Abstract: We included 41 studies (4224 participants). Participants underwent ambulatory or short length of stay surgical procedures, and were predominantly American Society of Anesthesiology (ASA) class I or II. There is one study awaiting classification and three ongoing studies. All studies took place in surgical centres, and were conducted in geographically diverse settings. Risk of bias was generally unclear across all domains. Supplemental intravenous crystalloid administration probably reduces the cumulative risk of postoperative nausea (PON) (risk ratio (RR) 0.62, 95% confidence interval (CI) 0.51 to 0.75; 18 studies; 1766 participants; moderate-certainty evidence). When the postoperative period was divided into early (first six hours postoperatively) and late (at the time point closest to or including 24 hours postoperatively) time points, the intervention reduced the risk of early PON (RR 0.67, 95% CI 0.58 to 0.78; 20 studies; 2310 participants; moderate-certainty evidence) and late PON (RR 0.47, 95% CI 0.32 to 0.69; 17 studies; 1682 participants; moderate-certainty evidence). Supplemental intravenous crystalloid administration probably reduces the risk of postoperative vomiting (POV) (RR 0.50, 95% CI 0.40 to 0.63; 20 studies; 1970 participants; moderate-certainty evidence). The intervention specifically reduced both early POV (RR 0.56, 95% CI 0.41 to 0.76; 19 studies; 1998 participants; moderate-certainty evidence) and late POV (RR 0.48, 95% CI 0.29 to 0.79; 15 studies; 1403 participants; moderate-certainty evidence). Supplemental intravenous crystalloid administration probably reduces the need for pharmacologic treatment of PONV (RR 0.62, 95% CI 0.51 to 0.76; 23 studies; 2416 participants; moderate-certainty evidence). The effect of supplemental intravenous crystalloid administration on the risk of unplanned postoperative admission to hospital is unclear (RR 1.05, 95% CI 0.77 to 1.43; 3 studies; 235 participants; low-certainty evidence). No studies reported serious adverse events that may occur following supplemental perioperative intravenous crystalloid administration (i.e. admission to high-dependency unit, postoperative cardiac or respiratory complication, or death). There is moderate-certainty evidence that supplemental perioperative intravenous crystalloid administration reduces PON and POV, in ASA class I to II patients receiving general anaesthesia for ambulatory or short length of stay surgical procedures. The intervention probably also reduces the risk of pharmacologic treatment for PONV. The effect of the intervention on the risk of unintended postoperative admission to hospital is unclear. The risk of serious adverse events resulting from supplemental perioperative intravenous crystalloid administration is unknown as no studies reported this outcome. The one study awaiting classification may alter the conclusions of the review once assessed.

Plain-language summary: We looked at studies where people had general anaesthesia for surgery, and received larger or smaller amounts of intravenous fluid, and were later checked to see if they developed nausea and vomiting after their surgeries were done. We found 41 studies, with 4224 participants analysed in our review. Our review suggests that giving people extra intravenous fluid during surgery under general anaesthesia probably decreases the risk of having either nausea or vomiting after surgery, and probably reduces the need for medication to treat nausea. It is unclear how giving extra intravenous fluid affects the risk of unexpectedly needing hospital admission after minor surgery. No studies looked at whether extra intravenous fluid makes other complications worse. There are two reasons why the conclusions of this review may not be exactly correct. First, many of the studies were not designed perfectly. Second, the studies did not agree on exactly how helpful the extra intravenous fluids were for preventing nausea and vomiting. Most studies did find it at least somewhat helpful.