[ProSeal™laryngeal mask in normal weight and obese patients : oxygenation under pressure-controlled ventilation and different end-expiratory pressures].

BACKGROUND

Most of the data on combining pressure-controlled ventilation (PCV) with positive end-expiratory pressure (PEEP) come from studies with an endotracheal tube (ETT) whereas data on utilization of PEEP with a laryngeal mask airway (LMA) are limited. The LMA-ProSeal® (PLMA) forms a more effective seal of the airway than the LMA-Classic™ (CLMA). The application of PEEP when PCV is used with the PLMA could have an impact on oxygenation in adult patients.

METHODS

For this study 148 patients with an mean age of 44 years (range18-65 years) and mean weight of 86 kg (range 49-120 kg) were recruited in 2 groups: group N ((Normal)): body-mass index (BMI) <30 kg/m(2) and group O ((Obesity)) BMI ≥30 and <36 kg/m(2). Cardiovascular and pulmonary disease and a history of smoking were exclusion criteria in addition to the usual LMA contraindications. The bispectral index-guided (BIS) anesthesia technique was used with propofol, fentanyl, and remifentanil without muscle relaxants. Measurement of PLMA seal pressure served as recruitment maneuver and PCV was randomly combined with 0 cmH(2)O, 5 cmH(2)O or 8 cmH(2)O PEEP. An arterial blood gas sample was taken 50 min after induction of anesthesia under an inspiratory oxygen fraction (F(I)O(2)) of 0.3. In the first part partial oxygen pressure (p(a)O(2)) under 0 cmH(2)O was compared with p(a)O(2) under 5 cmH(2)O and in the second part p(a)O(2) under 5 cmH(2)O was compared with p(a)O(2) under 8 cmH(2)O. A significant difference was set as p<0.025.

RESULTS

The PLMA could be placed after 3 attempts in 147 patients. The mean seal pressure was in the range of 24-30 cm H(2)O. Application of randomized PEEP was possible in all patients and ventilation was comparable between corresponding groups. In group N no differences were found in part 1 (139±28 vs. 141±28 mmHg, p=0.88) or part 2 (127±24 vs. 134±26 mmHg, p=0.35). In group O there was a significant difference in p(a)O(2) in part 1 (75±12 vs. 94±18 mmHg, p=0.02) but not in part 2 (92±21 vs. 103±18 mmHg, p=0.04).

CONCLUSIONS

The application of PEEP when PCV is used with the PLMA results in improved oxygenation in obese patients with a BMI ≥30 and <36 kg/m(2) but not in normal weight patients. Alveolar recruitment produced by seal pressure measurements below 30 cm H(2)O was sufficient to produce a clinically significant improvement in oxygenation in most obese patients and there was a significant improvement of oxygenation with PEEP=5 cmH(2)O. Both findings are in contrast to findings of studies using an ETT which suggests that higher pressures (40 cmH(2)O) are needed for recruitment of collapsed alveoli and higher PEEP (10 cmH(2)O) is needed to produce a clinically significant improvement in oxygenation in obese patients. The results of this study support data showing that the consequences of bronchopulmonary airway reactions known to occur with an ETT are less pronounced or absent when an LMA is used.