Prolonged use of heat and moisture exchangers does not affect device efficiency or frequency rate of nosocomial pneumonia.

OBJECTIVE: To determine whether use of a single heat and moisture exchanger (HME) for < or =120 hrs affects efficiency, resistance, level of bacterial colonization, frequency rate of nosocomial pneumonia, and cost compared with changing the HME every 24 hrs. DESIGN: Prospective, controlled, randomized, unblinded study. SETTING: Surgical intensive care unit at a university teaching hospital. PATIENTS: A total of 220 consecutive patients requiring mechanical ventilation for >48 hrs. INTERVENTIONS: Patients were randomized to one of three groups: a) hygroscopic HME (Aqua+) changed every 24 hrs (HHME-24); b) hydrophobic HME (Duration HME) changed every 120 hrs (HME-120); and c) hygroscopic HME (Aqua+) changed every 120 hrs (HHME-120). Devices in all groups could be changed at the discretion of the staff when signs of occlusion or increased resistance were identified. MEASUREMENTS AND MAIN RESULTS: Daily measurements of inspired gas temperature, inspired relative humidity, and device resistance were made. Additionally, daily cultures of the patient side of the device were accomplished. The frequency rate of nosocomial pneumonia was made by using clinical criteria. Ventilatory support variables, airway care, device costs, and clinical indicators of humidification efficiency (sputum volume, sputum efficiency) were also recorded. Prolonged use of both hygroscopic and hydrophobic devices did not diminish efficiency or increase resistance. There was no difference in the number of colony-forming units from device cultures over the 5-day period and no difference between colony-forming units in devices changed every 24 hrs compared with devices changed after 120 hrs. The average duration of use was 23+/-4 hrs in the HHME-24 group, 73+/-13 hrs in the HME-120 group, and 74+/-9 hrs in the HHME-120 group. Mean absolute humidity was greater for the hygroscopic devices (30.4+/-1.1 mg of H2O/L) compared with the hydrophobic devices (27.8+/-1.3 mg of H2O/L). The frequency rate of nosocomial pneumonia was 8% (8:100) in the HHME-24 group, 8.3% (5:60) in the HME-120 group, and 6.6% (4:60) in the HHME-120 group. Pneumonia rates per 1000 ventilatory support days were 20:1000 in the HHME-24 group, 20.8:1000 in the HME-120 group, and 16.6:1000 in the HHME-120 group. Costs per day were $3.24 for the HHME-24 group, $2.98 for the HME-120 group, and $1.65 for the HHME-120 group. CONCLUSIONS: Changing the hydrophobic or hygroscopic HME after 3 days does not diminish efficiency, increase resistance, or alter bacterial colonization. The frequency rate of nosocomial pneumonia was also unchanged. Use of HMEs for >24 hrs, up to 72 hrs, is safe and cost effective.

Anaesthesia circuits, humidity output, and mucociliary structure and function.

We compared the effects of humidity delivered by the circle system at low fresh gas flows (FGF) with a conventional two-limb and coaxial circuit on the structure and function of the tracheobronchial epithelium in dogs. Animals were anaesthetized and mechanically ventilated using an anaesthesia ventilator to maintain normocarbia. Group I (control) animals received a FGF equal to the required minute ventilation mimicking an open circuit technique. Group II and III animals had FGF set at 20% of the required minute ventilation. Group II used a two-limb circuit and Group III used a coaxial circuit. Relative humidity and temperature of inspired gases were measured at baseline and hourly afterwards. In the first experiment, biopsies of the tracheobronchial tree were obtained bronchoscopically at baseline and then hourly for six hours. Microscopic examination of these samples allowed calculation of mean ciliary length. In the second experiment, tracheal mucus flow velocity (TMFV) was measured at baseline and hourly afterward, using a cinebroncho-fibrescopic method. Delivered absolute humidity was greatest with low FGF and the coaxial circuit, followed by low FGF and a conventional circuit, and high FGF (15 +/- 1.4 vs 9 +/- 0.8 vs 5 +/- 0.4 mg H2O, P < 0.01) after two hours. Mean cilia length (micron) and TMFV (mm/min) fell during the first hour in all three groups. At hour two TMFV returned to baseline in Group III and was significantly greater than Groups I and II (0.8 +/- 0.4 vs 8.6 +/- 1.1 vs 15.4 +/- 2.1, P < 0.001). Mean ciliary length demonstrated a similar pattern with reductions from baseline in all three groups for the first two hours. Groups II and III had an increase in cilia length beginning at hour three and were both significantly greater than Group I at hours 3 through 6 (1.3 +/- 0.5 vs 3.2 +/- 1.1 vs 4.2 +/- 0.8, P < 0.001). Alterations in tracheobronchial structure and function result from exposure to dry gases and are amplified by the duration of exposure. Our findings suggest a minimum of 12 to 15 mg H2O/l is necessary to prevent these alterations. In this study, the combination of low FGF and a coaxial anaesthesia circuit reached this minimum threshold more quickly than a conventional two-limb circuit.

Comparison of volume control and pressure control ventilation: is flow waveform the difference?

OBJECTIVE: To examine the hypothesis that a decelerating inspiratory flow waveform is responsible for improvements in gas exchange during pressure control ventilation for acute lung injury. DESIGN: Prospective, controlled, crossover study. MEASUREMENTS AND MAIN RESULTS: Twenty-five patients with acute lung injury requiring mechanical ventilation with a positive-end expiratory pressure > or = 10 cm H2O, ventilator frequency of > or = 8 bpm, inspired oxygen concentration of > or = 0.50, peak inspiratory pressure > or = 40 cm H2O, and requiring sedation and paralysis were studied. Patients were ventilated at a tidal volume of 10 mliters/kg, respiratory frequency was set to maintain a pH > 7.30 and PaCO2 < 50 mm Hg, and positive end-expiratory pressure (PEEP) set to maintain Pao2 > 70 mm Hg or Sao2 > 93% with an Fio2 < or = 0.50. In random sequence, ventilator mode was changed from volume control with a square flow waveform, pressure control ventilation with a decelerating flow waveform, or volume control ventilation with a decelerating flow waveform. Tidal volume, minute ventilation, and airway pressures were continuously measured at the proximal airway. After 2 hours of ventilation in each mode, arterial and mixed venous blood gases were drawn and cardiac output determined by thermodilution. Dead space to tidal volume ratio was determined from mixed expired gas concentrations and Paco2. During volume control ventilation with a square flow waveform, Pao2 was decreased (75 +/- 11 mm Hg vs. 85 +/- 9 mm Hg and 89 +/- 12 mm Hg), p < 0.05, and peak inspiratory pressure was increased (50 +/- 9 cm H2O vs. 42 +/- 7 cm H2O and 39 +/- 9 cm H2O) p < 0.05 compared to volume control with a decelerating flow waveform and pressure control ventilation. Mean airway pressure was also lower with volume control with a square flow waveform (17 +/- 4 cm H2O vs. 20 +/- 4 cm H2O and 21 +/- 3 cm H2O) compared to volume control with a decelerating flow waveform and pressure control ventilation. There were no differences in hemodynamic parameters. CONCLUSIONS: Both pressure control ventilation and volume control ventilation with a decelerating flow waveform provided better oxygenation at a lower peak inspiratory pressure and higher mean airway pressure compared to volume control ventilation with a square flow waveform. The results of our study suggest that the reported advantages of pressure control ventilation over volume control ventilation with a square flow waveform can be accomplished with volume control ventilation with a decelerating flow waveform.

Transesophageal echocardiography.

This article presents an overview of the benefits and efficacy of transesophageal echocardiography (TEE) in the critically ill patient. The echocardiographic evaluation of ventricular function both regional and global, is discussed with special emphasis on ischemic heart disease; assessment of preload, interrogation of valvular heart disease (prosthetic and native) and its complications; endocarditis and its complications; intracardiac and extracardiac masses, including pulmonary embolism; aortic diseases (e.g., aneurysan, dissection, and traumatic tears); evaluation of patent foramen ovale and its association with central and peripheral embolic events; advancements in computer technology; and finally, the effect of TEE on critical care.

Assessment of left ventricular function and hemodynamics with transesophageal echocardiography.

Transesophageal echocardiography (TEE) plays an important role in the evaluation of left ventricular function and hemodynamics in the critical care setting. The technique provides immediate data regarding regional myocardial ischemia, global ventricular function, volume, and the presence of cardiac tamponade. This article outlines the role of TEE in the evaluation of left ventricular function in the intensive care unit and presents practical information for the use of TEE in evaluating systolic function, diastolic function, and cardiac tamponade.

Analysis of catecholamine and vasoactive peptide release in intracranial arterial venous malformations.

Craniotomy for resection of cerebral arterial venous malformation has been associated with postoperative hypertension, which necessitates administration of large doses of antihypertensive medications to control blood pressure. Controlling blood pressure is essential because hypertensive episodes can lead to postoperative cerebral hemorrhage with increases in morbidity and mortality. We measured vasoactive peptide and catecholamine release in 13 patients who underwent resection of an arterial venous malformation and in a control group of 6 patients who presented for clipping of unruptured cerebral aneurysms. Plasma renin activity, angiotensin I and II, vasopressin, aldosterone, epinephrine, and norepinephrine levels were measured intraoperatively and for 36 h postoperatively. Analysis of variance was used to assess sample and group effects. A significant interaction between sample and groups was found for norepinephrine (p < 0.001) and renin (p = 0.002). Our data suggest that elevated plasma renin and norepinephrine levels are in part responsible for postoperative hypertension in patients undergoing resection of arterial venous malformations. Blocking the release of these hormones may help control blood pressure after surgery for removal of arterial venous malformations.

Echocardiographic evaluation of bupivacaine cardiotoxicity.

In nine pentobarbital anesthetized dogs, the global effects of bupivacaine on the heart were examined during and after the onset of bupivacaine cardiotoxicity. The onset of bupivacaine cardiotoxicity was followed by the use of echocardiography to determine the sequence of events. The overall sequence of changes in the heart, demonstrated by the echocardiographic images, was markedly impaired systolic function and right ventricular dilation. The right ventricular dilation was so profound that it was associated with a septal shift into the left ventricle. Right ventricular dilation was so profound that the ability to maintain the whole ventricle within the echocardiographic image was lost. Areas obtained from the left ventricle at the two time points studied (the half-time from the beginning of injection to the occurrence of asystole referred to as midway through the toxic episode and at asystole) exhibited a significant systolic dilation only midway through the toxic episode. The mean total dose of bupivacaine resulting in the dilation of the ventricles was 14.0 +/- 3.3 mg/kg. The mean arterial pressure was reduced from control by 46.9% +/- 8.8% midway through the toxic episode. The mean pulmonary arterial pressure exhibited no significant change from before the bupivacaine injection sequence. A variety of conduction changes seen midway through the toxic episode were widening of the QRS complex, inversion, bradycardia, premature ventricular contractions (PVCs), or a combination of these. PVCs, if seen at all, were only beginning to develop and no heart block was seen in any dog midway through the toxic episode.(ABSTRACT TRUNCATED AT 250 WORDS)

Humidification in the intensive care unit. Prospective study of a new protocol utilizing heated humidification and a hygroscopic condenser humidifier.

STUDY OBJECTIVE: Determine the utility of a proposed algorithm in allowing safe, efficient humidification in mechanically ventilated patients using both a hygroscopic condenser humidifier (HCH) and heated humidifier (HH). DESIGN: A prospective study using an algorithm to chose humidification devices based on physical examination and sputum characteristics. SETTING: All patients admitted to the surgical ICU. PATIENTS: One hundred twenty consecutive patients requiring mechanical ventilation (MV) were studied. INTERVENTIONS: Patients were examined by the attending respiratory care practitioner and given either an HCH or HH. If patients demonstrated any of the following--thick or tenacious secretions, core temperature < 32 degrees C, or bloody secretions--they were given an HH. All others used an HCH. If any of the above conditions occurred during HCH use, the patient was given an HH. MEASUREMENTS AND RESULTS: Duration of ventilation, incidence of nosocomial pneumonia, ventilator circuit colonization, and mortality were determined for patients in each group. Cost of humidification devices, number of suctioning procedures per day, and volume of saline solution instilled were also recorded. Initially, 27 percent (32/120) of patients used an HH and 73 percent (88/120) used an HCH. During the study, ten patients required changing to an HH during HCH use. Patients in the HH group were more likely to have preexisting lung disease and had a longer duration of ventilation (83 +/- 21 h) and higher mortality (21 percent). Patients in the HCH group were more likely to be postoperative, had shorter durations of ventilation (38 +/- 14 h), and lower mortality (9 percent). There was no difference in the incidence of nosocomial pneumonia between the two groups (9 percent vs 6 percent) and endotracheal tube occlusion did not occur in either group. Circuit colonization was common in the HH group (64 percent) but rate in the HCH group (5 percent). Cost per day was significantly less for the HCH group ($4 vs $19.80). Patients who required a change from HCH to HH did so at a mean of 5 days. CONCLUSION: The proposed algorithm resulted in cost-efficient and safe application of humidification devices in patients in the surgical ICU.

The addition of sighs during pressure support ventilation. Is there a benefit?

The purpose of this study was to determine if sigh breaths delivered during pressure support ventilation (PSV) were beneficial in maintaining arterial oxygenation (PaO2) and pulmonary mechanics. Ten patients being weaned from mechanical ventilation in the PSV mode were studied. All patients were ventilated for 4 h without sighs, 4 h with sighs, and again for 4 h without sighs. During each 4-h period, continuous measurements of ventilatory volumes and airway pressures were accomplished. At the end of each 4-h period, an arterial blood gas determination was obtained. There were no statistically significant differences in any of the measured variables during the different periods of ventilation. We conclude that the sigh breath is of no benefit during PSV.

The pathophysiologic changes following bile aspiration in a porcine lung model.

Aspiration of bile is an underpublicized aspiration syndrome. Using a porcine lung model, the physiologic response and the histopathology of lung tissue were evaluated after the intratracheal instillation of sublethal doses of bile. Twenty-one domestic swine (11 to 19 kg) were the studied population. Three groups of five swine were evaluated: a control group received intratracheal physiologic saline (pH 7.45); study group 1 received strained gastric contents (pH 2.24); and study group 2 received strained bile (pH 7.19). All animals received the solutions at 0.5 ml/kg intratracheally. Lungs of six additional animals were studied (two gastric, two bile, and two physiologic saline) after aspiration by scanning electron microscopy (SEM). A seventh untreated animal was used as the SEM control. The physiologic data were analyzed using analysis of variance for repeated measures. The SEM and histopathologic results were graded by an observer blinded to the groups and were analyzed using the analysis of variance (ANOVA) and Scheffe tests. The group with bile aspiration was consistently characterized by significant deterioration of PaO2, the alveolar-arterial (A-a) gradient, shunt fraction, and static compliance (p < 0.01); and the light histopathologic and SEM findings demonstrated pathologic changes in the bile-exposed lung (p < 0.05) greater than the gastric- or saline-exposed lungs. It is concluded that bile aspiration produces a severe chemical pneumonitis leading to noncardiac pulmonary edema.

Cardiovascular abnormalities in sepsis.

The cardiovascular response in sepsis is the result of subcellular dysfunction and impaired metabolism from the complex interaction of cytokine and mediator with cellular involvement. The typical cardiovascular abnormalities seen are tachycardia, hypotension (relative decrease in preload), increased cardiac index, decrease in left ventricular stroke work index, decrease in ejection fraction (which is load dependent), and an apparent decrease in contractility. After augmentation of preload, the ventricles dilate in a response similar to the Frank-Starling mechanism. By challenging these patients with the augmentation of preload and contractility to increase oxygen delivery would theoretically minimize microcirculatory dysfunction and lactic acid production. Survivors have an amplification of this biventricular response. This response would temporarily normalize within a week, while the nonsurvivors would still have increased hemodynamics (tachycardia) without the ventricular dilation as a compensatory response. Even though the survivor response is not predictable, therapeutic end-points have been proposed as a guide to therapy in these critically ill patients. Conflicting results have been reported regarding contractility and ventricular compliance measurements in septic models. The development of pressure-volume loops would be the ideal technique for the evaluation of ventricular diastolic compliance, true preload, and contractility (from the end-systolic pressure relationship, which is load independent) in sepsis. More research has to be done with this type of evaluation to further understand the dynamic cardiovascular response in sepsis. This question still persists. Why can't some patients be hemodynamically challenged to increase right and left ventricular end-diastolic volumes and oxygen delivery?

Knowledge-based image analysis for automated boundary extraction of transesophageal echocardiographic left-ventricular images.

A system for automatically determining the contour of the left ventricle (LV) and its bounded area, from transesophageal echocardiographic (TEE) images is presented. It uses knowledge of both heart anatomy and echocardiographic imaging to guide the selection of image processing methodologies for thresholding, edge detection, and contour following and the center-based boundary-finding technique to extract the contour of the LV region. To speed up the processing a rectangular region of interest from a TEE picture is first isolated and then reduced to a coarse version, one-ninth original size. All processing steps, except the final contour edge extraction, are performed on this reduced image. New methods developed for automatic threshold selection, region segmentation, noise removal, and region center determination are described.

Endotracheal epinephrine is unreliable.

When intravenous access cannot be obtained in an emergency, the endotracheal route of emergency drug administration can be used for epinephrine, atropine, and lidocaine. Optimal drug dosages for endotracheal administration as well as the amount and type of diluent are presently unknown. We compared central intravenous, peripheral intravenous, intraosseous, and intratracheal administration of epinephrine 1:10,000 in both normotensive and hemorrhagic shock dogs. The shock model consisted of 50% blood volume depletion over 15 min. Epinephrine was administered in a dose of 0.01 mg/kg (0.1 cc/kg) by the intraosseous route, central, and peripheral intravenous routes followed by a 5 cc normal saline flush. Intratracheal administration consisted of epinephrine 0.01 and 0.02 mg/kg diluted 1:1 and 1:2 with normal saline or sterile water and administered deep into the tracheo-bronchial tree using a 30-cm catheter. The effect of epinephrine was assessed by the response of the arterial blood pressure. Epinephrine was equally effective by the intraosseous, central intravenous, and peripheral intravenous routes in terms of time to onset of action, time to peak effect, and magnitude of effect on systolic, diastolic, and mean arterial pressures in both the shock and non-shock animals. The duration of effect was significantly longer (P less than 0.02) for the intraosseous route of administration. The endotracheal route of administration was unreliable and not reproducible in either the normotensive or shock animals. In 8/12 episodes in normotensive animals, including 5 trials with double doses of 0.02 mg/kg and dilutions of 1:1 and 1:2, and in 4/9 studies with shock animals including three with double doses, there was no discernable response of systolic or diastolic blood pressure.

Comparison study of intraosseous, central intravenous, and peripheral intravenous infusions of emergency drugs.

Intraosseous infusion of emergency drugs is a lifesaving alternative to intravenous administration when intravenous access cannot be rapidly established. We studied the comparative pharmacokinetics of the following six emergency drugs and solutions: epinephrine hydrochloride, 0.01 mg/kg; sodium bicarbonate, 1 mEq/kg; calcium chloride, 10 mg/kg; hydroxyethyl starch, 10 mL/kg; 50% dextrose in water, 250 mg/kg; and lidocaine hydrochloride, 1 mg/kg. Studies were conducted in normotensive, anesthetized dogs, with three animals studied with each of the drugs or solutions and each animal being treated with all three routes of administration (central intravenous, peripheral intravenous, and intraosseous) in randomized sequence. The effects of epinephrine were also assessed in a shock model. The intraosseous route of administration was comparable with the central and peripheral intravenous routes for all of the emergency drugs and solutions studied, with equivalent magnitudes of peak effect or drug level and equal or longer durations of action. Time to placement of the intraosseous needle varied from 15 seconds to 5 minutes, with a mean of 60 seconds. Time to placement of the needle varies with the skill and experience of the individual. With experience, all individuals could place the intraosseous needle in 60 seconds or less. The intraosseous route is comparable in effect to the central and peripheral intravenous routes of drug administration for epinephrine, sodium bicarbonate, hydroxyethyl starch, calcium chloride, 50% dextrose in water, and lidocaine and is a clinically feasible alternative when intravenous access will be critically delayed.