Roy D. Cane

Perioperative complications of elective tracheostomy in critically ill patients

This study was designed to examine prospectively the incidence of perioperative complications associated with elective tracheostomy in critically ill patients. An experienced surgeon and anesthesiologist participated in every tracheostomy procedure. In 81 procedures, there was no loss of airway cont

Preliminary evaluation of an intra-arterial blood gas system in dogs and humans

The reliability and accuracy of an intra-arterial fluorescent optode system to measure continuously pHa, PaCO2, and PaO2 were evaluated in a dog model and in a group of critically ill patients. Six hundred sixty-three arterial blood gas (ABG) samples were analyzed for pHa, PaCO2, and PaO2 in the dog studies. The intra-arterial blood gas system (IBGS) indicated a steady state in 420 instances for pH, 359 instances for PaCO2, and 256 instances for PaO2. Comparison of these ABG and IBGS values by linear regression analysis revealed r = .97 for pHa, .95 for PaCO2, and .96 for PaO2. The mean +/- SD of the difference between ABG and IBGS was -0.02 +/- 0.03 for pHa, 1.05 +/- 3.8 for PaCO2, and -17 +/- 13 for PaO2. Nonsteady states were correctly identified by the IBGS in every instance. Comparisons between 79 temporally matched ABG and IBGS values, exclusive of in vivo calibration samples, in 12 critically ill patients revealed r = .97 for pHa, .96 for PaCO2, and .99 for PaO2. The difference was 0.002 +/- 0.02 for pHa, 0.44 +/- 2.97 for PaCO2, and -1.22 +/- 9.34 for PaO2. We conclude that it is possible to measure continuously pHa, PaCO2, and PaO2 with the IBGS in critically ill patients for periods from 3 to 25.5 h while maintaining the ability to monitor BP and withdraw blood samples from the arterial cannula. Agreement between the two techniques is within clinically acceptable ranges for pHa and PaCO2, whereas PaO2 measurement by the IBGS requires further refinement.(ABSTRACT TRUNCATED AT 250 WORDS)

Unreliability of oxygen tension-based indices in reflecting intrapulmonary shunting in critically ill patients.

Measurement of intrapulmonary shunting (Qsp/Qt), a widely used method for monitoring disturbances of pulmonary oxygen transfer in critically ill patients, involves calculation of arterial and mixed venous oxygen contents. In circumstances where mixed venous blood samples are not readily available, oxygen tension-based indices such as the alveolar to arterial oxygen tension differences (P[A-a]O2), arterial oxygen tension to alveolar oxygen tension ratio (PaO2/PAO2), PaO2 to FIO2 ratio (PaO2/FIO2) and respiratory index (RI) are widely utilized to reflect Qsp/Qt. Oxygen content-based indices such as the estimated shunt are not as widely utilized as the oxygen tension indices. In 75 critically ill patients in whom a pulmonary artery catheter was being utilized to augment clinical care, comparisons were made between Qsp/Qt and P(A-a)O2, PaO2/PAO2, PaO2/FIO2, RI, and estimated shunt to determine which index best reflected Qsp/Qt. Correlations between Qsp/Qt and estimated shunt were good (r = .94) and poor for the P(A-a)O2 (r = .62), PaO2/PAO2 (r = .72), PaO2/FIO2 (r = .71), and RI (r = .74). We conclude that there are no real substitutes for venous oxygen contents in critically ill patients. When pulmonary artery blood is not available for analysis, oxygen tension-based indices are unreliable reflectors of Qsp/Qt while the estimated shunt, an oxygen content-based index, provides a more reliable reflection of Qsp/Qt.

Intensive care unit patients with acquired immunodeficiency syndrome and Pneumocystis carinii pneumonia: Suggested predictors of hospital outcome

ObjectiveTo define our ICU experience with AIDS patients, Pneumocystis carinii pneumonia, and respiratory failure, and to delineate factors predictive of hospital survival. DesignA retrospective study in which logistic regression analysis was applied to data obtained during the first 144 hrs of ICU admission. SettingA university hospital medical ICU associated with a national AIDS treatment center. PatientsTwenty-seven male patients with AIDS, P. carinii pneumonia, and respiratory failure who desired full supportive and resuscitative care. Measurements and Main ResultsOf 27 patients who met study criteria, 19 (70%) were nonsurvivors and eight (30%) were survivors. The relative risk of death was 2.2 times greater in patients who exhibited the combination of pH <7.35 and a base deficit >4 mEq/L, at any time in their ICU course, than in patients who did not (95% confidence interval = 1.01, 4.81). Furthermore, the relative risk of death was 3.7 times greater in patients who required positive end-expiratory pressure >10 cm H2O after 96 hrs of ICU care than in those patients who did not (95% confidence interval = 1.09,12.33). Indices of oxygen transfer, severity of chest radiograph abnormalities, concurrent lung infections, and most laboratory studies on hospital admission were not different between the two groups nor predictive of hospital survival. ConclusionsWhen dealing with AIDS/P. carinii pneumonia/ICU patients, it is not possible to distinguish who will survive to hospital discharge based on information routinely available before ICU admission. Those patients with the greatest chance of survival demonstrate a significant decrease in the required level of respiratory support within the first 4 days of ICU care. The presence of a metabolic acidemia (pH <7.35 and base deficit >4 mEq/L), at any time during the ICU course, is a poor prognostic sign. We suggest that such objective variables should be included in the development of any new outcome predictor model for this group of ICU patients. (Crit Care Med 1991; 19:892)

Tongue extrusion as an aid to blind nasal intubation

Blind nasal intubation often results in esophageal placement of the tube because reflex swallowing and supralaryngeal structures direct the tube posteriorly. Extrusion of the tongue, which inhibits swallowing and shifts the supralaryngeal structures anteriorly, facilitated blind placement of a nasotracheal tube in 14 of 16 critically ill patients. The technique avoids manipulation of the neck, the use of heavy sedation or anesthesia, and requires no specialized training or equipment.

The Spectrophotometric Absorbance of Intralipid

The spectral absorbance of Intralipid, a phospholipid emulsion, was investigated to discern its effect, when parenterally administered, on the spectrophotometric measurement of hemoglobin (Hb), oxyhemoglobin (HbO2), and carboxyhemoglobin (HbCO). While accounting for dilutional factors, various concentrations of Intralipid in both water and hemoglobin solutions were analyzed at six wavelengths commonly used to measure Hb, HbO2 and HbCO. Absorbance increased linearly with Intralipid concentration at all wavelengths, and ranged from 0.034 at 505 nm to 0.019 at 626.6 nm per mg of Intralipid. Therefore, in patients receiving Intralipid, significant errors in Hb, HbO2 and HbCO measurements can be introduced if these measurements are made by oximetry, and the authors suggest that such measurements should be accomplished by methods other than spectrophotometry.

Minimizing errors in intrapulmonary shunt calculations.

In 100 critically ill patients, intrapulmonary shunts (Qsp/Qt) calculated by assuming a carboxyhemoglobin (HbCO) of zero and a hemoglobin saturation (HbO2) derived from the Severinghaus nomogram were compared to shunts calculated utilizing measured values of HbCO and HbO2. The differences were statistically significant (p < 0.001). These 100 patients had a mean Hb of 11.9 g/dl and a mean HbCO of 1.7%. Measured shunt calculations in 30 critically patients were prospectively compared with shunt calculations utilizing the mean assumed values derived from the 100 patients initially studied. No statistically significant differences occurred between these two shunts.It is, therefore, concluded that errors attributable to the common practice of assuming zero HbCO and deriving HbO2 from nomograms will produce falsely high calculated intrapulmonary shunt values in critically ill patients. It is, therefore, important to measure accurately HbCO and HbO2 concentrations when monitoring intrapulmonary shunting in critically ill patients. However, if such measurements cannot be obtained, utilization of an assumed value of 1.5% for HbCO and HbO2 nomogram values will minimize errors in the shunt calculation.

The reliability of electrolyte measurements in plasma

The difference between serum and plasma electrolyte measurements and the effects of delay, cooling and addition of sodium heparin on plasma electrolyte measurements were observed. Delay of more than 30 min from sampling to analysis renders plasma potassium measurements unreliable. All other factors assessed produced no changes in plasma electrolyte measurements. Arterial blood gas laboratories can, therefore, reliably provide rapid or serial measurements of plasma sodium and potassium provided the analysis is performed within 30 min of obtaining an appropriate arterial blood sample.

Methemoglobin levels in the patient population of an acute general hospital

Spectrophotometric analysis of arterial blood samples from 695 hospitalized patients revealed a mean methemoglobin value of 0.44% (±0.3%) of total hemoglobin. Since values of methemoglobin greater than one percent exceed two standard deviations from the mean, it is concluded that methemoglobinemia in the hospitalized patient should be defined as a methemoglobin concentration of greater than one percent of total hemoglobin. This study demonstrates that no statistically significant differences exist in the incidence of methemoglobinemia among various populations within the hospital.

Adaptation of pressure support ventilation to increasing ventilatory demand during experimental airway obstruction and acute lung injury

ObjectiveTo estimate the changes in the relative amount of ventilatory assistance offered by inspiratory pressure support during changing ventilatory demand with external airway obstruction and with oleic acid-induced acute lung injury. DesignProspective, controlled, crossover study. SettingExperimental laboratory in a university anesthesiology department. SubjectsEight dogs anesthetized with pentobarbital. InterventionsAn external resistor was placed in the breathing circuit to produce increased resistance to breathing. Acute lung injury was produced with oleic acid. Ventilatory demand was increased by increasing the CO2 concentration in inspired gas to produce an increase of 20 torr (2.7 kPa) in end-tidal CO2 tension. During airway obstruction, pressure support was adjusted to reduce the inspiratory decrease in intrathoracic pressure to the level present during unobstructed breathing. During acute lung injury, pressure support was applied to reduce the maximum negative deflection of intrathoracic pressure by 50%. Measurements and Main ResultsThe ventilator effort was estimated by calculating the pressure-time integral of proximal airway pressure; the spontaneous ventilatory effort was estimated in a similar manner from esophageal pressure. The pressure support averaged 10 ± 3 cm H2O during airway obstruction and 7 ± 2 cm H2O during lung injury. The CO2 challenge effected an average increase in mean minute ventilation of 78% during airway obstruction (p < .001) and 120% during acute lung injury (p < .01). The augmentation of minute ventilation was accomplished by increasing the ventilatory rate and the transpulmonary pressure while inspiratory time remained unchanged. The pressure-time integrals measured using both airway (p < .001) and esophageal pressure (p < .01) increased significantly during each CO2 challenge, reflecting an increase in the contribution of both the ventilator and the animal to the required breathing effort. Significant decreases in the relative magnitude of the ventilator effort both during airway obstruction (p < .05) and during lung injury (p < .01) indicated that the increase in the spontaneous effort was predominant over the increase in mechanical ventilatory support. ConclusionsA ventilatory rate-dependent adaptation of pressure support to increased ventilatory demand occurs in an experimental setting both during airway obstruction and lung injury. The results of this study confirm an advantage of breath-to-breath inspiratory pressure support over techniques designed to supply a predetermined mechanical minute volume. (Crit Care Med 1993; 21:562–566)