Selection of pulse oximetry equipment for ambulatory monitoring

PRIMARY OBJECTIVE

This communication describes the initial stage of a research project concerning the monitoring of SpO2 in infants prone to periods of spontaneous oxygen desaturation whilst freely moving around their home environment. The primary aim was to determine an appropriate probe type and site together with an assessment of the suitability of two commercially available oximeter units.

RESEARCH DESIGN

The study comprised 19 comparative tests, totalling 162 hours of recordings at resolution one sample every four seconds. Comparisons are drawn between probes, probe sites and pulse oximeters. MAIN OUTCOMES/RESULTS: The bias and precision is presented with respect to the probe and measurement site. Also, correlation between the trial and reference recordings is considered.

CONCLUSIONS

It is concluded that ambulatory recording of SpO2 in infants utilizing equipment suitable for home monitoring can produce diagnostic data equivalent to that of the Ohmeda 3700 biox, but that an indication of movement artefact may be required for confirmation of accuracy. It became apparent that 'wrap around' probes, used on the index finger or big toe are the most suitable.

False aneurysm following modified Blalock-Taussig shunt

A nine month old infant with life threatening tracheal compression due to a Blalock-Taussig shunt aneurysm is described. Successful surgical management is discussed.

Chronic granulomatous disease with renal stones

A case of chronic granulomatous disease with hydronephrosis and renal calculi is presented. This is to our knowledge the first such case to be reported. The calculi were successfully ablated by extracorporeal shockwave lithotripsy.

Acute purulent pericarditis in Omani children

A total of eight children admitted to the Royal Hospital, Muscat with purulent pericardial effusions were analysed. Six of the cases were in children less than 2 years of age. Five of the eight children had positive blood cultures: Haemophilus influenzae was cultured from two patients, Streptococcus pneumoniae from one patient, E. coli from one patient and Streptococcus viridans from the remaining child. In three children both blood and pericardial cultures were sterile; two of these children had received prior antibiotics. In our experience early diagnosis by cross-sectional echocardiography followed by adequate surgical drainage and parenteral administration of broad spectrum antibiotics helped prevent the high morbidity and mortality usually reported in this condition in developing countries.

Lead lines in young infants with acute lead encephalopathy: a reliable diagnostic test

Fifteen Omani infants, ranging between 2 and 4 months of age, with acute lead encephalopathy underwent plain skeletal radiology. X-rays in all 15 infants revealed dense metaphyseal bands in long bones. These were best seen around the knee joint. Six infants had evidence of multiple lead lines indicating previous episodes of exposure to lead while four infants also had lead lines in the axial skeleton. We suggest that any young infant presenting with an unexplained encephalopathy should undergo an X-ray of the knee and that the presence of dense metaphyseal bands strongly supports the diagnosis of lead poisoning. A plain X-ray of the knee is a cheap, widely available investigation which can be rapidly obtained.

A comparison of enteric coated microspheres with enteric coated tablet pancreatic enzyme preparations in cystic fibrosis. A controlled study

A comparative study of the efficacy of pH sensitive enteric coated microspheres (ECM) with an enteric coated tablet (ECT) pancreatic enzyme preparation was carried out in 20 children with cystic fibrosis in a double-blind double-placebo crossover manner. Steatorrhoea was assessed by 3 day faecal fat analysis and dosage of medication, stool frequency and consistency; abdominal pain and appetite were documented by a patient-kept diary card. ECM controlled steatorrhoea (11.8 +/- 9.2 g vs 23.2 +/- 18.9 g, P less than 0.02), stool frequency (1.7 +/- 0.6 vs 2.1 +/- 0.9, P less than 0.01) and abdominal pain (8.8 +/- 13.8 vs 23.4 +/- 24.1, P less than 0.05) significantly better than ECT. Out of 20 patients 17 preferred ECM to ECT (P less than 0.00036). ECM preparations should allow more satisfactory dietary management of patients with cystic fibrosis with longterm beneficial effect.

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.

Transcutaneous oxygen monitoring beyond the neonatal period

Transcutaneous O2 (PtcO2) tensions were compared with PaO2 measurements in 57 infants and children (age range 2 wk to 15.5 yr) using electrode temperatures of 43 degrees and 44 degrees C. At both temperatures, the relationships between PtcO2 and PaO2 were linear over the whole range of data (PaO2 39.75 to 120 torr) although mean PtcO2/PaO2 fell from 44 degrees to 43 degrees C. Skin stripping by repeated applications of adhesive tape immediately before electrode placement did not improve these relationships. In an additional 20 children with a mean age of 2.4 yr (range 0.08 to 15.85) who were being investigated for sleep-disordered breathing, the mean PaO2/PtcO2 ratio of 1.22 at 44 degrees C was used as a correction factor during air calibration for PtcO2. This resulted in a mean PtcO2/PaO2 of 0.99 (range 0.83 to 1.15) provided blood flow is not impaired. Extending the monitoring period from 4 to 8 h between site changes did not result in any burns or persisting erythema. In hemodynamically stable infants and children, and at electrode temperatures of 44 degrees C and 43 degrees C, PtcO2 is linearly related to PaO2 over a wide range of PaO2 values. At an electrode temperature of 44 degrees C, PtcO2 can be arterialized effectively by allowing for transepidermal O2 loss during air calibration; at this electrode temperature, intervals between site changes can be extended safely up to 8 h.

Randomized trial of artificial surfactant (ALEC) given at birth to babies from 23 to 34 weeks gestation

Artificial surfactant (ALEC) composed of dipalmitoylphosphatidylcholine and unsaturated phosphatidylglycerol in a ratio of 7:3 (w/w) and a dose of 50-100 mg was suspended in 1 ml of cold saline and used at birth as a prophylaxis against the respiratory distress syndrome and its complications in a two centre randomized prospective trial involving 341 babies from 23 to 34 weeks gestation regardless of their antenatal problems. The surfactant had little effect in babies above 29 weeks gestation and was most beneficial in babies under 30 weeks gestation (67 controls and 69 surfactant treated babies). In this subgroup the artificial surfactant significantly reduced the inspired oxygen and peak ventilator pressure requirements during the first 96 h, the incidence of intraventricular haemorrhages from 40% to 19% (P less than 0.01), the overall mortality from 36% to 17% (P less than 0.02), the mortality due to RDS from 31% to 9% (P less than 0.01), the need for more than 28 days oxygen from 37% to 21% (P = 0.05) and the use of pancuronium in ventilated babies from 52% to 27% (P less than 0.01). There were no apparent side effects. This protein free, artificial surfactant should be a useful addition to the therapy of babies under 30 weeks gestation to reduce the severity of their RDS and the incidence of serious complications.

Endotracheal resuscitation of preterm infants at birth

The adequacy of initial ventilation in 21 preterm babies (25-36 weeks' gestation), who required endotracheal intubation and positive pressure ventilation, were studied. Pressure and flow were measured at the proximal end of the endotracheal intubation tube and expiratory volume calculated from the flow trace. The results were compared with those from a group of 26 term infants who also required resuscitation. Five of 21 preterm babies (24%) had adequate tidal ventilation with the first inflation. This rose to seven of 21 (33%) by the third inflation. This was significantly less than the results in the term infants (chi 2 = 4.38 p less than 0.05). Respiratory reflex responses to resuscitation were seen in 41% of inflations in preterm and 56% of inflations in term infants. There was a significant correlation between reflex activity and adequate ventilation in the preterm group (chi 2 = 11.83, p less than 0.001) but not in the term group (chi 2 = 0.212, p = NS). No correlation was seen between initial ventilation and outcome.

Determinants of the first inspiratory volume and functional residual capacity at birth

We have investigated the pattern of pressure and volume changes that occur in vaginally delivered, full-term infants during the onset of spontaneous respiration. Within a few seconds of delivery of the head, simultaneous measurements were made of stomach and esophageal pressure changes together with volume changes determined at the mouth. Values obtained for volume were very similar, but pressure changes were of a greater magnitude than previously reported. A significant correlation has been shown between first inspiratory volume and functional residual capacity (FRC) at the end of the first breath (p less than 0.004). No significant relationship was found between first inspiratory pressure and FRC. However, using a calculated index of inspiratory pressure and time ("inspiratory effort"), a significant relationship of this to FRC was observed (p less than 0.02).

The child health clinic: results of a new strategy of community care in a deprived area

Substantial changes were made in the organisation of a child health clinic serving an underprivileged population in Nottingham. A community paediatric team approach was adopted, routine medical checks were reduced, and referrals from elsewhere (including parents) were encouraged. The changes resulted in an older and more deprived population of preschool children being seen by the clinic doctors. More treatable medical disorders were detected with this approach.

Continuous positive airway pressure via a single nasal catheter in preterm infants

We present the results of giving continuous positive airway pressure (CPAP) via a single nasal catheter to 20 preterm infants. A beneficial effect in terms of reduced work of breathing (P less than or equal to 0.01) and improved pattern of respiration (P less than or equal to 0.05) are demonstrated. CPAP via a single nasal catheter does not seem to mediate effects inside the thorax unlike CPAP delivered by a tight fitting face mask. Gross variations in CPAP level may result from altering the infant's position.

Efficacy of facemask resuscitation at birth

The efficacy of facemask resuscitation was assessed by measuring the expiratory tidal volume during the first three inflations in nine babies with birth asphyxia and comparing the results with those obtained in a further nine babies resuscitated after endotracheal intubation. The facemask system was relatively inefficient, with tidal exchange less than one third of that seen after intubation and rarely sufficient to produce adequate alveolar ventilation. Successful resuscitation depended on stimulating the baby to make his own respiratory efforts.

Effect of exogenous surfactant on total respiratory system compliance

We measured total respiratory system compliance (Crs) before and after instilling 25 mg artificial surfactant in 1 ml saline down the endotracheal tube of preterm babies requiring resuscitation at birth, and compared results with data from 6 similar babies receiving saline only. Surfactant did not produce a significant improvement in Crs.

Role of labour in the establishment of functional residual capacity at birth

Intrathoracic pressure and volume changes were measured during the spontaneous first breath in 11 healthy term neonates delivered by emergency caesarean section (CS). Although inspiratory and expiratory rates were higher than those found among babies delivered by elective CS, inspiratory volume was very similar and these babies, unlike those delivered by elective CS, had all formed a functional residual capacity at the end of the first breath. We obtained cord arterial and venous samples for catecholamine analysis concurrently, and found that most of the babies had concentrations of plasma noradrenaline similar to babies delivered by elective CS--high values were found only among infants who had suffered fetal distress. Both catecholamine excretion and method of delivery may be important in the formation of the functional residual capacity at birth.

Effects of artificial surfactant on lung function and blood gases in idiopathic respiratory distress syndrome

We have investigated the effect of giving two 25 mg doses of dry surfactant powder to the airways of 10 preterm babies with severe idiopathic respiratory distress syndrome requiring intermittent positive pressure ventilation. No useful change in static total compliance or blood gases was seen. We conclude that dry surfactant powder does not have a role in the management of severe idiopathic respiratory distress syndrome.

Face mask resuscitation: does it lead to gastric distension?

Inflation and oesophageal pressures were recorded simultaneously during bag and mask resuscitation of 9 asphyxiated babies. After half a minute of standard inflation pressures, higher pressures were applied for at least 5 inflations by occluding the blow-off valve. No air entered the oesophagus until a high mean inflation pressure of 5.4 kPa was exceeded. These findings were confirmed in 4 fresh stillborn babies studied similarly. We conclude that resuscitation using bag and mask, applying pressures less than 3.5 kPa, should not lead to gastric distension.

Amniocentesis and fetal lung development

The crying vital capacity was measured in 10 healthy, term babies after amniocentesis during pregnancy, and in 10 control babies after normal pregnancies. The mean ratio of crying vital capacity to body weight was significantly lower after amniocentesis. This may be caused by the alteration in the lung fluid volume and the diminished intrauterine respiratory movements.

Relationship between apnoea and bradycardia in preterm infants

Nine studies were carried out on seven babies who were having repeated episodes of bradycardia without any clinically obvious apnoea. Their mean gestational age was 31.7 weeks (range 29 to 36 weeks) and the mean birth weight was 1.56 kg (range 1.08 kg to 2.16 kg). Investigations were carried out in a total body plethysmograph. Face mask with a pneumotachograph attached to it measured flow. Tidal volume was obtained by integrating these signals. An oesophageal balloon measured intrathoracic pressure changes and the heart rate was measured from ECG chest electrodes. A total of 172 episodes of apnoea were observed. In 50% of these apnoeas, the airway was closed as determined by the absence of cardiac artefact on the flow signals. Apnoea was associated with bradycardia in just over 25% of all apnoea. It tended to occur early (11 to 14 sec). Whether the apnoea was central or obstructive had no effect on the pattern provided the baby did not make any inspiratory efforts. Inspiration against a closed airway produced bradycardia in over 50% of obstructive apnoea, the heart rate falling precipitously within 1 to 2 sec. These findings indicate that often bradycardias occur too early in apnoea to be due to central hypoxia and must be due to a peripheral mechanism.

Intrathoracic pressure and volume changes during the spontaneous onset of respiration in babies born by cesarean section and by vaginal delivery

We studied the first breath of newborn infants delivered by cesarean section. Inspiratory pressure and volume were found to be similar to those in infants born vaginally. However, the expiratory and delivery pressures were found to be smaller. Functional residual capacity was formed less frequently after cesarean section than in the vaginally delivered group.

Physiologic responses to prolonged and slow-rise inflation in the resuscitation of the asphyxiated newborn infant

Measurements of thoracic volume, inflation pressure, and intrathoracic pressure have been recorded at the resuscitation of nine newborn babies. The initial inflation pressure was maintained for approximately five seconds which produced a twofold increase in inflation volume compared to standard resuscitation techniques and always led to formation of an FRC. When the inflation pressure was increased slowly over three to five seconds, the apparent opening pressure which occurred universally in square wave inflation was rarely seen.

Hormonal abnormalities of the pancreas and gut in cystic fibrosis

We have investigated the effect of cystic fibrosis on alimentary hormones in 10 children by measuring the pancreatic and gut hormone rsponse to a milk drink. Plasma insulin and gastric inhibitory peptide were both significantly reduced (P < 0.05 and P < 0.005, respectively, at 15 min) in the patients with cystic fibrosis, compared with controls, even though the early glucose rise was greater in the former group (P < 0.05 at 15 min). Fasting levels of pancreatic polypeptide were significantly lower in the fibrocystic children (P < 0.01), and the normal response to milk was completely abolished in these patients (P < 0.001). Fasting plasma enteroglucagon concentrations were grossly abolished in the cystic fibrosis patients (P < 0.001) and these remained elevated throughout the test. No significant differences were seen in basal or postmilk responses of plasma glucagon, gastrin, secretin, vasoactive intestinal peptide, or motilin in cystic fibrosis. It would thus appear that the pancreatic polypeptide cell is more susceptible to the effects of the disease process than the beta or alpha cell in cystic fibrosis. Some aspects of the abnormalities in the gastrointestinal endocrine system were similar to those seen in celiac disease and tropical sprue and may, therefore, effect a similar hormonal response in these patients with cystic fibrosis to those with mucosal damage.