Effects of various ventilation modes on immunocompetence in surgical patients

The effects of controlled mechanical ventilation with PEEP (CMV), and spontaneous ventilation with continuous positive airway pressure (CPAP), CPAP with high frequency ventilation (CPAP-HFV) and spontaneous respiration without CPAP (SV) on immunocompetence were compared in open-heart surgery patients undergoing the weaning phase. T-lymphocyte and T-helper cell ratios decreased during CPAP (P less than 0.01) and SV (P less than 0.05). PWM-induced lymphocyte proliferative responses were decreased during CPAP-HFV (P less than 0.05), CPAP and SV (P less than 0.01) in whole blood and separated lymphocyte cultures compared to values during CMV. Con A-induced responses were also depressed during SV in whole blood cultures (P less than 0.01). When the synthesis and secretion of immunoglobulins were studied, only IgM production showed a decrease in PWM-stimulated cultures during SV (P less than 0.05). In spite of an increase in the cardiac index in the three spontaneous ventilation modes compared to CMV, a slight decrease instead of an immediate improvement was seen in immune responses on weaning to spontaneous ventilation modes.