ABSTRACT
OBJECTIVE: To determine the inspired gas temperature at points from the endo-tracheal tube (ETT) circuit manifold to the tip of the ETT in a model neonatal lung. DESIGN: A model lung attached to standard ventilator circuit, autofeed chamber and humidifier was ventilated using typical pressure-limited, time cycled settings. Temperatures were measured at various distances along the ETT using a K-type thermocouple temperature probe. RESULTS: The inspired gas temperature dropped from the circuit temperature probe site (40 degrees C) to the proximal end of the ETT (37 degrees C). The temperature dropped further as it passed through the exposed part of the ETT (34 degrees C) but then warmed again on entering the lung model so that the inspired gas at the distal end of the ETT was 37 degrees C. Statistically significant differences were found with a one-way ANOVA P-value of <0.0001. The differences between each pair of mean temperatures were statistically significant (all P<0.001) except when comparing the proximal end of the ETT with midway down the ETT (Bonferroni's Multiple Comparison Test, P>0.05). CONCLUSIONS: Inspired gas temperature drops as it passes through the circuit temperature probe site, the proximal end of the ETT and the exposed part of the ETT. The inspired gas rewarms on entering the model lung and exits the ETT at the desired temperature. The effect of measuring temperature closer to the patient, setting the circuit temperature higher and/or increasing the ambient temperature through which the circuit passes, need to be evaluated.
Subject(s)
Inhalation , Intubation, Intratracheal/instrumentation , Models, Biological , Respiration, Artificial/instrumentation , Temperature , Environment, Controlled , Equipment Design , Humans , Infant, Newborn , Respiration, Artificial/methods , Ventilators, MechanicalABSTRACT
The objective of this paper is to establish a reference range of central venous pressure (CVP) values during the first 4 days of life in very low birth weight (VLBW) infants. A prospective observational study with continuous monitoring of CVP in VLBW newborns who had an umbilical venous catheter (UVC) positioned in or near the right atrium is conducted. All UVCs were inserted as part of normal care of the infants. The mean CVP (mCVP) was monitored for 72 h from recruitment, or until the UVC was removed. The mean mCVP was calculated for each infant. The median of the mean mCVPs was then calculated. Data were analysed in 17 infants. The median gestational age was 27 weeks and median birth weight was 940 g. Sixteen were mechanically ventilated and of these, six also received continuous positive airway pressure (CPAP) during the study period. One infant received no respiratory support. One infant died during the study period. The lowest mean mCVP was 2.8 mmHg and the highest was 13.9 mmHg. The median mean mCVP was 4.9 mmHg (interquartile range 4.4-6.1). The normal range of CVP in VLBW infants during the first 4 days of life is wider than previously suggested.
Subject(s)
Central Venous Pressure/physiology , Infant, Very Low Birth Weight/physiology , Female , Gestational Age , Humans , Infant, Newborn , Male , Reference Values , RespirationABSTRACT
The warming and humidification of inspired gases for ventilated neonates are routine. There are no data on the temperature of the gas at the airway opening in ventilated neonates. Is the inspired gas temperature at the airway opening, as expected and set on the humidifier, around 37 degrees C? We aimed to measure temperature at the airway opening and compare this with the circuit temperature. This was an observational study in a neonatal intensive care unit. Twenty-five mechanically ventilated infants were studied. All had humidifiers with chamber temperature set at 36 degrees C and the circuit temperature set at 37 degrees C. Two temperature probes were inserted and rested at the circuit-exit and at the airway opening, and temperatures were measured for 2 min in each infant. At this time, the circuit temperature was also noted. The mean (SD) temperature at the airway opening in infants nursed in incubators was 34.9 (1.2) degrees C, compared with radiant warmers where the mean (SD) was 33.1 (0.5) degrees C. The mean (SD) difference in temperature from the circuit temperature probe to the airway opening was greater under radiant warmers, with a mean (SD) drop of 3.9 (0.6) degrees C compared with a mean (SD) drop of 2.0 (1.3) degrees C in the incubators. In conclusion, the temperature at the circuit temperature probe does not reflect the temperature at the airway opening. Inspired gas temperatures are lower than the expected 37 degrees C with the normal circuits and usual humidifier settings.
Subject(s)
Body Temperature/physiology , Hyaline Membrane Disease/therapy , Respiration, Artificial/methods , Ventilators, Mechanical , Equipment Design , Equipment Safety , Female , Follow-Up Studies , Humans , Humidity , Hyaline Membrane Disease/diagnosis , Incubators , Infant, Newborn , Intensive Care Units, Neonatal , Lung Diseases/diagnosis , Lung Diseases/therapy , Male , Risk Assessment , Temperature , Treatment OutcomeABSTRACT
OBJECTIVE: To determine whether perfluorocarbon liquid can be condensed from gases containing perfluorocarbon vapour and whether the amount recovered varies with background flow rate. DESIGN AND SETTING: Bench-top experimental study in a neonatal laboratory. INTERVENTIONS: The expiratory limb of a standard ventilator circuit set-up was mimicked, with the addition of a chilled water jacket (Liebig) condenser. Perfluorocarbon vapour was passed through the circuit at a number of flow rates. MEASUREMENTS AND RESULTS: Perfluorocarbon vapour was passed through the circuit and the percentage recovery of liquid measured. More than 60% of the perfluorocarbon vapour was recovered at all flow rates (1, 2, 5 and 10 l/min), with significantly higher recovery obtained (up to 74%) at low flow rates (1 l/min). CONCLUSIONS: Using a simple condenser, more than 60% of perfluorocarbon liquid can be recovered without altering the function of an expiratory limb of a ventilator circuit.
