alveolar recruitment maneuvers under general...

Alveolar Recruitment Maneuvers Under General Anesthesia:A Systematic Review of the Literature

Benjamin L Hartland RN, Timothy J Newell RN, and Nicole Damico MSNA CRNA

IntroductionDescription of ConditionDescription of InterventionsSignificance of Review

ObjectivesMethods

Types of StudiesTypes of SubjectsSearch Methods for Identification of Studies

Data Collection and AnalysisSelection of StudiesAssessment of Risk of Bias in Included StudiesSensitivity Analysis

ResultsResults of SearchIncluded StudiesRisk of Bias of Included StudiesPrimary OutcomesSecondary Outcomes

DiscussionSummary of Main ResultsPrimary Outcome MeasuresSecondary Outcome MeasuresMajor Clinical ThemesOverall Completeness and Applicability of EvidenceQuality of EvidencePotential Bias in the Review Process

ConclusionsImplications for PracticeImplications for Research

BACKGROUND: The sigh is a normal homeostatic reflex that maintains lung compliance anddecreases atelectasis. General anesthesia abolishes the sigh reflex with rapid onset of atelectasis in100% of patients. Studies show a strong correlation between atelectasis and postoperative pulmo-nary complications, raising health-care costs. Alveolar recruitment maneuvers recruit collapsedalveoli, increase gas exchange, and improve arterial oxygenation. There is no consensus in theliterature about the benefits of alveolar recruitment maneuvers. A systematic review is necessary todelineate their usefulness. METHODS: The search strategy included utilizing PubMed, CINAHL,the Cochrane Library, the National Guideline Clearinghouse, and all subsequent research referencelists up to January 2014. Inclusion criteria involved studies that compared the use of an alveolar

RESPIRATORY CARE • ● 2015 VOL ● NO ● 1

RESPIRATORY CARE Paper in Press. Published on November 25, 2014 as DOI: 10.4187/respcare.03488

Copyright (C) 2015 Daedalus Enterprises ePub ahead of print papers have been peer-reviewed, accepted for publication, copy edited and proofread. However, this version may differ from the final published version in the online and print editions of RESPIRATORY CARE

recruitment maneuver with a control group lacking an alveolar recruitment maneuver in adultsurgical subjects not suffering from ARDS or undergoing cardiac or thoracic surgeries. RESULTS:Six randomized controlled trials of the 439 studies initially identified achieved a score of > 3 on theJadad scale and were included in this review. Alveolar recruitment maneuvers consisted of astepwise increase in tidal volume to a plateau pressure of 30 cm H2O, a stepwise increase in PEEPto 20 cm H2O, or sustained manual inflations of the anesthesia reservoir bag to a peak inspiratorypressure of 40 cm H2O. Subjects in the alveolar recruitment maneuver groups experienced a higherintraoperative PaO2

with improved lung compliance. Different alveolar recruitment maneuvers wereequally effective. There was a significant advantage when alveolar recruitment maneuvers werefollowed by PEEP application. CONCLUSIONS: Alveolar recruitment maneuvers followed byPEEP should be instituted after induction of general anesthesia, routinely during maintenance, andin the presence of a falling SpO2

whenever feasible. They allow the anesthesia provider to reduce theFIO2

while maintaining a higher SpO2, limiting the masking of shunts. Utilization of alveolar re-

cruitment maneuvers may reduce postoperative pulmonary complications and improve patientoutcomes. Key words: sigh breaths; alveolar recruitment maneuvers; lung-protective ventilation. [RespirCare 2015;60(3):1–•. © 2015 Daedalus Enterprises]

Introduction

Description of Condition

In 1964, Bendixen et al1 found that awake adults sigh anaverage of 9–10 times/h. The sigh breath is a normalhomeostatic reflex characterized by a complex interactionbetween vagally mediated input and peripheral chemore-ceptors that results in an increase in inspiration.2 The sighbreath functions to maintain pulmonary compliance.3 In agroup of spontaneously breathing subjects, pulmonary com-pliance decreased in the absence of periodic sighs andreturned to baseline after only 2 sigh breaths. Sigh breathsalso minimize the alveolar-arterial oxygen difference(P(A-a)O2

) and maintain venous admixture within normalrange.4

Sigh breaths help to release new surfactant and distrib-ute it evenly on the alveolar surface and the distal air-ways.5,6 The fusion pore is the area on the alveolar type IIcell that acts as a mechanical barrier to prevent furthersurfactant release. Sigh breaths open this barrier and re-plenish the available supply of surfactant.6

If sigh breaths occur in everyday life to prevent atelec-tasis as a normal homeostatic reflex, what happens whenpatients receive neuromuscular blocking drugs, are intu-bated, and are exposed to high concentrations of oxygenwith a fixed tidal volume (VT) on a ventilator? Generalendotracheal anesthesia causes compression and absorp-tion atelectasis through 3 main mechanisms: dyskinesis,increased FIO2

, and ablation of the sigh breath. Dyskinesiscauses a restriction in the movement of a patient’s depen-dent diaphragm, resulting in a decrease in lung compli-ance.7 It also decreases movement of the dependent por-tion of the lungs, thereby decreasing functional residualcapacity.8 These factors contribute to compression atelec-tasis, which occurs when the pressure distending the alve-olus is reduced.9 In a study using computed tomography,atelectasis was noted to occur in 100% of subjectsundergoing general anesthesia.10

Absorption atelectasis occurs when the flux of oxygenfrom alveolar gas into capillary blood exceeds waste gasreturning to the alveoli (as oxygen diffuses faster thannitrogen). This frequently occurs during induction of an-esthesia when the FIO2

is increased to 100%. Since oxy-genated gas leaves the alveoli for the blood faster thanwaste gas (mostly nitrogen) returns to the alveoli, the al-veoli shrink and eventually collapse, increasing atelecta-sis.11

In 1964, Bendixen et al4 hypothesized that constant ven-tilation with adequate but static VT in anesthetized patientswould result in progressive atelectasis and shunting whensigh breaths were absent. They found that, on average,PaO2

fell 22% and pulmonary compliance fell 15% in theabsence of sigh breaths. After a few minutes of slow, deep,sustained breaths, PaO2

rose an average of 150 mm Hg,reducing the shunt created by static VT. The law of Laplaceexplains the increase in PaO2

: pressure � 2T/r, where

The authors are affiliated with the Department of Nurse Anesthesia,Virginia Commonwealth University, Richmond, Virginia.

Supplementary material related to this paper is available at http://www.rcjournal.com.

The authors have disclosed no conflicts of interest.

Correspondence: Benjamin L Hartland RN-BSN, Department of NurseAnesthesia, Virginia Commonwealth University, 1200 E Broad Street,Richmond, VA 23298. E-mail: [email protected].

DOI: 10.4187/respcare.03488

ALVEOLAR RECRUITMENT MANEUVERS UNDER GENERAL ANESTHESIA

2 RESPIRATORY CARE • ● 2015 VOL ● NO ●



T � surface tension, and r � radius. When the radius of analveolus is decreased, the pressure required to re-inflatethat alveolus increases. Alveolar recruitment maneuversprovide the elevated pressure necessary to re-inflate col-lapsed alveoli and may help to prevent impending col-lapse.

Induction and maintenance of anesthesia with muscleparalysis and a fixed VT eliminate a patient’s ability togenerate the sigh breath. Without this inherent ability todecrease atelectasis and improve gas exchange, the patientis vulnerable to the consequences of atelectasis.

Description of Interventions

Alveolar recruitment maneuvers are described as vitalcapacity breaths, double VT breaths, and sigh breaths.12

Sigh breaths are to awake, spontaneously breathing pa-tients as alveolar recruitment maneuvers are to anesthe-tized, mechanically ventilated patients. They use sustainedincreases in airway pressure (breath-holds) to recruit col-lapsed alveoli and improve arterial oxygenation.13

The method for achieving an alveolar recruitment ma-neuver tends to fall into 2 groups. Some authors considersustained inflation of the lungs for 5–30 s to a prescribedpeak inspiratory pressure (PIP) as representative of alve-olar recruitment maneuvers.14-18 Others describe incremen-tally increasing PEEP in a stepwise manner as an alveolarrecruitment maneuver.19,20 Both methods include the useof PEEP following an alveolar recruitment maneuver tomaintain its benefit. For the purpose of this review, studiesutilizing both methods will be used to determine the mosteffective application of an alveolar recruitment maneuver.

Significance of Review

Atelectasis likely occurs in up to 100% of patients un-dergoing general anesthesia.10 The intraoperative effectsof atelectasis include an increase in the P(A-a)O2

, an in-crease in pulmonary shunting, and a decrease in SpO2

.4,15

Atelectasis may increase the risk of volutrauma as a con-stant volume is imparted to a dwindling alveolar volume.Postoperative pulmonary complications are defined as anyrespiratory condition that adversely influences the clinicalcourse of patients after surgery.21 Studies show a strongcorrelation between atelectasis and postoperative pulmo-nary complications. Atelectasis appears to be one of theprimary mechanisms underlying acute lung injury, is amajor cause of postoperative hypoxemia, and is associatedwith a prolonged ICU and hospital stay.21 Atelectasis mayalso contribute to serious postoperative pulmonary com-plications such as respiratory failure and pneumonia.22 Fol-lowing cardiac bypass surgery, atelectasis causes hypox-emia and pulmonary shunting.23 Postoperative pulmonarycomplications represent a substantial economic burden due

to longer hospital stays and increased health-care costs.21

In 2010, postoperative pulmonary complications were es-timated to add nearly 3.5 billion dollars to annual health-care costs.24

Despite their proposed benefits, there is no general con-sensus in the literature regarding the appropriate methods,timing, evaluation, and benefits of alveolar recruitmentmaneuvers during general anesthesia. Study outcomesrange from improving arterial oxygenation, to no effect, todecreases in cardiac output and blood pressure.19,25 A thor-ough and focused systematic review regarding alveolarrecruitment maneuvers is necessary to delineate their use-fulness in improving patient outcomes both during andafter general anesthesia.

Objectives

The primary objectives of this systematic review were:(1) to identify existing evidence in the literature; (2) todetermine the usefulness, appropriate method, surgical pop-ulation, and timing of alveolar recruitment maneuvers inthe intraoperative period; (3) to determine the role of PEEPin alveolar recruitment maneuvers; (4) to identify methodsfor evaluating the efficacy of alveolar recruitment maneu-vers; and (5) to highlight areas of future research related toalveolar recruitment maneuvers.

Methods

Types of Studies

Studies published before January 2014 were reviewedand were not limited by language. Studies based on sub-jects with ARDS were excluded because these subjectsoften require the use of different ventilatory strategies thatmay limit or skew the effects of standard alveolar recruit-ment maneuvers. Studies involving cardiac and thoracicsurgeries were excluded because of surgical factors im-pacting normal heart and lung physiology. Animal studieswere excluded because of the questionable generalizabilityof findings. To limit the effects of bias and covariates,only systematic reviews, quantitative meta-analyses, andrandomized controlled trials (RCTs) were included. Fi-nally, studies were limited to the intraoperative period,with assessment continuing in the immediate postopera-tive period for subjects undergoing general endotrachealanesthesia (Fig. 1).

Types of Subjects

Only adult subjects age 16 y and older were representedin these studies because of potential differences stemmingfrom neonatal and pediatric anatomies. Alveolar recruit-ment maneuvers included either a stepwise increase in





PEEP or VT using a ventilator or manual inflation of asubject’s lungs to a predetermined PIP using an anesthesiareservoir bag. Each treatment group was compared with acontrol group that did not receive an alveolar recruitmentmaneuver. See Table 1 for a description of outcome mea-sures.

Search Methods for Identification of Studies

The search included PubMed, CINAHL, the CochraneLibrary, and the National Guideline Clearinghouse. Addi-tional studies were detected by searching the reference

lists of all included research reports. Search terms includ-ed: lung recruitment measures, alveolar recruitment mea-sures, perioperative recruitment maneuvers, PEEP, generalanesthesia and chest x-rays, preventing atelectasis duringanesthesia/anesthesia, atelectasis and shunting during an-esthesia/anesthesia, lung atelectasis and anesthesia/anes-thesia, anesthesia/anesthesia and atelectasis development,sigh breaths, sigh breaths during ventilation, lung recruit-ment maneuvers, and perioperative atelectasis.

Data Collection and Analysis

Selection of Studies

Two reviewers (BLH and TJN) independently assessedall potential studies from the search strategy for inclusion.Consensus was reached through discussion or, if required,by consultation with a third reviewer (ND). The reviewerswere not blinded to the authors or results of the studies.Data were independently extracted by the reviewers andcross-checked. Consensus was reached through discussionor, if required, by consultation with the third reviewer. Astandard data extraction form was used (see the supple-mentary materials at http://www.rcjournal.com).

Assessment of Risk of Bias in Included Studies

The Jadad scale was used to evaluate methodologicalquality.26 The methodological quality assessment wasperformed by 2 reviewers as stated above. In cases of adiscrepancy in the scores assigned by the primary re-viewers, the third reviewer was used to reach a consen-sus. The Jadad scale includes 5 questions to evaluate thequality of RCTs. Each question is given a maximumscore of 1 point. The questions include qualifiers thatmust be met to obtain a point: (1) Was the trial de-scribed as randomized? (The words random, randomly,or randomization must be used.) (2) Is the method ofrandomization appropriate? (The methods used to gen-erate the sequence of randomization must be described.)(3) Was the study described as double-blind? (The wordsdouble-blind must be used.) (4) Is the method of blind-ing appropriate? (If not, 1 point is deducted.) (5) Isthere a description of withdrawals and dropouts” (Thereasons need to be included, and if there are no with-drawals, it must be stated as such.)

The scale awards 1–5 points to RCTs. RCTs with � 2points or less are considered low-quality studies, andRCTs with � 3 points are considered high-quality stud-ies.26

Sensitivity Analysis

The following strategies were used for the sensitivityanalysis: excluding unpublished RCTs, excluding RCTs

Potential studies439

Excluded390

Animal, pediatric, ARDS,or irrelevant: 245Non-RCT: 145

Remaining studies49

Excluded37

ICU or non-ETGA: 37

Eligible studies12

Excluded 6

Included studies6

Poor methodological qualityper Jadad scale: 6

Fig. 1. Flow chart. RCT � randomized controlled trial. ETGA � en-dotracheal general anesthesia.

Table 1. Primary and Secondary Outcome Measures

Primary Outcome Measures Secondary Outcome Measures

Intraoperative PaO2Postoperative pulmonary complications

Pulmonary compliance Postoperative PaO2or SpO2

P(A-a)O2Alveolar recruitment maneuver

complicationsPaO2

/FIO2Alveolar recruitment maneuver frequencyAirway resistance

P(A-a)O2 � alveolar-arterial oxygen difference





published as abstracts, and excluding RCTs of lower qual-ity as assessed by the Jadad scale (score of � 3).

Results

Results of Search

See Table 2 for inclusion and exclusion criteria andTable 3 for demographic variables. Of the 439 studiesoriginally identified, 12 studies that met the inclusion cri-teria were retrieved for further scrutiny. Agreement be-tween reviewers was achieved in all but 2 studies, whichwere subsequently sent to the third reviewer for furtherevaluation. Only one of these 2 studies was included, fora total of 6 studies receiving a Jadad score of � 3.14,19,20,27-29

The 2013 study by Futier et al30 was not included becauseof the excessively large VT in the control group (10–12 mL/kg), as well as the lack of a protocol to account forconfounding variables with their primary outcome mea-surements.

Included Studies

Interventions. The primary intervention in all 6 studieswas the utilization of alveolar recruitment maneuvers. Themethod for performing an alveolar recruitment maneuvervaried among studies. In addition, the amount of PEEPand VT differed between control and intervention groupsamong the studies (Table 4). For example, 3 studies com-pared subjects with higher VT and no PEEP with subjectswith lower VT, alveolar recruitment maneuvers, andPEEP.14,20,28 The frequency of the alveolar recruitmentmaneuvers also varied depending upon the study.

Subjects. Subjects in all studies underwent abdominalsurgery. Three studies involved open procedures,20,28,29 and3 studies involved laparoscopic surgery.14,19,27 The sub-jects in all 3 laparoscopic studies were rated as AmericanSociety of Anesthesiologists classification I–III.14,19,27 Sub-jects in 5 studies had an average body mass index of� 25 kg/m2.19,20,27-29 Two studies included subjects with a

Table 2. Inclusion and Exclusion Criteria in Studies Included in This Review

Study Inclusion Criteria Exclusion Criteria

Almarakbi et al27 ASA II, 18–60 y old, BMI � 30 kg/m2,elective laparoscopic banding surgery

Asthma, COPD, restrictive lung disease, increased intracranial pressure,smoking history

Pang et al14 ASA I–II, 16–70 y old, elective laparoscopiccholecystectomy

Pre-existing cardiac and respiratory disease requiring treatment,spontaneous pneumothorax history, evidence of hemodynamicinsufficiency

Severgnini et al28 Elective non-laparoscopic abdominal surgeryunder general anesthesia expected to last� 2 h, � 18 y old

BMI � 40 kg/m2; laparoscopic or emergency surgery; previous lungsurgery; persistent hemodynamic instability; intractable shockconsidered unsuitable for the study by the subject’s managingphysician; COPD history; repeated systemic corticosteroid therapyfor exacerbations of COPD, asthma, or sleep disorders; recentimmunosuppressive medication defined as need for chemotherapy orradiation therapy; � 2 months after chemotherapy or radiationtherapy; severe cardiac disease defined as New York HeartAssociation class III or IV or acute coronary syndrome; persistentventricular tachyarrhythmias; pregnancy (by lab testing); acute lunginjury or ARDS, expected to require prolonged postoperativemechanical ventilation; any neuromuscular disease; contraindicationsto position an epidural catheter because of major clotting disordersor sign of infection at the site of the procedure

Sprung et al29 BMI � 40 kg/m2, open bariatric surgery Abnormalities in spirometry (FEV1 � 50% of predicted, FVC � 50%of predicted), active asthma (requiring bronchodilator therapy),previous lung surgery, home oxygen therapy

Weingarten et al20 � 65 y old, major open abdominal surgery Significant pulmonary disease with abnormalities in spirometryconsistent with either obstructive or restrictive pulmonary disease,active asthma (requiring chronic bronchodilator therapy), previouslung surgery, home oxygen therapy, significant cardiac dysfunction(left ventricular ejection fraction � 40%), BMI � 35 kg/m2

Whalen et al19 ASA II/II/III, 25–65 y old, BMI � 40 kg/m2,laparoscopic bariatric Roux-en-Y operations

No significant preoperative pulmonary disease (FEV1 � 50% ofpredicted, FVC � 50% of predicted), active asthma, home oxygentherapy

ASA � American Society of AnesthesiologistsBMI � body mass index





body mass index � 50 kg/m2.19,29 In 5 studies, the averageage of subjects was � 40 y. Two studies included subjectswith a mean age of � 65 y.14,20,28,29 The ratio betweenmen and women varied with each study, but overall, therewas a slightly higher number of male subjects. Specificexclusion criteria are shown in Table 2. All studies ex-cluded subjects with significant pre-existing lung disease.

Duration of Studies. Most studies finished the majorityof their outcome measures in the immediate postoperativeperiod. Although postoperative protocols were not delin-eated, 4 of the 6 studies included hospital stay as a sec-ondary outcome measure.19,20,27,28 The time to hospitaldischarge varied from days to weeks.

Risk of Bias of Included Studies

All studies were RCTs that received a Jadad score of� 3. All of the study reports included a description of therandomization technique. Three of the studies included anassessment of blinding.19,27,28 Whalen et al19 also includedblinding by the researcher collecting postoperative data.There were no dropouts in 4 studies.14,19,20,27 In the other2 studies, the researchers explained the reason for drop-outs. Neither of these studies included an intention-to-treatanalysis.28,29

Primary Outcomes

See Table 5 for primary and secondary outcomes ofincluded studies.

Intraoperative PaO2. There was an increase in intra-

operative PaO2in the alveolar recruitment maneuver groups

compared with control groups in the 4 studies in whichthis outcome was measured.14,19,20,27 Sprung et al29 in-cluded PaO2

/FIO2in their results, whereas Severgnini et al28

included only intraoperative SpO2.

Pulmonary Compliance. There was an increase in pul-monary compliance in the alveolar recruitment maneuvergroups compared with the control groups in 4 of the 5studies in which this outcome was measured.19,20,27,29 Sev-ergnini et al28 found no difference in pulmonary compli-ance among groups, whereas Pang et al14 did not includethis outcome measure in their study.

P(A-a)O2. None of the studies included P(A-a)O2

mea-surements in their results.

PaO2/FIO2

. There was an increase in PaO2/FIO2

in thealveolar recruitment maneuver groups compared with thecontrol groups in the 3 studies that included this outcomemeasure.19,20,29

Secondary Outcomes

Postoperative Pulmonary Complications. Four stud-ies found no difference in the occurrence of postoperativepulmonary complications. Almarakbi et al27 found thatsubjects in the alveolar recruitment maneuver group withPEEP had the shortest hospital stays. Severgnini et al28

reported a higher occurrence of postoperative pulmonary

Table 3. Demographic Variables in Studies Included in This Review

Study

Age (y) Males/Females (n) ASA Score Anesthesia Time (min) BMI (kg/m2)

ControlRecruitmentManeuver





Almarakbiet al27

38 � 3 38 � 3 8/7 9/6 Not given Not given 93 91 33 � 2 33 � 138 � 3 7/8 95 34 � 138 � 4 8/7 93 34 � 1

Pang et al14 52.16 � 13.63 49.14 � 13.91 3/9 6/6 I/II (10/2) I/II (9/3) 60 � 16(operation)

70.7 � 28(time)

Not given Not givenAverage weight55 � 21 kg (21)

Average weight56 � 8 kg

Severgniniet al28

67 � 9 65.5 � 11.4 16/11 18/10 I/II/III(4/21/2)

I/II/III(6/19/3)

223 � 80 193 � 64 25.9 � 4.2 25 � 4.9

Sprunget al29

48 � 9 52 � 9 4/5 4/4 Not given Not given 433 � 137 458 � 177 51 � 5 56 � 11

Weingartenet al20

72.1 73.8 16/4 15/5 I/II (6) I/II (9) 344 � 103 308 � 112 27.9 � 4.4 27.8 � 4.3III/IV (14) III/IV (11)

Whalenet al19

38 � 11 44 � 9 4/6 2/8 Not given Not given 231 � 91(operation)

185 � 33(time)

53 � 11 48 � 6

Values are expressed as mean � SD unless indicated otherwise.ASA � American Society of AnesthesiologistsBMI � body mass index





complications in the control group on postoperative day 1compared with the alveolar recruitment maneuver group,but they found no significant difference thereafter.

Postoperative PaO2or SpO2

. Four studies found nosignificant difference in postoperative PaO2

or SpO2be-

tween groups. Almarakbi et al27 found that the highestSpO2

occurred in the alveolar recruitment maneuver groupwith PEEP. Severgnini et al28 reported a statistically sig-nificant decrease in SpO2

in the control group on postop-erative days 1 and 3, whereas the SpO2

remained the samein the alveolar recruitment maneuver group.

Complications of Alveolar Recruitment Maneuvers.Four of the studies reported no complications with the useof alveolar recruitment maneuvers. Complications of al-

veolar recruitment maneuvers were variably defined ashypotension (mean arterial blood pressure of � 60 mm Hg),hypertension (systolic blood pressure of � 150 mm Hg),an SpO2

of � 90%, pneumothorax requiring a chest tube, aheart rate of � 60 beats/min, and a need to give a fluidbolus or vasoactive medication. Severgnini et al28 notedcomparable complications between the alveolar recruit-ment maneuver and control groups. Whalen et al19 iden-tified an increase in the amount of vasopressors used in thealveolar recruitment maneuver group compared with thecontrol group, but this difference was not statistically sig-nificant.

Frequency of Alveolar Recruitment Maneuvers. Asstated earlier, the frequency of alveolar recruitment ma-neuvers varied among the studies in this review. Pang

Table 4. Description of Intervention and Control Groups

Study Control Group Intervention Group

Almarakbi et al27 PEEP � 10 cm/H2O (n � 15) Experimental groups (n � 15 in each group):(1) Single alveolar recruitment maneuver group without PEEP: PIP � 40 cm/H2O

held for 15 s(2) Single alveolar recruitment maneuver group with PEEP: PIP � 40 cm/H2O

held for 15 s, then PEEP � 10 cm/H2O for rest of surgery(3) Repeated alveolar recruitment maneuver group with PEEP: PIP � 40 cm/H2O

held for 15 s, then PEEP � 10 cm/H2O, repeated every 10 minPang et al14 VT � 10 mL/kg, PEEP � 0 (n � 12) Following intubation, manual inflation to PIP � 40 cm/H2O without PEEP for 10

breaths for 1 min, then placed back on ventilator with PEEP � 5 cm/H2O andVT � 10 mL/kg (n � 12)

Severgnini et al28 VT � 9 mL/kg of IBW, PEEP � 0(n � 27)

VT � 7 mL/kg of IBW, PEEP � 10 cm H2O, alveolar recruitment maneuverperformed after intubation, after any disconnect, and before extubation, providedstable vital signs; alveolar recruitment maneuver defined as setting PIP at45 cm H2O, I:E � 3:1, then VT increased in steps of 4 mL/kg of IBW untilplateau pressure � 30 cm H2O, then 3 breaths, then returned to baseline (n � 28)

Sprung et al29 VT � 8 mL/kg, PEEP � 4 (n � 9) Stepwise increase in PEEP from 4 to 10 cm H2O for 3 breaths, 10 to 15 cm H2O for3 breaths, 15 to 20 cm H2O for 10 breaths, with maximum PIP � 50 cm H2O;PEEP then set at 12 cm H2O; alveolar recruitment maneuvers repeated 30 and60 min after first recruitment (following intubation and placement of arterial line),then hourly (n � 8)

Weingarten et al20 VT � 10 mL/kg of IBW, PEEP � 0(intrinsic PEEP � 2.5 cm H2O)(n � 20)

VT � 6 mL/kg of IBW, PEEP � 4 cm H2O, alveolar recruitment maneuverperformed after intubation (exact time not given), 30 and 60 min after the firstalveolar recruitment maneuver, hourly thereafter; alveolar recruitment maneuverdefined as incrementally increasing PEEP from 4 to 10 cm H2O for 3 breaths,15 cm H2O for 3 breaths, then 20 cm H2O PEEP for 10 breaths; after alveolarrecruitment maneuver, PEEP set to 12 cm H2O, not stated if subsequentrecruitment maneuvers decreased to 4 cm H2O to start (n � 20)

Whalen et al19 VT � 8 mL/kg of IBW, PEEP � 4(n � 10)

VT � 8 mL/kg of IBW, PEEP � 4 cm H2O, after pneumoperitoneum, PEEPincreased in a stepwise manner from 4 to 10 cm H2O for 3 breaths, 15 cm H2Ofor 3 breaths, 20 cm H2O for 10 breaths, with PEEP�12 cm H2O; alveolarrecruitment maneuvers repeated until a baseline PaO2

was recorded if PaO2kept

increasing after the first series of alveolar recruitment maneuvers; an alveolarrecruitment maneuver also instituted anytime the PaO2

decreased by � 25 mm Hgof the baseline value (n � 10)

VT � tidal volumeIBW � ideal body weightPIP � peak inspiratory pressureI:E � inspiratory-expiratory ratio





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et al14 utilized an alveolar recruitment maneuver only once,whereas Sprung et al29 and Weingarten et al20 performedalveolar recruitment maneuvers after intubation, 30 and60 min following intubation, and every hour thereafter.The study by Almarakbi et al27 was unique in that it wasthe only study to include the effects of different frequen-cies of alveolar recruitment maneuvers. These researcherscompared alveolar recruitment maneuvers performed oncewith those performed every 10 min.

Discussion

Summary of Main Results

This review of alveolar recruitment maneuvers included6 RCTs, all of which achieved a score of � 3 on the Jadadscale. The studies differed in their subjects, independent/de-pendent variables, control and intervention groups, tech-nique of applying an alveolar recruitment maneuver, andoutcome measures, making absolute quantitative compar-isons treacherous. We included the major clinical themessection below to qualitatively approach comparisons inthis systematic review. Despite differences in methods,certain comparisons can be made among the 6 studies.Subjects in all studies underwent abdominal surgery. Mostsubjects had a body mass index of � 25 kg/m2 and nosignificant pre-existing lung disease. Most studies utilizedone of 2 methods for the application of alveolar recruit-ment maneuvers, with the exception of Severgnini et al.28

Alveolar recruitment maneuvers consisted of either a step-wise increase in PEEP with sustained breaths or sustainedmanual inflations of an anesthesia reservoir bag to a PIP of40 cm H2O. All studies reported P � .05 as a statisticallysignificant outcome difference.

Primary Outcome Measures

Overall, subjects in the alveolar recruitment maneuvergroups experienced a higher intraoperative PaO2

, greaterlung compliance, and higher PaO2

/FIO2.

Secondary Outcome Measures

Overall, there were no significant differences in the rateof postoperative pulmonary complications, postoperativePaO2

, SpO2, or intraoperative airway resistance between sub-

jects in the alveolar recruitment maneuver and controlgroups in the 6 studies in this review. Despite the varietyof maximum PIP allowed during alveolar recruitment ma-neuvers in the studies (ranging from 40 to 50 cm H2O), theoccurrence of complications associated with alveolar re-cruitment maneuvers appeared minimal to nonexistent. Fiveof the 6 studies reported no complications associated withthe use of alveolar recruitment maneuvers. The study that

reported complications in the alveolar recruitment maneu-ver group had similar complications in the control group.28

The frequency of alveolar recruitment maneuvers variedamong studies in this review.14,19,20,27-29

Major Clinical Themes

Is There Evidence to Support Alveolar RecruitmentManeuvers in Open Abdominal Surgery? Of the 3 stud-ies involving open abdominal surgery, only Weingartenet al20 included the effects of alveolar recruitment maneu-vers on intraoperative PaO2

, which increased solely in thealveolar recruitment maneuver group. Sprung et al29 andWeingarten et al20 reported an increase in pulmonary com-pliance along with an increase in PaO2

/FIO2in the alveolar

recruitment maneuver groups. Severgnini et al28 found nosignificant difference in pulmonary compliance amonggroups and did not report on PaO2

/FIO2. None of the studies

reported statistically significant complications during orafter alveolar recruitment maneuvers. There was no con-sensus on the benefit of alveolar recruitment maneuvers inthe postoperative period.

Is There Evidence to Support Alveolar RecruitmentManeuvers in Laparoscopic Abdominal Surgery? All3 studies involving laparoscopic abdominal surgery showedan increase in intraoperative PaO2

with alveolar recruitmentmaneuvers.14,19,27 Both Almarakbi et al27 and Whalen et al19

also reported an increase in pulmonary compliance, whereasPang et al14 did not include pulmonary compliance in theirresearch. Only Whalen et al19 reported on intraoperativePaO2

/FIO2, which was increased in the alveolar recruitment

maneuver group. There was no consensus of evidence re-garding postoperative benefits of alveolar recruitment ma-neuvers. Almarakbi et al27 reported a higher SpO2

and shorterhospital stays with the alveolar recruitment maneuvergroups, whereas Whalen et al19 found no differences in thepostoperative period between groups. The lack of consen-sus for the benefits of alveolar recruitment maneuvers ex-tending into the postoperative period will be discussedbelow in the implications for practice section.

Which Alveolar Recruitment Maneuver Is the Best?Excluding the study by Severgnini et al,28 the differenttypes of alveolar recruitment maneuvers were found to beequally effective. Both Almarakbi et al27 and Pang et al14

utilized sustained manual inflations up to a PIP of40 cm H2O for their alveolar recruitment maneuvers. Al-marakbi et al27 utilized single sustained manual inflationsfor 15 s, whereas Pang et al14 utilized 10 sustained manualinflations over 1 min. Both studies found an increase inintraoperative PaO2

in the alveolar recruitment maneuvergroups. However, only Almarakbi et al27 reported on pul-monary compliance, which showed an increase exclusively





in the alveolar recruitment maneuver groups. Neither studyreported on PaO2

/FIO2or airway resistance.

Three studies utilized stepwise increases in PEEP start-ing at 4 cm H2O and ending at 20 cm H2O as alveolarrecruitment maneuvers.19,20,29 Of the 2 studies that includedintraoperative PaO2

,19,20 there was a statistically significantincrease in the alveolar recruitment maneuver groups. All3 studies showed an improvement in pulmonary compli-ance in the alveolar recruitment maneuver groups. OnlySprung et al29 and Whalen et al19 included PaO2

/FIO2as an

outcome measure, which was significantly increased in thealveolar recruitment maneuver groups in the intraoperativeperiod.

Manual sustained hyperinflations require a shorteramount of time to perform, whereas stepwise increases inPEEP or VT may prevent untoward subject responses suchas straining or coughing when the depth of anesthesia isequivocal.

How Long Should Alveolar Recruitment ManeuversBe Held to Be Effective? The time that the manual al-veolar recruitment maneuver is held to a set PIP varies inthe literature. As stated previously, some authors considerinflation of the lungs for 5–30 s to a prescribed PIP asrepresentative of alveolar recruitment maneuvers.15-18 Al-marakbi et al27 held alveolar recruitment maneuvers for15 s. Pang et al14 did not specify a period of time forholding the alveolar recruitment maneuver. They utilized10 alveolar recruitment maneuvers over 1 min, whichleaves, at best, a few seconds for an inspiratory hold if itindeed was utilized. The 3 studies involving stepwise in-creases in PEEP all performed them in the same man-ner.19,20,29 Subjects received 3 breaths when the PEEP wasincreased from 4 to 10 cm H2O, then received 3 breathswhen the PEEP was increased from 10 to 15 cm H2O, andfinally 10 breaths when the PEEP was increased to20 cm H2O. Severgnini et al28 defined an alveolar recruit-ment maneuver as setting PIP to 45 cm H2O with an in-spiratory/expiratory ratio of 3:1. The VT was then increasedin steps of 4 mL/kg of ideal body weight until a plateaupressure of 30 cm H2O was reached, at which time 3 breathswere given.

Is There Evidence to Support the Use of Repeated Alve-olar Recruitment Maneuvers? The repeated-measures al-veolar recruitment maneuver group in the study by Alma-rakbi et al27 showed the greatest improvement inintraoperative PaO2

, pulmonary compliance, and postoper-ative PaO2

. Most of the studies repeated alveolar recruit-ment maneuvers at various times throughout the surgery.The study by Almarakbi et al27 was the only study tomeasure the effects of different frequencies of alveolarrecruitment maneuvers. One of the experimental groupsreceived an alveolar recruitment maneuver once, whereas

another received alveolar recruitment maneuvers every10 min until completion of surgery. The researchers notedthat the benefit of an elevated PaO2

in the single alveolarrecruitment maneuver group was temporary, whereas thebenefit was sustained in the repeated-measures alveolarrecruitment maneuver group. The subjects in the repeated-measures alveolar recruitment maneuver group also hadthe shortest hospital stay.

Is There Evidence to Support Using Alveolar Recruit-ment Maneuvers Followed By PEEP? The only studyto isolate the differences in the utilization of PEEP fol-lowing an alveolar recruitment maneuver was undertakenby Almarakbi et al.27 As stated above, these researcherscompared the effects of repeated alveolar recruitment ma-neuvers versus a single alveolar recruitment maneuver.They also included a third experimental group that re-ceived a single alveolar recruitment maneuver followed byzero PEEP. There were no significant differences betweenthe single alveolar recruitment maneuver group withoutPEEP and the control group (PEEP of 10 cm H2O only).Neither group showed an improvement in respiratory com-pliance, intraoperative or postoperative PaO2

, or a reduc-tion in hospital stay. There was, however, a significantadvantage in compliance, intraoperative and postoperativePaO2

, and reduction in hospital stay in the alveolar recruit-ment maneuver groups followed by PEEP.

What Is the Best Method for Determining the Effec-tiveness of Alveolar Recruitment Maneuvers? Besidesobtaining an arterial blood gas and calculating the P(A-a)O2

,there is a more practical and less invasive approach. Fourof the 5 studies found a statistically significant increase inpulmonary compliance in alveolar recruitment maneuvergroups.19,20,27,29 Dynamic pulmonary compliance is calcu-lated by dividing VT by the difference between PIP andPEEP: dynamic compliance � VT/(PIP � PEEP). Staticpulmonary compliance is calculated by dividing VT by thedifference between the plateau pressure (Pplat) and PEEP:static compliance � VT/(Pplat � PEEP). An increase in pul-monary compliance immediately following the applicationof an alveolar recruitment maneuver would presumablyreflect a reduction in atelectasis and result in an increase inPaO2

due to better matching of ventilation and perfusion.To avoid the need to perform the above calculations, amore clinically relevant method for determining whetheran increase in compliance has occurred can be utilized.During volume control continuous mandatory ventilation,the provider would note that the same VT is delivered at alower PIP following application of alveolar recruitmentmaneuvers. With pressure control continuous mandatoryventilation, the provider would note that an increased VT

is delivered at the same inspiratory pressure setting. Con-temporary anesthesia ventilators often include options to





display the pressure-volume loop and calculated dynamiccompliance values, making it even easier to measure theeffectiveness of alveolar recruitment maneuvers.

Overall Completeness and Applicability of Evidence

Evidence from the 6 included studies regarding the ben-efit of alveolar recruitment maneuvers in the postoperativeperiodwas lacking.14,19,20,27-29 Althoughpostoperativemea-surements were evaluated, no study included a postoper-ative pulmonary protocol accounting for confounding vari-ables. In addition, only one study included dosages usedfor reversal of neuromuscular blockade.14 Other primary andsecondary outcomes were compared as noted. The applica-bility of the evidence summarized in this review is limited toadult subjects without extensive pre-existing pulmonary dis-ease who are undergoing abdominal surgery.

Quality of Evidence

This systematic review was limited to RCTs, systematicreviews, and quantitative meta-analyses. Only high-qual-ity RCTs that matched the inclusion criteria were selected.Of concern, the sample sizes of the included studies weresmall, which brings into question the ability of the studiesto control and account for confounding variables. Thisstatistical fragility may have elevated the risk of type I ortype II errors. The lack of specific emergence or postop-erative pulmonary protocols limits the applicability of post-operative measurements.

Potential Bias in the Review Process

The reviewers did not examine the results of individualstudies until after all studies met the inclusion criteria,including achieving a score of � 3 on the Jadad scale.Reviewers were therefore unaware of the content of theincluded studies as it related to the benefit of alveolarrecruitment maneuvers until after the studies were selected.

Conclusions

Implications for Practice

Depending on the type of surgery and patient status, thepractitioner should utilize alveolar recruitment maneuversfollowed by PEEP after induction of general endotrachealanesthesia, routinely, and in the presence of a decreasingSpO2

. Although evidence from this review limits the applica-tion of alveolar recruitment maneuvers to adults undergoingabdominal surgery, there is a wealth of literature to supportalveolar recruitment maneuvers in other surgeries.31-34 Tele-ologically, a healthy human sighs an average of 9–10 times/h.Thus, most patients undergoing general endotracheal anes-

thesia would benefit from this homeostatic reflex in the formof an alveolar recruitment maneuver.

Compared with the control group, all types of alveolarrecruitment maneuvers were beneficial in the intraopera-tive period. Manual sustained hyperinflations require ashort amount of time to perform, whereas stepwise in-creases in PEEP or VT may prevent untoward subject re-sponses such as coughing or straining when the depth ofanesthesia is questionable. Alveolar recruitment maneu-vers should be performed instead of solely increasing FIO2

during the maintenance phase of anesthesia. Continuallyincreasing FIO2

in the face of a decreasing SpO2may main-

tain an elevated SpO2, but may also mask a physiological

shunt. Oxygen can also adversely affect respiratory con-trol, ventilation/perfusion ratios, and hypoxic pulmonaryvasoconstriction, as well as cause vasoconstriction of sys-temic arterioles.35 Oxygen products from reduced nicotin-amide adenine dinucleotide phosphate oxidase also increaseinflammation and tissue injury through a complex inter-action among neutrophils, macrophages, and platelets.36

Alveolar recruitment maneuvers allow the anesthesia pro-vider to reduce the FIO2

yet maintain a higher SpO2.

Current evidence does not support the assumption thatthe benefit of alveolar recruitment maneuvers extends tothe postoperative period because none of the studies in-cluded a specific emergence or postoperative pulmonaryprotocol. Emergence from anesthesia and the immediatepostoperative period can leave a patient susceptible to at-electasis and hypoxemia. Patients often breathe low VT

without PEEP and on 100% oxygen for minutes duringthis time. Given the negative consequences of absorptionatelectasis, low VT, and the absence of PEEP, techniquesfor emergence need to be re-examined to prevent the ne-gation of intraoperative alveolar recruitment maneuvers.Teleologically, it seems implicit that reducing intraopera-tive risk may decrease postoperative issues.

Implications for Research

Most studies involve the use of alveolar recruitmentmaneuvers during the maintenance phase of anesthesia. Tomaximize the benefits of alveolar recruitment maneuversfor patients in the postoperative period, a study incorpo-rating sigh breaths following extubation with the utiliza-tion of CPAP should be undertaken. Sigh breaths in thepostoperative period can be quantified with the use of anincentive spirometer. After extubation, patients control theirown gas composition and may benefit from CPAP in thepost-anesthesia care unit to prevent atelectasis secondaryto diminished VT. The use of CPAP in the postoperativeperiod significantly decreases the incidence of pneumonia,sepsis, and hypoxemia.37 A study on the use of intraoper-ative alveolar recruitment maneuvers combined with theuse of CPAP and sigh breaths following extubation may





extend the benefits of alveolar recruitment maneuvers intothe recovery period, reducing postoperative pulmonarycomplications and improving subject outcomes.

Patient position during emergence and following extu-bation may also improve patient outcomes and reduce at-electasis formation. A study comparing elevated head-of-bed and supine positions during emergence and in thepostoperative period may show a reduction in atelectasisand improvement in oxygenation.

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