Cause of Device-Related Incident
Device factors; External factors; Support system failures; User errors

Clinical Specialty or Hospital Department
Anesthesia; Clinical/Biomedical Engineering; Emergency Medicine; Obstetrics and Gynecology; OR / Surgery; Pulmonary / Respiratory Therapy

Device Factors
Improper modification

Document Type
Hazard Reports

External Factors
Medical gas and vacuum supplies

Mechanism of Injury or Death
Overdose; Suffocation; Underdose; Wrong drug

Support System Failures
Lack or failure of incoming and pre-use inspections

Tampering and/or Sabotage
*Not stated

User Errors
Improper connection

UMDNS
Analgesia Units, Inhalation [16-953]; Fittings/Adapters, Pin-Indexed [16-795]; Fittings/Adapters, Pneumatic, DISS [11-727]; Medical Gas Cylinders [16-501]

Nonstandard User Modification of Gas Cylinder Pin Indexing



Hazard [Health Devices Jul-Aug 1989;18(7-8):289-90]

Problem

A member hospital reported that a nitrous oxide cylinder was connected to the wrong gas cylinder yoke after the hospital's machinist had modified the yoke's pin indexing for use with cylinders containing Entonox, a mixture of oxygen and nitrous oxide used for analgesia. However, the machinist had drilled the hole intended for the yoke's single large pin completely through. Although some manufacturers have also made the error of drilling pinholes all the way through the yoke, that was not the case in this incident.

Discussion

When a user attempted to install the nitrous oxide cylinder, which has holes to accept two small pins, the holes in the cylinder did not align with the yoke's large pin. As the user tightened the screw clamp, the large yoke pin was pressed into the large hole in the yoke; the user believed that the yoke pin was penetrating the hole in the cylinder header. Administration of pure nitrous oxide can produce hypoxia and subsequent death. Fortunately, the misconnection was discovered before the equipment was used with a patient.

The Compressed Gas Association's (CGA) Standard V-1 establishes dimensions for indexing and specifies a pin projection as well as other dimensions for the yoke. According to the standard, the hole into which a pin is installed should be blind (i.e., have a specified depth). The International Organization for Standardization (ISO) Standard 407 allows through-holes for pins; however, this standard permits only those designs that require proper mating before they can be tightened (e.g., gated yokes) and thus present no potential for damage when the pins do not correspond to the holes. Although the hospital machinist may have carefully positioned the hole when he made the modification in this incident, he did not conform to the depth specification.

Recommendation

Conform to standard specifications in their entirety when modifying or making gas fittings.

UMDNS Terms

  • Analgesia Units, Inhalation [16-953]
  • Fittings/Adapters, Pin-Indexed [16-795]
  • Fittings/Adapters, Pneumatic, DISS [11-727]
  • Medical Gas Cylinders [16-501]

Cause of Device-Related Incident

Device factor: Improper modification

User error: Improper connection

External factor: Medical gas and vacuum supplies

Support system failure: Lack or failure of incoming and pre-use inspections

Mechanism of Injury or Death

Overdose; Suffocation; Underdose; Wrong drug


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