Open Access

Spontaneous breathing trial and post-extubation work of breathing in morbidly obese critically ill patients

  • Martin Mahul1,
  • Boris Jung1, 4,
  • Fabrice Galia1,
  • Nicolas Molinari2,
  • Audrey de Jong1,
  • Yannaël Coisel1, 4,
  • Rosanna Vaschetto3,
  • Stefan Matecki4,
  • Gérald Chanques1, 4,
  • Laurent Brochard5, 6 and
  • Samir Jaber1, 4Email author
Contributed equally
Critical Care201620:346

https://doi.org/10.1186/s13054-016-1457-4

Received: 19 April 2016

Accepted: 16 August 2016

Published: 27 October 2016

Abstract

Background

Predicting whether an obese critically ill patient can be successfully extubated may be specially challenging. Several weaning tests have been described but no physiological study has evaluated the weaning test that would best reflect the post-extubation inspiratory effort.

Methods

This was a physiological randomized crossover study in a medical and surgical single-center Intensive Care Unit, in patients with body mass index (BMI) >35 kg/m2 who were mechanically ventilated for more than 24 h and underwent a weaning test. After randomization, 17 patients were explored using five settings : pressure support ventilation (PSV) 7 and positive end-expiratory pressure (PEEP) 7 cmH2O; PSV 0 and PEEP 7cmH2O; PSV 7 and PEEP 0 cmH2O; PSV 0 and PEEP 0 cmH2O; and a T piece, and after extubation. To further minimize interaction between each setting, a period of baseline ventilation was performed between each step of the study. We hypothesized that the post-extubation work of breathing (WOB) would be similar to the T-tube WOB.

Results

Respiratory variables and esophageal and gastric pressure were recorded. Inspiratory muscle effort was calculated as the esophageal and trans-diaphragmatic pressure time products and WOB. Sixteen obese patients (BMI 44 kg/m2 ± 8) were included and successfully extubated. Post-extubation inspiratory effort, calculated by WOB, was 1.56 J/L ± 0.50, not statistically different from the T piece (1.57 J/L ± 0.56) or PSV 0 and PEEP 0 cmH2O (1.58 J/L ± 0.57), whatever the index of inspiratory effort. The three tests that maintained pressure support statistically underestimated post-extubation inspiratory effort (WOB 0.69 J/L ± 0.31, 1.15 J/L ± 0.39 and 1.09 J/L ± 0.49, respectively, p < 0.001). Respiratory mechanics and arterial blood gases did not differ between the five tests and the post-extubation condition.

Conclusions

In obese patients, inspiratory effort measured during weaning tests with either a T-piece or a PSV 0 and PEEP 0 was not different to post-extubation inspiratory effort. In contrast, weaning tests with positive pressure overestimated post-extubation inspiratory effort.

Trial registration

Clinical trial.gov (reference NCT01616901), 2012, June 4th

Keywords

WeaningMechanical ventilationObeseWork of breathingAcute respiratory failure

Background

Extubation is a critical decision in the Intensive Care Unit (ICU). Extubation failure may occur in up to 20 % [1] of patients and is associated with morbidity. Excessive and non-sustainable work of breathing (WOB) is likely a major reason for extubation failure [25]. Evaluation of how the critically ill patient is breathing with no assistance or a minimal level of assistance (the period known as the weaning test or the spontaneous breathing trial) [4] is therefore recommended before extubation [3, 4, 6, 7]. Different weaning tests are suggested for non-selected adult patients: a T-piece trial (oxygen supply without positive pressure), continuous positive airway pressure (CPAP) and low pressure support ventilation (PSV), with a low level of PSV, from 5 to 8 cmH2O, to compensate for the imposed workload due to the ventilator circuit [3, 4, 6, 7]. Although these weaning tests are not equivalent in term of the WOB [8, 9] and studies are underpowered to assess the risk of extubation failure, they are recommended to assess whether a patient is ready to be extubated [3, 6].

Predicting whether an obese critically ill patient can be successfully extubated may be specially challenging. Obesity decreases respiratory system compliance, inspiratory and expiratory lung volumes, functional residual capacity, upper airway mechanical function and neuromuscular strength [10]. Moreover, in obese patients, oxygen consumption is increased, with a high proportion of this consumption spent in the WOB [1113]. Although the T piece, CPAP and low PSV levels have been used to reproduce post-extubation conditions in non-selected critically ill patients, the weaning test modality that would best reproduce post-extubation inspiratory effort (WOB and pressure time product indexes) in obese critically ill patients has never been evaluated and many clinicians are worried about using no support during the test [14, 15].

The aim of our study was thus to assess which weaning test would best reproduce post-extubation inspiratory effort in obese critically ill patients. We compared a T-piece trial to weaning tests with PSV 7 and positive end-expiratory pressure (PEEP) 7 cmH2O; PSV 0 and PEEP 7 cmH2O; PSV 7 and PEEP 0 cmH2O; PSV 0 and PEEP 0 cmH2O, in this particular population. We hypothesized that the T-tube or PSV 0 and PEEP 0 cmH2O would best approximate the post-extubation WOB.

Methods

Study

This was a physiological prospective randomized crossover study (Additional file 1: Table S1), approved by the Ethics Committee of the Saint-Eloi Teaching Hospital (2012 A-00294-39, Comité de Protection des Personnes Sud Méditerranée III, Montpellier, France), and registered on clinical trial.gov (reference NCT01616901, registered June 4th, 2012). All patients provided their written informed consent.

Patients

Upon admission, height and weight were measured using the bed scale and a tape measure. All morbidly obese patients, defined by a body mass index (total body weight in kg/height in m2) >35 kg/m2 [16], were considered eligible for inclusion in the study if they were mechanically ventilated for at least 24 h and were considered by the physician on duty to be ready for extubation. Patients were not included in the study if there was any contraindication to the insertion of an esophageal catheter.

Experimental procedure and study design

A 15-minute period corresponding to a baseline state was first recorded (using PSV and PEEP set by the clinician in charge of the patient before inclusion). Patients were then randomly assessed using computer-driven software with five settings: PSV 7 and PEEP 7 cmH2O; PSV 0 and PEEP 7 cmH2O; PSV 7 and PEEP 0 cmH2O; PSV 0 and PEEP 0 cmH2O or the T piece. Each setting lasted 15 minutes with a 10-minute period of return to baseline steady state between each setting (Fig. 1). Steady state was defined clinically as a period sufficient to ensure clinical stability in respiratory and hemodynamic variables assessed by a physical exam which took into account heart rate, respiratory rate, paradoxical breathing pattern, accessory muscle use, grunting at end expiration and nasal flaring [17], and as previously performed by our group [18, 19].
Fig. 1

Study design. Eleven morbidly obese patients ventilated in pressure support ventilation (PSV) and positive end-expiratory pressure (PEEP), considered as baseline settings, were included to randomly perform the five weaning test modalities of the study before extubation: PSV 7 cmH2O + PEEP 7 cm H2O; PSV 0 cmH2O + PEEP 7 cmH2O; PSV 7 cmH2O + PEEP 0 cmH2O; PSV 0 cmH2O + PEEP 0 cmH2O or the T piece. All measurements were obtained after 15 minutes of each test. A 10-minute period of return to baseline state (with initial settings of ventilation parameters before the first weaning test) was performed between each test and before extubation. WT weaning test

After being explored with these five settings, and in the case of clinical success in the different weaning trials, patients were ventilated for 10 minutes using baseline state variables and then were extubated if the clinical state was judged adequate by the clinician in charge. A post-extubation measurement was performed 20 minutes after extubation using an oro-nasal oxygen mask with a flow of 5 L/minute (equivalent to inspired oxygen fraction (FiO2) of 0.4 [20]). According to our local protocol described in detail in a previous review [21], and after having achieved each step of the protocol, non-invasive ventilation was performed as a prophylactic routine measure in the immediate post-extubation period, for between 30 and 45 minutes every 4 to 6 h. Settings were adjusted to target the following: tidal volume (VT) 6–10 ml/kg of ideal body weight, respiratory rate (RR) 12–20 c/minute and pulse arterial oxygen saturation (SpO2) equal or above 95 %. Non-invasive ventilation was never performed before the end of the protocol.

Measurements

All patients were studied in a semi-recumbent position with the head of the bed elevated to an angle from 30 to 45 degrees, according to patient comfort. [22] Procedures are detailed in the additional material. Briefly, the respiratory mechanics measurements comprised flow, airway pressure, esophageal (Pes) and gastric (Pga) pressure swings. Trans-diaphragmatic swings (Pdi) were calculated by subtracting Pes from Pga. Minute ventilation (VE), tidal volume (VT), inspiratory (Ti), expiratory time (Te), total cycle duration (Ttot) and RR were calculated from the numerical integration of the flow signal.

The inspiratory WOB per breath performed by the patient was calculated from a Campbell diagram taking into account the presence of intrinsic PEEP. Eesophageal and trans-diaphragmatic pressure-time products (PTPes and PTPdi) were also measured as previously reported [23, 24]. Analyses of arterial blood gases were obtained at the end of each test.

Statistical analysis

All values are presented as mean ± SD. To assess differences between the weaning tests, we used the Friedman test and then pairwise comparisons with the Wilcoxon test if a significant difference appeared. Statistical analysis was performed by an independent statistician (NM) using R software© (R Foundation for Statistical Computing, Auckland, New Zealand).

Based on the literature review, we hypothesized that the post-extubation WOB would be similar to the T-tube WOB [25, 26] and would approximate 1.5 +/- 0.9 J/L in obese critically ill patients. We also hypothesized that WOB in PSV 7 cmH2O and PEEP 7 cmH2O would approximate 0.7 +/- 0.5 J/L [27]. Then, with an alpha risk at 0.05 and a power at 0.90, 12 patients would be needed. We decided to include 17 patients in order to make sure that 12 patients would complete the study. Significance was set at p < 0.01 after correction for the number of multiple comparisons, i.e., using the Bonferroni test.

Results

Patients

Between March and December 2012, 40 obese patients with body mass index ≥35 kg/m2 were admitted in our center. Among them, 17 met the inclusion criteria. Sixteen patients (13 women and 3 men) with mean body mass index of 44 kg/m2 (±8 kg/m2) were prospectively enrolled in the present study, as shown in Fig. 2. Characteristics of the subjects are detailed in Table 1. Mean duration of invasive mechanical ventilation before enrollment in the study was 6 days (±7 days). The five weaning tests were well-tolerated by all patients and all of them but one were successfully extubated.
Fig. 2

Flow chart of the study. One patient fulfilled the inclusion criteria but was not included because of extubation during the weekend with no investigator available. BMI body mass index, SBT spontaneous breathing trial

Table 1

Characteristics of the patients

Patient

Sex

Age

SAPS II

Height

Weight

BMI

Underlying

Etiology of respiratory failure

ETT ID

MV before extubation

PSV at baseline

PEEP at baseline

Extubation failure

Outcome (D/S)

number

 

(years)

 

(cm)

(kg)

(kg/m2)

diseases

(mm)

(days)

(cmH2O)

(cmH2O)

(Y/N)

1

F

83

109

150

80

35

CHF

Small bowel ischemia

7.5

7

8

6

N

D

2

F

85

68

163

115

43

NIDDM

Pneumonia

7.5

4

15

7

N

S

3

M

64

50

170

130

44

NIDDM

Acute pancreatitis

8

3

12

8

N

S

4

F

59

60

155

95

39

None

Peritonitis

7.5

3

12

8

N

S

5

F

49

66

160

174

67

COPD, OSA

Septic shock

7.5

6

10

10

N

S

6

F

25

29

172

145

49

None

Asthma

7.5

1

10

8

N

S

7

F

54

19

153

121

51

Asthma, HTN

Post abdominal surgery

7.5

1

10

8

N

S

8

M

37

54

180

130

40

None

Acute pancreatitis

8

14

8

10

N

S

9

F

78

90

155

87

36

None

Bowel obstruction

7.5

4

8

5

N

S

10

F

49

78

167

112

41

Asthma, OSA

Peritonitis

7.5

30

8

5

N

S

11

F

73

77

150

93

41

CHF, AF

Septic shock

7.5

4

12

6

N

D

12

F

50

45

162

94

36

None

Necrotizing fasciitis

7.5

2

9

7

N

S

13

M

63

64

175

180

56

NIDDM, HTN

Small bowel bleeding

7.5

1

8

10

N

S

14

F

43

48

155

105

43

OSA, home ventilation

Pneumonia

7.5

3

12

7

N

S

15

F

77

41

155

84

36

NIDDM, HTN

Pancreatitis

7.5

7

9

7

Y

S

16

F

50

64

164

124

46

OSA, home ventilation

Post abdominal surgery

7.5

8

14

8

N

S

Mean

 

59

60

162

117

44

.

  

6

10

7

  

SD

 

17

22

9

30

8

.

  

7

2

2

  

Abbreviations: AF atrial fibrillation, BMI body mass index; CHF chronic heart failure, D deceased; ETT ID endotracheal tube internal diameter; F female; M male; HTN hypertension, mechanical ventilation; NIDDM non-insulin-dependent diabetes mellitus; OSA obstructive sleep apnoea, PEEP positive end-expiratory pressure; PSV pressure support ventilation; SAPS II Simplified Acute Physiology Score II [34]; S survived

The first patient was initially unable to complete the five weaning tests. She was re-challenged 72 h later, and succeeded the tests and extubation. Seven days after extubation, she developed cardio-respiratory distress and was re-intubated. Patient number 15 developed hypoxemic acute respiratory failure and was re-intubated 12 h after extubation. One patient had accidental nasogastric catheter removal after extubation, preventing the measurement of respiratory muscle work variables after extubation. This patient was excluded from the final analysis.

Respiratory variables and gas exchange

There was no statistical difference in any of the different respiratory variables (shown in Table 2) among the five weaning tests or at 20 minutes after extubation. In particular, differences in the RR/VT ratio were not statistically significant between the five weaning tests or at 20 minutes after extubation. There was no statistically significant difference in arterial blood gases or hemodynamic variables among the six steps of the study, as shown in Table 3.
Table 2

Respiratory variables during the five different weaning tests and 20 minutes after extubation

 

PSV

PSV

PSV

PSV

T piece

After extubation

+7 cmH2O PEEP

0 cmH2O PEEP

+7 cmH2O PEEP

0 cmH2O PEEP

+7 cmH2O

+7 cmH2O

0 cmH2O

0 cmH2O

Ti, s

0.90 ± 0.2

0.93 ± 0.23

0.82 ± 0.24

0.84 ± 0.28

0.81 ± 0.3

0.89 ± 0.43

Ttot, s

2.6 ± 0.8

2.4 ± 0.6

2.2 ± 0.6

2.1 ± 0.6

2.1 ± 0.6

2.2 ± 0.8

Ti/Ttot, %

35.7 ± 3.6

38.7 ± 4.2

37.8 ± 4.2

39.3 ± 4.4

38.7 ± 4.7

40.8 ± 4.3

VT, L

0.43 ± 0.12

0.41 ± 0.1

0.38 ± 0.1

0.37 ± 0.1

0.35 ± 0.1

0.36 ± 0.1

RR, breaths/minute

25 ± 6

26 ± 7

29 ± 6

30 ± 8

31 ± 7

30 ± 8

RR/VT, minutes/mL

64.5 ± 26.8

69.7 ± 25.0

83.1 ± 34.4

87.8 ± 36.4

94.7 ± 38.1

88.6 ± 34

VE, L/minute

10.3 ± 2.4

10.41 ± 2.9

10.8 ± 2.6

10.8 ± 3.3

10.5 ± 3.2

11.2 ± 4.4

PEEPi, cmH2O

1.1 ± 0.9

1.7 ± 1.2

2.5 ± 2.3

2.6 ± 2.2

2.4 ± 2.6

2.2 ± 2.3

There were no statistically significant differences between respiratory variables among the successive tests. Abbreviations: PSV pressure support ventilation; PEEP positive end-expiratory pressure; PEEPi intrinsic positive end-expiratory pressure; RR respiratory rate; Ti inspiratory time; Ttot total respiratory time; VE volume per minute; V T tidal volume

Table 3

Arterial blood gases and hemodynamic variables during the five different weaning tests and at 20 minutes after extubation

 

PSV

PSV

PSV

PSV

T piece

After extubation

+7 cmH2O PEEP

0 cmH2O PEEP

+7 cmH2O PEEP

0 cmH2O PEEP

+7 cmH2O

+7 cmH2O

0 cmH2O

0 cmH2O

Ph

7.45 ± 0.06

7.44 ± 0.06

7.44 ± 0.06

7.44 ± 0.06

7.43 ± 0.06

7.42 ± 0.06

PaCO2, mmHg

41 ± 11

42 ± 11

43 ± 12

43 ± 12

44 ± 13

44 ± 10

PaO2/FIO2

277 ± 76

257 ± 81

252 ± 73

230 ± 65

217 ± 65

224 ± 51

SBP, mmHg

148 ± 22

148 ± 26

148 ± 26

146 ± 30

150 ± 18

147 ± 24

DBP, mmHg

72 ± 12

71 ± 12

73 ± 12

72 ± 15

69 ± 13

70 ± 15

HR, beats/minute

96 ± 14

97 ± 16

98 ± 16

100 ± 16

99 ± 14

101 ± 15

There were no statistically significant differences between respiratory variables among the successive tests. Abbreviations: DBP diastolic blood pressure, HR heart rate, ND not done, PEEP positive end-expiratory pressure, PSV pressure support ventilation, SBP systolic blood pressure

Inspiratory effort

Figures 3, 4, and 5 show the individual and mean values of the main variables studied, and representative tracings of Pes, Pga and Pdi can be seen in Fig. 6. There was a significant difference in all respiratory effort variables (swings of Pes and Pdi, PTPes and PTPdi, WOB in J/L and in J/min) between the weaning tests and after the extubation period (p < 0.001) (Table 4). Weaning tests performed with positive pressure constantly overestimated post-extubation inspiratory effort. Inspiratory effort measured with either the T tube or PSV 0 + PEEP 0 cmH2O was not different to post-extubation inspiratory effort. We then identified both PSV 0 + PEEP 0 cmH2O and the T-piece trial as the weaning tests that reproduce post-extubation inspiratory effort and the WOB (Additional files 2, 3, 4, 5, 6 and 7).
Fig. 3

Esophageal (a) and trans-diaphragmatic (b) swings. Individual and mean changes in esophageal and trans-diaphragmatic swings during the five weaning tests and 20 minutes after extubation. All the tests show that the weaning tests that best reproduce respiratory muscle work after extubation were pressure support ventilation (PSV) 0 cmH2O + positive end-expiratory pressure (PEEP) 0 cmH2O and the T piece, with no statistically significant difference between the two. *p < 0.001 when compared with after extubation. Pdi transdiaphragmatic pressure, pes esophageal pressure

Fig. 4

Esophageal (a) and trans-diaphragmatic (b) pressure time products. Individual and mean changes in esophageal and trans-diaphragmatic pressure time products during the five weaning tests and 20 minutes after extubation. All the tests show that the weaning tests that best reproduce respiratory muscle work after extubation were pressure support ventilation (PSV) 0 cmH2O+ positive end-expiratory pressure (PEEP) 0 cmH2O and the T piece, with no statistically significant difference between the two. *p < 0.001 when compared with after extubation. PTPdi trans-diaphragmatic pressure-time product, PTPes trans-esophageal pressure-time product

Fig. 5

Work of breathing (WOB) in J/L (a) and in J/minute (b). Individual and mean changes in the WOB during the five weaning tests and 20 minutes after extubation. All the tests show that the weaning tests that best reproduced respiratory muscle work after extubation were pressure support ventilation (PSV) 0 cmH2O cmH2O + positive end-expiratory pressure (PEEP) 0 cmH2O and the T piece, with no statistically significant difference between the two. *p < 0.001 when compared with after extubation

Fig. 6

Ventilatory pattern during the five weaning tests and twenty minutes after extubation. One patient is presented with the acquisition of flow (L/s), esophageal (Pes, cmH2O), airway (Paw, cmH2O), gastric (Pga, cmH2O) and trans-diaphragmatic (Pdi, cmH2O) pressure signals. PSV pressure support ventilation, PEEP positive end-expiratory pressure

Table 4

Inspiratory muscle effort during the five different weaning tests and 20 minutes after extubation

 

PSV

PSV

PSV

PSV

T piece

After extubation

+7 cmH2O PEEP

0 cmH2O PEEP

+7 cmH2O PEEP

0 cmH2O PEEP

+7 cmH2O

+7 cmH2O

0 cmH2O

0 cmH2O

Swing Pes, cmH2O

7.2 ± 5.0*

13.4 ± 5.5*

12.3 ± 6.3*

19.1 ± 7.7

19.8 ± 7

19.1 ± 5.4

Swing Pdi, cmH2O

8.4 ± 5.5*

15.4 ± 5.7*

14.2 ± 6.4*

21.2 ± 8.1

21.7 ± 7.0

20.9 ± 5.5

PTP es, cmH2O.s/minute

141 ± 54*

259 ± 84*

231 ± 82*

346 ± 97

332.9 ± 85.9

365 ± 87

PTP di, cmH2O.s/minute

157 ± 80*

318 ± 113*

302 ± 111*

451 ± 151

439 ± 152

465 ± 117

WOB, J/L

0.69 ± 0.31*

1.15 ± 0.39*

1.09 ± 0.49*

1.58 ± 0.57

1.57 ± 0.56

1.56 ± 0.5

WOB, J/minute

7.15 ± 3.5*

12.2 ± 6.8*

12.4 ± 7.1*

17.7 ± 10.2

16.8 ± 8.0

17.8 ± 9.1

Abbreviations: Pdi trans-diaphragmatic pressure, PEEP positive end-expiratory pressure, Pes esophageal pressure, PTPdi trans-diaphragmatic pressure time product, PTPes esophageal pressure time product, PSV pressure support ventilation, WOB work of breathing. *p < 0.001 when compared with after extubation

Discussion

To our knowledge, this is the first physiological study that specifically investigates the inspiratory effort during weaning of mechanical ventilation in a population of critically ill morbidly obese patients. The main result of this study is that for obese patients, the T piece and PSV 0 + PEEP 0 cmH2O weaning tests are the tests that best predict post-extubation inspiratory effort and WOB.

Because of a lack of consensus on the best test to use before extubation in this population, we aimed to determine which one reflects the breathing effort after extubation. Some authors described extubation of obese patients after a 30-minute period of CPAP 5 cmH2O [14], others after a trial of FiO2 100 % combined with a CPAP of 10 cmH2O. [15] An ongoing multicenter observational study in France (FREEREA study), will provide some epidemiological data about weaning and extubation in this particular population. The preliminary results (unpublished) show that among 64 critically ill morbidly obese patients extubated, 22 (34 %) were extubated after a T tube, 28 (44 %) after a low PSV trial, 12 (19 %) with no spontaneous breathing trial and 2 (3 %) after a different weaning trial. These data justify our study as there is wide heterogeneity of extubation practice in this population, with a high proportion of patients being extubated from a substantial level of support.

Our study presents limitations. First, we investigated the inspiratory effort indexes twenty minutes after extubation and the study was not designed to explore long-term consequences of several weaning tests on oxygenation, end-expiratory lung volume or outcome. Because outcome was not a study endpoint, we cannot make any final recommendation about which weaning test is associated with the highest rate of weaning success. Ideally, a weaning test would perfectly predict the ability of the patient to breathe alone and without being ventilatory assisted by simulating the post-extubation respiratory constraint [26]. Second, post-extubation intermittent non-invasive ventilation is routinely used in our unit for high-risk patients [14, 21] to rest the inspiratory muscles and improve lung aeration. It may have contributed to our low rate of re-intubation (6 %).

The present study focused on morbidly obese patients and found results consistent with the studies published by Straus et al. [25] and Cabello et al. [8], which included non-obese patients. We report that the T piece and PSV 0 + PEEP 0 cmH2O weaning tests were the two tests that best approximated the WOB after extubation. We also found that the PSV 7 + PEEP 0 cmH2O test leads to a major underestimation of the WOB after extubation in obese patients with significantly less inspiratory effort in comparison with both the T piece test and 20 minutes after extubation. Straus et al demonstrated that post-extubation WOB was well-approximated by the WOB during a T-piece test and that the endotracheal tube was responsible for about 11 % of the total work of breathing. [25] More recently, Cabello et al. compared a spontaneous breathing trial on a T-piece with low PSV (7 cm H2O) with or without PEEP in a subpopulation of patients with heart failure who were difficult to wean. [8] The authors concluded that performing the weaning test while maintaining a positive pressure in the circuit underestimates the post-extubation WOB and unmasks a possible effect on left ventricular function, and suggested the T piece as the weaning test of choice in these patients.

In a landmark physiological study, Brochard et al. demonstrated that breathing through the T piece overestimates the WOB by 27 ± 18 % compared to the post-extubation period [26]. Contrary to the present study, Brochard et al. included a high proportion of patients with chronic obstructive pulmonary disease, and used ventilators with higher ventilatory circuit-resistive load [28] and lower pressurization performance, especially in terms of inspiratory-trigger-imposed WOB [29, 30].

As compared to the literature on non-obese patients, WOB values evaluated in the present study were higher [26, 31]. In morbidly obese patients, an elevation of pharyngeal collapsibility and upper airway resistance related to fatty deposits on pharynx and oral soft tissue and associated with local inflammation can increase the WOB [32]. Weaning trials performed with positive pressure underestimated post-extubation WOB by 33 % (0.5 J/L) up to 50 % (0.8 J/L) according to the ventilator setting. An increase of 0.5–0.8 J/L represents a significant additional workload, as WOB in healthy subjects during quiet breathing is about 0.35–0.5 J/L [33, 34]. Furthermore, WOB ≥0.8 J/L has been reported as being associated with weaning failure [35]. Extubating an obese patient after having performed a weaning test without positive pressure could lead to early onset atelectasis if the patient was unable to control for end-expiratory lung volume without PEEP.

Conclusions

For the first time the present study reports new insights into respiratory physiology in morbidly obese critically ill candidates to be weaned from the ventilator. These data may be useful for clinicians managing these challenging patients and help make difficult decisions about extubation. We report that either a T piece or a PSV 0 and PEEP 0 cmH2O test are the trials that predict post-extubation work of breathing in morbidly obese patients. The consequences on mid-term oxygenation and lung aeration, and on the weaning success rate of such weaning tests were, however, not studied.

Abbreviations

BMI: 

Body mass index

CPAP: 

Continuous positive airway pressure

FiO2

Inspired oxygen fraction

ICU: 

Intensive Care Unit

Pdi: 

Trans-diaphragmatic pressure

PEEP: 

Positive end-expiration pressure

Pes: 

Esophageal pressure

Pga: 

Gastric pressure

PSV: 

Pressure support ventilation

PTPdi: 

Trans-diaphragmatic pressure-time product

PTPes: 

Trans-esophageal pressure-time product

RR: 

Respiratory rate

SBT: 

Spontaneous breathing trial

SpO2

Pulse arterial oxygen saturation

Te: 

Expiratory time

Ti: 

Inspiratory time

Ttot: 

Total cycle duration

VE: 

Minute ventilation

VT

Tidal volume

WOB: 

Work of breathing

Declarations

Acknowledgements

We thank Albert Prades, Research Nurse, MSc, Department of Critical Care Medicine and Anesthesiology, Saint Eloi Teaching Hospital, Montpellier, France for his help conducting research in this topic.

Funding

Departmental resources funded the present study.

Availability of data and materials

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Authors’ contributions

MM and BJ contributed equally to this work. MM performed the study, analyzed the data and wrote the manuscript. BJ participated in the study design and wrote the manuscript. FG analyzed the data and made critical manuscript revisions. RV analyzed the data and made critical manuscript revisions. YC helped in designing the study, enrolled patients, analyzed the data and made critical manuscript revisions. NM and AJ performed the statistical analysis and made critical manuscript revisions. SM helped in designing the study and extensively corrected the manuscript. GC helped in designing the study and extensively corrected the manuscript. SJ designed the study, analyzed the data and made critical manuscript revisions. LB analyzed the data and made critical manuscript revisions. All authors read and approved the final manuscript.

Competing interests

Martin Mahul has nothing to disclose; Boris Jung reports personal fees from Merck (Whitehouse station, NJ) and Astellas (Tokyo, Japan) unrelated to the present study; Fabrice Gallia has nothing to disclose; Nicolas Molinari has nothing to disclose; Audrey De Jong has nothing to disclose; Yannaël Coisel has nothing to disclose; Rosanna Vaschetto has nothing to disclose; Stefan Matecki has nothing to disclose; Gerald Chanques has nothing to disclose; Laurent Brochard reports a research contract with Draeger, General Electric and Covidien and honorarium from Draeger unrelated to the present study; Samir Jaber reports personal fees from Maquet, Draeger, Hamilton Medical, Fisher Paykel and Abbott unrelated to the present study.

Consent for publication

Not applicable.

Ethics approval and consent to participate

The present study was approved by the Ethics Committee of the Montpellier Teaching Hospital (2012 A-00294-39, Comité de Protection des Personnes Sud Méditerranée III, Montpellier, France), and registered on clinical trial.gov (reference NCT01616901). All patients provided their written informed consent.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
Intensive Care Unit, Anaesthesia and Critical Care Department, Saint Eloi Teaching Hospital, Centre Hospitalier Universitaire Montpellier
(2)
Department of Statistics, University of Montpellier Lapeyronie Hospital, UMR 729 MISTEA
(3)
Anaesthesia and Intensive Care Medicine, Maggiore della Carità Hospital
(4)
Centre National de la Recherche Scientifique (CNRS 9214) - Institut National de la Santé et de la Recherche Médicale (INSERM U-1046), Montpellier University
(5)
Keenan Research Centre, St Michael’s Hospital
(6)
Interdepartmental Division of Critical Care Medicine, University of Toronto

References

  1. Sellares J, Ferrer M, Cano E, Loureiro H, Valencia M, Torres A. Predictors of prolonged weaning and survival during ventilator weaning in a respiratory ICU. Intensive Care Med. 2011;37:775–84.View ArticlePubMedGoogle Scholar
  2. Brochard L, Rauss A, Benito S, Conti G, Mancebo J, Rekik N, et al. Comparison of three methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation. Am J Respir Crit Care Med. 1994;150:896–903.View ArticlePubMedGoogle Scholar
  3. Boles JM, Bion J, Connors A, Herridge M, Marsh B, Melot C, et al. Weaning from mechanical ventilation. Eur Respir J. 2007;29:1033–56.View ArticlePubMedGoogle Scholar
  4. Thille AW, Richard J-CM, Brochard L. The decision to extubate in the intensive care unit. Am J Respir Crit Care Med. 2013;187:1294–302.View ArticlePubMedGoogle Scholar
  5. Jubran A, Grant BJB, Laghi F, Parthasarathy S, Tobin MJ. Weaning prediction: esophageal pressure monitoring complements readiness testing. Am J Respir Crit Care Med. 2005;171:1252–9.View ArticlePubMedGoogle Scholar
  6. MacIntyre NR, Cook DJ, Ely Jr EW, Epstein SK, Fink JB, Heffner JE, et al. Evidence-based guidelines for weaning and discontinuing ventilatory support: a collective task force facilitated by the American College of Chest Physicians; the American Association for Respiratory Care; and the American College of Critical Care Medicine. Chest. 2001;120:375S–95.View ArticlePubMedGoogle Scholar
  7. McConville JF, Kress JP. Weaning patients from the ventilator. New England J Med. 2012;367:2233–9.View ArticleGoogle Scholar
  8. Cabello B, Thille AW, Roche-Campo F, Brochard L, Gómez FJ, Mancebo J. Physiological comparison of three spontaneous breathing trials in difficult-to-wean patients. Intensive Care Med. 2010;36:1171–9.View ArticlePubMedGoogle Scholar
  9. Tobin MJ. Extubation and the myth of “minimal ventilator settings”. Am J Respir Crit Care Med. 2012;185:349–50.View ArticlePubMedGoogle Scholar
  10. Jones RL, Nzekwu M-MU. The effects of body mass index on lung volumes. Chest. 2006;130:827–33.View ArticlePubMedGoogle Scholar
  11. Kress JP, Pohlman AS, Alverdy J, Hall JB. The impact of morbid obesity on oxygen cost of breathing (VO(2RESP)) at rest. Am J Respir Crit Care Med. 1999;160:883–6.View ArticlePubMedGoogle Scholar
  12. Littleton SW. Impact of obesity on respiratory function. Respirology. 2012;17:43–9.View ArticlePubMedGoogle Scholar
  13. Salome CM, King GG, Berend N. Physiology of obesity and effects on lung function. J Appl Physiol. 2010;108:206–11.View ArticlePubMedGoogle Scholar
  14. El-Solh AA, Aquilina A, Pineda L, Dhanvantri V, Grant B, Bouquin P. Noninvasive ventilation for prevention of post-extubation respiratory failure in obese patients. Eur Respir J. 2006;28:588–95.View ArticlePubMedGoogle Scholar
  15. Zoremba M, Kalmus G, Begemann D, Eberhart L, Zoremba N, Wulf H, et al. Short term non-invasive ventilation post-surgery improves arterial blood-gases in obese subjects compared to supplemental oxygen delivery - a randomized controlled trial. BMC Anesthesiol. 2011;11:10.View ArticlePubMedPubMed CentralGoogle Scholar
  16. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults–the evidence report. national institutes of health. Obes Res. 1998;6 Suppl 2:51S–209S.Google Scholar
  17. Persichini R, Gay F, Schmidt M, Mayaux J, Demoule A, Morélot-Panzini C, et al. Diagnostic accuracy of respiratory distress observation scales as surrogates of dyspnea self-report in intensive care unit patients. Anesthesiology. 2015;123:830–7.View ArticlePubMedGoogle Scholar
  18. Coisel Y, Chanques G, Jung B, Constantin J-M, Capdevila X, Matecki S, et al. Neurally adjusted ventilatory assist in critically ill postoperative patients: a crossover randomized study. Anesthesiology. 2010;113:925–35.View ArticlePubMedGoogle Scholar
  19. Clavieras N, Wysocki M, Coisel Y, Galia F, Conseil M, Chanques G, et al. Prospective randomized crossover study of a new closed-loop control system versus pressure support during weaning from mechanical ventilation. Anesthesiology. 2013;119:631–41.View ArticlePubMedGoogle Scholar
  20. Baillard C, Fosse J-P, Sebbane M, Chanques G, Vincent F, Courouble P, et al. Noninvasive ventilation improves preoxygenation before intubation of hypoxic patients. Am J Respir Crit Care Med. 2006;174:171–7.View ArticlePubMedGoogle Scholar
  21. Jaber S, Chanques G, Jung B. Postoperative noninvasive ventilation. Anesthesiology. 2010;112:453–61.View ArticlePubMedGoogle Scholar
  22. Deye N, Lellouche F, Maggiore SM, Taillé S, Demoule A, L’Her E, et al. The semi-seated position slightly reduces the effort to breathe during difficult weaning. Intensive Care Med. 2013;39:85–92.View ArticlePubMedGoogle Scholar
  23. Jaber S, Carlucci A, Boussarsar M, Fodil R, Pigeot J, Maggiore S, et al. Helium-oxygen in the postextubation period decreases inspiratory effort. Am J Respir Crit Care Med. 2001;164:633–7.View ArticlePubMedGoogle Scholar
  24. Sassoon CS, Light RW, Lodia R, Sieck GC, Mahutte CK. Pressure-time product during continuous positive airway pressure, pressure support ventilation, and T-piece during weaning from mechanical ventilation. Am Rev Respir Dis. 1991;143:469–75.View ArticlePubMedGoogle Scholar
  25. Straus C, Louis B, Isabey D, Lemaire F, Harf A, Brochard L. Contribution of the endotracheal tube and the upper airway to breathing workload. Am J Respir Crit Care Med. 1998;157:23–30.View ArticlePubMedGoogle Scholar
  26. Brochard L, Rua F, Lorino H, Lemaire F, Harf A. Inspiratory pressure support compensates for the additional work of breathing caused by the endotracheal tube. Anesthesiology. 1991;75:739–45.View ArticlePubMedGoogle Scholar
  27. Mehta S, Nelson DL, Klinger JR, Buczko GB, Levy MM. Prediction of post-extubation work of breathing. Crit Care Med. 2000;28:1341–6.View ArticlePubMedGoogle Scholar
  28. Lyazidi A, Thille AW, Carteaux G, Galia F, Brochard L, Richard J-CM. Bench test evaluation of volume delivered by modern ICU ventilators during volume-controlled ventilation. Intensive Care Med. 2010;36:2074–80.View ArticlePubMedGoogle Scholar
  29. Jaber S, Tassaux D, Sebbane M, Pouzeratte Y, Battisti A, Capdevila X, et al. Performance characteristics of five new anesthesia ventilators and four intensive care ventilators in pressure-support mode: a comparative bench study. Anesthesiology. 2006;105:944–52.View ArticlePubMedGoogle Scholar
  30. Thille AW, Lyazidi A, Richard J-CM, Galia F, Brochard L. A bench study of intensive-care-unit ventilators: new versus old and turbine-based versus compressed gas-based ventilators. Intensive Care Med. 2009;35:1368–76.View ArticlePubMedPubMed CentralGoogle Scholar
  31. Nathan SD, Ishaaya AM, Koerner SK, Belman MJ. Prediction of minimal pressure support during weaning from mechanical ventilation. Chest. 1993;103:1215–9.View ArticlePubMedGoogle Scholar
  32. Zerah F, Harf A, Perlemuter L, Lorino H, Lorino AM, Atlan G. Effects of obesity on respiratory resistance. Chest. 1993;103:1470–6.View ArticlePubMedGoogle Scholar
  33. Vaschetto R, De Jong A, Conseil M, Galia F, Mahul M, Coisel Y, et al. Comparative evaluation of three interfaces for non-invasive ventilation: a randomized cross-over design physiologic study on healthy volunteers. Crit Care. 2014;18:R2.View ArticlePubMedPubMed CentralGoogle Scholar
  34. Mancebo J, Isabey D, Lorino H, Lofaso F, Lemaire F, Brochard L. Comparative effects of pressure support ventilation and intermittent positive pressure breathing (IPPB) in non-intubated healthy subjects. Eur Respir J. 1995;8:1901–9.View ArticlePubMedGoogle Scholar
  35. Kirton OC, DeHaven CB, Morgan JP, Windsor J, Civetta JM. Elevated imposed work of breathing masquerading as ventilator weaning intolerance. Chest. 1995;108:1021–5.View ArticlePubMedGoogle Scholar

Copyright

© The Author(s). 2016

Advertisement