# Patient Selection and Risk Stratification for Ambulatory Surgery

## Introduction

Ambulatory (same-day) surgery now accounts for over 70% of all surgical procedures in the United States. Advances in surgical technique, anesthetic agents, and multimodal pain management have expanded the range of patients and procedures eligible for outpatient care. Proper patient selection and risk stratification remain the cornerstones of safe ambulatory anesthesia, balancing efficiency with patient safety.

## Advantages of Ambulatory Surgery

Ambulatory surgery offers reduced healthcare costs and resource utilization, lower rates of hospital-acquired infections, improved patient satisfaction and faster return to normal activity, decreased risk of venous thromboembolism associated with early ambulation, and reduced exposure to nosocomial pathogens including multidrug-resistant organisms.

## Patient Selection Criteria

### Medical Factors

ASA Physical Status I through III patients are generally appropriate for ambulatory surgery. Select ASA IV patients with stable, optimized disease may be considered at experienced centers. Regarding obesity, BMI alone is not an absolute contraindication; the assessment should focus on associated comorbidities such as OSA, difficult airway, and cardiovascular disease, and most centers accept a BMI up to 50 kg/m2 with appropriate resources.

For obstructive sleep apnea, the STOP-BANG questionnaire should be used for screening. High-risk patients require careful consideration of opioid-sparing analgesia and post-discharge monitoring. Patients with stable coronary artery disease, well-controlled heart failure (NYHA I-II), and controlled arrhythmias are generally acceptable. Well-controlled diabetes (HbA1c less than 8 to 9%) is appropriate, and these patients should be scheduled as the first case to minimize fasting duration. Advanced age is not an independent contraindication; frailty and functional status are more predictive than chronological age.

### Surgical Factors

Appropriate procedures include those with an expected duration of less than 3 to 4 hours, anticipated blood loss less than 500 mL, low likelihood of postoperative airway compromise, manageable postoperative pain with oral analgesics and regional techniques, and no requirement for specialized postoperative nursing or monitoring.

### Social and Logistic Factors

Requirements include a responsible adult available for 24-hour supervision post-discharge, reliable transportation home (the patient cannot drive), access to a telephone and proximity to emergency medical services (within 30 to 60 minutes), ability to understand and comply with discharge instructions, and a stable home environment for recovery.

![Flowchart showing the patient selection algorithm for ambulatory surgery, incorporating medical, surgical, and social screening criteria](images/ambulatory-selection-algorithm.png)

## Preoperative Assessment and Testing

### Evidence-Based Approach to Testing

Routine laboratory testing is not recommended in healthy patients (ASA I-II) undergoing low-risk procedures. Pregnancy testing is required per institutional policy for females of childbearing age. An ECG should be considered for patients with known cardiovascular disease, symptoms, or significant risk factors undergoing intermediate-to-high-risk procedures. CBC is indicated if there is anticipated blood loss or known anemia. BMP or electrolytes should be obtained if the patient is on diuretics, ACE inhibitors, ARBs, or has renal disease or diabetes. Coagulation studies are needed only if the history suggests a bleeding diathesis or the patient is on anticoagulants. HbA1c is reasonable for diabetic patients without recent values to guide perioperative glucose management.

### Preoperative Optimization

Most chronic medications should be continued on the morning of surgery with a sip of water. SGLT2 inhibitors should be held due to the risk of euglycemic DKA, and GLP-1 agonists should be held due to gastroparesis risk per 2023 ASA guidance. Oral hypoglycemics are also held. There is institutional variation regarding ACE inhibitors and ARBs; holding them on the day of surgery to reduce intraoperative hypotension should be considered. Patients should be counseled on NPO guidelines per ASA fasting recommendations (clear liquids 2 hours, light meal 6 hours).

## Risk Stratification Tools

### Commonly Used Scores

The ASA Physical Status Classification is simple and widely used but subjective with limited predictive power for specific outcomes. The STOP-BANG Questionnaire screens for OSA risk, with a score of 5 to 8 indicating high risk. The Revised Cardiac Risk Index (RCRI) estimates cardiac risk, and a low RCRI of 0 to 1 supports ambulatory candidacy for appropriate procedures. The ACS NSQIP Surgical Risk Calculator provides procedure-specific risk estimates.

### Conditions Requiring Special Consideration

| Condition | Ambulatory Candidacy | Key Considerations |
|-----------|---------------------|---------------------|
| **Severe OSA on CPAP** | Usually acceptable | Opioid-sparing analgesia; bring CPAP to facility |
| **Morbid obesity (BMI >50)** | Center-dependent | Difficult airway preparedness; avoid deep sedation |
| **Stable angina** | Usually acceptable | Functional capacity >4 METs; continue beta-blockers |
| **ESRD on dialysis** | Selective procedures | Dialysis within 24 hours preop; electrolyte check |
| **Former premature infant** | Age >60 weeks PCA | Risk of postoperative apnea if <60 weeks PCA |

![Infographic comparing risk factors that favor versus contraindicate ambulatory surgery in a two-column layout](images/ambulatory-risk-factors.png)

## Day-of-Surgery Considerations

A final assessment by the anesthesiologist on the day of surgery is mandatory. NPO status, medication compliance, and absence of acute illness must be verified. The responsible adult escort and post-discharge plan should be confirmed. Anesthetic technique selection (regional anesthesia, MAC, or general anesthesia) is based on the procedure and patient factors. The plan should include multimodal analgesia to minimize opioid use and facilitate discharge.

## Discharge Criteria

### Modified Post-Anesthetic Discharge Scoring System (PADSS)

Vital signs should be stable and within 20% of the preoperative baseline. The patient should be able to ambulate without dizziness (age and procedure appropriate). Pain should be controlled with oral analgesics (NRS of 4 or less). Nausea and vomiting should be minimal or absent. Surgical bleeding should be consistent with the expected postoperative course. Oral fluid tolerance is no longer a mandatory criterion for most patients, as evidence supports bypassing mandatory oral intake requirements.

### Unanticipated Admission

Unanticipated admission occurs in 1 to 3% of ambulatory cases, with the most common reasons being uncontrolled pain, PONV, surgical complications, and drowsiness. Predicting and preventing these complications improves patient satisfaction and reduces costs.

![Photo of an ambulatory surgery discharge area showing a patient being reviewed by nursing staff with discharge checklist visible](images/ambulatory-discharge.png)

## Clinical Pearls

Patient selection is more about comorbidity optimization than absolute exclusion criteria; a well-controlled ASA III patient may be a better ambulatory candidate than an unoptimized ASA II patient. OSA is the most commonly underdiagnosed condition in the ambulatory population, and every patient should be screened with STOP-BANG. Regional anesthesia and multimodal analgesia are the foundation of successful ambulatory outcomes, reducing opioid-related PONV and sedation. The decision to proceed with ambulatory surgery should be a shared decision among the surgeon, anesthesiologist, and patient.

## References

1. Joshi GP, Ankichetty SP, Gan TJ, Chung F. Society for Ambulatory Anesthesia consensus statement on preoperative selection of adult patients with obstructive sleep apnea. *Anesth Analg*. 2012;115(5):1060-1068.
2. Apfelbaum JL, Connis RT, Nickinovich DG, et al. Practice advisory for preanesthesia evaluation. *Anesthesiology*. 2012;116(3):522-538.
3. Mathis MR, Naughton NN, Shanks AM, et al. Patient selection for day case-eligible surgery. *Anesthesiology*. 2013;119(6):1310-1321.
4. Chung F, Abdallah FW, Bhatt T. STOP-BANG questionnaire: a practical approach to screening for obstructive sleep apnea. *Chest*. 2016;149(3):631-638.