Question

A 48-year-old female presents to the emergency department with severe, constant epigastric pain that radiates to her mid-back. The pain began 12 hours ago and has been accompanied by multiple episodes of non-bilious emesis. She denies alcohol consumption, recent travel, or new medications.

Vital signs:
- Temperature: 38.2°C (100.8°F)
- Blood pressure: 112/68 mmHg
- Heart rate: 118/min
- Respiratory rate: 22/min

Physical examination reveals a distressed patient with severe epigastric tenderness to deep palpation, without guarding or rebound. Bowel sounds are hypoactive.

Laboratory results:
| Leukocyte count | $16,500/\text{mm}^3$ |
| Lipase | $4,200 \text{ U/L}$ |
| Total bilirubin | $1.0 \text{ mg/dL}$ |
| Aspartate aminotransferase (AST) | $110 \text{ U/L}$ |
| Alanine aminotransferase (ALT) | $155 \text{ U/L}$ |
| Thyroid-stimulating hormone (TSH) | $0.2 \mu\text{U/mL}$ (Normal: 0.5–5.0) |
| Free T4 | $1.2 \text{ ng/dL}$ (Normal: 0.9–1.7) |

Arterial blood gas (room air):
| pH | $7.32$ |
| $\text{pCO}_2$ | $32 \text{ mmHg}$ |
| $\text{HCO}_3^-$ | $16 \text{ mEq/L}$ |

An abdominal ultrasound demonstrates multiple echogenic foci within the gallbladder lumen with posterior acoustic shadowing. The common bile duct measures 4 mm in diameter, and the gallbladder wall is 2 mm thick without pericholecystic fluid. The pancreas is partially obscured by overlying bowel gas.

Which of the following is the most appropriate next step in the management of this patient?