The introduction of the pulse oximeter, a clinical monitor of oxygen saturation and pulsation levels, has made it possible to monitor perioperative hypoxaemia with a non-invasive continuous measuring technique (Severinghaus 1992).
The greatest value of pulse oximetry is its ability to provide an early warning of hypoxaemia. Hypoxaemia is one of the most feared adverse events during anaesthesia and in the recovery period. For the individual patient, it is unpredictable at which level of hypoxaemia the brain, heart, and other organs suffer from hypoxaemia and to what extent irreversible damage may arise. Many factors, such as cardiac output, haemoglobin concentration, and oxygen demand, affect the lowest tolerable value of oxyhaemoglobin saturation (Bendixen 1963). The occurrence and possible pathogenesis of perioperative hypoxaemia were described many years ago (Laver 1964; Nunn 1965).
Monitoring with pulse oximetry might improve patient outcomes by enabling an early diagnosis and, consequently, correction of perioperative events that might cause postoperative complications or even death (Cooper 1984). An operational definition of such an event is an undesirable incident that required intervention and did, or possibly could, cause complications or death. Such events may be attributed to pathophysiologic processes, malfunction of the gas supply or equipment, or human error, for example oesophageal intubation or anaesthetic mismanagement. For many of these events, hypoxaemia is possibly the most common mechanism responsible for the eventual adverse outcomes (Cooper 1987).
Recent studies have suggested that hypoxaemia is common in the operating theatre and recovery room. Monitoring with pulse oximetry permits early diagnosis and treatment of hypoxaemia, thus reducing the incidence and severity of this condition (Canet 1991; Cote 1991). Only a few randomized clinical trials of pulse oximetry have been performed during anaesthesia and in the recovery room that describe perioperative hypoxaemic events, postoperative cardiopulmonary complications, and cognitive dysfunction (Cote 1988; Cote 1991; Moller 1998; Møller 1994). It was recently hypothesized that continuous pulse oximetry would reduce unplanned respiratory and total admissions to the intensive care unit (ICU) for cardiothoracic postoperative patients in the general surgical care area, and decrease length of ICU readmission (Ochroch 2006).
Many departments and societies of anaesthesiology have adopted standards for perioperative patient monitoring, including the use of pulse oximetry, in order to improve anaesthesia care in accordance with the hypothesis that this may reduce perioperative complications.
To study the use of perioperative monitoring with pulse oximetry to clearly identify the adverse outcomes that might be prevented or improved by its use.
The following hypotheses were tested.
- The use of pulse oximetry is associated with an improvement in the detection and treatment of hypoxaemia.
- Early detection and treatment of hypoxaemia reduces morbidity and mortality in the perioperative period.
- The use of pulse oximetry per se reduces morbidity as well as mortality in the perioperative period.
- The use of pulse oximetry reduces unplanned respiratory admissions to the ICU and decreases length of ICU readmission, or both.
Criteria for considering studies for this review
Types of studies
We included all randomized and quasi-randomized controlled trials dealing with the use of pulse oximetry or no pulse oximetry during the perioperative period, including in the operating and recovery rooms. We included trials irrespective of blinding, number of patients randomized, or language of the article.
Types of participants
We included patients,18 years of age or older, undergoing surgery with anaesthesia.
Types of interventions
We included the following interventions: pulse oximetry or no pulse oximetry during the anaesthesia and recovery period.
Types of outcome measures
The primary outcome measures were postoperative complications and mortality from all causes, assessed at the end of the follow-up period scheduled for each trial.
- Any serious complications that occurred during anaesthesia or in the postoperative period: admittance to postoperative intensive care due to: respiratory insufficiency, circulatory insufficiency, or infections; respiratory insufficiency due to pneumonia (fever, chest x-ray, or positive culture), atelectasis (chest x-ray), pneumothorax (diagnosed on chest x-ray), or requiring intervention; cardiovascular insufficiency (cardiac arrest, cardiac failure, myocardial infarction); renal and hepatic insufficiency; neurologic and cognitive dysfunction (measuring memory function with the Weschler memory scale); serious infection requiring antibiotics.
- Intra- or postoperative mortality.
- Events detectable by pulse oximetry:
- hypoxaemia (pulse oximetry estimate of arterial oxyhaemoglobin saturation (SpO
2) less than 90%, corresponding to an arterial oxygen tension less than 7.9 kPa).
- Causes of events:
- patient respiratory causes of hypoxaemia (pneumothorax, bronchospasm, air embolus, respiratory depression, apnoea, airway obstruction, pneumonia, ventilatory failure, and pulmonary emboli;
- patient mechanical causes of hypoxaemia (oesophageal or main stem intubation, mucus plug, kinked endotracheal tube);
- delivery system causes of hypoxaemia (anaesthesia machine, and gas supply problems).
- Interventions that may prevent, attenuate, or shorten these events:
- airway support;
- endotracheal intubation;
- manual or mechanical ventilation;
- oxygen treatment;
- pressors and inotropes;
- fluid treatment.
Search methods for identification of studies
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2009), see Appendix 1; MEDLINE via OvidSP (1966 to May 2009), see Appendix 2; EMBASE via OvidSP (1980 to May 2009), see Appendix 3; CINAHL via EBSCO host (1982 to May 2009), see Appendix 4; ISI Web of Science (1956 to May 2009), see Appendix 5; and LILACS via the BIREME interface (1982 to May 2009), see Appendix 6. We searched the following databases of ongoing trials with the free text terms: oximetry, oxymetry or pulse oximetry.
- Current Controlled Trials including the UK Clinical Trials Gateway and The Wellcome Trust
We handsearched the bibliography of each article for relevant references.
We did not impose any language restriction.
Data collection and analysis
We selected trials to be included in the systematic review based on the results of the search strategy. One author (KH) scanned the titles and abstracts of reports identified by electronic searching to produce a list of possibly relevant reports. Two authors (TP, AM) independently assessed all studies for inclusion. We retrieved all eligible studies in full text.
We considered the methods and adequacy of randomization, blinding, and description of withdrawals in the quality assessment. We defined a clear account of a successful randomization as that where: adequate measures were taken to conceal allocation (for example central randomization; serially numbered, opaque, sealed envelopes; or another description that contained elements convincing of adequate concealment). The randomization and allocation concealment method was assessed for each study and defined as A (centralized randomization by telephone; numbered or coded identical containers administered sequentially; on-site computer system which could only be accessed after entering the characteristics of an enrolled participant; sequentially numbered, sealed, opaque envelopes); B (sealed envelopes but not sequentially numbered or opaque; list of random numbers read by someone entering patient into trial; a trial in which the description suggested adequate concealment but other features were suspicious, for example markedly unequal control and trial intervention groups; stated random but unable to obtain further details); C (any allocation procedure that was transparent before assignment, for example an open list of random numbers, alteration, date of birth, day of week, case record number); or D (not described).
We extracted the following data on the randomization and blinding procedures:
- number of randomized patients;
- number of patients not randomized and the reasons for this;
- exclusion after randomization;
- blinding of patients and observers.
We extracted data on perioperative complications and deaths.
We used the statistical package MetaView in Review Manager (RevMan 5.0) provided by The Cochrane Collaboration.
Description of studies
In this new update we re-ran our searches for the period from 2002 to May 2009. In our original review we found six studies (Pedersen 2003a) however two studies were ineligible for analysis, so four studies with 21,773 participants were included. In our updated search we found one new study with 1219 participants (Ochroch 2006).
|Figure 1. Search results|
Risk of bias in included studies
This section lists only the type of trial and methods of allocation concealment used. The identified reports of studies had other flaws which might affect the validity of the study findings. These are further described under 'Results'.
Randomized trial, single-blinded outcome assessment. Method of randomization unknown.
Randomized trial. Method of randomization unknown.
Quasi-randomized trial, blinded comparison. Patients were allocated to an operating theatre after pulse oximeters were allocated randomly to 50% of those theatres. Allocation concealment was by use of coded, sealed envelopes.
Quasi-randomized study. Elective patients admitted for an operation were allocated to an operating theatre after pulse oximeters were allocated randomly to 50% of those theatres. Allocation concealment was by use of coded, sealed envelopes. For emergency operations, a numbered envelope containing the random assignment for each patient was drawn from a stack.
Randomized trial. Patients were allocated using sequential, sealed envelopes containing randomly-generated group assignments.
Effects of interventions
Searching yielded five reports. All outcome measures in the included studies were extracted and are detailed in the table 'Characteristics of included studies'. The types of outcome measures were separated into events detectable by pulse oximetry that could result in complications, and perioperative complications. This is considered in the same way below.
Studies used a number of different ways of assessing the postoperative outcome.
- Events with hypoxaemia measured either with blood gas analysers or pulse oximetry (two trials).
- Tests of cognitive function: Wechsler memory scale, continuous reaction time, and subjective perception of cognitive dysfunction (test of memory) (one trial).
- Clinical outcome: respiratory, cardiovascular, and neurologic complications following anaesthesia (one trial).
- Unplanned respiratory admissions to the ICU, decreased length of ICU readmission, or both (one trial).
Studies using blood gas analysis and pulse oximetry to assess hypoxaemia
In the study of Bierman 1992 the staff were instructed to use the pulse oximetry data in lieu of arterial blood gas analysis, whenever possible, in group one. The desaturation alarm on the oximeters was set to sound at values less than or equal to 93%. For patients in group two, blood gas analyses were obtained every hour or more frequently as clinically indicated; these patients were monitored with a modified pulse oximeter from which the SpO
Moller 1992a found that hypoxaemia was reduced in the pulse oximetry group, both in the operating theatre and in the recovery room. During observation in the recovery room the incidence of hypoxaemia in the pulse oximetry group was 1.5 to 3 times less, and no patient experienced extreme or severe hypoxaemia. In the pulse oximetry group the lowest recorded SpO
As a consequence of pulse oximetry monitoring, changes were made in the recovery room for several interventions: the patients in the oximeter group received an increased fraction of inspired oxygen (FiO
Study using tests of cognitive dysfunction
Moller 1993b demonstrated that the postoperative cognitive function, as measured by the Wechsler memory scale and continuous reaction time, was independent of perioperative monitoring with pulse oximetry. The postoperative subjective reports (by questionnaire) of cognitive deficits revealed no statistically significant difference: 7% in the pulse oximetry and 11% in the group without pulse oximetry believed their cognitive abilities had decreased. There was no statistically significant difference in the ability to concentrate (10% versus 9%). The study showed no evidence of less postoperative cognitive impairment after perioperative monitoring with pulse oximetry.
Study using clinical measures of complications to the time of discharge
The study of Moller 1993c, including 20,802 surgical patients randomly assigned to monitoring with pulse oximetry or not, found that one or more postoperative complications occurred in 10% of the patients in the oximetry group and in 9.4% in the control group. The two groups did not differ in the number of cardiovascular, respiratory, neurologic, or infectious complications. The duration of hospital stay was a median of five days in both groups. An equal number of in-hospital deaths occurred in the two groups, 1.1% in the oximeter group and 1.0% in the control group; a total of seven deaths were classified as possibly anaesthesia related, three deaths in the oximetry group and four in the control group. The seven deaths did not display any specific pattern. A questionnaire that was completed by the anaesthesiologists revealed that 18% of the anaesthesiologists had experienced a situation in which a pulse oximeter helped to avoid a serious event or complication and that 80% of the anaesthesiologists felt more secure when they used a pulse oximeter. Although monitoring with pulse oximetry prompted a number of changes in patient care, there was no evidence of a reduction in the overall rate of postoperative complications using perioperative pulse oximetry.
Study using pulse oximetry monitoring on intensive care unit admissions from postsurgical care
The study of Ochroch 2006 included 1219 patients enrolled from approximately 8300 patients who met the eligibility criteria. Rates of readmission to the ICU were similar in the monitored and unmonitored groups. Of the 93 patients (8% of all participants) who were transferred to the ICU after enrolment, 40 were in the monitored group of 589 participants (6.7%) and 53 were in the unmonitored group of 630 participants (8.5%) (P < 0.33). Participants transferred to the ICU did not differ from those not transferred to the ICU (“discharged”) in terms of age, gender, race, or surgical service. Starting in the cardiothoracic intensive care unit (CTICU) before transfer to the study floor was significantly associated with return to an ICU (odds ratio (OR) 2.1; 95% confidence interval (CI) 1.3 to 4.9; P < 0.001). The reasons for transfer back to the ICU (determined by blinded review of the ICU transfer notes) differed between monitored and unmonitored groups, with more pulmonary events in the unmonitored group compared with the continuous pulse oximetry (CPOX) monitored group (27 versus 8; P < 0.003). The use of CPOX did not impact on duration of stay in the hospital or total estimated cost of hospitalization when examining the entire cohort. Routine CPOX and usual care groups had similar numbers of days from enrolment to discharge from the study, number of days from enrolment to discharge from the hospital, estimated costs while on the study floor, and estimated costs for the entire hospital stay. There were 14 in-hospital deaths in each group. The effects of the deaths on the study outcomes were assessed by re-examining the study outcomes without these patients’ data, in a sensitivity analysis. The deaths did not affect outcomes or produce or enhance differences between groups.
The studies confirmed that pulse oximetry can detect hypoxaemia and related events. The conflicting subjective and objective results of the studies, despite an intense methodical collection of data from a relatively large population, indicate that perioperative monitoring with pulse oximetry can reduce pulmonary events, but in general monitoring does not lead to improvements in patient outcomes, or effectiveness and efficiency of care.
Perioperative hypoxaemia and postoperative complications
Comparisons of the overall rates of perioperative hypoxaemia and postoperative complications are difficult with the present randomized studies because of the limited number of studies and participants, and differences in the types of outcomes investigated. It appears that the general rates of hypoxaemia and complications in the present studies are at the same level as reported in other studies (Mlinaric 1997; Moller 1998; Pedersen 1994; Rheineck 1996; Stausholm 1997).
The demonstration of reduced extent of hypoxaemia, the ability to detect and correct potential harmful events and to make several changes in patient care with pulse oximetry monitoring is in contrast to the fact that no reduction in the number of postoperative complications was found (Moller 1993c). The fact that patients monitored with pulse oximetry have no change in outcome, despite the fact that they tend to be given more oxygen and naloxone (Moller 1993c), is worth emphasizing. It indicates that merely increasing saturation levels from marginal to satisfactory is probably not going to make any difference in patient outcomes. In other words, the use of pulse oximetry as an early warning of moderate hypoxaemia does not appear to be beneficial even if the appropriate responses are instituted earlier than they would have been without pulse oximetry. This result conflicts with most anaesthesiologists' beliefs. In the closed claims analyses of adverse respiratory events in anaesthesia, reviewers judged that better monitoring would have prevented adverse outcome in 72% of the claims (Caplan 1990; Tinker 1989). In the general analysis of the role of monitoring devices in the prevention of anaesthetic mishaps, nearly 60% of the instances of death and brain damage were considered preventable by application of additional monitors. These studies exhibit a number of limitations including absence of a control group, a probable bias toward adverse outcomes, and reliance on data from the participants rather than objective observers.
The study of Moller 1993c showed that 18% of the participating anaesthesiologists reported one or more situations in which they thought pulse oximetry helped to avoid a serious event or complication. This subjective reporting suggests an effect of pulse oximetry monitoring on outcome, but objective figures for the rate of postoperative complications does not confirm this. There was also a large contrast between the objective results of the study of Moller 1993c and the subjective opinions of the participating anaesthesiologists regarding the usefulness of pulse oximetry.
Postoperative cognitive dysfunction
The relationship between perioperative hypoxaemia and impaired postoperative cognitive function is debated (Krasheninnikoff 1993). Moller 1993b found that 9% of the surgical patients thought that their mental function had deteriorated. In a more recent study (Moller 1998) postoperative cognitive dysfunction in the elderly, as identified with neuropsychological tests, was present in 25.8% of patients one week after surgery, and in 9.9% three months after surgery. However, hypoxaemia was not a significant risk factor for cognitive dysfunction at any time. Perioperative monitoring with pulse oximetry did not appear to affect the patients' postoperative cognitive function.
Pulse oximetry monitoring on intensive care unit admissions from postsurgical care
The randomized clinical trial of third generation CPOX technology (Ochroch 2006) reported that monitoring did reduce respiratory readmissions to an ICU after cardiothoracic surgery. It is possible that CPOX monitoring increases overall nursing vigilance, resulting in increased non-respiratory ICU transfers. If appropriate, such transfers may contribute to the benefits of CPOX observed in this study. If such transfers represent inappropriately aggressive care then there is the potential for routine CPOX monitoring to further reduce ICU readmissions with further training of nurses. If there is a real benefit of CPOX in reducing ICU transfer, the lack of reduction in the absolute rate of return to an ICU by CPOX use can also be considered a dilutional effect. The large group of patients who did well regardless of the monitoring overwhelms any beneficial effect of monitoring in the much smaller group who may have benefited from the monitoring. This is similar to the perioperative data, which show a decreased rate of hypoxaemia when pulse oximetry is used (Moller 1992a) but no change in rare outcomes (myocardial infarction, stroke, and death) (Moller 1993c). In conclusion, in this population of patients the use of CPOX was associated with reduced postoperative ICU admission for pulmonary complications. Routine CPOX monitoring was not associated with an overall decreased transfer to ICU or mortality.
Methods of assessing cognitive function
Tests of cognitive function are valuable when studying anaesthetic drug effects but a number of patients have unexplained complaints of impaired cognitive function that are not verified by objective tests (Moller 1998). One may speculate that application of a broader range of neuropsychological assessments than used in the Moller 1998 study could have detected varying deficits of an enduring nature. Using a broad range of tests, investigators have described moderate to severe cognitive dysfunction that lasted for several months after coronary bypass surgery (Townes 1989).
The quality of blinding and allocation concealment in the included studies was variable. Although pulse oximetry monitoring techniques were well standardized (Cullen 1992; Mateer 1993) these trials did not all use correct randomized designs or outcome variables. Three of the studies (Bierman 1992; Moller 1992a; Moller 1993b) used adequate randomization and were blinded, however two studies (Moller 1993c; Ochroch 2006) were not blinded and used sequential sealed envelopes (see table 'Characteristics of included studies'). Furthermore, power analyses were seldom conducted to determine adequate sample sizes. Consequently, even the studies with high-quality blinding and allocation concealment may still not provide reliable results.
Statistical analysis of data
Due to the variety of outcome variables used in the five studies, there are no two groups which could be compared directly by formal meta-analysis.
Has pulse oximetry monitoring improved the safety of anaesthesia?
The proliferation of monitors in anaesthesia is obvious. The goal of monitoring as an adjunct to clinical decision making is to directly reduce the incidence of complications. This is based on the premise that unambiguous and accurate information, which is readily interpretable and available, will help the anaesthetist in deciding and initiating correct therapeutic interventions. The unanswered question is whether the individual anaesthesiologist's performance, the human factor, is perhaps far more important than implementing new monitoring equipment or other new safety initiatives in a situation in which we wish to reduce the rate of postoperative complications. However, we do not know whether pulse oximetry might protect against the human factor, when that factor is negligent.
Other factors have to be considered. The overwhelming majority of patients in the included studies come from a region where standards of anaesthesia and nursing care are good. Almost all the data were collected by a single group of people. This reduces the generality of the results in terms of what might be found in other geographical areas where standards of care and assessment methods may be different. Since the detected hypoxic events were treated, we do not really know what the differences in outcomes would have been if hypoxic events were neither detected nor treated. The studies were relatively well controlled and did not reproduce situations where there is a high likelihood of disaster.
Implications for practice
Pulse oximetry monitoring substantially reduced the extent of perioperative hypoxaemia, enabled the detection and treatment of hypoxaemia and related respiratory events, and promoted several changes in patient care. The implementation of perioperative pulse oximetry monitoring was not, however, the breakthrough which could reduce the number of postoperative complications. The question remains whether pulse oximetry improves outcome in other situations. Pulse oximetry has already been adopted into clinical practice all over the world. It may be a tool that guides the anaesthesiologists in the daily management of patients, in teaching situations, emergencies, and especially in caring for children. Although the results of the studies are not conclusive, the data suggest that there may be a benefit for a population at high risk of postoperative pulmonary complications. The results of the studies of general surgery indicate that perioperative monitoring with pulse oximetry does not improve clinically relevant outcomes, effectiveness or efficiency of care despite an intense, methodical collection of data from a large population.
Implications for research
It is time to focus on which technologies are needed. The science of human factors includes the psychological and mental factors affecting performance in the workplace. Monitoring systems should fit naturally with the way the anaesthetist works, thinks, and interacts with the patient, equipment, and operating room environment so they can, together with vigilance and clinical decision-making, bring significant benefits.
Future work in this area would benefit from greater attention to methods of randomization, as we found only a few appropriately randomized studies. The impact of new monitoring equipment on outcomes should be evaluated and controlled in the same way as is customary when introducing new drugs. The potential for continuous pulse oximetry to allow for early intervention, or perhaps prevention of pulmonary complications, needs to be explored. As the present studies illustrate, the problems are multitudinous. The worst problem is clearly the huge number of patients needed. By limiting the inclusion criteria to a specific subgroup of patients (for example patients aged greater than 65 years, with cardiac risk factors, with ASA physical status III and IV, or undergoing acute abdominal surgery), isolating more rigorous outcome variables, and establishing wide co-operation between departments and countries new monitoring and anaesthesia safety studies could be launched in the future.
We thank Mathew Zacharias for editing the current updated version of this review.
We would like to acknowledge Nete Villebro, Janet Wale and Kathie Godfrey for their contribution to the plain language summary. We would also like to acknowledge Dr Bente Dyrlund Pedersen's contribution to our previous review (Pedersen 2003a).
Data and analyses
This review has no analyses.
Appendix 1. Search strategy for CENTRAL, The Cochrane Library
#1 (operation or peri?op* or post?op* or intra?op* or surg*):ti,ab
#2 (pulse near ox?met*)
#3 MeSH descriptor Oximetry explode all trees
#4 (#1 AND ( #2 OR #3 ))
Appendix 2. Search strategy for MEDLINE (Ovid SP)
1 (operation or perioperat* or postoperat* or intraoperat* or surg*).mp.
2 ((pulse adj6 oximet*) or (pulse adj6 oxymet*)).mp. or exp Oximetry/ or oxymet*.ti,ab.
3 ((randomized controlled trial or controlled clinical trial).pt. or randomized.ab. or placebo.ab. or clinical trials as topic.sh. or randomly.ab. or trial.ti.) and humans.sh.
4 1 and 3 and 2
Appendix 3. Search strategy for EMBASE (Ovid SP)
1 (operation or perioperat* or postoperat* or intraoperat* or surg*).mp.
2 exp Pulse Oximetry/ or exp Oximetry/
3 ((pulse adj6 oximet*) or (pulse adj6 oxymet*) or oxymet* or oximet*).mp.
4 3 or 2
5 (placebo.sh. or controlled study.ab. or "random*".ti,ab. or trial*.ti.) and human*.ec,hw,fs.
6 1 and 4 and 5
Appendix 4. Search strategy for CINAHL (EBSCOhost)
S1 TX (operation or perioperat* or postoperat* or intraoperat* or surg*)
S2 (MH "Perioperative Care+")
S3 (MH "Postoperative Care+")
S4 (MH "Intraoperative Care+") or (MH "Intraoperative Monitoring+")
S5 S4 or S3 or S2 or S1
S6 (MM "Pulse Oximeters") or (MM "Pulse Oximetry")
S7 TX (pulse and ox?met*)
S8 S7 or S6
S9 S8 and S5
S10 (MM "Random Assignment") or (MH "Clinical Trials+")
S11 AB random*
S12 TI trial
S13 AB placebo
S14 S13 or S12 or S11 or S10
S15 S14 and S9
Appendix 5. Search strategy for ISI Web of Science
# 1 TS=(operation or perioperat* or postoperat* or intraoperat* or surg*)
# 2 TS=((pulse SAME oximet*) or (pulse SAME oxymet*) or oxymet*)
# 3 #2 AND #1
# 4 TS=(random* or ((controlled or clinical) SAME trial*) or placebo)
# 5 #4 AND #3
Appendix 6. Search strategy for LILACS (BIREME)
("OXYMETER" or "OXYMETRY" or "puls oximet$") and (operation or perioperat$ or postoperat$ or intraoperat$ or surg$)
Last assessed as up-to-date: 30 April 2009.
Protocol first published: Issue 2, 2000
Review first published: Issue 3, 2001
Contributions of authors
Conceiving the review: TP, AM
Co-ordinating the review: TP, AM
Undertaking electronic and manual searches: TP, AM, KH
Screening search results: TP, AM, KH
Organizing retrieval of papers: KH
Screening retrieved papers against inclusion criteria: TP, AM, KH
Appraising quality of papers: TP, AM
Extracted data from papers: TP, AM
Writing to authors of papers for additional information: TP
Obtaining and screening data on unpublished studies: TP
Data management for the review: TP, AM
Entering data into Review Manager (RevMan 5.0): TP, KH
RevMan statistical data: TP, AM
Other statistical analysis not using RevMan: TP, AM
Double entry of data: ( data entered by person two:) TP, AM
Interpretation of data: TP, AM
Statistical inferences: TP, AM
Writing the review: TP, AM, KH
Securing funding for the review: TP
Performing previous work that was the foundation of the present study:
Guarantor for the review (one author): TP
Person responsible for reading and checking review before submission: TP
Declarations of interest
One of the authors (TP) is a co-author of one study included in the review (Moller 1993c).
All other authors: none known.
Medical Subject Headings (MeSH)
MeSH check words
* Indicates the major publication for the study