To the Editor:
We read with great interest a very informative and well-conducted study by Shono et al. titled “Positive End-expiratory Pressure and Distribution of Ventilation in Pneumoperitoneum Combined with Steep Trendelenburg Position” published in the Journal.1 The study has objectively shown that application of positive end-expiratory pressure (PEEP) of 15 cm H2O resulted in more homogeneous ventilation and favorable pulmonary physiologic effects during robot-assisted laparoscopic prostatectomy, but did not improve postoperative lung function. Whereas that authors have focused on the beneficial pulmonary effects of high PEEP values, the article would benefit readers considerably if the authors could address its potential ill effects on some other organ systems.
In this regard we wish to highlight our concern regarding application of high PEEP on intracranial pressure (ICP) in patients given a steep Trendelenberg position. It is known that ICP rises rapidly with pneumoperitoneum and this increase is more pronounced due to the effects of gravity in patients assuming the head-down Trendelenburg position.2,3 Increased intraabdominal pressure displaces the diaphragm cranially, narrowing the inferior vena cava and decreasing venous return which, in turn, increases the ICP.3 The high intrathoracic pressures due to positive pressure ventilation and high intraabdominal pressure due to pneumoperitoneum cause a triple compartment syndrome because of an increase in ICP. In susceptible populations such as patients with head injuries or patients who have undiagnosed intracranial pathology, neurologic deterioration could be a concern. Clinically, even minor adverse effects of raised ICP may present in different ways.4 In a study by Cooke et al., headache and nausea were found to be significantly higher after laparoscopic abdominal surgery, possibly due to raised ICP.4
Shono et al. have reported that phenylephrine requirement in the high PEEP group was significantly greater than in the normal PEEP group. For maintenance of cerebral perfusion pressure, a higher mean arterial pressure should have been targeted in view of the raised ICP. The authors have reported a raised arterial carbon dioxide of 49 ± 5 mm Hg which may also have detrimental effect on the ICP. Adjusting the respiratory rate to normalize the end tidal carbon dioxide could have been considered in the study design. In susceptible individuals, surgeries lasting 484 ± 81 min with a persistently high ICP resulting from a high PEEP of 15 cm H2O could result in a greater incidence of complications. These complications should be investigated before we can recommend universal application of a high PEEP in all patients. Prospective authors planning similar studies could consider adding incidence of adverse effects on ICP or intraocular pressure as one of their secondary objectives; otherwise, they could include these concerns as limitations of their study.
The authors declare no competing interests.