The Effect of Patient Warming During Caesarean Delivery
The Effect of Patient Warming During Caesarean Delivery
The flow diagram of the study selection is provided in Fig. 1. We retrieved all 34 shortlisted articles that were identified from the literature search. Six additional publications found from reference lists of retrieved articles were added to the literature search results, only one of which was included in the final meta-analysis. No additional unpublished positive or negative trials were identified on clinicaltrials.gov. The retrieved articles were examined by two authors (P.S. and B.C.) to assess eligibility for inclusion in the meta-analysis. Excluded studies are listed in Appendix 2. Thirteen articles met our inclusion criteria. Of the studies that met the inclusion criteria: 2 evaluated forced air warming; 8 evaluated fluid warming; 1 study utilized forced air warming for 15 min before anaesthesia with or without fluid warming; and 2 studies utilized warmed fluids with or without forced air warming. A total of 789 patients were recruited in all study groups (320 in the warmed fluids group, 96 patients in the forced air warming group, and 373 patients in the control groups). The methodology utilized in each study is summarized in Table 1. Temperatures of the warmed fluid groups among the studies ranged from 30 to 42°C.
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Figure 1.
Literature search outlining included and excluded studies.
394 patients in the warmed groups and 366 patients in the control groups from 12 studies were analysed for the primary outcome (298 warmed fluid and 96 forced air warming vs 270 and 96 controls respectively). Overall warming significantly reduced maximum temperature change compared with control (SMD −1.27°C [−1.86, −0.69]; P=0.00002; Fig. 2). The risk-of-bias graph and contour-enhanced funnel plot for the primary outcome are shown in Figs 3 and 4 respectively. There was significant heterogeneity for the primary outcome (I=92%). The Egger's test suggests risk of publication bias (P=0.001). Examination of the contour-enhanced funnel plot also suggests that publication bias might be a plausible explanation for the funnel plot asymmetry.
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Figure 2.
Forest plots of the primary outcome of maximum core temperature change.
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Figure 3.
Risk of bias figure for primary outcome of maximum temperature change.
(Enlarge Image)
Figure 4.
Contour-enhanced funnel plot for primary outcome of maximum temperature change.
Fluid warming and forced air warming were both associated with a reduced temperature change compared with control groups receiving no warming (Fig. 2). There was no significant difference between the two warming modalities for this outcome (P=0.511).
In subgroup analysis according to warming method, there was significant heterogeneity in the fluid warming studies (I=94%) and the forced air warming studies (I=85%). The heterogeneity remained even when restricting analysis to only spinal anaesthesia in the fluid warming studies (I=88%) and forced air warming studies (I 80%).
For the forced air warming studies, excluding the epidural anaesthesia study resulted in loss of statistical significance (SMD −0.7 [−1.4, 0.002]; P=0.05; I=78%), however, exclusion of the lower body warming study (SMD −1.3 [−2.2, −0.36]; P=0.006; I 85%) or analysing studies utilizing only spinal anaesthesia resulted in statistical significance (SMD −0.9[−1.8, −0.09]; P=0.03; I 80%) being maintained.
Temperature at the end of surgery (or on arrival to the post anaesthetic care unit) was assessed in 10 studies ( Table 2 ) and was found to be significantly higher in the warmed fluid group compared with the control group. Results for the effect of warming on shivering, hypothermia and thermal comfort are also demonstrated in Table 2 . Twelve studies explored the incidence of shivering. Warming was associated with significantly less shivering (NNT=7) and a reduced incidence of hypothermia (NNT=5). Most studies defined hypothermia as <36°C, except for one which defined it as ≤35.5°C. Thermal comfort was improved with forced air warming. Thermal comfort was measured in most studies as a VAS 0–100 scale (100=insufferably hot, 50=thermoneutral and 0=unimaginably cold), and one study utilized a −50 to +50 scale (−50=worst imaginable cold, 0=thermally neutral, +50=insufferably hot). The study by Chung utilized a 0–100 scale (0 mm insufferably hot, 50 mm as thermally neutral and 100 mm as worst imaginable cold). Two studies utilized a 0–10 scale, but were not included in the analysis because of a lack of reporting of sd in one study or only reporting the outcome in dichotomized form. Both those studies reported improved thermal comfort with warming.
The remaining maternal outcomes and side effects are summarized in Table 2 . Hypotension was evaluated in six studies. Two of these studies found no difference between groups but did not present the data. Three studies neither presented nor commented on whether hypotension differed between groups. Woolnough defined intraoperative hypotension as >30% decrease from baseline systolic pressure; Yokoyama defined hypotension as SBP below 90 mm Hg; Workhoven defined hypotension as <20% of preoperative baseline or SBP <100 mm Hg; and Jorgensen defined hypotension as SBP less than 30% of baseline or <100 mm Hg. For the studies analysed in this meta-analysis, warming did not significantly reduce the incidence of hypotension, vomiting or requirement for vasopressor.
Neonatal outcomes are shown in Table 2. Neonatal temperature at delivery was not significantly higher with active maternal warming. Umbilical vein blood pH was not significantly different in the warmed groups, however umbilical artery pH was significantly higher in the warmed group with a mean difference in pH of 0.02 [0.00–0.05]. Apgar scores at 1 and 5 min were not significantly higher in the warmed groups and incidence of Apgar score <7 was not significantly different in the warmed group.
Temperature at the end of surgery was significantly higher with the use of fluid warming (0.46°C), but not forced air warming (0.39°C) when compared with control groups (P<0.00001 and 0.09 respectively). Fluid warming was associated with significantly less shivering (NNT=7), whereas forced air warming did not result in significant reduction of shivering incidence compared with controls. Hypothermia was significantly reduced in fluid warming (NNT=5) group but not forced air warming group compared with control. Neonatal outcomes were not different with either warming method compared with controls.
Forest plots of maternal shivering, maternal thermal comfort, maternal hypothermia and umbilical artery pH are available as supplementary material online http://bja.oxfordjournals.org/content/115/4/500/suppl/DC1.
Results
The flow diagram of the study selection is provided in Fig. 1. We retrieved all 34 shortlisted articles that were identified from the literature search. Six additional publications found from reference lists of retrieved articles were added to the literature search results, only one of which was included in the final meta-analysis. No additional unpublished positive or negative trials were identified on clinicaltrials.gov. The retrieved articles were examined by two authors (P.S. and B.C.) to assess eligibility for inclusion in the meta-analysis. Excluded studies are listed in Appendix 2. Thirteen articles met our inclusion criteria. Of the studies that met the inclusion criteria: 2 evaluated forced air warming; 8 evaluated fluid warming; 1 study utilized forced air warming for 15 min before anaesthesia with or without fluid warming; and 2 studies utilized warmed fluids with or without forced air warming. A total of 789 patients were recruited in all study groups (320 in the warmed fluids group, 96 patients in the forced air warming group, and 373 patients in the control groups). The methodology utilized in each study is summarized in Table 1. Temperatures of the warmed fluid groups among the studies ranged from 30 to 42°C.
(Enlarge Image)
Figure 1.
Literature search outlining included and excluded studies.
Primary Outcome
394 patients in the warmed groups and 366 patients in the control groups from 12 studies were analysed for the primary outcome (298 warmed fluid and 96 forced air warming vs 270 and 96 controls respectively). Overall warming significantly reduced maximum temperature change compared with control (SMD −1.27°C [−1.86, −0.69]; P=0.00002; Fig. 2). The risk-of-bias graph and contour-enhanced funnel plot for the primary outcome are shown in Figs 3 and 4 respectively. There was significant heterogeneity for the primary outcome (I=92%). The Egger's test suggests risk of publication bias (P=0.001). Examination of the contour-enhanced funnel plot also suggests that publication bias might be a plausible explanation for the funnel plot asymmetry.
(Enlarge Image)
Figure 2.
Forest plots of the primary outcome of maximum core temperature change.
(Enlarge Image)
Figure 3.
Risk of bias figure for primary outcome of maximum temperature change.
(Enlarge Image)
Figure 4.
Contour-enhanced funnel plot for primary outcome of maximum temperature change.
Subgroup Analysis According to Method of Warming (Fluid Warming or Forced Air Warming) for the Primary Outcome
Fluid warming and forced air warming were both associated with a reduced temperature change compared with control groups receiving no warming (Fig. 2). There was no significant difference between the two warming modalities for this outcome (P=0.511).
In subgroup analysis according to warming method, there was significant heterogeneity in the fluid warming studies (I=94%) and the forced air warming studies (I=85%). The heterogeneity remained even when restricting analysis to only spinal anaesthesia in the fluid warming studies (I=88%) and forced air warming studies (I 80%).
For the forced air warming studies, excluding the epidural anaesthesia study resulted in loss of statistical significance (SMD −0.7 [−1.4, 0.002]; P=0.05; I=78%), however, exclusion of the lower body warming study (SMD −1.3 [−2.2, −0.36]; P=0.006; I 85%) or analysing studies utilizing only spinal anaesthesia resulted in statistical significance (SMD −0.9[−1.8, −0.09]; P=0.03; I 80%) being maintained.
Secondary Maternal Outcomes
Temperature at the end of surgery (or on arrival to the post anaesthetic care unit) was assessed in 10 studies ( Table 2 ) and was found to be significantly higher in the warmed fluid group compared with the control group. Results for the effect of warming on shivering, hypothermia and thermal comfort are also demonstrated in Table 2 . Twelve studies explored the incidence of shivering. Warming was associated with significantly less shivering (NNT=7) and a reduced incidence of hypothermia (NNT=5). Most studies defined hypothermia as <36°C, except for one which defined it as ≤35.5°C. Thermal comfort was improved with forced air warming. Thermal comfort was measured in most studies as a VAS 0–100 scale (100=insufferably hot, 50=thermoneutral and 0=unimaginably cold), and one study utilized a −50 to +50 scale (−50=worst imaginable cold, 0=thermally neutral, +50=insufferably hot). The study by Chung utilized a 0–100 scale (0 mm insufferably hot, 50 mm as thermally neutral and 100 mm as worst imaginable cold). Two studies utilized a 0–10 scale, but were not included in the analysis because of a lack of reporting of sd in one study or only reporting the outcome in dichotomized form. Both those studies reported improved thermal comfort with warming.
The remaining maternal outcomes and side effects are summarized in Table 2 . Hypotension was evaluated in six studies. Two of these studies found no difference between groups but did not present the data. Three studies neither presented nor commented on whether hypotension differed between groups. Woolnough defined intraoperative hypotension as >30% decrease from baseline systolic pressure; Yokoyama defined hypotension as SBP below 90 mm Hg; Workhoven defined hypotension as <20% of preoperative baseline or SBP <100 mm Hg; and Jorgensen defined hypotension as SBP less than 30% of baseline or <100 mm Hg. For the studies analysed in this meta-analysis, warming did not significantly reduce the incidence of hypotension, vomiting or requirement for vasopressor.
Neonatal Outcomes
Neonatal outcomes are shown in Table 2. Neonatal temperature at delivery was not significantly higher with active maternal warming. Umbilical vein blood pH was not significantly different in the warmed groups, however umbilical artery pH was significantly higher in the warmed group with a mean difference in pH of 0.02 [0.00–0.05]. Apgar scores at 1 and 5 min were not significantly higher in the warmed groups and incidence of Apgar score <7 was not significantly different in the warmed group.
Subgroup Analysis According to Method of Warming (Fluid Warming or Forced Air Warming) for Secondary Outcomes
Temperature at the end of surgery was significantly higher with the use of fluid warming (0.46°C), but not forced air warming (0.39°C) when compared with control groups (P<0.00001 and 0.09 respectively). Fluid warming was associated with significantly less shivering (NNT=7), whereas forced air warming did not result in significant reduction of shivering incidence compared with controls. Hypothermia was significantly reduced in fluid warming (NNT=5) group but not forced air warming group compared with control. Neonatal outcomes were not different with either warming method compared with controls.
Forest plots of maternal shivering, maternal thermal comfort, maternal hypothermia and umbilical artery pH are available as supplementary material online http://bja.oxfordjournals.org/content/115/4/500/suppl/DC1.
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