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the cuffed endotracheal tube ( ett ) has for long been considered the gold standard for securing airway , especially for procedures under general anesthesia .
the disadvantages of laryngoscopy and tracheal intubation are concomitant hemodynamic responses and damage to the oropharyngeal structures .
laryngeal mask airway ( lma ) was used instead to obviate the shortcomings of ett .
however , risk of gastric distension and inadequate ventilation with lma remained until the discovery of proseal lma ( plma ) in early 2000 .
plma has a dorsal cuff , in addition to the peripheral cuff of lma , which pushes the mask anterior to provide a better seal around the glottic aperture and permits use of high airway pressures without leak .
the drain tube parallel to the ventilation tube permits passive drainage of regurgitated gastric fluid away from the airway and serves as a passage for gastric tube .
many studies have compared plma with ett for ease of insertion , hemodynamic changes , and postoperative airway complications .
idrees and khan observed comparable peak airway pressures ( ppeak ) with both lma and ett .
few have compared the ventilatory efficacy and changes in airway dynamics seen with use of plma and ett in positive pressure ventilation .
hence , this study was conducted with the aim of comparing ventilatory parameters and airway dynamics , needed to maintain a state of normocarbia and stable hemodynamics , and postoperative complications between plma and ett in adult patients under general anesthesia .
a prospective , single blinded , randomized controlled clinical trial was undertaken and sample size was calculated by keeping power of study at 80% and confidence limits at 95% . to detect a 10% difference in tidal volume ( vt ) ,
we enrolled 30 patients undergoing elective surgeries under general anesthesia , in each group for better authenticity of results .
patients were randomly allocated using numbers generated from www.random.org into group plma and group ett .
patients belonging to american society of anaesthesiologists physical status i and ii aged between 20 and 40 years of either sex were included .
patients with anticipated difficult airway , hiatus hernia , gastroesophageal reflux disease , body mass index > 35 kg / m , head and neck surgeries , patients suffering from respiratory pathology and patients undergoing laparoscopic surgeries were excluded from the study .
all patients were premedicated with oral alprazolam 0.5 mg and ranitidine 150 mg on the night before surgery and were kept fasting overnight .
after shifting the patients to operation theatre , pulse oximeter , electrocardiograph and noninvasive blood pressure monitors were connected and basal parameters recorded .
propofol 2 mg / kg and intubation / insertion of device was facilitated by inj .
airway was secured with respective airway devices . in group plma , either plma size 3 ( weight 30 - 50 kg ) or plma size 4 ( weight 51 - 70 kg ) was inserted . in group ett ,
trachea was intubated under direct laryngoscopy using 7.5 mm ett in female patients or 8.5 mm i d in male patients .
correct placement of device was confirmed by adequate chest movement on ventilation and square wave on capnography .
adequacy of tight seal was confirmed by absence of audible leak from drain tube ( plma ) at ppeak of 20 cm h2o in plma group . in ett group ,
train of four ( tof ) , airway dynamics and ventilatory parameter monitors were connected following insertion of airway device .
ventilator settings consisted of respiratory rate 14 cycles / min , inspiratory : expiratory ratio 1:2 , fresh gas flow 2 l / min . vt was set at 6 ml / kg initially and adjusted subsequently with 1 ml / kg increments or decrements in vt if required , to maintain end tidal carbon dioxide ( etco2 ) between 35 and 40 mm hg .
anesthesia maintained with 65% n2o in oxygen , isoflurane 1 - 1.5% to maintain entropy values between 40 and 60 , inj .
atracurium 0.3 mg / kg bolus followed by infusion of 8 - 10 g / kg / min to maintain tof count < 1 .
peak airway pressure , vt , compliance ( compl . ) , airway resistance ( raw ) were recorded every minute after insertion for first 5 min and later every 10 min . other vital parameters such as heart rate ( hr ) , systolic and diastolic bp , mean arterial pressure ( map ) , oxygen saturation ( spo2 ) , etco2 were recorded after insertion of airway device , every minute for 1 5 min and then every 5 min till the end of surgery
. adequacy of ventilation was ensured by continuous monitoring of end tidal carbon di oxide and oxygen concentrations .
all parameters were recorded on spirometry and gas analysis module of s5 avance datex ohmeda anesthesia workstation .
patients were excluded from study , if a difference of > 3% between set and inspired vts , or a leak fraction > 10% was observed .
after removal of airway device , any complications such as coughing , laryngospasm , blood staining of airway device , tongue / dental trauma , and hoarseness of voice were observed .
data were analyzed using the spss version 17.0 chicago , il , usa statistical software .
demographic data of age , sex , weight and duration of surgery were comparable between the groups [ table 1 ] .
mean time for insertion of airway device in group plma was 16.43  12.31s , and in group ett it was 13.66  8.04s ( p = 0.308 ) . airway device was inserted in the first attempt in 28 patients in group plma as compared to 29 in group ett .
one patient in either group needed second attempt for securing airway , and one patient of group plma required 3 attempts .
mean spo2 in group plma was 99.40  0.0695% and in group ett , it was 98.45  0.83% ( p = 0.50 ) .
mean etco2 was 35.11  2.82 mm hg in group plma and 37.12  3.17 mm hg in group ett ( p = 0.656 ) [ table 2 ] .
spo2 , etco2 , tidal volume and insertion details the vt initially set at 6 ml / kg was comparable in both groups ( group plma-318  41.96 ml , group ett-329.67  43.98 ml p = 0.276 ) . mean adjusted vt to maintain etco2 between 35 and 40 mm hg was 317.68  51.90 ml in group plma as compared to 411.55  65.71 ml in group ett ( p < 0.01 ) .
the average difference between set vt and adjusted vt in group plma was 0.31 ml ( p = 0.974 ) as compared to 81.89 ml ( p < 0.01 ) in group ett . in group ett the vt had to be increased significantly from set vt to maintain etco2 between 35 and 40 mm hg .
the mean compl . in group plma was 29.02  4.54 ml / cm h2o while in group ett it was 33.52  2.89 ml / cm h2o .
the values were statistically significant in the 1 5 min after insertion of airway device ( p < 0.05 ) .
mean ppeak in group plma was 12.95  2.62 cm of h2 0 as compared to 16.02  2.59 cm of h2 0 in group ett ( p = 0.003 ) and was statistically significant throughout the surgery .
mean raw in group plma was 10.65  2.88 cm h2o / l / s compared to 10.01  2.05 cm h2o / l / s in group ett ( p = 0.256 ) [ figure 1 ] .
graph showing comparison of compliance , peak airway pressures and airway resistance heart rate was significantly lesser in the 1 min after insertion in group plma ( p = 0.043 ) , but comparable subsequently throughout surgery in both groups .
the systolic , diastolic and map s were lower in group plma at 1 and 2 min following insertion and after removal ( p < 0.05 ) [ figure 2 ] .
graph showing comparison of heart rate ( mean + standard deviation [ s.d ] ) and mean arterial pressure ( mean  s.d ) coughing was seen in one patient in group plma as compared to 10 patients in group ett , this was statistically significant ( p = 0.006 ) .
incidence of blood staining of device was comparable in both groups , 10 cases in group plma and 16 cases in group ett .
in the present study , plma maintained adequate ventilation using lower vt and ppeak compared to ett . unlike previous studies , where only ppeak was assessed , this study attempts to assess various additional parameters of respiratory mechanics , making it unique . achieving adequate ventilation and maintaining
in their review , observed that lower vt ventilation strategy had lesser incidence of developing acute lung injury in patients undergoing major abdominal , thoracic , and cardiovascular surgeries . in our study
the average vt needed to achieve adequate ventilation , as evidenced by spo2 and etco2 , was significantly lower in plma group .
berry and coworkers compared performance of lma with ett at different vts and noted that ppeak was lesser in lma group even at lower vt ventilation , along with significantly lower raw .
the design of plma has some influence on resistive load of the device and was found to offer greater resistive load compared to classic lma .
however , correct placement of the device and leak fraction play a crucial role in measurement of airway dynamics parameters .
natalini et al . observed that in obese patients undergoing general anesthesia , the ppeaks were comparable between plma and lma . in the present study ,
the ppeak was significantly lesser in plma group throughout surgery while the raw was comparable in both groups .
though the internal diameter of airway tube of proseal lma is narrow compared to that of ett in the present study , the shorter length of proseal lma compared to that of ett might be the nullifying factor accounting for similar raw in both groups .
all possible precautions were taken to minimize leak fraction and patients with leak fraction > 10% were excluded .
compared plma with laryngeal tube ; it was observed that ppeaks were clinically comparable between both devices . peripheral spo2 and etco2 monitoring have been considered as measures of adequate ventilation .
spo2 and etco2 were comparable in both groups in our study indicating adequate ventilation with both the devices .
we did not notice a difference between inspired and expired oxygen concentration of > 5% in any of the patients .
higher ppeaks and large vts have been implicated as risk factors for development of barotrauma and volutrauma in critically ill mechanically ventilated patients .
the plma maintained adequate ventilation at lower vts and airway pressures as compared with ett .
hence , possibility of barotrauma and volutrauma with plma may be low as compared to ett .
lower ppeaks noticed in patients receiving plma may be due to lower vts used during mechanical ventilation .
types of surgeries in both groups were comparable thus the possible effects of surgery on airway parameters are ruled out .
sympathetic stimulation by laryngoscopy and intubation is known to induce hemodynamic response during ett insertion .
we observed that hemodynamic parameters were lower in plma group immediately after insertion of airway device and also soon after removal the same , though hr did not alter in post removal period in plma group .
the incidence of coughing and hoarseness of voice was lower with plma as it is a supraglottic device .
the patient who developed laryngospasm in group ett was reintubated and electively ventilated for 20 min with 40% oxygen , which was followed by uneventful recovery .
there are limitations in the present study : 
 the double blinding was not possible in this study.incidentally most of the surgeries were of short duration lasting for 40 - 60 min .
hence the implications of this study need to be extrapolated with caution , to situations requiring longer duration of mechanical ventilation.late postoperative complications such as sore throat were not included in observations since it was focused mainly on intraoperative airway dynamics . 
 
incidentally most of the surgeries were of short duration lasting for 40 - 60 min .
hence the implications of this study need to be extrapolated with caution , to situations requiring longer duration of mechanical ventilation .
late postoperative complications such as sore throat were not included in observations since it was focused mainly on intraoperative airway dynamics .
the plma maintains adequate ventilation at significantly lower vts and peak pressures without increasing raw , and has minimal hemodynamic variations compared to ett .
background and aims : studies have demonstrated minimal hemodynamic variation and postoperative complications with proseal laryngeal mask airway ( plma ) compared to endotracheal tube ( ett ) . 
 hence , a study was conducted to compare the ventilatory parameters and airway dynamics required to maintain normocarbia and stable hemodynamics with plma and ett.material and methods : a prospective , randomized , single blinded study was conducted on 60 patients aged 20 - 40 years of american society of anesthesiologists class i and ii , divided into group plma and group ett . 
 standard anesthesia protocol was instituted . 
 group plma received plma sizes as per manufacturer 's recommendations and group ett received appropriate sized cuffed ett . 
 patients were initially ventilated at 14 bpm , i : e ratio 1:2 , tidal volume ( vt ) 6 ml / kg and later adjusted to maintain end tidal carbon dioxide ( etco2 ) between 35 and 40 mmhg . 
 peak airway pressure ( ppeak ) , compliance ( compl . ) , vt , airway resistance ( raw ) , hemodynamic parameters , oxygen saturation ( spo2 ) and etco2 were recorded throughout surgery . 
 postoperative complications if any , were noted.results:demographic parameters , raw , etco2 , spo2 were comparable between groups . 
 ppeak was lower and vt needed to maintain etco2 of 35 - 40 mmhg was lesser in group plma . 
 compl was low for 5 min after insertion of plma . 
 heart rate was significantly reduced at 1 min post insertion ; blood pressures were significantly lower upto 2 min after insertion and post removal in group plma . 
 incidence of cough was significantly lower in group plma.conclusion:proseal laryngeal mask airway maintains adequate ventilation at lower vts and minimal peak pressures , has lesser hemodynamic variations and lower incidence of postoperative cough compared to ett .