Continuous infiltration of a surgical wound after an operation is commonly used for analgesic purposes. Specific methods of wound infiltration include patient-controlled analgesia and continuous infusion . Research to determine the effectiveness of wound infiltration analgesia has examined a variety of metrics, in particular VAS pain scores and opioid use. This research has sought to determine not only how wound infusion compares to other analgesic techniques, but which drug types, drug doses, and surgical situations are optimal for this technique.
Most literature on this topic indicates that infiltration decreases postoperative pain as measured by VAS scores. In one trial, patients undergoing total knee arthroplasty were divided into two groups, one of which received wound infiltration for analgesia. The other received an epidural infusion. The former group had lower resting VAS scores in the 24 hours following surgery—7 compared to the epidural infusion group’s 30. The trend remained even between 48 and 96 hours, where respective VAS scores were 7.5 and 23 . Similarly, in a randomized trial, patients recovering from total hip arthroplasty received either wound infiltration or epidural infusion for analgesia. For 20 hours following surgery, the groups’ VAS scores showed little difference. However, from 20-96 hours, the infiltration group had significantly lower at-rest VAS scores: for instance, 8 rather than 20 between 24 and 48 hours .
However, in another study, thyroid surgery patients in the infiltration group showed no significant difference in pain scores compared to the placebo group . Wound infiltration also did not correlate with a significant reduction in opioid use. The total dose administered for the infiltration group was 64 mg, compared to 69 mg for the infusion group  . However, other research points to a significant reduction in opioid use for infiltration patients. In the above knee arthroplasty study, for instance, patients in the infiltration group were administered a mean of 7.5 mg of morphine in the 24 hours following surgery, while their counterparts received 18 mg on average . In the previously mentioned study of hip arthroplasty patients, meanwhile, the infiltration group consumed a mean of 258 mg in the 96 hours after surgery, while the infusion group consumed a mean of 324 mg . Finally, in a review of 203 articles examining the efficacy of the technique, researchers found that “a general reduction in pain intensity and in opioid consumption has been observed with continuous wound infiltration” .
In this review, Paladini et al. also found that wound infiltration has varying degrees of effectiveness for different procedures. Specifically, infiltration appeared most effective in areas with large amounts of connective and subcutaneous tissue. In addition, the effectiveness of infiltration varies depending on the type and amount of anesthetic being administered . In one study, patients undergoing shoulder surgery were divided into three groups. Two received a continuous infiltration of saline, while the others received infiltration of ropivacaine at different concentrations—2 mg/mL and 3.75 mg/mL respectively. While both ropivacaine groups enjoyed lower VAS scores and consumed fewer opioids than the saline group, the group receiving the higher concentration of the drug had significantly lower VAS scores and opioid consumption than the low-concentration group.
Thus, wound infiltration appears generally effective for reducing post-operative pain across a variety of metrics. However, the method may be more successful in the context of certain operations rather than others, and its success may also depend upon the dosage and type of anesthetic being used.
 Paladini, Giuseppe, et al. “Continuous Wound Infiltration of Local Anesthetics in Postoperative Pain Management: Safety, Efficacy and Current Perspectives.” Journal of Pain Research, vol. 13, 2020, pp. 285-294., doi:10.2147/JPR.S211234.
 Andersen, Karen V, et al. “A Randomized, Controlled Trial Comparing Local Infiltration Analgesia with Epidural Infusion for Total Knee Arthroplasty.” Acta Orthopaedica, vol. 81, no. 5, 2010, pp. 606–610., doi:10.3109/17453674.2010.519165.
 Andersen, Karen V, et al. “Reduced Hospital Stay and Narcotic Consumption, and Improved Mobilization with Local and Intraarticular Infiltration after Hip Arthroplasty: A Randomized Clinical Trial of an Intraarticular Technique versus Epidural Infusion in 80 Patients.” Acta Orthopaedica, vol. 78, no. 2, 2007, pp. 180–186., doi:10.1080/17453670710013654.
 Miu, Mihaela, et al. “Lack of Analgesic Effect Induced by Ropivacaine Wound Infiltration in Thyroid Surgery.” Anesthesia & Analgesia, vol. 122, no. 2, 2016, pp. 559–564., doi:10.1213/ane.0000000000001041.
 Gottschalk, Andre, et al. “Continuous Wound Infiltration with Ropivacaine Reduces Pain and Analgesic Requirement After Shoulder Surgery.” Anesthesia & Analgesia, 2003, pp. 1086–1091., doi:10.1213/01.ane.0000081733.77457.79.