Alan I. Fields

Validation of a Physiologic Stability Index for Use in Critically Ill Infants and Children

Summary: We developed a physiology-based scoring system, the Physiologic Stability Index (PSI) to assess severity of acute illness in the total population of pediatric Intensive Care Unit (ICU) patients. Thirty-four variables from seven physiologic systems were chosen, and the degree of abnormality of each variable was assigned a score reflecting the clinical importance of the derangements. Validity was demonstrated by comparing PSI to hospital mortality and to two other methods that reflect severity of illness, the Clinical Classification System (CCS) and the Therapeutic Intervention Scoring System (TISS). Four hundred and twenty three consecutive admissions to a multidisciplinary ICU were followed daily. Patients classified into higher CCS classes had significantly higher PSI scores (P < 0.001), and there was a highly significant correlation (P < 0.001) between PSI and TISS scores. The linear-logistic regression of observed mortality versus PSI was highly significant (P < 0.0001) and provided an excellent fit. Highly significant differences between survivors and nonsurvivors were observed for PSI scores (P < 0.001), as well as for composite slopes of the regression of PSI scores versus days of care (P < 0.001). These data demonstrate validity of the PSI scoring system.

Distributions of cardiopulmonary variables in pediatric survivors and nonsurvivors of septic shock.

The association of cardiopulmonary variables with outcome was investigated in 42 pediatric patients (18 survivors) with septic shock. All cardiopulmonary variables were obtained during active BP support. The variable distributions were separated into ranges by two empiric cutoff methods: normal ranges and the survivor median values. The proportion of survivors with normal values of wedge pressure and cardiac index was significantly (p < .05) higher than the proportion of survivors outside the normal range. The percentage of survival also significantly (p < .05) increased with above-normal values of oxygen consumption, arteriovenous O2 content difference, O2 extraction, pH, and core temperature. There were significantly (p < .05) more nonsurvivors with wedge pressure, pulmonary shunt, and pH values below the survivor medians. Therapeutic goals based on the distributions of these eight variables isolated patient groups with survival rates of 59% to 75%, compared to the overall survival rate of 43%.

Aspiration of activated charcoal and gastric contents

A case of aspiration of activated charcoal and gastric contents is reported. The patient developed immediate airway obstruction treated by endotracheal intubation and suctioning. Protracted respiratory insufficiency characterized by severe bronchospasm developed after airway obstruction was alleviated.

Sequential cardiopulmonary variables of infants and children in septic shock.

Sequential cardiopulmonary variables were analyzed in 32 infants and children with septic shock. Variables were staged by a system based on therapeutic efforts to control blood pressure. There were 14 survivors and 18 nonsurvivors. Systemic circulation variables (MAP, cardiac index [CI], systemic vascular resistance index [SVRI], wedge pressure [WP], left cardiac work index [LCWI]) and pulmonary circulation variables (mean pulmonary artery pressure [MPAP], pulmonary vascular resistance index [PVRI], CVP, right cardiac work index [RCWI]) were similar in survivors and nonsurvivors. Pulmonary variables (intrapulmonary shunt [Qsp/Qt], fraction of inspired oxygen [FiO2), Pao2, Paco2) revealed significantly more dysfunction in nonsurvivors than survivors during the postresuscitation (PR) and middle (M) shock stages. Even though oxygen delivery was equivalent in survivors and nonsurvivors, nonsurvivors demonstrated decreased oxygen utilization variables (oxygen consumption [Vo2], arteriovenous oxygen content difference [C(a-v)o2], O2 extraction index, core temperature) during the resuscitation (RS) and PR stages.

Assessment of pediatric intensive care--application of the Therapeutic Intervention Scoring System.

There are few reports analyzing the results of intensive care for children. We evaluated quantitatively the amount of care required in our multidisciplinary pediatric ICU using the Therapeutic Intervention Scoring System (TISS) and assessed qualitatively the severity of illness using the Clinical Classification System (CCS). Over a 6-month period, there were 323 patients (99 CCS Class II, 83 Class III, 141 Class IV) whose overall mortality at 1-month follow-up was 10% (Class II, 0%; Class III 2%; Class IV, 23%). A strong association was obtained between CCS and TISS admission scores (Class II-TISS, 11 +/- 0.6; Class III-TISS, 20 +/- 0.8; Class IV-TISS, 38 +/- 1.0). Class IV patients had a highly significant difference between survivors (S) and nonsurvivors (NS) for admission TISS (S = 36, NS = 47, p less than 0.001) and highest TISS (S = 38, NS = 54, p less than 0.001), as well as slopes of the regression of TISS points versus days of care (S = -4.2 vs. NS = +2.3). The mortality of our Class IV patients was lower than a comparable adult population with similar TISS scores; however, the TISS regression slopes for Class IV patients were similar. We conclude that CCS and TISS are both useful for describing the pediatric intensive care patient population. TISS is particularly helpful in assessing the amount of care received as well as providing a means of evaluating severity of illness.

Evaluation of pediatric intensive care.

A total of 294 Clinical Classification System (CCS) Classes III and IV patients in a pediatric ICU (PICU) were evaluated in terms of severity of illness and quantity of care. The group was comprised of patients from 3 services: medicine, cardiovascular surgery, and other surgery. Severity of illness was measured by the Physiologic Stability Index (PSI) and quantity of care was measured by the Therapeutic Intervention Scoring System (TISS). Comparisons were made between survivors and nonsurvivors and among the 3 services. Nonsurvivors had significantly higher (p < .01) PSI and TISS scores than survivors. Medical patients had the highest PSI scores while cardiovascular surgery patients had the highest TISS scores. Analysis of 7-day regression slopes for all survivor groups and medicine and other surgery nonsurvivor groups demonstrated slopes consistent with the expected clinical course. Cardiovascular surgery nonsurvivor slopes were unique and demonstrated increasing stability with stable amounts of care. The PSI/TISS ratio was used to relate levels of physiologic instability to the amount of therapy. Medical patients had the highest ratios and cardiovascular surgery patients had the lowest ratios. Comparisons of survivors and nonsurvivors for the PSI/TISS ratios and regression slopes demonstrated differences that were not evident through comparison of PSI and TISS scores alone.

Sequential physiologic interactions in pediatric cardiogenic and septic shock

We report that the pediatric cardiogenic shock and septic shock populations show similar hemodynamic and oxygen utilization physiologic relationships during aggressive intensive care therapy. We examined the mathematical relationships between vascular tone and flow, and oxygen utilization and oxygen delivery (DO2) in the early and middle stages of cardiogenic and septic shock. The fitted curves between cardiac index and systemic vascular resistance, and oxygen consumption (VO2) and DO2 were clinically and statistically similar in both shock populations. We found no evidence for decreased oxygen extraction in sepsis as compared to the cardiogenic shock population. In addition, it appears that the major determinant of VO2 in these populations is DO2, not oxygen extraction. We suggest that patients with cardiogenic or septic shock can be treated according to similar physiologic principles.

Pneumothorax and pneumomediastinum during pediatric mechanical ventilation.

The incidence of pulmonary barotrauma during mechanical ventilation in children beyond the neonatal age group was studied in two groups of patients. In the first group, 179 cases of pediatric mechanical ventilation for over 12 hours were retrospectively analyzed for the occurrence of pneumothorax and pneumomediastrinum. Eleven percent (6 of 57) of young infants (0--6 months) without hyaline membrane disease and 3% (4 of 122) of older infants and children (over 6 months) developed these complications. Pulmonary barotrauma in young infants occurred only after cardiothoracic surgery and involved the same site as the intraoperative repair in all cases. Pulmonary barotrauma in older infants and children occurred in patients with severe respiratory disease requiring high peak airway pressures, PEEP, and respiratory rates. In the second group, the incidence of pulmonary barotrauma during ventilation with PEEP greater than or equal to 15 cm H2O was analyzed in 14 patients including 4 patients from the previous group. Overall, 64% (9 of 14) of this group developed pulmonary barotrauma and 43% (6 of 14) developed pneumothorax. Of 9 patients receiving PEEP greater than or equal to 15 cm H2O for longer than 24 hours, 6 developed pulmonary barotrauma after the first 24 hours. The incidence of pneumothorax and pneumomediastinum in ventilated infants without hyaline membrane disease and children is comparable to adult series.

Shock following generalized hypoxic-ischemic injury in previously healthy infants and children.

Eighteen previously healthy patients with hypoxic-ischemic shock were observed longitudinally by means of data measured or derived from systemic arterial and pulmonary artery catheters. Shock was characterized by low cardiac index, elevated right and left heart filling pressures, elevated systemic and pulmonary vascular resistances, decreased oxygen consumption, and elevated oxygen extraction indices. Oxygen consumption was significantly correlated with oxygen delivery (r=0.74, P

High-frequency ventilation versus conventional ventilation in dogs with right ventricular dysfunction

A randomized crossover protocol was used to compare conventional mechanical ventilation (CMV) and high-frequency ventilation (HFV) in mongrel dogs experiencing right ventricular dysfunction after right ventriculotomy. When inspired oxygen, pH, Pco2, core temperature, and preload were held constant, cardiac output increased significantly (p < .05) from 1.16 ± 0.24 to 1.38 ± 0.25 L/min and pulmonary vascular resistance decreased significantly (p < .05) from 734 ± 257 to 554 ± 169 dyne sec/cm5 during HFV relative to CMV. We also noted a significant (p < .05) increase in mean arterial pressure from 116 ± 27 to 124 ± 23 mm Hg and a significant (p < .05) increase in left ventricular stroke work from 10.2 ± 3.5 to 12.3 ± 2.6 gm during HFV. During the inspiratory phase of CMV there were increases in CVP, pulmonary artery pressure, and systemic arterial pressure, and decreases in pulmonary artery flow which did not occur during HFV. HFV may be preferable to CMV in the presence of right ventricular dysfunction.