Frank R. Gioia

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. Comparison of hemodynamic measurements during high and low 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

1658 REGIONAL AND LOBAR PULMONARY BLOOD FLOW WITH HIGH FREQUENCY VENTILATION

7172 per PICU and

Electrocardiographic abnormalities in infants and children with neurological injury.

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.

Age-Specific Characteristics of Brain Death in Children

We compared regional and lobar pulmonary blood flow in conventional mechanical ventilation (CV) and high frequency ventilation (HFV) to determine whether changes occur in the distribution of lung perfusion. Fourteen supine anesthetized, paralyzed dogs were ventilated with room air using CV and HFV (tidal volume=2.5 ml/kg, frequency=10 Hz.) Blood gases, pulmonary and systemic arterial pressures, and cardiac output were allowed to reach a steady state, at which time radioactive microspheres were injected. Arterial blood gases with CV showed PO2=94.3 ± 2.2 torr (mean ± S.E.), PCO2=34.5 ± 1.5 torr, and pH=7.35 ± .02. These values remained unchanged with HFV. Comparison of systemic and pulmonary arterial pressures, cardiac output and venous admixture showed no significant differences. In 11 dogs, tissue samples from apical, nondependent, and dependent areas of the lungs were analyzed for changes in blood flow. Regional pulmonary blood flow for apical, nondependent and dependent regions using CV were 44.82±7.06, 44. 89±5.04, and 94.45±6.49 ml/min/gm.dry wt, respectively. The corresponding flows using HFV were 44.27±6.69, 46.47±4.47, and 93.83 ±6.38 ml/min/gm dry wt. These differences were not significant. In the remaining 3 animals, each lobe was analyzed for changes in total lobar blood flow under conditions of CV and HFV, and total lobar blood flows were not different. We conclude that HFV does not produce significant changes in regional or lobar distribution or pulmonary blood flow, or in overall hemodynamics.

CARDIOVASCULAR HARMONICS DURING HIGll FREQUENCY VENTILATION

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.