The effect of duration of dose delivery with patient-controlled analgesia on the incidence of nausea and vomiting after hysterectomy

Abstract

Aims: Postoperative nausea and vomiting (PONV) may be exacerbated by postoperative opioid analgesics and may limit patients' successful use of these medications when used with patient controlled analgesia (PCA). We tested the hypothesis that the rapid change in blood morphine concentration associated with PCA bolus delivery contributed to PONV, and that prolonging its delivery to a brief infusion would result in decreased PONV.

Methods: Patients, who were receiving morphine for pain relief via patient-controlled analgesia (PCA) after total abdominal hysterectomy, received 1 mg morphine sulphate incremental doses either over 40 s with a 5 min lockout interval or over 5 min delivery with a 1 min lockout interval. Episodes of nausea, retching and vomiting, along with the use of morphine and the pain relief obtained, were recorded.

Results: Data from 20 patients in each group were analysed. Contrary to expectations, most patients in both groups reported nausea postoperatively. Those patients receiving morphine over 5 min experienced more episodes of emesis (36) than those receiving the dose over 40 s (17). Most patients receiving the 40 s doses vomited in the first 12 h (median time 8 h), while those receiving the 5 min doses vomited between 12 and 24 h (median time 19 h) (P = 0.01). There were no differences between groups in the visual analogue pain scores or use of morphine between groups.

Conclusions: Reasons for these unexpected findings remain speculative. The high incidence of PONV appears to be inherently high in gynaecological surgery patients and standard antiemetic medication regimens appear to be poorly efficacious. Reasons for the differences in the time-course of emetic episodes between the two groups may be related to differences in the time-course of central opioid receptor occupancy.

Figures

Figure 1

Pharmacokinetic modelling of morphine sulphate delivered as 1 mg over 40 s (upper panels) and over 5 min (lower panels). Left panels show amounts of morphine in the various compartments of the three compartment open mamillary model; right panels show concentrations of morphine in the plasma-containing central compartment. [The parameters used for the simulations were Vc=16l; ke=0.08 min−1; k12=0.5 min−1; k21=0.2 min−1; k13=0.09 min−1; k31=0.008 min−1; Vss=236 l; CL=1.28 l min−1].

Figure 2

Individual patients’ cumulative dose of morphine sulphate by intravenous PCA with 1 mg incremental doses delivered over 40 s (upper panel) or 5 min (lower panel). Emetic episodes are indicated as dots.

Figure 3

Box and whisker plots showing total nausea scores (upper panels) and total vomiting scores (lower panels). Patients received morphine sulphate by intravenous PCA with 1 mg incremental doses delivered either over 40 s (left panels, □) or 5 min (right panels,). Data are shown as median with boxes of 25 and 75 percentiles, whiskers of 10 and 90 percentiles and data (circles) outlying these, for 12 h time segments.

Figure 4

Mean and s.d. of total pain scores (VAS in mm) for groups receiving intravenous PCA with 1 mg incremental doses of morphine sulphate delivered either over 40 s (□) or over 5 min () (upper panel). Mean and s.d. of morphine sulphate use by patients receiving intravenous PCA with delivery over 40 s or over 5 min (lower panel). Data for both panels are for 12 h time segments.