Ia Murdoch

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.

Cardiac output measured by lithium dilution and transpulmonary thermodilution in patients in a paediatric intensive care unit

Objective: To compare the results of cardiac output measurements obtained by lithium dilution and transpulmonary thermodilution in paediatric patients. Design: A prospective study.¶Setting: Paediatric intensive care unit in a university teaching hospital.¶Patients: Twenty patients (age 5 days–9 years; weight 2.6–28.2 kg) were studied.¶Interventions: Between two and four comparisons of lithium dilution cardiac output (LiDCO) and transpulmonary thermodilution (TPCO) were made in each patient.¶Measurements and results: Results from three patients were excluded: in one patient there was an unsuspected right-to-left shunt, in two patients there was a problem with blood sampling through the lithium sensor. There were 48 comparisons of LiDCO and TPCO in the remaining 17 patients over a range of 0.4–6 l/min. The mean of the differences (LiDCO–TPCO) was –0.1 ± 0.3 (SD) l/min. Linear regression analysis gave LiDCO = 0.11 + 0.90 × TPCO l/min (r2 = 0.96). There were no adverse effects in any patient.¶Conclusions: These results suggest that the LiDCO method can be used to provide safe and accurate measurement of cardiac output in paediatric patients. The method is simple and quick to perform, requiring only arterial and venous catheters, which will already have been inserted for other reasons in these patients.

Serum lactate as a predictor of mortality after paediatric cardiac surgery

OBJECTIVE To assess the value of sequential lactate measurement in predicting postoperative mortality after surgery for complex congenital heart disease in children. DESIGN Prospective observational study. SETTING Sixteen bedded paediatric intensive care unit (PICU). SUBJECTS Ninety nine children ( 90 survivors, nine non-survivors). MEASUREMENTS Serum lactate and base deficit were measured on admission and every six hours thereafter. Data were analysed by Mann-Whitney and Fisher’s exact tests. RESULTS There was considerable overlap in initial lactate values between the survivor and non-survivor groups. Initial lactate was significantly raised in non-survivors (median 8.7, range 1.9–17.6 mmol/l) compared with survivors (median 2.4, range 0.6–13.6 mmol/l) (p = 0.0002). Twenty one patients (21.1%) with initial lactate concentrations greater than 4.5 mmol/l survived to PICU discharge. Using receiver operating characteristic analysis an initial lactate of 6 mmol/l had the optimum predictive value for mortality. Initial postoperative serum lactate >6 mmol/l predicted mortality with sensitivity 78%, specificity 83%, and positive predictive value of only 32%. CONCLUSION Initial lactate concentrations have poor positive predictive value for mortality. The routine measurement of lactate for this purpose cannot be justified in clinical practice.

Incidence of hyponatraemia and hyponatraemic seizures in severe respiratory syncytial virus bronchiolitis

Aim: To document the incidence and early evolution of hyponatraemia (serum sodium <136 mmol 1−1) associated with respiratory syncytial virus (RSV) bronchiolitis in infants requiring intensive care. Methods: In a retrospective review over two winter seasons, 130 infants were admitted with confirmed RSV infection, of whom 39 were excluded because of either pre‐existing risk factors for hyponatraemia: diuretic therapy (n= 14), cardiac disease (n= 10), renal disease (n= 2) or lack of admission sodium data (n= 13). Results: The incidence of admission hyponatraemia in the remaining infants (median age 6 wk) was 33% (30/91), with 11% (10/91) exhibiting a serum sodium less than 130 mmol 1−1. Hyponatraemic and normonatraemic infants were of a similar age (median 6 vs 7 wk, p= 0.82). With fluid restriction and diuretic therapy, the incidence of hyponatraemia at 48 h had decreased to 3.3%, odds ratio 0.07 (95% confidence interval 0.02–0.24, p < 0.001). Four infants (4%) suffered hyponatraemic seizures at admission (sodium 114–123 mmol 1−1); three had received hypotonic intravenous fluids at 100–150 ml kg−1 d−1 before referral to intensive care. All four were managed successfully with hypertonic (3%) saline, followed by fluid restriction, resulting in immediate termination of seizure activity and normalization of serum sodium values over 48 h.

A comparison of pulmonary and femoral artery thermodilution cardiac indices in paediatric intensive care patients

We have assessed the agreement between pulmonary artery and femoral artery (COLD) thermodilution measurements of the cardiac index (C1) in a group of paediatric intensive care patients. The COLD method gave consistently higher cardiac index values than the pulmonary artery catheter (PAC); however, the difference was small, with a mean value of 0.191/min−1 m−2 or 4.4% of the mean cardiac index. This difference is not clinically important and suggests that, under these circumstances. the COLD system provides an acceptable alternative to the pulmonary artery catheter for measurement of the cardiac index at the bedside.

Hypoalbuminaemia in critically ill children: incidence, prognosis, and influence on the anion gap

Aims: Hypoalbuminaemia has significance in adult critical illness as an independent predictor of mortality. In addition, the anion gap is predominantly due to the negative charge of albumin, thus hypoalbuminaemia may lead to its underestimation. We examine this phenomenon in critically ill children, documenting the incidence, early evolution, and prognosis of hypoalbuminaemia (<33 g/l), and quantify its influence on the anion gap. Methods: Prospective descriptive study of 134 critically ill children in the paediatric intensive care unit (ICU). Paired arterial blood samples were taken at ICU admission and 24 hours later, from which blood gases, electrolytes, and albumin were measured. The anion gap (including potassium) was calculated and then corrected for albumin using Figge’s formula. Results: The incidence of admission hypoalbuminaemia was 57%, increasing to 76% at 24 hours. Neither admission hypoalbuminaemia, nor extreme hypoalbuminaemia (<20 g/l) predicted mortality; however, there was an association with increased median ICU stay (4.9 v 3.6 days). After correction for albumin the incidence of a raised anion gap (>18 mEq/l) increased from 28% to 44% in all samples (n = 263); this discrepancy was more pronounced in the 103 samples with metabolic acidosis (38% v 73%). Correction produced an average increase in the anion gap of 2.7 mEq/l (mean bias), with limits of agreement of ±3.7 mEq/l. Conclusion: Admission hypoalbuminaemia is common in critical illness, but is not an independent predictor of mortality. However, failure to correct the anion gap for albumin may underestimate the true anion gap, producing error in the interpretation of acid-base abnormalities. This may have treatment implications.

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.

Gastric tonometry in septic shock

OBJECTIVES To investigate the prognostic value of intramucosal pH (pHi) and the relation among pHi, arterial pH, base excess, and lactate in children with septic shock. DESIGN Children admitted to the paediatric intensive care unit with a diagnosis of septic shock were prospectively enrolled. A gastrointestinal tonometer (Tonometrics Division, Instrumentarium Corporation, Helsinki, Finland) was placed into the stomach and intramucosal pH, arterial pH, base deficit, and lactate were measured on admission and six hours later. Sequential data were analysed on 24 patients (17 survivors, seven non-survivors), median age 46 months (range: 2.8–168 months). RESULTS Median pHi on admission was 7.39 (interquartile range 7.36–7.51) in survivors compared with 7.2 (interquartile range 7.18–7.35) in non-survivors (p = 0.01). There was no significant difference in arterial pH, base excess, or lactate among survivors and non-survivors. Admission pHi < 7.32 predicted mortality with sensitivity (57%), specificity (94%), and positive predictive value (80%). Patients with admission pHi < 7.32 who failed to improve ⩾ 7.32 within six hours (n = 3) had 100% mortality. CONCLUSION In children with septic shock the admission pHi is significantly lower in non-survivors. pHi is a better prognostic indicator of mortality than either standard acid-base values or lactate. pHi < 7.32 that does not improve within six hours is associated with a poor prognosis.

Continuous haemodynamic monitoring in children: use of transoesophageal Doppler

A wide range of invasive and non‐invasive techniques for monitoring the haemodynamic condition of critically ill patients is now available. A general reluctance on the part of paediatric intensive care specialists to use pulmonary artery thermodilution catheters and the need for constant realignment of hand‐held Doppler probes has necessitated the search for a technique which is relatively non‐invasive and provides continuous information on the haemodynamic condition of critically ill paediatric patients. We sought to establish if transoesophageal Doppler fulfilled these criteria. Eleven children who had recently undergone cardiac surgery were studied. Median age was 39 months and weight 14.9 kg. Five simultaneous pairs of measurements of cardiac index (CI: thermodilution) and minute distance (MD: transoesophageal Doppler) were made, as a baseline, when each child was haemo‐dynamically stable. Following a fluid challenge, five repeat pairs of measurements were made. The mean percentage changes for CI and MD were 16.4% (range 5.3‐44%) and 16.6% (3.4‐47.7%), respectively. The average coefficients of variation for measurements of CI and MD were 3.5% and 2.9%, respectively. The mean difference in percentage change between CI and MD was ‐0.5% (95% confidence interval for the bias –4% to 3%; limits of agreement –10.7 to +9.7%). Our study indicates that transoesophageal Doppler is reproducible, easy to use and provides clinically acceptable information when following changes in CI in haemodynamically stable paediatric patients. ? Cardiac index, minute distance, pulmonary artery catheter, thermodilution, transoesophageal Doppler