Significant Difference In PaCO2 Research Articles

Ventilación no invasiva por soporte de presión en pacientes con enfermedad pulmonar obstructiva crónica en insuficiencia respiratoria aguda hipercápnica ingresados en una unidad de hospitalización convencional de neumología

In patients with acute exacerbations of chronic obstructive pulmonary disease (COPD), noninvasive ventilatory support (NPPV) with bilevel positive airway pressure (BiPAP) may improve clinical and physiological parameters. The present study used a randomized, prospective design to evaluate the possible benefits of NPPV plus standard therapy versus standard therapy alone in patients admitted with acute hypercapnic respiratory failure in a respiratory unit of a tertiary hospital. Forty-one patients were included in the study. Of them, 20 were randomly allocated to receive NPPV with a standard mask connected to a BiPAP ventilatory assist device (Respironics Inc, Murrysville, PA) and 21 to standard therapy. Both groups had similar characteristics upon their admission in the hospital. The use of noninvasive ventilation significantly reduced the respiratory rates and improved the conscious level within the first 2 h (p < 0.001). There were significant differences in PaCO2 and pH (p < 0.05) at 6 h of treatment. The need for intubation was 5% in the NPPV group vs 14% in the control group. The length of hospital stay was significantly shorter in the NPPV group (7 vs 10 days; p < 0.01). Nasal NPPV was well tolerated and complications were uncommon and mild. Early use of noninvasive ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease leads to a more rapid improvement of physiological variables. Moreover, it is possible to apply this treatment in a general respiratory ward.

Nasopharyngeal oxygen therapy produces positive end-expiratory pressure in infants.

The World Health Organisation recommends nasopharyngeal catheters as a safe and efficient method of oxygen administration in infants. However, little is known about the mechanisms of the improvement in oxygenation. The aim of the present study was to determine whether nasopharyngeal oxygen therapy produces positive end-expiratory pressure (PEEP). Nine spontaneously breathing infants (median age 13 months, range 10 days to 20 months) after heart surgery were investigated. All patients had normal pulmonary blood flow at the time of the study (Qp:Qs=1:1). Oxygen (oxygen fraction 1.0) was delivered by an 8 F catheter inserted into the nasopharynx (tip just visible below the soft palate). The pulmonary mechanics were analysed using a single compartment model of the respiratory system. Oesophageal pressure (Pes) at end-expiration, dynamic lung compliance (C(L)) and resistance (R(L)), minute ventilation, PaCO2 and PaO2 were measured at baseline without a nasopharyngeal catheter or oxygen, and at oxygen flows of 0.5 l/min, 1.0 l/min and 2.0 l/min. All the flows generated significant increases in PEEP. Mean difference in PEEP (SD, paired t-test versus baseline): 1.6 cm H2O (1.4, P=0.008) with 0.5 l/min of oxygen; 2.8 cm H2O (2.7, P=0.014) with 1.0 l/min of oxygen; and 4.0 cm H2O (2.9, P = 0.004) with 2.0 l/min of oxygen. There was a significant correlation between all the nasopharyngeal flows (in ml/kg per min) and the generated PEEP (P<0.001) and between the C(L) values and the generated PEEP (P < 0.05). There was no significant difference in PaCO2 and R(L). Minute ventilation was significantly less with nasopharyngeal oxygen than at baseline. As expected, PaO2 increased significantly with increasing oxygen flows. Administration of oxygen through an 8 F nasopharyngeal catheter at flow rates recommended by the World Health Organisation (0.5 l/min in newborns, 1.0 l/min in infants) produces moderate amounts of positive end-expiratory pressure. The levels achieved may contribute to an improvement in oxygenation by altering the visco-elastic properties of the lung.

Catheter position and blood gases during constant-flow ventilation.

We studied the effect of catheter position and flow rate on gas exchange during constant-flow ventilation (CFV) in eight anesthetized, paralyzed dogs. The distal tips of the insufflation catheters were positioned 0.5, 2.0, 3.5, and 5.0 cm from the tracheal carina. Flow rates were varied between 10 and 55 l/min and steady-state arterial blood gases were measured. At a given flow rate, arterial CO2 pressure (PaCO2) decreased as CFV was administered further into the lung up to a distance of 3.5 cm from the carina; there were no significant differences in PaCO2 at 3.5 and 5.0 cm. For a given catheter position, PaCO2 decreased with increasing flow rate up to a flow rate of 40 l/min. Further increases in flow rate had no significant effect on PaCO2. Arterial O2 pressure (PaO2) was relatively constant at all flow rates and catheter positions. We conclude that, up to a point, CO2 elimination can be improved by positioning the catheters further into the lung; advancing the catheters further than 3.5 cm from the carina may cause over-ventilation of specific lung regions resulting in a relative plateau in CO2 elimination and relatively constant PaO2's. Positioning the catheters further into the lung permits the use of lower flow rates, thus potentially minimizing the risk of barotrauma.

Effects of inspiratory flow pattern on gas exchange in normal and abnormal lungs.

To study the influence of inspiratory flow pattern on gas exchange in normal and abnormal lungs, 15 dogs were mechanically ventilated with the ascending or descending half of a rectified sine-wave flow pattern during pentobarbital anesthesia. Blood-gas status and cardiac output were monitored during each pattern. Pulmonary injury was induced in 9 animals by prior injection of oleic acid into the right atrium. Ventilation was with room air and zero end-expiratory pressure. Although no significant difference was seen between the patterns in animals with normal lung function (PaO2 greater than 85 Torr on the ascending pattern), the descending pattern resulted in a rise in PaO2 of about 10% (P less than 0.01) in animals with abnormal lung function (PaO2 less than 70 Torr on the ascending pattern). No significant difference in PaCO2 or cardiac output was detected when flow pattern was changed in any of the animals. We conclude that inspiratory flow pattern is not a significant factor when ventilating normal lungs, but may improve gas exchange significantly when severe ventilation-perfusion maldistributions exist.