Positive End-Expiratory Pressure Increases Plasma Catecholamine Levels in Non-Volume Loaded Dogs

Abstract

Positive end-expiratory pressure (PEEP) is commonly used in the treatment of critically ill patients whose sympathetic nervous system is stressed; however, PEEP's actions on sympathetic nervous system activity are unknown. We therefore measured the plasma noradrenaline response (an index of sympathetic nervous system activity) to graded doses of PEEP in nine mongrel dogs. After 30 minutes at each level of PEEP, plasma noradrenaline concentrations increased from baseline mean values of 300 (SD 108) pg/ml to 388 (SD 225) pg/ml (P< 0.05) at 5 cm, 433 (SD 255) pg/ml (P < 0.01) at 10 cm and 1194 (SD 882) pg/ml (P < 0.01) at 20 cm water pressure of PEEP. The increases in plasma noradrenaline concentrations correlated inversely (r =-0.43, P < 0.01) with PEEP-induced changes in cardiac output. Plasma adrenaline levels did not change significantly in response to 5 or 10 cm of PEEP; however, plasma adrenaline increased, while heart rate and mean arterial blood pressure fell, at 20 cm water pressure of PEEP (P < 0.05). Within 15 minutes after discontinuation of PEEP, the plasma catecholamine concentrations returned to baseline levels. Conclusions: 1. PEEP significantly increases sympathetic nervous system activity in a rapid, dosedependent, reversible manner; 2. the PEEP-induced increases in sympathetic activity may explain the reductions in organ blood flow which others have observed following the initiation of PEEP; 3. PEEP-related changes in sympathetic nervous system activity are a consequence of PEEPinduced reductions in cardiac output.

Constipation in long-term ventilated patients: Associated factors and impact on intensive care unit outcomes*

“…In accordance with experimental data (1,(12)(13)(14), the results of a univariate analysis suggest that in addition to the use of opiates and vasopressors, levels of PEEP applied, the severity of hypotension, and the severity of hypoxemia may have a significant impact on the production of stools in ventilated patients. A PaO 2 /FIO 2 ratio of Ͻ150 mm Hg and SBP values of Ͻ90 mm Hg a Passage of stools before Ͻ6 days after intensive care unit admission; b from the time of intubation; c selective decontamination of the digestive tract and nasal mupirocin with chlorhexidine body washing.…”

Effects of Dopexamine and Positive End-Expiratory Pressure on Intestinal Blood Flow and Oxygenation*

“…This increase in intrathoracic pressure results in the unloading of cardiopulmonary volume receptors, which usually elicits reflex sympathetic activation, increased norepinephrine release, and regional vasoconstriction. 44,45 However, increased plasma norepinephrine levels, 46 as well as unchanged systemic and regional norepinephrine levels, 47 have been reported during PEEP ventilation.…”

GI Complications in Patients Receiving Mechanical Ventilation

“…12 MV with PEEP is also associated with increased plasma-renin-angiotensin-aldosterone activity and elevated catecholamines because of sympathetic activation. [13][14][15] Moreover, these patients frequently receive catecholamine therapy for BP support. These neurohormonal alterations can contribute significantly to splanchnic hypoperfusion by leading to vasoconstriction and redistribution of blood away from the splanchnic vascular bed.…”