Inspiratory work and response times of a modified pediatric volume ventilator during synchronized intermittent mandatory ventilation and pressure support ventilation.

Volume ventilation by demand flow ventilators significantly increases work of breathing during inspiration. Although various ventilator modifications and different modes of ventilation have been developed, there have been few studies regarding imposed work of breathing in infants and children. This study was designed to evaluate several modifications of a commercially available demand flow ventilator designed to shorten response time (tr) and decrease the imposed work (Wi) involved in opening the demand valve. Minimum withdrawal volume (Vmin), maximum negative pressure (P mneg), and tr were measured. Wi was defined as the product of Vmin and P mneg. Seven Siemens Servo 900C ventilators were tested under 16 different trial conditions with four variables: 1) mode of ventilation (synchronized intermittent mandatory ventilation [SIMV] vs. pressure support ventilation [PSV]); 2) caliber of circuit tubing (adult vs. pediatric); 3) location of airway pressure monitor (distal vs. proximal); and 4) ventilator trigger sensitivity (0 cm H2O--high vs. -2 cm H2O--low). Vmin, Pmneg, and Wi were all decreased (P less than .05) while tr was unaffected by changing ventilator trigger sensitivity from low to high. Wi was decreased by pediatric tubing and proximal airway pressure monitoring only when low trigger sensitivity was used. PSV and proximal airway monitoring shortened tr. The authors conclude that the use of pediatric circuit tubing and proximal airway pressure monitoring with a Siemens Servo 900C ventilator significantly improved ventilator performance.

Age-specific characteristics of brain death in children.

Clinical and neuropathologic characteristics of 45 children who met criteria for brain death were analyzed. Children between 2 months and 1 year of age were compared with children older than 1 year and children older than 5 years. The observation period to fulfill brain death criteria was not different between the age groups. Deep tendon and spinal reflexes were preserved significantly less frequently in children younger than 1 year old. Diabetes insipidus and the necessity of inotropic support were significantly more frequent in children older than 5 years. Fifty-eight percent (26/45) of patients had no cerebral perfusion pressure before death. However, 18% (8/45) of patients never had a cerebral perfusion pressure below 40 mm Hg. No relationships could be shown between the clinical or physiologic factors and neuropathologic findings. We found no support for using different brain-death criteria for children between 2 months and 1 year of age.

High frequency ventilation.

High frequency ventilation (HFV) presents a new respiratory therapy modality that has taught us much about the theories of gas transport in the lung. Both experimental and clinical applications are summarized. Although the future clinical role of HFV remains uncertain, pediatric applications and investigation continue at the forefront of this new technology.

Organ blood flow during high-frequency ventilation at low and high airway pressure in dogs.

Using the radiolabeled microsphere technique, the authors studied hemodynamic variables and regional blood flow to multiple peripheral organs during conventional positive-pressure ventilation (CV) and high-frequency ventilation (HFV) at low and high mean airway pressure (Paw). Twenty supine anesthetized, paralyzed dogs were ventilated using CV (14-16 breaths/min) and HFV (rate = 10 Hz) in random order. In the first group (low Paw, n = 10), Paw was maintained at 3 cmH2O during CV and HFV. In the second group (high Paw, n = 10), Paw was increased to 13 cmH2O during CV and HFV. Pulmonary capillary wedge pressure and right atrial pressure remained constant during low and high Paw trials. No differences in heart rate, systemic arterial pressure, intracranial pressure, or cardiac output were noted during CV and HFV within the low and high Paw groups. In addition, blood flow to multiple peripheral organs during CV and HFV remained constant within each Paw group, except for a small decrease in cerebellar blood flow during HFV at high Paw trials showed a significant decrease in hepatic arterial and outer kidney cortical flow at high Paw. Total cerebral blood flow was decreased at high Paw, as were regional flows to diencephalon, midbrain, pons, medulla, and cerebellum. However, these differences were not attributable to differences in cerebral perfusion pressure or intracranial pressure, and cerebral oxygen delivery was not different between high Paw and low Paw groups. It is concluded that under conditions of similar Paw in anesthetized dogs, HFV does not significantly alter hemodynamic patterns or regional circulation relative to CV.

Lack of validity of diagnosis-related group payment systems in an intensive care population.

Case mix based on diagnosis-related groups (DRGs) was studied over 3 years for duration of stay and mean charges for a pediatric intensive care unit (PICU) and a general ward (WARD) population. Case mix variation for 2403 PICU and 14,552 WARD patients was analyzed, and a subset of 856 PICU and 2222 WARD patients examined for variations in duration of stay and mean charges in nine DRGs. Whereas case mix by DRG was consistent over time for both groups, the PICU case mix differed consistently from WARD case mix (P less than 0.001). After adjustment for inflation and for differences in case mix, average stay for the PICU was 10.7 days, versus 6.1 for the WARD (P less than 0.025), with a mean charge of $7172 per PICU and $2946 per WARD patient (P less than 0.01). Furthermore, the case mix-adjusted differences in duration of stay and mean charge between the PICU and WARD populations increased over time. Pediatricians will need to address DRG-based reimbursement systems that place intensive care units, and their institutions, at a significant financial disadvantage.

Pulse oximetry in critically ill children.

To confirm the clinical applicability of a commercial pulse oximeter, we compared arterial hemoglobin saturation values determined by in-vitro oximetry and pulse oximetry in 15 critically ill children. One hundred ninety-two paired hemoglobin saturations were determined by both noninvasive pulse oximetry and direct measurement of arterial blood samples. The correlation between these two methods of measurement was statistically significant (r = 0.895; p less than 0.001). The mean percentage difference between the two measurements was 1.8%. Pulse oximetry was found to be safe and less cumbersome than other methods of monitoring arterial oxygen content. Overall, pulse oximetry was precise and provided a clinically satisfactory noninvasive method for continuously monitoring arterial hemoglobin saturation in critically ill children.

High-frequency ventilation attenuation of hypoxic pulmonary vasoconstriction. The role of prostacyclin.

In order to determine the effects of high-frequency ventilation on the pulmonary vascular response to hypoxia, we assessed pulmonary vascular resistance at 2 levels of inspired oxygen tension (PlO2), 200 and 30 mmHg, during conventional and high-frequency ventilation in the isolated, blood-perfused lungs of 10 sheep, 5 treated with indomethacin (40 micrograms/ml of perfusate) and 5 untreated. Resistance was assessed by measuring pulmonary artery pressure-flow curves generated over a wide range of flows (20 to 140 ml X min-1 X kg body wt-1). Conventional ventilation was provided by an animal ventilator at a rate of 10 min-1 and a tidal volume of 10 ml X kg body wt-1. High-frequency ventilation was provided by a flow interrupter at a rate of 1,200 min-1 and a tidal volume less than 1.5 ml X kg body wt-1. In the 5 untreated lungs, the normoxic pressure-flow curve was unaltered by high-frequency ventilation, but the hypoxic pulmonary vasoconstrictor response was significantly attenuated. Furthermore, the net rate of change of 6-keto-prostaglandin F1 alpha concentration in the perfusate during hypoxia was significantly greater with high-frequency ventilation (65.4 +/- 8.9 pg X ml-1 X min-1) than with conventional ventilation (2.8 +/- 18.7 pg X ml-1 X min-1). In the 5 indomethacin-treated lungs, production of 6-keto-prostaglandin F1 alpha was markedly depressed, and the attenuation of the hypoxic vasoconstrictor response by high-frequency ventilation was abolished.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiographic abnormalities in infants and children with neurological injury.

Electrocardiographic (ECG) abnormalities were found in 15 of 20 consecutive children (75%) admitted to the Pediatric ICU (PICU) with central nervous system injury produced by trauma or neurosurgical procedures. The ECG abnormalities included prolonged qTc, U waves, and notched T waves as well as ventricular arrhythmias. The high frequency and potential seriousness of this problem in infants and children suggests that neurogenic ECG changes should be looked for in all infants and children with neurological insults.