyperbaric environment.

We have experience with this problem. Electronic infusion pumps function in a fashion similar to a patient-controlled analgesia pump. We have observed unexplained low blood pressure in some patients treated by hyperbaric oxygen therapy at 2.5 absolute atmospheres (ATA). These patients were receiving inotropic drugs (epinephrine or norepinephrine), either for therapy of septic shock or for air embolism after cardiac surgery. Alterations in pump (DPS Becton-Dickinson & Company, Franklin Lakes, NJ) performance were suspected. We conducted a series of pressurizations with two pump models: the DPS Becton-Dickinson (the most recent model) and the P 300 (Ivac Medical Systems, Basingstoke, UK). 2To minimize the risk of explosion, the pumps ran on a battery with less than 50 V, as recommended in French legislation. 3 

As in the case report, the DPS pump stopped between 2 and 2.1 ATA. With the P 300 pump, we compared the functioning in a normobaric and a hyperbaric environment at different flows and pressures. In these conditions, the P 300 pump was reliable; the three liquid crystal display screens did not blink, the alarm did not ring, the pump did not stop, and the released flows were equal at each pressure. This difference in reliability could be related to the airtightness of the DPS pump.

We believe that pumps could be used after being tested in hyperbaric chambers. There is a real need to establish international norms.

Sanchez-Guijo JJ, Benavente MA, Crespo A: Failure of a patient-controlled analgesia in a hyperbaric environment. A nesthesiology 1999; 91:1540–2
Vincenti-Rouquette I, Lévecque JP, Schiano P, Rousseau JM, Brinquin L: Evaluation du fonctionnement d’un pousse-seringue électrique en caisson hyperbare (abstract R 240). Ann Fr Anesth Reanim 1999; 18:S158
Journal official de la République Française du 2-4-70 (70-17) arrêté du 28-2-70: Conditions techniques relatives aux appareils de réanimation de la catégorie II