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Continuous positive airway pressure (CPAP) during the postoperative period for prevention of postoperative morbidity and mortality following major abdominal surgery

  1. Claire J Ireland1,*,
  2. Timothy M Chapman2,
  3. Suneeth F Mathew3,
  4. G Peter Herbison4,
  5. Mathew Zacharias1

Editorial Group: Cochrane Anaesthesia, Critical and Emergency Care Group

Published Online: 1 AUG 2014

Assessed as up-to-date: 15 SEP 2013

DOI: 10.1002/14651858.CD008930.pub2


How to Cite

Ireland CJ, Chapman TM, Mathew SF, Herbison GP, Zacharias M. Continuous positive airway pressure (CPAP) during the postoperative period for prevention of postoperative morbidity and mortality following major abdominal surgery. Cochrane Database of Systematic Reviews 2014, Issue 8. Art. No.: CD008930. DOI: 10.1002/14651858.CD008930.pub2.

Author Information

  1. 1

    Dunedin Hospital, Department of Anaesthesia & Intensive Care, Dunedin, New Zealand

  2. 2

    Christchurch Public Hospital, Department of Anaesthesia, Christchurch, New Zealand

  3. 3

    University of Auckland, Medical Student at School of Medicine, Auckland, New Zealand

  4. 4

    Dunedin School of Medicine, University of Otago, Department of Preventive & Social Medicine, Dunedin, New Zealand

*Claire J Ireland, Department of Anaesthesia & Intensive Care, Dunedin Hospital, Great King Street, Dunedin, New Zealand. claireireland@hotmail.com.

Publication History

  1. Publication Status: New
  2. Published Online: 1 AUG 2014

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Characteristics of included studies [ordered by study ID]
Bohner 2002

MethodsStudy was done in the hospitals of Heinrich-Heine University, Germany


ParticipantsAdults undergoing midline laparotomy for elective vascular surgery; abdominal aortic aneurysm surgery; and surgery of visceral, renal and iliac arteries or thrombectomy of IVC

Excluded were emergency surgery, thoracoabdominal surgery or retroperitoneal approach

Participants were randomly assigned to 2 groups with use of a random list:

Control group: 105 participants; age, years: 64.5 ± 11.3; male/female: 82:23; BMI: 25.0 ± 3.3

Intervention group: 99 participants; age, years: 64.1 ± 12.3; male/female: 84:15; BMI: 25.4 ± 3.5

All participants received similar fluid regimen, analgesic routine and medications

All participants were extubated soon after surgery and were admitted to intermediate care unit or intensive care unit


InterventionsControl group: Oxygen was administered at ambient pressure via a non-occlusive face mask, including mouth and nose or nose cannulas to keep oxygen saturation > 95%; FiO2 was adjusted to achieve this

Intervention group: received prophylactic nCPAP. nCPAP mask was placed on admission to the unit, using a high gas flow source and a standard PEEP valve set at 10 cm H2O. FiO2 was adjusted to keep SpO2 > 95% and to keep nCPAP mask on for at least 12 hours


OutcomesDuration of intervention: 14.0 ± 4.3 hours

Duration of follow-up: longer than 7 days

All-cause mortality: control group, 0/105: intervention group, 4/99

Major respiratory complications as defined in individual studies

Significant atelectasis: none reported

Pneumonia: control group, 5/105: intervention group, 2/99

Respiratory failure: none reported

Severe hypoxia: control group, 17/105: intervention group, 5/99

Severe delirium: control group, 12/105: intervention group, 6/99

Need for tracheal intubation and invasive ventilation: control group, 5/105: intervention group, 1/99

Readmission to ICU/IMC: control group, 14/105: intervention group, 6/99

Length of stay in hospital: control group, 11.81 ± 18.61 days: intervention group, 9.45 ± 6.79 days

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia):

Cardiac arrest: control group, 2/105: intervention group, 1/99

Other postoperative complications (wound infection, anastomotic leak, renal failure):

Renal failure: control group, 3/105: intervention group, 3/99

Adverse effects of the intervention (pulmonary aspiration, upper airway or facial injury):

Nose ulcers: control group, 0/105: intervention group, 4/99


NotesBMI = body mass index

FiO2 = Inspired oxygen fraction

IVC = inferior vena cava

nCPAP = nasal CPAP

PEEP = positive end-expiratory pressure

ICU = intensive care unit

IMC = intermediate care unit

No response to email


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskRandomization using a random list

Allocation concealment (selection bias)Unclear riskRandomization using a random list, but no description of allocation concealment

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskAnaesthesiologist at the operation site did not receive any information about the results of randomization; no evidence of anyone else being blinded

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNot described in the text

Incomplete outcome data (attrition bias)
All outcomes
Low riskDropouts described because 9/99 participants did not want to continue with nCPAP after 5.75 ± 4.80 hours

Selective reporting (reporting bias)Low riskNo evidence of selective reporting in text

Other biasUnclear riskNone reported

Carlsson 1981

MethodsStudy done at University Hospital, Lund, Sweden


ParticipantsHealthy patients undergoing open elective cholecystectomy using right subcostal incision (no intercostal blocks)

Control group: 11 participants; age, years: 68.09 ± 9.72; male/female: 2:9

Intervention group: 13 participants; age, years: 62.08 ± 9.52; male/female: 8:5

20/24 participants in total were > 20% overweight according to Broca Index


InterventionsMale/female, 10:14; age, years: 50-78

Control group: 11 participants; 30% prewarmed and humidified oxygen without a rubber bag, but with no PEEP

Intervention group: 13 participants; 30% prewarmed and humidified oxygen via a rubber bag and PEEP of 5 to 10 cm H2O

Treatment and control for 4 hours during the immediate postoperative period in the ward


OutcomesDuration of intervention: 4 hours

Duration of follow-up: 24 hours (1 day)

All-cause mortality: none reported

Major respiratory complications as defined in individual studies:

Significant atelectasis (seen on 24-hour x-ray): control group, 10/11; intervention group, 10/13

Pneumonia: none reported (changes on x-ray "such as atelectasis and pneumonia" were noted but not distinguished further; hence the data are included under atelectasis)

Respiratory failure: none reported

Severe hypoxia: not reported

Need for tracheal intubation and invasive ventilation: none reported

Admission to ICU/IMC: none reported

Length of stay in hospital: not reported

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia): none reported

Other postoperative complications (wound infection, anastomotic leak, renal failure): none reported

Adverse effects of the intervention (pulmonary aspiration, upper airway or facial injury): none reported


NotesPEEP = positive end-expiratory pressure

ICU = intesive care unit

IMC = intermediate care unit

Old study, no chance of getting additional information


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskOn the postoperative ward, participants were randomly assigned to 2 groups; no details

Allocation concealment (selection bias)Unclear riskNot described

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNot described

Blinding of outcome assessment (detection bias)
All outcomes
Low riskRadiologist was unaware of treatments

Incomplete outcome data (attrition bias)
All outcomes
Low riskAll participants accounted for

Selective reporting (reporting bias)Unclear riskNot sure

Other biasUnclear riskNot sure

Christensen 1991

MethodsStudy done in Department of Anesthesiology and Respiratory Medicine, University Hospital of Aarhus, Denmark


ParticipantsHigh-risk adult patients scheduled for upper abdominal surgery (elective biliary and ventricular surgery). Participants were divided into 3 groups: control group; PEP group (PEP group used a mask similar to a CPAP mask, employs an expiratory resistance during breathing); and RMT group (RMT group is similar to PEP group, but the mask provides both inspiratory and expiratory resistance). We combined PEP and RMT groups as the intervention (CPAP) group for inclusion in the review

Control group: 17 participants; male/female, 5:12; age, years: 62 (51-83); weight, kg: 68.5 (53-94)

Intervention group:

PEP group: 17 participants; male/female: 8/9; age, years: 63.7 (range 50-80); weight, kg: 68.7 (range 39-88)

RMT group: 17 participants; male/female: 3/14; age, years: 64.2 (53-79); weight, kg: 63.5 (range 43-90)


InterventionsControl group: conventional physiotherapy, given to all participants in all groups; started during preoperative period; continued into postoperative period for 3 days; consisted of breathing exercises and forced expiration techniques; twice a day for 3 days and every hour during waking hours by participants

Intervention group: conventional physiotherapy as well as CPAP using a PEEP mask; 5 to 15 cm H2O expiratory pressure, given preoperatively for practice; continued during postoperative period, twice daily for 3 days. RMT group had PEP mask (5-7 cm H2O) + inspiratory resistance chosen according to participants' ability to tolerate the mask

We combined CPAP and RMT groups for the purpose of this review and interventions

Oxygen was given only if hypoxia was present


OutcomesDuration of intervention: 3 days

Duration of follow-up: 3 days

All-cause mortality: none reported

Major respiratory complications as defined in individual studies:

Atelectasis: control group, 9/17; intervention groups: PEP group, 11/17; RMT, 9/17

Pneumonia: control group, 5/17; intervention groups; PEP group, 6/17; RMT, 1/17

Respiratory failure: none reported

Severe hypoxia: control group, 2/17; intervention groups: PEP, 4/17; RMT, 2/17

Need for tracheal intubation and invasive ventilation: control group, 0/17; intervention groups: PEP, 1/17; RMT, 1/17

Admission to ICU/IMC: none reported

Length of stay in hospital, days: control group: 10.4 (95% CI 4 to 26) (SD = 1.9); intervention groups: PEP, 16.4 (range 5-42); RMT, 11.5 (range 5-42)

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia): none reported

Other postoperative complications (wound infection, anastomotic leak, renal failure):

Pulmonary embolism: control group: 0/17; intervention groups: PEP, 0/17; RMT, 1/17

Wound infection: control group: 0/17, intervention groups: PEP, 4/17; RMT, 3/17

Adverse effects of the intervention (pulmonary aspiration, upper airway or facial injury): none reported


NotesCI = confidence interval

CPAP = continuous positive airway pressure

ICU = intensive care unit

IMC = intermediate care unit

PEP = positive expiratory pressure, variable, mask

RMT = PEP mask with inspiratory resistance, mask

SD = standard deviation


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear risk'Randomly allocated' into 3 groups; no other details

Allocation concealment (selection bias)Unclear riskNo evidence for it

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNo evidence for it

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo evidence for it

Incomplete outcome data (attrition bias)
All outcomes
Low riskReasonable account given

Selective reporting (reporting bias)Unclear riskNot sure

Other biasUnclear riskNot sure

Denehy 2001

MethodsRCT done at Austin and Repatriation Medical Centre, Melbourne, Australia


ParticipantsAdult patients undergoing upper abdominal surgery. Inclusion criteria: incision above the umbilicus; FEV1 greater than 50% predicted


InterventionsAll participants received preoperative education on effects of surgery on lung function and were instructed on deep breathing exercises, including sustained maximal inspiration

Post surgery, all participants received physiotherapy twice daily for 3 days, for a minimum of 10 minutes each session. This traditional physiotherapy consisted of deep breathing exercises, forced expiration technique and supported cough. Early ambulation was encouraged, and physiotherapy was done in the sitting position on bed or chair

Control group: received the above traditional physiotherapy

Intervention groups (CPAP, 15 minutes; CPAP, 30 minutes): nasal mask for CPAP, PEEP set at 10 cm H2O. 30% O2 was used for CPAP. This was given 4 times each day, following traditional physiotherapy

Control group: 18 participants; male/female: 15:3; age, years: 73.3 ± 5.8; no data on BMI

Intervention group (2 groups combined): 17 and 15 participants; male/female: 12:5 and 12:3; age, years: 72.5 ± 6.5 and 70.5 ± 6.3; no data on BMI


OutcomesDuration of intervention: 3 postoperative days

Duration of follow-up: at least 5 days

No differences in pain scores between groups

All-cause mortality: 1 participant died after 32 days, but no details of surgical complications are given

Major respiratory complications as defined in individual studies:

Postoperative pulmonary complications: control, 4/18; intervention, 2/17 and 1/15

Significant atelectasis: not reported

Pneumonia: not reported ("chest radiograph changes" reported but not significant (88% control group, 58.5% intervention group))

Respiratory failure: not reported

Severe hypoxia: not reported

Severe delirium: not reported

Need for tracheal intubation and invasive ventilation: not reported

Readmission to ICU/IMC: intervention group: not reported

Length of stay in hospital, days: control group, 12.3 ± 4.8; intervention group, 11.5 ± 4.1 and 12.5 ± 4.8

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia): none reported 

Cardiac arrest: not reported

Other postoperative complications (wound infection, anastomotic leak, renal failure): not reported

Adverse effects of the intervention (pulmonary aspiration, upper airway or facial injury): not reported


NotesBMI = body mass index

CPAP = continuous positive airway pressure

FEV1 = forced expiratory volume in 1 second

ICU = intensive care unit

IMC = intermediate care unit

PEEP = positive end-expiratory pressure

RCT = randomized controlled trial


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskRandomly allocated into 3 groups with use of sealed envelopes

Allocation concealment (selection bias)Low riskRandomly allocated into 3 groups with use of sealed envelopes, but no details of allocation concealment provided

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNot discussed, but physiotherapists blinded to FRC (functional residual capacity) values, so only partially blinded

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskOnly radiologist possibly blinded (partial blinding only)

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskNot described, but only those who completed 5 days of lung volume measurements (40/50) were included in FRC and VC (vital capacity) analyses

Selective reporting (reporting bias)High riskPoor reporting of participant demographics (no weight) and no details on complications

Other biasUnclear riskNot sure

Gaszynski 2007

MethodsStudy done at Medical University of Lodz, Poland


ParticipantsPatients undergoing open Roux-en-Y gastric bypass

Male/female, 8:11; BMI, kg/m2: 42.43 ± 3.3; age, years: 35.84 ± 9.05


InterventionsAfter surgery, participants were monitored in PACU (postanaesthesia care unit) for 8 hours

Control group: 9 participants; oxygen via nasal cannula, 4 L/min

Intervention group: 10 participants; CPAP Boussignac device, + 9.4 cm H2O

Continuous SpO2 monitoring and frequent blood gases


OutcomesDuration of intervention: 8 hours

Duration of follow-up: most likely less than 1 day

No differences in pain scores between groups

All-cause mortality: none

Major respiratory complications as defined in individual studies:

Postoperative pulmonary complications: none

Significant atelectasis: not reported

Pneumonia: not reported

Respiratory failure: not reported

Severe hypoxia: not reported

Severe delirium: not reported

Need for tracheal intubation and invasive ventilation: no

Admission to ICU/IMC: intervention group: not reported

Length of stay in hospital: not reported

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia): none reported 

Other postoperative complications (wound infection, anastomotic leak, renal failure): none, not sure for how long

Adverse effects of intervention (pulmonary aspiration, upper airway or facial injury): not reported


NotesBMI = body mass index

CPAP = continuous positive airway pressure

ICU = intensive care unit

IMC = intermediate care unit

PACU = postanaesthesia care unit

SpO2 = oxygen saturation


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear risk'Randomly divided into two groups,' no further description

Allocation concealment (selection bias)Unclear riskNo description in text

Blinding of participants and personnel (performance bias)
All outcomes
High riskNot stated

Blinding of outcome assessment (detection bias)
All outcomes
High riskNot stated

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskNot clear

Selective reporting (reporting bias)Unclear riskNot clear

Other biasUnclear riskNot sure

Lindner 1987

MethodsStudy done at Ulm University Clinic, Ulm, Germany


ParticipantsParticipants undergoing elective major upper abdominal surgery; all were moderately healthy patients

Control group: 17 participants; male/female: 6:11; age, years: 65 (range 52-77); weight, kg: 65 (range 47-85)

Intervention group: 17 participants; male/female: 12:5; age, years: 66 (range 50-77); weight, kg: 66 (50-95)


InterventionsControl group: standard physiotherapy (deep breathing and coughing) at 3-hourly intervals during daytime for 48 hours

Intervention group: standard physiotherapy as well as continuous CPAP at FiO2 of 0.35, 12 cm H2O, 3 hours per day for 5 days


OutcomesDuration of intervention: 5 days

Duration of follow-up: 5 days

All participants received same analgesic routine

All-cause mortality: none reported

Major respiratory complications as defined in the study by radiograph (3rd day):

Atelectasis: control group, 4/17; intervention group, 0/17

Consolidation: control group, 1/17; intervention group, 1/17

Need for tracheal intubation and invasive ventilation: none in either group

Admission to ICU/IMC: intervention group: not reported

Length of stay in hospital: not reported

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia): none reported 

Other postoperative complications (wound infection, anastomotic leak, renal failure): none reported

Adverse effects of the intervention (pulmonary aspiration, upper airway or facial injury): not reported


NotesCPAP = continuous positive airway pressure

FiO2 = inspired oxygen fraction

ICU = intensive care unit

IMC = intermediate care unit


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear risk'Randomized' into 2 groups

Allocation concealment (selection bias)High riskNo description for it (randomly assigned into 2 groups)

Blinding of participants and personnel (performance bias)
All outcomes
High riskNot stated

Blinding of outcome assessment (detection bias)
All outcomes
Low risk"Pulmonary function measurements were performed by a researcher who was not aware of which group the patients were in"

Radiologist interpreted x-ray films "without knowledge of whether the patient was receiving CPAP or not"

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskProbably OK

Selective reporting (reporting bias)Unclear riskNot sure

Other biasUnclear riskNot sure

Lotz 1984

MethodsStudy done at Universitat Ulm/Donau, Germany


ParticipantsPatients undergoing upper abdominal surgery. Participants were randomly allocated into 4 groups. ZEEP (zero end-expiratory pressure) or PEEP (positive end-expiratory pressure) was given during surgery, followed by oxygen via mask or CPAP, thus making up 4 groups. For this review, we have chosen only 2 groups: control group, received ZEEP (no PEEP) and no CPAP after surgery. Intervention group received ZEEP during surgery and CPAP after surgery

Control group: ZEEP during anaesthesia, followed by oxygen via mask during the postoperative period: 16 participants; male/female, 9:6; age, years: 58 ± 8; BMI: weight not given (only Broca Index given)

Intervention group: ZEEP during anaesthesia, followed by CPAP during postoperative period: 16 participants; male/female: 8:8; age, years: 58 ± 10; BMI: weight not given (only Broca Index given)


InterventionsControl group: Participants received oxygen via nasal cannula in the recovery ward

Intervention group: Participants received CPAP (+ 5 cm H2O) for 2 hours in the recovery ward


OutcomesDuration of intervention: 2 hours in the recovery ward

Duration of follow-up: up to 10 days (days 2, 5 and 10)

All-cause mortality: not indicated

Major respiratory complications as defined in the study: not differentiated between atelectasis, pneumonia and consolidation, but we have included it as atelectasis on day 2

Atelectasis (day 2): control group, 6/16; intervention group, 3/16

Consolidation/Pneumonia: not sure

Need for tracheal intubation and invasive ventilation: control, 0/16; intervention, 0/16

Admission to ICU/IMC: no data

Length of stay in hospital: no data

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia):

Other postoperative complications (wound infection, anastomotic leak, renal failure): no data

Adverse effects of intervention (pulmonary aspiration, upper airway or facial injury): no data


NotesCPAP = continuous positive airway pressure

ICU = intensive care unit

IMC = intermediate care unit

PEEP = positive end-expiratory pressure

ZEEP = zero end-expiratory pressure


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskYes, randomly assigned to 4 groups

Allocation concealment (selection bias)Unclear riskNo details given, but possible

Blinding of participants and personnel (performance bias)
All outcomes
High riskNo details given

Blinding of outcome assessment (detection bias)
All outcomes
High riskNo details

Incomplete outcome data (attrition bias)
All outcomes
High riskNo outcome data of interest reported

Selective reporting (reporting bias)High riskNo information in text

Other biasUnclear riskNot sure

Ricksten 1986

MethodsStudy done at Sahlgren's Hospital, Gothenburg, Sweden


ParticipantsPatients having elective upper abdominal surgery

Groups were stratified by preoperative lung function, age, sex, body weight and smoking habit


InterventionsGeneral anaesthesia and epidural morphine (for at least 2 days) were given to all participants

Participants were randomly assigned to 3 groups:

Control group: deep breathing exercises every waking hour (30 breaths)

CPAP group: hourly 30 breaths with CPAP mask (+ 10-15 cm H2O) given every waking hour

PEP (positive expiratory pressure) group: hourly 30 breaths with a mask, which generated + 10 to 15 cm H2O during expiration, given every waking hour

We combined CPAP and PEP groups for the purpose of this review

All treatments continued for 3 postoperative days if participants tolerated it

Control group: 15 participants; male/female, 6:9; age, years: 51.7 ± 4.7; weight, kg: 90.4 ± 7.4

CPAP: 13 participants; male/female, 7:6; age, years: 52.5 ± 3.5; weight, kg: 93.4 ± 6.3

PEP group: 15 participants; male/female, 8:7; age, years 56.9 ± 3.8; weight, kg: 89.0 ± 7.0


OutcomesDuration of intervention: 3 days

Duration of follow-up: 3 days

All-cause mortality: none reported

Major respiratory complications as defined in individual studies:

Postoperative pulmonary complications:

Significant atelectasis/consolidation (radiology confirmation): 1st postop day: control, 5/15; CPAP group: 2/13; PEP group, 1/15

Significant atelectasis/consolidation (radiology confirmation): 3rd postop day: control, 6/15; CPAP group: 1/13; PEP group, 0/15

Pneumonia: not reported

Respiratory failure: not reported

Severe hypoxia: lower A-a difference reported, but no numbers given

Need for tracheal intubation and invasive ventilation: none reported

Admission to ICU: intervention group: not reported

Length of stay in hospital: not reported

Cardiovascular complications (myocardial infarction, unstable angina, acute cardiac failure, arrhythmia): none reported 

Other postoperative complications (wound infection, anastomotic leak, renal failure): none reported

Adverse effects of the intervention (pulmonary aspiration, upper airway or facial injury): not reported


NotesCPAP = continuous positive airway pressure

ICU = intensive care unit

PEP = positive expiratory pressure


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskAfter stratification, randomly assigned into 3 groups, not sure how

Allocation concealment (selection bias)High riskNo evidence

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNot sure

Blinding of outcome assessment (detection bias)
All outcomes
Low riskRadiologist blinded, not sure whether anyone else was blinded

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskNot clear

Selective reporting (reporting bias)Unclear riskNot clear

Other biasUnclear riskNot sure

Squadrone 2005

MethodsPatients undergoing elective abdominal surgery from centres of the Piedmont Intensive Care Units Network, Italy


ParticipantsAdult patients undergoing elective abdominal surgery, requiring laparotomy and visceral exposure for longer than 90 minutes


InterventionsRandomization was done after surgery and 1 hour of monitoring (and PaO2/FiO2 < 300). Inclusion and exclusion criteria clearly detailed

Control group: 104; male/female: 64:40; age, years: 65 ± 10; BMI, kg/m2: 26.3 ± 4.5

Intervention group: 105; male/female: 71:34; age, years: 66 ± 9; BMI, kg/m2: 26.5 ± 4.7

Control group: Venturi mask with FiO2 of 0.5 for 6 hours, followed by further assessment of PaO2/FiO2, followed by further treatment of Ventimask with FiO2 of 0.5 if PaO2/FiO2 ratio < 300

Intervention group: CPAP mask with FiO2 of 0.5 and CPAP of + 7.5 cm H2O for 6 hours, followed by further assessment of PaO2/FiO2, followed by further use of CPAP mask with FiO2 of 0.5 and CPAP of + 7.5 cm H2O if PaO2/FiO2 ratio < 300


OutcomesDuration of intervention: minimum of 6 hours

Duration of follow-up: longer than 3 days (up to 7 days)

All-cause mortality: control group, 3/104; intervention group, 0/105

Major respiratory complications as defined in individual studies:

Pneumonia: control group, 10/104; intervention group, 2/105

Need for tracheal intubation and invasive ventilation: control group, 10/104; intervention group, 1/105

ICU length of stay: control group, 2.6; intervention group, 1.4

Length of stay in hospital: control group: 17 ± 15 days; intervention group, 15 ± 13 days

Other postoperative complications (wound infection, anastomotic leak, renal failure):

Infection: control group, 11/104; intervention group, 3/105

Sepsis: control group, 9/104; intervention group, 2/105

Anastomotic leakage: control group, 6/104; intervention group, 1/105


NotesBMI = body mass index

CPAP = continuous positive airway pressure

FiO2 = inspired oxygen fraction

ICU = intensive care unit

PaO2 = arterial oxygen pressure


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskConcealed randomization was conducted centrally through dedicated website using computer-generated block randomization schedule

Allocation concealment (selection bias)Low riskConcealed randomization was conducted centrally through dedicated website using computer-generated block randomization schedule

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNot described

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNot described

Incomplete outcome data (attrition bias)
All outcomes
Low riskOutcomes reported

Selective reporting (reporting bias)Unclear riskNot sure; premature stopping of trial by data monitoring committee

Other biasUnclear riskNot sure

Stock 1985

MethodsStudy done at Mercy Hospital, Northwest University, Chicago, USA


ParticipantsPatients having elective upper abdominal surgery were selected.


InterventionsA computer random number generator was used to assign each participant to 1 of 3 treatment groups for postoperative respiratory therapy

Three groups were studied

CBD group was given coughing and deep breathing exercises, starting 4 hours after extubation. This was given for 15 minutes, every 2 hours during waking hours. Duration of treatment was 4 to 72 hours

IS group received incentive spirometry for 15 minutes, every 2 waking hours, for 4 to 72 hours (starting 4 hours after extubation)

We combined CBD and IS groups as controls for the purpose of this review

CPAP group received continuous positive airway pressure using a soft self-sealing mask, + 7.5 cm H2O, for 15 minutes, every 2 waking hours, for 4 to 72 hours (starting 4 hours after extubation)

Control groups: CDB group: number of participants, 20; male/female: 9:11; weight/ BMI, not given; age, years: 48 ± 4 (SEM); duration: 4 to 72 hours

IS group: number of participants, 22; male/female: 8:14; weight/BMI: not given; age, years: 54 ± 4 (SEM); duration: 4 to 72 hours

Intervention group: 23 participants; male/female: 8:15; weight/ BMI: not given; age, years: 49 ± 5 (SEM); duration: 4 to 72 hours


OutcomesDuration of intervention: 4 to 72 hours

Duration of follow-up for 3 days

All-cause mortality: not given

Major respiratory complications as defined in individual studies:

X-ray confirmed atelectasis at 24 hours: control group: CDB, 6/20; IS, 11/22 = 17/42; intervention group, 9/23

X-ray confirmed atelectasis at 72 hours: control group: CDB, 8/20; IS, 9/22 = 17/42; intervention group, 5/23

Pneumonia: CDB, 1/20, IS, 1/22 (control, 2/42); intervention group, 0/23

No other information offered in the paper


NotesBMI = body mass index

CDB = coughing and deep breathing

CPAP = continuous positive airway pressure

IS = incentive spirometry

SEM = standard error of the mean


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskA computer random number generator was used to assign each participant to 1 of the different groups

Allocation concealment (selection bias)Unclear riskA computer random number generator was used to assign each participant to 1 of the different groups; most likely adequate, but no description of allocation concealment

Blinding of participants and personnel (performance bias)
All outcomes
High riskNot described

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskRadiologists blinded for x-ray interpretation, but not sure of others

Incomplete outcome data (attrition bias)
All outcomes
Low riskProbably all participants accounted for

Selective reporting (reporting bias)Unclear riskProbable

Other biasUnclear riskProbable

 
Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion

Anderes 1979Participants in one group were intubated for 3 hours, whereas participants in the other group were extubated soon after surgery. Unequal treatment of groups

Celli 1984Intervention is not CPAP, but positive-pressure breathing

Conti 2007Study is a case-controlled study, not an RCT

Drummond 2002Even though this is an RCT (stratified), study was done mainly to observe effects of CPAP on sleep pattern and hypoxaemia. Study lasted only 1 day; no relevant data available from this publication for the purpose of the review

Ebeo 2002This RCT deals with BiPAP ventilation, which is different from CPAP; hence excluded from this review

Huerta 2002This is not an RCT

Jaber 2005This study of participants who already have established respiratory failure is not an RCT; it also falls into the exclusion criteria for the review

Joris 1997This RCT uses BiPAP (bilevel positive airway pressure) during the postoperative period. This is an exclusion criterion

Kindgen-Milles 2005This RCT is dealing with thoraco-abdominal aortic surgery and does not conform with inclusion criteria

Neligan 2009A randomized trial, but the intervention group receives the same treatment as the control group, except that onset of treatment is delayed by 30 minutes. Therefore, this study was excluded

Olsen 2002This RCT is dealing with thoraco-abdominal operations, an exclusion criterion for the review

Rieg 2012This is not an RCT; participants were allocated into 2 groups on 2 different timelines

Roeseler 1982Study population is a mixture of randomized and non-randomized cases, allocated into 2 groups. Therefore, excluded from review

Vartanov 2007Intervention group received BiPAP ventilation during the postoperative period, even though the study was an RCT

Wong 2011Used PEEP during surgery; follow-up with CPAP in the recovery ward, but only for 1 hour

 
Characteristics of studies awaiting assessment [ordered by study ID]
Damgaard 1982

MethodsWaiting for a translation

ParticipantsWaiting for a translation

InterventionsWaiting for a translation

OutcomesWaiting for a translation

NotesWaiting for a translation

 
Characteristics of ongoing studies [ordered by study ID]
McKay 2012

Trial name or titleProphylactic nCPAP Following Bowel Surgery (Bio-REB File 11-27)

MethodsRandomized controlled trial

ParticipantsAdults undergoing bowel surgery

InterventionsOxygen via nCPAP vs via masks in the postoperative period

OutcomesSome relevant to this review

Starting date2012

Contact informationDr William McKay, University of Saskatchewan, Canada

NotesStudy being repeated

Wong 2010

Trial name or titleOxygenation and Pulmonary Function in Morbidly Obese Patients Undergoing Bariatric Surgery

MethodsBoussignac(TM) CPAP compared with Venturi mask

ParticipantsAdult patients undergoing bariatric surgery

InterventionsBoussignac(TM) CPAP

OutcomesPaO2/FiO2 ratio for 24 hours

Starting date2010

Contact informationEmailed lead author, Dr David Wong, University Health Network, Toronto, Canada

NotesStudy should have been finished by 2012, but not yet published

 
Comparison 1. Reported mortality

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Mortality2413Risk Ratio (M-H, Fixed, 95% CI)1.28 [0.35, 4.66]

 
Comparison 2. Adverse outcomes

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Significant atelectasis6249Risk Ratio (M-H, Fixed, 95% CI)0.62 [0.45, 0.86]

 2 Pneumonia5563Risk Ratio (M-H, Fixed, 95% CI)0.43 [0.21, 0.84]

 3 Severe hypoxia2255Risk Ratio (M-H, Fixed, 95% CI)0.48 [0.22, 1.02]

 4 Reintubation2413Risk Ratio (M-H, Fixed, 95% CI)0.14 [0.03, 0.58]

 
Summary of findings for the main comparison.

CPAP during postoperative period for participants having major abdominal surgery

Patient or population: patients having major abdominal surgery

Settings: major abdominal surgery

Intervention: CPAP during postoperative period as intervention

Comparison: usual postoperative care as control

OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No. of participants
(studies)
Quality of the evidence
(GRADE)
Comments

Assumed riskCorresponding risk

ControlCPAP during postoperative period

Reported mortality

As reported in the trials
Follow-up: up to 5-7 days
Study populationRR 1.28

(0.35 to 4.66)
413
(2 studies)
⊕⊝⊝⊝
very lowa,b,c
Data contain only mortality figures reported in the studies

14 per 100018 per 1000
(5 to 65)

Moderate

14 per 100018 per 1000
(5 to 63)



Atelectasis

As reported in the trials
Follow-up: up to 1-10 days
Study population RR 0.62

(0.45 to 0.86)
249
(6 studies)
⊕⊝⊝⊝
very lowd,e,f
Data include only the numbers identified in included studies

441 per 1000240 per 1000
(148 to 371)

Moderate

402 per 1000212 per 1000
(129 to 335)



Pneumonia

As reported in the included trials
Follow-up: up to 5-7 days
Study populationRR 0.43

(0.21 to 0.84)
563
(5 studies)
⊕⊝⊝⊝
very lowg,h,i
Data include only documented cases in included studies

81 per 100032 per 1000
(16 to 67)

Moderate

59 per 100023 per 1000
(11 to 49)



*The basis for the assumed risk (e.g. median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).

CI: Confidence interval; RR: Risk ratio.

GRADE Working Group grades of evidence.
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

 aRisk of bias for the 2 included studies (Bohner 2002; Squadrone 2005) assessed as unclear.
bHeterogeneity is considerable in the methods of intervention and controls in the 2 studies (Bohner 2002; Squadrone 2005).
cEven though the 2 studies (Bohner 2002; Squadrone 2005) included around 400 participants, the rate of (mortality) is very low.
dFour of the 6 studies in this analysis (Carlsson 1981; Christensen 1991; Lindner 1987; Lotz 1984; Ricksten 1986: Stock 1985) are marked as high risk of bias, and Stock 1985, Carlsson 1981 and Christensen 1991 are marked as unclear risk of bias.
eHeterogeneity between the 6 studies included in this analysis is considerable; intervention groups and control groups were somewhat different; duration of intervention and period of observations were also different in these studies.
fNumbers of participants and event rates in included trials were low in the included trials.
gThree of the selected studies (Bohner 2002; Christensen 1991; Squadrone 2005) were assessed as unclear risk of bias and two of the studies (Lindner 1987; Stock 1985) were assessed as high risk of bias.
hIn the included trials, differences in control and intervention groups, methods of assessing outcomes (pneumonia) and time when outcomes were assessed were inconsistent, resulting in important clinical heterogeneity.
iThe 5 included studies have varying numbers of participants and low rates of pneumonia. This leads to serious imprecision.
 
Table 1. Details of study groups

Study IDSurgical procedureDuration of trialDuration of follow-upControl group: detailsControl group: numberIntervention

group: details
Intervention group: numberComments

Bohner 2002Midline laparotomy14.0 ± 4.3 hoursLonger than 7 daysO2 via mask105nCPAP at + 10 cm H2O99 

Carlsson 1981Open cholecystectomy4 hours1 day30% O2 via bag1130% O2 via bag, + 5 to 10 cm H2O13 

Christensen 1991Upper abdominal surgery3 days postop3 daysConventional physiotherapy17Conventional physio + CPAP using PEP mask17High-risk patients; O2 only if hypoxia

Denehy 2001

 
Upper abdominal surgery3 days postop5 daysTraditional physiotherapy13Traditional physiotherapy + nasal CPAP at + 10 cm H2O32Intervention groups × 2, CPAP for 15 and 30 minutes each

Gaszynski 2007Roux-en-Y gastric bypass8 hours1 day?O2 via nasal cannula9CPAP Boussignac device, + 9.4 cm H2O10 

Lindner 1987

 
Upper abdominal surgery5 days5 daysStandard physiotherapy17Standard physio + CPAP for 5 days17 

Lotz 1984

 
Upper abdominal surgery2 hours in recovery ward10 daysO2 by face mask16CPAP during postoperative period162 further groups, both receiving PEEP during anaesthesia, excluded

Ricksten 1986

 
Upper abdominal surgery3 days3 daysDeep breathing, hourly15Hourly, CPAP + 10 to 15 cm H2O28Combined CPAP and PEP groups combined

Squadrone 2005Abdominal surgery12 hours3-7 daysVenturi mask (FiO2  0.5)104CPAP mask, + 7.5 cm H2O (FiO2  0.5)105 

Stock 1985

 
Upper abdominal surgery4-72 hours3 daysCough and deep breathing or incentive spirometry42CPAP mask23Combined 2 groups as control

 

 
Table 2. Reported outcomes

Study IDAll cause mortalityMajor respiratory complicationsLength of hospital stay, daysCardiovascular complicationsOther postop complicationsAdverse effects of interventionComments

Bohner 20020/105; 5/99Pneumonia:

5/105; 2/99

Severe hypoxia:

17/105; 5/99

Intubation:

5/105; 1/99
11.8 ± 18.6; 9.5 ± 6.8Cardiac arrest:

2/105; 1/99
Delirium:

12/105; 6/99

Renal failure:

3/105; 3/99

 
Nose ulcers:

0/105; 4/99
ICU admission:

14/105; 6/99

Carlsson 1981

 
-Atelectasis (24 hours):

10/11; 10/13
-----

Christensen 1991-Atelectasis:

9/17; 11/17

Pneumonia:

5/17; 6/17

Intubation:

0/17; 1/17
10.4 ± 1.9/

16.4 ± 3.2
-0/17; 0/17-Converted 95% CI into SD:

Mean 10.4; 95% CI 4 to 26; 26 to 10.4 = 15.6

95% CI implies z = 1.96

Error = z (SE)

15.6= 1.96 (SE)

8.0 = SE

SE = SD/SQRT (N)

8.0 = SD/SQRT (17)

1.9 = SD

Denehy 2001

 
1 death (no

 group)
Postop pulmonary complications:

4/18; 3/32
12.3 ± 4.8;

12.0 ± 4.5
----

Gaszynski 20070/9; 0/11Intubation:

0 /9; 0/11
-----

Lindner 1987-Atelectasis:

4/17; 0/17

Consolidation:

1/17; 1/17

Intubation:

0/17; 0/17

 
-----

Lotz 1984

 
-Respiratory complications (?atelectasis): 6/16; 3/16-----

Ricksten 1986

 
-Atelectasis:

6/15; 1/28
-----

Squadrone 20053/104; 0/105

 
Pneumonia:

10/104; 2/105
17 ± 15; 15 ± 13-Infection:

11/104; 3/105

Sepsis:

9/104; 2/105
--

Stock 1985-Atelectasis:

17/42; 5/23
-----

 
Table 3. Risk of bias data

Study IDRandom sequence generation (selection bias)Allocation concealment (selection bias)Blinding of participants and personnel (performance bias)Blinding of outcome assessment (detection bias)Incomplete outcome data (attrition bias)Selective reporting (reporting bias)Other biasOverall risk of bias judgement

Bohner 2002Randomization using a random listNo description of allocation concealmentAnaesthesiologist; not sure of anyone elseNot described in the textDropouts describedNo evidence for thisNone reported

 
Unclear

Carlsson 1981No details of randomizationNot describedNot described

 
Radiologist was unaware of treatmentsAll participants accounted forNot sureNot sureUnclear

Christensen 1991Randomly allocated into 3 groupsNo evidence for itNo evidence for itNo evidence for itReasonable accountNot sure

 
Not sure

 
Unclear

Denehy 2001Randomly allocated into 3 groups with use of sealed envelopesSealed envelopesNot describedOnly radiologist possibly blinded (partial blinding only)Not describedNo detailed demographics of any complicationsNot sureHigh

Gaszynski 2007'Randomly divided into two groups,' no further descriptionNo description

 
Not statedNot statedNot clear

 
Not clear

 
Not sureHigh

Lindner 1987Randomized into 2 groupsNo description for itNot statedNot statedProbably OKNot sureNot sureHigh

Lotz 1984

 
Randomized into 4 groupsNo description in text, but possibleNo detailsNo detailsScarcity of outcomes of interestNo informationNot sureHigh

Ricksten 1986Stratification and randomization (unclear method)No evidence

 
Not sure

 
Blinded radiologist, not sure of othersNot clearNot clearNot sureHigh

Squadrone 2005Centrally through dedicated website using computer-generated block randomization scheduleYes, concealed central randomizationNot described

 
Not described

 
YesPremature stopping of trial

 
Not sureUnclear

Stock 1985

 
A computer random number generator was used to assign each participantMost likely adequate

 
Not described

 
Not described

 
Probably all participants accounted for

 
Probable

 
Probable

 
High