Anesthesia: Essays and Researches  Login  | Users Online: 591 Home Print this page Email this page Small font sizeDefault font sizeIncrease font size
Home | About us | Editorial board | Ahead of print | Search | Current Issue | Archives | Submit article | Instructions | Copyright form | Subscribe | Advertise | Contacts

Table of Contents  
Year : 2017  |  Volume : 11  |  Issue : 3  |  Page : 758-761  

Single minute of positive end-expiratory pressure at the time of induction: Effect on arterial blood gases and hemodynamics in morbidly obese patients undergoing laparoscopic bariatric surgery

1 Department of Anesthesiology, Sri Aurobindo Institute of Medical Sciences, Indore, Madhya Pradesh, India
2 Department of Bariatric and Metabolic Surgeries, Mohak Hi Tech Hospital, Indore, Madhya Pradesh, India

Date of Web Publication26-Apr-2017

Correspondence Address:
Dipti Saxena
Department of Anesthesiology, Sri Aurobindo Institute of Medical Sciences and Mohak Hi-Tech Hospital, Indore, Madhya Pradesh
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aer.AER_17_17

Rights and Permissions

Background: The effect of positive end-expiratory pressure (PEEP) has been studied in detail after induction of general anesthesia especially in obese individuals. However, sparse information can be gathered from the literature regarding its effect when applied at the time of induction and the time of onset of its effect. Thus, this study was planned to assess the effect of PEEP when applied for a single minute in morbidly obese patients. Materials and Methods: This was a randomized prospective study comprising seven morbidly obese patients (body mass index ≥40 kg/m2). Control group included 30 patients who received no PEEP at the time of induction. The study group consisted of thirty patients who were given a PEEP of 10 cmH2O. Serial arterial blood gas samples were taken preoperatively, at the time of intubation, 5 min after intubation and 10 min after intubation. Results: PaO2was significantly higher in test group (242.0 ± 116.0 mmHg) than in control group (183.0 ± 107.0 mmHg) just after intubation. PaCO2was comparable in control group (43.73 ± 6.32 mmHg) and test group (44.52 ± 6.33 mmHg) just after intubation but was significantly less in test group than in control group at 5 and 10 min thereafter. Hemodynamic parameters were comparable in both groups at all time intervals. Conclusion: Application of even a single minute of PEEP at the time of induction improves oxygenation without any adverse effects on hemodynamics, in morbidly obese patients undergoing laparoscopic Bariatric surgery.

Keywords: Bariatric surgery, blood gas analysis, laparoscopy, morbid obesity, positive end-expiratory pressure

How to cite this article:
Saxena D, Singh P, Dixit A, Arya B, Bhandari M, Sanwatsarkar S. Single minute of positive end-expiratory pressure at the time of induction: Effect on arterial blood gases and hemodynamics in morbidly obese patients undergoing laparoscopic bariatric surgery. Anesth Essays Res 2017;11:758-61

How to cite this URL:
Saxena D, Singh P, Dixit A, Arya B, Bhandari M, Sanwatsarkar S. Single minute of positive end-expiratory pressure at the time of induction: Effect on arterial blood gases and hemodynamics in morbidly obese patients undergoing laparoscopic bariatric surgery. Anesth Essays Res [serial online] 2017 [cited 2020 Jun 1];11:758-61. Available from:

   Introduction Top

Obesity has now been termed as globosity indicating its widespread prevalence. With it comes a load of diseases for which more and more obese patients go under the knife. General anesthesia is known to alter respiratory mechanics in normal weight, healthy adult controls within minutes of induction and preoxygenation with 100% oxygen has been recommended to reduce hypoxemia.[1],[2] This enhances atelectasis formation during induction itself. The exaggerated effect is seen in morbidly obese patients resulting in significant impairment of pulmonary gas exchange and respiratory mechanics.[3],[4] Thus, this patient population desaturate more rapidly than nonobese patients during apnea.[5] Recruitment maneuver along with positive end-expiratory pressure (PEEP) has been shown to be the most effective method in reducing atelectasis and improving oxygenation.[6] The effect of PEEP alone remains controversial with some studies refuting any effect on atelectasis. But if PEEP is applied at the time of induction, before atelectasis sets in, it should improve oxygenation. Maisch et al.[7] had shown that an optimal PEEP was 10 cmH2O because at this pressure level the highest compliance value in conjunction with the lowest dead space fraction indicated a maximum amount of effectively expanded alveoli. Therefore, we proposed to study the effect of PEEP of 10 cmH2O when applied at the time of induction for a single minute on arterial blood gases (ABGs) and hemodynamics.

   Materials and Methods Top

After taking Local Ethics Committee approval (Ethical and Research Committee, SAMC and PGI, Indore, protocol No. Saims/IEC/14/02/35, on February 25, 2014), this prospective study was conducted in the Department of Anaesthesiology and Critical Care over a period of 1 year. Seventy morbidly obese patients, American Society of Anesthesiologists physical Status II or III, aged 20–65 years with body mass index >40 kg/m 2, scheduled for elective laparoscopic bariatric surgery were selected, and a written informed consent was obtained. Patients who denied consent, those undergoing emergency and/or open surgery and those requiring more than two attempts for intubation were excluded from the study.

Using a computer generated random number tables, patients were divided into two groups, study group (with PEEP) and control group (without PEEP). Arterial line was inserted preoperatively, and ABG sample was taken and hemodynamic parameter recording done while the patient was breathing room air. Both groups were preoxygenated for 3 min with 100% oxygen. Standard procedure was used for induction of anesthesia in all the patients. No premedication was given. All the patients were induced with intravenous (IV) glycopyrolate (0.005–0.01 mg/kg), IV fentanyl (2 μg/kg) and IV propofol on the basis of loss of verbal response. Once the patient became unresponsive to verbal commands, succinylcholine was then administered in a dose of 1–1.5 mg/kg. This was immediately followed by mechanical ventilation with 100% oxygen using volume-controlled mode on anesthesia machine. Tidal volume was set according to 7 ml/kg ideal body weight and a respiratory rate of 14/ min. PEEP of 10 cmH2O was added to ventilator settings in study group while the control group received zero PEEP. Mask was held using four hand techniques. After 1 min endotracheal intubation was done. PEEP was continued in study group after intubation for a minimum of 10 min. ABG analysis and hemodynamic parameters were recorded at following stages: preoperatively, just after inflation of cuff of endotracheal tube, 5 min postintubation, 10 min postintubation.

   Results Top

This study comprised total seventy patients. Eight patients in whom arterial line could not be placed preoperatively were excluded from the study. Two patients had to be excluded from the study as they were not able to tolerate a PEEP of 10 cm and showed marked hemodynamic instability. Thus, thirty patients each in study group and control group were included. The demographic profile was similar in both groups [Table 1]. All the patients were intubated in single attempt and time for placement and inflation of cuff did not require more than 1 min. Hence, the analysis of first sample was done at 1½–2 min of onset of PEEP and continued till 10 min thereafter.
Table 1: Patient characteristics

Click here to view

The results obtained were collected, tabulated, and analyzed by unpaired Student's t-test. Categorical variable was compared between groups by Student's t-test with two sample proportions. Paired t-test was employed for intra-group comparison of numerical variables. P < 0.05 was considered statistically significant for 95% confidence interval.

Systolic and diastolic BP was found to be comparable (P > 0.05) in both groups at all the times of measurement [Table 2]. Pulse rate was found to decrease significantly in the study group at 5 min of induction [Table 3]. [Table 4] shows a comparison of ABGs between both groups. Significant improvement was seen in arterial oxygenation (PaO2) with a PEEP of 10 cmH2O just after induction. Thus, single minute of PEEP had improved oxygenation with the effect continuing after 5 and 10 min. Arterial carbon dioxide (PaCO2) did not show any significant difference just after induction but reduced significantly at 5 and 10 min.
Table 2: Comparison of hemodynamic parameters (systolic and diastolic blood pressure)

Click here to view
Table 3: Comparison of hemodynamic parameters (pulse rate beats/min)

Click here to view
Table 4: Comparison of blood gases (mmHg)

Click here to view

   Discussion Top

In this study, we found that application of PEEP during induction of anesthesia especially in morbidly obese patients even for a single minute significantly increases oxygenation.

It has been shown by Reinius et al.[6] that in morbidly obese patients, induction of anesthesia and paralysis reduces end expiratory lung volume, promotes atelectasis in dependent lung regions and causes a marked fall in arterial oxygenation. PEEP alone increases the normally aerated lung fraction. There is a reduction of poorly aerated lung tissue while atelectasis remains unchanged. Thus, there is no change in oxygenation. However, PEEP at the time of induction improves oxygenation by all three actions, namely, decreased atelectasis due to general anesthesia, increased normally aerated lung fraction and decreased hypoxic pulmonary vasoconstriction. Thus, oxygenation was significantly improved in our study [Table 4], thereby giving a longer period of nonhypoxic apnea. All the patients were intubated in single attempt. However, five patients were difficult to ventilate. Three patients belonged to control Group while two patients belonged to Study Group. It was found that even in these patients if PEEP was continued, arterial oxygenation either remained same as preoperative value or improved marginally. Oxygenation decreased when no PEEP was applied.

In our study, PaCO2 was comparable in two groups preoperatively [Table 4]. At the time of intubation, no significant difference was found between the two groups. However, after 5 and 10 min of ventilation with PEEP, PaCO2 significantly decreased. This shows that PEEP takes longer time to produce an effect on PaCO2. Reduction in PaCO2 occurs possibly due to increased fraction of normally ventilated lung and decreased ventilation-perfusion mismatch.

PEEP increases both peak inspiratory pressures and the mean airway pressures; it has the potential to decrease venous return and cardiac output. However, in our study, both groups were comparable regarding hemodynamics [Table 2]. No hemodynamic consequences were observed at high airway pressures. Although the pulse rate decreased significantly after 5 min, it did not alter the BP in the study group. Only two patients showed signs of severe hemodynamic instability and had to be excluded from the study, probably due to prolonged fasting and inappropriate preloading. Bohm et al.[8] have also shown that after optimization of preload, high positive airway pressures are hemodynamically well tolerated in morbidly obese patients with or without capnoperitoneum. Jellinek et al.[9] have demonstrated the absence of any hemodynamic compromise at high levels of PEEP if central venous pressures were kept higher than 10 mmHg. Therefore, PEEP can be used without any adverse effects on hemodynamics in patients who are adequately hydrated.

Only one similar study, which was done by Coussa et al.[10] could be found in which the effect of PEEP at the time of induction of general anesthesia was studied. They had shown that despite the use of 100% oxygen, application of PEEP throughout the induction period nearly completely prevents atelectasis formation in morbidly obese patients. However, they had studied the effect of PEEP given for 5 min along with continuous positive airway pressure (CPAP) and computed tomography scans were compared of patients receiving PEEP with those receiving no PEEP. Our study corroborates the above findings even without the application of CPAP.

A potential risk of mechanical ventilation by mask with PEEP is exposing sedated and paralyzed patient to stomach insufflations thereby, increasing the risk for regurgitation and aspiration. Gastric distension was found in some patients in our study, but it was not so significant so as to cause any major problem during the creation of pneumoperitoneum or thereafter. In our study, postoperative ABG analysis was not done which could have determined whether such a short duration of PEEP at the time of induction helps postoperatively or not.

With this study, we can conclude that PEEP of 10 cmH2O effectively improves oxygenation without altering the hemodynamic parameters even when applied for a single minute at the time of induction.


We would like to thank the management of our institute for supporting us in our study. We also acknowledge the efforts and faith of the staff and patients who have made this work possible.

Financial support and sponsorship

Mohak Hi Tech Institute, Indore.

Conflicts of interest

There are no conflicts of interest.

   References Top

Marshall BE, Wyche MQ Jr. Hypoxemia during and after anesthesia. Anesthesiology 1972;37:178-209.  Back to cited text no. 1
Moller JT, Johannessen NW, Berg H, Espersen K, Larsen LE. Hypoxaemia during anaesthesia – An observer study. Br J Anaesth 1991;66:437-44.  Back to cited text no. 2
Pelosi P, Croci M, Ravagnan I, Cerisara M, Vicardi P, Lissoni A, et al. Respiratory system mechanics in sedated, paralyzed, morbidly obese patients. J Appl Physiol 1997;82:811-8.  Back to cited text no. 3
Eichenberger A, Proietti S, Wicky S, Frascarolo P, Suter M, Spahn DR, et al. Morbid obesity and postoperative pulmonary atelectasis: An underestimated problem. Anesth Analg 2002;95:1788-92.  Back to cited text no. 4
Berthoud MC, Peacock JE, Reilly CS. Effectiveness of preoxygenation in morbidly obese patients. Br J Anaesth 1991;67:464-6.  Back to cited text no. 5
Reinius H, Jonsson L, Gustafsson S, Sundbom M, Duvernoy O, Pelosi P, et al. Prevention of atelectasis in morbidly obese patients during general anesthesia and paralysis: A computerized tomography study. Anesthesiology 2009;111:979-87.  Back to cited text no. 6
Maisch S, Reissmann H, Fuellekrug B, Weismann D, Rutkowski T, Tusman G, et al. Compliance and dead space fraction indicate an optimal level of positive end-expiratory pressure after recruitment in anesthetized patients. Anesth Analg 2008;106:175-81.  Back to cited text no. 7
Bohm SH, Thamm OC, von Sandersleben A, Bangert K, Langwieler TE, Tusman G, et al. Alveolar recruitment strategy and high positive end-expiratory pressure levels do not affect hemodynamics in morbidly obese intravascular volume-loaded patients. Anesth Analg 2009;109:160-3.  Back to cited text no. 8
Jellinek H, Krafft P, Fitzgerald RD, Schwarz S, Pinsky MR. Right atrial pressure predicts hemodynamic response to apneic positive airway pressure. Crit Care Med 2000;28:672-8.  Back to cited text no. 9
Coussa M, Proietti S, Schnyder P, Frascarolo P, Suter M, Spahn DR, et al. Prevention of atelectasis formation during the induction of general anesthesia in morbidly obese patients. Anesth Analg 2004;98:1491-5.  Back to cited text no. 10


  [Table 1], [Table 2], [Table 3], [Table 4]


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

  In this article
    Materials and Me...
    Article Tables

 Article Access Statistics
    PDF Downloaded96    
    Comments [Add]    

Recommend this journal