Colonoscopy is an efficient, invasive, and commonly used diagnostic tool with promising therapeutic capacity. Common colonoscopy-related complications include prolonged pain and distension, and rarely draw medical attention or lead to hospitalisation. Severe complications, including bleeding and perforation, are potentially life-threatening and require urgent management. Although death is uncommon, occurring in no more than 3 per 10 000 procedures, the incidence of post-polypectomy bleeding and perforation ranges from 1.6 to 14.8 and 0.2 to 1.0 per 1000 procedures, respectively.1 2 3 4 5 6 It is difficult to accurately benchmark direct colonoscopy-related complications due to the different outcome measure definitions used in studies. For example, some studies include immediate complications only, while others extend the complication period to 7 or 30 days, and some studies include an extensive list of complications while others include only bleeding and perforation.1 2 5 7 8 9 10 Furthermore, the efficacy and safety of the procedure vary across clinical settings and the targeted populations. With no available local data, consensus for complication incidence remains inconclusive.

Intravenous sedation is routinely used during colonoscopy to minimise the discomfort and pain associated with the procedure. Endoscopists are equipped to give sedatives and to monitor their side-effects, but anaesthetists are often invited to provide monitored anaesthetic care (MAC) when the patient is considered to be at high risk for complications, for instance, older patients and those with multiple co-morbidities are particularly vulnerable to complications. Systemic complications vary from prolonged drowsiness to fatal events such as cardiovascular or cerebrovascular events. Cardiovascular events following sedation, such as hypotension and myocardial infarction, during colonoscopy have been reported to range from 0.1 to 59.1 per 1000 procedures. Cerebrovascular events such as stroke range from 0.1 to 1.3 per 1000 procedures.3 6 10 The outcome variables are highly heterogeneous, for example, Nelson et al’s study3 included myocardial infarction, vasovagal event, and arrhythmia in the cardiovascular incidents, while Ma et al’s study10 recorded hypotension only.10 Some endoscopists opted to study complications related to the use of carbon dioxide (CO₂) insufflation and absence of sedative use.11 12 13 This study aimed to record all complications systematically and to determine the relevant risk factors.

This prospective study collected data for all colonoscopies done from 1 June 2011 to 31 May 2012 at the Endoscopy Centre of the Hong Kong Sanatorium & Hospital (HKSH), which is a private hospital in Hong Kong. Prior to colonoscopy, patients were invited to give their written consent for their participation in the study, including for the 30-day follow-up telephone interview. The Hospital Management Committee involving the Research Ethics Committee of the HKSH approved the study.

The complications were recorded by nurses on a standard form during and immediately after the procedure. The standard audit forms for immediate and delayed colonoscopy complications were designed by a research doctor, with the most common complications based on literature review.

The immediate complications audit form included patients’ demographics, use of sedation/analgesic/antispasmodic, use of MAC, gross indications for colonoscopy (therapeutic or diagnostic), type of therapeutic procedures performed such as polypectomy, the reason for incomplete colonoscopy (caecum intubation failure), quality of bowel preparation (adequate – good/adequate or not – fair/poor, which was rated by the endoscopist), and the use of CO₂ insufflation. Complication data were divided into systemic and colonoscopy-related complications. For systemic complications, we captured data for nausea/vomiting, hypotension (systolic blood pressure <100 mm Hg), bradycardia/tachycardia (heart rate <50 to >100 beats/min), vasovagal fainting, and other cardiovascular or cerebrovascular events. For colonoscopy-related complications, data for perforation, persistent pain/discomfort, abdominal distension, and haemorrhage were gathered.

Delayed complications were defined as the above events happening from the day after the initial colonoscopy to the 30th day that required readmission or admission to other hospitals. For those readmissions, we automatically inspected the records for the reasons and interventions if the readmissions were complication-related. Otherwise, trained student nurses or a research doctor telephoned all consented participants to interview for the 30-day complications using the delayed complication audit form. A participant was declared lost to follow-up after three telephone attempts. The student nurses were trained by senior nurses and the research doctor with standard instructions.

Data analysis was performed by the Statistical Package for the Social Sciences (Windows version 14.0; SPSS Inc, Chicago [IL], US). Descriptive statistics (mean, percentage, incidence, and/or 95% confidence interval [CI]) were used to display the characteristics of the sample. For those complications with zero events, only 95% CIs were given.14 Backward logistic regression analyses were performed to draw prediction models for immediate complications, including colonoscopy-related complications or systemic complications, and overall complications, including immediate and delayed complications, from the sample; entering variables were chosen from age, sex (male or female), use of MAC (yes or no), sufficiency of bowel preparation (adequate or not), and completion of colonoscopy (yes or no) according to the results of the univariate analyses by Pearson Chi squared tests of all potential independent variables, with a significance level set at 10%; variable inclusion in the iteration was set at P<0.1 for backward logistic regression analyses. Returning coefficients of the variables were interpreted as adjusted odds ratio (OR_adjusted) with 95% CI provided. All significance levels were set at two-sided α=0.05.

A total of 6196 colonoscopies (3143 women; mean age 53.7 years; standard deviation, 12.7 years) were done during the study period. Most patients were aged between 45 and 64 years, were in-patients, had undergone diagnostic colonoscopy, and received intravenous sedation (60.5%, 70.5%, 53.0%, and 99.4% respectively; Table 1). The data for immediate complications were complete, while the 30-day follow-up was completed for 3657 procedures (803 were lost to follow-up and 1736 refused; compliance rate 59.0%; Table 2).

Of the 6196 colonoscopies, 2912 were therapeutic with 99.7% dedicated to polypectomy (Table 1). There were 73 (1.2%) cases of incomplete colonoscopy, 18 (24.7%) of which were due to inadequate preparation. Other reasons for incomplete colonoscopy were tumour obstruction (15 of 73; 20.5%) and intention of sigmoidoscopy or stent insertion (26 of 73; 35.6%). A total of 149 patients were readmitted within 30 days after the procedure, of which six (4.0%) were related to complications. The other reasons were cancer, gastro-intestinal disease, or cardiac events (Table 2).

Regarding the choice of sedation, midazolam and pethidine were the most used at 81.5% and 82.0%, respectively, while 15.9% of patients underwent MAC. Immediate complications reported included hypotension, vasovagal fainting, and nausea/vomiting, or a combination (6.1, 0.6, 0.3, and 0.5 per 1000 procedures, respectively; Table 3). There were no severe cardiovascular events such as heartbeat irregularity or myocardial infarction or cerebrovascular events such as stroke. Furthermore, none of the patients reported delayed systemic complications in the 30-day follow-up.

Modelling to study the potential risk factors showed that being female, use of MAC, and inadequate bowel preparation were the significant independent predictors for systemic immediate complications (OR_adjusted=2.0, 2.6, and 3.7, respectively; all were P<0.05; Table 4).

Immediate colonoscopy-related complications were recorded for 48 patients (7.7 per 1000 procedures), including extensive pain/discomfort, abdominal distension, and perforation (Table 3). The only perforation was at the sigmoid-rectal junction and was due to adhesion, which might be related to previous abdominal surgery (total hysterectomy and bilateral salpingo-oophorectomy was done 10 years previously). In the 30-day follow-up, six patients reported complication-related readmissions, five of whom were for bleeding after discharge from hospital and one was for inflammation; all were caused by polypectomy.

Modelling was done to formulate a predictive algorithm for significant independent risk factors and outcome events (Table 4). Inadequate bowel preparation and incomplete colonoscopy were the significant predictors for immediate colonoscopy-related complications (OR_adjusted=3.5 and 6.2, respectively; both were P<0.05) and for all immediate complications (OR_adjusted=3.5 and 4.5, respectively; both were P<0.05). In the model for all immediate complications, being female and use of MAC were also predictors (OR_adjusted=1.6 and 1.8, respectively; all were P<0.05).

A predictive model was also done for overall complications, including all immediate and delayed complications among those who completed follow-up at 30 days. The effect of previous significant predictors was transient in that they did not predict the overall complications occurring in the 30-day post-colonoscopy period. Monitored anaesthetic care was the only predictor during the 30-day period (OR_adjusted=2.0; P=0.019).

Inadequate bowel preparation and incomplete colonoscopy were identified as risk factors for colonoscopy-related complications. Other complications were mostly hypotension and abdominal distension. No myocardial infarction, transient ischaemic attack, or death relating to colonoscopy was reported.

Colonoscopy is rarely a complication-free procedure, but a good understanding of the possible complications can help to minimise them. While experienced endoscopists, diagnostic procedures, and young patients are protective factors for colonoscopy complications, trainee endoscopists, therapeutic procedures, advanced age, female sex, obesity, co-morbidity, anticoagulant use, and previous abdominal surgery are risk factors for complications.3 5 6 10 15 16 17 The relatively low incidence of complications recorded in this study could be attributed to the fact that more than half of the procedures were diagnostic, thus reducing the potential for polypectomy-associated complications.

Other events—such as abdominal pain and distension, hypotension, vasovagal fainting, and nausea/vomiting—accounted for 98.9% of all immediate complications; these events were mostly reported by women (60.6%; OR_adjusted=1.6; Table 4). This result is consistent with the literature.17 This effect could possibly be explained by different perceptions of somato-sensation, which could be traced back to the socio-emotional cultivation and cultural expectation of the different sexes.18

Despite the sex effect, use of MAC, inadequate bowel preparation, and incomplete colonoscopy were all related to immediate complications. The use of MAC, in particular, requires more interpretation because it has not been found to be a risk factor in other studies and its use ought not be a cause of complications. However, MAC is designed for patients who are vulnerable to the complications of sedation and the procedure, especially those with co-morbidities and who are at an advanced age. In this study, co-morbidity was not reviewed, but patients who underwent MAC were significantly older than those who did not (mean age, 56.1 vs 53.3 years; P<0.001, t test) which may be partly contributory. However, age was not significantly associated with any of the complications after adjustment for other factors. Age might have a greater impact if co-morbidity was also considered and this may be an area for further study.

Inadequate bowel preparation, in which faeces obscure the inner lining of the colon, impedes the vision and heightens the risk for complications. Likewise, incomplete colonoscopy due to inadequate bowel preparation or unbearable discomfort inevitably increases the risk for complications. These results are consistent with other studies.2 3 10

A large proportion (59%) of the study population completed the study. Per protocol univariate analyses showed that use of MAC was the sole significant factor related to overall complications (Table 4).

Sedation-free colonoscopy is a feasible alternative that could reduce the risk of systemic complications; use of CO₂ insufflation might increase its tolerability while maintaining visibility. In this study, a sedation-free procedure was performed in only 36 patients, with no complications; CO₂ insufflation was done for 647 (10.9%) patients instead of gas (room air), with only minor complications encountered (two patients reported abdominal distension and seven reported hypotension/vasovagal fainting). Insufflation with CO₂ could be adopted more widely because it is non-explosive, absorbable, and does not affect the mucosal blood flow, thus minimising discomfort and the risk of colonic ischaemia. According to Bretthauer et al,19 CO₂ insufflation leads to quicker recovery, and less pain and complications. These advantages are supported by other studies including local research.11 19 20 These factors might inspire greater use of CO₂ insufflation and minimise use of sedation for selected patients.12 13 21

Inadequate bowel preparation not only hampers completion of the procedure, but also increases the risk for complications. As evidenced from the prediction models, inadequate bowel preparation significantly increases the occurrence of complications. In addition to implementing the current standardised bowel preparation protocol, enforcement of patient education, compliance, and early admission for monitored bowel preparation might help to further suppress the rate for inadequate bowel preparation.

Many of the patients were lost to contact by telephone. In this study, we assumed that the pattern of missing patients was random and was not affected by whether or not the patients had complications. However, self-selection bias might exist. If patients without complications were more likely to be lost to contact, the rate of delayed complications would be overestimated. However, the rate of delayed complications would be underestimated if the patients had been admitted to other hospitals or had died. Endoscopist experience, and patient characteristics of co-morbidities and severe symptoms before the procedure were not recorded for analysis in this study. These are potential risk factors for complications. In view of the importance of monitoring the complications of colonoscopy, further study might include the missing variables of co-morbidity, endoscopist experience, symptoms at presentation and oxygen level, and explore factors such as the influence of body mass index and medical history, sedation dose, indication for colonoscopy, use of laxatives and compliance, and post-colonoscopy diagnosis/pathology that might help to minimise the variance on prediction of complications.

We would like to thank Dr Sheri Lim, former Administrative Officer (Medical) who proposed and developed the audit. We are grateful to Dr KM Lai, Head of Department of Anaesthesiology for his expert advice on the anaesthetic terminology; Dr Raymond Yung and Dr KN Lai, Assistant Medical Superintendents for their valuable suggestions and encouragement; Ms Grace Wong, Medical Records Manager for coordinating with different departments; and Ms Sara Fung, former Research Nurse for coordinating the project. Also, thanks to all doctors who contributed their knowledge and data, for this study would not have been accomplished without them.

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