Surgical Endoscopy

, Volume 24, Issue 5, pp 1099–1103 | Cite as

Positive end-expiratory pressure in pressure-controlled ventilation improves ventilatory and oxygenation parameters during laparoscopic cholecystectomy

  • Ji Young Kim
  • Cheung Soo Shin
  • Hong Soon Kim
  • Wol Sun Jung
  • Hyun Jeong Kwak
Article

Abstract

Background

During laparoscopy, pneumoperitoneum may result in intraoperative atelectasis, which impairs normal gas exchange. This study investigated whether positive end-expiratory pressure (PEEP) of 5 cmH2O in pressure-controlled ventilation (PCV) mode can improve ventilatory and oxygenation parameters during pneumoperitoneum.

Methods

Thirty patients, aged 18–65 years, undergoing laparoscopic cholecystectomy were randomly allocated to the ZEEP (PEEP = 0 cmH2O) or PEEP (PEEP = 5 cmH2O) group. PCV was started after induction of anesthesia. Apart from PEEP level, all other ventilator settings were identical for both groups. Peak airway pressure was set at induction and reset after pneumoperitoneum to deliver tidal volume of 8 ml/kg in both groups. Hemodynamic, ventilatory, and oxygenation parameters were measured after induction of anesthesia (T1) and 30 min after pneumoperitoneum (T2).

Results

Oxygenation index (PaO2/FiO2) was significantly higher in the PEEP group than in the ZEEP group at T2 (P = 0.031). In both groups, dynamic compliance significantly decreased over 40 min from T1 to T2. There were no significant differences in hemodynamics between the two groups during the study period.

Conclusion

Application of PEEP of 5 cmH2O should be considered in PCV during laparoscopic surgeries to decrease intraoperative atelectasis caused by pneumoperitoneum to improve gas exchange and oxygenation.

Keywords

Pneumoperitoneum Pressure-controlled ventilation Cholecystectomy Oxygenation 

In the last decade, laparoscopic surgeries have been replacing many laparotomy procedures. During laparoscopy, the peritoneal space is insufflated with gas and this pneumoperitoneum may result in intraoperative atelectasis, which impairs normal gas exchange [1]. Ventilatory parameters must be adjusted to overcome the respiratory consequences of pneumoperitoneum such as elevated peak and plateau airway pressure (Ppeak and Pplat) and decreased dynamic compliance of the respiratory system [2].

Several ventilatory strategies have been proposed to prevent intraoperative atelectasis and improve arterial oxygenation in laparoscopic surgeries but they remain controversial. Pressure-controlled ventilation (PCV) can be used in the management of patients with elevated Ppeak, which occurs with pneumoperitoneum. The use of PCV during laparoscopy produced different results depending on the application of positive end-expiratory pressure (PEEP) [3, 4]. However, during prolonged pneumoperitoneum, PEEP plays an important role in counteracting intraoperative atelectasis and has been shown to improve respiratory function [5, 6].

To date, studies investigating the effect of PEEP on oxygenation during laparoscopy have been carried out in volume-controlled ventilation (VCV) but not in PCV. Therefore, the purpose of this study was to investigate the effect of PEEP of 5 cmH2O in PCV on ventilatory and oxygenation parameters during laparoscopic cholecystectomy.

Methods

This study was approved by the Institutional Review Board of Gil Medical Center, and informed consent was obtained from all patients. From March to September 2008, 30 consecutive patients, with American Society of Anesthesiologists (ASA) physical status I or II, aged 18–65 years undergoing laparoscopic cholecystectomy were prospectively enrolled in the study. All cholecystectomies were elective and not emergent. Patients with cardiorespiratory disease and obesity (body mass index >35 kg/m2) were excluded from the study. Patients were randomized to either the ZEEP group (n = 15, PCV without PEEP) or the PEEP group (n = 15, PCV with PEEP of 5 cmH2O) using sealed envelope system.

On arrival in the operating room, patients were monitored with standard anesthetic monitors. Anesthetic management and intraoperative care were standardized. The patients were premedicated with intramuscular 0.5 mg/kg midazolam and 0.2 mg glycopyrrolate 1 h before induction of anesthesia. For induction and maintenance of anesthesia, propofol and remifentanil were infused at target effect-site concentration of 4–6 μg/ml and 3–5 ng/ml, respectively, using target-controlled infusion system (TCI) (Orchestra®, Base Primea, Fresenius Kabi, Homburg, Germany). Tracheal intubation was facilitated with 0.6 ml/kg rocuronium. Patients received 300 ml colloids before pneumoperitoneum, and crystalloids were then infused during operation at basal rate of 8 kg/ml/h.

All patients were ventilated with a S/5 Avance anesthetic machine (GE Healthcare, Madison, WI). PCV with a decelerating flow and an I:E ratio 1:2 was started after induction of anesthesia. PEEP was set to either 0 or 5 cmH2O according to the group. Apart from the PEEP level, all other ventilator settings were identical for both groups. Ppeak was set initially after induction of anesthesia to deliver a tidal volume (VT) of 8 ml/kg and then reset after pneumoperitoneum to match the initial expired VT. Respiratory rate (RR) was adjusted to maintain an end-tidal carbon dioxide tension (ETCO2) of 35–40 mmHg, and the fraction of inspired oxygen (FIO2) was set at 60% in air during surgery. The magnitude of Ppeak and mean airway pressure (Pmean) was obtained directly from the ventilator. Ppeak, Pmean, RR, VT, and minute ventilation (MV) were recorded 10 min before pneumoperitoneum (T1) and 30 min after pneumoperitoneum (T2). Dynamic compliance of the respiratory system was calculated as VT/(Ppeak − PEEP). Arterial blood gas (ABG) was analyzed at T1 and T2. The alveolar dead space-to-tidal volume ratio (VD/VT) at T1 and T2 were estimated using the Hardman and Aitkenhead equation: VD/VT = 1.135 × (PaCO2 − ETCO2)/(PaCO2 − 0.005) [7]. The alveolar-arterial oxygen gradient [D(A − a)O2] and oxygenation index (PaO2/FIO2) were calculated at T1 and T2, and alveolar oxygen tension (PAO2) was estimated from the following equation; PAO2 = FIO2 × (PB − PH2O) − (PaCO2/0.8), where PB is barometric pressure and PH2O is vapor pressure of water.

Carbon dioxide pneumoperitoneum was created with a closed Veress needle technique maintaining a 14-mmHg intra-abdominal pressure. After insufflation, patients were placed in a 20° reverse Trendelenburg position. Laparoscopic cholecystectomy was performed through two ports of 10 mm and two of 5 mm in the standard position with the legs closed.

Statistical analyses were performed using the statistical package (SPSS 11.0, SPSS Inc, Chicago, IL for Windows). Data are expressed as mean ± standard deviation (SD) or median (interquartile range, IQR). The distribution of data was determined using Kolmogorov–Smirnov analysis. Statistical analysis was performed using t-test. Sample size was predetermined using a power analysis based on the assumptions that (a) PaO2/FIO2 values, regarded as the primary-end point, would be 458 ± 64 for patients with PCV during laparoscopic surgery based on the previous study [4], (b) a 20% higher PaO2/FIO2 with PEEP of 5 cmH2O was considered of clinical importance based on the findings of the study in regard to PEEP in laparoscopic surgery by Meininger et al. [5], and (c) α = 0.05 with a power (1 − β) of 0.9. The analysis showed that 12 patients per group would be sufficient to detect the effect of PEEP. Allowing for possible dropouts due to conversion to open cholecystectomy or inability to collect an ABG sample with a single puncture, 15 patients were enrolled in this study. A P value of 0.05 was considered statistically significant.

Results

Thirty patients were recruited but one patient in the ZEEP group was excluded due to conversion to open cholecystectomy. There were no significant differences in demographic between the two groups (Table 1).
Table 1

Patient characteristics

 

ZEEP (n = 14)

PEEP (n = 15)

P-value

Age (years)

42 (32–57)

35 (27–51)

0.524

Sex (M/F)

6/8

6/9

1.00

Weight (kg)

65.6 ± 11.2

66.2 ± 10.1

0.888

Height (cm)

162 ± 9

164 ± 8

0.665

BMI (kg/m2)

24.6 ± 2.8

25.1 ± 2.6

0.63

Operation time (min)

78 ± 22

73 ± 22

0.647

Insufflation time (min)

51 ± 20

47 ± 13

0.606

Values are mean ± SD, median (IQR) or number of patients. ZEEP group: pressure-controlled ventilation with no external positive end-expiratory pressure (PEEP); PEEP group: pressure-controlled ventilation with PEEP of 5 cmH2O. BMI, body mass index

Ventilatory parameters are summarized in Table 2. During the study period, VT, RR, MV, and ETCO2 were comparable between the two groups. However, Pmean in the PEEP group was significant higher than that in control group (p < 0.0001), whereas Ppeak was slightly higher in the PEEP group without statistical significance during the study period. Compared with values at T1 within the group, the increase in PaO2/FIO2 and the decrease in D(A − a)O2 at T2 were statistically significant in the PEEP group. In the ZEEP group, PaO2/FIO2 was decreased and D(A − a)O2 was increased at T2 compared with at T1 but without statistical significance. Between groups at T2, the PEEP group had significantly higher PaO2/FIO2 and lower D(A − a)O2 compared with the ZEEP group (p = 0.031 and p = 0.03, respectively). In both groups, dynamic compliance significantly decreased 30 min after pneumoperitoneum (T2) compared with that before pneumoperitoneum (T1) (Fig. 1).
Table 2

Variables of ventilatory parameters during laparoscopic cholecystectomy

 

ZEEP (n = 14)

PEEP (n = 15)

T1

T2

T1

T2

VT (ml)

557 ± 110

531 ± 72

619 ± 117

570 ± 116

RR (breaths/min)

10.7 ± 2.0

12.6 ± 2.8

10.6 ± 1.8

11.9 ± 3.1

MV (L/min)

6.0 ± 1.8

6.8 ± 1.6

6.4 ± 1.7

6.8 ± 1.4

ETCO2 (mmHg)

33.5 ± 3.1

36.1 ± 3.3

33. 1 ± 3.4

34.3 ± 3.4

Airway pressure (cmH2O)

    

Peak

13.3 ± 2.5

19.7 ± 2.5

15.0 ± 2.0

21.1 ± 3.2

Mean

6.2 ± 0.9

8.5 ± 0.8

8.0 ± 1.3*

11.0 ± 1.1*,†

PEEP

2.0 ± 1.0

2.6 ± 0.6

5.0 ± 0.0*

5.0 ± 0.0*

PaCO2 (mmHg)

39.0 ± 3.1

40.1 ± 3.5

37.1 ± 3.2

39.4 ± 3.9

Values are mean ± SD. ZEEP group: pressure-controlled ventilation with no external positive end-expiratory pressure (PEEP); PEEP group: pressure-controlled ventilation with PEEP of 5 cmH2O. T1, 10 min before pneumoperitoneum; T2, 30 min after pneumoperitoneum; VT, tidal volume; RR, respiratory rate; MV, minute ventilation; ETCO2, end-tidal carbon dioxide tension

* p < 0.05, compared with ZEEP group

p < 0.05, compared with T1 value within the group

Fig. 1

Oxygenation and ventilatory parameters during laparoscopic cholecystectomy, mean values and standard deviation: (A) oxygenation index (PaO2/FIO2), (B) alveolar–arterial oxygen gradient [D(A − a)O2], (C) alveolar dead space-to-tidal volume ratio (VD/VT), (D) dynamic compliance of the respiratory system. * p < 0.05, compared with ZEEP group, p < 0.05, compared with values 10 min before pneumoperitoneum within the group

Hemodynamic data are listed in Table 3. There were no significant differences in mean blood pressure and heart rate between the two groups during the study period.
Table 3

Hemodynamic data

 

Group

T0

T1

T2

MBP (mmHg)

ZEEP (n = 14)

103 ± 17

82 ± 15*

92 ± 13

PEEP (n = 15)

95 ± 12

88 ± 12

99 ± 13

HR (beats/min)

ZEEP (n = 14)

68 ± 11

68 ± 12

74 ± 16

PEEP (n = 15)

69 ± 7

72 ± 12

80 ± 12*

Values are mean ± SD. ZEEP: pressure-controlled ventilation with no external positive end-expiratory pressure (PEEP); PEEP: pressure-controlled ventilation with PEEP of 5 cmH2O. T0, before anesthesia induction; T1, before pneumoperitoneum; T2, 30 min after pneumoperitoneum; MBP, mean blood pressure; HR, heart rate

* p < 0.05, compared with T0 value within the group

Discussion

This study demonstrated that PCV with PEEP of 5 cmH2O significantly improves PaO2/FIO2 and decreases D(A − a)O2 without hemodynamic change during laparoscopic cholecystectomy.

PCV has been proposed as an alternative to VCV in patients with adult respiratory distress syndrome to achieve adequate oxygenation and normocarbia [8]. Unlike VCV, PCV uses a decelerating flow, which tends to compensate for any potential reduction in ventilation caused by pressure limitation [9]. As a result, PCV has different gas distribution and fast VT delivery that depends on the pressure limitation and the chest compliance. In PCV mode, alveoli with short time constant may initially be overinflated, but a more homogeneous distribution of the VT in all the ventilated alveoli follows, reducing the amount of atelectasis by improved alveolar recruitment [10]. Furthermore, even if inspiratory flow is very low at the end of inspiration in PCV, it does not drop to zero during the whole plateau time. The better preserved ventilation/perfusion ratio during PCV mode is marked by the decrease in D(A − a)O2 [11]. Cadi et al. [3] reported that, despite similar values for MV, D(A − a)O2 and PaCO2 were significantly higher and PaO2/FIO2 was lower in the VCV group when compared with those in the PCV group during laparoscopic obesity surgery. These results support the hypothesis of a better ventilation/perfusion ratio in PCV.

Since the main disadvantage of PCV is the variability of VT delivery, Ppeak was reset after pneumoperitoneum in this study [12]. If Ppeak had not been reset, a smaller VT might have resulted due to the decrease in compliance during pneumoperitoneum, which may lead to intraoperative atelectasis [13]. However, just resetting Ppeak to deliver the same VT was not enough to overcome respiratory consequences following pneumoperitoneum in this study because, although without statistical significance, oxygenation index was decreased after pneumoperitoneum. Balick-Weber et al. [4] also reported that PCV without PEEP during laparoscopy had no short-term beneficial effect on arterial oxygenation after switching from VCV to PCV, despite significant improvement in dynamic compliance. On the other hand, addition of PEEP of 5 cmH2O in PCV increased oxygenation index significantly after pneumoperitoneum in this study. It is likely that application of PEEP of 5 cmH2O recruited more lung tissues that have been collapsed during pneumoperitoneum.

This study demonstrated improved oxygenation index at 30 min after pneumoperitoneum. In studies reporting favorable results with PEEP in VCV, that improvement started from 120 min after pneumoperitoneum in patients without heart or lung diseases [5, 6]. Further study is needed to elucidate the long-term effect of PCV with PEEP during prolonged pneumoperitoneum or in patients with heart or lung diseases.

Compared with the value before pneumoperitoneum, D(A − a)O2, which is one of the useful tools to evaluate intrapulmonary shunt, was decreased after pneumoperitoneum in the PEEP group but was increased in the ZEEP group. The three key determinants of PO2 are inspired oxygen pressure, alveolar ventilation, and ventilation/perfusion ratio. Since FIO2 was set at 0.6 and VT was kept at 8 ml/kg in this study, the difference in oxygenation by PEEP must come from the change in the lung ventilation/perfusion ratio. Andersson et al. [14] confirmed the decrease in functional residual capacity (FRC) during pneumoperitoneum using spiral computer tomography. Since the major effect of PEEP on the lungs consists of the increase in FRC, reversal of intrapulmonary shunt caused by pneumoperitoneum must have resulted in improvement of oxygenation in patients with PEEP.

The hemodynamic effect of PEEP during pneumoperitoneum has been studied, with varying results from minimal to significant decrease in preload and cardiac output [15, 16, 17]. This is likely due to different factors affecting intravascular volume, intra-abdominal pressure, and baseline cardiac function. In this study, hemodynamic variables were comparable between two groups.

In conclusion, application of PEEP should be considered in PCV during laparoscopic surgeries to decrease intraoperative atelectasis caused by pneumoperitoneum to improve gas exchange and oxygenation.

Notes

Disclosures

Drs. Ji Young Kim, Cheung Soo Shin, Hong Soon Kim, Wol Sun Jung, and Hyun Jeong Kwak have no conflicts of interest or financial ties to disclose.

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Ji Young Kim
    • 1
  • Cheung Soo Shin
    • 1
  • Hong Soon Kim
    • 2
  • Wol Sun Jung
    • 2
  • Hyun Jeong Kwak
    • 2
  1. 1.Department of Anesthesiology and Pain Medicine, Anesthesia and Pain Research InstituteYonsei University College of MedicineSeoulKorea
  2. 2.Department of Anesthesiology and Pain MedicineGachon University of Medicine and Science Gil Medical CenterIncheonKorea

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