Preoperative Assessment

Successful ambulatory surgery requires careful selection of patients and consideration of the experience of the team involved. Therefore, what may be appropriate for one specialty (and indeed one particular operation) in one setting may not be appropriate for another. For example, a cataract extraction performed under topical local anaesthesia can be performed on a much older and more frail population when compared to a shoulder arthroscopy. As an additional example, settings that are not prepared to handle young children as outpatients might not be appropriate for such patients in spite of a preoperative assessment showing clinical stability and low risk for surgery.

Proper pre-operative assessments are essential for smooth-running ambulatory surgery schedules. The goals of effective pre-operative assessments are to be organized, efficient, informative, and relatively simple (yet comprehensive). Having such adequate assessments will lead to no surprises on the day of surgery, and ideally no delays or cancellations.
Pre-operative assessments can be primarily performed in two different ways. Patients can be seen and evaluated in an assessment clinic or they can be contacted via telephone to gather their medical history. Each system has advantages and disadvantages, and a combination of the two has also been used successfully in several countries.

Seeing patients in an assessment clinic has the advantage of having personal interactions, being able to do a physical exam, and performing pre-operative testing if needed. A disadvantage is that it might not be convenient for patients to attend the session. The assessment clinic can be run by suitably trained nursing staff with all patients being seen in advance of their surgery – this is typically the model in the UK whereas other countries run these clinics with anaesthetists.
Pre-operative telephone interviews is the most common system used in the US. Such a system has proven to be easy and convenient, but it relies on patients having adequate knowledge of their medical histories. It also hinges on a physical exam and pre-operative testing being done at outside facilities and results being delivered in.
Whichever model is used leadership of this service is best provided by a clinical lead from the Anaesthetic Department. It is important that they develop guidelines for screening of patients that are accepted by their anaesthetic colleagues. It is also necessary to have a system for dealing with problems identified by the staff during this screening process. In general, pre-operative testing should be limited to circumstances in which the results affect the patient treatment and outcomes. Each country may well have their own guidelines but those produced by NICE (UK), the American Society of Anesthesiologists (US) and the Society for Ambulatory Anesthesia (US) have been used by many other countries. Arrangements should be put in place for all appropriate tests to be carried out at the time of assessment (or close to the time of assessment if telephone interviews are being performed) and there must also be a mechanism in place to review all investigations undertaken. It should be remembered that the preoperative assessment is also an important time to start educating the patient and their carers about the operation and postoperative care.
Assessment falls into two main categories.
  1. Social
  2. Medical


The patient must be willing to undergo surgery in a day case setting and in most cases there should be a responsible adult able and willing to care for the patient for at least the first twenty four hours. Patients and/or their carers should have easy access to a telephone and the patients’ home situation should be compatible with postoperative care. Travel time from where surgery is being performed is procedure dependent, but generally 1 hour is considered as a reasonable limit.


The patient and their carer should be able to understand the planned procedure and subsequent postoperative care. The patient should be either fully fit or chronic diseases such as asthma, diabetes, hypertension or epilepsy should be well controlled. Patients should be selected according to their physiological status as found at assessment. Routine laboratory testing has been shown in multiple studies to NOT reduce the incidence of perioperative events in ambulatory surgery patients. Such testing should be focused on items that would alter the perioperative management of patients. As previously mentioned it is important for the clinical lead to establish agreement with anaesthetic colleagues about the medical screening.


Physiological status and fitness should be considered rather than arbitrary age limits. One exception to this would be infants who were born prematurely and are within 60 weeks post-gestational age. It is routinely accepted that such patient should be admitted post-operatively for observation due to risk of apnoea of prematurity.

Body Mass Index (BMI)

BMI is used as part of selection criteria by most ambulatory surgery units. It is one measure of obesity and is calculated by dividing the patient’s weight (measured in kilograms) by the square of their height (measured in metres).
This is an area that has seen major change – a few years ago patients with a BMI of more than 30 were deemed unsuitable for ambulatory surgery. Advances in surgical and anaesthetic techniques have meant that patients with a much higher BMI, who are otherwise fit, are now accepted. Though some units now accept a BMI of 40 or more it is prudent to start with a lower limit and increase this as you gain experience and confidence in management of these patients.


Much has been written in the past about the importance of blood pressure control and anaesthesia. However more recent publications have separated out the need for long term control of hypertension as part of general health of the patient from the risks associated with anaesthesia and surgery. There is no evidence to support the cancellation of patients with mild to moderate hypertension from having elective surgery. Much has been written in the past about the importance of blood pressure control and anaesthesia. However more recent publications have separated out the need for long term control of hypertension as part of general health of the patient from the risks associated with anaesthesia and surgery. There is no evidence to support the cancellation of patients with mild to moderate hypertension from having elective surgery. They must however be highlighted to their primary care physician so that assessment of their hypertension can be undertaken.

Sleep Apnoea

Patients with sleep apnoea undergoing ambulatory surgery has been a major topic of debate in many countries, particularly since many of these patients do not have a formal diagnosis of such at the time of surgery. Interestingly, several studies have shown that there is no difference in complications between OSA and non-OSA patients undergoing ambulatory surgery. However there are several categories of sleep apnea patient for which ambulatory surgery is not recommended:
  • Patients with central sleep apnea
  • Patients with severe OSA without optimized comorbid conditions
  • Patients’ inability to follow post-discharge instructions including compliance with Continuous Positive Airway Pressure (CPAP)
  • Patients who adamantly refuse to use nighttime CPAP after discharge
  • Patients where long acting opioids are required
Management of such patients can be complicated and there needs to be proper coordination of availability of equipment (such as CPAP machines) to patients post-operatively.

Diabetes Mellitus

Diabetes affects 2-3% of the population and should not be a contraindication to ambulatory surgery. However when considering diabetic patients for ambulatory surgery it is important to assess the stability of the disease and the patients understanding of their diabetic control. The British Association of Day Surgery has produced a useful handbook on the management of these patients. Link here - but this requires purchase.(external link)

Finally it is important to re-emphasise that this section has been about the assessment of the patient. Patient selection in your ambulatory surgery unit will also be influenced by
  • the type of unit – free standing, with or without availability of overnight beds etc and
  • the type of surgery to be undertaken  

Further Reading

Preoperative assessment and preparation:the role of the anaesthetist(external link)
This document is produced by the Association of Anaesthetists in the UK.