A randomized trial of the effect of midazolam on intraocular pressure.

PURPOSE: The effect of midazolam on intraocular pressure (IOP) in adults was studied as an initial step in determining whether it can be used as a preoperative anxiolytic or sedative agent in children with glaucoma who are undergoing examination for IOP measurements. METHODS: This study followed a prospective, placebo controlled, randomized, double masked design. Fifty-five participants were enrolled after informed consent was obtained. Each enrolled patient underwent a brief history and eye examination. Measurements of IOP were taken at baseline and 5, 10, and 15 minutes after intravenous administration of 1 mg midazolam or placebo. IOP was the primary outcome measured. RESULTS: There was no difference in IOP fluctuation from baseline between patients who received midazolam and those who received placebo. CONCLUSION: Early results indicate that because midazolam does not lower IOP, it may be a useful adjunct to ketamine anesthesia in children with glaucoma undergoing ophthalmologic examination under anesthesia. However, studies of midazolam must be conducted in children and patients with glaucoma before its use in these populations can be recommended.

Intramuscular atropine sulfate in children: comparison of injection sites.

In children undergoing inhaled induction of anesthesia with halothane who suffer bradycardia, submental glossal injection of atropine may result in more rapid onset of vagolysis than traditional intramuscular sites. We compared the intervals between injection and onset of heart rate acceleration (tHR increases) after intramuscular injection of atropine into the deltoid, vastus lateralis, and glossa in children between 1 mo and 10 yr of age scheduled for elective surgery. The tHR increases was determined by measuring the interval between atropine injection and the time point at which the slope of the heart rate curve initially became positive. To ensure that the drug had taken effect before surgical stimulation, heart rate observation was continued until it increased at least 5% above baseline with evidence of continuing acceleration. Anesthesia was induced in all subjects by mask with nitrous oxide and halothane. After tracheal intubation, constant inspired concentrations of the anesthetics were administered for 3 min. While heart rate was monitored, atropine (0.02 mg/kg) was injected into one of the three sites. Each patient's end-tidal anesthetic concentrations were recorded, and minimum alveolar anesthetic concentrations (MAC) were subsequently calculated and adjusted for age. The tHR increases was recorded and averaged for each group. The study groups did not differ by age, weight, end-tidal anesthetic concentrations, age-adjusted MAC, or heart rate at the time atropine was administered. After submental glossal injection (n = 11), tHR increases increase was fastest (3.0 +/- 1.1 min) and was significantly faster than that found with deltoid injection (n = 16; 4.4 +/- 1.1 min) or vastus lateralis injection (n = 8; 6.4 +/- 2.4 min) (P < 0.05 compared with both). The tHR increases also differed significantly between the deltoid and the vastus lateralis (P < 0.05). We conclude that submental glossal injection of atropine results in a more rapid onset of vagolysis than injection at traditional intramuscular sites.

Artificial surfactant for therapy in hydrocarbon-induced lung injury in sheep.

OBJECTIVE: To document the effect of administering artificial surfactant into the trachea, either by instillation or aerosolization, on acute lung injury experimentally induced with kerosene in sheep. DESIGN: Randomized, prospective, controlled study. SETTING: Research laboratory. SUBJECTS: Sheep (n = 24), weighing 8.5 to 25.2 kg (average 16.6). INTERVENTIONS: In anesthetized, tracheally intubated sheep with pulmonary and femoral artery catheters inserted, lung injury was induced by instilling kerosene (0.3 mL/kg) into the trachea. After 15 mins of spontaneous breathing, mechanical ventilation was instituted with a uniform F10(2) and a tidal volume of 10 mL/kg. Sheep were then assigned randomly to one of four regimens as follows: exogenous surfactant or saline (5 mL/kg each) was administered as a bolus intratracheally or by aerosolization for 6 hrs. MEASUREMENTS AND MAIN RESULTS: Arterial and mixed venous blood gases, pH, airway pressure, and static respiratory system compliance were measured and compared between aerosol saline and aerosol surfactant and between bolus saline and bolus surfactant. For all variables except static respiratory system compliance, the hourly rate of change from 15 mins, 1 hr, and 6 hrs after kerosene instillation was determined for each animal, and group rank sums of hourly rates of change were compared. For static respiratory system compliance, the slope of the pressure-volume curve with volumes of 100, 200, 300, 400, and 500 mL was computed for each animal at baseline and at 3 and 6 hrs after kerosene instillation. Group rank sums for static respiratory system compliance at 3 and 6 hrs were compared. Also, the 3- and 6-hr static respiratory system compliance values at each of the volumes were compared. With saline, six of eight sheep died; with surfactant, no sheep died (p = .001). When compared with saline at 15 mins, 1 hr, and 6 hrs after kerosene instillation, surfactant, regardless of whether administered by aerosol or bolus, significantly increased rate of change of arterial oxygen saturation, mixed venous oxygen saturation, and PO2. CONCLUSIONS: In the present animal study, artificial surfactant was an effective treatment for hydrocarbon aspiration. Aerosolized surfactant achieved results similar to instilled surfactant but at a lower total dose.

A new pediatric respiratory monitor that accurately measures imposed work of breathing: a validation study.

OBJECTIVE: A new, microprocessor-controlled respiratory monitor (model CP-100 Pediatric, Bicore Monitoring Systems, Irvine, CA) that measures imposed work of breathing and a variety of respiratory parameters for pediatric patients receiving ventilatory support has recently been developed. To validate its accuracy, measurements obtained using this monitor were compared with those obtained using conventional laboratory equipment. METHODS: An in vitro lung model was used to simulate spontaneously breathing pediatric patients ranging from infancy to 10 years of age. Tidal volume, respiratory rate, and peak inspiratory flow rates were simulated in a stepwise manner. Values for imposed work, tidal volume, peak inspiratory flow rate, and change in airway pressure for both methods were compared using regression analysis. RESULTS: The coefficients of determination (r2) describing the relationships of both methods of measuring imposed work, tidal volume, peak inspiratory flow rate, and the change in airway pressure ranged from 0.99 to 1.00, and were highly significant (p < 0.001). For all measurements, bias was minimal and precision was calculated. CONCLUSIONS: Our data reveal that this pediatric respiratory monitor accurately measures imposed work of breathing, as well as tidal volume, flow rate, and airway pressure. Imposed work of breathing measurements obtained from the monitor may be used to adjust pressure support ventilation, so that the imposed work of the breathing apparatus is reduced to zero and the patient's total work of breathing is thus decreased.

Prolonged neuromuscular blockade for relaxation in two pediatric intensive care patients.

Newer neuromuscular blocking drugs provide optimum blockade and can facilitate ventilation, yet if they are discontinued, they allow predictable reversal. This article documents the use of these drugs in the treatment of two pediatric intensive care unit patients who had different physiologic problems and pharmacologic needs and who were ventilator dependent for a prolonged period. In each case, neuromuscular blockade significantly facilitated ventilation and allowed time for treatment of the underlying pathology without deleterious pharmacologic side effects resulting in a favorable outcome for both patients. The article discusses some of the unique pharmacologic properties of these drugs and the rationale for their use.

Kerosene aspiration: immediate and early pulmonary and cardiovascular effects.

Hydrocarbon aspiration is responsible for substantial morbidity and mortality in both children and domestic animals. To better understand the pathogenesis of hydrocarbon poisoning, we evaluated the effects of aspiration of 0.5 ml/kg of kerosene on various pulmonary and cardiovascular variables over a 4-hr period in a canine model. Heart rate and blood pressure decreased immediately after kerosene aspiration but returned to control values within 60 min. Respiratory rate and intrapulmonary shunting were increased and PaO2 was decreased for up to 4 hr after kerosene aspiration. PaCO2 increased and pH decreased immediately after aspiration but returned to baseline within 45 and 90 min, respectively. Intrapleural pressure became more negative after kerosene was aspirated, which suggests that total lung compliance was diminished. Kerosene aspiration resulted in severe and persistent intrapulmonary physiologic shunting, hypoxemia, bradycardia, and hypotension.

Capnographic detection of anaesthesia circle valve malfunctions.

To determine whether capnographic waveforms can characterize valve malfunction of the anaesthesia circle, which would enable such problems to be identified and rectified immediately, we monitored capnographic respiratory waveforms during anaesthesia with simulated circle valve malfunctions. Ten mongrel dogs were anaesthetized with pentobarbitone, 25 mg.kg-1 IV, and halothane, 0.5 to 1 per cent. Respiratory gas was sampled from the elbow of the circle system for capnographic monitoring. At fresh gas flow rates of 2.5 or 5 L.min-1 during consecutive periods of controlled and spontaneous ventilation, the inspiratory valve, the expiratory valve, or both valves of the circle system were opened for 15 min. Inspired CO2 concentration increased significantly every time a valve was opened, except during spontaneous breathing at 5 L.min-1. At 2.5 L.min-1, inspired CO2 increased from baseline to 0.41 +/- 0.28 per cent with the inspiratory valve opened and to 2.22 +/- 1.72 per cent with the expiratory valve opened during controlled ventilation and to 0.43 +/- 0.20 per cent and 2.02 +/- 1.28 per cent, respectively, during spontaneous ventilation. Inspired CO2 increased to almost 1 per cent when the inspiratory valve was open and to greater than or equal to 1.89 per cent when the expiratory valve was open. The effects with the expiratory valve open and with both valves open were similar. Capnograms were affected in characteristic ways by the valve malfunctions.

Wakefulness during cesarean section after anesthetic induction with ketamine, thiopental, or ketamine and thiopental combined.

Thirty-six pregnant women (ASA class I or II) at term who underwent general anesthesia and cesarean section received either ketamine, 1 mg/kg (n = 12); thiopental, 4 mg/kg (n = 13); or a combination of ketamine, 0.5 mg/kg, and thiopental, 2 mg/kg (n = 11). A blood pressure cuff inflated to 250 mm Hg isolated one arm from the effects of succinylcholine so that awareness during anesthesia could be assessed by asking the patient to move her hand. Although only one patient receiving ketamine responded to commands during anesthesia, 46% of patients receiving either thiopental or the combination responded to commands intraoperatively. No patient hallucinated, the incidence of dreams was low (11%), and no postoperative dysphoria was noted. Three patients (8%) had postoperative recall of intraoperative awareness; one had received thiopental and two the combination. Maternal intraoperative cardiovascular responses among the groups were similar, as were umbilical blood gas values, newborn Apgar scores, and neonatal neurobehavioral test scores at 4 and 24 hr. Ketamine more effectively blocked maternal responsiveness to commands and strong stimuli during the first few minutes after anesthetic induction for cesarean section than did thiopental or a combination of thiopental and ketamine, each at a lower dose.

Prolonged use of high-frequency jet ventilation for a pediatric patient.

A 10-yr-old boy who developed postoperative respiratory failure with evidence of significant barotrauma was treated with high-frequency jet ventilation (HFJV). HFJV reduced peak inflation pressure, enhanced oxygenation, and improved ventilation. The patient could not be weaned from HFJV by decreasing drive pressure. Instead, he was successfully weaned by decreasing the HFJV rate to 80 cycle/min and then switching to conventional intermittent mandatory ventilation at initially similar rate and pressure levels.

Inspiration: expiration ratio. Is mean airway pressure the difference?

Mechanical ventilation with different ratios of inspiratory to expiratory times (I:E ratio) and levels of positive end-expiratory pressure (PEEP) were applied to 9 dogs after the aspiration of fresh water and then were compared. The dogs were ventilated with an I:E ratio of 2:1 with 0 PEEP; an I:E ratio of 2:1 with 5 torr PEEP; and an I:E ratio of 1:2 with 5 torr PEEP. Peak airway pressures were regulated to maintain a mean airway pressure of 13 mm Hg. Arterial oxygenation was better with an I:E ratio of 1:2 with PEEP than with an I:E ratio of 2:1 either with or without PEEP (60 +/- 15 torr as compared with 42 +/- 11 torr and 43 +/- 10 torr). Cardiac index was depressed with all ventilatory modes, but oxygen delivery did not significantly differ among all the modes of ventilation. A ratio of prolonged I:E was not seen to benefit blood gas tension.

The PaO2 response to changes in end expiratory pressure in the newborn respiratory distress syndrome.

To quantitate the effect of changes in end-expiratory pressure (EEP) upon PaO2 in infants with the respiratory distress syndrome, arterial blood gas (ABG) data was reviewed in 28 neonates. A total of 94 ABG specimen pairs were analyzed (specimen I taken before EEP adjustment; specimen II taken after EEP change). An overall change in PaO2 of 15 torr was noted per cm H2O change in EEP. Patients in whom the level of EEP was low (0-3 cm H2O) at the time of Sample I had a greater change in PaO2 (p less than 0.01) than infants whose Sample I ABG was taken at mid-range of EEP (4-6 cm H2O) or at high ranges (7-12 cm H2O). At the high ranges of EEP a minimal and variable PaO2 response was observed. The PaO2 response was not statistically different between neonates on controlled ventilation and those breathing spontaneously. Survivors had a greater PaO2 response than did nonsurvivors, but because of the variables affecting respiratory distress syndrome (RDS) patients, it could not be determined if this PaO2 response had a prognostic value. From this data, the clinician is provided with a guide to the expected PaO2 response when a change in EEP is made.

Tracheal extubation of the neonate at 2 to 3 cm H2O continuous positive airway pressure.

To investigate the efficacy of extubation at higher levels of continuous positive airway pressure (CPAP), 49 newborns (0.95 to 4.0 kg) were extubated at 2 to 3 cm H2O following 1 to 47 days of CPAP therapy. Pre- and postextubation measurements of Po2, PCO2, pH, FiO2, and CPAP were made in all infants. No significant differences (P less than.05) were found between pre- and post-extubation arterial blood gas values for all patients. Comparison of pre- and post-extubation blood gas data with respect to birthweight (less than 2.0 kg vs greater than 2.0 kg) and intubation time (less than 8 days vs. greater than 8 days) also indicated no statistical differences. Mean alveolar-arterial oxygen differences and FiO2 for 41 infants showed progressive decreases following extubation. Six of the 49 infants required reintubation within 72 hours following extubation. The results of this study indicate that newborns with respiratory disease requiring CPAP may be extubated at 2 to 3 cm H2O with no significant changes in arterial blood gas values, thus preventing prolonged intubation associated with weaning to 0 cm H2O CPAP.

Optimum levels of CPAP for tracheal extubation of newborn infants.

Arterial oxygen tension and functional residual capacity were studied in 16 intubated, spontaneously breathing newborn infants recovering from respiratory disease. Studies were made at 2 cm H2O continuous positive airway pressure, at zero end expiratory pressure, and following extubation. The study showed that PaO2 and FRC at 2 cm H2O CPAP were the same as observed following extubation, but that both values were significantly lower at ZEEP.

The therapeutic application of end-expiratory pressure in the meconium aspiration syndrome.

The effectiveness of end-expiratory pressure (EEP) in relieving hypoxemia in the meconium aspiration syndrome (MAS) was studied in 14 patients with the disorder. These infants demonstrated a direct, mean PO2 response of 12 torr/cm H2O EEP. A maximum PO2 response was observed in an EEP range of 4 to 7 cm H2O. EEP was equally effective whether patients were breathing spontaneously or were being mechanically ventilated. EEP is useful in the treatment of hypoxemia in the infants with meconium aspiration syndrome.