Root-cause analysis of an airway filter occlusion: a way to improve the reliability of the respiratory circuit

P. Garnerin*,1,2, E. Schiffer1, E. Van Gessel1 and F. Clergue1

1 Anaesthesiology Division and 2 Quality of Care Unit, Geneva University Hospitals, Rue Micheli-du-Crest 24, CH-1211 Geneva 14, Switzerland*Corresponding author

Accepted for publication: May 30, 2002


    Abstract
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Background. To show how root-cause analysis can identify system-level factors causing critical incidents and accidents, we present an investigation of the occlusion of an airway filter during anaesthesia.

Method. The investigation was based on a framework specifically developed for the analysis of medical accidents. This framework helped to identify the chronology and outcome of the case, the care management problems and the factors that led to the event. Information was obtained by interviewing the anaesthesiologist in charge of the patient.

Results. Occlusion was not recognized because the filter was hidden under the drapes and below the patient’s head. To reduce the frequency of this event, we recommend that filters should be visible, placed above the level of the patient’s body, or mounted on the expiratory circuit, at a distance from patient’s airway.

Conclusions. To allow appropriate corrective actions, critical incidents and accidents should be systematically investigated using root-cause analysis.

Br J Anaesth 2002; 89: 633–5

Keywords: audit, root cause analysis; ventilation, respiratory circuit; risk


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Root-cause analysis is a structured and systematic approach used to identify key system-level factors that contribute to the occurrence of critical incidents and accidents. Even though this approach has proved instrumental in understanding major industrial breakdowns, root-cause analysis is seldom used in medicine to study clinical adverse events.

To illustrate the potential of such an approach, we describe the root-cause analysis of a case of filter occlusion by water and secretions during anaesthesia that could have been fatal.


    Methods and results
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Critical incidents and accidents are caused by a combination of equipment, active and latent failures. Active failures are errors or violations committed by operators directly involved in the provision of care (e.g. administration of the wrong drug). Latent failures or root causes depend on decisions made at the upper echelons of an organization and correspond to system problems (e.g. vials look alike).1

To identify the root cause of the event, we used a framework developed for the investigation of medical accidents.2 We first established the chronology and the outcome of the case. We then identified care management problems, which were defined as either equipment failures or active failures represented by deviations beyond safe limits. Finally, we listed and categorized the different factors that facilitated the occurrence of these problems. A contributory factor was considered specific when it was related to chance and general when it was a permanent feature of the system and as such represented a root cause of the incident. Information was obtained by interviewing the anaesthesiologist in charge of the case.

To devise corrective actions, we relied on two principles that are commonly combined when managing risks, namely prevention and absorption.3 Prevention aims at removing the root causes which increase the opportunity of equipment or active failures whereas absorption is intended at eliminating root causes that hinder the early identification and correction of active failures.

Chronology and outcome
A 13-yr-old boy with maxillo-facial Cacrum Oris (Noma) was to have elective plastic reconstruction. Patient history, examination, and laboratory findings were otherwise normal.

During surgery, the respiratory system consisted of a ventilator connected via a breathing tubing to an airway pressure and gas analyser and a Y-piece, fitted to a BB 25 airway filter (Pall Medical, Ann Arbor, MI, USA). The filter was connected to a catheter mount tubing connector and a tracheal tube. The ventilator was checked before surgery. To provide convenient access to the surgical site, the filter was positioned below the patient’s head under the drapes.

The beginning of the procedure was uneventful but after 2 h, the peak airway pressure progressively increased, exceeding the 30 cm H2O threshold. Both ventilator and analyser pressure alarms sounded. The junior anaesthesiologist in charge of the case immediately increased the inspired oxygen concentration. Noisy chest sounds were heard on auscultation, which decreased after large amounts of secretion were removed using a suction catheter inserted into the tracheal tube. However, the peak airway pressure remained greater than 40 cm H2O. Four minutes after the alarms were triggered, inflation of the patient’s lungs became impossible. Oxygen saturation decreased to 80%. When the junior anaesthesiologist connected a self-inflating bag directly to the tracheal tube, immediate lung ventilation was possible. The ventilator and the respiratory circuit were then replaced and the tracheal tube was reconnected using the same analyser, filter, and tubing connector. Ventilation remained impossible. Finally, occlusion of the filter by water and secretions was identified and the filter was changed. The patient recovered quickly and without sequel.

Identification of care management problems and contributory factors
In this critical incident, two care management problems occurred, namely an equipment failure (the occlusion of the airway filter), and its delayed identification. These two events, the combination of which led to severe hypoxaemia, were facilitated by a set of specific or general contributory factors presented in Table 1.


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Table 1 Synoptic summary of the critical incident. S=specific; G=general
 
Corrective actions
To increase the ability of anaesthesiologists to detect filter occlusion, this critical incident was presented at several meetings and the problem was described in the information bulletin of our division. In addition, it was recommended that the airway filter always be visible. Finally, during training sessions on the management of airway and respiratory circuit occlusions, more emphasis was put on the risk of filter clogging.

To prevent liquids from accumulating in the filter, it was decided that the filter should be routinely placed above the lung level or, when this was not possible it should be mounted on the expiratory circuit at a distance from patient’s airways.

New instructions for use of filters were printed on posters and displayed in all operating rooms.


    Comment
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
This critical incident could be considered as the consequence of the anaesthesiologist’s failure to apply basic knowledge. However, similar difficulties have been observed elsewhere. In two cases of mechanical occlusion of the respiratory circuit,4 5 the first hypothesis made by anaesthesiologists with regard to the origin of restricted ventilation was bronchospasm. The true cause of the problem was only discovered by disconnecting the patient from the respiratory circuit and obtaining an appropriate oxygenation using a self-inflating bag.

In most cases, the problem is not the individual but the system. Our analysis shows that occlusion was possible because the filter had a hydrophobic membrane and was placed below the patient’s head. The ability of the anaesthesiologists to detect airway filter occlusion was limited by the lack of information on the risk associated with the use of this device and by its position under the drapes. The identification of latent failures that are organizational root causes of accidents or critical incidents is, therefore, essential for devising appropriate corrective actions.

At first glance, our strategy, which combines prevention and absorption, could be perceived as convoluted. Compared with the prevailing approach of risk management which, as noted by Cooper,6 ‘depends almost solely on the anaesthetist’s ability to react instinctively and flawlessly every time a problem arises’, this method is much more efficient. Indeed, if Po is the probability of airway filter occlusion and Pr the probability of not recognizing in time the problem, PoxPr will be the probability Pc of the critical incident. As a consequence, any x-fold decrease in both Po and Pr will have a multiplicative effect and result in a x2-fold decrease of Pc whereas a x-fold decrease in Pr alone will only cause an equivalent decrease in Pc.

Given the usefulness of root-cause analysis with regard to patient safety, it is clear that we should systematically investigate critical incidents and accidents. However, reporting and analysis of such events on a routine basis and setting up appropriate corrective actions will require considerable cultural and organizational changes. Is there any alternative?


    Acknowledgement
 
We are indebted to PALL (Schweiz) AG for providing the posters presenting the filter instructions for use.


    References
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Reason J. Understanding adverse events: human factors. Qual Health Care 1995; 4: 80–9[Abstract]

2 Vincent CA, Taylor-Adams S, Chapman EJ, et al. A Protocol for the Investigation and Analysis of Clinical Incidents. London: University College London/Association of Litigation and Risk Management, 1999

3 Leape LL. Error in medicine. JAMA 1994; 272: 1851–7[ISI][Medline]

4 Norman PH, Daley MD, Walker JR, Fusetti S. Obstruction due to retained carbon dioxide absorber canister wrapping. Anesth Analg 1996; 83: 425–6[ISI][Medline]

5 Aarhus D, Soreide E, Holst-Larsen H. Mechanical obstruction in the anaesthesia delivery-system mimicking severe bronchospasm. Anaesthesia 1997; 52: 992–4[ISI][Medline]

6 Cooper JB, Newbower RS, Kitz RJ. An analysis of major errors and equipment failures in anesthesia management: considerations for prevention and detection. Anesthesiology 1984; 60: 34–42[ISI][Medline]





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