Hajo Reissmann

Use of dynamic compliance for open lung positive end-expiratory pressure titration in an experimental study

Objective: We tested whether the continuous monitoring of dynamic compliance could become a useful bedside tool for detecting the beginning of collapse of a fully recruited lung. Design: Prospective laboratory animal investigation. Setting: Clinical physiology research laboratory, University of Uppsala, Sweden. Subjects: Eight pigs submitted to repeated lung lavages. Interventions: Lung recruitment maneuver, the effect of which was confirmed by predefined oxygenation, lung mechanics, and computed tomography scan criteria, was followed by a positive end‐expiratory pressure (PEEP) reduction trial in a volume control mode with a tidal volume of 6 mL/kg. Every 10 mins, PEEP was reduced in steps of 2 cm H2O starting from 24 cm H2O. During PEEP reduction, lung collapse was defined by the maximum dynamic compliance value after which a first measurable decrease occurred. Open lung PEEP according to dynamic compliance was then defined as the level of PEEP before the point of collapse. This value was compared with oxygenation (Pao2) and CT scans. Measurements and Main Results: Pao2 and dynamic compliance were monitored continuously, whereas computed tomography scans were obtained at the end of each pressure step. Collapse defined by dynamic compliance occurred at a PEEP of 14 cm H2O. This level coincided with the oxygenation‐based collapse point when also shunt started to increase and occurred one step before the percentage of nonaerated tissue on the computed tomography exceeded 5%. Open lung PEEP was thus at 16 cm H2O, the level at which oxygenation and computed tomography scan confirmed a fully open, not yet collapsed lung condition. Conclusions: In this experimental model, the continuous monitoring of dynamic compliance identified the beginning of collapse after lung recruitment. These findings were confirmed by oxygenation and computed tomography scans. This method might become a valuable bedside tool for identifying the level of PEEP that prevents end‐expiratory collapse.

Compliance and dead space fraction indicate an optimal level of positive end-expiratory pressure after recruitment in anesthetized patients.

BACKGROUND:“Optimal” positive end-expiratory pressure (PEEP) can be defined as the PEEP that prevents recollapse after a recruitment maneuver, avoids over-distension, and, consequently, leads to optimal lung mechanics at minimal dead space ventilation. In this study, we analyzed the effects of PEEP and recruitment on functional residual capacity (FRC), compliance, arterial oxygen partial pressure (Pao2) and dead space fraction, and we determined the most suitable variables indicating optimal PEEP. METHODS:We studied 20 anesthetized patients with healthy lungs undergoing faciomaxillary surgery. After a stepwise increase of PEEP/inspiratory pressures (0/10, 5/15, 10/20, 15/25 cm H2O, each level lasting for 20 min) using a pressure-controlled ventilation mode, a recruitment maneuver (at 20/45 cm H2O for a maximum of 20 min) was performed, followed by a stepwise pressure reduction (15/25, 10/20, 5/15, 0/10 cm H2O, with 20 min at each level). At each pressure level, FRC, compliance, Pao2, and dead space fraction were measured. RESULTS:When comparing the values before and after recruitment at identical PEEP levels, all variables showed significant changes at 10/20 cm H2O; compliance was also significantly higher at the pressure step 15/25 cm H2O. In addition, FRC values showed significant differences at 5/15 cm H2O and 15/25 cm H2O. CONCLUSIONS:All variables showed the positive effects of PEEP in conjunction with a recruitment maneuver. Optimal PEEP was 10 cm H2O because at this pressure level the highest compliance value in conjunction with the lowest dead space fraction indicated a maximum amount of effectively expanded alveoli. FRC and Pao2 were insensitive to alveolar over-distension.

Reduction of anesthesia process times after the introduction of an internal transfer pricing system for anesthesia services

To improve operating room workflow, an internal transfer pricing system (ITPS) for anesthesia services was introduced in our hospital in 2001. The basic principle of the ITPS is that the department of anesthesia receives reimbursement only for the surgically controlled time, not for anesthesia-controlled time (ACT). A reduction in anesthesia process times is therefore beneficial for the anesthesia department. In this study, we analyzed the ACT (with its parts: preparation before induction, induction, extubation, and recovery room transfer) for 3 yr before and 3 yr after the introduction of the ITPS in 55,776 cases. Furthermore, the anesthesia cases were subsegmented into 10 different anesthesia techniques, and the process times were studied. The average total ACT was reduced from 40.4 ± 23.5 min in 1998 to 34.3 ± 21.7 min in 2003. The main effect came from reductions in anesthesia preparation time and recovery room transfer time, whereas induction and extubation time changed little. A significant reduction in average ACT was seen in 7 of 10 analyzed anesthesia techniques, ranging from 4 to 18 min. We conclude that transfer pricing of anesthesia services based on the surgically controlled time can be a successful approach to reduce anesthesia process times.