Indian Journal of Anaesthesia

: 2016  |  Volume : 60  |  Issue : 11  |  Page : 833--837

A nested case-control study to determine the incidence and factors associated with unanticipated admissions following day care surgery

Madhurita Singh1, Manickam Ponniah2, KS Jacob3,  
1 Department of Neurological Sciences, Neurosciences Critical Care Unit, Christian Medical College, Vellore, Tamil Nadu, India
2 Department of Anaesthesia, Christian Medical College, Vellore, Tamil Nadu, India
3 Department of Psychiatry, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
Madhurita Singh
Department of Neurological Sciences, Neurosciences Critical Care Unit, Christian Medical College, Vellore - 632 004, Tamil Nadu


Background and Aims: Day care surgery offers respite from hospitalisation for specific surgical procedures and has many advantages. However, occasionally patients who undergo such surgery require hospitalisation for unanticipated complications. We aimed to determine their incidence and to identify factors associated with unanticipated admissions in a tertiary care hospital in South India. Methods: During the 3-month study, 63 cases requiring admission and 126 randomly selected controls were taken from the 776 procedures that were performed were compared. The variables studied were patients«SQ» demographic characteristics, pre-operative medical illness, personal habits, American Society of Anesthesiologists status, the diagnosis and surgical procedures, time since last meal, duration of anaesthesia and surgery, experience of the surgeon and anaesthetist, and intraoperative management (techniques, drugs, monitoring, etc.). Univariate and bivariate statistics were used to determine factors associated with unanticipated admissions. Results: The incidence of unanticipated admissions following day care surgery was 8.11%. The reasons for admission were anaesthetic (33.33%), surgical (15.87%), medical (6.34%) and social (44.44%). The factors significantly associated with unanticipated admissions included duration of anaesthesia more than 50 min (odds ratio [OR]: 3.179; 95% confidence interval [CI]: 1.503-6.722), and starting the last case after 3 pm (OR: 10.095; 95% CI: 2.418-42.148). Conclusion: Unanticipated admissions following day care surgery occur mainly due to anaesthetic, surgical, medical and social reasons.

How to cite this article:
Singh M, Ponniah M, Jacob K S. A nested case-control study to determine the incidence and factors associated with unanticipated admissions following day care surgery.Indian J Anaesth 2016;60:833-837

How to cite this URL:
Singh M, Ponniah M, Jacob K S. A nested case-control study to determine the incidence and factors associated with unanticipated admissions following day care surgery. Indian J Anaesth [serial online] 2016 [cited 2021 Jan 23 ];60:833-837
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Day care or ambulatory anaesthesia is as old as the history of anaesthesia itself. In the last few decades, it has gained significant popularity mainly because of the enormous cost savings [1] and has therefore been accepted by the hospitals, patients and the insurance companies alike. However, the quality and excellence of care needs to be defined and defining good care is a challenge. Unanticipated admission, whatever the cause, is an indicator of the quality of care [2] because it negates the basic goal of preventing hospitalisation and same day discharge. While day care surgery in India is limited to a few hospitals, [3] there is a dearth of data on hospitalisation following such intervention. This study aimed to examine the incidence and factors associated with unanticipated admission following day care surgery at a tertiary level hospital in South India.


The Institutional Review Board approved the study protocol. All patients were evaluated pre-operatively in the pre-anaesthetic clinic. Patients belonging to American Society of Anesthesiologists (ASA) physical status Classes 1 and 2, undergoing surgeries under general or regional anaesthetic techniques along with appropriate nerve blocks for post-operative pain relief were included.Cases done under local anaesthesia were excluded from this study.

It was planned to use the median value of controls for continuous exposure variables (such as time of anaesthesia and time of starting last case) to define exposure status. We required 70 cases and 70 controls to detect an odds ratio (OR) of 2.5 with a power of 80% and α error of 0.05%. To permit adjustment for confounders, two controls per case were chosen, which required the number of subjects to be 53 cases and 106 controls.

Demographic characteristics, patients' weight, pre-operative medical illness, personal habits, ASA status, the diagnosis and surgical procedures, time since last meal, duration of anaesthesia and surgery, experience of the surgeon and anaesthesiologist, and intraoperative management (techniques, drugs, monitoring, etc.) were documented. The number of hours fasted was divided into 6-8 h, 9-11 h and >11 h. The outcomes measured were the admission of patients following day care surgery, and the causes of unanticipated admissions.

Discharge of the patient was decided after both the surgeon and the anaesthesiologist cleared the patient. The admission of the patient to the hospital was also decided by the surgeon or the anaesthetist depending on the complication the patient had. Those who need to stay overnight from the day care centre were considered as unanticipated admissions (the centre functions from 7 am to 9 pm with the morning session from 7:30 am to 11:30 am and the afternoon session from 12:30 pm to 4:30 pm. All patients are usually discharged on the same day).

The reasons for unanticipated admission were classified into four main groups: (i) anaesthetic reasons included nausea vomiting, giddiness, prolonged general anaesthesia and others, (ii) surgical reasons included pain, bleeding, complicated surgery requiring wound dressing, wound drainage or antibiotics, (iii) medical reasons such as fever, drug allergies and other complications, (iv) social reasons included patients or surgeons request.

A nested case-control study design was used to assess risk factors. Descriptive statistics in the form of frequencies, median and means, standard deviations and percentages were calculated. The Chi-square test and OR were calculated to determine which factors were associated with unanticipated admission. The OR, their 95% confidence intervals (CIs) and corresponding P values were calculated for all variables. P < 0.5 was considered statistically significant. For the statistically significant variables, the Mantel Haenszel OR was calculated to identify confounding, if any. For analysing the different narcotics used, each narcotic was given a score using morphine as a reference; 10 mg of morphine = 100 μg of fentanyl = 75 mg of pethidine = 100 mg of tramadol. Hence, a narcotic score of one equals 1 mg of morphine = 10 μg of fentanyl = 7.5 mg of pethidine = 10 mg of tramadol. For example, if a patient received 100 μg of fentanyl and 6 mg of morphine during the surgery, the patient would have a narcotic score of 16. The equivalent narcotic dose was totalled and the narcotic score for each patient was then calculated. A narcotic score of 10 was used as the cut-off and the tests of significance done. These were then built into a bivariate logistic regression model. Data were analysed using the  Statistical Package for Social Sciences (SPSS) version 13.0 (SPSS Inc. Version 13.0. Chicago, SPSS Inc).


During the 3-month study, from the cohort of 776 patients, 63 patients with unanticipated admission formed the case group and were compared to twice the number of unhospitalised patients, which formed the control group. At the end of the day, after all the patients had been discharged or admitted from the day care centre, lots were drawn from the discharged group, which randomly selected controls.

The rate of unanticipated admission was 8.11%. Of these, anaesthetic complications accounted for 33.33%, surgical complications were 15.87%, medical were 6.35% and social reasons were 44.44%. Social reasons included admission on request of the surgeon and admission on request of the patient or parents of a child. If these social reasons were removed, the overall incidence was 4.51%.

The reasons for anaesthetic admission were post-operative nausea and vomiting (PONV), sweating and giddiness in the recovery room, prolonged general anaesthetic (>2 h), probable aspiration, urinary retention, a failed anaesthetic, which required switching to another technique and post-operative pain. The surgical reasons were bleeding; complicated surgery needing wound drainage, dressings or antibiotics. Medical causes were persistent high blood pressure needing treatment, fever, seizures and drug reactions. The rest were social admissions [Table 1].{Table 1}

The orthopaedic surgery speciality had the maximum admissions (34.9%), followed by abdominal surgeries, 27%. Procedures on the perineum resulted in 23.8% of the admissions. Ear Nose and Throat (ENT) had 11.1% admissions; vascular surgeries accounted for 3.17% whereas urology had none. The type of surgery and technique of anaesthesia among unanticipated admissions are shown in [Table 2] and [Table 3].{Table 2}{Table 3}

Individual risk factors for admissions and OR's were calculated using univariate logistic regression [Table 4]. The possibility of confounding was investigated using stratified analysis and calculation of the Mantel Haenszel OR.{Table 4}

The factors significantly associated with unanticipated admissions were the duration of anaesthesia, duration of surgery, experience of the surgeon, time of starting last case, hours of fasting and a high narcotics score. The median of controls was taken as the cut-off.

Anaesthesia lasting more than 50 min and surgery lasting more than 35 min were at a higher risk of admission. Patients whose surgery started after 3 pm were also at a significantly high risk of admission. The study found that patients operated on after 3 pm are 8 times at risk of being admitted than if their surgery started before 3 pm. It was also found that duration of fasting was a risk factor for admission. It was found that those fasting shorter hours (6-8 h) had 2.2 times greater risk of admission. Intraoperative use of narcotics was analysed in both groups, and this was not statistically significant. (P = 0.06 with an OR of 0.84 and a 95% CI of 0.41-1.71)

The dose of narcotic used during anaesthesia was analysed using the narcotic score and patients with a score of >10 were 2.86 times at a greater risk of admission with a 95% CI of 1.17-7.09. It was also found that patients operated on by consultant surgeons were 3.2 times more likely to be admitted but this was not analysed further as consultant surgeons operated upon almost 90% of patients.

The above statistically significant variables were entered into a bivariate logistic regression model [Table 5]. Anaesthesia time ≥50 min and surgery time ≥35 min were highly correlated and hence only anaesthesia time ≥50 min was entered into the model. The anaesthesia time ≥50 min (P = 0.002; OR: 3.18; 95% CI: 1.50-6.72) and starting of last case after 3 pm (P = 0.002; OR: 10.10; 95% CI: 2.42-42.15) remained statistically significant for unanticipated admissions. Fasting times and the narcotic score were not significant in the bivariate analyses.{Table 5}


The Day Care Centre is an architecturally and functionally integrated independent unit with areas for admission, surgery, recovery and discharge. It consists of an admission area with a lounge for relatives, two operating theatres, and a four-bedded recovery room with adequate monitoring facilities, oxygen and suction apparatus and in addition a six bedded day surgery ward. The surgical disciplines using the Day Care Centre include ENT, orthopaedics, general surgery, vascular surgery and urology.

Unanticipated admissions following day care surgery are a quality marker of efficiency of ambulatory surgery services. The incidence of unanticipated admission in this study was 4.51% that compares favourably with other published reports, which document rates between 1.04% and 5.4%. [2],[4],[5],[6],[7],[8],[9],[10],[11],[12] Patients were admitted for an average of 4.5 days however 70% of patients were admitted only for 1 day.

The factors associated with unanticipated admissions identified by the study were long duration of anaesthesia and surgery, starting of last case after 3 pm, shorter hours of fasting and greater dose of narcotics used. Duration of anaesthesia and surgery are both important interdependent predictors of unanticipated admissions. Anaesthesia lasting longer than 50 min and surgery lasting longer than 35 min were significantly associated with an increased risk of admissions. The study has found that longer anaesthesia is associated with a 3.85 times greater and longer surgery has four times increased risk of admissions. Mingus et al. [6] and Gold et al. [4] have reported similar findings.

This study documented that surgeries started after 3 pm had a higher risk of unanticipated admissions and is consistent with those reported in literature. Fortier et al. [5] have reported that completion of surgery after 3 pm was a significant factor. This may be because patients having surgery later in the day had less time to recover and be fit for discharge as compared to patients whose surgery was started earlier in the day.

The use of intraoperative narcotics was statistically significant on the univariate analysis but after adjusting for confounders using bivariate analysis, it was not significant. The study showed that the incidence of PONV was one of the major anaesthetic risk factors for admission, which accounted for 51.14% of anaesthetic admissions. It has also showed that there were only 3.17% admissions due to pain. Therefore, a comparison between the narcotic score and PONV was made, and a significant association was found. Patients with a narcotic score of >10 were nine times more likely to have PONV requiring admission. The ability to provide adequate pain relief without exacerbating PONV remains one of the major challenges for providers of outpatient anaesthesia and surgery. To minimise these opioid-related adverse effects, 'balanced' analgesia techniques involving the use of opioids and other groups of analgesic drugs such as local anaesthetics and non-steroidal anti-inflammatory drugs are now being commonly used. Post-operative pain is the most commonly reported complication of day care anaesthesia with up to 50% of patients experiencing wound pain. [13] However, this study did not show that instead it demonstrated that the use of opiates can lead to PONV requiring admission.

The duration of fasting was another risk factor in our study. It was found that shorter fasting time of <8 h induced a greater risk of unanticipated admission. This when stratified was found that fasting for 6-8 h was at greatest risk. The univariate analysis showed that shorter fasting time was at 2.2 times the risk of admission. The bivariate analysis showed that shorter fasting times had 1.9 times the risk of admission though not statistically significant. This group of patients may be the patients who are on the afternoon list starting at 12:30 pm, are allowed a light breakfast at 6 am and therefore have a higher risk of PONV. The duration of fasting and time of starting last case were stratified, and the Mantel Haenszel OR calculated. Since both the crude OR and the Mantel Haenszel odd ratio were almost equal it was concluded that there was no confounding factor involved. Both these were statistically significant, independent risk factors.

The uncorrected incidence of unanticipated admission in our study was 8.11%, and this is because our Day Care facility was relatively new and the threshold level for admission was very low. This can be explained by the fact that admission due to 'surgeons request' accounted for 36.5% of all cases when no real discernable reason could be made out. It may be that the surgeon suspects that he might have done a little more extensive procedure on the patient than anticipated, but does not fall under the category of complications. A small number (7.9%) also included request for admission from the patient or parents of a child. The idea that patients can go home on the same day as the surgery is a novel one and one which patients find difficult to reconcile to and therefore request for admission. Therefore, if both these groups are removed, the overall incidence works out to the value of 4.51%.

Our setup is part of a large tertiary hospital and in case of any apprehension, admission from the day care centre to the ward is relatively easy and more readily facilitated. The variables that were not significant were weight of the patient, distance travelled, pre-existing medical disease, and ASA status, type of anaesthetic and experience of the anaesthetist. Type of surgery and gender also had no detectable effect on admission, as evidenced in other studies. [6]

Although it was expected that pre-existing medical disease, type of anaesthetic and type of surgery would be significant, it was not so in our study. A large sample size and doing ASA 3 and 4 patients in the Day Care facility might have given different results.


The incidence of unanticipated admission following day care surgery was 4.51%. The factors associated with unanticipated admissions included longer duration of anaesthesia and surgery, later time of starting last case, shorter hours of fasting and the greater dose of narcotics used. These factors can guide decision making to facilitate improved efficiency of the day care centre. The low rates of medical causes of admissions reflect a good pre-anaesthetic assessment in terms of the suitability of patients.


We would like to show our gratitude to Dr. JP Muliyil, Former Professor and HOD, Department of Community Health, Christian Medical College, Vellore for providing expertise and assistance with designing the methodology and in the statistical analysis of this research paper.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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