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Biomedical subjects

P Helms

Publications and source records attributed to P Helms.

At least 55 records · Page 3Linked to original sources
PubMed1989

Effects of posture on the distribution of pulmonary ventilation and perfusion in children and adults.

In the adult the distributions of ventilation and of perfusion show the same directional dependence on gravity. In children, however, the distribution of ventilation in response to gravity is the reverse of that seen in adults. The aim of the current study was to determine whether perfusion showed the same reversal in children or followed the adult pattern. Distribution of perfusion was measured with intravenous technetium-99m macroaggregated albumin and distribution of ventilation with inhaled krypton-81m. Eighteen children and seven adults were studied; they had been referred for lung scanning for various respiratory problems. The effect of gravity was examined by giving aliquots of macroaggregated albumin and 81mKr by inhalation to the subject in the supine and the lateral decubitus position. Counts in the dependent lung were compared with those in the upper lung. The dependent lung in the lateral decubitus position received more of the total perfusion than it did in the supine position in seven children with a normal chest radiograph (mean 7.0%, range 4.8-10.9% more) and in 11 children with an abnormal radiograph (mean 3.4%(0.1-10.0%)). Ventilation, however, changed in the opposite direction, falling by 7.1% (-3.2% to -12.8%) in five children with a normal chest radiograph and 11.2% (-2.8% to -19.3%) in eight children with an abnormal radiograph. Fractional V/fractional Q (an index of the ventilation:perfusion ratio) decreased in the dependent lung in the children when they moved from the supine to the decubitus position. The same directional change was recorded in adults, but it was significantly less than in the children, irrespective of whether the chest radiograph was abnormal. In children and adults with various respiratory problems the effect of posture on the distribution of perfusion is similar.

Adult↗
PubMed1988

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.

Adolescent↗
PubMed1988

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.

Arteries↗
PubMed1988

Monitoring in non-traumatic coma. Part I: Invasive intracranial measurements.

The arterial blood pressure, intracranial pressure, and organ system failure scores were reviewed for 49 infants and children with non-traumatic coma from various causes. The neurological outcome was good in 21 patients, moderate in five, and poor in 23. There was no significant difference in maximum intracranial pressures between patients with a good outcome and those with a poor one, but patients with a poor outcome had significantly lower minimum cerebral perfusion pressures. During the period of admission 18 patients had cardiovascular failure, none had renal failure, and two developed severe coagulopathy. Seventeen of the 19 patients in whom at least one of these systems failed died. Our findings emphasise the diversity of illnesses associated with raised intracranial pressure in children and the number who develop multiple organ failure, and the values and limitations of using minimum cerebral perfusion pressure and the organ system failure scores as guides to severity of illness and prognosis.

Acute Disease↗
PubMed1986

Once a day theophylline in chronic childhood asthma?

The therapeutic effects of either morning or evening administration of a once-daily controlled release theophylline preparation (Uniphyllin) were studied in 17 asthmatic children. Neither morning nor evening administration produced therapeutic plasma theophylline levels throughout 24h. Similarly, bronchodilation was not maintained during the same period. However, morning peak expiratory flow rates were significantly improved following evening dosage, suggesting a role for evening administration when nocturnal symptoms predominate.

Adolescent↗
PubMed1986

Foot and hand length for prediction of vital capacity in scoliotic children.

Expected values of vital capacity (VC) and other lung function variables in children are usually predicted from regression equations of the index test on stature. In children with scoliosis, arm span or an "uncoiled" stature derived from the observed stature and the degree of spinal angulation have been used to predict expected values. Stature and hand and foot length were measured and all three anthropometric indices were used as independent variables for the prediction of VC in 489 normal children and adolescents (aged 4-18 years). VC was highly correlated with stature for boys and girls with regression coefficients of 0.93 and 0.91, respectively. For foot length, corresponding coefficients were 0.90 and 0.83, and for hand length 0.90 and 0.80. In 14 scoliotic children, aged 5.9-18.4 years, a close agreement was found for predictions of VC from arm span, uncoiled stature and hand and foot length. When accurate measurements of stature cannot be made, hand or foot length can be used to predict expected VC. This approach may be an alternative to the use of arm span or uncoiled stature to predict VC in children with scoliosis.

Adolescent↗
PubMed1986

Recognition and early management of Reye's syndrome.

Reye's syndrome continues to be associated with a high mortality. Out of 12 cases treated on our intensive care unit over a four year period, seven died, one suffered minimal cerebral damage, and four were normal. Rapid progression through coma stages and high peak ammonia concentrations worsened prognosis. Reye's syndrome was suspected in only 50% of cases at the referring hospital and resulted in prompt referral to the intensive care unit in only one case. Late referral to the unit was associated with a poor outcome. Sudden neurological deterioration followed diagnostic lumbar puncture in six children. Papilloedema was an unreliable sign of raised intracranial pressure and was absent in all cases. While computed tomography of the brain was useful in providing additional evidence of raised intracranial pressure, this could only be confirmed by direct measurement. Lumbar puncture in the presence of rapidly progressive coma should be deferred until raised intracranial pressure has been excluded. To this end, early admission to a paediatric intensive care unit with facilities for computed tomography and monitoring of intracranial pressure is recommended.

Child↗
PubMed1986

Transcutaneous estimation of arterial carbon dioxide in intensive care. Which electrode temperature?

Transcutaneous and arterial carbon dioxide were measured simultaneously in 57 children (age range 10 days to 14.3 years) undergoing intensive care. All were haemodynamically stable at the time of study. Mean calibration time with 5 and 10% carbon dioxide was 43 (range 38-58) minutes and mean arterialisation time was 10.5 (range 3-30) minutes. Duplicate hourly arterial samples over a four hour period showed that transcutaneous: arterial carbon dioxide correlation was independent of electrode temperatures over the range 42-44 degrees C and was independent of child age. One and a half hours after electrode placement transcutaneous carbon dioxide (kPa) = arterial carbon dioxide X 1.41 + 0.02. Use of a simple ratio (arterial carbon dioxide = transcutaneous carbon dioxide/1.40) resulted in a mean estimate of arterial carbon dioxide within 3% of the actual value with coefficients of variation of 11 and 15% at 1.5 and 4.5 hours, respectively. For prediction of arterial carbon dioxide 95% confidence limits around the regression mean rose from +/- 1.04 kPa (7.8 mm Hg) at 1.5 hours to +/- 1.56 (11.7 mm Hg) at 4.5 hours. Baseline drift was more than +/- 0.67 kPa (5 mm Hg) during 22% of the studies. For a drift of less than 0.67 kPa 95% confidence limits were 0.87 and 1.12 kPa, respectively. Arterial carbon dioxide can be estimated with clinically acceptable tolerances from surface electrodes operating at temperatures between 42-44 degrees C. Improved electrode stability and speed of calibration should make this a valuable monitoring technique.

Adolescent↗
PubMed1985

Regional ventilation in infancy. Reversal of adult pattern.

There is evidence that in infants with unilateral lung disease, oxygenation improves when the good lung is uppermost--the reverse of the situation in adults. We performed krypton-81m ventilation scanning in 18 infants and very young children (11 days to 27 months old) with and without abnormal chest radiographs. Scanning was performed with the subject supine, in the left decubitus posture (right lung uppermost), and in the right decubitus posture (right lung dependent). Fractional ventilation to the right lung fell when that lung was dependent and rose when it was uppermost (P less than 0.001). This pattern was seen regardless of the appearance of the chest radiograph. The distribution of ventilation away from dependent lung regions represents a reversal of the adult pattern, which may be due to differences between infants and adults in lung mechanics and diaphragmatic function. This study adds further weight to the argument that infants and very young children with unilateral lung disease should be positioned with their normal lung uppermost to optimize gas exchange. It also offers a rational explanation for the observation that infants with unilateral gas trapping can be successfully treated by placing them so that the diseased lung is dependent.

Age Factors↗
PubMed1985

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.

Adolescent↗
PubMed1985

[Transcutaneous oxygen and carbon dioxide measurement in pediatric intensive care patients].

Transcutaneous partial pressures of oxygen (PtcO2) and carbon dioxide (PtcCO2) were measured in 16 haemodynamically stable patients of a paediatric intensive care unit and were compared with simultaneously measured arterial partial pressures (PaO2 and PaCO2). For the transcutaneous measurement a sensor temperature of 44 degrees C was chosen, blood gas analysis was performed on 2 different automatic blood gas analysers. Comparisons of 82 pairs of oxygen and 60 pairs of carbon dioxide partial pressures were made. Our data show a tight linear correlation between cutaneous and arterial partial pressures of oxygen and carbon dioxide, defined by regression equations and correlation coefficients: PtcO2 = 1.22 + 0.8 X PaO2 (r = 0.93) and PtcCO2 = 5.52 + 1.26 X PaCO2 (r = 0.88). We conclude that transcutaneous measurements of oxygen and carbon dioxide partial pressures are reliable noninvasive techniques for monitoring arterial gas tensions in haemodynamically stable paediatric patients.

Blood Gas Analysis↗