10.

2478/AMB-2019-0005

APPLICATION OF POSITIVE END-EXPIRATORY PRESSURE

(PEEP) IN PATIENTS DURING PROLONGED GYNECOLOGICAL
SURGERY
V. Koritarova, S. Georgiev

Department of Anesthesiology and Intensive Care, University Hospital of Obstetrics and Gynecology
“Maichin dom”, Medical Faculty, Medical University – So¿a, Bulgaria

Abstract. Introduction: A lot of clinical studies have shown that during prolonged surgery
protective ventilation strategy, including low tidal volume, PEEP and recruitment maneu-
vers (RM) can reduce the rate of postoperative pulmonary complications, which are the
second most common cause for postoperative mortality. Therefore, it is important to inves-
tigate clinical methods for preventing them. The strategy of protective ventilation is easy
and safe for the patients and inexpensive for application during prolonged surgery. Aims:
The objective of this trial was to study whether application of PEEP in patients during pro-
longed gynecological surgery could decrease the postoperative complications. Material
and Methods: We compared the rates of postoperative complications in patients after
prolonged open gynecological surgery, who were divided into 2 groups – group A, which
was the control group on non-protective ventilation (35 patients) and group B on protective
ventilation (35 patients). The patients in the control group were ventilated with tidal volume
(VT) of 8-10 ml/kg without PEEP and RM; the patients in group B were ventilated with
VT = 6-8 ml/kg according to their Predicted Body Weight, with a PEEP of 6 cm H2O and
RM, which consisted of applying continuous positive airway pressure of 30 cm H2O for 30
seconds. RM was performed after intubation, after every disconnection from ventilator and
before extubation. The study was successfully performed without a need for a change in
the type of ventilation strategy because of hypoxia or hemodynamic instability. Statistical
nonparametric test (e.g. chi- square) was applied. Results: Total rate of all postoperative
complications observed in both groups was 27,1%. We found a signi¿cant relationship
between application of PEEP and lower rates of postoperative pulmonary complications
in group A (39,4%) compared to group B (12,1%), lower rate of respiratory failure (33,3%
in group A vs. 9,1% in group B -) and atelectasis (21,2% in group A vs. 0% in group B).
Conclusion: The protective ventilation strategy (low VT, PEEP and RM) in patients during
prolonged gynecological surgery can reduce the rate of postoperative pulmonary complica-
tions such as respiratory failure and atelectasis.

Key words: PEEP, RM, low VT, protective ventilation, postoperative pulmonary complications

Corresponding author: Velislava Koritarova, University Hospital of Obstetrics and Gynecol-

ogy “Maichin dom”, Medical Faculty, Medical University, 2 Zdrave Str., 1431 So¿a, Bulgaria,
tel.: 0892076008, e-mail: velislava_koritarova@abv.bg

28 Acta Medica Bulgarica, Vol. XLVI, 2019, ʋ 1 // Original article

 INTRODUCTION the inclusion criteria: adult patients – over 18 years;
non pregnant women; patients undergoing non-lapa-

G
eneral anesthesia with muscle relaxation roscopic open gynecological operations, lasting more
and supine position can decrease functional than 2 hours.
residual capacity [1, 2] and lead to collapse Patients were excluded from the study if they met
of alveoli in the lung`s bases. This results in perfu- one of the exclusion criteria: patients who have been
sion without ventilation in these segments of the lung mechanically ventilated the last month before sur-
– the zones of atelectasis [3, 4], where left-to-right gery and patients with previous pulmonary surgery;
shunt increases leading to hypoxia [4, 5]. In fact, patients with severe chronic obstructive pulmonary
the application of positive end-expiratory pressure disease (COPD), requiring non-invasive ventilation
(PEEP) in patients during general anesthesia in the with CPAP (continuous positive airway pressure)
end of expiration prevents the alveoli from collapsing masks, oxygen therapy or systemic corticosteroid
and atelectasis [3, 4]. The use of a recruitment ma- therapy; patients with morbid obesity-body mass in-
neuver (RM) can open the alveoli, which were previ- dex < 40 kg/m2; hemodynamically unstable patients –
ously collapsed [6]. According to some randomized these ones with acute coronary syndrome, persistent
studies the intraoperative application of PEEP can ventricular tachycardia, heart failure  NYHA IV; in
reduce the number of patients who develop postop- case of emergency surgery; patients with neuromus-
erative atelectasis and hypoxia [7, 8, 9, 10, 11, 12, cular diseases.
13]. Studies showing that postoperative pulmonary
complications as pneumonia, respiratory failure, etc. We used data from preoperative consultations with
also decrease are scarce. specialists in anesthesiology and internal medicine,
data from preoperative laboratory tests, imaging
Mechanical ventilation with high tidal volume in patients studies and other specialized consultations to deter-
without any pulmonary diseases can lead to volume as- mine ASA and ARISCAT score. The last one can be
sociated trauma of the lung [14]. But ventilation with a used as predictive factor for development of postop-
low tidal volume without application of PEEP can cause erative complications [19]. We calculated ARISCAT
atelecto-trauma, because of cycle opening and clos- score using the following criteria: open gynecological
ing of alveoli during the respiratory cycle. Ventilation- operations  15 points (p.); patient`s age – under 50
induced lung injury (VILI) can also include bio-trauma, years – 0 p., from 51 to 80 years – 3 p., over 80 years
which is de¿ned by increased level of pulmonary and – 16 p.; preoperative saturation – over 96% – 0 p.,
systemic inÀammatory factors in mechanically ventilat- from 95% to 91% – 8 p., under 90% – 24 p.; respira-
ed patients [15, 16]. The strategy of protective ventila- tory infection during last month – 17 p.; preoperative
tion includes low tidal volume and application of PEEP anemia  11 p.; expected duration of operation less
together with RM [17, 18]. The level of optimal PEEP is than 2 hours – 0 p., from 2 to 3 hours – 16 p., over 3
a matter of controversy because of its negative effect hours – 23 p.
on the patient`s hemodynamics [19].
The selected patients were divided in 2 groups: con-
trol group (group A) – in which non-protective strate-
AIMS
gy of mechanical ventilation was used – tidal volume
The objective of this study was to investigate the (Vt) – 8-10 ml/kg, without PEEP, RM; exposed group
effect of positive end-expiratory pressure (PEEP), (group B) – in which protective strategy of mechani-
which is applied together with recruitment maneuver cal ventilation was used – PEEP  6 cm H2O with
(RM) and low tidal volume (calculated with Predicted RM, low Vt – 6-8 ml/kg, which was calculated accord-
Body Weight) in patients undergoing prolonged gy- ing to the patient`s Predicted Body Weight (PBW).
necological operations (lasting morɟ than 2 hours), We used the following formula for calculating PBW
on the frequency of postoperative complications. for women:
 45,5 + 0,91*(heigh – 152,4).
We hypothesized that the application of PEEP in pa-
tients during prolonged gynecological surgery would The Recruitment maneuver (RM) consisted of use of
decrease the rate of postoperative pulmonary com- continuous positive airway pressure (CPAP) = 30 cm
plications. H2O for 30 s. It was performed after intubation, after
each disconnection of the patient from mechanical
MATERIAL AND METHODS ventilation, and before extubation. The purpose of
this maneuver is to expand alveoli which have been
In this prospective cohort study from November, 2016 already collapsed. On the other hand, the application
to May, 2017 we followed 70 patients, who ful¿lled of PEEP aims at preventing the alveoli from collaps-

Application of positive end-expiratory pressure (PEEP)... 29

ing. RM was not performed in hemodynamically un- was rejected and a signi¿cant relationship between
stable patients, because it decreases cardiac output. the application of PEEP and lower rates of postop-
In both groups we used Volume Control Mechanical erative complications such as respiratory failure,
Ventilation, respiratory rate = 10-14/min and inspi- atelectasis, need for non-invasive ventilation with
ration: expiration ratio- I:E-1:2, Fio2 = 0.6. We used CPAP masks, was registered. However, this study
the method of side stream spirometry in order to de- didn`t prove any statistically signi¿cant relationship
termine peak inspiratory pressure (Ppeak) and pla- between the application of PEEP during prolonged
teau pressure (Pplat.), pulse oximetry to determine gynecological operations and the frequencies of
saturation(SpO2), capnometry for estimating end ex- postoperative pneumonia, bronchospasm, pleural ef-
piratory CO2 concentration (EtCO2), ECG monitoring fusion, extra-pulmonary complications. In this study
and a non-invasive methods formeasuring systolic there weren`t any cases of pneumothorax, pulmo-
blood pressure (SBP), mean blood pressure (MBP) nary edema, pulmonary thromboembolism.
and diastolic blood pressure (DBP). The total dose
of vasopressors used – ephedrine, noradrenaline, Table 1. Postoperative pulmonary complications
adrenaline, also the amount of infused crystalline and in both groups
colloidal solutions, freshly frozen plasma and eryth-
rocyte concentrate during the operations, were cal- Patient number Percent %
culated. Intraoperative blood loss and diuresis were None 51 72,9
also measured. Postoperative laboratory tests like Pulmonary complication 19 27,1
complete blood count, hemostasis, blood biochemistry
– glucose, urea, creatinine, liver enzymes, total pro-
tein, albumin, electrolytes, arterial blood gas analysis The percent of pulmonary postoperative complica-
were analyzed. The study was successfully performed tions in the control group A was 39,4% and it was
without a need for a change in the type of ventilation 12,1% in group B (Table 2).
strategy because of hypoxia or hemodynamic insta-
bility. The participants were followed for a period of 5 Table 2. Postoperative pulmonary complications
postoperative days for development of pulmonary and in each group
extra-pulmonary complications. Pulmonary complica-
tions included respiratory failure; pneumonia; acute Type of group None Pulmonary Total
respiratory distress syndrome (ARDS); atelectasis; complication
pulmonary edema; bronchospasm; pneumothorax; Control group – N 20 13 33
pleural effusion; application of non-invasive ventilation PEEP = 0 cm H2O
with CPAP masks. Extra-pulmonary complications in-
cluded sepsis, severe sepsis, septic shock; anastomo- Control group – % 60,6% 39,4% 100,0%
PEEP = 0 cm H2O
sis insuf¿ciency; acute renal failure; acute myocardial
infarction; new atrial ¿brillation; bleeding from gastro- Exposed group – N 29 4 33
intestinal tract. Diagnosis was based on symptoms as PEEP = 6 cm H2O
fever, tachypnea, dyspnea, cough with sputum, physi-
Exposed group – % 87,9% 12,1% 100,0%
cal examination – wheezing, weak breathing in the
PEEP = 6 cm H2O
lung bases etc., laboratory tests, imaging exams.
Total N 51 19 70
Statistical considerations: According to the null
hypothesis there should be no statistically signi¿cant % 72,9 % 27,1% 100,0%
association of the use of PEEP in patients during pro- Abbr.: PEEP-positive end – expiratory pressure
longed gynecological operations with the rate of post-
operative complications. This hypothesis was veri¿ed
by the crosstab method, analyzing the frequencies The rate of postoperative pulmonary complications in
of each complication in both groups. The observed the control group A (PEEP – 0 cm H2O) was signi¿-
frequencies (rates) were presented as percentages. cantly higher compared to the rate of these complica-
The level of signi¿cance was set at p ” 0,05. The tions in the exposed group B (PEEP – 6 cm H2O) .
nonparametric chi- square test was applied. The percent of patients who developed postoperative
atelectasis was 21,2% in group A and 0,0% in group
RESULTS B (Table 4).
The total rate of all postoperative complications in Table 5 shows the occurrence of atelectasis in both
both groups was 27.1% (Tabl. 1). The null hypothesis groups.

30 V. Koritarova, S. Georgiev
Table 3. Statistical chi-square test for cases of pul- Table 6. Rates of patients with respiratory failure in
monary complications both groups

Chi-Square Tests Not observed Observed Total

Control group N 22 11 33
Pearson Chi-Square 7,327a Value 0,026 (group A, % 66,7% 33,3% 100,0%
Likelihood Ratio 7,682 2 ,021 Ɋɟɟɪ  0)
Group B N 30 3 33
Number of Valid Cases 70 (peep-6) % 90,9% 9,1% 100,0%
Table 4. Ocurrence of atelectasis in each group Total N 54 16 70
% 77,1% 22,9% 100,0%
Not observed Observed Total PEEP – positive end-expiratory pressure
Group A, control N 26 7 33 The rate of the cases of observed postoperative re-
group % spiratory failure was signi¿cantly higher in the control
(Ɋɟɟɪ – 0 cm 78,8% 21,2% 100,0% group compared to the other group.
H2O)
Group B N 33 0 33 Table 7. The Chi-square test for cases of respiratory
(Peep – 6 cm % failure
100,0% 0,0% 10, 00%
H2O)
Value Degree of Asymptotic
Total N 62 8 70 freedom signiÀcance
% 88,6% 11,4% 100,0% (2-sided)
Abbrev.: PEEP = positive end–expiratory pressure Pearson Chi-square 7,272 2 0,026
Likelihood ratio 7,595 2 0,022
Table 5. Statistical chi-square test for atelectasis Number of valid cases 70
Value Degree of Asymptotic
freedom signiÀcance Effects of PEEP on intraoperative hemodynamic
(2-sided) stability of patients (intraoperative SBP, MBP, DBP,
Ppeak, Pplat and the amount of infused crystalline
Pearson Chi-square 8,106 2 0,017
or colloidal solutions, the dose of used vasopressors,
Likelihood ratio 11,149 2 0,004 saturation and bleeding).
Number of valid cases 70 The application of PEEP – 6 cm H2O does not change
in a signi¿cant way the intraoperative values of SBP,
The rate of observed postoperative atelectasis was MBP, DBP, Ppeak, Pplat and also the amount of in-
signi¿cantly higher in the control group A compared fused crystalline or colloidal solutions, the dose of
to the active group. used vasopressors, saturation and blood loss.
The percent of patients who developed postoperative Table 8 below displays the mean values of ASA, du-
respiratory failure in group A was 33,3% and in group ration of operation, ARISCAT score, crystalline and
B was 9,1% (Table 6). colloidal infusions, dose of ephedrine, blood loss.

Table 8. Mean values of ASA score, operation duration time, ARISCAT score, infusion volume, dose of
ephedrine, bleeding

American society of anes- Operation dura- ARISCAT Infusion Ephedrine Blood

thesiologists score (ASA) tion time score volume dose loss
Peeɪ  0 Mean 2,79 2,9500 37,45 2430,30 5,61 909,09
Number 33 33 33 33 33 33
Standard Deviation 0,696 0,77701 5,922 825,562 9,743 837,915
Peep  6 Mean 2,73 2,8621 37,15 2224,24 4,84 733,33
Number 33 33 33 33 32 33
Standard Deviation 0,626 0,73261 5,397 640,815 11,742 458,712
Total Mean 2,79 2,9200 37,19 2332,86 5,07 828,57
Number 70 70 70 70 69 70
Standard Deviation 0,657 0,73165 5,504 728,851 10,449 657,210
PEEP – positive end-expiratory pressure

Application of positive end-expiratory pressure (PEEP)... 31

Most of the patients in this study were estimated as operatively the risk for postoperative complications
ASA 3 – 52,9%, as ARISCAT score – 34 p. – 51,4%. using the ARISCAT score [18, 19, 20]. This score
The duration of the surgical procedure was usually 2 can de¿ne the patients in whom the strategy of pro-
h 30 min, intraoperative blood loss – 1000 ml – 18%. tective mechanical ventilation may reduce the post-
operative complications.
DISSCUSION The pulmonary postoperative complications can pro-
long a patient`s hospital stay and increase its price.
This study proves the hypothesis according to which According to some randomized studies general an-
the application of PEEP – 6 cm H2O together with esthesia with mechanical ventilation applied to pa-
RM, and low Vt (calculated on PBW) during gyneco- tients with healthy lungs during prolonged surgery
logical surgery lasting longer than 2 hours decreases leads to ventilator-induced lung injury (VILI). Many
the rate of postoperative pulmonary complications. multicenter randomized trials try to discover the saf-
Pulmonary complications are the second most com- est and most effective strategy of intraoperative me-
mon cause for postoperative mortality. So it is neces- chanical ventilation. Their principal aim is to reduce
sary to look for ways to reduce them. In this study we postoperative pulmonary and extra-pulmonary com-
used PEEP at a constant level of 6 cm H2O, which plications. Agreement on the parameters of protec-
protects the alveoli from collapsing. On the other tive ventilation – the measure of tidal volume, level of
hand, RM re-expands the alveoli which have already PEEP, application of RM has not yet been achieved.
collapsed. This double effect of PEEP and RM should There is not clear evidence if only low tidal volume
theoretically prevent the development of postopera- without PEEP or PEEP without low tidal volume or
tive atelectasis. The clinical importance of atelecta- the both parameters decrease postoperative pulmo-
sis is related to the risk of development of respira- nary complications.
tory failure. Our study proves statistically signi¿cant
lower rate of the cases of postoperative atelectasis
CONCLUSION
and respiratory failure in the lung-protective ventila-
tion group. We didn`t observe statistically signi¿cant We conclude that the use of protective ventilation
effect of the application of PEEP at a level of 6 cm strategy – low tidal volume, application of PEEP at
H2O on the patients’ hemodynamics, the amount of level 6 cm H2O and RM, can reduce the cases of
crystalline and colloidal infusions, or the dose of va- postoperative pulmonary complications as atelec-
sopressors used. There weren`t cases of barotrauma tasis, respiratory failure and application of non – in-
and pneumothorax. vasive ventilation with CPAP masks. In our study
In our study we didn`t estimate separately the ef- there is no signi¿cant difference between intraopera-
fect of PEEP and low tidal volume on the rate of tive haemodynamic parameters of patients in both
postoperative pulmonary complications. Some ran- groups and also of doses of used vasopressor and
domized studies also have the same limitation [17, quantity of infused crystalline and colloidal solutions.
18, 19, 20]. According to randomized studies, the In conclusion, the investigated strategy of protective
strategy of protective ventilation-low tidal volume, ventilation is easy for application, effective and safe
in combination with PEEP and RM decreases the for the patients.
rate not only of postoperative atelectasis, but also
of postoperative respiratory failure, ARDS, non-in-
vasive ventilation with CPAP masks, re-intubation
and postoperative mechanical ventilation [17, 18]. Conflict of interests: None declared
In the group exposed to protective ventilation these Acknowledgements: None
studies proved a shorter hospital and intensive care
unit stay and lower mortality rate also compared to
control groups [7, 18]. The optimal level of PEEP
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