The article presents the findings of a study to assess the efficacy of positive end-expiratory pressure (PEEP) in treating intraoperative hypoxemia during one-lung ventilation (OLV). The primary goals of the research were to assess the effectiveness of PEEP during OLV, assess preoperative predictors of response to PEEP, and explore settings that would heighten the effects of PEEP on oxygenation (Hoftman, Canales, Leduc, & Mahajan, 2011).PEEP is gaining popularity in thoracic surgery over alternatives such as continuous airway pressure (CPAP) that have been found unsuitable when coupled with video-assisted thorascopic surgery (VATS).
Having met all statutory requirements, 41 surgery patients from a university care center were selected for the study. Data collection was performed after OLV was initiated following the fiberoptic positioning of a double-lumen tracheal tube and general anesthesia (Hoftman, Canales, Leduc, & Mahajan, 2011). A number of variables that could predict or enhance response to PEEP were tested and analyzed. These included arterial oxygen partial pressure (PDO), cardiovascular performance parameters, and suggested perioperative variables (age, BMI, FEVI, and FEVI/FVC) (Hoftman, Canales, Leduc, & Mahajan, 2011).
Only Patients with a predefined PaO value (PaO [sub] 2 ≥ 20% during either PEEP5 or PEEP10 were defined as “PEEP responders” ( (Hoftman, Canales, Leduc, & Mahajan, 2011). T-tests and c [sub] 2O were used to analyze continuous and categorical variables in responders and non-responders. Cardiovascular-based measures were compared using repeated measures of ANOVA. For the study model, a P-value <0.05 was considered statistically significant ( (Hoftman, Canales, Leduc, & Mahajan, 2011).
The findings of the study indicate that the application of PEEP did not produce a positive change in arterial PaO from the pre-study value in reference to the whole study group (Hoftman, Canales, Leduc, & Mahajan, 2011). Changes in PaO were not statistically significant. Out of all the study participants, only 12(29%) demonstrated an increase in PaO. Of the 13 clinical variables analyzed, only intraoperative tidal volume/kg (Vt/kg) differed significantly between the two study groups. Additionally, no positive results were obtained for all the preoperative variables’ usefulness in predicting PEEP responsiveness.
However, multivariate analysis derived several combinations of Vt/kg, plateau pressure, and FEVI that were statistically significant predictors of PEEP responsiveness, although all lack clinical clarity ( (Hoftman, Canales, Leduc, & Mahajan, 2011). Importantly, the study augmented the findings of other previous ones that the application of PEEP to ventilated lungs is well tolerated in most patients with no bearing on heart rate or blood pressure (Hoftman, Canales, Leduc, & Mahajan, 2011).
The researchers concluded that PEEP ( 5 or 10) cmH [sub] 2 O applied to ventilated lungs during thoracic surgery does not improve PaO [sub] 2 in the majority of patients (Hoftman, Canales, Leduc, & Mahajan, 2011). However, they pointed out some patients do respond positively to PEEP but were unable to pinpoint the underlying triggering factors for this effect. Also, it could not be established which preoperative variables predicted positive response to PEEP. Only a high tidal volume of vt/kg was found to have a positive response to PEEP.
The study lacks validity in various aspects chief among them lack of randomness in the selection of sample. This predisposes it to a high degree of unintended bias and confounders that can significantly alter the results. The researchers employed an observational design. I found it narrow in scope and this gives it low generalizability value. This is primarily due to the low sample size (n=41). The study also did not incorporate best practices such as study controls.
However, the study was accurate in their analysis and findings through the choice and interpretation of t-tests and multivariate analysis. Although I found the article somewhat understandable, extensive medical jargon may lower its comprehensibility by beginners. A good statistical background is also necessary to connect the outcomes of the study. The high number of failed response rates and contradictions with similar studies also calls into question the nature of the study design.
References
Hoftman, N., Canales, C., Leduc, M., & Mahajan, A. (2011). Positive end-expiratory pressure during one-lung ventilation: Selecting ideal patients and ventilator settings with the aim of improving arterial oxygenation. Annals of Cardiac Anaesthesia, 14(3), 183.