Perioperative Increase in Blood Flow and Postop Outcomes
Perioperative Increase in Blood Flow and Postop Outcomes
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2012, Issue 1), MEDLINE via OvidSP (1966 to March 2012), and EMBASE via OvidSP (1982 to March 2012). For searching in MEDLINE, we combined our topic-specific key words with the Cochrane highly sensitive search strategy for identifying randomized controlled trials (RCTs). We modified this filter for use in EMBASE. We used specific keywords to identify potential studies (Appendix).
We searched the proceedings of the following major, relevant European and North American conferences from the year 2011 backwards for any eligible studies:
We included RCTs, with or without blinding, that were available as full published papers. We applied no language restrictions. We included adults (aged 16 years or older) undergoing surgery in an operating theatre. Perioperative administration (initiated within 24 h before surgery and lasting up to 6 h after surgery) of fluids, with or without inotropes/vasoactive drugs, to increase blood flow (relative to control) against explicit measured goals: cardiac output (CO), CI, DO2 or oxygen delivery index (DO2I), oxygen consumption or oxygen consumption index (VO2 I), SV or stroke volume index, mixed venous oxygen saturation SO2, oxygen extraction ratio (O2ER), and lactate.
Two independent authors identified titles and abstracts of potentially eligible studies. We resolved any disagreement by discussion. We obtained the full texts of potentially eligible studies. We abstracted the study characteristics including: study design; patient population; interventions; and outcomes. Two authors independently extracted data. We achieved consensus by resolving any disparity in data collection by discussion. In the absence of appropriate published data, we made at least three attempts to contact authors of eligible studies to obtain any required data. Some studies were conducted by the authors of this review. They were not involved in study selection, data extraction or risk of bias assessment. We performed the risk of bias assessment according to the Cochrane risk of bias tool.
We included studies with different treatment groups, interventions and outcomes. Consequently, we performed subgroup analyses of these differences. Many studies reported the number of complications, arrhythmias and infections as total numbers, leaving unclear what the denominators were for these episodes. We have not analysed variables for which the denominator was unknown. We contacted the authors of the studies for further information and the analysis was performed with the best available information when there was no response.
We assessed inconsistencies and variability in the outcomes among the studies by the I statistic. Variations of >40% in the outcomes may not be explained by sampling variation. We assumed substantial heterogeneity when the I statistic exceeded 40%. We assessed graphical evidence of reporting biases using contour enhanced funnel plots with a subsequent Harbord or Egger's test. We performed statistical analysis using Review Manager 5.1. We applied the intention-to-treat method for all analyses. We used both fixed-effect and random-effects models for the primary outcome analysis and the fixed-effect model for the secondary outcomes. We used relative risks (RRs) and 95% confidence intervals (95% CI) for dichotomous outcomes and mean difference [standard deviation (sd) of the mean or 95% CI] for continuous variables.
Because of the heterogeneous nature of the selected studies, we conducted subgroup analyses in the following areas:
We analysed mortality, both over the longest follow-up and hospital or 28-day mortality, with fixed-effect and random-effects models. In addition, we excluded studies with fewer than 100 participants. The intervention in the protocol group varied. The control group in some studies had explicit blood flow goals to standardize care. Further, some studies did not fully control for co-interventions, for instance admission to critical care. We performed sensitivity analysis excluding these studies.
We assessed mortality (at longest available follow-up) as the primary outcome. Mortality (all reported time frames), morbidity measures such as rates of overall complications [rates of renal impairment, arrhythmia, respiratory failure or acute respiratory distress syndrome (ARDS), infection, myocardial infarction, congestive heart failure or pulmonary oedema, and venous thrombosis] and length of intensive care unit stay, length of hospital stay as secondary outcomes.
Methods
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2012, Issue 1), MEDLINE via OvidSP (1966 to March 2012), and EMBASE via OvidSP (1982 to March 2012). For searching in MEDLINE, we combined our topic-specific key words with the Cochrane highly sensitive search strategy for identifying randomized controlled trials (RCTs). We modified this filter for use in EMBASE. We used specific keywords to identify potential studies (Appendix).
We searched the proceedings of the following major, relevant European and North American conferences from the year 2011 backwards for any eligible studies:
American College of Surgeons (2011–1996).
American Society of Anesthesiologists (2011–1995).
American Thoracic Society (2011–1997*) (*=not available for searching before 1997).
Association of Surgeons of Great Britain and Ireland (2011–1996).
European Society of Anaesthesiologists (2011–1995).
European Society of Intensive Care Medicine (2011–1983).
International Anesthesia Research Society (2011–1994).
Society of Critical Care Medicine (2011–1986).
We included RCTs, with or without blinding, that were available as full published papers. We applied no language restrictions. We included adults (aged 16 years or older) undergoing surgery in an operating theatre. Perioperative administration (initiated within 24 h before surgery and lasting up to 6 h after surgery) of fluids, with or without inotropes/vasoactive drugs, to increase blood flow (relative to control) against explicit measured goals: cardiac output (CO), CI, DO2 or oxygen delivery index (DO2I), oxygen consumption or oxygen consumption index (VO2 I), SV or stroke volume index, mixed venous oxygen saturation SO2, oxygen extraction ratio (O2ER), and lactate.
Two independent authors identified titles and abstracts of potentially eligible studies. We resolved any disagreement by discussion. We obtained the full texts of potentially eligible studies. We abstracted the study characteristics including: study design; patient population; interventions; and outcomes. Two authors independently extracted data. We achieved consensus by resolving any disparity in data collection by discussion. In the absence of appropriate published data, we made at least three attempts to contact authors of eligible studies to obtain any required data. Some studies were conducted by the authors of this review. They were not involved in study selection, data extraction or risk of bias assessment. We performed the risk of bias assessment according to the Cochrane risk of bias tool.
We included studies with different treatment groups, interventions and outcomes. Consequently, we performed subgroup analyses of these differences. Many studies reported the number of complications, arrhythmias and infections as total numbers, leaving unclear what the denominators were for these episodes. We have not analysed variables for which the denominator was unknown. We contacted the authors of the studies for further information and the analysis was performed with the best available information when there was no response.
We assessed inconsistencies and variability in the outcomes among the studies by the I statistic. Variations of >40% in the outcomes may not be explained by sampling variation. We assumed substantial heterogeneity when the I statistic exceeded 40%. We assessed graphical evidence of reporting biases using contour enhanced funnel plots with a subsequent Harbord or Egger's test. We performed statistical analysis using Review Manager 5.1. We applied the intention-to-treat method for all analyses. We used both fixed-effect and random-effects models for the primary outcome analysis and the fixed-effect model for the secondary outcomes. We used relative risks (RRs) and 95% confidence intervals (95% CI) for dichotomous outcomes and mean difference [standard deviation (sd) of the mean or 95% CI] for continuous variables.
Because of the heterogeneous nature of the selected studies, we conducted subgroup analyses in the following areas:
The urgency of surgery (elective or emergency).
The type of surgery (general, vascular, cardiac, other).
The timing of the intervention (perioperative, intraoperative, and postoperative).
The type of intervention (fluids, fluids with vasoactive agents).
The intervention goals (CO, SV, and oxygen indices).
We analysed mortality, both over the longest follow-up and hospital or 28-day mortality, with fixed-effect and random-effects models. In addition, we excluded studies with fewer than 100 participants. The intervention in the protocol group varied. The control group in some studies had explicit blood flow goals to standardize care. Further, some studies did not fully control for co-interventions, for instance admission to critical care. We performed sensitivity analysis excluding these studies.
We assessed mortality (at longest available follow-up) as the primary outcome. Mortality (all reported time frames), morbidity measures such as rates of overall complications [rates of renal impairment, arrhythmia, respiratory failure or acute respiratory distress syndrome (ARDS), infection, myocardial infarction, congestive heart failure or pulmonary oedema, and venous thrombosis] and length of intensive care unit stay, length of hospital stay as secondary outcomes.
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