Pilot investigation of anterior fontanelle photoplethysmographic signals and their suitability in estimating arterial oxygen saturation

There is a need for more reliable, non-invasive and alternative measurement sites for the monitoring of arterial blood oxygen saturation in critically ill newborns at times of peripheral compromise. A pilot investigation on 14 Intensive Care Unit (ICU) newborns was conducted utilizing custom-made reflectance photoplethysmographic (PPG) sensors placed at the fontanelle and foot. The results suggest that the fontanelle is sensitive to changes in saturation, where saturation values obtained from the custom sensor were compared against commercial pulse oximeter values and results from a blood gas analyzer, however careful placement of the sensor at the fontanelle is an issue that needs further investigation.

Investigation of photoplethysmographs from the anterior fontanelle of neonates

Photoplethysmography (PPG) signals have been investigated at a new anatomical site, the anterior fontanelle (ANTF), on the hypothesis that blood supply at this location is preferentially preserved during cases of poor peripheral circulation which might cause the commercial pulse oximeters to fail to estimate accurately arterial blood oxygen saturation (SpO2). Two custom built reflectance PPG sensors have been developed, one for placement on the fontanelle and one on the periphery (foot). A PPG processing system and software were also developed to process the raw PPG signals and to estimate SpO2. A pilot study on sixteen babies, (9 male, 7 female) with a median age of 15.5 d (interquartile range = 46.8 d) and a median weight of 3.15 kg (SD = 0.93 kg), on a neonatal intensive care unit (NICU) has been carried out. PPG signals from the ANTF were of good quality and high signal-to-noise ratio. The amplitudes of the ANTF PPGs were found to be sensitive to changes in amplitude when amplitudes were observed at the reference PPG site. Bland-Altman analysis of the gold standard blood gas analysis reveals that all three sensors are inaccurate at SaO2 < 85-90 %, but the ANTF sensor shows better mean difference than the commercial device.

Esophageal SpO2 measurements from a pediatric burns-patient: a case study

Pulse oximetry is being used in everyday clinical practice in anesthesia utilizing peripheral saturation sensors. However, it may be unreliable in certain clinical situations such as peripheral hypoperfusion. Similar situations occur in burns patients and more importantly burns to extremities which limit the sites available for measurement of peripheral oxygen saturation (SpO2). To overcome these limitations, the esophagus has been investigated as an alternative measurement site, as perfusion may be preferentially preserved centrally. A miniaturized reflectance esophageal saturation (SpO2 probe has been constructed utilizing infrared and red photodiodes and a photodetector. Our case study was aimed at evaluating the reliability of esophageal pulse oximetry in a major burns infant. Measurable photoplethysmographic (PPG) traces and SpO2 values were obtained in the neonatal esophagus. It was found that the esophageal pulse oximeter results were in good agreement with oxygen saturation measurements obtained by a commercial ear lobe pulse oximeter. This study suggests that the esophagus can be used as an alternative site for monitoring arterial blood oxygen saturation by pulse oximetry in burned infants.

Photoplethysmographic and SpO(2) readings from the neonatal anterior fontanelle: a case study

There is a need for a more reliable, non-invasive and alternative measurement site for the monitoring of arterial blood oxygen saturation in critically ill neonates when peripheral perfusion is poor. The anterior fontanelle, a unique anatomical feature of the neonate, has been presented as an alternative site for the estimation of arterial blood oxygen saturation (SpO(2)). A new fontanelle photoplethysmographic sensor and processing system has been developed to investigate fontanelle photoplethysmographic (PPG) signals and estimate SpO(2) values at this anatomical location. Preliminary clinical trials have shown that good quality PPG signals with large amplitudes and high signal to noise ratio can be obtained from the neonatal fontanelle. The estimation of SpO(2) values from the fontanelle were in broad agreement with a commercial foot pulse oximeter.

Development of an optoelectronic sensor for the investigation of photoplethysmographic signals from the anterior fontanel of the newborn

There is a need for more reliable, non-invasive and alternative measurement sites for the monitoring of arterial blood oxygen saturation in critically ill newborns at times of peripheral compromise. The anterior fontanelle, a unique anatomical feature of the newborn, has been presented as an alternative site for the estimation of oxygen saturation. A multi-wavelength non-invasive optoelectronic sensor has been designed and developed for the investigation of photoplethysmographic (PPG) signals and blood oxygen saturation values from the fontanelle. In vivo thermal tests of the optical sensor show that under normal operating conditions the heating at the skin surface was negligible (<0.1 °C). Good quality PPGs with large amplitudes and high signal to noise ratio were recorded at all three (red, infrared and green) wavelengths prior to clinical measurements.

Stabilisation of critically ill children at the district general hospital prior to intensive care retrieval: a snapshot of current practice

OBJECTIVE

To describe current practice during stabilisation of children presenting with critical illness to the district general hospital (DGH), preceding retrieval to intensive care.

DESIGN

Observational study using prospectively collected transport data.

SETTING

A centralised intensive care retrieval service in England and referring DGHs.

PATIENTS

Emergency transports to intensive care during 2-month epochs from 4 consecutive years (2005-2008).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Proportion of key airway, breathing, and circulatory and neurological stabilisation procedures, such as endotracheal intubation, mechanical ventilation, vascular access, and initiation of inotropic agents, performed by referring hospital staff prior to the arrival of the retrieval team.

RESULTS

706 emergency retrievals were examined over a 4-year period. The median age of transported children was 10 months (IQR, 18 days to 43 months). DGH staff performed the majority of endotracheal intubations (93.7%, CI 91.3% to 95.5%), initiated mechanical ventilation in 76.9% of cases (CI 73.0% to 80.4%), inserted central venous catheters frequently (67.4%, CI 61.7% to 72.6%), and initiated inotropic agents in 43.7% (CI 36.6% to 51.1%). The retrieval team was more likely to perform interventions such as reintubation for air leak, repositioning of misplaced tracheal tubes, and administration of osmotic agents for raised intracranial pressure. The performance of one or more interventions by the retrieval team was associated with severity of illness, rather than patient age, diagnostic group, or team response time (OR 3.62, 95% CI 1.47 to 8.92).

CONCLUSIONS

DGH staff appropriately performs the majority of initial stabilisation procedures in critically ill children prior to retrieval. This practice has not changed significantly for the past 4 years, attesting to the crucial role played by district hospital staff in a centralised model of paediatric intensive care.

How many oxygen cylinders do you need to take on transport? A nomogram for cylinder size and duration

When undertaking patient retrieval, it is important to take adequate supplies of oxygen to ensure patient safety. Oxygen can be delivered via a flowmeter into a facemask or used to drive pneumatic ventilators. Given the lack of space in the back of an ambulance or helicopter, the numbers of cylinders that can be taken is limited, hence the number needed to complete the journey must be carefully calculated prior to embarking. We have produced nomograms to predict how many oxygen cylinders will be consumed during a given journey when using either a flowmeter or a commonly used transport ventilator.

Challenges in the provision of ICU services to HIV infected children in resource poor settings: a South African case study

The HIV/AIDS epidemic has placed increasing demands on limited paediatric intensive care services in developing countries. The decision to admit HIV infected children with Pneumocystis carinii pneumonia (PCP) into the paediatric intensive care unit (PICU) has to be made on the best available evidence of outcome and the ethical principles guiding appropriate use of scarce resources. The difficulty in confirming the diagnosis of HIV infection and PCP in infancy, issues around HIV counselling, and the variance in the outcome of HIV infected children with PCP admitted to the PICU in African studies compound this process. Pragmatic decision making will require evaluation of at least three ethical questions: are there clinical and moral reasons for admitting HIV positive children with PCP to the PICU, should more resources be committed to caring for HIV children who require the PICU, and how can we morally choose candidates for the PICU? Those working in the PICU in HIV endemic regions need to make difficult personal decisions on effective triage of admissions of HIV infected children with PCP based on individual case presentation, availability of resources, and applicable ethical principles.

Handwashing in the intensive care unit: a big measure with modest effects

Handwashing is widely accepted as the cornerstone of infection control in the intensive care unit. Nosocomial infections are frequently viewed as an indicator of poor compliance of handwashing. The aim of this review is to evaluate the effectiveness of handwashing on infection rates in the intensive care unit, and to analyse the failure of handwashing. A literature search identified nine studies that evaluated the impact of handwashing or hand hygiene on infection rates, and demonstrated a low level of evidence for the efforts to control infection with handwashing. Poor compliance cannot be blamed as the only reason for the failure of handwashing to control infection. Handwashing on its own does not abolish, but only reduces transmission, as it is dependent on the bacterial load on the hand of healthcare workers. Finally, recent studies, using surveillance cultures of throat and rectum, have shown that, under ideal circumstances, handwashing can only influence 40% of all intensive care unit infections. A randomised clinical trial with the intensive care as randomisation unit is required to support handwashing as the cornerstone of infection control.

Non-invasive diagnosis of tracheobronchomalacia using a modified ventilation radioisotope lung scan

The use of radionuclide ventilation lung scan to characterise the physiological effects of tracheobronchomalacia is a novel application of this non-invasive technique. In the reported case the right upper lobe was found to be not ventilated below a pressure of 20 cm H2O despite evidence from a dynamic tracheobronchogram of the right upper lobe bronchus opening at the lower pressure of 15 cm H2O.

Cerebro-splanchnic oxygenation ratio (CSOR) using near infrared spectroscopy may be able to predict splanchnic ischaemia in neonates

OBJECTIVE

To investigate whether near infrared spectroscopy (NIRS) can detect differences in oxyhaemoglobin signal when applied to the abdomens of neonates with surgically proven splanchnic ischaemia.

DESIGN

Prospective, observational cohort study.

SETTING

Tertiary neonatal referral centre.

PATIENTS

Medical and surgical neonates were studied. Two groups were identified, neonates with acute abdomens referred for surgery and those with normal abdomens admitted for medical reasons.

INTERVENTIONS

Tissue oxygenation indexes (TOI) of cerebral and splanchnic regions were measured using near infrared spectroscopy (NIRS) and their relative values expressed as a cerebro-splanchnic oxygenation ratio (CSOR). Measurements were made on admission or immediately prior to surgery and subsequently repeated on a daily basis, whenever possible, until discharge from our unit. The area under the receiver operating characteristic (ROC) curve was evaluated and optimum diagnostic cut-off values determined.

RESULTS

Forty neonates were studied: 10 with acute abdomens, including four with necrotising enterocolitis (NEC), 29 controls with normal abdomens and one with cerebral hypoxic ischaemic injury. Median CSOR for the control group was 0.96 (interquartile range 0.83-1.02) whereas the acute abdomen group had a significantly lower median CSOR value of 0.66 (0.45-0.69) (p<0.001). The area under the ROC was 0.91 (95% confidence limits 0.78-1.00) for CSOR. Taking a boundary value of CSOR for the prediction of splanchnic ischaemia as less than 0.75, intestinal ischaemia was identified with a positive predictive value of 0.75 (0.43-0.95) and excluded with a negative predictive value of 0.96 (0.81-1.0). This was a better performance than using abdominal TOI alone.

CONCLUSIONS

By comparing the TOI of cerebral and splanchnic regions it may be possible to establish the presence of normal splanchnic perfusion and detect when splanchnic ischaemia develops. CSOR had a 90% (56-100%) sensitivity to detect splanchnic ischaemia in neonates. Further work is necessary to confirm these early findings and establish whether abdominal NIRS has a clinical role in detecting splanchnic ischaemia.

Prolonged use of tissue plasminogen activator for bilateral lower limb arterial occlusion in a neonate

The authors report the case of a 29-week-gestation twin with very severe vascular compromise of both lower limbs secondary to premature twin-twin transfusion. A tissue plasminogen activator (tPA) infusion was used locally for 13 days with complete recovery of perfusion to both legs, demonstrated by serial angiograms, thereby avoiding bilateral amputation. There were no side effects as a result of the continuous administration of tPA. The authors therefore suggest that the benefits of thrombolysis from a local infusion of tPA in neonates may outweigh the potential risks. This case report thus supports the view that under certain circumstances infusion of tPA in neonates may offer significant benefits. J Pediatr Surg 36:654-656.

Energy metabolism of infants and children with systemic inflammatory response syndrome and sepsis

OBJECTIVE

To evaluate whether critically ill children with systemic inflammatory response syndrome (SIRS) or sepsis have altered resting energy expenditure (REE) and substrate utilization.

SUMMARY BACKGROUND DATA

Studies in adults with sepsis have shown increased energy expenditure and mobilization of endogenous fat. In infants and children, energy metabolism and substrate utilization during sepsis have not been characterized.

METHODS

Metabolic studies were performed in 21 critically ill children with SIRS or sepsis. Twenty-one stable control children, matched for weight, were also studied. Seven patients required inotropic support and 17 received mechanical ventilation. Fifteen patients with SIRS had evidence of bacterial, fungal, or viral infection and were considered septic. Respiratory gas exchange was measured by computerized indirect calorimetry for 1 to 2 hours continuously.

RESULTS

The REE of patients with SIRS or sepsis was not different from that of controls. Similarly, there were no differences in carbon dioxide production and oxygen consumption. Resting energy metabolism was not different between patients with SIRS and patients with sepsis. In addition, the presence of low platelet count or inotropic support did not affect resting energy metabolism. The median respiratory quotient of patients with SIRS or sepsis was 0.88 (range 0.75-1.12), indicating mixed utilization of fat and carbohydrate; this was not significantly different from that of controls. The Pediatric Risk of Mortality Score was not significantly correlated with REE or respiratory quotient.

CONCLUSIONS

The energy requirements of children with SIRS or sepsis are not increased. Their resting metabolism is based on both carbohydrate and fat utilization. The authors speculate that these children divert the energy for growth into recovery processes.

Systemic antibiotics fail to clear multidrug-resistant Klebsiella from a pediatric ICU

STUDY OBJECTIVES

To determine the magnitude of infection rate and antimicrobial resistance in a pediatric ICU (PICU), and to evaluate the efficacy of using broad-spectrum antibiotics.

DESIGN

A 3-month, prospective, observational cohort audit.

SETTING

A 12-bed tertiary, referral PICU.

PATIENTS OR PARTICIPANTS

All children admitted to the PICU for > 72 h.

INTERVENTIONS

Surveillance cultures of throat and rectum on admission and once weekly thereafter.

MEASUREMENTS AND RESULTS

Of the 150 admissions during the 3-month period, a total of 52 patients (24 girls and 28 boys) requiring mechanical ventilation for a minimum of 3 days were enrolled in the audit. The median age and interquartile range (IQR) was 17 months (IQR, 5.8 to 63); length of stay, 6.5 days (IQR, 4 to 13); ventilation days, 5 (IQR, 3 to 11); pediatric risk of mortality score, 14 (IQR, 9 to 19); and risk of mortality, 0.03 (IQR, 0.014 to 0.087). Fifteen patients (29%) developed 21 infections, mainly lower-airway infections and septicemias. Of the 52 children, 7 children carried multidrug-resistant bacteria and 3 patients progressed to develop four infections with those resistant bacteria. Of the seven carriers, six patients carried gentamicin-resistant Klebsiella. Methicillin-resistant Staphylococcus aureus, penicillin-resistant Streptococcus pneumoniae and gentamicin-resistant Pseudomonas aeruginosa each were carried by one child. Six of those nine resistant isolates were present in the admission flora. Despite the potent combination of piperacillin/tazobactam and amikacin, three children acquired the multidrug-resistant Klebsiella while in the PICU and became nosocomial carriers.

CONCLUSIONS

Only surveillance cultures allow the distinction between import of multidrug-resistance and resistant bacteria acquired while in PICU. In this study, two thirds of the resistant isolates were imported. The introduction of newer potent systemic antibiotic combinations failed to control the endemic reservoir of multidrug-resistant Klebsiella and suggests that such policies have little impact.

Use of the laryngeal mask airway during repair of atrial septal defect in children

We describe the elective use of the laryngeal mask airway in two children undergoing cardiopulmonary bypass for repair of an atrial septal defect. Total surgical time was short and cardiopulmonary bypass performed at normothermia allowing removal of the laryngeal mask airway on the operating table on completion of surgery. We were able to adequately oxygenate and ventilate the children throughout the procedure using positive pressure ventilation and spontaneous ventilation. The use of caudal fentanyl and rectal diclofenac aided postoperative pain management. Atrial septal defect repair has become one of the more straightforward cardiac operations partly as a result of new cardiopulmonary bypass techniques. Avoidance of intubation and postoperative ventilation in appropriate patients would make this procedure ideal for 'fast tracking' and offers the potential advantages of decreased length of stay in hospital and reduction in overall costs.

Hydrogen peroxide and catalase are inversely related in adult patients undergoing cardiopulmonary bypass: implications for antioxidant protection

Adult patients undergoing cardiopulmonary bypass (CPB) surgery are subjected to increased oxidative stress and show a spectrum of lung injury. Increased levels of hydrogen peroxide (H2O2) are often seen during episodes of oxidative stress, such as the use of high FiO2s, and this molecule plays a key role in the formation of highly damaging oxidants such as the hydroxyl radical. Oxidative damage to plasma proteins was assessed by measuring free thiol groups, and antioxidant protection against H2O2 by measuring catalase activity. CPB patients (n = 39) receiving either 100% or 50% oxygen at the end of bypass were studied by measuring levels of H2O2 in breath condensate and levels of catalase in their plasma, and comparing these to pre-bypass levels. Post-bypass, all CPB patients exhaled significantly lower levels of H2O2 (P < 0.0001) at a time when they had significantly increased activity (0.809 +/- 0.11 versus 1.688 +/- 0.18 U/mg protein) of catalase in their plasma. There were no significant differences in these parameters between the 100% and 50% oxygen groups. At a time when oxidative stress is greatest, there appears to be a corresponding plasma increase in the antioxidant catalase. Whether this change is fortuitous or a response to oxidative stress is at present under consideration.

A wandering nasal prong-a thing of risks and problems

We describe an unusual complication of nasal continuous positive airway pressure (nCPAP) ventilation in a preterm low birth weight neonate being weaned from respiratory support. The tube used to administer nasal CPAP became dislodged from its metal connector whilst in the nasopharynx and slipped into the stomach. After waiting eight days the tube showed no signs of passing spontaneously through the gastrointestinal tract and retrieval was then successfully achieved by means of a 3.5 mm paediatric fibreoptic bronchoscope without complication.

Nitric oxide production in meningococcal disease is directly related to disease severity

OBJECTIVES

Meningococcal disease is a homogeneous and well-characterized form of sepsis. Cardiovascular collapse is prominent in severe meningococcal disease. Nitric oxide overproduction may be a mediator of cardiovascular collapse. We relate the level of nitric oxide metabolites, nitrates and nitrites, to disease severity in meningococcal disease.

DESIGN

Prospective, nonrandomized study.

SETTING

Tertiary referral pediatric intensive care unit.

PATIENTS

Children admitted with a clinical diagnosis of meningococcal disease.

INTERVENTIONS

Blood was sampled from children with meningococcal disease. Disease severity was scored using the Glasgow meningococcal septicemia prognostic score and pediatric risk of mortality score. Plasma nitrates and nitrites were measured in stored plasma using the Greiss reaction after conversion of all the nitrate to nitrite.

MEASUREMENTS AND MAIN RESULTS

Twenty-two children were studied. In 19, the final diagnosis was meningococcal disease. Of the 19 children with meningococcal disease, 7 had a Glasgow meningococcal septicemia prognostic score of <8 (mild) and 12 had a Glasgow meningococcal septicemia prognostic score > or = 8 (severe). Three children died, all of these being in the severely affected group. Higher levels of nitrates and nitrites were seen in the more severely affected children (median admission nitrates and nitrites, 27.5 vs. 59.7 nmol/mL; p = 0.063; median peak nitrates and nitrites, 49.9 vs. 114 nmol/mL; p = .01) or those with an increased predicted mortality using pediatric risk of mortality (Spearman's p 0.742; p = .0003).

CONCLUSIONS

Higher levels of nitrates and nitrites are seen in sicker children with meningococcal disease.

Position of the internal jugular vein in children. A study of the anatomy using ultrasonography

The relative anatomy of the internal jugular vein (IJV) was studied in 25 patients undergoing cardiac catheterization under general anaesthesia, with the use of a portable ultrasound probe. In 14 of cases the IJV was anterior, 1 anterolateral and in 10 lateral to the carotid artery between the two heads of the sternocleidomastoid muscle. At the level of the cricoid cartilage, in six cases the IJV was anterior, three anterolateral and in 16 of children the IJV was lateral to the carotid artery. When attempting to cannulate the IJV, because of the variability in relationship of the IJV to CA the technique used should be modified depending upon the level at which cannulation is attempted. The position of the IJV in the child appears to be so variable extra care should be taken when cannulating the IJV and it should not be assumed that the techniques used in adults are directly transferable.

Familial persistent pulmonary hypertension of the newborn resulting from misalignment of the pulmonary vessels (congenital alveolar capillary dysplasia)

Misalignment of the pulmonary veins with congenital alveolar capillary dysplasia, although rare, has been reported as a cause of persistent pulmonary hypertension of the newborn. Reported cases have been mainly sporadic. Familial occurrence has been reported in only three instances. We present affected sibs with this condition. In addition to pulmonary abnormalities, urogenital abnormalities, including ureteric and urethral obstruction, seem to be common. Autosomal recessive inheritance is suggested.

Cardiopulmonary interactions in healthy children and children after simple cardiac surgery: the effects of positive and negative pressure ventilation

OBJECTIVE

To investigate the effects of cuirass negative pressure ventilation on the cardiac output of a group of anaesthetised children after occlusion of an asymptomatic persistent arterial duct, and a group of paediatric patients in the early postoperative period following cardiopulmonary bypass.

DESIGN

Prospective study.

SETTING

The paediatric intensive care unit and catheter laboratory of a tertiary care centre.

PATIENTS

16 mechanically ventilated children were studied: seven had undergone surgery for congenital heart disease, and nine cardiac catheterisation for transcatheter occlusion of an isolated asymptomatic persistent arterial duct.

INTERVENTIONS

Cardiac output was measured using the direct Fick method during intermittent positive pressure ventilation and again after a short period of negative pressure ventilation. In five of the postoperative patients a third measurement was made following reinstitution of positive pressure ventilation.

RESULTS

Negative pressure ventilation was delivered without complication, with no significant change in systemic arterial oxygen and carbon dioxide tension. The mixed venous saturation increased from 74% to 75.8% in the healthy children, and from 58.9% to 62.3% in the postoperative group. Negative pressure ventilation increased the cardiac index from 4.0 to 4.5 l/min/m2 in the healthy children, and from 2.8 to 3.5 l/min/m2 in the surgical group. The increase was significantly higher in the postoperative patients (28.1%) than the healthy children (10.8%).

CONCLUSIONS

While offering similar ventilatory efficiency to positive pressure ventilation, cuirass negative pressure ventilation led to a modest improvement in the cardiac output of healthy children, and to a greater increase in postoperative patients. There are important cardiopulmonary interactions in normal children and in children after cardiopulmonary bypass, and by having beneficial effects on these interactions, negative pressure ventilation has haemodynamic advantages over conventional positive pressure ventilation.

Metabolic, biochemical and haemodynamic effects of infusion of propofol for long-term sedation of children undergoing intensive care

We have studied prospectively, in nine children requiring sedation to facilitate mechanical ventilation, the metabolic, biochemical and haemodynamic effects of infusion of propofol. Children were given infusions of propofol 1-4mg kg-1 h-1 and fentanyl 1-5 micrograms kg-1 h-1 for 48 h. Heart rate, arterial pressure, central venous pressure, fluid balance and urine output were recorded hourly and sedation scores every 4 h. In addition to routine haemodynamic and biochemical measurements in the intensive care, 6-hourly arterial blood-gas analysis and 12-hourly measurements of serum concentrations of glucose, lactate and electrolytes, renal function, triglycerides and liver function tests were performed. Urine was analysed for ketones. There were no significant differences in haemodynamic or biochemical variables during the 48-h period. In this small sample of children, propofol combined with fentanyl provided excellent sedation with no evidence of cardiac, renal or hepatic impairment. Under these very proscriptive conditions we did not encounter lipaemia or acidosis with infusion of propofol. Thus propofol may be a safe sedative agent for use in paediatric intensive care if used appropriately. Further large scale studies are needed to determine if warnings against the use of this agent in paediatric intensive care units are justified.

Endotracheal suctioning causes right upper lobe collapse in intubated children

OBJECTIVE

Right upper lobe collapse is a common radiographic finding in intubated children. We hypothesized that deep suctioning and uncontrolled negative pressures during endotracheal tube suctioning were significant contributory factors.

METHODS

The incidence of right upper lobe (RUL) collapse in intubated, ventilated children on a paediatric cardiac intensive care unit was determined over a 3-month period (n = 102). Graduated suction catheters and suction vacuums of < 165 cm H2O were then introduced. Another prospective audit was carried out 3 months later (n = 60).

RESULTS

We found that 24% developed RUL collapse and 4 developed an apical pneumothorax. Following the introduction of graduated catheters and controlled vacuums pressures; a significant reduction in the incidence of RUL collapse, to 7%, was observed (p < 0.05).

CONCLUSIONS

We conclude that high negative pressure and deep-suctioning causes RUL collapse in children. Any lobar collapse not only prolongs the child's stay in intensive care, but can be associated with further morbidity which may have a serious implication. By improving suctioning technique this morbidity can be significantly reduced.

An effective method of scavenging nitric oxide

We report an effective method of scavenging nitric oxide and nitrogen dioxide. We have compared three agents, a commercially available filter, soda lime and activated charcoal, for their effectiveness and duration of action. Complete absorption of nitric oxide and nitrogen dioxide for a period of 170 h was obtained using the commercial filter. However, soda lime and charcoal were unable to successfully scavenge either gas. The resistance characteristics of this filter when dry or humidified were determined.

High-frequency oscillatory ventilation combined with intermittent mandatory ventilation in critically ill neonates and infants

We have evaluated the high-frequency oscillatory ventilation (HFOV) combined with intermittent mandatory ventilation (IMV) in critically ill neonates and infants using the Babylog 8000 SW 4.0. We used HFOV combined with IMV as a rescue mode in 10 neonates and infants aged 1 day to 17 months, who were receiving maximal conventional ventilation for severe respiratory failure. There was a significant reduction in inspired oxygen requirement when starting HFOV combined with intermittent mandatory ventilation (IMV), from a baseline mean of 0.90 (CI95 0.79-1.01) to 0.55 (CI95 0.40-0.71) at 6h and 0.44 (CI95 0.37-0.52) at 12h. There was also an overall improvement in gas exchange with complete haemodynamic stability. These data suggest that HFOV-IMV mode offers significant improvement as a rescue mode for neonates and infants with severe respiratory failure.

External high frequency oscillation in normal subjects and in patients with acute respiratory failure

External high frequency oscillation was performed on 20 healthy volunteers using a cuirass-based system, the Hayek Oscillator. Five-min periods of oscillation were carried out on each subject at frequencies of 1, 2, 3, 4 and 5 Hz. Effective ventilation was measured in terms of the fall in alveolar partial pressure of carbon dioxide immediately after oscillation. The optimum frequency for oscillation was 1-3 Hz but most of the subjects were adequately ventilated over a wide range of frequencies. Thus, the Hayek Oscillator is capable of adequately ventilating normal subjects by means of chest wall oscillation. We also compared external high frequency oscillation with intermittent positive pressure ventilation in five patients with respiratory failure. Using the same inspired oxygen fraction, the external high frequency oscillation replaced intermittent positive pressure ventilation for a 30-min period. External high frequency oscillation improved oxygenation by 16% and reduced the arterial carbon dioxide by 6%. These preliminary findings suggest that normal subjects and intensive care unit patients can be adequately ventilated by means of external high frequency oscillation.

Cost implications of using inhaled nitric oxide compared with epoprostenol for pulmonary hypertension

OBJECTIVE

To compare the cost of using intravenous epoprostenol with that of inhaled nitric oxide (NO) for treating episodes of pulmonary hypertension in children with congenital heart disease.

DESIGN

An analysis of the cost of epoprostenol and NO use over the previous 18 months was performed. Three 6-month periods were identified, two in which epoprostenol was used and the third in which inhaled NO was introduced for the treatment of pulmonary hypertension.

SETTING

A 10-bed pediatric cardiac intensive care unit, Royal Liverpool Children's Hospital, Alder Hey, Liverpool, England.

SUBJECTS

Children with congenital heart disease and persistently elevated pulmonary artery pressure following cardiac surgery.

MAIN OUTCOME MEASURES

The total duration of use of epoprostenol and inhaled NO was documented. The costs per hour for epoprostenol and inhaled NO were calculated and the annual cost of each agent was estimated.

RESULTS

In the two 6-month periods prior to the introduction of inhaled NO, epoprostenol was used on 14 occasions (5 in the first period, 3 in the second). In the last 6-month period, nine children required pulmonary vasodilator therapy on 14 occasions. All nine children were treated successfully with inhaled NO; none were given or needed epoprostenol, as NO always was effective in providing pulmonary vasodilatation. For resistant pulmonary hypertension, increasing the concentration of NO would have been the next therapeutic option. The cost for the two 6-month periods using epoprostenol was $19,483.48 for the drug and $283.25 for equipment costs (total cost $19,766.73). There was no expenditure on epoprostenol in the final 6-month period. The cost of NO was $465. However, the total expenditure, including the delivery and monitoring system, was $4,722.85.

CONCLUSIONS

Using inhaled NO in our pediatric cardiac intensive care unit abolished the use of epoprostenol during the reported monitoring period. The cost savings were significant, amounting to 12% of the annual drug budget for the unit. The cost of setting up the inhaled NO delivery system is recouped rapidly. The ease of delivery and measurement of inhaled NO also may have contributed to its increased clinical use.

The Hayek oscillator. Nomograms for tidal volume and minute ventilation using external high frequency oscillation

The Hayek Oscillator is a recent development in external high frequency ventilation and is a useful mode of ventilatory support during anaesthesia, in chronic respiratory failure and weaning in intensive care. The Hayek Oscillator is new and its application is growing, as are the number of patients who have benefited from its use. However, there are no clear guidelines on how best to adjust the oscillator to achieve optimum ventilation. A simple method of predicting changes in tidal volume and minute ventilation following adjustment would make the oscillator more useful. We present nomograms for tidal volume, minute ventilation and effective alveolar ventilation when the three variables, oscillator frequency, mean chamber pressure and peak-to-trough pressure span were adjusted. The frequency-tidal volume relationship was unaffected by a mean chamber pressure of 0, -5, -10 cmH2O, but altered with changes in peak-to-trough pressure span. We have also determined the effect of increasing negative extrathoracic pressure on functional residual capacity. The relationship between tidal volume and frequency was non-linear and related to the peak-to-trough pressure span. Mean functional residual capacity significantly increased from 2.25 l (SEM 0.10) without the cuirass at rest to 2.61 l (SEM 0.14) at -10 cmH2O (p < 0.05; n = 5) and 2.47 (SEM 0.12) at -20 cmH2O of mean chamber pressure. Vital capacity was unchanged by increasing extrathoracic pressure as was total lung capacity.

The expandable metal stent for tracheal obstruction

A 10 month old boy with stridor persisting from birth was found to have tracheal narrowing secondary to myofibromatosis of the tracheal wall. An expandable metal stent was positioned across the tracheal stenosis with immediate clinical improvement. There were no complications relating to stent insertion. The child remained clinically asymptomatic and repeat bronchoscopy at nine months' follow up showed that the stent had become completely endothelialised with no evidence of granuloma formation.