Migrating motility complexes persist after severe traumatic shock in patients who tolerate enteral nutrition.

BACKGROUND: Postinjury small bowel ileus is poorly characterized and may be an important factor in intolerance to enteral nutrition (EN). We, therefore, placed jejunal manometry catheters in high-risk trauma patients. Our hypothesis was that the presence of "fasting migrating motility complex (MMC)" activity and conversion to a "fed pattern" at goal rate of EN would be present in those patients who tolerate jejunal feeding. METHODS: After obtaining baseline fasting manometry pressure tracings, jejunal feeding was advanced stepwise to a set goal while tolerance was monitored and intolerance was treated by a standard approach. RESULTS: Of the 10 study patients, 7 were able to be maintained on EN. Five (50%) had "fasting MMCs" and had good tolerance to early advancement of EN. The remaining five patients did not exhibit "fasting MMCs" and four had poor tolerance to early advancement of EN. Overall, nine patients reached goal rate of EN of which four converted to a "fed pattern." This, however, was not associated with later tolerance to EN. CONCLUSION: EN is feasible following severe traumatic shock. Surprisingly, half of the patients had fasting MMCs. This requires intact neural and motor function and was associated with good tolerance of early EN.

Computerized decision support for mechanical ventilation of trauma induced ARDS: results of a randomized clinical trial.

BACKGROUND: Variability and logistic complexity of mechanical ventilatory support of acute respiratory distress syndrome, and need to standardize care among all clinicians and patients, led University of Utah/LDS Hospital physicians, nurses, and engineers to develop a comprehensive computerized protocol. This bedside decision support system was the basis of a multicenter clinical trial (1993-1998) that showed ability to export a computerized protocol to other sites and improved efficacy with computer- versus physician-directed ventilatory support. The Memorial Hermann Hospital Shock Trauma intensive care unit (ICU) (Houston, TX; a Level I trauma center and teaching affiliate of The University of Texas Houston Medical School) served as one of the 10 trial sites and recruited two thirds of the trauma patients. Results from the trauma patient subgroup at this site are reported to answer three questions: Can a computerized protocol be successfully exported to a trauma ICU? Was ventilator management different between study groups? Was patient outcome affected? METHODS: Sixty-seven trauma patients were randomized at the Memorial Hermann Shock Trauma ICU site. "Protocol" assigned patients had ventilatory support directed by the bedside respiratory therapist using the computerized protocol. "Nonprotocol" patients were managed by physician orders. RESULTS: Of the 67 trauma patients randomized, 33 were protocol (age 40 +/- 3; Injury Severity Score [ISS] 26 +/- 3; 73% blunt) and 34 were nonprotocol (age 38 +/- 2; ISS 25 +/- 2; 76% blunt). For the protocol group, the computerized protocol was used 96% of the time of ventilatory support and 95% of computer-generated instructions were followed by the bedside respiratory therapist. Outcome measures (i.e., survival, ICU length of stay, morbidity, and barotrauma) were not significantly different between groups. Fio2 > or = 0.6 and Pplateau > or = 35 cm H2O exposures were less for the protocol group. CONCLUSION: A computerized protocol for bedside decision support was successfully exported to a trauma center, and effectively standardized mechanical ventilatory support of trauma-induced acute respiratory distress syndrome without adverse effect on patient outcome.

Vacuum-assisted wound closure provides early fascial reapproximation in trauma patients with open abdomens.

BACKGROUND: Damage control and decompressive laparotomies salvage severely injured patients who would have previously died. Unfortunately, many of these patients develop open abdomens. A variety of management strategies exist. The end result in many cases, however, is a large ventral hernia that requires a complex repair 6 to 12 months after discharge. We instituted vacuum-assisted wound closure (VAWC) to achieve early fascial closure and eliminate the need for delayed procedures. METHODS: For 12 months ending June 2000, 14 of 698 trauma intensive care unit admissions developed open abdomens and were managed with VAWC dressing. This was changed every 48 hours in the operating room with serial fascial approximation until complete closure. RESULTS: Fascial closure was achieved in 13 patients (92%) in 9.9 +/- 1.9 days, and 2.8 +/- 0.6 VAWC dressing changes were performed. There were 2 wound infections, no eviscerations, and no enteric fistulas. CONCLUSIONS: Use of VAWC can safely achieve early fascial closure in more than 90% of trauma patients with open abdomens.

Nitroprusside in resuscitation of major torso trauma.

OBJECTIVE: Patients with thoracic aortic injury (TAI) usually have sustained other major trauma, and may require aggressive shock resuscitation. In the 24 hours after aortic repair and during resuscitation, our cardiothoracic surgeons request intravenous nitroprusside to maintain mean arterial pressure (MAP) less than 90 mm Hg to minimize bleeding at the repair. We compared the resuscitation response of patients who sustained major torso trauma (MTT) and TAI with that of patients who had MTT with no TAI to determine whether nitroprusside can effectively control MAP during resuscitation and whether use of nitroprusside, because of its peripheral vasodilatory effects, is associated with a favorable resuscitation response. METHODS: During the 9-month study period, 11 patients who sustained TAI and 38 patients who sustained MTT with no TAI met multiple organ failure risk/shock criteria and were resuscitated by a standardized protocol emphasizing volume loading and hemoglobin replacement to maintain systemic oxygen delivery index (DO2I) > or = 600 mL O2/min-m2 for the first 24 intensive care unit hours. For TAI patients, postoperative management included intravenous nitroprusside infusion titrated by the bedside nurse to maintain mean arterial pressure (MAP) less than 90 mm Hg during the same 24 hours. Data were obtained prospectively during resuscitation. Retrospectively, the resuscitation response of TAI and non-TAI patients was compared. RESULTS: For the TAI group, nitroprusside effectively controlled MAP (range, 77-87 mm Hg); for the non-TAI group, mean MAP exceeded 95 mm Hg within 5 hours. During the first 8 hours, MAP, pulmonary capillary wedge pressure, and systemic vascular resistance index were less, and DO2I was greater for the TAI than for the non-TAI group. The resuscitation goal of DO2I > or = 600 mL O2/ min-m2 was attained at 4 hours for the TAI group, and was attained at 12 hours for the non-TAI group. No revisions of aortic repairs were required during or as a result of resuscitation. CONCLUSION: During aggressive shock resuscitation, control of MAP using nitroprusside is feasible and is associated with a favorable resuscitation response. Nitroprusside may be a useful adjunct during shock resuscitation of MTT as a vasoactive agent that promotes peripheral tissue perfusion.

Blunt trauma resuscitation: the old can respond.

HYPOTHESIS: Old and young trauma patients are capable of hyperdynamic response during standardized shock resuscitation. DESIGN: The responses of old and young trauma patients resuscitated using a standardized protocol are compared in an inception cohort study. A standardized resuscitation protocol was used to attain and maintain an oxygen delivery index of 600 mL/min x m2 or greater (DO2I > or = 600) for the first 24 hours in the intensive care unit. Interventions, responses, and outcomes for old (> or = 65 years) and young (<65 years) patients are described. Data were analyzed using analysis of variance, the chi2 test, and the t test; P<.05 was considered significant. SETTING: A 20-bed shock trauma intensive care unit in a regional level I trauma center. PATIENTS: Patients at high risk of postinjury multiple organ failure, ie, major organ or vascular injury and/or skeletal fractures, initial base deficit of 6 mEq/L or greater, need for 6 units or more of packed red blood cells in the first 12 hours, or age of 65 years or older with any 2 previous criteria. INTERVENTIONS: Pulmonary artery catheter, crystalloid fluid infusion, packed red blood cell transfusion, and moderate inotrope support, as needed in that sequence, to attain DO2I > or = 600. MAIN OUTCOME MEASURES: Intensive care unit length of stay and survival. RESULTS: During 19 months ending June 1999, 12 old patients (58% male; age, 76 +/- 2 years [mean +/- SEM] [P<.0011; Injury Severity Score, 20 +/- 2 [P=.02]) and 54 young patients (61% male; age, 37 +/- 2 years; Injury Severity Score, 32 +/- 2) were resuscitated. Initially, for old patients (cardiac index, 2.0 +/- 0.2 L/min x m2) and for young patients (cardiac index, 3.0 +/- 0.2 L/min x m2; P=.01), 24-hour volumes were as follows: 16 +/- 3 L of crystalloid and 12 +/- 3 units of packed red blood cells for the old patients and 21 +/- 2 L of crystalloid and 19 +/- 2 units of packed red blood cells for the young patients. For old patients, 9 (75%) attained DO2I > or = 600, and 11 (92%) survived 7 or more days and 5 (42%) 30 or more days. For young patients, 45 (83%) attained the DO2I goal, and 48 (89%) survived 30 or more days. Intensive care unit length of stay was 25 +/- 9 days for the old patients and 23 +/- 2 days for the young patients. CONCLUSIONS: Elderly patients have initially depressed cardiac index but generate hyperdynamic response. Although ultimate outcome is poorer than in the younger cohort, resuscitation is not futile.

Tissue hemoglobin O2 saturation during resuscitation of traumatic shock monitored using near infrared spectrometry.

BACKGROUND: Near infrared (NIR) spectrometry offers a noninvasive monitor of tissue hemoglobin O2 saturation and has been developed to report a quantitative clinical variable, StO2 [= HbO2/(HbO2 + Hb)]. In this study, a prototype NIR oximeter was used to investigate the hypothesis that changes in systemic O2 delivery index (D(O2)I) would be reflected by changes in StO2 in skeletal muscle, subcutaneous tissue, or both, as reperfusion occurs during shock resuscitation. StO2 was also compared with other indices of severity of shock or adequacy of resuscitation, including arterial base deficit, lactate, gastric mucosal P(CO2) (PgCO2), and mixed venous hemoglobin O2 saturation (S(VO2)). METHODS: Skeletal muscle and subcutaneous tissue StO2 were monitored simultaneously in eight severely injured trauma patients (88% blunt mechanism; age, 42 +/- 6 years; Injury Severity Score, 27 +/- 3) during standardized shock resuscitation in the intensive care unit with the primary goal of D(O2)I > or = 600 mL O2/min/m2 for 24 hours, and for an additional 12 hours during transition from resuscitation to standard intensive care unit care. RESULTS: Skeletal muscle StO2 increased significantly from 15 +/- 2% (mean +/- SEM) at the start of resuscitation to 49 +/- 14% at 24 hours, and to approximately 55% from 25 to 36 hours. Subcutaneous tissue StO2 approximately 82% and was significantly greater than skeletal muscle StO2 throughout. D(O2)I increased significantly from 372 +/- 54 to 718 +/- 47 mL O2/min/m2 during resuscitation. Over 36 hours, mean D(O2)I and skeletal muscle StO2 were highly correlated (r = 0.95). Neither D(O2)I-PgCO2 nor D(O2)I-S(VO2) were significantly correlated; neither S(VO2) nor subcutaneous tissue StO2 changed significantly. CONCLUSION: Hemoglobin O2 saturation was monitored noninvasively and simultaneously in skeletal muscle and subcutaneous tissues as StO2 (%) by using a prototype NIR oximeter. Skeletal muscle StO2 tracked systemic O2 delivery during and after resuscitation. As a rapidly deployable, noninvasive monitor of peripheral tissue oxygenation and O2 delivery, skeletal muscle StO2 obtained using NIR spectrometry would be useful to guide resuscitation in the intensive care unit, to monitor resuscitation status in the operating room, and, potentially, in combination with indicators such as base deficit and lactate, to detect shock during initial assessment of the severe trauma patient in the emergency department.

Nonocclusive bowel necrosis occurring in critically ill trauma patients receiving enteral nutrition manifests no reliable clinical signs for early detection.

BACKGROUND: Nonocclusive bowel necrosis (NOBN) has been associated with early enteral nutrition (EN). The purpose of this study was to determine the incidence of this complication in our trauma intensive care unit population and to define a typical patient profile vulnerable to NOBN. METHODS: Thirteen cases of NOBN were identified among 4,311 patients (0.3%) over a 64-month period ending October 1998. Their charts were analyzed for a variety of clinical data, including prospective EN tolerance data in 4. RESULTS: Twelve (92%) patients were enterally fed prior to diagnosis for 10 +/- 8 days (range 3 to 21). Tachycardia (n = 12, 92%); fever/hypothermia, (n = 12, 92%), and an abnormal white blood cell count (n = 11, 85%) were consistently present. Abdominal distention was common but tended to be a late sign (n = 12). Seven (56%) survived. In 4 patients with tolerance data, 3 reached the goal rate of feeds prior to diagnosis. Two became distended at >12 hours from diagnosis. Gastric tonometry demonstrated a decreased NgpHi (<7.30) after starting EN in all 3 in whom it was monitored. CONCLUSIONS: NOBN developed in 0.3% of our trauma patients. Onset occurs in the second week in high-acuity patients who have had a period of EN tolerance. Clinical findings resemble bacterial sepsis with tachycardia, fever, and leukocytosis. Gastrointestinal specific signs are not consistent or occur late. Thus, we could not identify an early, useful clinical indicator. Gastric carbon dioxide tonometry may detect a vulnerable subgroup of patients.

Comparison of skeletal muscle PO2, PCO2, and pH with gastric tonometric P(CO2) and pH in hemorrhagic shock.

OBJECTIVES: To monitor PO2, PCO2, and pH in the interstitium of skeletal muscle (PmO2, PmCO2, and pHm) during hemorrhage, shock, and resuscitation using fiber-optic sensors and to compare Pco2 and pH in the interstitium of gastric mucosa (PrCO2 and pHi) obtained using gastric CO2 tonometry. DESIGN: Prospective, controlled observational study in an acute experimental preparation. SETTING: Physiology laboratory in a university medical school. SUBJECTS: Nine mongrel dogs (20 to 35 kg). INTERVENTIONS: Anesthesia was induced with pentobarbital (25 mg/kg iv) and maintained (10 mg/hr) after hemorrhagic shock. Mechanical ventilation was established to maintain baseline PaCO2 approximately 35 torr. Arterial, venous, and pulmonary artery catheters were placed. Blood flow probes were placed around the right femoral artery and vein. A probe (0.5 mm in diameter) with fiber-optic PO2, PCO2, and pH sensors was placed percutaneously in the adductor muscle of the right thigh. A gastric tonometer catheter was placed in the stomach lumen. After baseline data collection, controlled hemorrhage to mean arterial pressure (MAP) of 45 to 50 mm Hg was maintained for 1 hr. Shed blood was then reinfused. Blood gas, hemodynamic, and gastric tonometric data were collected during shock and reinfusion at 30-min intervals and hourly after reinfusion for 4 hrs. Normothermia was maintained. MEASUREMENTS AND MAIN RESULTS: PmO2 decreased rapidly from 42 +/- 13 torr (mean +/- sD) to 13 +/- 9 torr within 15 mins and to 6 +/-4 torr within 30 mins of MAP reaching 45 mm Hg, and it recovered to baseline with reinfusion. pHm decreased gradually from 7.23 +/-0.09 to 6.89 +/- 0.25 during the 1-hr shock period and increased slowly toward baseline after reinfusion. pHi decreased from 7.43 +/- 0.14 to 6.91 +/- 0.23, and on average it returned to baseline 2 hrs after reinfusion. PmCO2 increased from 50 +/- 12 to 113 +/- 49 torr, increased further to 124 +/- 73 torr during reinfusion, and returned slowly toward baseline after reinfusion. PrCO2 increased from 35 +/- 8 to 60 +/- 19 torr and returned to baseline within 15 mins after reinfusion. During shock and reinfusion, oxygen delivery, mixed venous PO2, mixed venous oxygen saturation, and PmO2 responded with similar time courses. After reinfusion, on average, PmO2 exceeded baseline PmO2 and mixed venous PO2, and oxygen availability exceeded demand, suggesting an oxygen consumption defect. On average, PmCO2 and pHm did not return to baseline values 4 hrs after reinfusion, suggesting the persistence of anaerobic metabolic effects in skeletal muscle beyond the relatively short time that is required to reestablish baseline MAP, blood flow rates, oxygen delivery, PrCO2, and pHi. CONCLUSIONS: PmO2, PmCO2, and pHm, monitored simultaneously using fiber-optic sensors in a single, small probe placed percutaneously, appear to indicate greater severity of shock and more prolonged resuscitation than conventional systemic or gastric tonometric variables.

Standardized management of intracranial pressure: a preliminary clinical trial.

OBJECTIVE: To test a standardized protocol for management of intracranial pressure (ICP) after severe head injury (i.e., traumatic brain injury), consistent with published guidelines. METHODS: We compared prospective use of a standardized protocol for ICP management in 12 patients with severe head injuries and retrospective ICP management using preprinted hospital orders in combination with ad hoc physician orders in 12 historical control patients with severe head injuries. With the standardized protocol, flow-chart decision logic diagrams were applied at patient bedside by critical care practitioners, with nursing shift review. RESULTS: ICP and its variation during the first 6 intensive care unit days was less for the standardized protocol- than for the preprinted order-managed group (p <0.001), indicating better process control with the standardized protocol. ICP exceeded 25 mm Hg for less time for the standardized protocol group (182 hours; 15+/-23 hours/patient) than for prescribed order group (429 hours; 36+/-28 hours/patient) (p = 0.03). On average, ICP exceeded 20 mm Hg for 2.3 days for the standardized protocol-managed group and for 4.7 days for the prescribed order-managed group. Cerebral perfusion pressure was significantly greater and its variation less for the standardized protocol- than for the preprinted order-managed group. Fewer interventions were made for ICP management for the standardized protocol- than for the preprinted order-managed patients (601 vs. 876), suggesting more effective nursing time using the standardized protocol. CONCLUSION: ICP management was more consistent, and intracranial hypertension was better controlled, in patients managed according to a standardized, data-driven protocol for escalation and weaning of therapies in response to immediate patient needs. We recommend computerized implementation and a randomized clinical trial to compare the protocol with prescribed orders.

Clinical trial of an ex vivo arterial blood gas monitor.

PURPOSE: The purpose of this study was to test the performance of a patient attached, on demand ex vivo arterial blood gas (ABG) monitor, and to compare the frequency of ABG analysis using the monitor, where the monitor was operated by intensive care unit (ICU) staff on shock trauma and neurosurgical intensive care patients for < or = 6 days, with standard clinical laboratory analysis. MATERIALS AND METHODS: The ABG monitor (SensiCath; Optical Sensors Inc., Minneapolis, MN) incorporates fiber optic pH, PCO2, PO2, and thermistor temperature sensors in a 0.3-mL sensor chamber that attaches in line with the patient's arterial pressure tubing and connects via a fiberoptic cable to a bedside instrument. The monitor and standard clinical laboratory performance were compared following an institutionally approved protocol. Adult ICU patients (n = 30) were studied for whom an arterial cannula was required, the expected ICU stay was > 72 hours, > or = 2 ABG analyses/day were anticipated, and informed consent had been obtained. Paired comparison ABG analyses and quality assurance checks were performed daily. The frequency of ABG analyses in this study, for which monitor values were used for clinical decision making, was compared with the frequency previously reported for the same ICUs, for which the monitor and laboratory results were compared but only the latter were used for clinical decision making. RESULTS: Five hundred ABG analyses, 436 over the first 72 hours, were obtained using the monitor for patient management over 3,248 patient hours (85 +/- 47 hours/patient). Monitor-laboratory comparison ABG analyses (n = 258) indicated stable performance over 6 days: For pH, the range of laboratory measurements was 7.200 to 7.540, accuracy (mean difference between monitor and laboratory measurement) was +0.013, and precision (standard deviation of difference between monitor and laboratory measurements) was +/-0.031. For PCO2, range: 18 to 78.5, accuracy: -0.8, precision: +/-3.4 mm Hg. For PO2, range: 41.0 to 344.0, accuracy: +2.3, precision: +/-12.8 mm Hg. The frequency of ABG analyses obtained using the monitor (ie, 15.0 +/- 11.6 ABGs/patient/72 hours) was significantly greater than that using the clinical laboratory (ie, 8.8 +/- 4.2 ABGs/patient/72 hours) (P = .01). CONCLUSION: The ABG monitor provides performance comparable to standard clinical laboratory analysis for < or = 6 days (< or = 144 hours), consistent with ICU arterial cannula changeout schedules. More frequent ABG analyses are obtained by critical care practitioners using the monitor compared with the clinical laboratory system, suggesting that clinical decision making based on ABG data may be limited by the frequency of ABG analysis.

Effects of injury and therapy on brain parenchyma pO2, pCO2, pH and ICP following severe closed head injury.

Simultaneous monitoring of brain parenchyma pO2, pCO2, and pH (PbO2, PbCO2 and pHb) has been tested in ICU environments using fiber optic sensors incorporated in probes 0.5 mm in diameter. An Institutionally approved protocol was used to test the concept and technology for monitoring PbO2, PbCO2 and pHb, and to observe the effects of injury and therapy interventions on each of the variables monitored, including ICP, the clinical standard. ICP and fiber optic pO2, pCO2 and pH probes were placed in 10 SCHI patients at bedside in the ICU using sterile technique. The probes remained in place for the duration of ICP monitoring, and were functional in the ICU environment for up to 10 days. Trend patterns recurred in this series of SCHI patients: Extreme PbCO2 (high) and pHb (low) are associated with poor perfusion; increasing pbCO2 and decreasing pHb may be early indicators of ICP crisis, i.e. ICP > 20 mm Hg that tends to be unresponsive to therapy, and; pentobarbital "loading" and maintenance is associated with increased pbO2. These preliminary results from monitoring pbO2, pbCO2 and pHb in SCHI patients indicate that fiber optic sensor technology functions and is able to be used in this application. Trend patterns from this data may further indicate practical utility as a more direct monitor of the delicate balance between tissue perfusion and cell metabolism than ICP alone.

Skeletal muscle PO2, PCO2, and pH in hemorrhage, shock, and resuscitation in dogs.

OBJECTIVE: To test fiber-optic PO2, PCO2, and pH sensors placed in skeletal muscle as monitors of hemorrhage, shock, and resuscitation, compared with mean arterial blood pressure, cardiac output, and blood gas variables. DESIGN: Observational study in physiology laboratory, using a canine controlled hemorrhagic shock model. MATERIALS AND METHODS: Mongrel dogs (20-35 kg; n = 10) were monitored with arterial, venous, and pulmonary artery catheters. A probe (0.5 mm in diameter) with fiber-optic PO2, PCO2, and pH sensors was placed percutaneously in the adductor muscle of the right medial thigh. Mean arterial blood pressure of 45 to 50 mm Hg was maintained for 1 hour with controlled hemorrhage, after which shed blood was reinfused. The animals were monitored for 4 hours after reinfusion. MEASUREMENTS AND MAIN RESULTS: Skeletal muscle PO2 (PmO2) decreased from 31+/-9 to 5+/-4 mm Hg during shock and recovered with reinfusion. Skeletal muscle pH (pHm) decreased from 7.24+/-0.10 to 6.94+/-0.12 during shock, to 6.90+/-0.13 with reinfusion, and recovered to near baseline 2 hours after reinfusion. PmCO2 increased from 48+/-14 to 134+/-86 mm Hg during shock, to 138+/-92 mm Hg with a time course inverse to pHm, and recovered to near baseline 30 minutes after reinfusion. On average, skeletal muscle PCO2 (PmCO2) and pHm did not recover to baseline, possibly indicating persistent anaerobic metabolic effects. O2 delivery, mixed venous PO2, mixed venous O2, saturation and PmO2 responded with similar time courses. CONCLUSION: PmO2, PmCO2, and pHm can be monitored simultaneously for several hours with fiber-optic sensors in a single, small probe. PmO2 may provide information comparable to O2 delivery. PmCO2 may reflect adequacy of perfusion. pHm may indicate success of resuscitation. This technology may offer new insight into the extent of injury and refinement of shock resuscitation and monitoring.

Preliminary clinical trial of an ex vivo arterial blood gas monitor.

PURPOSE: The purpose of this study was to test the analytical performance of a new ex vivo arterial blood gas (ABG) monitor based on fiberoptic sensor technology (SensiCath; Optical Sensors, Inc., Minneapolis, MN) when operated by critical care practitioners in intensive care environments. MATERIALS AND METHODS: Arterial blood analyses using a new ex vivo ABG monitor and standard clinical laboratory bench top analyzers were compared according to an institutionally approved protocol. The subjects were adult intensive care unit (ICU) patients (n = 20) with an arterial cannula for pressure monitoring, expectation of ICU stay > 72 hours, need for > or = 2 ABG analyses per day, and written informed consent. The clinical setting was two ICUs, a shock trauma ICU, and a neurological ICU in a metropolitan area trauma center. RESULTS: One hundred seventy-five paired ABG analyses were obtained over 1,146 hours of monitor use (52 +/- 20 hours per patient). Comparison of ABG monitor and laboratory analyses of blood samples obtained at the time of measurement by the monitor provided the following results: For pH, the range of laboratory measurements was 7.197-7.512, accuracy (mean difference between the monitor and laboratory measurement) was +0.010, precision (standard deviation of the difference between monitor and laboratory measurements) was +/- 0.027, and the correlation coefficient (r) = 0.913. For PCO2, the range of laboratory measurements was 24.5-61.5 mm Hg, accuracy was +1.4 mm Hg, precision was +/- 3.3 mm Hg, and r = 0.942. For PO2, the range of laboratory measurements was 47.3-163.3 mm Hg, accuracy was +4.0 mm Hg, precision was +/- 7.9 mm Hg, and r = 0.970. No adverse events occurred associated with the monitor. CONCLUSION: A practical ex vivo ABG monitor has been developed that offers accurate data and potential advantages to the critical care practitioner and the critically ill patient over other ABG analysis systems: one 10-minute calibration procedure; 1-minute analysis time; no permanent blood removal from the patient; and a closed arterial monitoring system. Precision performance is comparable to standard laboratory ABG analysis. The ABG monitor offers reliability and ease of use, and the ability of the critical care practitioner (nurse, respiratory therapist, or physician) to obtain accurate ABG analyses as needed at bedside.

Brain parenchyma PO2, PCO2, and pH during and after hypoxic, ischemic brain insult in dogs.

OBJECTIVES: 1) The investigation of fiberoptic PO2, PCO2, and pH sensor technology as a monitor of brain parenchyma during and after brain injury, and 2) the comparison of brain parenchyma PO2, PCO2, and pH with intracranial pressure during and after hypoxic, ischemic brain insult. DESIGN: Prospective, controlled, animal study in an acute experimental preparation. SETTING: Physiology laboratory in a university medical school. SUBJECTS: Fourteen mongrel dogs (20 to 35 kg), anesthetized, room-air ventilated. INTERVENTIONS: Anesthesia was induced with thiopental and maintained after intubation using 1% to 1.5% halothane in room air (FiO2 0.21). Mechanical ventilation was established to maintain end-tidal PCO2 approximately 35 torr (-4.7 kPa). Intravenous, femoral artery, and pulmonary artery catheters were placed. The common carotid arteries were surgically exposed, and ultrasonic blood flow probes were applied. A calibrated intracranial pressure probe was placed through a right-side transcranial bolt, and a calibrated intracranial chemistry probe with optical sensors for PO2, PCO2, and pH was placed through a left-side bolt into brain parenchyma. Brain insult was induced in the experimental group (n = 6) by hypoxia (FiO2 0.1), ischemia (bilateral carotid artery occlusion), and hypotension (mean arterial pressure [MAP] approximately 40 mm Hg produced with isoflurane approximately 4%). After 45 mins, carotid artery occlusion was released, FiO2 was reset to 0.21, and anesthetic was returned to halothane (approximately 1.25%). The control group (n = 5) had the same surgical preparation and sequence of anesthetic agent exposure but no brain insult. MEASUREMENTS AND MAIN RESULTS: Monitored variables included brain parenchyma PO2, PCO2, and pH, which were monitored at 1-min intervals, and intracranial pressure, MAP, arterial hemoglobin oxygen saturation (by pulse oximetry), end-tidal PCO2, and carotid artery blood flow rate, for which data were collected at 15-min intervals for 7 hrs. Arterial and mixed venous blood gas analyses were done at approximately 1-hr intervals. Baseline data agreed closely with other published results: brain parenchyma PO2 of 27 +/- 7 (SD) torr (3.6 +/- 0.9 kPa); brain parenchyma PCO2 of 69 +/- 12 torr (9.2 +/- 1.6 kPa); and brain parenchyma pH of 7.13 +/- 0.09. Postcalibration data were accurate, indicating stability and durability over several hours. In six experiments, during the brain insult, brain parenchyma PO2 decreased to 16 +/- 2 torr (2.1 +/- 0.3 kPa), brain parenchyma PCO2 increased to 105 +/- 44 torr (14 +/- 5.9 kPa) (p < .05), and brain parenchyma pH decreased to 6.75 +/- 0.08 (p < .05). Intracranial pressure (ICP) remained nearly constant (baseline 16 +/- 6 to 14 +/- 5 mm Hg at the end of the brain insult). Cerebral perfusion pressure (CPP = MAP - ICP) decreased (baseline 95 +/- 15 to 28 +/- 8 mm Hg; p < .05). On release of brain insult stresses, ICP increased to 30 +/- 9 mm Hg and CPP increased to 71 +/- 19 mm Hg (p < .05). A biphasic recovery was observed for brain parenchyma pH, which had the slowest recovery of the monitored variables. On average, brain parenchyma pH gradually returned toward baseline, and was no longer significantly different from baseline 3 hrs after release of insult stresses. Brain parenchyma PCO2 continued to decrease rapidly after brain insult and then remained approximately 52 +/- 10 torr (approximately 6.9 +/- 1.3 kPa) (p < .05). Brain parenchyma PO2 increased from a minimum at the end of brain insult to a maximum of 43 +/- 17 torr (5.7 +/- 2.3 kPa) within 1.25 hrs (p < .05), and then gradually decreased to approximately 35 +/- 10 torr (approximately 4.7 +/- 1.3 kPa). Cerebral perfusion pressure gradually decreased as ICP increased 3 to 5 hrs after insult. CONCLUSIONS: Intracranial chemistry probes with optical sensors demonstrated stable, reproducible monitoring of brain parenchyma PO2, PCO2, and pH in dogs for periods lasting > 8 hrs. Significant changes in brain p

Perception of the medical risk of spaceflight.

We conducted an opinion survey to improve the characterization of medical risk during spaceflight, using a questionnaire designed to elicit space medicine experts' perceptions of the probability, health effect, and mission impact of selected medical events occurring during spaceflight missions of 30-90 d. This questionnaire was directed toward those events about which little data currently exist, therefore medical events that have occurred during spaceflights with some frequency, such as space motion sickness, were excluded from the questionnaire. The questionnaire was mailed to 99 clinical and research professionals involved with NASA medical programs; 65 responses were returned, of which 60 could be analyzed. The experts rated skin disorders as the most likely to occur, but which would have little effect on mission completion or astronaut health. Circulatory diseases were rated as having the lowest probability of occurrence, but the highest effect on the mission or on a crewmember's health. The results of this survey will be combined with data from analogous populations and existing astronaut health data to establish a data set to support decisions about allocation of health care resources.

Arterial blood sampling devices influence ionized calcium measurements.

OBJECTIVE: To determine the effect of commercially available arterial blood sampling devices on ionized calcium measurements. DESIGN: Prospective study. SETTING: Neurosurgical and shock-trauma intensive care units (ICU) at a tertiary care teaching hospital. PATIENTS: Fourteen patients admitted to the ICU. Each patient had an indwelling arterial catheter. INTERVENTIONS: Arterial blood sampling. MEASUREMENTS AND MAIN RESULTS: In 14 ICU patients, measurements of arterial blood ionized calcium concentrations were performed, using 12 different commercially available arterial blood sampling devices. Significant underestimation of ionized calcium in blood samples compared with the reference test tube (Vacutainer 45) was seen in seven of the devices. Arterial blood ionized calcium concentrations measured, using one commercially available syringe, were significantly higher compared with the reference test tube. There was no correlation between either the amount or type of heparin in the arterial blood sampling devices and arterial blood ionized calcium measurement. CONCLUSIONS: This study demonstrates that various commercially available arterial blood sampling devices alter arterial blood ionized calcium measurements. These alterations are clinically important because ICU patients may be treated with inappropriate calcium supplementation.

The clinical chemistry and immunology of long-duration space missions.

Clinical laboratory diagnostic capabilities are needed to guide health and medical care of astronauts during long-duration space missions. Clinical laboratory diagnostics, as defined for medical care on Earth, offers a model for space capabilities. Interpretation of laboratory results for health and medical care of humans in space requires knowledge of specific physiological adaptations that occur, primarily because of the absence of gravity, and how these adaptations affect reference values. Limited data from American and Russian missions have indicated shifts of intra- and extracellular fluids and electrolytes, changes in hormone concentrations related to fluid shifts and stresses of the missions, reductions in bone and muscle mass, and a blunting of the cellular immune response. These changes could increase susceptibility to space-related illness or injury during a mission and after return to Earth. We review physiological adaptations and the risk of medical problems that occur during space missions. We describe the need for laboratory diagnostics as a part of health and medical care in space, and how this capability might be delivered.

Preliminary evaluation of an experimental clinical chemistry analyzer developed for space medicine.

An experimental clinical chemistry analyzer system was designed and built to demonstrate the feasibility of clinical chemistry as part of a medical-care system at NASA's planned space station Freedom. We report the performance of the experimental analyzer, called a medical development unit (MDU), for selected analytes in a laboratory setting in preparation for a preliminary clinical trial at patients' bedsides in an intensive-care unit. Within-run CVs ranged from 0.7% for sodium to 7.1% for phosphorus; day-to-day CVs ranged from 1.0% for chloride to 23.4% for calcium. Correlation of patients' blood sample analyses compared well with those by Ektachem E700 and other high-volume central laboratory analyzers (r ranged from 0.933 for creatine kinase MB isoenzyme to 0.997 for potassium), except for hemoglobin (r = 0.901) and calcium (r = 0.823). Although several CVs obtained in this study exceeded theoretical desired precision limits based on biological variations, performance was adequate for clinical laboratory diagnosis. We examined the effect of potentially interfering concentrations of hemoglobin, bilirubin, and lipids: the only effect was negative interference with calcium analyses by high concentrations of bilirubin. We also examined the effects of preanalytical variables and the performance of experimental sample-transfer cups designed to retain sample and reference liquid in microgravity. Continued development of the MDU system is recommended, especially automation of sample processing.

Continuous monitoring of interstitial fluid potassium during hemorrhagic shock in dogs.

It appears that ISFET probes can reliably and continuously monitor IF K+ in vivo for intervals of at least several hours. The consistently observed increase in IF K+ in response to hemorrhage, a phenomenon invisible systemically, suggests that such probes may provide clinically valuable information regarding perfusion related events at the cellular level during onset of and resuscitation from hypoperfusion states. Precise correlation of ISFET signal to specific cellular dysfunction awaits investigation in which muscle cell membrane potential, muscle surface pH, and postexperiment cellular histology are studied concurrently.