Noise measurements during high-frequency oscillatory and conventional mechanical ventilation.

OBJECTIVE: To evaluate the noise levels with high-frequency oscillatory ventilation and conventional mechanical ventilation. DESIGN: An observational, prospective study. SETTING: Pediatric intensive care unit. SUBJECTS: The caretakers and environment of the pediatric intensive care unit. INTERVENTIONS: High-frequency oscillatory and conventional mechanical ventilation. MEASUREMENTS AND MAIN RESULTS: Caretakers evaluated noise using a visual analog scale. Noise was measured with a decibel meter and an octave band frequency filter. There was twice as much noise perceived by the caretakers and as measured on the decibel A scale. All measures showed significantly greater noise, especially at low frequencies, with high-frequency oscillatory ventilation. CONCLUSIONS: High-frequency oscillatory ventilation exposes the patient to twice as much noise as does the use of conventional mechanical ventilation.

Postnatal remodeling of the leptomeningeal vascular network as assessed by intravital fluorescence video-microscopy in the rat.

An intriguing characteristic of the ontogenic development of the cerebral vasculature is the rapid differentiation of the neonatal leptomeningeal vascular plexus into the mature, adult network form. The physiological and cellular mechanisms of this cerebrovascular remodeling process are unclear. The objective of this work was to determine and correlate changes in vascular density, network pattern and flow velocity in leptomeningeal microvessels of the rat during postnatal development in vivo. To this end, microvascular diameter, segment length, and vascular density of reconstructed leptomeningeal networks were measured from video-recordings of the microcirculation visualized through a cranial window in 0-15-day-old Sprague-Dawley rats. The velocity of erythrocytes in the microvessels was measured by frame to frame tracking of fluorescently labeled red blood cells. We found that surface vascular density (total vessel length per area), node density and segment density (object per area) decreased significantly by the second week after birth. Anastomosing vascular polygons, characteristic to newborn networks, became less numerous and larger in diameter during the postnatal 2-week period, indicating progressive rarefaction of the networks. Vessel diameter and red cell velocity showed transient increases at 1.5 weeks. The velocity/diameter ratio (V/D), an index of wall shear rate, increased by the age of 1.5 weeks and remained unchanged afterwards. There was a negative correlation between V/D and diameter at 1 week; this relationship was reversed to a positive correlation at 2 weeks. We conclude that postnatal remodeling of the leptomeningeal vascular network is associated with rarefaction and an adaptation of vessel caliber to wall shear rate. These changes may contribute to arterio-venous differentiation and redistribution of blood flow from the superficial to the intracortical vasculature in the developing brain.

Continuous measurement of jugular venous oxygen saturation in response to transient elevations of blood pressure in head-injured patients.

Following traumatic brain injury, continuous jugular venous oxygen saturation (SjvO2) measurements have been made and used to assess cerebral oxygenation. Transients of SjvO2 may reflect cerebral blood flow (CBF) changes if measurements are made over a short period of time during which cerebral metabolic rate for oxygen is assumed unchanged. In response to alterations in perfusion pressure, transients of SjvO2 may indicate the extent to which autoregulation has been preserved after injury. The effect of arterial pressure changes on SjvO2 was measured in 14 severely head-injured patients (Glasgow Coma Scale score < 8) within 36 hours of injury. Mean arterial blood pressure (MABP), arterial oxygen saturation, and intracranial pressure (ICP) data were also continuously recorded by a computer at the patients' bedside. The reliability of the SjvO2 oximetry measurements varied among patients, and an average 38% of SjvO2 measurements were off by more than 6% saturation, necessitating recalibration. During periods of satisfactory catheter performance, 120 instances were found in which MABP was elevated more than 8 torr (mean +/- standard deviation: 32 +/- 13 torr) due to endotracheal suctioning. In 94 of these measurements, there was an associated increase in the ICP of 5 torr or more, averaging 16.6 +/- 10.2 torr. The SjvO2 was 0.62 +/- 0.10 before the increase in MABP and rose to a peak of 0.77 +/- 0.10 during the maximum MABP elevation, suggesting increased CBF during the transient hypertension. In 34 of 37 instances of persistent blood pressure elevations lasting for more than 10 minutes (mean 16.0 +/- 8.0 minutes), the SjvO2 elevation persisted (average duration 15.0 +/- 12.4 minutes), suggesting impaired or lost autoregulatory vasoconstriction. The presence or absence of hyperemia was unrelated to the extent of the autoregulation response. Results indicate that SjvO2 rises with increasing perfusion pressure during and after endotracheal suctioning, suggesting a feeble or absent autoregulatory response following traumatic brain injury.

Noise analysis of three newborn infant isolettes.

OBJECTIVE: The purpose of this study was to evaluate the noise of three newborn infant isolettes. STUDY DESIGN: An observational, prospective study evaluated noise in three isolettes (Ohmeda, Air Shields, and Drager). The study measured interior isolette noise production during quiet noise situations and isolette noise attenuation of added low- and high-frequency noise. Noise was measured on the decibel A scale and in the 125 Hz and 1000 Hz bands. RESULTS: During quiet conditions the Ohmeda and Drager isolettes had the least noise production on the basis of decibel A levels (p < 0.001). Low-frequency noise on the decibel A scale was attenuated the most by the Drager isolette (p < 0.001), although the overall difference may be clinically insignificant. The Ohmeda isolette attenuated high-frequency noise by 28.4 dB as measured on the decibel A scale, which was greater than values for the Drager (22.8 dB) and Air Shields (14 dB) isolettes (p < 0.001). CONCLUSIONS: High-frequency noise attenuation by the Ohmeda and Drager isolettes is clinically and statistically greater than high-frequency noise attenuation by the Air Shields isolette.

Cost analysis of ceiling tile replacement for noise abatement.

OBJECTIVE: Our purpose was to evaluate the cost and benefit of noise reduction after replacement of acoustic ceiling tile in an open ward neonatal intensive care unit (NICU). STUDY DESIGN: An observational, prospective study evaluated noise in an open ward NICU before and after suspended ceiling tiles were replaced. Noise was rated by a 10-point visual analog scale and measured with a decibel meter. RESULTS: The mean decibel level was 55 before and 53 after renovation (p < 0.05). The median visual analog score was 5 before and 4 after renovation (p = 0.09). The cost of ceiling tile replacement was $2400. CONCLUSIONS: The renovation resulted in a small decrease in the decibel level in the NICU, although this measured decrease was not perceived by observers. With a formal prerenovation noise evaluation, a more efficient ceiling tile might have been selected or the project may have been aborted or modified because of the low levels of noise already present.

The Internet, the electronic medical record, the pediatric intensive care unit, and everything.

This article details how computers have changed life for those of us in pediatric intensive care. A week of clinical activity is described, with a focus on the interactions with computer systems that have become an integral part of patient-care activities for many of us. It becomes clear that the boundaries between personal computers, hospital systems, and the Internet are often not sharply defined. Resources that are used every week may include those residing on a personal digital assistant, on the hospital's electronic medical record, or on a distant site on the World Wide Web. Key resources on the Internet (World Wide Web and e-mail) are identified. The technical underpinnings, particularly the network that provides the infrastructure for various resources, are described.

Arterial pH modulation of regional cerebral blood flow during hyperammonemia in dogs.

Acute hyperammonemia at normal arterial pH causes selective increases in midbrain blood flow in dogs. Unexpectedly, further increases occur with hypocapnia. We investigated whether metabolic acidemia and alkalemia modulate the distribution of ammonium across the blood-brain barrier and if, in turn, midbrain blood flow is effectively modulated. In dogs anesthetized with pentobarbital sodium, hyperammonemia (approximately 940 microM) was produced by a 210-min infusion of ammonium acetate. Concurrent infusion of NaHCO3 increased arterial pH to 7.53 +/- 0.02 (SE), whereas HCl infusion decreased pH to 7.11 +/- 0.01. Normocapnia was maintained. Cerebrospinal fluid [HCO3-] increased 5 mM with alkalemia (one-half of the increase in blood) and was unchanged with acidemia. Thus cerebrospinal fluid [H+]/blood [H+] was greater with alkalemia than acidemia. The corresponding ratio for ammonium was likewise greater with alkalemia (0.70 +/- 0.06) than acidemia (0.44 +/- 0.08). Microsphere-determined blood flow to midbrain more than doubled in the alkalemic group but was unchanged in the acidemic group. No other region along the neuraxis or in cerebrum showed increased blood flow in either hyperammonemic group. Alkalemia without hyperammonemia did not increase midbrain blood flow. Thus metabolic acidemia-alkalemia significantly alters ammonium partitioning into cerebrospinal fluid, and this alteration is sufficiently great to exert a specific physiological effect manifested by changes in midbrain blood flow.

Control and variability of gastric pH in critically ill children.

OBJECTIVES: To determine the effect of illness severity and acute central nervous system injury on the control and variability of gastric pH in pediatric intensive care unit (ICU) patients receiving ranitidine. DESIGN: Prospective, descriptive study. SETTING: Pediatric ICU of a children's hospital. PATIENTS: Fourteen pediatric ICU patients. INTERVENTIONS: Ranitidine (4 mg/kg/day) was administered to all patients. MEASUREMENTS AND MAIN RESULTS: Patients enrolled in the study were divided into two groups based on illness type and severity. Illness severity was measured by the Pediatric Risk of Mortality (PRISM) score, with a PRISM score of > or = 20 defining severe illness. Illness type was designated as central nervous system or noncentral nervous system. Gastric pH was continuously monitored in all patients using an intragastric, pH-sensitive electrode. Poor control of gastric pH was defined as a pH of < 4.0 for > 20% of the time monitored. The statistical significance of the differences between groups was measured using the Wilcoxon two-sample test or Fisher's exact test. Patients with severe illness or acute central nervous system injury had a lower mean gastric pH than all other patients (4.6 vs. 6.4; p = .008) and spent more time with a gastric pH of < 4.0 than other patients (47.5% of time monitored vs. 12.5% of time monitored; p = .003). Poor control of gastric pH occurred in 100% of patients with severe illness or acute central nervous system injury, while only 20% of the remaining patients had poor control of gastric pH (p = .01). Using power-spectrum analysis to evaluate gastric pH variability, gastric pH in patients receiving bolus ranitidine was more variable than gastric pH in patients receiving ranitidine continuously (p = .045). Illness severity or type had no effect on gastric pH variability (p = .78). CONCLUSIONS: a) Continuous infusion of ranitidine decreases variability of gastric pH in pediatric ICU patients; b) gastric pH variability may make intermittent monitoring of gastric pH inaccurate; c) children with acute central nervous system injury or PRISM scores of > or = 20 have poor control of gastric pH; d) type of injury and PRISM scores predict response to ranitidine therapy.

Skin breakdown in children and high-frequency oscillatory ventilation.

OBJECTIVE: To investigate the relationship of high-frequency oscillatory ventilation (HFOV) to skin breakdown on the scalp and ears in mechanically ventilated children. STUDY DESIGN: Retrospective cohort study of 32 patients supported with HFOV paired with 32 patients supported with conventional mechanical ventilation (CV) in a pediatric intensive care unit (PICU). RESULTS: By univariate analysis, more HFOV patients had skin breakdown than did the CV patients (53% vs 12.5%, p=.001); HFOV patients also had greater severity of illness (Pediatric Risk of Mortality scores), higher mortality, and longer durations of neuromuscular blockade, low systolic blood pressure, and time exposed to risk. Life table analysis demonstrated no difference in the rate of skin breakdown between HFOV and CV patients. Multifactorial analysis showed that only PICU time at risk was a risk factor for skin breakdown. CONCLUSIONS: HFOV was not an independent risk factor for the development of skin breakdown. PICU time at risk was the sole risk factor for the development of skin breakdown in all mechanically ventilated patients in the PICU.

Use of active noise cancellation devices in caregivers in the intensive care unit.

OBJECTIVE: Recent development of noise cancellation devices may offer relief from noise in the intensive care unit environment. This study was conducted to evaluate the effect of noise cancellation devices on subjective hearing assessment by caregivers in the intensive care units. DESIGN: Randomized, double-blind. SETTING: Adult medical intensive care unit and pediatric intensive care unit of a teaching hospital. SUBJECTS: Caregivers of patients, including nurses, parents, respiratory therapists, and nursing assistants from a medical intensive care unit and pediatric intensive care, were enrolled in the study. INTERVENTION: Each participant was asked to wear the headphones, functional or nonfunctional noise cancellation devices, for a minimum of 30 mins. MEASUREMENTS: Subjective ambient noise level was assessed on a 10-point visual analog scale (VAS) before and during headphone use by each participant. Headphone comfort and the preference of the caregiver to wear the headphone were also evaluated on a 10-point VAS. Simultaneously, objective measurement of noise was done with a sound level meter using the decibel-A scale and at each of nine octave bands at each bedspace. RESULTS: The functional headphones significantly reduced the subjective assessment of noise by 2 (out of 10) VAS points (p < 0.05) in environments of equal objective noise profiles, based on decibel-A and octave band assessments. CONCLUSION: Noise cancellation devices improve subjective assessment of noise in caretakers. The benefit of these devices on hearing loss needs further evaluation in caregivers and critically ill patients.

Reduction of morbidity in interhospital transport by specialized pediatric staff.

OBJECTIVE: We prospectively compared the occurrence of morbidity during high-risk interhospital transport in two types of transport systems: specialized tertiary center-based vs. nonspecialized, referring hospital-based. DESIGN: Concurrent, prospective comparison of morbidity at two pediatric centers that use different types of transport team. SETTING: Two tertiary care pediatric intensive care units (ICU). The specialized team consisted of a pediatric resident, pediatric intensive care nurse, and a pediatric respiratory therapist. Comparison was made with referring institution transports by nonspecialized personnel to a second center. The two centers were similar in size and patient mix, with referral areas of similar population and rural/urban ratio. PATIENTS: One hundred forty-one patients transported to two tertiary pediatric ICUs. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Two types of events were assessed: vital signs and other observable clinical events were described as "physiologic deteriorations." Events such as loss of intravenous access, endotracheal tube mishaps, and exhaustion of oxygen supply were described as "intensive care-related adverse events." Pretransport severity of illness and therapy were described by Pediatric Risk of Mortality (PRISM) and Therapeutic Intervention Scoring System (TISS) scores. Only high-risk patients with PRISM scores of > or = 10 were analyzed. Intensive care-related adverse events occurred in one (2%) of 49 transports by the specialized team and 18 (20%) of 92 transports by nonspecialized personnel. The difference is statistically significant (p < .05). Physiologic deterioration was similar in the two groups occurring in five (11%) of 47 specialized team transports and 11 (12%) of 92 transports by the nonspecialized team. CONCLUSION: We conclude that specialized pediatric teams can reduce transport morbidity. This is the first published study to compare two models of pediatric transport using identical definitions of severity and morbidity.

Video microscopy of cerebrocortical capillary flow: response to hypotension and intracranial hypertension.

Although autoregulation of cerebral blood flow is well established, the response of cerebral capillary circulation to reduced cerebral perfusion pressure (CPP) is unclear. The objective of this study was to determine whether red cell flow velocity in individual capillaries of the cerebral cortex is maintained during acute decreases in CPP. Microcirculation of the superficial parietal cerebral cortex of adult barbiturate-anesthetized artificially ventilated rats was visualized using a new design of closed-perfused cranial window and epifluorescent-intensified video microscopy. Fluorescein-isothiocyanate-labeled red blood cells (FRBC) injected intravenously were used as markers of capillary flow. CPP, defined as mean arterial pressure minus intracranial pressure, was reduced by controlled hemorrhage or by stepwise elevation of local intracranial pressure. The movement of FRBC in the parenchymal capillary network was video recorded at each pressure level, and FRBC velocity in each capillary was measured off-line with use of the dual-window digital cross-correlation technique. FRBC flux in the capillaries was measured by automated cell counting. FRBC velocity at normal perfusion pressure was 1.47 +/- 0.58 (SD) mm/s and changed little in the perfusion pressure range of 70-120 mmHg. The autoregulatory index in this pressure range was 0.0049 mm.s-1.mmHg-1. Opening of previously unperfused capillaries was not observed. FRBC flux correlated with FRBC velocity, but the latter was maintained in a narrower range than FRBC flux, suggesting a decrease in capillary diameter or hematocrit with decreasing perfusion pressure. The results suggest that flow autoregulation is associated with the maintenance of capillary flow velocity and that capillary recruitment does not contribute to flow autoregulation in the rat cerebral cortex.

Altered skin integrity in children admitted to a pediatric intensive care unit.

As part of a quality improvement study, the incidence and severity of altered skin integrity in a tertiary pediatric intensive care unit (PICU) were investigated in an attempt to identify contributing risk factors. Demographic, severity of illness, and practice variables were collected on 271 of 357 admissions during an 18-week period. Data were analyzed from the date of PICU admission until a change in skin integrity occurred or until PICU discharge. Altered skin integrity occurred in 26 percent of admissions; 7 percent of the cases had skin breakdown. By multivariate analysis, only the Pediatric Risk of Mortality Score and white race were associated with altered skin integrity.