A five-year assessment of clinical incidents requiring transfer in a dental hospital day surgery unit


Dr Arun Chandu
Department of Oral and Maxillofacial Surgery
Royal Dental Hospital of Melbourne
720 Swanston Street
Carlton VIC 3053
Email: chandua@unimelb.edu.au


Background:  Previous studies regarding general anaesthesia related morbidity and mortality rates for dental surgery have taken the form of a retrospective survey. The Australian and New Zealand College of Anaesthetists also do not record morbidity and mortality for dental/oral and maxillofacial procedures. The aim of this study was to document the clinical incidents requiring transfer to another hospital and mortality.

Methods:  Records from patients transferred to another hospital after having treatment under general anaesthesia performed at the Royal Dental Hospital of Melbourne between 1 January 2005 and 31 December 2009 were prospectively reviewed.

Results:  There were 17 557 general anaesthesia procedures performed during the review period, including paediatric, special needs and minor oral and maxillofacial surgery procedures. The incidence of morbidity requiring transfer to a hospital with overnight stay facilities was 0.13%. There were no cases of mortality recorded. The most common complication was low oxygen saturation.

Conclusions:  The low incidence of morbidity seen is most likely attributed to the safety of modern anaesthesia and appropriate patient selection. Dentists and dental specialists performing general anaesthesia procedures should be aware of the complications that arise so that informed consent can be obtained. This study also provides a benchmark for general anaesthesia morbidity/mortality for dental procedures.

Abbreviations and acronyms:

Australian and New Zealand College of Anaesthetists


Royal Dental Hospital of Melbourne


General anaesthesia is an important tool in the armamentarium of dentists for providing optimum patient management. General anaesthesia provides major benefits to the patient and clinician, most notably a non-reliance on intraoperative patient cooperation, a lack of awareness of unpleasant procedures by the patient and improved oral access in the majority of cases. However, it is important for dentists and dental specialists who offer procedures under general anaesthesia to understand and know the complications that can occur as it forms the basis of informed consent and allows management of postoperative complications, as the dentist is usually the first person contacted in these circumstances.

Currently in Australia, the Australian and New Zealand College of Anaesthetists (ANZCA) safety of anaesthesia review has reported anaesthesia related mortality for all cases is approximately 1:53 000.1 Therefore, the choice of general anaesthesia needs to be a considered one. The excellent safety record of general anaesthesia in day stay oral and maxillofacial surgery is exemplified by studies that show a mortality rate that is much lower than that seen with inpatient hospital anaesthesia cases.2 However, this information must be evaluated in light of the fact that these day stay patients are generally healthy, and experience surgical and anaesthesia events that are much briefer and less complicated than those that are performed in the general hospital setting.2 D’Eramo recently retrospectively surveyed the Massachusetts Society of Oral and Maxillofacial Surgeons and reported a five-year mortality rate of 1:100 000.3 In addition, a morbidity rate of 0.5% was reported for this group for 19 separate categories of morbid events about which members were asked to report.3

The Royal Dental Hospital of Melbourne (RDHM) is a dental and oral and maxillofacial facility offering day stay general anaesthesia for paediatric dentistry, special needs dentistry and minor oral and maxillofacial surgery procedures. There is no facility for overnight stay and therefore stringent selection criteria for patients treated at this facility are required to minimize morbidity and mortality. The aims of this study were to review the morbidity requiring transfer to another hospital and mortality at the RDHM over a five-year period from 2005 to 2009.

Patients and methods

All patients identified by the prospective clinical incidents review for the day surgery unit at the RDHM between 1 January 2005 and 31 December 2009 were included for the study. The RDHM’s day surgery unit is comprised of three full-time operating theatres with the capacity to have a fourth theatre. It is equipped with a six-bed first stage recovery capacity and a six-bed second stage recovery capacity with an additional two single-bed rooms.

All patients planned for general anaesthesia by their treating clinician are required to fill out a pre-anaesthesia questionnaire regarding their medical history. A senior nursing staff member then reviews these questionnaires and a consultant anaesthetist reviews those patients that met certain medical condition criteria. If required, the consultant anaesthetist then seeks further information from the patient’s general practitioner, other hospitals or requests appropriate pathology tests to determine which patients are reviewed in an outpatient setting to determine their suitability for treatment at the RDHM. Patients not meeting the criteria for admission are then referred to a hospital with overnight stay facilities and the required medical support. Treating clinicians are also able to directly refer a patient to another hospital when they are aware the patient is unsuitable for treatment at the RDHM.

In regards to selection of patients, the RDHM sourced its guidelines for patient selection in conjunction with the Australian and New Zealand College of Anaesthetists guideline PS15 Recommendations for the Perioperative Care of Patients Selected for Day Care Surgery.4 Patients who fulfil any of the following criteria are deemed not appropriate for general anaesthesia at the RDHM and are referred to an inpatient facility in their local area. The broad exclusion criteria of patients are: (1) patients over 85 years of age; (2) insulin dependent diabetic patients; (3) patients with cardiac problems including recent myocardial infarction, coronary syndrome, past history of congestive cardiac failure, inability to walk up stairs, patients with significant cardiac valve pathology and patients requiring arterial lines or central venous pressure for monitoring purposes; (4) patients with significant functional or anatomical airway problems, including marked difficulty with intubation; (5) patients with bleeding disorders, e.g. haemophilia, severe von Willebrand disease; (6) renal dialysis patients; (7) patients with a history of asthma or chronic obstructive airway disease with repeated admissions to hospital; (8) patients with a weight of greater than 140 kg or BMI greater than 45 kg/m2; (9) patients suffering from quadraplegia; (10) patients with no escort home; and (11) patients who are unable to be supervised overnight.

There are numerous clinical incident reporting parameters relating to postoperative vital signs (heart rate, blood pressure, respiratory rate, pulse oximetry oxygen saturation) at the RDHM. When these criteria are met the first report is made to senior nursing staff and the anaesthetist, who implement the appropriate intervention to correct the abnormality. All patients requiring further intervention, including those requiring transfer, are recorded and the outcomes audited at regular audit meetings. The outcomes of transfer and the potential interventions to avoid transfer are followed up at this meeting.

Data collected for the present study included complications requiring ambulance transfer to a hospital with overnight stay facilities, the patient’s age, gender, weight, ASA score, treating specialty, medical comorbidities, type of anaesthetic used, medications used, type of procedure, complication encountered, treatment given and outcome at transferred hospital were all recorded. This study was approved by the Human Research Ethics Committee of the RDHM.

Results were presented in a descriptive fashion for descriptive analysis. Statistical analysis was performed using Statview version 5 (SAS, Cary, NC, USA). Comparison between and within groups was performed using Mann Whitney U tests and chi-squared tests between groups. A p value of less than 0.05 was taken as being significant.


There were 17 557 general anaesthesia procedures performed over the review period. Separately, there were also 2416 patients referred for pre-anaesthetic consultation during the same time period of which 139 patients did not meet the criteria for treatment at the day surgery unit and were therefore referred to other hospitals with overnight stay facilities for their treatment.

During the review, 22 cases (0.13%) of morbidity requiring transfer to a hospital with overnight stay facilities were reported. There were no cases of mortality noted postoperatively related to the procedure or general anaesthesia. The mean age of patients requiring transfer was 34.4 years (SD = 20 years, range 2.5 to 63 years). The mean weight of patients requiring transfer was 65 kg (SD = 28 kg, range 14.8 to 99 kg). The mean operating time was 70 minutes (standard deviation = 37.1 minutes, range 40 to 180 minutes). In regards to type of procedure performed, the majority were special needs dentistry or minor oral and maxillofacial surgery comprising 47.6% and 38.1% of the 22 cases respectively. Only 14.3% of cases were from paediatric dentistry.

The most commonly identified complication was low oxygen saturation postoperatively, with 6 recorded incidents. The second most common complication was drowsiness postoperatively, with 3 recorded cases (Table 1). Other complications were intraoperative tachycardia (1 case); intraoperative ST elevation (1 case); febrile and increased respiratory rate postoperatively (1 case); chest pain and breathlessness postoperatively (1 case); rising CO2 after failed intubation (1 case); increased respiratory rate and tachycardia postoperatively (1 case); postoperative abdominal pain (1 case); return to theatre after postoperative bleed (1 case); laryngospasm post-extubation (1 case); acute pulmonary oedema (1 case); postoperative leg pain (1 case); and one patient unable to return to his usual accommodation. There was one case where the postoperative complication was not recorded.

Table 1.   Patient factors
FactorsTotal % of complicationsTotal % ofpatients
  1. *Weights were not recorded for 2 patients on the inpatient record.

  2. **This also includes 3 patients under the age of 10.

ASA Score 127.3% (6/22)0.03%
ASA Score 236.4% (8/22)0.05%
ASA Score 331.8% (7/22)0.04%
ASA Score 44.5% (1/22)0.01%
Hypoxia27.3% (6/22)0.03%
Weight <65 kg*40.9% (9/22)0.05%
Weight >65 kg*50% (11/22)0.06%
Age <34.4 yrs**40.9% (9/22)0.05%
Age >34.4 yrs59.1% (13/22)0.07%
Endotrachael tube50% (11/22)0.06%
Laryngeal mask50% (11/22)0.06%
Medical comorbidities77.3% (17/22)0.10%
No medical comorbidities22.7% (5/22)0.03%

In regards to factors that may contribute to low oxygen saturation ASA grade, comorbidities, type of procedures or the type of tube were not found to be related to low oxygen saturation using chi-square tests. Using Mann Whitney U tests, patient age, weight or length of procedure were also found to be not related to low oxygen saturation rates.


General anaesthesia is an important tool in the armamentarium of dentists and maxillofacial surgeons. It is considered a safe procedure with a mortality rate of approximately 1:53 000.1 With an increase in accurate record keeping, audit and statistical analysis, both patients and medical staff have become aware that morbidity and mortality related to general anaesthesia does occur and that patient outcome can be improved as a result of clinical governance and benchmarking.

Complications and side effects following general anaesthesia can commonly occur. These side effects and their frequency as reported by the Royal College of Anaesthetists5 are included in Table 2. More specifically, these figures included nausea and vomiting (1 in 3); sore throat (1 in 5); chest infections (1 in 5 after abdominal surgery); postoperative confusional dementia (1 in 5 after major surgery); damage to teeth lips or tongue (1 in 4500) and life-threatening allergic reactions (1 in 10 000 to 1 in 20 000). Intraoperative awareness ranged from 1 in 1000 to 1 in 42 000 depending on risk factors present while the risk of death from general anaesthesia was found to be 1 in 100 000.5

Table 2.   Frequency and side effects of general anaesthesia
FrequencySide effects
1/10 to 1/100Post-anaesthetic nausea and vomiting, sore throat, hypotension, hypothermia, headache, itching, backache, aches and pains, bruising, soreness at injection site and confusion or memory loss
1/1000Chest infection, muscle pains, slowed breathing, damage to teeth, lips or tongue, worsening of an existing medical condition and awareness
1/10 000 to 1/200 000Damage to the eyes, serious allergy to drugs, equipment failure and death

The modern practice of general anaesthesia requires protocols and procedures that are now required within the operating theatre setting to minimize or reduce the risk of such complications or adverse outcomes. Outcomes are routinely audited as a requirement of both institutional governance and state/federal reporting. One may surmise that inability to follow correct procedure and guidelines may contribute to adverse outcomes occurring. However, the results of this study show that most adverse outcomes were in fact shown to not be predictable and were not related to ASA Category, comorbidities, age or any particular medication given.

There are many factors which may lead to adverse events in the operating theatre. The broad outline of categories includes: accidents – unexpected or chance events, that are unpredictable and may not be preventable; mistakes – the wrong decision on what to do; fixation errors – failure to revise a diagnosis or plan of action; protocols or procedures not followed; equipment failures or faults; non-reporting of events – allowing the same event to occur in multiple instances; inadequate knowledge; latent errors and last, but not least, stupidity. Most institutions now have systems in place to help report and limit potential errors, hopefully before they lead to any patient or operator morbidity or mortality.

The RDHM provides general anaesthesia services for the full range of dental surgery day stay procedures. The hospital is without an overnight stay facility and is not connected to a hospital with overnight stay facilities. This combination has the potential for significant negative outcomes. However, the low incidence of anaesthesia related morbidity seen in this study can most likely be attributed to appropriate patient selection. Even with the most stringent patient selection criteria and preoperative analysis in a day stay facility, there should always be contingency for transfer to a hospital with facilities for overnight admissions to manage unexpected outcomes.

The morbidity seen in this study correlates with data produced by the Royal College of Anaesthetists1,5 and previously published results.1,3,5,6 This would suggest the practices at the RDHM are in standing with current expected norms in relation to morbidity and mortality. The reporting guidelines for the RDHM include a large number of clinical indicators, which when acted on potentially prevent further deleterious events, and thus transfer to another institution.

The main morbidity requiring transfer in this patient group was low postoperative oxygen saturation or post-emergence hypoxaemia. Although this was not related to any other clinical factor, there are a number of different conditions that can contribute to this complication in dental or oral and maxillofacial surgery procedures under general anaesthesia. The most important of these is the possibility of aspiration, either blood or gastric contents, causing pulmonary collapse with shunting which may lead to pneumonia. Respiratory depression as a result of drugs used in general anaesthesia, particularly opiates and volatile agents are also important causes of hypoxaemia. One must also consider either partial or total upper airway obstruction. This may be related to a floppy upper airway as a result of drugs or muscle relaxants, foreign bodies such as retained throat packs, discoordination of laryngeal musculature or laryngospasm in total airway obstruction.

Most of the data relating to anaesthesia morbidity and mortality in dentistry and minor oral and maxillofacial surgery emanates from the USA and deals with ‘office general anaesthesia’, commonly referred to as intravenous sedation in Australia. Looking at this form of anaesthesia, Lytle and Stamper7 reported a mortality rate of 1 per 671 000 over a 20-year period while Mandal et al.8 in the UK reported that morbidity in the form of unplanned admissions was greater in patients above 80 years of age, a body mass index greater than 30 kg/m2, duration of surgery greater than 45 minutes and waiting time in the day surgery unit of greater than 2.5 hours. The unplanned admission rate from the study by Mandal et al.8 was 3.55% which was similar to what has been advocated by the Royal College of Surgeons of England.9 These rates are much higher than our current reported rate in this study of 0.13%. The importance of pre-admission assessment is highlighted by the study performed by Jastak and Peskin,10 who reported that 10 out of 13 cases of morbidity were considered avoidable either by use of appropriate patient selection criteria or, most particularly, by timely monitoring and effective response to adverse occurrences. Looking at mortality with inpatient general anaesthesia, Lee and Roberts reported no cases of mortality for 22 615 paediatric patients undergoing dental procedures over a 10-year period.11 A number of studies have confirmed the findings of the present study that the main cause of morbid events tends to be hypoxia secondary to airway obstruction or respiratory depression.8,11

It needs to be stressed that dentists and dental specialists utilizing general anaesthesia within the hospital setting need to be aware of the potential complications that can arise which can influence the outcome of the patient. Knowledge of the risks and alternative anaesthetic management strategies are important in regards to informed consent of the patient prior to hospitalization. Also important is a preoperative assessment of risk, which may be ascertained by a patient history of general anaesthesia. If no general anaesthesia procedures have occurred, then questions assessing the family history are also important to exclude such disorders as malignant hyperthermia or other familial reactions to anaesthesia. If significant medical issues are found on taking a comprehensive medical history, a preoperative work-up which may require blood tests, a 12-lead ECG or even a chest X-ray may be required. Preoperative consultations with the anaesthetist or specialist physicians may also be required, particularly in older patients with special needs. Knowledge of the postoperative sequelae of a dentistry performed under general anaesthesia is also important as the treating dentist or specialist often is the first port of call with a patient with problems, particularly dental or surgical, therefore such practitioners also need to be contactable out of hours.

In conclusion, the present study has found a low morbidity rate requiring transfer to another hospital with a day surgery facility providing specialist dentistry and oral and maxillofacial services. As previously published data regarding these forms of anaesthesia in this setting is low, this study can be used in regards to benchmarking similar facilities providing similar forms of treatment in Australia.