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

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 functional 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. Sixty obese patients [BMI >/= 35 kg m -2] with ASA 1 or 11 undergoing surgery with general anaesthesia were randomly assigned to one of three groups: Group 1 [PEEP, n=20], Group 2 [25° head-up position n=20] and Group 3 [supine position [control], n=20]. In the PEEP group, patients breathed 100% 02 through a continuous positive airway pressure device [10 cm H 2O] for 5 mm. After induction of anesthesia, they were mechanically ventilated with PEEP [10 cm H 2O] for another 5 mm until tracheal intubation. In 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 Spo 2 reached 90% and we performed arterial blood gases analyses before induction [base line], just before apnea and at 90% Spo 2. Values were compared with two-way ANOVA and unpaired Student's test. Nonhypoxic apnea duration was longer in the PEEP group compared with the other two groups [188 +/- 46 versus 165 +/- 35, 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. Pao 2 was higher before apnea and at 90% Spo 2 in the PEEP group than the other two groups [P = 0.038, 0.221]. There was a significant increase in the Pao 2 before apnea and at 90% Spo 2 in the 25° head-up position group than the supine position group [P = 0.001, 0.226] while there was insignificant change in Pao 2 between 25° head-up position group and PEEP group. 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

Mechanical ventilation with traditional large tidal volume versus lower tidal volune in patients with acute lung injury: pulmonary and hemodynamic study

This study was carried out in the ICU of Assuit University Hospital. A total of 30 patients who fulfilled the criteria of acute lung injury [AL1] and ARDS with lung injury score of 2.5 were enrolled in the study. The patients were randomly classified into 2 groups namely traditional tidal volume group which was managed with TV of 10- 12 ml/kg, and lower tidal volume group which was managed with TV of 6 ml/kg. The patients were mechanically ventilated using SIMV mode. In the traditional group of patients, the plateau pressure was kept >/= 40 cm H2O, respiratory rate was adjusted to maintain PaCO2 of 35-45 mmHg. PEEP level was >/= 5cmH2O. in the lower tidal volume group, the PaCO2 was allowed to increase [permissive hypercarbia], unless the pH was severely affected 7.2, to allow lowering of the plateau pressure to 25-30 cmH2O. PEEP was used according to the calculation of optimal PEEP. In both groups of patients, the FiO2 was adjusted to maintain PaO2 60 mmHg, and arterial oxygen saturation >/= 90%. Traditional or protective mechanical ventilation was maintained until the patient was extubated or died. The following parameters were studied for 17 days including: hemodynamics [HR. MAP, CVP, MPAP, PCWP, and CI], arterial blood gases and oxygenation parameters [pH, PaCO2, HCO3, PaO2, PvO2, QS/QT, PaO2/Fi02]; lung mechanics [PP, PIP, CST]. The present results demonstrated that the mean value of HR was mildly decreased in the traditional tidal volume group while it was increased in the lower tidal volume group throughout all days of the study. An initial decrease in MAP, which was followed by an increase, was found in the traditional tidal e group. But lower tidal volume group demonstrated a continuous rise in MAP. Both groups of patients demonstrated an increase in CVP, MPAP and PCWP levels in most of investigated days especially in lower tidal volume group. Reasonable values of CI were observed in both groups. The mean value of PaCO2 was found to be increased in the lower tidal volume group in the early period of the study resulting in a lower PH. The greater rise in HCO3 found in later period resulting in methiogation of the increase in pH. In the conventional TV group of patients, the PH, PaCO2 and HCO3 were within its normal limits. The conventional tidal volume group revealed more elevation in PaO2 levels than lower tidal volume group in the earlier period of the study. Later on, the PaO2 levels in the lower tidal volume group were increased to greater levels than traditional tidal volume group. Similar effects were obtained concernbg PaO2/FiO2 levels in both groups. The shunt fraction was mildly improved in both studied groups especially in lower TV group, but still it did not achieve its normal levels. In both groups there was an increase in the levels of the PvO2 during most investigated days of mechanics ventilation Better respiratory mechanics were found in lower tidal volume group The plateau pressure was less, the peak inspiratory pressure was also less, and static compliance was greater in this group as compared with traditional tidal volume group. In conclusion, the consequences of application of this lung protective strategy resulted in modest effects regarding the investigated hemodynamics due to modest increments in PaCO2. Lower tidal volume group of patients demonstrated better oxygenation parameters and better improvement in lung mechanics. Further studies may be needed to investigate the combined use of other ventilatory strategies, for example: prone positioning in addition to the one applied in this work to obtain better results regarding the studied oxygenation