European Journal of Cardiovascular Medicine

The growing modern epidemic of non-communicable diseases and its correlation with obesity cannot be stressed on further. WHO factsheets state that at present, 1.9 billion adults worldwide are overweight and 650 million obese.¹ Contrary to conventional wisdom, the obesity pandemic is not limited to developed cultures; it is estimated that over 115 million people in developing countries experience obesity-related illnesses. ² Mechanical ventilation becomes challenging in obese patients because of decreased FRC, decreased lung oxygen reserves, waning of lung compliance and rapid experiences of desaturation. Thus considering obesity and pneumoperitoneum as special conditions ³, because of the complexity of the pathophysiological mechanisms and the murkiness of the clinical outcome after usage of varied ventilation strategies has led to curiosity and debates regarding this topic. There is no fixed set of guidelines for adequate ventilation of overweight patients.¹ Trending today are lung protective ventilation strategies, establishment of benefits of different modes of ventilation, significance of PEEP, Recruitment maneuvers, patient ventilator synchrony etc. Patients under the WHO classification of overweight and obese are taken up to get a well-defined idea of ventilator settings in an operative set up in our population who is facing the double burden of malnutrition¹. Hence, the distribution of BMI has included overweight patients in our study population to fill the existing lacunae in studies in our population.Our study assesses and compares pressure controlled ventilation and volume controlled ventilation on the basis of oxygenation parameters and respiratory dynamics in patients with body mass index 25Kg/m² undergoing laparoscopic cholecystectomy.

The present study is a Hospital based Cross Sectional Comparative study  conducted in the Department of Anaesthesiology, Assam Medical College and Hospital,from june 2021 to May 2022 Assam, India covering all patients with BMI ≥25Kg/m² undergoing laparoscopic cholecystectomy under general anaesthesia in Assam Medical College and Hospital.

By considering 95% confidence interval with 90% power the sample size for the present study was calculated to be 42 (21 for pressure controlled group and 21 for volume controlled group).

Inclusion Criteria:

• Patients who have given informed consent.
• WHO classification of obesity – Overweight 25-29.9 kg/m2 BMI and Obese ≥ 30 kg/m²
• ASA class I and II
• AGE 18-60 years
• Absence of severe pulmonary disease
• Planned for elective laparoscopic cholecystectomy.
• Pulmonary function test >70% predicted value.

Exclusion Criteria:

• Patient’s refusal
• Patients with anticipated difficult intubation
• All patients who have inability to maintain stable mechanical ventilation for more than 30 minutes.
• Inability to maintain ETCO₂ in the range 35-45 mm Hg.
• Conversion to open cholecystectomy/laparotomy.
• In Volume control group, patients who need >10ml/kg of tidal volume and respiratory rate ≥ 25 to maintain target ETCO₂ (35-45) mm Hg.
• In PCV group, patients who need Peak pressure >35cm of H₂O and respiratory rate ≥25/min to maintain target ETCO₂ (35-45)mm Hg.
• Less than 70% predicted values for pulmonary function test.

• Patients with cardiovascular disease, obstructive sleep apnea, obesity hypoventilation syndromes

Preoperative Preparation:

Detailed pre-anaesthetic evaluation of all patients keeping target BMI≥ 25 kg/m² (WHO classification overweight and obese) were done in their respective wards before the surgery. The patients were explained about the study procedure and about the arterial blood gas sampling preoperatively and a written informed consent  was taken .

Allocation of Groups: All patients were randomly assigned into two groups, the group receiving Volume Controlled Ventilation (group I; n=21) and the group receiving Pressure Controlled Ventilation (group II; n=21), 15 Mins After insufflation of Pneumoperitoneum.

TECHNIQUE OF ANAESTHESIA-

All patients posted for elective surgery who fulfilled the inclusion criteria were taken for the study till the sample size was covered.A multi parameter monitor consisting of pulse oximeter, electro-cardiogram, non-invasive blood pressure, temperature and capnography were connected. The pre-induction heart rate, oxygen saturation, and systolic, diastolic blood pressure values were recorded. Premedication were given with injection Ondansetron 0.15mg/kg, injection Glycopyrrolate 0.04mg/kg, injection Fentanyl 2 microgram/kg IV is given prior to induction. Pre-oxygenation with 100% oxygen was done for 3 minutes. Then patients were induced with injection Propofol 2mg/kg followed by inj Succinylcholine chloride 1mg/kg) to facilitate orotracheal intubation in ramping position. Endotracheal intubation were performed using an appropriate sized Macintosh blade and with an appropriate sized cuffed endotracheal tube. The timing of the events was noted. Loading dose of Atracurium besylate (0.5mg/kg) was given after wear off from succinylcholine hydrochloride. Anaesthesia was maintained with 50% oxygen, 50% nitrous oxide and sevoflurane (0.6%-1%) and intermittent doses of IV Atracurium besylate one fourth (1/4th) of the intubating dose when required. For adequate analgesia inj Fentanyl iv, Inj Ketorolac iv were given.Ventilation was controlled by using Mindray ventilator. Tidal volume 8ml/kg I:E ratio of 1:2 and PEEP were adjusted to 5cm of H₂O the ETCO₂ between 35-45 mmHg was maintained as the target ETCO₂. At the time of induction and before pneumoperitoneum insufflation the recordings of every ventilator parameter namely Respiratory Rate, ETCO₂, Tidal volume, Peak airway pressure, Plateau pressure were done and Arterial blood Gas sample were taken.

This was the Baseline reading for the study. Then the subjects were randomly assigned to one of the two equal groups (21 each) using a computer-generated table of random numbers after 15 minutes of pneumoperitoneum. After insufflation of pneumoperitoneum the recordings of every parameter were taken at 15 minutes interval. Patients were positioned head up 25 degrees with 10-12 mmHg IAP. Ventilatory and pulmonary indices ETCO₂, respiratory rate, tidal volume, peak airway pressure, plateau pressure were recorded at 15 minutes after insufflation of pneumoperitoneum, at 30 minutes and 45 minutes after pneumoperitoneum. Intra operative heart rate, systolic blood pressure, diastolic blood pressure was monitored throughout the procedure. For evaluation of oxygenation parameters Arterial blood gas analysis was done from the sample from radial artery. Under all aseptic and antiseptic conditions sample was taken via a heparinized syringe at baseline at the time of induction (before insufflation of pneumoperitoneum), 15 mins after pneumoperitoneum; at 30 mins after pneumoperitoneum ; at 45 mins after pneumoperitoneum and one post operatively in the ward three hours after surgery. The i-STAT EG7+ cartridge for i-STAT 1 Abott was used for sampling. “Allen’s test” was performed for every patient to check patency of collateral circulation prior to obtaining ABG samples.

Patients in the VCV group were assigned tidal volume of 8ml/kg and increased incrementally by 1ml/kg to 10ml/kg each 5 mins and respiratory rates were increased by 2 every five mins to 25/min as and when required. If the target ETCO₂ was not maintained or tidal volume > 10ml/kg or RR ≥25/min required patients were excluded from the study. Patients in the PCV group peak pressure were set to deliver target tidal volume of 8ml/kg. Respiratory rates were optimised to set the patient in target ETCO₂ range. If the patient needed peak pressure (Peak P) more than 35cm of H₂O or RR ≥25/minute they were excluded from the study. At the end of the surgery sevoflurane and nitrous oxide was discontinued and 100% oxygen was continued. After returning of respiratory efforts residual neuromuscular blockade was reversed by injection Neostigmine 0.05mg/kg and Injection Glycopyrrolate 0.01mg/kg intravenously. When the criteria for extubation were fulfilled extubation was done in ramping position. Upon arrival in the post operative ward, Arterial blood gas for the post operative sample and the heart rate, blood pressures– SBP, DBP were recorded again. The 3 hour post operative sample was used in this study.

The multitude of ventilatory and oxygenation challenges related to obesity and its aggravation by pneumoperitoneum during laparoscopic cholecystectomy have been extensively researched. This is a culmination of altered physiology and is multi systemic in nature. Many newer modes have been utilised for such cases but the efficacy still stands to be established.

Heterogeneous findings in various publications and the clarity to which mode is superior is under trial.

Study conducted by Reza Movassagi et al.⁴ (2017) where values at baseline before pneumoperitoneum and at 15 mins, 35 minutes and 55 minutes after carboperitoneum found comparable values in both the groups (p>0.05). Erhan Ozyurt et al.⁵(2019) conducted a similar study in which they found no significant difference in the ETCO₂ values at 5 minutes after insufflation and 30 minutes after pneumoperitoneum and at the end of surgery (p>0.05). P.Cadi et al.⁶(2008) when comparing VCV and PCV in laparoscopic obesity surgery did not find any significant difference in ETCO₂. The reading was taken intraoperatively at 45 minutes after pneumoperitoneum while maintaining a definite algorithm based on Ideal body weight of the subjects.They had taken target ETCO₂ of 4.40-4.60 kPa for 36 patients with BMI≥ 35 kg/m^2.Thomas Breining et al.⁷(2002) no significant variations in ETCO₂ findings at supine position (phase1), 45⁰ reverse Trendelenburg position (phase 2) and after insufflation of pneumoperitoneum (phase 3) in both VCV and PCV modes(P>0.05).

The study was conducted in bariatric surgery patients and target ETCO₂ to be maintained was (30-35) mmHg.60 obese patients scheduled for laparoscopic cholecystectomy were compared for ETCO₂ values by Jyoti Khanna et al.(2015)⁸. The target ETCO₂ for the study was 35-40 mm Hg. In the pre-operative, 10 mins after pneumoperitoneum and 30 mins after pneumoperitoneum, the ETCO₂ values for both the groups-PCV and VCV were not significant (p>0.05). Similar findings were seen in Apoorwa Kothari et al.(2017)⁹ who compared VCV and PCV in 15 mins after pneumoperitoneum(T2) and and after desufflation T3.They found no significant difference in both the modes.(p>0.05). The study was done in patients undergoing laparoscopic cholecystectomy where the PCV and VCV groups were compared separately and PCV-VG group with PCV and VCV group.

The findings were  consistent with the findings of the study by Aydin et al.¹⁰(2014)  where higher respiratory rates were encountered in PCV group at 10 mins, 20 mins after insufflation of pneumoperitoneum, after removal of gall bladder and post operative values (p<0.05) in laparoscopic cholecystectomy.Jyoti Khanna et al.⁸ (2015) have found statistically significant difference in respiratory rates in both groups at 30 mins after pneumoperitoneum in cases of obese patients undergoing laparoscopic cholecystectomy. Higher rates were found in PCV group as in our study. However, the respiratory rates in 10 mins and 20 mins after pneumoperitoneum were not statistically significant for PCV and VCV.The findings was not comparable to the study conducted by Reza Movassagi et al.⁴ (2017) where  Respiratory Rates at 35 minutes and 55 minutes were statistically significant values in both the groups (p<0.05). VCV has higher respiratory rates than PCV. Heterogeneity in finding can be because of the target ETCO₂ range being 35-40 mm Hg unlike our study where the target ETCO₂ range was 35-45 mm Hg.These findings were not similar to our study. Sampa Gupta et al.¹¹ (2012) have found respiratory rates higher in the VCV Group than in the PCV group 15 mins, 25 mins and 35 mins after insufflation of pneumoperitoneum and it was statistically significant at 35 mins after pneumoperitoneum(p<0.05) in laparoscopic cholecystectomy.

These findings were not similar to our study. Gregory A. Hans et al.¹²(2007) who have included respiratory rate intraoperatively in abdominal surgeries- laparascopy and laparotomy to find comparable values in PCV and VCV modes every 15 mins after pneumoperitoneum (p=0.8). P.Cadi et al.⁶(2008)  when comparing PCV and VCV in laparoscopic obesity surgery did not find any significant difference in Respiratory rates in PCV and VCV mode. The reading was taken intraoperative at 45 minutes after pneumoperitoneum while maintaining a definite algorithm based on Ideal body weight of the subjects in laparoscopic gastric banding surgery. Erhan Ozyurt et al.⁵(2019) conducted a similar study in which they found no significant difference in the respiratory rate values at 5 minutes after insufflation and 30 minutes after pneumoperitoneum and at end of surgery. There was heterogeneity in the findings of respiratory rates in various studies  could have been the result of usage of different algorithms to ventilate the patients with different target ETCO_2.

In the present study, we have found that the Tidal volume was higher for VCV group at 45 mins of pneumoperitoneum (p<0.01) than in the PCV group. Similar findings were established by Sampa Dutta Gupta et al.¹¹ (2012) at 35 minutes (p<0.05) after pneumoperitoneum during laparoscopic cholecystectomy than PCV. This was consistent with the findings of the study by Aydin et al.¹⁰(2014) where higher tidal volumes were encountered in VCV group at 10 mins and 20 mins after insufflation of pneumoperitoneum (p<0.05) in laparoscopic cholecystectomy.70 adult volunteers were taken up for laparoscopic cholecystectomy.Reza Movassagi et al.⁴ (2017) found statistically significant higher tidal volumes for the VCV group (p<0.01) at 55 minutes after pneumoperitoneum in laparoscopic cholecystectomy cases. Jyoti Khanna et al.⁸ (2015) have found no significant difference tidal volumes in both groups at 10 mins and 20 mins after pneumoperitoneum in PCV and VCV. They had found tidal volume higher in VCV group than PCV (p<0.05) at 30 minutes after pneumoperitoneum in cases of obese patients undergoing laparoscopic cholecystectomy.

In the present study, we have found statistically significant findings in the Peak Airway Pressure (Peak P) at 15 minutes (p<0.05), 30 minutes (p<0.05) and 45 minutes (p<0.01) after insufflation of pneumoperitoneum .Gregory A. Hans et al.¹² (2007) who found lower Peak Pressures (Peak P) in PCV group than VCV group at 30 minutes after insufflation of pneumoperitoneum in abdominal laparoscopic surgeries than the VCV group.The present study correlates with the studies done by Reza Movassagi et al.⁴ (2017) who has found significant decrease in the peak airway pressure at 35 minutes and 55 minutes after pneumoperitoneum in the PCV mode than in the VCV mode in laparoscopic cholecystectomy. (p<0.05)Sampa Dutta Gupta et al.¹¹ (2012) also found lower Peak pressure at 25 mins and 35 mins after insufflation of pneumoperitoneum in PCV mode than in the VCV mode in laparoscopic cholecystectomy cases (p<0.05).The values at 15mins after pneumoperitoneum did not produce significant variation (p>0.05).

The findings were similar to the study conducted by Sangbong Choi et al.¹³ (2019) who have found Peak pressure (Peak P) at 40 mins after pneumoperitoneum higher in the VCV group. They also concluded with an overall decrease in peak pressures in PCV mode. Thomas Breining et al.³ (2002) found that PCV allowed significant peak airway pressure decrease as compared without jeopardising the gas exchange at reverse Trendelenburg position -T2 and after insufflation of pneumoperitoneum -T3Jia Jiang et al.¹⁴ (2016) in a systematic review and meta- analysis found after reviewing 25 (N=1460) studies in a pooled analysis, Peak Pressure (P_peak) in PCV having lower values than VCV.Aydin et al.¹⁰(2014) found statistically higher peak pressures for the VCV mode which was taken as group V at 10 mins, 20 mins after insufflation and after the gall bladder was excised and after extubation. Wang et al.(2015)¹⁵ compared PCV and VCV in laparoscopic surgeries in 8 RCT s. A total of 428 participants, 214 cases using PCV and 214 using VCV were included in the meta-analysis. PCV was associated with lower Peak pressures slightly but in significant range.

Jia Jiang et al.¹⁴ (2016) in a systematic review and meta- analysis found after reviewing 25 (N=1460) studies in a pooled analysis, Plat P in PCV has lower pressures than VCV intraoperatively. Oznur Sen et al.¹⁶(2016) studied effects of PCV and VCV on respiratory mechanics and systemic stress response during prone position found lower Plateau pressures in PCV mode as in our study(p<0.05). The plateau pressure in PCV mode was lower than the VCV mode .Plateau pressure were lower in PCV group for both supine and prone position. P values were Supine- (p= 0.009); prone (p=0.035) position. Sangbong Choi et al.¹³ (2019) who have found Plateau pressure (Plat P) higher in the VCV group at 40 mins after pneumoperitoneum (T2) (p<0.05) and T3 at skin closure(p<0.05) in laparoscopic colectomy cases.

In the current study, the PaO₂ at 45 mins after pneumoperitoneum ABG showed values higher in the PCV Group than in the VCV group(p<0.05).Gradual increasing trends in ABG PaO₂ was found in the PCV group.The PaO₂ findings at pre operative, intraoperative and 30 mins, 12 hrs and 24 hrs after extubation were taken by Ramy Mohammed Hassan et al.¹⁷ (2020) and they found statistically significant PaO₂ increase in the PCV group than in the VCV group at intraoperative readings of ABG in laparoscopic gastric sleeve surgery (p=0.011).The post operative values can give a better idea of whether PCV can alter post operative oxygenation. At present, according to this study no difference was found in post op PaO_2. The target PETCO₂ taken for both modes were 38±2 mm Hg.These findings were similar to the studies done by Reza Movassagi et al.⁴ (2017) who found PaO₂ higher in the PCV group than in the VCV 35 and 55 minutes after insufflation of pneumoperitoneum in laparoscopic cholecystectomy cases (p<0.05).