Circuit leak with D-vapor.

To the Editor,

We are writing to inform you of a possibly hazardous condition that can occur with Drager D-vapor. Routine check of the Ohmeda Aestiva/5 machine (Datex-Ohmeda; GE Healthcare; Helsinki, Finland) with D-vapor (Drager, Baxter) and Tec-7 sevoflurane vaporizers did not detect any leaks.[1] An 8-year-old child received inhalational induction with sevoflurane. Laryngeal mask airway (LMA) was inserted and the desflurane vaporizer turned on. The gas analyzer showed decreasing end-tidal sevoflurane concentrations, but desflurane was not observed to be present. Partial collapse of the bellows was noted and attributed to a leak in the LMA. Surgery lasted for 20 min. In next case, induction was started but the gas analyzer did not show any end-tidal sevoflurane. Bag of Jackson-Reese circuit also collapsed. There was no clear audible leak in the anesthesia machine. At this stage, we noticed that a small knob that protrudes from the tip of the lever to fit in the slot at the top of the dial of D-vapor was missing, and the vaporizer was in unlock position. Closer look revealed a slight tilt of the vaporizer. D-vapor was then removed, and anesthesia maintained with sevoflurane with no leak in the circuit.

The locking mechanism of the D-vapor consists of a small knob at the tip of the lever, which fits on the slot at the top of the dial [Figure 1]. The knob moves along the slot in transport (T)-position and at the same time the pin protruding from the base of the locking lever rotates on a spring located in a small cavity between the two prongs onto which the vaporizer slots. This movement unlocks the dial and at the same time locks the vaporizer on to the machine. Further, the knob does not allow the vaporizer to unlock till dial settings are at T-position. In our case, on a previous evening, one of the anesthesia technician who was not familiar with the use of the D-vapor, used excessive force to lock the vaporizer on anesthesia machine in the T-position. This dislodged the knob from the lever. He further locked the vaporizer onto the machine with rotation of the lever through 45° only [Figure 2].

Figure 1

D-vapor in transport-position. Arrow indicates the knob at the tip of the locking lever

Figure 2

A knob absent from the tip of the locking lever (black arrow). Also note that the lever of the D-vapor is positioned somewhere in between the locked and the transport-position (white arrow)

As no knob was present to restrict the movement of lever over the dial, unrecognized brushing of the lever while switching on/off the sevoflurane vaporizer moved the lever of the D-vapor to unlock position next morning and allowed a tilt in vaporizer [Figure 3].

Figure 3

The dial can be rotated freely even when the D-vapor is improperly locked. Also note that knob is absent from the tip of locking lever (arrow)

Representative from the firm attributed the break to excessive force used during previous handling and asserted that instructions for use state that “D-vapor has to be handled with care”. This type of fault has not been reported previously.[234] Incidence reinforces the importance of carrying out checkout guidelines before the start of every case.[1] Vaporizer should not be changed/mounted on the machine during an ongoing case. However, if it becomes necessary to do so, leak test should be repeated again. Failure to do so is one of the most common causes of avoidable critical incidents.[5] Further, training of the operating room staff using the anesthesia system regarding the use of new equipment should be conducted when a new instrument is introduced into the practice of a hospital.