Inspired gas humidity during mechanical ventilation: effects of humidification chamber, airway temperature probe position and environmental conditions.

OBJECTIVES: To determine the inspired gas humidity during mechanical ventilation with: (i) four different humidification chambers; (ii) two airway temperature probe (ATP) positions; (iii) five different humidicrib temperatures; and (iv) insulating the inspiratory limb with bubble wrap. METHODOLOGY: An observational study in the Neonatal Laboratory and Neonatal Intensive Care Unit, Westmead Hospital. The humidity of the inspired gas was measured at the proximal end of the endotracheal tube (ETT) during mechanical ventilation. Inspired humidity measurements were made with four different humidification chambers (Fisher & Paykel (F&P Healthcare Pty Ltd, Auckland, New Zealand) auto refill MR290. F&P manual refill MR310, Suruga (Suruga Inc. Humidifiers, Vincent Medical, Dongguan, China) manual refill MI-20 and MI-10F) with the humidity control (relative humidity setting) set at - 2. Measurements were made with the ATP positioned either; (A) at the distal end of the inspiratory tube inside the humidicrib or (B) outside the humidicrib 50 cm proximal to the ETT. The inspired gas temperatures were set at 36.5 degrees C and at 39.0 degrees C, respectively. For each of the different humidification chambers and ATP positions, inspired humidity measurements were made with the humidicrib temperature set at 30.8, 32.9, 35.2, 36.2, or 37.2 degrees C. Two further sets of measurements were made, one with the inspiratory limb insulated with bubble wrap and the second set without bubble wrap. RESULTS: There were significant differences in inspired humidity with the four humidification chambers at both ATP positions at all humidicrib temperatures. Both Suruga humidification chambers produced significantly higher inspired gas humidities under most conditions. Positioning the ATP outside the humidicrib produced significantly higher inspired gas humidities than with the ATP inside the humidicrib. Insulating the inspiratory tubing with bubble wrap also significantly improved the inspired gas humidity. CONCLUSIONS: Significant differences in inspired gas humidity were found with the humidification chambers tested. The position of the ATP and the set temperature had a significant impact on the absolute humidity of the inspired gas. In general, higher inspired gas humidities were obtained with the ATP outside the humidicrib. However, condensation of water close to the ETT appeared at low humidicrib temperatures (< 36.2 degrees C) with the ATP outside the humidicrib and extreme care should be taken that particulate water does not enter the lungs under these conditions.

Inspired gas temperature during mechanical ventilation: effects of environmental temperature and airway temperature probe position.

OBJECTIVES: To determine the inspired gas temperature during mechanical ventilation with: (i) five different humidicrib temperatures; (ii) two airway temperature probe (ATP) positions; and (iii) four ATP adaptors. METHODOLOGY: An observational study in the Neonatal Intensive Care Laboratory, Westmead Hospital. The inspired gas temperature was measured at the proximal end of the endotracheal tube (ETT) during conventional mechanical ventilation using a Tele-thermometer. Inspired gas temperature measurements were made with: (i) the humidicrib temperature set at 30.8. 32.9, 35.2, 36.2. or 37.2 degrees C; (ii) the ATP either (A) positioned inside the humidicrib at the distal end of the inspiratory tubing or (B) positioned outside the humidicrib 50 cm proximal to the ETT, with the inspired gas temperatures set at 36.5 and 39.0 degrees C, respectively; and (iii) the measurements repeated with four different ATP adaptors at each humidicrib temperature and each ATP position. RESULTS: With the ATP inside the humidicrib, there were no significant differences between set and actual inspired gas temperature. However, with the ATP outside the humidicrib, there were significant decreases in inspired gas temperature at each humidicrib temperature. For instance, with the ATP outside the humidicrib and set at 39.0 degrees C, the inspired gas temperature decreased to 34.7+/-0.2 degrees C at a humidicrib temperature of 30.8 degrees C and to 37.7+/-0.2 degrees C at a humidicrib temperature of 37.2 degrees C. The type of ATP adaptor also had a significant effect on inspired gas temperature. CONCLUSIONS: With the ATP placed outside the humidicrib and with variations of humidicrib temperature, infants are likely to have inspired gas temperatures that are significantly different to the desired temperature. Certain ATP adaptors cause these variations in inspired gas temperature to be more pronounced. Extreme care must be used to avoid suboptimal inspired gas temperatures with these environmental variations and the ATP positioned outside the humidicrib.

Serial phospholipid analysis in preterm infants: comparison of Exosurf and Survanta.

The initial clinical response to synthetic or natural surfactant is different and long-term complications from meta-analysis suggest that bronchopulmonary dysplasia and retinopathy of prematurity may be increased in infants given synthetic surfactant. It is possible that this is due to differences in the phospholipid composition of lung fluid following administration of these surfactants. Infants less than 32 weeks gestation with respiratory distress syndrome (RDS) were randomly assigned to receive either Exosurf, an artificial surfactant, or Survanta, a natural surfactant. Endotracheal or hypopharyngeal aspirates were obtained from these infants and from control infants who had normal lungs. The aspirates were taken prior to and up to 28 days following surfactant administration. The different phospholipids were separated by thin layer chromatography and expressed as a percent of total phospholipid measured. Infants with normal lungs had a higher proportion of phosphatidylcholine than those with RDS prior to treatment. The infants with normal lungs had a greater proportion of phosphatidylinositol in their lung aspirates than both treatment groups at 24 h. Infants in the Survanta group had a higher proportion of phosphatidylglycerol at 48 h than the group with normal lungs. No other differences were found in phospholipid composition up to 28 days. There were no major differences in the phospholipid profile in infants with RDS treated with either Exosurf or Survanta. In conclusion, neither the clinical differences initially seen between infants treated with either Exosurf or Survanta, nor the long-term outcome could be explained by the phospholipid composition of serial samples of lung aspirates.

Cytological changes in endotracheal aspirates associated with chronic lung disease.

Endotracheal aspirates taken serially from mechanically ventilated premature infants born at < 28 weeks gestation between March 1992 and August 1993 were studied to determine whether early cytological changes would be a good predictor of lung damage in infants who develop chronic lung disease (CLD). CLD was diagnosed if the infant required supplemental oxygen at 36 weeks corrected gestational age. Fifty-five infants were enrolled in the study, five died and of the 50 infants remaining, 17 (34%) developed CLD. The infants with CLD had a significantly lower gestation (25.5 +/- 1.8 (mean +/- 1 SD) versus 26.2 +/- 0.9 weeks, p < 0.05), significantly more required surfactant (14/17 vs. 16/33, p < 0.05) and were ventilated for a significantly longer period (43.3 +/- 26.6 vs. 19.3 +/- 12.8 days, p < 0.0001). Endotracheal aspirate cytology showed that infants with CLD had significantly more degenerated columnar epithelial cells on day 3 (p = 0.001), and more neutrophils on day 10 (p = 0.007). Though not predictive of CLD, cytological changes consistent with bronchial epithelial and pulmonary damage followed by an inflammatory response were found in the tracheal aspirates of a group of infants clinically diagnosed with CLD.

Chronic oxygen dependency in infants born at 24-32 weeks' gestation: the role of antenatal and neonatal factors.

OBJECTIVES: To study the incidence of chronic oxygen dependency (COD) among ventilated survivors born at 24-32 weeks gestation from 1986 to 1994 and to identify antenatal and neonatal factors that may have changed with time; and to identify antenatal and neonatal factors that could contribute to the development of COD in infants born at 24-32 weeks gestation using a case control model. METHODOLOGY: Infants born at 24-32 weeks gestation in one tertiary referral centre between 1986 and 1994 and admitted to the neonatal intensive care unit for respiratory support were studied. Data accumulated prospectively since 1986 in survivors of ventilation were analyzed to identify antenatal and neonatal factors that could have changed with time. The cohort of infants who developed COD were matched for gestation and time of birth with a control group of infants who did not have COD. Significant factors that could have contributed to the development of COD were identified using forward logistic regression analysis. RESULTS: The number of mothers admitted for threatened premature labour (TPL), and pregnancy induced hypertension decreased with time while the use of antenatal steroids and maternal antibiotics increased. More infants were delivered by Caesarean section during the later years. There was an increase in neonatal septicaemia with time while there were decreases in hyaline membrane disease, pneumothorax, pulmonary interstitial emphysema, use of high peak inspiratory pressure (PIP) and high inspired oxygen. The incidence of COD decreased. The case controlled study revealed a significant positive association between COD and male gender, birthweight less than the 10th percentile for gestation, PIP over 30 cm H2O, septicaemia and significant patent ductus arteriosus (PDA) requiring indomethacin. There was a negative association with TPL. CONCLUSIONS: Further decrease in COD can be achieved only if septicaemia, PDA and the use of high PIP can be avoided. The most effective way of reducing the incidence of COD is by reducing the incidence of prematurity.

Retinopathy of prematurity in infants less than 29 weeks' gestation: 3 1/2 years pre- and postsurfactant.

OBJECTIVE: To determine the effects of surfactant on retinopathy of prematurity (ROP). DESIGN: We compared infants for 3 1/2 years both before and after the introduction of surfactant in our neonatal intensive care unit (NICU) using prospectively collected data. Exogenous surfactant (Exosurf) was introduced into our NICU on July 1, 1991. METHODS: We compared the incidence and severity of ROP in two groups of infants born at less than 29 weeks' gestation who required cryo- or laser therapy. Premature infants born during the first 3 1/2 years following the introduction of surfactant were compared with those born during the 3 1/2-year period prior to its introduction. The infants were examined by one ophthalmologist (J.K.) and classified according to the International Classification of ROP. RESULTS: A total of 124 infants born presurfactant and 152 infants born postsurfactant were examined for the presence of ROP. No significant difference between the two groups regarding any stage of ROP or the necessity for treatment was found. In infants of less than 27 weeks' gestation, a significant reduction in the number requiring cryo- or laser therapy was noted (12 of 48 examined [25.0%] vs 6 of 62 examined [9.7%], respectively; P < 0.05). This decreased need for treatment, however, was found in infants without hyaline membrane disease who did not receive surfactant. CONCLUSION: Exosurf has had no significant impact on the incidence or severity of ROP. Due to its effect on improved survival rates, the surfactant produces a larger proportion of infants at risk of developing ROP. Other changes in NICU protocol may be causing a reduction in the incidence of severe ROP.

Retinopathy of prematurity in infants less than 29 weeks' gestation at birth.

From January 1986 to December 1991 we examined the eyes of 206 infants born at Westmead Hospital, Neonatal Intensive Care Unit who were less than 29 weeks' gestation at birth to determine the incidence of retinopathy of prematurity. Eighty-five infants (41.3%) had no retinopathy of prematurity (ROP) in either eye, 82 infants had stages 1 or 2 ROP (39.8%), 29 had stage 3 ROP (14.1%) and 11 had stage 4 ROP (5.3%). Of these, cryotherapy was performed in 18; six now have bilateral retinal detachment and are blind. The more severe stages of ROP were significantly associated with an increase in the number of days of oxygen supplementation, an increase in the number of days of mechanical ventilation and the presence of patent ductus arteriosus. Infants receiving steroids for mechanical ventilator dependence had a significantly greater chance of requiring cryotherapy (11 or 22 receiving steroids versus seven of 43 without steroids; P < 0.01).

Recovery of tracheal epithelium following high frequency ventilation at low inspired humidity.

We used scanning electron microscopy (SEM) and light microscopy (LM) to study the recovery of tracheal epithelium in newborn lambs damaged by high frequency flow interrupted ventilation (HFFIV) at low inspired humidity (30%). Newborn lambs were mechanically ventilated for 6 h, allowed to recover and subsequently killed at 2, 7 or 14 days. The recovery of the trachea above and below the tip of the endotracheal tube (ETT) was studied at these time periods and compared to a control non-intubated group and a group killed immediately after 6 h of ventilation. Above and below the ETT, SEM and LM revealed deciliation to be greatest 2 days after ventilation. The damaged tracheal mucosa had converted to non-ciliated epidermoid squamous metaplastic cells. Recovery was not complete by 14 days, although the squamous cells had already differentiated into goblet and ciliated columnar epithelial cells. No difference was seen in the rate of recovery of the tracheal mucosa above or below the tip of the ETT.