Pre-oxygenation in the obese patients : effects of peep versus position on tolerance to apnoea

الملخص EN

Background.

Obesity is associated with a reduction in time to desaturate during apnoea following standard pre-oxygenation and induction of anaesthesia.

Obese patients have more often difficult airway management; moreover arterial desaturation develops more rapidly than in non-obese patients.

In obese patients, reduced junctional residual capacity exacerbated by supine position might decrease the effectiveness of preoxygenation and the tolerance to apnoea.

Positive end expiratory pressure (PEEP) applied during induction of general anesthesia prevents atelectasis formation in non-obese as well as in obese patients.

Patients: Sixty obese patients (BM t35 kg m2) with ASA lor 11 undergoing surgery with general anaesthesia were randomly assigned to one of three groups: Group l(PEEP, n=20), Group 2 (25° head-up position n=20) and Group 3 (supine position (control), n=20).

Method: In the PEEP group, patients breathed 100% 02 through a continuous positive airway pressure device (10 cm H2O) for 5 min After induction of anesthesia, they were mechanically ventilated with PEEP (10 cm H20) for another 5 min until tracheal intubation.

In the the 25° head-up position (the 25° to the horizontal, as measured by a builder's inclinometer calibrated with a spirit level, was achieved by breaking the operating table at the hips to prevent patients from sliding off the table) and in the supine position group, the sequence was the same without any continuous positive airway pressure or PEEP.

We measured apnea duration until Spo2 reached 90% and we performed arterial blood gases analyses before induction (base line), just before apnea and at 90% Spo2.

Values were compared with two-way ANOVA and unpaired Student's t-test.

Results: Nonhypoxic apnea duration was longer in the PEEP group compared with the other two groups (188 ± 46 versus 165 ± 55, 127 ± 43 s).

There was a significant increase in the duration of apnea in the 25° head-up position group than the supine position group (P = 0.002) while there was insignificant change between 25° head-up position group and PEEP group.

Pao2 was higher before apnea and at 90% Spo2 in the PEEP group than the other two groups (P = 0.038, 0.221).

There was a significant increase in the Pao2 before apnea and at 90% Spo2 in the 25° head-up position group than the supine position group (P = 0.001, 0.226) while there was insignificant change in Pao2 between 25° head-up position group and PEEP group.

Conclusion: Application of positive airway pressure or 25° head-up position during induction of general anesthesia in obese patients increases nonhypoxic apnea duration and improved oxygenation.

This study proved that both methods (application of PEEP or 25° head-up position) during induction of general anesthesia were statistically similar as regard the effects on nonhypoxic apnea duration and oxygenation during induction of general anesthesia in obese patients.