Volume-targeted ventilation and arterial carbon dioxide in neonates

OBJECTIVES: To review the arterial carbon dioxide tensions (PaCO(2)) in newborn infants ventilated using synchronized intermittent mandatory ventilation (SIMV) in volume guarantee mode (using the Dr?ger Babylog 8000+) with a unit policy targeting tidal volumes of approximately 4 mL/kg. METHODS: Data on ventilator settings and arterial PaCO(2) levels were collected on all arterial blood gases (ABG; n = 288) from 50 neonates (<33 weeks gestational age) ventilated using the Dr?ger Babylog 8000+ ventilator (Dr?ger Medizintechnik GmbH, Lübeck, Germany) in SIMV plus volume guarantee mode. Data were analysed for all blood gases done on the entire cohort in the first 48 h of life and a subanalysis was done on the first gas for each infant (n = 38) ventilated using volume guarantee from admission to the nursery. The number of ABG showing severe hypocapnoea (PaCO(2) < 25 mmHg) and/or severe hypercapnoea (PaCO(2) > 65 mmHg) were determined. RESULTS: The mean (SD) PaCO(2) during the first 48 h was 46.6 (9.0) mmHg. The mean (SD) PaCO(2) on the first blood gas of those infants commenced on volume guarantee from admission was 45.1 (12.5) mmHg. Severe hypo- or hypercapnoea occurred in 8% of infants at the time of their first blood gas measurement, and in <4% of blood gas measurements in the first 48 h. CONCLUSIONS: Infants ventilated with volume guarantee ventilation targeting approximately 4 mL/kg (range: 2.9-5.1) have acceptable PaCO(2) levels at the first blood gas measurement and during the first 48 h of life; and avoid severe hypo- or hypercapnoea over 90% of the time.     

Effects of intravenous glucose loading on oxygen consumption, carbon dioxide production, and resting energy expenditure in infants with bronchopulmonary dysplasia

To determine the effects of intravenous glucose loading on basal oxygen consumption, resting energy expenditure, and basal carbon dioxide production in infants with bronchopulmonary dysplasia who were still oxygen dependent, we administered intravenous glucose loads of 4 and 12 mg/kg-1/min-1 on 2 consecutive days, under identical experimental conditions, to six infants with bronchopulmonary dysplasia and six healthy control subjects. Infants were not fed for 9 hours before and during the 4- to 6-hour study periods; the intravenous glucose infusion, along with an amino acid mixture (2 gm.kg-1.24 hr-1), was started at the beginning of the fasting period. Oxygen consumption and carbon dioxide production and resting energy expenditure were measured by a flow-through indirect calorimetry technique under basal conditions. Infants with oxygen-dependent bronchopulmonary dysplasia had significantly higher basal oxygen consumption and resting energy expenditure than did control infants and significantly higher basal carbon dioxide production during the high glucose infusion. With glucose loading, infants with bronchopulmonary dysplasia had a significant rise in basal oxygen consumption (7.91 +/- 0.91 ml.kg-1.min-1 to 9.65 +/- 1.35 ml.kg-1.min-1, p less than 0.05), basal carbon dioxide production (5.93 +/- 0.72 ml.kg-1.min-1 to 7.10 +/- 1.04 ml.kg-1.min-1), and resting energy expenditure (53.8 +/- 5.75 kcal.kg-1.24 hr-1 to 65.3 +/- 7.0 kcal.kg-1.24 hr-1, all p values less than 0.05). Control infants had no significant changes with intravenous glucose loading. We conclude that intravenous glucose loading in infants with bronchopulmonary dysplasia resulted in a net increase in resting energy expenditure, which should be taken into account in assessing their energy intake during nutritional management. The risk of pulmonary stress caused by an increase in basal oxygen consumption and carbon dioxide production resulting from glucose load should also be considered.     

Effect of limb cooling on peripheral and global oxygen consumption in neonates

AIM: To evaluate peripheral oxygen consumption (VO(2)) measurements using near infrared spectroscopy (NIRS) with arterial occlusion in healthy term neonates by studying the effect of limb cooling on peripheral and global VO(2). SUBJECTS AND METHODS: Twenty two healthy term neonates were studied. Peripheral VO(2) was measured by NIRS using arterial occlusion and measurement of the oxyhaemoglobin (HbO(2)) decrement slope. Global VO(2) was measured by open circuit calorimetry. Global and peripheral VO(2) was measured in each neonate before and after limb cooling. RESULTS: In 10 neonates, a fall in forearm temperature of 2.2 degrees C (mild cooling) decreased forearm VO(2) by 19.6% (p < 0.01). Global VO(2) did not change. In 12 neonates, a fall in forearm temperature of 4 degrees C (moderate cooling) decreased forearm VO(2) by 34.7% (p < 0.01). Global VO(2) increased by 17.6% (p < 0.05). CONCLUSIONS: The NIRS arterial occlusion method is able to measure changes in peripheral VO(2) induced by limb cooling. The changes are more pronounced with moderate limb cooling when a concomitant rise in global VO(2) is observed. Change in peripheral temperature must be taken into consideration in the interpretation of peripheral VO(2) measurements in neonates.     

Arterialisation of transcutaneous oxygen and carbon dioxide.

We compared previously calculated global correction factors for oxygen and carbon dioxide arterial/transcutaneous ratios with individual in vivo calibrations from the first arterial sample. In infants beyond the neonatal period and older children in vivo calibration confers little benefit over the use of a global calibration correction factor for transcutaneous carbon dioxide, and may reduce the precision with which arterial oxygen can be estimated from transcutaneous oxygen.     

无创经皮监测氧气和二氧化碳在新生儿的应用

无创经皮监测(transcutaneous monitoring,TCM)氧气和二氧化碳是新生儿重症监护室(neo-natal intensive care unit,NICU)的常用技术,具有连续性、无创性的特点,能直观反映危重新生儿呼吸和循环功能的变化,对新生儿监护意义重大.该文阐述TCM的使用方法,比较TCM与其他监测手段的优缺点,并介绍其在新生儿转运及NICU的应用.     

Transcutaneous oxygen and carbon dioxide monitoring in intensive care.

Transcutaneous oxygen (TcPo2) and carbon dioxide (TcPco2) tensions were compared with arterial values in 23 children aged 4 months to 14 years, all requiring some form of respiratory support, but not in shock. Electrodes were placed on the upper chest and were heated to 45 degrees C. For TcPo2 and arterial oxygen (Pao2) a tight linear correlation over the range 6 to 14 kPa was found. Arterial carbon dioxide (Paco2) ranged between 2.63 and 6.8 kPa, and over this range a linear regression adequately described the relation of TcPco2 to Paco2. No effects of age were found for the relation between TcPo2 and Pao2. Over a four hour period, the mean ratio TcPo2/Pao2 rose significantly from 0.96 to 1.04, while the mean ratio of TcPco2/Paco2 fell from 1.65 to 1.62. Five children developed superficial burns which were still present at 48 hours. In children who require respiratory support but are not in shock, TcPo2 and TcPco2 bear a constant and predictable relation to Pao2 and Paco2, and can predict arterial values within clinically acceptable tolerances.     

Ventilatory interaction between oxygen and carbon dioxide in the preterm primate

The steady state ventilatory response to inhaled CO2 was measured in eleven unanesthetized premature Macaca nemestrina during the first 3 wk of life in different steady state background O2 mixtures hypoxia (FIO2 = 0.08 or 0.12), normoxia (FIO2 = 0.21) and hyperoxia (FIO2 = 0.96). Hyperoxic delta VI/delta PACO2 and delta P0.2/ delta PACO2 were significantly greater than hypoxic delta VI/ delta PACO2 and delta P0.2/delta PACO2, respectively, at both 2 and 21 days postnatal age by the Mann Whitney test of nonparametric ranking (2 days: 89.. and 80.2 degrees versus 88.7 and 56.4 degrees, respectively; 21 days: 89.3 and 76.6 degrees versus 50.2 and 57.1 degrees, respectively; p less than 0.05). Hypoxic delta VI/delta PACO2 was significantly depressed compared to normoxic delta VI/ delta PACO2 only at 21 days of age (50.2 versus 89.4 degrees, respectively; p less than 0.05); hyperoxic CO2 sensitivity and normoxic CO2 sensitivity did not differ at either age. The ventilatory interaction between O2-CO2 in the neonatal primate appears to be the inverse of the typical adult ventilatory interaction. It is hypothesized that differential changes in brain stem blood flow between neonates and adults might explain this difference in O2-CO2 ventilatory interaction.     

Effect of a change in global metabolic rate on peripheral oxygen consumption in neonates

AIM: To evaluate the effect of an induced change in global metabolic rate on peripheral oxygen consumption (VO(2)) in healthy full term neonates. SUBJECTS AND METHODS: Twenty four healthy full term neonates were studied. Peripheral VO(2) was measured by near infrared spectroscopy (NIRS) using arterial occlusion and measurement of the oxyhaemoglobin (HbO(2)) decrement slope. Global VO(2) was measured by open circuit calorimetry. Global and peripheral VO(2) were measured in each neonate before and after a routine bath. Abdominal and forearm skin temperatures were also recorded. RESULTS: Nineteen neonates completed the study. Global VO(2) increased by 30.7% (p = 0.001), and peripheral VO(2) by 23.1% (p = 0.001). A correlation between the fractional changes in global and peripheral VO(2) was apparent (r = 0.76, p = 0.001). Abdominal skin temperature decreased by 0.8 degrees C (p = 0.001), and forearm skin temperature by 0.6 degrees C (p = 0.04). CONCLUSIONS: Measurement of peripheral VO(2) using NIRS with arterial occlusion is responsive to conditions that increase global metabolic rate. Any change in global VO(2) must be taken into consideration during the interpretation of peripheral VO(2) measurements in neonates.     

Evaluation of two combined oxygen and carbon dioxide transcutaneous sensors.

Two combined oxygen and carbon dioxide electrodes were assessed in neonates, infants, and children up to 16 years. They were convenient to use and the measurement error for PtcCO2 was acceptable. In both models, however, the PtcO2 electrode had a reduced performance compared with a single electrode.     

Blood oxygen, carbon dioxide and pH levels prior to diagnosis of retinopathy of prematurity

We examined the eyes of all infants in our Neonatal Intensive Care Unit from 1979 to 1981 who were premature and/or had exposure to increased ambient oxygen. From these 1,012 neonates, 19 were found to have Grade III or worse acute retinopathy of prematurity (ROP) in at least one eye. We studied the graphic relationship of the mean daily values for blood Pc02, Pa02, PC02, and pH and the production of retinopathy of prematurity in these infants and compared the results with a similar group of infants who had similar birthweight, gestational age and Vitamin E administration. The comparison group patients were in the hospital during this same period of time and did not have Grade III ROP. There was no characteristic level, peak or pattern of these values that could identify or predict which infants would develop ROP.     

主流呼气末二氧化碳动态监测在机械通气早产儿呼吸窘迫综合征中的临床应用

目的 探讨呼气末二氧化碳监测在新生儿呼吸窘迫综合征(NRDS)临床中的应用.方法 对23例气管插管机械通气的NRDS早产儿进行持续主流呼气末二氧化碳(PetCO2)监测,并同时配对检测112例次动脉血气分析,比较呼气末二氧化碳分压与动脉二氧化碳分压(PaCO2)的关系.结果 112例次NRDS早产儿动脉血气分析PaC2平均为(38.2±5.6)mmHg,对应的Pet-CO2平均为(32.4±4.9)mmHg,两者有显著相关性,相关系数r为0.68,P<0.01;肺部病变较轻者(Ⅱ级NRDS)比肺部病变较严重者(Ⅲ级、Ⅳ级NRDS)PetCO2更能准确地反应PaCO2的状况.结论 无创性主流呼气末二氧化碳监测适用于气管插管机械通气的NRDS的早产儿,能较准确地反映PaCO2的水平,但对重型NRDS有局限性.     

Measurement of carbon dioxide production rate in sick ventilated premature infants

A new method is described for measuring the rate of carbon dioxide production, and hence for estimating energy expenditure, in preterm infants receiving assisted ventilation. In a validation study, the mean error in carbon dioxide measurement was 1.9%. Measurements were made, over a 45-min period, on 11 sick, ventilated subjects and carbon dioxide production rate was 5.2 +/- 0.7 (SD) ml/min X kg body weight. We suggest that continuous monitoring of carbon dioxide output will contribute to the clinical assessment of the effects of different ventilator settings on pulmonary gas exchange and that estimated values for energy expenditure will be of value in nutritional studies on sick ventilated infants.     

Measurement of carbon dioxide production in very low birth weight babies

BACKGROUND: CO2 production is most commonly measured by using indirect calorimetry to quantify elimination of CO(2) in breath (VCO2). An alternative is to measure the rate at which CO2 appears in the body pool (RaCO2) by infusing a (13)C labelled bicarbonate tracer. VCO2 and RaCO2 generally differ but are related by c, a factor that adjusts for the incomplete recovery of infused tracer in the breath. The literature relating to human studies cites a wide range of values for c but the only neonatal study to determine c empirically estimated a mean value of 0.77. AIM: To estimate fractional recovery rate, c, in very low birthweight babies, and assess the feasibility of using the isotopic technique to measure CO2 production during mechanical ventilation. METHOD: Eleven spontaneously breathing, continuously fed, very low birthweight infants (median birth weight 1060 g, median gestational age 29 weeks) were studied. RESULTS: Mean (SD) VCO2 was 9.0 (2.0) ml/min (standard temperature and pressure dry, STPD) and mean (SD) RaCO2 was 9.6 (2.1) ml/min (STPD). The mean (SD) value of c was estimated as 0.95 (0.13). The 95% confidence intervals of the mean were 0.87-1.03. CONCLUSIONS: The results emphasise the importance of measuring c for a given study population rather than assuming a value based on adult studies. The close approximation of RaCO2 and VCO2 in this group of babies implies that the labelled bicarbonate infusion technique could be used to measure simply CO2 production during mechanical ventilation.     

Hepatic oxygen consumption, lactate uptake, and glucose production in neonatal lambs

Previous studies have evaluated neonatal hepatic metabolism in vitro, and neonatal hepatic oxygen consumption has been measured in vivo, but direct measurements of neonatal hepatic metabolism have not been reported. We studied seven neonatal lambs at age 7-10 days after placing catheters chronically in the hepatic vein, portal vein, descending aorta, left ventricle, and inferior vena cava. Hepatic blood flow was measured by the radioactive microsphere technique. Oxygen consumption and glucose and lactate fluxes were measured using the Fick principle. 14C-lactate was infused intravenously and lactate and glucose specific activities were measured and used to calculate hepatic gluconeogenesis from lactate. Neonatal hepatic blood flow was 254.5 +/- 50.3 ml/min/100 g (mean +/- SD) with 5.4 +/- 4.6% from the hepatic artery and 94.6 +/- 4.6% from the portal vein. Hepatic oxygen consumption was 7.2 +/- 2.4 ml/min/100 g and oxygen extraction was 44.9 +/- 15.4%. Oxygen extraction correlated inversely with oxygen delivery. In the seven lambs, there was net hepatic lactate uptake of 10.2 +/- 5.0 mg/min/100 g (1.13 +/- 0.56 mM) and hepatic glucose production of 30.8 +/- 11.3 mg/min/100 g (1.71 +/- 0.62 mM). In the five lambs in which hepatic gluconeogenesis was measured, 12.4 +/- 5 mg (1.37 +/- 0.56 mM) of lactate was converted to glucose per 100 g liver, accounting for 38.4% of the hepatic glucose production in these lambs. Blood flow and oxygen and substrate delivery to the neonatal liver are lower than those to the fetal liver but the neonatal liver extracts more oxygen and substrates and is able to produce glucose by gluconeogenesis from lactate.     

Evaluation of a transcutaneous oxygen and carbon dioxide monitor in a neonatal intensive care department

Transcutaneous-PO2 (tc-PO2 (tc-PCO2) at 44 degrees C and transcutaneous-PCO2) at 38, 42, 43 and 44 degrees C were measured with a currently available monitoring system (TCM222, Radiometer, Copenhagen) in 64 newborn infants with severe respiratory insufficiency during the first five days of life. Tc-PCO2 at all four temperatures correlated better with arterial blood-PCO2 (aB-PCO2), than tc-PO2 with aB-PO2. However, the sensitivity and specificity of tc-PO2 and tc-PCO2 were similar with regard to maintaining aB-PO2 and aB-PCO2 within specified limits. Tc-PCO2 increased relatively with increasing electrode temperature by a factor which was similar to the anaerobic temperature coefficient of PCO2 in blood. The coefficient of variation of duplicate measurements was 10% for tc-PO2 and 5% for tc-PCO2. Electrode drift after an average of 3 hours patient monitoring was 2% +/- 6% (1 SD) for tc-PO2 and -3% +/- 6% for tc-PCO2. We conclude that tc-PO2 and tc-PCO2 are a valuable supplement to arterial blood gas measurements, but the variable correlation with arterial blood gas values and the electrode drifts which may occur, mean that they cannot fully replace arterial sampling.     

Noninvasive, continuous monitoring of artificial respiration in premature and newborn infants by the constant measurement of respiratory minute volume, oxygen consumption and carbon dioxide release

A system of instrumentation for the continuous measurement of the respiratory gases during assisted ventilation of neonates and premature infants based upon "breath-by-breath-method" is described. The four respiratory parameters flow (V), ventilation pressure (p), oxygen-concentration and carbon dioxide-concentration are measured. These datas are processed by a computer to generate a continuous display of the respiratory minute volume, the tidal volume, the breath rate, the oxygen consumption and the carbon dioxide production. All parameters are stored and can be displayed or plotted as trends. The flow-measurement is performed using hot-wire-anemometry. The very small flow sensor is adapted directly to the tube. Next to this sensor, the respiratory gas for the analysis of the O2- and CO2- concentration is suctioned off continuously. First clinical experience in mechanically ventilated newborns is characterized.