A first portable medical device is adapted for use in an interlocking system for interlocking the first medical device to a second medical device. The first device includes a housing having opposite sides, a selective element, a blocking element, and a clamp mechanism. At least one of the opposite sides includes a matable element to detachably attach a second medical device. The selective element restricts the attachment of the second device to only one side of the first device. The blocking element prevents a third medical device from attaching to the first and second devices once the first and second devices are attached. The clamp restricts the attachment of the second device to only one side of the first device when the clamp is attached to a support member. The clamp permits slide-ratcheting axial movement of a clamp shaft.