Psychological preparation and postoperative outcomes for adults undergoing surgery under general anaesthesia

Rachael Powell, Neil W. Scott, Anne Manyande, Julie Bruce, Claus Vögele, Lucie M. T. Byrne-Davis, Mary Unsworth, Christian Osmer, Marie Johnston

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Abstract

BACKGROUND: In a review and meta-analysis conducted in 1993, psychological preparation was found to be beneficial for a range of outcome variables including pain, behavioural recovery, length of stay and negative affect. Since this review, more detailed bibliographic searching has become possible, additional studies testing psychological preparation for surgery have been completed and hospital procedures have changed. The present review examines whether psychological preparation (procedural information, sensory information, cognitive intervention, relaxation, hypnosis and emotion-focused intervention) has impact on the outcomes of postoperative pain, behavioural recovery, length of stay and negative affect.

OBJECTIVES: To review the effects of psychological preparation on postoperative outcomes in adults undergoing elective surgery under general anaesthetic.

SEARCH METHODS: We searched the Cochrane Register of Controlled Trials (CENTRAL 2014, Issue 5), MEDLINE (OVID SP) (1950 to May 2014), EMBASE (OVID SP) (1982 to May 2014), PsycINFO (OVID SP) (1982 to May 2014), CINAHL (EBESCOhost) (1980 to May 2014), Dissertation Abstracts (to May 2014) and Web of Science (1946 to May 2014). We searched reference lists of relevant studies and contacted authors to identify unpublished studies. We reran the searches in July 2015 and placed the 38 studies of interest in the `awaiting classification' section of this review.

SELECTION CRITERIA: We included randomized controlled trials of adult participants (aged 16 or older) undergoing elective surgery under general anaesthesia. We excluded studies focusing on patient groups with clinically diagnosed psychological morbidity. We did not limit the search by language or publication status. We included studies testing a preoperative psychological intervention that included at least one of these seven techniques: procedural information; sensory information; behavioural instruction; cognitive intervention; relaxation techniques; hypnosis; emotion-focused intervention. We included studies that examined any one of our postoperative outcome measures (pain, behavioural recovery, length of stay, negative affect) within one month post-surgery.

DATA COLLECTION AND ANALYSIS: One author checked titles and abstracts to exclude obviously irrelevant studies. We obtained full reports of apparently relevant studies; two authors fully screened these. Two authors independently extracted data and resolved discrepancies by discussion.

Where possible we used random-effects meta-analyses to combine the results from individual studies. For length of stay we pooled mean differences. For pain and negative affect we used a standardized effect size (the standardized mean difference (SMD), or Hedges' g) to combine data from different outcome measures. If data were not available in a form suitable for meta-analysis we performed a narrative review.

MAIN RESULTS: Searches identified 5116 unique papers; we retrieved 827 for full screening. In this review, we included 105 studies from 115 papers, in which 10,302 participants were randomized. Mainly as a result of updating the search in July 2015, 38 papers are awaiting classification. Sixty-one of the 105 studies measured the outcome pain, 14 behavioural recovery, 58 length of stay and 49 negative affect. Participants underwent a wide range of surgical procedures, and a range of psychological components were used in interventions, frequently in combination. In the 105 studies, appropriate data were provided for the meta-analysis of 38 studies measuring the outcome postoperative pain (2713 participants), 36 for length of stay (3313 participants) and 31 for negative affect (2496 participants). We narratively reviewed the remaining studies (including the 14 studies with 1441 participants addressing behavioural recovery). When pooling the results for all types of intervention there was low quality evidence that psychological preparation techniques were associated with lower postoperative pain (SMD -0.20, 95% confidence interval (CI) -0.35 to -0.06), length of stay (mean difference -0.52 days, 95% CI -0.82 to -0.22) and negative affect (SMD -0.35, 95% CI -0.54 to -0.16) compared with controls. Results tended to be similar for all categories of intervention, although there was no evidence that behavioural instruction reduced the outcome pain. However, caution must be exercised when interpreting the results because of heterogeneity in the types of surgery, interventions and outcomes. Narratively reviewed evidence for the outcome behavioural recovery provided very low quality evidence that psychological preparation, in particular behavioural instruction, may have potential to improve behavioural recovery outcomes, but no clear conclusions could be reached.

Generally, the evidence suffered from poor reporting, meaning that few studies could be classified as having low risk of bias. Overall,we rated the quality of evidence for each outcome as 'low' because of the high level of heterogeneity in meta-analysed studies and the unclear risk of bias. In addition, for the outcome behavioural recovery, too few studies used robust measures and reported suitable data for meta-analysis, so we rated the quality of evidence as `very low'.

AUTHORS' CONCLUSIONS: The evidence suggested that psychological preparation may be beneficial for the outcomes postoperative pain, behavioural recovery, negative affect and length of stay, and is unlikely to be harmful. However, at present, the strength of evidence is insufficient to reach firm conclusions on the role of psychological preparation for surgery. Further analyses are needed to explore the heterogeneity in the data, to identify more specifically when intervention techniques are of benefit. As the current evidence quality is low or very low, there is a need for well-conducted and clearly reported research.

Original languageEnglish
Article numberCD008646
Pages (from-to)1-283
Number of pages283
JournalCochrane Database of Systematic Reviews
Issue number5
DOIs
Publication statusPublished - 26 May 2016

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General Anesthesia
Psychology
Length of Stay
Meta-Analysis
Outcome Assessment (Health Care)
Hypnosis
Confidence Intervals
Emotions
Psychological Techniques
Relaxation Therapy
General Anesthetics
MEDLINE
Publications
Language
Randomized Controlled Trials
Morbidity
Research

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Psychological preparation and postoperative outcomes for adults undergoing surgery under general anaesthesia. / Powell, Rachael; Scott, Neil W.; Manyande, Anne; Bruce, Julie; Vögele, Claus; Byrne-Davis, Lucie M. T.; Unsworth, Mary; Osmer, Christian; Johnston, Marie.

In: Cochrane Database of Systematic Reviews, No. 5, CD008646, 26.05.2016, p. 1-283.

Research output: Contribution to journalArticle

Powell, Rachael ; Scott, Neil W. ; Manyande, Anne ; Bruce, Julie ; Vögele, Claus ; Byrne-Davis, Lucie M. T. ; Unsworth, Mary ; Osmer, Christian ; Johnston, Marie. / Psychological preparation and postoperative outcomes for adults undergoing surgery under general anaesthesia. In: Cochrane Database of Systematic Reviews. 2016 ; No. 5. pp. 1-283.
@article{a435c291d46c4a3eb44a41a940c55975,
title = "Psychological preparation and postoperative outcomes for adults undergoing surgery under general anaesthesia",
abstract = "BACKGROUND: In a review and meta-analysis conducted in 1993, psychological preparation was found to be beneficial for a range of outcome variables including pain, behavioural recovery, length of stay and negative affect. Since this review, more detailed bibliographic searching has become possible, additional studies testing psychological preparation for surgery have been completed and hospital procedures have changed. The present review examines whether psychological preparation (procedural information, sensory information, cognitive intervention, relaxation, hypnosis and emotion-focused intervention) has impact on the outcomes of postoperative pain, behavioural recovery, length of stay and negative affect.OBJECTIVES: To review the effects of psychological preparation on postoperative outcomes in adults undergoing elective surgery under general anaesthetic.SEARCH METHODS: We searched the Cochrane Register of Controlled Trials (CENTRAL 2014, Issue 5), MEDLINE (OVID SP) (1950 to May 2014), EMBASE (OVID SP) (1982 to May 2014), PsycINFO (OVID SP) (1982 to May 2014), CINAHL (EBESCOhost) (1980 to May 2014), Dissertation Abstracts (to May 2014) and Web of Science (1946 to May 2014). We searched reference lists of relevant studies and contacted authors to identify unpublished studies. We reran the searches in July 2015 and placed the 38 studies of interest in the `awaiting classification' section of this review.SELECTION CRITERIA: We included randomized controlled trials of adult participants (aged 16 or older) undergoing elective surgery under general anaesthesia. We excluded studies focusing on patient groups with clinically diagnosed psychological morbidity. We did not limit the search by language or publication status. We included studies testing a preoperative psychological intervention that included at least one of these seven techniques: procedural information; sensory information; behavioural instruction; cognitive intervention; relaxation techniques; hypnosis; emotion-focused intervention. We included studies that examined any one of our postoperative outcome measures (pain, behavioural recovery, length of stay, negative affect) within one month post-surgery.DATA COLLECTION AND ANALYSIS: One author checked titles and abstracts to exclude obviously irrelevant studies. We obtained full reports of apparently relevant studies; two authors fully screened these. Two authors independently extracted data and resolved discrepancies by discussion.Where possible we used random-effects meta-analyses to combine the results from individual studies. For length of stay we pooled mean differences. For pain and negative affect we used a standardized effect size (the standardized mean difference (SMD), or Hedges' g) to combine data from different outcome measures. If data were not available in a form suitable for meta-analysis we performed a narrative review.MAIN RESULTS: Searches identified 5116 unique papers; we retrieved 827 for full screening. In this review, we included 105 studies from 115 papers, in which 10,302 participants were randomized. Mainly as a result of updating the search in July 2015, 38 papers are awaiting classification. Sixty-one of the 105 studies measured the outcome pain, 14 behavioural recovery, 58 length of stay and 49 negative affect. Participants underwent a wide range of surgical procedures, and a range of psychological components were used in interventions, frequently in combination. In the 105 studies, appropriate data were provided for the meta-analysis of 38 studies measuring the outcome postoperative pain (2713 participants), 36 for length of stay (3313 participants) and 31 for negative affect (2496 participants). We narratively reviewed the remaining studies (including the 14 studies with 1441 participants addressing behavioural recovery). When pooling the results for all types of intervention there was low quality evidence that psychological preparation techniques were associated with lower postoperative pain (SMD -0.20, 95{\%} confidence interval (CI) -0.35 to -0.06), length of stay (mean difference -0.52 days, 95{\%} CI -0.82 to -0.22) and negative affect (SMD -0.35, 95{\%} CI -0.54 to -0.16) compared with controls. Results tended to be similar for all categories of intervention, although there was no evidence that behavioural instruction reduced the outcome pain. However, caution must be exercised when interpreting the results because of heterogeneity in the types of surgery, interventions and outcomes. Narratively reviewed evidence for the outcome behavioural recovery provided very low quality evidence that psychological preparation, in particular behavioural instruction, may have potential to improve behavioural recovery outcomes, but no clear conclusions could be reached.Generally, the evidence suffered from poor reporting, meaning that few studies could be classified as having low risk of bias. Overall,we rated the quality of evidence for each outcome as 'low' because of the high level of heterogeneity in meta-analysed studies and the unclear risk of bias. In addition, for the outcome behavioural recovery, too few studies used robust measures and reported suitable data for meta-analysis, so we rated the quality of evidence as `very low'.AUTHORS' CONCLUSIONS: The evidence suggested that psychological preparation may be beneficial for the outcomes postoperative pain, behavioural recovery, negative affect and length of stay, and is unlikely to be harmful. However, at present, the strength of evidence is insufficient to reach firm conclusions on the role of psychological preparation for surgery. Further analyses are needed to explore the heterogeneity in the data, to identify more specifically when intervention techniques are of benefit. As the current evidence quality is low or very low, there is a need for well-conducted and clearly reported research.",
author = "Rachael Powell and Scott, {Neil W.} and Anne Manyande and Julie Bruce and Claus V{\"o}gele and Byrne-Davis, {Lucie M. T.} and Mary Unsworth and Christian Osmer and Marie Johnston",
note = "Acknowledgements We wish to dedicate this work to the memory of Christian Osmer, a dedicated, caring doctor who was committed to achieving the best care for his patients and their relatives. He saw his contribution to this project as a way of advancing best care for surgical patients. We are very grateful for his valuable input to this work and the pleasure we had in working with him. We are grateful to Karen Hovhanisyan (former Trials Search Co-ordinator, Cochrane Anaesthesia, Critical and Emergency Care Group (ACE)) for carrying out the electronic database searches and to Jane Cracknell (Managing Editor, ACE) for her support throughout the review process. We would also like to thank W Alastair Chambers and Manjeet Shehmar for clinical advice relating to judgements about general anaesthesia usage, and Yvonne Cooper and Louise Pike who retrieved documents and screened papers as research assistants in earlier stages of the review. We are grateful to the following colleagues who helped us with foreign language papers - either by screening papers or by providing translation: Stefano Carrubba, Chuan Gao, Chen Ji, Kate Rhie, Reza Roudsari and Alena Vasianovich. We would like to thank Andy Smith (content editor), Nathan Pace (statistical editor), Michael Donnelly, Allan Cyna and Michael Wang (peer reviewers), and Shunjie Chua (consumer referee) for their help and editorial advice during the preparation of this systematic review. We would also like to thank Andrew Smith (content editor), Nathan Pace (statistical editor), Michael Wang and Allan Cyna (peer reviewers), and Lynda Lane (Cochrane Consumer Network representative) for their help and editorial advice during the preparation of the protocol (Powell 2010). Sources of support Internal sources Manchester Centre for Health Psychology, University of Manchester, UK. An award of £2000 was received to support research assistant costs. External sources British Academy, UK. We received a small research grant of £7480 to support research assistant costs.",
year = "2016",
month = "5",
day = "26",
doi = "10.1002/14651858.CD008646.pub2",
language = "English",
pages = "1--283",
journal = "Cochrane Database of Systematic Reviews",
issn = "1469-493X",
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TY - JOUR

T1 - Psychological preparation and postoperative outcomes for adults undergoing surgery under general anaesthesia

AU - Powell, Rachael

AU - Scott, Neil W.

AU - Manyande, Anne

AU - Bruce, Julie

AU - Vögele, Claus

AU - Byrne-Davis, Lucie M. T.

AU - Unsworth, Mary

AU - Osmer, Christian

AU - Johnston, Marie

N1 - Acknowledgements We wish to dedicate this work to the memory of Christian Osmer, a dedicated, caring doctor who was committed to achieving the best care for his patients and their relatives. He saw his contribution to this project as a way of advancing best care for surgical patients. We are very grateful for his valuable input to this work and the pleasure we had in working with him. We are grateful to Karen Hovhanisyan (former Trials Search Co-ordinator, Cochrane Anaesthesia, Critical and Emergency Care Group (ACE)) for carrying out the electronic database searches and to Jane Cracknell (Managing Editor, ACE) for her support throughout the review process. We would also like to thank W Alastair Chambers and Manjeet Shehmar for clinical advice relating to judgements about general anaesthesia usage, and Yvonne Cooper and Louise Pike who retrieved documents and screened papers as research assistants in earlier stages of the review. We are grateful to the following colleagues who helped us with foreign language papers - either by screening papers or by providing translation: Stefano Carrubba, Chuan Gao, Chen Ji, Kate Rhie, Reza Roudsari and Alena Vasianovich. We would like to thank Andy Smith (content editor), Nathan Pace (statistical editor), Michael Donnelly, Allan Cyna and Michael Wang (peer reviewers), and Shunjie Chua (consumer referee) for their help and editorial advice during the preparation of this systematic review. We would also like to thank Andrew Smith (content editor), Nathan Pace (statistical editor), Michael Wang and Allan Cyna (peer reviewers), and Lynda Lane (Cochrane Consumer Network representative) for their help and editorial advice during the preparation of the protocol (Powell 2010). Sources of support Internal sources Manchester Centre for Health Psychology, University of Manchester, UK. An award of £2000 was received to support research assistant costs. External sources British Academy, UK. We received a small research grant of £7480 to support research assistant costs.

PY - 2016/5/26

Y1 - 2016/5/26

N2 - BACKGROUND: In a review and meta-analysis conducted in 1993, psychological preparation was found to be beneficial for a range of outcome variables including pain, behavioural recovery, length of stay and negative affect. Since this review, more detailed bibliographic searching has become possible, additional studies testing psychological preparation for surgery have been completed and hospital procedures have changed. The present review examines whether psychological preparation (procedural information, sensory information, cognitive intervention, relaxation, hypnosis and emotion-focused intervention) has impact on the outcomes of postoperative pain, behavioural recovery, length of stay and negative affect.OBJECTIVES: To review the effects of psychological preparation on postoperative outcomes in adults undergoing elective surgery under general anaesthetic.SEARCH METHODS: We searched the Cochrane Register of Controlled Trials (CENTRAL 2014, Issue 5), MEDLINE (OVID SP) (1950 to May 2014), EMBASE (OVID SP) (1982 to May 2014), PsycINFO (OVID SP) (1982 to May 2014), CINAHL (EBESCOhost) (1980 to May 2014), Dissertation Abstracts (to May 2014) and Web of Science (1946 to May 2014). We searched reference lists of relevant studies and contacted authors to identify unpublished studies. We reran the searches in July 2015 and placed the 38 studies of interest in the `awaiting classification' section of this review.SELECTION CRITERIA: We included randomized controlled trials of adult participants (aged 16 or older) undergoing elective surgery under general anaesthesia. We excluded studies focusing on patient groups with clinically diagnosed psychological morbidity. We did not limit the search by language or publication status. We included studies testing a preoperative psychological intervention that included at least one of these seven techniques: procedural information; sensory information; behavioural instruction; cognitive intervention; relaxation techniques; hypnosis; emotion-focused intervention. We included studies that examined any one of our postoperative outcome measures (pain, behavioural recovery, length of stay, negative affect) within one month post-surgery.DATA COLLECTION AND ANALYSIS: One author checked titles and abstracts to exclude obviously irrelevant studies. We obtained full reports of apparently relevant studies; two authors fully screened these. Two authors independently extracted data and resolved discrepancies by discussion.Where possible we used random-effects meta-analyses to combine the results from individual studies. For length of stay we pooled mean differences. For pain and negative affect we used a standardized effect size (the standardized mean difference (SMD), or Hedges' g) to combine data from different outcome measures. If data were not available in a form suitable for meta-analysis we performed a narrative review.MAIN RESULTS: Searches identified 5116 unique papers; we retrieved 827 for full screening. In this review, we included 105 studies from 115 papers, in which 10,302 participants were randomized. Mainly as a result of updating the search in July 2015, 38 papers are awaiting classification. Sixty-one of the 105 studies measured the outcome pain, 14 behavioural recovery, 58 length of stay and 49 negative affect. Participants underwent a wide range of surgical procedures, and a range of psychological components were used in interventions, frequently in combination. In the 105 studies, appropriate data were provided for the meta-analysis of 38 studies measuring the outcome postoperative pain (2713 participants), 36 for length of stay (3313 participants) and 31 for negative affect (2496 participants). We narratively reviewed the remaining studies (including the 14 studies with 1441 participants addressing behavioural recovery). When pooling the results for all types of intervention there was low quality evidence that psychological preparation techniques were associated with lower postoperative pain (SMD -0.20, 95% confidence interval (CI) -0.35 to -0.06), length of stay (mean difference -0.52 days, 95% CI -0.82 to -0.22) and negative affect (SMD -0.35, 95% CI -0.54 to -0.16) compared with controls. Results tended to be similar for all categories of intervention, although there was no evidence that behavioural instruction reduced the outcome pain. However, caution must be exercised when interpreting the results because of heterogeneity in the types of surgery, interventions and outcomes. Narratively reviewed evidence for the outcome behavioural recovery provided very low quality evidence that psychological preparation, in particular behavioural instruction, may have potential to improve behavioural recovery outcomes, but no clear conclusions could be reached.Generally, the evidence suffered from poor reporting, meaning that few studies could be classified as having low risk of bias. Overall,we rated the quality of evidence for each outcome as 'low' because of the high level of heterogeneity in meta-analysed studies and the unclear risk of bias. In addition, for the outcome behavioural recovery, too few studies used robust measures and reported suitable data for meta-analysis, so we rated the quality of evidence as `very low'.AUTHORS' CONCLUSIONS: The evidence suggested that psychological preparation may be beneficial for the outcomes postoperative pain, behavioural recovery, negative affect and length of stay, and is unlikely to be harmful. However, at present, the strength of evidence is insufficient to reach firm conclusions on the role of psychological preparation for surgery. Further analyses are needed to explore the heterogeneity in the data, to identify more specifically when intervention techniques are of benefit. As the current evidence quality is low or very low, there is a need for well-conducted and clearly reported research.

AB - BACKGROUND: In a review and meta-analysis conducted in 1993, psychological preparation was found to be beneficial for a range of outcome variables including pain, behavioural recovery, length of stay and negative affect. Since this review, more detailed bibliographic searching has become possible, additional studies testing psychological preparation for surgery have been completed and hospital procedures have changed. The present review examines whether psychological preparation (procedural information, sensory information, cognitive intervention, relaxation, hypnosis and emotion-focused intervention) has impact on the outcomes of postoperative pain, behavioural recovery, length of stay and negative affect.OBJECTIVES: To review the effects of psychological preparation on postoperative outcomes in adults undergoing elective surgery under general anaesthetic.SEARCH METHODS: We searched the Cochrane Register of Controlled Trials (CENTRAL 2014, Issue 5), MEDLINE (OVID SP) (1950 to May 2014), EMBASE (OVID SP) (1982 to May 2014), PsycINFO (OVID SP) (1982 to May 2014), CINAHL (EBESCOhost) (1980 to May 2014), Dissertation Abstracts (to May 2014) and Web of Science (1946 to May 2014). We searched reference lists of relevant studies and contacted authors to identify unpublished studies. We reran the searches in July 2015 and placed the 38 studies of interest in the `awaiting classification' section of this review.SELECTION CRITERIA: We included randomized controlled trials of adult participants (aged 16 or older) undergoing elective surgery under general anaesthesia. We excluded studies focusing on patient groups with clinically diagnosed psychological morbidity. We did not limit the search by language or publication status. We included studies testing a preoperative psychological intervention that included at least one of these seven techniques: procedural information; sensory information; behavioural instruction; cognitive intervention; relaxation techniques; hypnosis; emotion-focused intervention. We included studies that examined any one of our postoperative outcome measures (pain, behavioural recovery, length of stay, negative affect) within one month post-surgery.DATA COLLECTION AND ANALYSIS: One author checked titles and abstracts to exclude obviously irrelevant studies. We obtained full reports of apparently relevant studies; two authors fully screened these. Two authors independently extracted data and resolved discrepancies by discussion.Where possible we used random-effects meta-analyses to combine the results from individual studies. For length of stay we pooled mean differences. For pain and negative affect we used a standardized effect size (the standardized mean difference (SMD), or Hedges' g) to combine data from different outcome measures. If data were not available in a form suitable for meta-analysis we performed a narrative review.MAIN RESULTS: Searches identified 5116 unique papers; we retrieved 827 for full screening. In this review, we included 105 studies from 115 papers, in which 10,302 participants were randomized. Mainly as a result of updating the search in July 2015, 38 papers are awaiting classification. Sixty-one of the 105 studies measured the outcome pain, 14 behavioural recovery, 58 length of stay and 49 negative affect. Participants underwent a wide range of surgical procedures, and a range of psychological components were used in interventions, frequently in combination. In the 105 studies, appropriate data were provided for the meta-analysis of 38 studies measuring the outcome postoperative pain (2713 participants), 36 for length of stay (3313 participants) and 31 for negative affect (2496 participants). We narratively reviewed the remaining studies (including the 14 studies with 1441 participants addressing behavioural recovery). When pooling the results for all types of intervention there was low quality evidence that psychological preparation techniques were associated with lower postoperative pain (SMD -0.20, 95% confidence interval (CI) -0.35 to -0.06), length of stay (mean difference -0.52 days, 95% CI -0.82 to -0.22) and negative affect (SMD -0.35, 95% CI -0.54 to -0.16) compared with controls. Results tended to be similar for all categories of intervention, although there was no evidence that behavioural instruction reduced the outcome pain. However, caution must be exercised when interpreting the results because of heterogeneity in the types of surgery, interventions and outcomes. Narratively reviewed evidence for the outcome behavioural recovery provided very low quality evidence that psychological preparation, in particular behavioural instruction, may have potential to improve behavioural recovery outcomes, but no clear conclusions could be reached.Generally, the evidence suffered from poor reporting, meaning that few studies could be classified as having low risk of bias. Overall,we rated the quality of evidence for each outcome as 'low' because of the high level of heterogeneity in meta-analysed studies and the unclear risk of bias. In addition, for the outcome behavioural recovery, too few studies used robust measures and reported suitable data for meta-analysis, so we rated the quality of evidence as `very low'.AUTHORS' CONCLUSIONS: The evidence suggested that psychological preparation may be beneficial for the outcomes postoperative pain, behavioural recovery, negative affect and length of stay, and is unlikely to be harmful. However, at present, the strength of evidence is insufficient to reach firm conclusions on the role of psychological preparation for surgery. Further analyses are needed to explore the heterogeneity in the data, to identify more specifically when intervention techniques are of benefit. As the current evidence quality is low or very low, there is a need for well-conducted and clearly reported research.

U2 - 10.1002/14651858.CD008646.pub2

DO - 10.1002/14651858.CD008646.pub2

M3 - Article

C2 - 27228096

SP - 1

EP - 283

JO - Cochrane Database of Systematic Reviews

JF - Cochrane Database of Systematic Reviews

SN - 1469-493X

IS - 5

M1 - CD008646

ER -