Fentanyl is the most commonly used opioid during anesthesia at Massachusetts General Hospital. Compared to other opioids, e.g. sulfentanil and remifentanil, fentanyl's pharmacokinetic properties are more problematic as the context sensitive half-time increases with duration of fentanyl infusion. This may lead to respiratory complications particularly in patients who receive fentanyl for surgical procedures of long duration. Considering the common use of fentanyl during surgery and its duration of action that is hard to predict during long surgical procedures, we will evaluate the association between intraoperative fentanyl dose and postoperative respiratory complications within 3 days of surgery.

Our team has conducted a series of studies to define the optimal anesthesia plan that minimizes the risk of postoperative respiratory complications. Opioids are almost always used in the perioperative management of patients undergoing surgery during anesthesia. Intraoperatively they are administered to achieve adequate surgical conditions. Opioids are respiratory depressants. They decrease dose-dependently the drive to the respiratory pump muscles and upper airway dilator muscles, which leads to respiratory acidemia and hypercapnia. Fentanyl is the most commonly used opioid during anesthesia at MGH. Compared to other opioids, e.g. sulfentanil and remifentanil, fentanyls pharmacokinetic is more problematic as the context sensitive half-life increases with duration of fentanyl administration. This may lead to respiratory complications. Considering the common use of fentanyl during surgery and its duration of action that is hard to predict during long surgical procedures, we will evaluate the association between intraoperative fentanyl dose and postoperative respiratory complications within 3 days of surgery.

To account for other factors that may affect the incidence of postoperative respiratory complications, we included the following confounder model in all of our analyses:

• Gender
• Age
• BMI (body mass index)
• ASA status classification
• CCI (Charlson Comorbidity Index)
• Inhalational anesthetics as MAC
• Long lasting opioids as IV-morphine milligram equivalent including morphine, hydromorphone, methadone and sufentanil.
• Use of neuraxial anesthesia
• Intraoperative vasopressor dose
• Intraoperative NMBA (neuromuscular blocking agent) dose
• Intraoperative hypotension as number of minutes of an MAP (mean arterial pressure) <55 mmHG
• Duration of surgery
• Emergency status
• Intraoperative fluids
• PRBC (packed red blood cells) units
• Work RVU [relative value unit]
• Surgical service
• Admission type (ambulatory vs inpatient)
• SPORC (Score for Prediction of Postoperative Respiratory Complications)
• SPOSA (Score for Prediction of Obstructive Sleep Apnea)
• Inspiratory O2 - Fraction
• Protective ventilation (defined as PEEP=5 and plateau pressure between 0 and 16)
• Perioperative naloxone use
• Prescription of any of the following opioids within 90 days prior to surgery: oxycodone, codeine, hydrocodone, buprenorphine, butorphanol, opium, hydromorphone, fentanyl, meperidine, morphine, levorphanol, methadone, nalbuphine, tapentadol, oxymorphone, roxicodone, tramadol
• Code status (DNR)

Inclusion Criteria:

• Surgical patients at Massachusetts General Hospital and two affiliated community hospitals
• 18 years of age and older
• Only patients who required general anesthesia with an endotracheal tube for the surgical procedure and were extubated in the operating room at the end of the procedure.

Exclusion Criteria:

• Brain dead patients (ASA greater than 5)

Patients with surgeries performed between 01/2007 and 12/2015 at Massachusetts General Hospital and two affiliated community hospitals.