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Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 13  |  Issue : 2  |  Page : 347-353  

Pressure-controlled ventilation with volume guarantee compared to volume-controlled ventilation with equal ratio in obese patients undergoing laparoscopic hysterectomy


1 Department of Anesthesia and Surgical Intensive Care, Faculty of Medicine, Mansoura University, Mansoura, Egypt
2 Department of Surgical Oncology, Mansoura Oncology Center, Mansoura University, Mansoura, Egypt
3 Department of Obstetrics and Gynecology, Faculty of Medicine, Mansoura University, Mansoura, Egypt

Date of Web Publication28-May-2019

Correspondence Address:
Mona Gad
Department of Anesthesia and Surgical Intensive Care, Faculty of Medicine, Mansoura University, Mansoura
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/aer.AER_82_19

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   Abstract 

Background: Laparoscopic hysterectomy operations especially for obese patients necessitate Trendelenburg position and pneumoperitoneum with carbon dioxide, which could affect cardiac and pulmonary functions. The present study aimed to compare the impact of pressure-controlled ventilation with volume-guaranteed (PCV-VG) and volume-controlled ventilation (VCV) with equal ratio ventilation (ERV), i.e., I: E ratio of 1:1 on hemodynamics, respiratory mechanics, and oxygenation. Patients and Methods: Eighty females with body mass index (BMI) >30 kg/m2 and with physical status American Society of Anesthesiologists Classes I and II undergoing laparoscopic hysterectomy were allocated randomly to either PCV-VG (Group P) or VCV with ERV (Group V). The ventilation parameters, hemodynamics, and arterial blood gases (ABGs) analysis were recorded at four times: (T1): after the anesthetic induction while in supine position by 10 min, (T2 and T3): after the CO2 pneumoperitoneum and Trendelenburg positioning by 30 and 60 min, respectively, and (T4): after desufflation and resuming the supine position. Results: The peak inspiratory pressure in Group P recorded significant lower values than in Group V while the dynamic compliance was greater significantly in Group P than in Group V. No significant differences were reported as regards the ABG analysis, oxygenation, and hemodynamic data between both groups. Conclusion: In obese females undergoing laparoscopic hysterectomy surgeries, PCV-VG was superior to VCV with ERV as it provided higher dynamic compliance and lower peak inspiratory pressure that could be preferable, especially in those patients in whom cardiopulmonary function could be more susceptible to impairment.

Keywords: Equal ratio ventilation, laparoscopic hysterectomy, pressure, volume guaranteed


How to cite this article:
Gad M, Gaballa K, Abdallah A, Abdelkhalek M, Zayed A, Nabil H. Pressure-controlled ventilation with volume guarantee compared to volume-controlled ventilation with equal ratio in obese patients undergoing laparoscopic hysterectomy. Anesth Essays Res 2019;13:347-53

How to cite this URL:
Gad M, Gaballa K, Abdallah A, Abdelkhalek M, Zayed A, Nabil H. Pressure-controlled ventilation with volume guarantee compared to volume-controlled ventilation with equal ratio in obese patients undergoing laparoscopic hysterectomy. Anesth Essays Res [serial online] 2019 [cited 2019 Aug 25];13:347-53. Available from: http://www.aeronline.org/text.asp?2019/13/2/347/257592


   Introduction Top


Laparoscopic hysterectomy operation is a considerable option for both surgeons and females. Laparoscopy has several advantages, especially clarification of the anatomy and pathology by magnification. In addition, it provides lower morbidity and mortality rates as it reduces the postoperative pain, hospital stay, and infection incidence.[1]

Pneumoperitoneum with carbon dioxide affects the cardiac and the pulmonary functions in different ways. Carbon dioxide absorption leads to acidosis, mean arterial pressure (MAP) raisins, lung volumes decrease, all of which can lead to cardiac and pulmonary distress.[2],[3] To facilitate the exposure of lower abdomen and pelvis, surgeons are routinely requested Trendelenburg position which could result in serious physiologic consequences with prolonged use.[4] In addition, the upward displacement of diaphragm by CO2 pneumoperitoneum and intra-abdominal contents decreases functional residual capacity and pulmonary compliance; also, it increases the ventilation/perfusion mismatch. Obese patients or those with chronic lung disease are more susceptible to these effects.[3],[5]

There are many techniques to compensate for the physiologic changes of obesity which include recruitment maneuvers, positive end expiratory pressure (PEEP), and equal ratio ventilation (ERV) during controlled ventilation.[6],[7] ERV is a mechanical ventilation strategy that is suggested to improve oxygenation. In the respiratory cycle, as the inspiratory time is increased, it opens additional alveoli and decreases the incidence of atelectasis. Several recent researches stated that ERV during anesthesia improves oxygenation and respiratory mechanics.[8],[9],[10],[11]

Pressure-controlled ventilation with volume guaranteed (PCV-VG) is considered one of the pressure-regulated volume control (PRVC) ventilation modes that represent criteria from volume-controlled ventilation (VCV) and PCV. Hence, it can deliver a perpetual inspiratory pressure with a perpetual tidal volume by the usage of a decelerating flow pattern. Hence, this recent mode of ventilation can keep the target minute ventilation with a lower barotrauma incidence.[12],[13]

So, PCV-VG that combines the advantages of VCV and PCV with a lower incidence of barotrauma and VCV with ERV that improves oxygenation and respiratory mechanics were compared in this study to detect which one of them is superior regarding its effects on oxygenation, respiratory mechanics, and hemodynamics in obese females subjected to laparoscopic hysterectomy.


   Patients and Methods Top


The current study was carried out after approval by Institutional Research Board (R1902417). 80 females with physical status American Society of Anesthesiologists (ASA) classes I and II, aged 20–60 years, with body mass index (BMI) >30 kg/m2 subjected to laparoscopic hysterectomy operation under general anesthesia (GA) were included in the present study. An informed written consent was obtained from all participants in this study. Patients with physical status ASA classes III and IV, with preexisting lung diseases, or respiratory infections in the previous 2 weeks were excluded from the study. Patients with ventilator settings could not be established within 30 min of pneumoperitoneum in the allocated modes or when the surgery turned to open procedure were also excluded from the study.

Patients were allocated randomly through sealed envelopes to either PCV-VG (P group, n = 39) or VCV with ERV (i.e., I: E 1:1 ratio) (V group, n = 38) using a computer-generated randomization schedule. Although the attending anesthesiologist was not blinded to the group allocation, the patients, surgeon, and data collector were blinded to the group allocation.

Anesthetic management

Each patient was premedicated with 1–2 mg of midazolam intravenously, 20 min before induction of GA and intravenous ondansetron (4 mg) for prophylaxis for postoperative nausea and vomiting after a peripheral i.v. cannula (18 G) was inserted. Lactated Ringer's solution was infused to compensate the overnight fasting hours at a rate of 8 mL/kg. On arrival to the operating room, standard monitoring was applied including automated noninvasive blood pressure monitor, pulse oximeter, continuous electrocardiogram, and capnogram. GA was inducted with a bolus of propofol 2 mg/kg, fentanyl 1.5 μg/kg, and 0.5 mg/kg of atracurium; then, tracheal intubation was done by a cuffed endotracheal tube. Maintenance of anesthesia was achieved by isoflurane in a 50% oxygen/air mixture with minimum alveolar concentration that kept a BIS value between 40 and 60, intravenous fentanyl 0.5 μg/kg was given as the heart rate (HR) or the blood pressure of any patient increased >20% of the basal measurements, and atracurium 5–10 μg/kg/min was administrated to maintain the neuromuscular block. A percutaneous arterial catheter (20 G) was inserted into the radial artery of nondominant hand for continuous blood pressure monitoring and for blood sampling. All anesthetic agents were stopped at the end of the operation, and 100% oxygen was administered. Neostigmine 2.5 mg and atropine 0.5 mg were administered intravenously to reverse the neuromuscular blockade.

Ventilation management

According to the group allocation, the ventilation mode was adjusted using GE health care Carestation 650.USA to either VCV mode using an I: E ratio of 1:1 (ERV), inspired oxygen concentration (FIO2) 0.5 with air, a tidal volume of 6–8 mL/kg, no PEEP in V group or PCV-VG mode with the same initial settings but an I: E ratio of 1:2 inPgroup. Respiratory rate (RR) was adjusted to maintain an end tidal CO2 pressure (ETCO2) of 35–45 mmHg throughout the surgery in the studied groups. Pneumoperitoneum with CO2 was done with an intra-abdominal pressure of 12–15 mmHg while the patient was placed in supine position; then, the operative table was turned to achieve a 30° Trendelenburg position.

Measurements

Data were recorded at four time points: Time1 (T1): after the anesthetic induction while in supine position by 10 min, time2 and time3 (T2 and T3): after the CO2 pneumoperitoneum and Trendelenburg positioning by 30 and 60 min, respectively, and time4 (T4): after desufflation and resuming the supine position by 10 min. The data collected were arterial blood gas (ABG) analysis which included PH, arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2), and oxygen saturation. Respiratory mechanics included peak airway pressure (P peak), mean airway pressure (P mean), dynamic compliance (C dyn), ETCO2, and RR. Hemodynamic data included MAP and HR. Any complication that resulted from anesthesia, Trendelenburg positioning, or pneumoperitoneum through or after the operation was assessed and managed.

The peak airway pressure (P peak) was considered as the primary end point while the other respiratory mechanics, ETCO2, RR, ABG analysis, and the hemodynamics data, were considered as the secondary endpoint.

Statistical analysis

In a pilot study on ten patients, a difference in peak airway pressures (P peak) was observed (25 ± 7.8 cm H2O in PCV-VG compared to 30 ± 6 cm H2O in VCV with ERV). Considering α error of 5% and β error of 10%, power 90%. The calculated sample size was 34 patients in each group. For a potential 20% dropout rate, 40 patients were enrolled in each group. Kolmogorov–Smirnov test was used to detect normality of data distribution. Quantitative data were described using mean and standard deviation. Independent samples Student t and Mann–Whitney tests were used for normally and abnormally distributed continuous data, respectively.


   Results Top


Ninety-one women were screened for the present study. Six patients declined the study, two patients with physical status ASA Class III, and three patients had respiratory infections in the previous 2 weeks, all of whom were removed from the study. The remaining 80 patients were allocated into the groups of this study. One patient in P group turned to open hysterectomy and two patients in V group had hypercarbia with the ventilator settings could not be established within 30 min of pneumoperitoneum. Hence, the results of 39 patients in thePgroup and 38 patients in V group were analyzed [Figure 1].
Figure 1: The flow diagram of patient progress through the randomized trial

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The patient's characteristics and the operative duration showed no significant differences between both studied groups [Table 1].
Table 1: The demographic data and the operative duration of the studied groups (mean±standard deviation)

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As regards ABG analysis results, there were no significant differences between the studied groups. PaO2 slightly descended at T2, T3, and T4, in comparison with T1 but without recorded statistical significant differences whereas PaCO2 ascended at T2, T3, and T4 when all compared to T1 in significant values (P < 0.001) [Table 2].
Table 2: Arterial blood gas analysis at time points of the study

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P peak at T2, T3, and T4 in both groups was increased significantly when compared to T1 (P < 0.0001). However, it was significantly lower in P group than V group at T2, T3, and T4 (P = 0.0009, 0.0006, and 0.0005, respectively) without significant difference between both groups at T1. Moreover, C dyn was significantly decreased at T2, T3, and T4 in the studied groups in comparison with T1, but inPgroup, it was higher than in V group at T2, T3, and T4 (P < 0.001). Pmean increased significantly in both groups at T2, T3, and T4 in comparison with T1 (P < 0.001) with more elevation in V group thanPgroup but without intergroup clinical significance [Table 3].
Table 3: Ventilation parameters

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Other ventilator parameters recorded no significant differences between the two studied groups. ETCO2 elevated significantly during pneumoperitoneum and Trendelenburg position at T2, T3, and T4 in both groups compared with T1 (P < 0.001) without intergroup significant difference. RR increased intentionally to compensate for the increased ETCO2; so, it recorded higher values at T2, T3, and T4 compared with T1 in each group (P < 0.05) with no intergroup significant difference [Table 3].

Hemodynamic variables (HR and MAP) did not differ between the two groups [Figure 2] and [Figure 3].
Figure 2: Heart rate at the studied time points (beat/min). Data are in mean ± standard deviation. T = Time, Group P = Pressure-controlled ventilation with volume guaranteed, Group V = Volume-controlled ventilation with equal ratio ventilation

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Figure 3: Mean arterial pressure at the studied time points (mmHg). Data are in mean ± standard deviation. T = Time, Group P = Pressure-controlled ventilation with volume guaranteed, Group V = Volume-controlled ventilation with equal ratio ventilation

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   Discussion Top


The present study showed a superior role for PCV-VG ventilation mode over VCV with ERV in obese women with BMI >30 kg/m2 subjected to laparoscopic hysterectomy in a Trendelenburg position 30°. In P group, there were significantly lower P peak and a greater dynamic compliance compared to V group. P mean was higher in V group but without statistical significant difference between the studied groups. Other ventilator parameters and gas exchange assessment were comparable between both studied groups. In addition, HR and MAP showed no significant difference between both groups.

During the pneumoperitoneum, the intrathoracic pressure increases. This leads to diminution of the lung volumes, decrease in the lung compliance, increase ofPpeak and early airway closure and atelectasis in the dependent parts of the lungs.[14] Obese patients are more susceptible to atelectasis as the functional residual capacity decreased and the compliance of both chest wall and lungs also decreased.[15],[16] Increasing either the RR or the tidal volume failed to improve PaO2 during laparoscopy in obese patients, while applying PEEP[6],[17] or alveolar recruitment maneuver during either laparoscopic bariatric surgery[18] or laparoscopic surgery in obese patients[19] could improve PaO2 but was associated with significantly higher P peak.

PCV-VG is a type-controlled ventilation mode with a dual character as it has the criteria of both PCV and VCV. This recent ventilation mode which is one of the PRVC that include AutoFlow ventilation, offers the ability to reduce the inspiratory pressure and as a result the incidence of atelectasis.[20]

Theoretically, dual-controlled ventilation is considered of choice for preserving an appropriate tidal volume throughout the laparoscopic surgeries in which abrupt changes in the intra-abdominal pressure can occur due to frequent position change and the CO2 pneumoperitoneum. With PCV, frequent changes in thePpeak values may be needed to achieve adequate ventilation coinciding with the changes that happened in the lung compliance.[21] In spite of these theoretical advantages, many researches that evaluating PCV-VG were conducted as cross-over researches.[21],[22],[23] Hence, the information about the favorability of PCV-VG mode of ventilation over the other ventilation modes during the laparoscopic surgeries is still insufficient.

The aims of anesthetic management in the laparoscopic surgeries are to preserve the oxygenation and avoiding the barotrauma. However, many studies recommended that VCV with ERV enhances oxygenation in acute respiratory distress syndrome;[24],[25] but, the impact of VCV with ERV on oxygenation during surgeries is still controversial. In a meta-analysis of seven prospective trials about CO2 pneumoperitoneum or one lung ventilation, VCV with ERV improved oxygenation after 60 min from intervention, but that was not after 20 or 30 min from intervention.[11] The principle mechanism for oxygenation improvement by ERV is the alveolar recruitment through increasing P mean.[26] A higher P mean permits the collapsed alveoli to reopen in a way like using an extrinsic PEEP, that leads to improvement of arterial oxygenation.[27],[28] In spite of this theoretical benefit, VCV with ERV has the disadvantages of impeding the venous return and lowering the cardiac output. These negative effects on the hemodynamics limit its widespread clinical application during surgeries. Therefore, the current study was conducted to compare the PCV-VG and VCV with ERV clinical benefits regarding oxygenation and ventilation parameters during laparoscopic hysterectomy for obese females.

This study reported that neither PCV-VG nor VCV with ERV when compared with each other recorded superiority regarding oxygenation improvement. PaO2 was slightly higher with VCV with ERV group but this failed to reach to statistical significance in comparison with PCV-VG group at the same time points of the study. Furthermore, P mean which is considered a major determinant of arterial oxygenation did not record statistical significant difference between the studied groups, and it was to some extent higher with VCV with ERV group. PaO2 was comparable all over the study that could be explained by the issue stated that ERV improves oxygenation through increasing P mean only when alveoli are recruitable. Kim et al.[10] reported that PaO2 was lowest (153–155 cm H2O) compared with their basal values during Trendelenburg position in the 1:2 I: E ratio group with a lower P mean and a higher P peak; but in this study, PaO2 recorded little decreases during Trendelenburg position and CO2 pneumoperitoneum compared with their basal values without significant differences, and there was a relatively lower P peak and higher P mean. Although P peak might not accurately reflect alveolar pressure when the flow pattern is modified,[29] P peak is considered a major clinical determinant of the alveolar pressure and consequently the barotrauma.[30] In the present study, PCV-VG lowered P peak significantly in comparison to VCV with ERV. Hence, PaO2 that maintained in this study suggests that both PCV-VG and VCV with ERV are quite enough to keep the oxygenation and to recruit the alveoli with the Trendelenburg position and CO2 pneumoperitoneum but PCV-VG was more superior regarding keeping P peak at lower values. Aldenkortt et al.[31] reported that with ventilation mode either PCV or VCV in obese adults with BMI ≥30 kg/m2 undergoing abdominal procedures, neither oxygenation nor ventilation recorded any significant difference between both modes. Davis et al.[32] showed that the PCV-VG could achieve oxygenation improvement when compared with VCV on condition I: E; VT and PEEP were kept constant in ARDS patients.

In the present study, the RR was increased intentionally in both studied groups to compensate the increased ETCO2 that resulted from CO2 pneumoperitoneum keeping it between 35 and 45 and as a result maintaining PaCO2 values between 40 and 50 mmHg. Hence, no negative effects were reported from the ventilation of patients on CO2 removal, and the pH values were within the normal range without any clinical effect observed, and as a result, normocapnia was maintained. As previously mentioned that P peak is a major clinical determinant of the alveolar pressure and moreover, a determinant of the barotrauma.[30] Although no patient in the present study showed a P peak >40 cm H2O, Again to remember that PCV-VG recorded significantly lower values of P peak with slight lower P mean values than VCV with ERV. These findings might be useful regarding PCV-VG as a ventilating mode during laparoscopic hysterectomy for obese patients. As those patients are more susceptible to hemodynamic changes, and with a little change in the cardiac output this can lead to evident hemodynamic effects thus the ventilation plane that could decrease the affection of the cardiac function are important. As mentioned previously, however, an increase in P mean with ERV improved oxygenation, it reduced the venous return and the cardiac output through increased intrathoracic pressure.[33] Although the present study recorded no cardiovascular collapse, its findings suggested that PCV-VG could be clinically more suitable and an easier mode of ventilation than VCV with ERV, particularly this category of patients, because PCV-VG preserves oxygenation as effective as VCV with ERV, but without a great increase in P mean.

Pneumoperitoneum with 45° Trendelenburg position can increase the left ventricular filling pressures by about 2–3 fold, but the cardiac output may be decreased.[34] Furthermore, the systemic vascular resistance, CVP, and MAP, all are increased while the portal, renal, and the splanchnic flow are decreased,[35] and the renin–angiotensin system is activated, and the levels of vasopressin are increased. Torrielli et al.[36] reported that when the IAP increased to 10 mm, this leads to a decrease in the cardiac index which returned to its basal value after 10 min from 10° Trendelenburg positioning. In addition, the elevated IAP was accompanied with higher MAP and SVR, and these elevations did not come back to normal after the peritoneal exsufflation. Therefore, to minimize these effects, this study did not exceed 30° Trendelenburg position. The current study reported that the MAP values were within the normal ranges.

Again, Trendelenburg positioning and CO2 pneumoperitoneum when combined, they resulted in several pulmonary problems, for example, atelectasis and ventilation/perfusion mismatch. This study reported that Trendelenburg positioning and CO2 pneumoperitoneum both affect the respiratory data greatly but in PCV-VG with a lower extent as it recorded higher C dyn and a lower P peak compared to VCV with ERV. In agreement with these findings, Oǧurlu et al.[37] recorded lower values of P peak and P plateau, and the lung compliance was higher with PCV. In contrast, Kalmar et al.[2] showed that the pulmonary parameters were kept within physiological ranges in their study; so, they concluded that CO2 pneumoperitoneum and Trendelenburg positioning both were well tolerated.

In aggregate, the results of this study clarified that PCV-VG was superior to VCV with ERV due to its lower P peak and slight lower P mean with no difference in oxygenation. These findings are in accordance with the previous researches in which PCV-VG, VCV, and PCV were compared and showed that PCV-VG recorded a lower P peak and P mean with preserving similar oxygenation.[21],[22],[23] Otherwise speaking, the usage of PCV-VG offers tight control on tidal volume and efficient oxygenation plus better compromise regarding P peak.[38] Hence, the usage of PCV-VG could be suitable in patients susceptible to airway pressure changes. PCV-VG might be helpful for obese patients undergoing laparoscopic surgery, without concerns of hemodynamic instability or possibility of auto PEEP.

The current study showed some limitations. First, this study was not in a complete blind fashion as the anesthesiologist was aware of the mode of ventilation that used. Second, the patients with respiratory diseases which are important factors for compromising respiratory mechanics and affecting oxygenation were not included in this study. Third, no extrinsic PEEP was used in the strategies of ventilation in the present study; auto-PEEP could not be measured during surgery as its measurement required an end-expiratory hold.[39] These limitations should be considered in the future, and further studies are necessary to clarify the effects of different modes of ventilation on the respiratory mechanics in different patients. In addition, more researches are advised to determine the impact of various ventilation modes on the outcome of the patients.


   Conclusion Top


During laparoscopic hysterectomy, PCV-VG is considered as a favorable ventilation strategy that could be used as an alternative to VCV with ERV. Although both of these types of ventilation maintained oxygenation indicating that both of them are acceptable for laparoscopic hysterectomy, PCV-VG recorded lowerPpeak values with greater dynamic compliance; these findings may recommend PCV-VG to be more beneficial than VCV with ERV in obese patients who are more susceptible to cardiovascular and respiratory functions' compromise during laparoscopic surgeries. Finally, without regard of ventilation mode, cautious supervision is important to preserve efficient ventilation, sufficient oxygenation, and acceptable airway pressures with CO2 pneumoperitoneum and Trendelenburg positioning.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

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