Search Results
The databases we searched identified 1,839 articles, including 346 duplicates. We screened a total of 1,490 titles and abstracts and selected 79 articles for full-text evaluation. We identified no additional articles from the reference lists of the included studies or review articles, and of the 79 articles that underwent full-text evaluation, we excluded 71 for the reasons stated in the PRISMA flowchart (Figure 1). A total of eight studies met the inclusion criteria, including six crossover RCTs [36-41] and two nonrandomised crossover studies [42,43].
Characteristics of Included Studies
An overview of included studies is presented in Table 2. We identified no studies that evaluated the effect of maternal positioning during CPR on primary outcomes; therefore, no data were available on survival rates and the return of spontaneous circulation following maternal cardiac arrest. Fetal/neonatal outcomes were also unavailable. The only outcomes available constituted indirect evidence of the quality of CPR, which was obtained from simulation-based studies using hypothetical cardiac arrest maternal patient mannequins. The studies originated from the United Kingdom (n = 4), South Korea (n = 2) and Japan (n = 2). Of these, one randomised crossover study [39] examined the effect of the manual left uterine displacement in the supine position using a silicone pregnancy bump to simulate a woman in the third trimester of pregnancy and compared the results to those obtained in the left-lateral tilt achieved with a firm wedge. The remaining four randomised crossover studies [36-38,40] and one nonrandomised crossover study [42] compared the quality of chest compression on a mannequin lying supine with that of one lying on a 27°–30° left-inclined lateral tilting surface [36-38,40] or resting on the thighs of a kneeling assistant (‘human wedge’)[42]. One randomised crossover study examined the optimal methods for producing lateral tilt comparing soft pillow wedge: firm foam wedge, hard wooden wedge or human wedge [41], and one nonrandomised crossover study [43] examined the effect of chest compression at various angles between 0° and 90° of inclination. All participants in the included studies were health professionals (including medical students) and performed two or more sequential interventions. The quality of CPR was measured for chest compression (e.g. compression rate, depth, correct compression depth rate, correct recoil rates and/or correct hand position rate) and air ventilation. Subjective stability and difficulty (or ease) of chest compression also were assessed in some trials.
Table 2
Characteristics of included studies.
Authors/Year
|
Country
|
Study Design
|
Participants
|
Comparison
|
Device
|
Outcomes
|
Rees & Willis., 1988 [43]
|
UK
|
Simulation based non-randomised crossover study
|
8 medical doctors
(7 anaesthetists and one cardiologist)
|
Chest compression (CC) in various angles; 0°, 27º, 32º, 49º and 90º left lateral tilt (LTT)
|
Calibrated force transducer fitted on the plane
|
- Resuscitative (compression) force as % of body weight (mean, standard deviation [SD])
|
Goodwin 1992 [42]
|
UK
|
Simulation based non-randomised crossover study
|
18 midwives
|
CC in supine without manual left uterine displacement (LUD) vs. CC in lateral tilt produced by human wedge (the degree of tilt not reported)
|
Laerdal
Resusci Anne®
Skill Reporting System
|
- Correct chest compressions (definition not described), % (mean, SD)
- Correct expired air ventilations (definition not described), (mean, SD)
|
Lee et al., 2011 [36]
|
South Korea
|
Simulation-based crossover RCT
|
30 emergency medical residents and technicians
|
CC in supine without manual LUD vs. CC in 30° LLT surface
|
Laerdal
Resusci Anne®
Skill Reporting System (Stavanger, Norway)
|
- Compression rate, per minute (mean, 95% confidence interval [CI])
- Compression depth, mm (mean, 95% CI)
- Correct compression depth rate, 50–60 mm, % (mean, 95% CI)
- Correct recoil rate, % (mean, 95% CI)
- Correct hand position rate, % (mean, 95% CI)
- Highest compression angle (mean, 95% CI)
- Lowest compression angle (mean, 95% CI)
- Subjective difficulty of CC, 5-point Likert scale (mean, 95% CI)
|
Kim et al., 2013
[37]
|
South Korea
|
Simulation-based crossover RCT
|
32 BLS-trained medical students (inexperienced rescuers without CPR experience)
|
CC in supine without manual LUD vs. CC in 30° LLT surface
|
Laerdal
Resusci Anne® Skill Reporting System (Stavanger, Norway)
|
- Compression rate, per minute (mean, 95% CI)
- Compression depth, mm (mean, 95% CI)
- Correct compression depth rate, 50–60 mm, % (mean, 95% CI)
- Correct recoil rate, % (mean, 95% CI)
- Correct hand position rate, % (mean, 95% CI)
- Highest compression angle (mean, 95% CI)
- Lowest compression angle (mean, 95% CI)
- Subjective difficulty of CC, 5-point Likert scale (mean, 95% CI)
|
Komasawa et al., 2013 [38]
|
Japan
|
Simulation-based crossover RCT
|
27 male medical doctors (with CPR experience)
|
CC in supine without manual LUD vs. CC in 27° LLT surface
(by standing on the left and right
sides of the patient)
|
Laerdal
Resuci Anne®
Skill Reporting System
(Stavanger, Norway)
|
- Compression rate, per minute (mean, SD)
- Compression depth mm (mean, SD)
- Correct compression depth rate (> 50 mm), % (mean, 95% CI)
- Correct recoil rate, % (mean)
|
Ip et al. 2013 [41]
|
UK
|
Simulation-based crossover RCT
|
40 healthcare professionals (anaesthetists and midwives)
|
CC in the LLT with the soft wedge (pillow) vs. firm wedge (foam-rubber) vs. hard wedge (wooden) vs. human wedge
|
Laerdal
Resusci Anne® Skill Reporting System (Kent, UK),
|
- Compression rate, per minute (mean, 95% CI)
- Compression depth mm (median, interquartile range [IQR])
- Correct compression depth rate (> 50 mm), % (median, IQR)
- Correct recoil rate (proportion of compressions adequately released), % (mean, 95% CI)
- Subjective stability of CC, 5-point Likert scale (median, IQR)
|
Butcher et al., 2014 [39]
|
UK
|
Simulation-based crossover RCT
|
20 BLS/ALS-trained healthcare professionals
(10 anaesthetists and 10 midwives)
|
CC in supine with manual displacement of uterus vs. CC in LLT produced by a preformed firm-rubber wedge on the floor and on a bed (angle not reported)
|
Laerdal
Resusci Anne® Skill Reporting System (Kent, UK), with ‘pregnancy bump’
|
- Compression rate, per minute (mean, SD)
- Compression depth mm (median, IQR)
- Correct compression depth rate (> 50 mm; median, IQR)
- Correct recoil rate, % (median, IQR)
- Subjective stability and ease of CC, 5-point Likert scale (median, IQR)
|
Dohi et al., 2017 [40]
|
Japan
|
Simulation-based crossover RCT
|
20 BLS-certified healthcare professionals
|
CC in supine without manual LUD vs. 30° LLT surface
|
Laerdal
Skill Reporting System
|
- Compression rate, per minute (mean, SD)
- Compression depth mm (mean, SD)
- Correct compression depth rate (50–60 mm), % (mean, SD)
- Correct recoil rate (within 5 mm of baseline chest height), % (mean, SD)
- Correct hand position rate, % (mean, SD)
- Subjective ease of CC, 5-point Likert scale (mean, 95%CI)
|
Abbreviations: RCT=Randomized Controlled Trial; CC=chest compression; LUD=left uterine displacement; LLT=left lateral tilt; CPR=cardiopulmonary resuscitation; BLS=Basic life support; ALS=advanced life support; SD=standard deviation; CI=confidence interval; IQR=interquartile range. |
Risk of Bias Assessment
Bias due to randomisation:
Of the randomised crossover trials included in this review [36-41],none except one [41] reported the processes used to generate the random allocation sequence and/or allocation concealment. Bias due to deviations from intended interventions: Given the nature of the interventions, participants (rescuers) in all studies were aware of their assigned intervention (e.g. chest compression in the supine or lateral tilting positions) during each period of the trial. Four studies [36,37,40,41] ensured a washout period to minimise the carryover effect (after 2 minutes of chest compressions in the first assigned position, the participants rested for 10 minutes to minimise rescuer fatigue), whereas no information was available to assess the carryover effect in the remaining studies [38,39,42,43]. Bias due to missing outcome data: There were no missing outcomes [36-40,42,43], or the proportion of missing outcomes was small [41]. Bias due to outcome measurement: The outcomes were assessed using the PC SkillReporting software system, which was connected to the patient mannequin (Laerdal Resusci Anne®) in all the included studies [36-42] except one [43]. Where the participants could not see the monitor screen displaying the outcomes during the chest compressions, the risk of bias was considered low [37,40]; however, where information regarding blinding of the outcomes was not provided, the risk of bias was rated as of some concern by taking into account the possibility that knowing the outcomes altered the participants’ performance [36,38,39,41-43]. Bias due to selection of the reported result: No studies provided a trial protocol. Overall: Six RCTs [36-41] were rated as having some concern for risk bias, whereas the two nonrandomised crossover studies [42,43] were considered of high risk for bias because at least one domain had a high risk of bias (Table 3).
Table 3
Risk of bias assessment (judgement and supporting evidence) in the included studies using a revised Cochrane risk-of-bias tool for crossover trials.
|
Bias due to randomisation
|
Bias due to deviations from intended interventions
|
Bias due to missing outcome data
|
Bias due to outcome measurement
|
Bias due to selection of the reported result
|
Overall
|
RCTs
|
Butcher 2014 [39]
|
Some concerns: Methods used for randomisation and allocation concealment not stated
|
Some concerns: Washout period to minimise the carryover effect not stated
|
Low risk: Outcome data available for all participants randomised
|
Some concerns: Outcomes assessed with a PC SkillReporting system; blinding to the assessor not reported
|
Some concerns: Insufficient information available to assess the reporting bias
|
Some concerns
|
Dohi 2017 [40]
|
Some concerns: Methods used for randomisation and allocation concealment not stated
|
Low risk: ‘Resting for 10 min ... and repeating CPR for 2 min in the second assigned position’
|
Low risk: Outcome data available for all participants randomised
|
Low risk: ‘To avoid potential bias, rescuers were blinded to the monitor screen displaying compression rate or hand position’
|
Some concerns: Insufficient information available to assess the reporting bias
|
Some concerns
|
Ip 2013 [41]
|
Some concerns: Randomisation by drawing lots/allocation concealment not stated
|
Low risk: ‘Sufficient breaks between tests’ were taken to minimise the carryover effect
|
Low risk: Outcome data available for almost all participants, although ‘one of the participants … [was] excluded from analysis due to incomplete data capture’
|
Some concerns: Outcomes assessed with a PC SkillReporting system; blinding to the assessor not reported
|
Some concerns: Insufficient information available to assess the reporting bias
|
Some concerns
|
Kim 2012 [37]
|
Some concerns: Methods used for randomisation and allocation concealment not stated
|
Low risk: ‘The participant rested for 10 min to minimise rescuer fatigue’ between tests
|
Low risk: Outcome data available for all participants randomised
|
Low risk: ‘To avoid potential bias, participants were blinded to the monitor screen’
|
Some concerns: Insufficient information available to assess the reporting bias
|
Some concerns
|
Komasawa 2013 [38]
|
Some concerns: Methods used for randomisation and allocation concealment not stated
|
Some concerns: Washout period to minimise the carryover effect not stated
|
Low risk: Outcome data available for all participants randomised
|
Some concerns: Outcomes assessed with a PC SkillReporting system; blinding to the assessor not reported
|
Some concerns: Insufficient information available to assess the reporting bias
|
Some concerns
|
Lee 2011 [36]
|
Some concerns: Methods used for randomisation and allocation concealment not stated
|
Some concerns: Washout period to minimise the carryover effect not stated
|
Low risk: Outcome data available for all participants randomised
|
Some concerns: Outcomes assessed with a PC SkillReporting system; blinding to the assessor not reported
|
Some concerns: Insufficient information available to assess reporting bias
|
Some concerns
|
Non-RCTs
|
Goodwin 1992 [42]
|
High risk:
Not stated as being randomised
|
Some concerns: Washout period to minimise the carryover effect not stated
|
Low risk: Outcome data available for all participants randomised
|
Some concerns: Outcomes assessed with a PC SkillReporting system; blinding to the assessor not reported
|
Some concerns: Insufficient information available to assess the reporting bias
|
High risk
|
Rees and Wills 1988 [43]
|
High risk:
Not stated as being randomised
|
Some concerns: Washout period to minimise the carryover effect not stated
|
Low risk: Outcome data available for all participants randomised
|
Some concerns: Outcomes assessed with a transducer; blinding to the assessor not reported
|
Some concerns: Insufficient information available to assess the reporting bias
|
High risk
|
Intervention Effectiveness
Maternal and Fetal (or Neonatal) Outcomes
Because all the studies included in this review were conducted on mannequins, no data regarding maternal or fetal/neonatal outcomes were available for our analysis.
Quality of CPR and Subjective Stability/Difficulty of Chest Compression
All eight studies included in this review provided data regarding the quality of the CPR, and some provided data on subjective stability or difficulty (or ease) of chest compression (Table 4).
Table 4
Quality of CPR and subjective stability/difficulty of chest compression (Cont.).
Study
|
Design
|
Comparison groups (Chest compression [CC] from right/left side of patients)
|
Floor/
Bed
|
N
|
Correct hand position rate; %
|
Resuscitation (compression) force; %
|
Correct chest compressions; %
|
Subjective stability of CC
|
Mean (SD or 95%CI)
|
P
|
Mean (SD or 95%CI)
|
P
|
Mean (SD or 95%CI)
|
P
|
Median (IQR)
|
P
|
Left lateral tilt
|
Supine
|
Left lateral tilt
|
Supine
|
Left lateral tilt
|
Supine
|
Left lateral tilt
|
Supine
|
Comparison 1: Left lateral tilt position (LLT) vs. supine position with manual left uterine displacement (LUD)
|
Bucher et al. 2014 [39]
|
RCT
|
LLT- angle not reported (right)
|
Supine
(right)
|
Floor
|
20
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
median=4.0*
(IQR=3-4)
|
median=4.5*
(IQR=4-5)
|
0.048a
|
Bed
|
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
median=3.0* (IQR=3-3)
|
median=4.0* (IQR=4-4)
|
0.007a
|
Comparison 2: LLT vs. supine position without manual left uterine displacement
|
Dohi et al. 2017 [40]
|
RCT
|
LLT 30º
(--)
|
Supine (--)
|
Bed
|
20
|
88.8
(SD=28.6)
|
99.7
(SD=1.1)
|
<0.05b
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Kim et al. 2013 [37]
|
RCT
|
LLT 30º (left)
|
Supine (--)
|
Floor
|
32
|
72.0
(95%CI=
59.8-84.2)
|
78.1
(95%CI=
65.8-90.3)
|
0.47 c
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Komasawa et al. 2013 [38]
|
RCT
|
LLT 27º (left)
|
Supine (left)
|
Bed
|
27
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
LLT 27º (right)
|
Supine (right)
|
Bed
|
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Lee et al. 2011 [36]
|
RCT
|
LLT 30º
(left)
|
Supine
(--)
|
Floor
|
30
|
75.8
(95%CI=
63.0-88.6)
|
84.9
(95%CI=
72.2-97.7)
|
0.09c
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Goodwin 1992 [42]
|
Non-RCT
|
probably right lateral tilt
|
Supine
(--)
|
Floor
|
18
|
--
|
--
|
--
|
--
|
--
|
--
|
67.6
(SD=21)
|
32.5 (SD=24.9)
|
0.0005f
|
--
|
--
|
--
|
Comparison 3: Methods for producing LLT (soft wedge vs. firm wedge vs. hard wedge vs. human wedge)
|
Ip et al. 2013 [41]
|
RCT
|
LLT with:
Soft wedge (pillow)
vs.
Firm wedge (foam-rubber) vs.
Hard wedge (wooden)
vs.
Human wedge
|
n/a
|
Floor
|
20
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Soft: median=3*
(IQR=2-4)
Firm: median=4*
(IQR=3-4)
Hard: median=5*
(IQR=5-5)
Human:
median=3*
(IQR=1-4)
|
--
|
<0.0001
|
Bed
|
19
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Soft: median=2*
(IQR=1-3)
Firm: median=4*
(IQR=3-4)
Hard: median=4*
(IQR=3-4)
Human:
median=4*
(IQR=3-5)
|
--
|
<0.0001
|
Comparison 4: Various angles (0°, 27°, 32°, 49° and 90°) of inclination
|
Rees & Willis 1988 [43]
|
Non-RCT
|
LLT 27º, 32º, 49º, and 90º (left)
|
Supine
(--)
|
Floor
|
7
|
--
|
--
|
--
|
LLT 27º: 55.3
(SD=5.5)
LLT 32º: 46.4
(SD=3.9)
LLT 49º: 41.5
(SD=3.5)
LLT 90º: 36.3
(SD=5.4)
|
66.7
(SD=6.5)
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Table 4
Quality of CPR and subjective stability/difficulty of chest compression (Cont.).
Study
|
Design
|
Comparison groups (Chest compression [CC] from right/left side of patients)
|
Floor/
Bed
|
N
|
Subjective difficulty of CC
|
Subjective ease of CC
|
Correct expired air ventilations
|
Mean (SD or 95%CI)
|
P
|
Mean (SD or 95%CI)
|
P
|
Mean (SD or 95%CI)
|
P
|
Left lateral tilt
|
Supine
|
Left lateral tilt
|
Supine
|
Left lateral tilt
|
Supine
|
Comparison 1: Left lateral tilt position (LLT) vs. supine position with manual left uterine displacement (LUD)
|
Bucher et al. 2014 [39]
|
RCT
|
LLT- angle not reported (right)
|
Supine
(right)
|
Floor
|
20
|
--
|
--
|
--
|
median=3.0* (IQR=3-4)
|
median=4.0*
(IQR=4-4)*
|
0.011a
|
--
|
--
|
--
|
Bed
|
|
--
|
--
|
--
|
median=4.0* (IQR=3-4)
|
median=5.0 (IQR=4-5)
|
NS a
|
--
|
--
|
--
|
Comparison 2: LLT vs. supine position without manual left uterine displacement
|
Dohi et al. 2017 [40]
|
RCT
|
LLT 30º
(--)
|
Supine (--)
|
Bed
|
20
|
--
|
--
|
--
|
3.95†
(95%CI=
3.68-4.22)
|
1.75†
(95%CI=
1.31-2.19)
|
<0.001b
|
--
|
--
|
--
|
Kim et al. 2013 [37]
|
RCT
|
LLT 30º (left)
|
Supine (--)
|
Floor
|
32
|
68.8‡
(95%CI=
62.8-74.9)
|
58.3‡
(95%CI=
52.2-64.4)
|
0.007c
|
--
|
--
|
--
|
--
|
--
|
--
|
Komasawa et al. 2013 [38]
|
RCT
|
LLT 27º (left)
|
Supine (left)
|
Bed
|
27
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
LLT 27º (right)
|
Supine (right)
|
Bed
|
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Lee et al. 2011 [36]
|
RCT
|
LLT 30º
(left)
|
Supine
(--)
|
Floor
|
30
|
68.4‡
(95%CI=
62.1-74.8)
|
64.4‡
(95%CI=
58.2-71.0)
|
0.28c
|
--
|
--
|
--
|
--
|
--
|
--
|
Goodwin 1992 [42]
|
Non-RCT
|
probably right lateral tilt
|
Supine
(--)
|
Floor
|
18
|
--
|
--
|
--
|
--
|
--
|
--
|
56.7 (SD=27.7)
|
62.2 (SD=21.4)
|
NS
|
Comparison 3: Methods for producing LLT (soft wedge vs. firm wedge vs. hard wedge vs. human wedge)
|
Ip et al. 2013 [41]
|
RCT
|
LLT with:
Soft wedge (pillow)
vs.
Firm wedge (foam-rubber) vs.
Hard wedge (wooden)
vs.
Human wedge
|
n/a
|
Floor
|
20
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Bed
|
19
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Comparison 4: Various angles (0°, 27°, 32°, 49° and 90°) of inclination
|
Rees & Willis 1988 [43]
|
Non-RCT
|
LLT 27º, 32º, 49º, and 90º (left)
|
Supine
(--)
|
Floor
|
7
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
--
|
Note: CC=chest compression; LUD=left; LLT=left lateral tilt; NS=not significant.
For Dohi et al. 2017, data were obtained from the authors.
Statistical analysis used in the original studies: a) Wilcoxon signed rank sum; b) Student’s t-test; c) mixed model; d) two-way repeated ANOVA; d) repeated ANOVA; f) paired t-tests; unless specified, statistical tests used were not reported in the original studies.
* 5-point Likert-scale: 1=extremely (or very) poor; 2=poor; 3=adequate; 4=good; 5=excellent or very good (higher score =better stability or easier)
† 5-point Likert-scale: 1=very easy; 2=easy; 3=normal; 4=difficult; 5=very difficult (higher score = more difficult)
‡ Visual analogue scale from 0 mm=extremely east to 100 mm=extremely difficult (higher score = more difficult)
|
Comparison 1: Left lateral tilt position vs. manual left uterine displacement
Quality of Chest Compression
Based on one crossover RCT [39] involving 20 health professionals, there was no statistically significant difference in the quality of chest compressions as measured with compression rates, compression depth, correct compression depth (> 50 mm) rates and correct recoil rates between the manual left uterine displacement in the supine position and the left lateral tilt position produced by a firm-rubber wedge. The results were consistent both on the floor and on the bed. The mean compression rates observed ranged from 114.5/min to 118.5/min and were within the range of adequate compression rates recommended by clinical guidelines. However, insufficient compression depth (median ranging from 40 to 44 cm) and low rates of correct compression depth (median ranging from 25% to 57%) were observed across all groups, indicating generally poor performance of chest compressions in the sample of this study.
Subjective Ease and Stability of Chest Compression
One study [39] involving inexperienced rescuers reported greater ease and stability of chest compressions in the supine position with manual left uterine displacement than in the left-lateral tilt position; the differences were statistically significant.
Comparison 2: Left lateral tilt position (27°–30°) vs. supine position without manual left uterine displacement
Quality of Chest Compression
A total of five studies including four crossover RCTs [36-38,40] and one nonrandomised crossover study [42] provided data on this outcome. Due to the methodological heterogeneity (i.e. RCTs or nonrandomised studies), only RCTs were included in the meta-analyses and results from nonrandomised study were presented separately in narrative form.
The four RCTs consistently showed no statistically significant differences between the supine and the left-lateral tilt position groups. Of these RCTs, one [38] was excluded from the meta-analysis (Figure 2) because of insufficient data provided in the original study (the means and standard deviations were unreported).
A total of four RCTs [36-38,40] assessed the rate of correct chest compression depth. The meta-analysis of these RCTs revealed the mean percentage of correct chest compression depth decreased by 17.25% when the left-lateral tilt position was used instead of the supine position; the difference was statistically significant (four RCTs, mean difference [MD] = -18.77, 95% CI = -28.89, -8.64, tau2 =48.95, I2 = 47%; Figure 3). Subgroup analyses stratified by chest compression delivery surfaces (floor or bed) resulted in similar findings.
In addition, a meta-analysis of three RCTs [36-38] including a total of 89 health professionals revealed the mean chest compression depth was 2.88 mm lower in the 27°–30° left-lateral tilt position than in the supine position; the difference was statistically significant (three RCTs, MD = -2.88 mm, 95% CI = -4.19, -1.57, tau2 = 0, I2 = 0%; Figure 4). The results were consistent across subgroups defined by the surface (floor or bed).
A total of four RCTs [36-38,40] reported the recoil rates, none of which indicated statistically significant differences between the supine and the left-lateral tilt groups, either on the floor or on the bed.
A total of three RCTs [36,37,40] reported the rate of correct hand positioning during chest compressions. The results of the meta-analysis indicated the correct hand position rate was 9% lower with the patient mannequin in the left-lateral tilt position than with it in the supine position (three RCTs, MD = -9.14, 95% CI = -17.8, -0.48, tau2 = 0, I2 = 0%; Figure 5).
There was one non-randomised crossover study conducted in 1992 [42] which reported that chest compression was significantly better (with the mean percentage of correct cardiac compression being approximately 34% higher) in the wedged position than in the supine position. The common reason for inaccuracy was ‘compression of too great a force’ (p. 434), but the study described neither the definition of correct cardiac compression nor the amount of compression force. The result was inconsistent from RCTs included in this review all of which were conducted more recently, in the 2010s. The inconsistency could possibly due to both clinical and methodological heterogeneity — i.e. the difference in the outcome measures and study design (RCTs vs. non-randomised crossover study) reflecting the time when studies were conducted.
Subjective Difficulty (or Ease) of Chest Compressions
Two RCTs [37,40] involving both experienced and inexperienced rescuers reported that performing chest compressions in the left-lateral tilt position was significantly more difficult than doing so in the supine position, whereas another RCT [36] including only experienced emergency medical doctors reported no difference in the subjective difficulty between the two positions.
Quality of Ventilation
One nonrandomised crossover study [42] involving 18 midwives reported there was no statistically significate difference in the percentage of correct expired air ventilations (during performance of mouth-to-mouth resuscitation) between the supine and the left literal tilt positions (mean [SD] = 62.2% [21.4] in the supine vs. 56.7% [27.7] in the left literal tilt positions). However, the definition of correct expired air ventilations was not described in the original study; it noted only that the commonest course of inaccurate ventilation was the ventilation of small volume.
Comparison 3: Methods for producing left lateral tilt position (soft vs. firm vs. hard vs. human wedge)
Quality of Chest Compression
One crossover RCT reported that the type of wedge — the soft wedge (pillow), firm wedge (foam-rubber), hard wedge (wooden) or human wedge — had no effect on the average rate or adequate release of chest compressions. The study consistently indicated that the depth of compressions (compression depth [mm] and rate of correct compression depth > 50 mm) was reduced with the human wedge compared with other wedges; the differences were statistically significant during chest compressions on the floor but not on the bed.
Subjective Stability of Chest Compressions
One crossover RCT reported that the firm and hard wedges were the most stable (stability rated as ‘good’ or ‘very good’), whereas the soft wedges were the least stable during chest compressions during chest compression on either the floor or bed.
Comparison 4: Chest compressions in various angles (0°, 27°, 32°, 49° and 90°) of inclination
Quality of Chest Compression
In one nonrandomised trial [43] involving eight medical doctors, the maximum possible resuscitative force (as measured with calibrated force transducer fitted on the plane) decreased as the angle of inclination of the plane increased, from 67% of body weight in the supine position to 36% in the full lateral.
Quality of Evidence
For all the outcomes included in this review related to the quality of CPR (chest compression and ventilation) and subjective stability or difficulty of chest compressions, the quality of evidence was rated as very low using the GRADE criteria and was downgraded for risk of bias (all evidence came from studies with some limitations for multiple domains), indirectness (simulation-based) and imprecision (wide CIs).