Protocol No: SAP001

Version 1.0, 21st November 2011

Study Title: ProSeal TM LMA increases safe apnea period in morbidly obese patients undergoing surgery under general anesthesia

Protocol No:SAP001

Version: 1.0

Date: 21st November 2011

Sponsor:MaxSuperSpecialityHospital

Research Team

1 / Investigator / Dr. Aparna Sinha
2 / Co Investigators / Dr. Lakshmi Jayaraman
3 / Dr. Dinesh Punhani
4 / Statistician / Miss Kalpana Singh

Back ground and Introduction:

The daunting task of managing difficult airway is often encountered during conduction of anesthesia in a morbidly obese patient. However the role of BMI as a predictor of difficult airway has remained controversial. 1-3

This sub-population is unique in that these patients are at increased risk of difficult airway 4,5 and, at the same time, have is limited reserve of oxygen as they will develop much more atelectasis during induction of general anesthesia than nonobese patients 6.In view of the limited oxygen reserves and higher demand, there is baseline hypoxemia and hypercarbia and these patients poorly tolerate apnea. The desaturation is much faster than the non-obese. The changes in lung functions and pulmonary gas exchange following induction of general anesthesiadirectly correlate with the BMI, even at high percentage of inspired oxygen.1,7-12.

Apnea during laryngoscopy following induction of general anesthesia can be potentially dangerous if inadequately managed, particularly in obese patients. Airway in these patients is more prone to collapse and occlusion hence maintenance of its patency and ventilation are of paramount importance. Repeated attempts at laryngoscopyare invariably required and carry risks of precipitous desaturation.The upper airway management in morbidly obese patients mandates a management strategy that would allow sufficient time for securing airway without producing hypoxemia.

Several airway management and ventilatory strategies have been suggested to prevent critical desaturation and increase oxygen reserves in the morbidly obese patients. 9,13,16Application of positive end expiratory pressure (PEEP) at induction of anesthesia has been shown to increase oxygen reserves by preventing atelectasis in obese and non-obese patients,despite the use of 100% O216-27. The benefits of ventilatory strategies have been objectively analysed by measuring safe apnea time (SAT) or the nonhypoxemic apnea time.

Conventionally facemasks with oropharyngeal airway (FM) have been used to mechanically ventilate patients and apply PEEP, following induction, prior to securing tracheal tube. This however is associated with continuous insufflation of gases in the stomach, may further compromise lung volumes and increase changes of regurgitation and aspiration. This will ultimately compromise the safe apnea time. Recently the ProSealTM laryngeal mask airway (PLMA) has proved to be a useful temporary tool in airway management of the morbidly obese patients. The drain of PLMA allows continuous decompression of the stomach and the high oropharyngeal seal allows application of PEEP. 28-30

Though PLMA has proved to be efficacious, its benefits have not been compared to facemask with oropharyngeal airway with respect to safe apnea time (SAT) which has a direct bearing on the outcome of the airway management in this sub population.

We hypothesised that application of PEEP using PLMA,when used as a conduit prior to laryngoscope guided intubation,improves the SAT. We conducted this single blind randomized prospective study with the primary objective of comparing the effect of ventilation with PEEP, through PLMA and FM, on SAT in morbidly obese patients undergoing surgery under general anesthesia.

Study Objectives:.

Primary Objective:To compare safe apnea time using PLMA to FM in morbidly obese patients undergoing surgery under general anaesthesia

Secondary objective: We wish to study the associated changes in the arterial gases at varioustime points.

Primary Endpoint: SAT

SAT or the time of reaching SpO2 92 %

Secondary endpoint:

Recovery Time or the time taken to recover SpO2 to 98%

pO2bl: pO2 baseline

pO2Preox: pO2 at end of preoxygenation

pO2Apnea:pO2prior to commencement of ventilation

pO2Hypox: pO2at the time of reaching SpO2 92 %

Study Design: Prospective, randomised, single blind study

Subjectselection:

This is a prospective study which will be conducted in MaxSuperSpecialityHospital after the approval of Scientific Committee and Institutional Ethics committee.

A total of 100 Subjects with BMI >35 kg/m2, either sex and age more than 18 years, scheduled for any elective procedure will be recruited.

Recruitment and study period will for a period of _ yr_ month after approval of Ethics committee. The Study will be registered to prior to enrolment of first subject.

All Subjects will be enrolled according to the defined inclusion and exclusion criteria mentioned below;

Inclusion & Exclusion Criteria

The following Inclusion and Exclusion Criteria will be followed prior to randomization.

Inclusion criteria

  1. Patients of age 18-60 years
  2. BMI >35 kg/m2
  3. Posted for elective surgery

Exclusion criteria

  1. Patients with mouth opening < 2.5 cm
  2. Any obvious difficult airway
  3. > one episode of gastro-esophageal reflux per week will be excluded
  4. Pregnancy
  5. Cardiac or pulmonary disease
  6. SpO2 atambient air < 94%
  7. Carotid stenosis

Methods:

With approval of InstitutionalEthics Committeeof Max Super Speciality Hospital (A unit of DDF), New Delhi, a total of 100 patients with BMI >35 kg/m2, either sex and age more than 18 years, scheduled for any elective procedure will be recruited. They will be randomly divided into groups A and B to receive ProSeal TM laryngeal mask airway (PLMA) as airway device for group A whereas in group B will receive facemask with oropharyngeal airway of appropriate size.

Patients will be premedicated with ranitidine 150 mg per os 2 h prior to surgery, with few sips of water. Monitors will be applied prior to induction and will include an electrocardiograph, pulse oximeter, gas analyzer, arterial line, tidal volume monitor, airway pressure monitor and Bispectral index.

Anesthesia will be administered to the patients in the ramp position with the patient’s head on a standard pillow and sheets to keep external auditory meatus at same level as suprasternal notch. All patients will be preoxygenated with 100% oxygen and CPAP of 10 cm H2O for 5 minutes. They will receive propofol, midazolam and fentanyl (based on ideal body weight) for induction and sevoflurane 1-2 % and oxygen in air with FiO2 (1.0). On confirming ventilation paralysis will be achieved with atracurium besylate 0.5mg/kg (iBW). Propofol will be given over 30 seconds and on achieving absence of jaw thrust oropharyngeal airway of appropriate size will be inserted in the two groups.The size of the devices will be in accordance with the ideal body weight. The PLMA will be secured as per manufacturer’s guidelines, and oropharyngeal leak pressure will be determined. On any evidence of leak or inability to ventilate, the PLMA will be removed and reinserted. In the event of PLMA requiring more than 3 attempts to establish effective ventilation, patient will be ventilated using FM in the conventional manner. Patient will be ventilated using FM, if the SpO2 dropped to less than 92% between the attempts. Number of attempts at PLMA insertion will be documented. On being able to ventilate, paralysis will be achieved with atracurium 0.5mg/kg. On being unable to establish ventilation using PLMA or FM, patient will be allowed to wake up and alternative technique will be opted.

All patients will be mechanically ventilated receive volume control ventilation with PEEP at FiO2 of 1.0 for 5 minutes. Ventilator settings used will be: tidal volume 8 ml/kg, frequency 12 min, Inspiratory/Expiratory 1: 2with a fresh gas flow of 6 l/min of oxygen.At the end of 5 minutes, ventilation will be seized and time from cessation of ventilation to point when SpO2 drops to 92% will be recorded as SAT. Following this,mechanical ventilation will be resumed and time to achieve SpO2 of 98% will be recorded. Arterial samples will be obtained at baseline (pO2bl), end of preoxygenation (pO2Preox), prior to cessation of ventilation (pO2apnea) and at time of reaching SpO2 92 %(pO2Hypox). SpO2 will be monitored continuously.

If case of any difficulty encountered during induction, the anesthesiologist would optimize patient care,ensure safety, and take all appropriate actions exclude the patient from the study.

Hypoxia will be defined as SpO2 <92%. All cases will be performed by anesthesiologists experienced in PLMA insertion and who have conducted anesthesia in > 200 morbidly obese patients.

Statistical Plan:

Sample Size;

On the basis of our preliminary data the mean percent difference of SAT between PLMA and FM groups is 27%.For a 90% power and 5% level of significance we will need to recruit a minimum of 35 patients in each group.

Statistical Analysis;

Descriptive statistical methods will be used to summarize the data from this study, with hypothesis testing performed for the outcome variable. The term “descriptive statistics” refers to number of subjects (n), mean, median, standard deviation (SD), minimum, and maximum for continuous data and frequencies and percentages for categorical data.

Normally distributed data are presented as mean and standard deviation; Skewed data are presented as medians quartiles (inter-quartile range)

Comparisons will be made using the chi-square test or Fisher Exact test for categorical variables, Mann-Whitney U test for skewed variables, and Student’s t-test for normally distributed variables.

All data collected during the study will be included in data listings. All statistical testing will be two-sided and will be performed using a significance (alpha) level of 0.05.

All statistical analyses will be conducted with the STATA System, version 9.0.

Randomization procedure:

Randomization will follow a computer generated allocation schedule (R version 2.12), using allocation concealment to prevent prior knowledge of treatment assignment. Numbers will be assigned in strict chronological sequence and study participants will be entered in sequence. Each study participant will be allocated a unique randomization number on successful completion of screening.

Patients will be randomized to receive either control or intervention group using a computer generated random number generated by using a computer generated randomization sequence. The randomization code will be sent to the Investigator (or designee) who will prepare treatments according to the randomization code.

To decrease bias and confounders the decision to accept or reject a participant will be made using inclusion and exclusion criteria. Informed consent will be obtained from participants prior to obtaining the randomization code. The codes will only be revealed to the researchers once the recruitment, data collection and wound measurement analysis are completed.

Abbreviations:

PLMA: ProSeal Laryngeal Mask Airway

FM: Facemask with oropharyngeal airway

BMI: Body Mass Index

IEC: Institutional Ethics Committee

PEEP:

SAT:

Participants Rights and Confidentiality

Institutional ethics committee (IEC) review

This protocol and the informed consent document and any subsequent modifications will be reviewed and approved by the IEC responsible for oversight of the study.

Informed Consent Forms

Informed consent forms will be taken by Investigator after explaining purpose, risks and benefits of the study. For the subjects who cannot read and write English, informed consent form in Hindi would be taken.

Participant Confidentiality

Any data, forms reports, and other records that leave the site will be identified only by a participant identification number (Participant ID) to maintain confidentiality. All records will be kept in a locked file cabinet. All computer entry and networking programs will be done using PIDs only. Information will not be released without written permission of the participant, except as necessary for monitoring by IEC and any regulatory authority.

Publications of Research Findings

After the completion of this study, we intend to immediately publish the results in international and national journals.

References

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