M Hatherill

Clinical validation of cardiac output measurements using femoral artery thermodilution with direct Fick in ventilated children and infants.

Objective: To validate clinically cardiac output (CO) measurements using femoral artery thermodilution in ventilated children and infants by comparison with CO estimated from the Fick equation via a metabolic monitor. Design: Prospective, comparison study. Setting: Paediatric intensive care unit of a university hospital. Patients: 24 ventilated infants and children, aged 0.3 to 175 months (median age 19 months). Interventions: Oxygen consumption measurements were made and averaged over a 5-min period, at the end of which arterial and mixed venous blood samples were taken and oxygen saturations measured by co-oximetry, with CO being calculated using the Fick equation. Over this 5-min period, five sets of femoral arterial thermodilution (FATD) measurements were made and averaged. One comparison of CO values was made per patient. Results: Mean Fick CO was 2.55 l/min (range 0.24 to 8.71 l/min) and mean FATD CO was 2.51 l/min (range 0.28–7.96 l/min). The mean bias was 0.03 l/min (95 % confidence interval –0.07 to 0.14 l/min), with limits of agreement of –0.45 to 0.52 l/min. When indexed to body surface area, the mean Fick cardiac index became 3.51 l/min per m2 (1.52–6.98 l/min per m2) and mean FATD 3.49 l/min per m2 (1.74–6.84 l/min per m2). The mean bias was 0.02 l/min per m2 (95 % confidence interval –0.11 to 0.15 l/min per m2) with limits of agreement of –0.57 to 0.61 l/min per m2. The mean FATD coefficient of variation was 5.8 % (SEM 0.5 %). Conclusions: FATD compares favourably with Fick derived CO estimates in infants and children and may represent an advance in haemodynamic monitoring of critically ill children.

Early hyperlactataemia in critically ill children

Objective: To examine the relationships between early hyperlactataemia, acidosis, organ failure, and mortality in children admitted to intensive care.¶Design: Prospective observational study. Children with lactate levels > 2 mmol/l were eligible for enrolment. Post-operative patients and those with inherited metabolic disease were excluded. Seven hundred and five children admitted to intensive care were screened, and 50 children with hyperlactataemia (incidence 7 %), aged 20.3 months (0.1–191) were enrolled and followed up. The Paediatric Risk of Mortality (PRISM) score, Multiorgan System Failure (MOSF) score, length of ICU stay, and outcome were recorded. Data were collected for lactate (mmol/l), pH, and base excess (BE) until 24 h after admission. Data are reported as median (range) and were analysed by the Mann-Whitney, Fishers Exact, and Kruskal-Wallis tests, and chi-squared test for trend.¶Results: Overall mortality in the screening group was 70/705 (10 %). In the study group (n = 50) median PRISM score was 19 (4–49), median MOSF score 2 (1–4), and observed mortality 32/50 (64 %). Median duration of ICU stay was 6 days (2–32) in survivors, and median time until death 3 days (0–13) in nonsurvivors. Eleven nonsurvivors (34 %) died within 24 h. In the screening group, hyperlactataemia on admission identified mortality with likelihood ratio = 15. In the study group, neither the admission lactate (3.8 vs 4.6 mmol/l, P = 0.27), pH (7.32 vs 7.30, P = 0.6), nor BE (–7.5 vs –8, P = 0.45) differed significantly between survivors and nonsurvivors. Neither the admission nor peak lactate increased with increasing MOSF score (P = 0.5 and 0.54). The median peak lactate level was 5 mmol/l (2–9.3) in survivors compared to 6.8 mmol/l (2.3–22) in nonsurvivors (P = 0.02), and the cumulative average lactate level was 2.4 mmol/l (1–4.9) in survivors, compared to 4.5 mmol/l (1.6–21) in nonsurvivors (P = 0.0003). Persistent hyperlactataemia 24 h after admission identified mortality with likelihood ratio = 7.¶Conclusion: Hyperlactataemia on admission to intensive care is associated with a high mortality in children. Nonsurvivors within this group may be distinguished by the peak lactate level, or by persistent hyperlactataemia after 24 h of treatment.

A comparison of three scoring systems for mortality risk among retrieved intensive care patients

Aims: To assess the impact of two paediatric intensive care unit retrieval teams on the performance of three mortality risk scoring systems: pre-ICU PRISM, PIM, and PRISM II. Methods: A total of 928 critically ill children retrieved for intensive care from district general hospitals in the south east of England (crude mortality 7.8%) were studied. Results: Risk stratification was similar between the two retrieval teams for scores utilising data primarily prior to ICU admission (pre-ICU PRISM, PIM), despite differences in case mix. The fewer variables required for calculation of PIM resulted in complete data collection in 88% of patients, compared to pre-ICU PRISM (24%) and PRISM II (60%). Overall, all scoring systems discriminated well between survival and non-survival (area under receiver operating characteristic curve 0.83–0.87), with no differences between the two hospitals. There was a tendency towards better discrimination in all scores for children compared to infants and neonates, and a poor discrimination for respiratory disease using pre-ICU PRISM and PRISM II but not PIM. All showed suboptimal calibration, primarily as a consequence of mortality over prediction among the medium (10–30%) mortality risk bands. Conclusions: PIM appears to offer advantages over the other two scores in terms of being less affected by the retrieval process and easier to collect. Recalibration of all scoring systems is needed.

Use of permissive hypercapnia in the ventilation of infants with respiratory syncytial virus infection

Abstract We wished to retrospectively evaluate the effects of permissive hypercapnia (PHY) on barotrauma, mortality and length of stay when applied to ventilated infants with respiratory syncytial virus (RSV) bronchiolitis. Nineteen control infants with RSV induced respiratory failure were treated with conventional ventilation (April 1991–January 1994), after which time PHY was adopted as unit policy. A further 28 infants were then treated with PHY (January 1994–April 1996). Demographic and physiological data were collected from admission, and outcome variables including length of stay, barotrauma and mortality were recorded. The PHY group showed a significantly higher mean pCO2 (7.6 vs 5.2 kPa), a lower mean pH (7.34 vs 7.40), and a reduction in maximal peak inspiratory pressures (25 vs 30 cmH2O). Mortality, barotrauma, use of neuromuscular blockade and nosocomial infection did not differ between groups. There was a trend towards increased length of ventilation in the PHY group (median 7 vs 5 days). Conclusion Based on this retrospective data we can show no benefit for the use of permissive hypercapnia as a ventilatory strategy in this patient group. A prospective randomised controlled trial is warranted to accurately assess the outcome variables and cost implications of this strategy.

Early detection of necrotizing enterocolitis by gastrointestinal tonometry

The diagnosis of necrotizing enterocolitis (NEC) in neonates has traditionally depended on a combination of clinical signs, biochemical parameters and radiological changes. The measurement of intramucosal pH by gastrointestinal tonometry provides a simple means of long‐term monitoring which may detect the development of NEC before conventional techniques. We present our experience of tonometry in two‘at risk’term neonates with Hypoplastic Left Heart Syndrome.

Evaluation of the 5-French saline paediatric gastric tonometer.

Objective: To evaluate the paediatric 5-French (Fr) saline-filled gastric tonometer. Design: (a) In vitro comparison of saline bath reference pCO2 with tonometric pCO2 measured by normal saline-filled and phosphate-buffered saline-filled 5-Fr tonometers, and by a recirculating gas tonometer. ( b) In vivo comparison of gastric intramucosal pCO2i, measured by normal saline-filled 5-Fr tonometer (NST) and simultaneously by recirculating gas tonometer (RGT) in ten paediatric intensive care patients. (c) In vivo comparison of pCO2i measured simultaneously by 2 NST 5-Fr tonometers, before and after enteral feeding, in ten paediatric intensive care patients. Measurements and main results: (a) Twenty consecutive measurements of pCO2 were made at constant reference pCO2 of 19, 38, 56, and 75 mmHg (2.5, 5.0, 7.5, and 10.0 kPa), respectively. The NST tonometer underestimated reference pCO2 by mean bias (limits of agreement) of 58 % (20 %), and the phosphate-buffered saline-filled tonometer by 6 % (26 %). The RGT showed mean bias 5.7 % with narrow limits of agreement (1.5 %). (b) In 50 paired (NST vs. RGT) in vivo measurements over pCO2i range 23–73 mmHg (3.0–9.7 kPa), the NST underestimated RGT pCO2i by a mean bias of 10 mmHg (1.3 kPa), with limits of agreement + /–10 mmHg (1.5 kPa). This resulted in NST consistently overestimating pHi and underestimating pCO2 gap (both P < 0.001). (c) One hundred simultaneous paired NST measurements were assessed (50 without, and 50 with enteral feeding). The mean biases (limits of agreement) were identical in the fasted and fed states 0.4 ± 6 mmHg, with no difference between the fed and fasting states (P = 0.7). Conclusions: There are inherent problems in the methodology of saline tonometry, which adversely affect the accuracy and reliability of the 5-Fr paediatric gastric tonometer in comparison to recirculating gas tonometry.