Ocular surface flora in drowning victims.

Contaminated allograft donor tissue represents a potential source of infection unique to keratoplasty. We prospectively studied perilimbal cultures of drowning victims over 30 months to determine if the ocular surface flora of drowning victims was unique. Twenty-eight donor eyes were cultured from 14 drowning victims. Ninety-three percent of limbal cultures were positive for one or more organisms, compared to results of a previous study of surface contamination of donor globes in which 65% were found to be culture positive. Fifty-seven percent (16 of 28) of donor eyes grew at least one streptococcal species, while 46% (13 of 28) grew two or more streptococcal species. A previous study identified streptococcal species in 7.9% of perilimbal cultures from nondrowning donor eyes, which demonstrates the unique effect of drowning on the ocular flora. The incidence of gram-negative isolates was also markedly higher in drowning victims, compared to previous studies of donor globes. This prospective study has shown that the ocular surface flora of drowning victims harbors markedly increased numbers of streptococcal species as well as gram-negative organisms. These findings demand careful globe decontamination, and emphasize the need for appropriate antibiotic coverage in corneal storage media.

Effects of dexamethasone on pulmonary function following extubation.

Dexamethasone is often given to intubated neonates to facilitate successful extubation. To study the effects of dexamethasone on pulmonary function immediately following extubation, we conducted a randomized, blinded, placebo-controlled trial in 51 infants. All infants had been intubated for a minimum of 3 days but no more than 30 days. Mean weight at extubation was 2.41 kg in treated infants, 2.25 kg in control infants. When infants were deemed ready for extubation, dexamethasone 0.5 mg/kg/dose or an equal volume of normal saline was given in three doses 8 hours apart. The final dose was given 1 hour before extubation. Esophageal pressure, air flow integrated to tidal volume (Vt), respiratory rate, and heart rate were measured before extubation, immediately following extubation, and every 20 minutes for 80 minutes. Total pulmonary resistance (RTP), dynamic lung compliance (CL), and minute ventilation (VE) were calculated. Forty-two infants completed the study; 19 infants received dexamethasone and 23 received placebo. There was no difference between the two groups in gestational age, weight at study, or length of intubation. Vt, RTP, VE, and CL were not significantly different between the two groups over time; however, RTP increased over time in the placebo group. Heart rate was significantly lower in the dexamethasone group. We conclude that dexamethasone appears to have limited effect on pulmonary function immediately following extubation in the population studied. Further studies should evaluate the drug effect beginning at least 1 hour after extubation.

Cardiorespiratory effects of changing inspiratory to expiratory ratio during high-frequency oscillation in an animal model of respiratory failure.

To examine the effects of varying inspiratory/expiratory ratio (I/E) on cardiorespiratory function during high-frequency oscillation (HFO), 11 saline-lavaged rabbits were ventilated at I/E = 1:2, 1:1.5, 1.5:1, and 2:1 in a paired comparison to a baseline of I/E = 1:1. HFO was delivered by a SensorMedics model 3100 oscillator at a frequency of 10 Hz. Pressure amplitude and proximal mean airway pressure (PPaw) were held constant as I/E was varied from baseline to the experimental I/E. During each paired observation, PaO2, PaCO2, cardiac output, blood pressure, and distal mean airway pressure (DPaw) were measured. We found that as I/E was increased or decreased from 1:1, no significant changes in PaO2, PaCO2, blood pressure, or cardiac output occurred. We conclude that in this model, varying I/E has no significant effect on oxygenation, ventilation, or cardiovascular function.

Measurement of tidal volume using a pneumotachometer during high-frequency oscillation.

To assess the accuracy of a pneumotachometer (PN) for tidal volume (VT) measurements during high-frequency oscillation (HFO), we determined simultaneously VT using a PN and a full body plethysmograph (PL) in 12 rabbits. HFO was delivered with an oscillator at a frequency of 10 Hz, mean airway pressure of 8 cm H2O, and inspiratory time of 50%. Pressure amplitude (delta P) was varied as follows: 40, 60, 80, 20, 100, 40 cm H2O. Finally, in ten rabbits a spacer equal in deadspace (VD) to that of the PN (15 ml) was left in-line for 5 min. Blood gases were obtained before and after the spacer was added. We found that VT-PN correlates well with VT-PL (r = .92), although the difference between VT-PN and VT-PL is greater at large VT. Significant respiratory acidosis developed with the spacer in-line. PN may be used to trend VT during HFO but PN must not be left in-line, as increased VD seriously affects ventilation.

Capillary blood gases in the neonate. A reassessment and review of the literature.

Heel puncture capillary blood gas (CBG) measurements continue to be used in neonates for estimating arterial blood gas values. Review of the literature reveals general agreement that CBG PO2 values are of little use in predicting arterial PO2 and that CBG pH values are reliable predictors of arterial pH; opinion varies regarding CBG PCO2. We conducted a two-part study comparing postductal arterial and CBG values. First, 50 infants were studied, each only once. All infants had umbilical arterial catheters in place. Blood was obtained simultaneously from the umbilical artery catheter and the warmed heels. Results demonstrated poor predictability of arterial values from CBG pH and PCO2 as well as for PO2. Second, to determine if variation both within and among individuals was similar, repeated measurements were made in 27 additional infants comparable to the first group. We obtained 3 to 28 simultaneous postductal arterial and CBG samples from each infant. A random-effects nested analysis of variance indicated that for pH, variation was largely the result of between-subject or within-subject replicates effects, while for PO2 and PCO2, most variation was explained by differences between the two techniques (umbilical artery catheter vs CBG). The results indicate that CBG measurements do not accurately predict arterial values in neonates. Extreme caution should be used when management decisions are based on CBG values.

Cardiopulmonary effects of high frequency positive-pressure ventilation versus jet ventilation in respiratory failure.

Conventional ventilators are frequently used at high rates in the intensive care nursery to achieve adequate oxygenation and ventilation with reduced peak inspiratory pressure. The efficacy and limitations of high frequency positive-pressure ventilation (HFPPV) using a conventional ventilator were studied by comparing the cardiopulmonary effects of HFPPV with those of high frequency jet ventilation (HFJV) in an animal model of respiratory failure. Sixteen saline-lavaged rabbits were ventilated with either HFPPV or HFJV for 2 h using rates of 200 breaths/min, inspiratory to expiratory ratio of 1:2, and FIO2 of 1.0. As controls an additional eight lavaged rabbits were ventilated at conventional rates (40 to 60 breaths/min). Proximal peak inspiratory pressure as indicated on the ventilator manometer or drive pressure was adjusted to maintain acceptable blood gases. Cardiac output (CO) was measured by thermodilution. Although there was a significant decrease in cardiac function over time, there were no significant differences between the groups in CO or stroke volume. Satisfactory oxygenation and ventilation were maintained in all groups. Static respiratory system compliance and mean airway pressure were similar among the groups. Histologic examination of the lungs revealed no differences between the three ventilator groups. The results of this study indicate that both HFPPV and HFJV are effective in short-term maintenance of normal blood gases in respiratory failure without any discernable differences in their effects on cardiovascular function. At very high rates, however, increases in VT are not possible with HFPPV, which limits its usefulness and flexibility in respiratory failure.