Barry A. Shapiro

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.

Changes in venous blood lactate, venous blood gases, and somatosensory evoked potentials after tourniquet application.

The effects of inflation of a 7-cm tourniquet applied to the upper arm of eight volunteers on venous lactate, venous blood gases, and ulnar nerve somatosensory evoked potentials (SSEPs) were investigated. The inflation pressure was 100 mmHg over the systolic pressure. Venous blood samples for lactate and blood gas determinations were withdrawn before tourniquet inflation; immediately and at 2, 5, 10, 15 min after tourniquet deflation; and additionally at 30, 45, and 60 min after deflation in the last four volunteers. SSEP stimulating surface electrodes were placed over the ulnar nerve at the wrist. Recording electrodes were placed over the ipsilateral ulnar groove of the elbow, Erbs point, and on the contralateral cortex. Averaged responses were acquired before inflation of the tourniquet, every 5–10 min during tourniquet inflation, and every 5–10 min for 45–60 min after tourniquet deflation. The tourniquet was inflated for 36 ± 11 min. After deflation of the tourniquet, postdeflation pain and paresthesias were felt by five volunteers; these occurred at 30–120 s after deflation and lasted for 75–120 s. The postdeflation pains were characterized as burning, cramping, paresthesias, buzzing, or severe expansion of the hand. The venous blood lactate levels were significantly elevated for 10 min, and the time course of its change did not correlate with reperfusion pain. The Po2 and O2Hb saturation in venous blood were significantly elevated for 10–15 min after deflation. The elevated lactate and Po2 levels in the presence of a restored blood flow probably result from continued anaerobic muscle metabolism secondary to capillary closure from the tourniquet-induced ischemia. The Erbs and cortical SSEPs were abolished after inflation of the tourniquet; time to 100% depression of the amplitude was 22 ± 6 min for the Erbs and 25 ± 6 min for the cortex. These changes probably resulted from nerve compression and ischemia. The percentage depression of the ulnar nerve SSEP at the elbow was 84 ± 16%, presumed to result solely from nerve ischemia. The SSEPs recovered after deflation of the tourniquet.

Respiratory management after cardiac surgery with inhalation anesthesia.

Improvements in cardiac surgery techniques and anesthetic management have given us cause to re-evaluate the necessity for postoperative mechanical ventilation and delayed extubation after open-heart surgery with inhalational anesthesia. One hundred consecutive patients undergoing various types of cardiac surgery were entered into this study; 94 patients met the requirements for spontaneous ventilation in the immediate postoperative time period and mechanical ventilation was not utilized. Of these 94 patients, 40 (45%) met extubation requirements within 90 min and were subsequently extubated. No patient required reintubation. Six (6%) patients failed to meet the requirements for spontaneous ventilation and, therefore, required mechanical ventilatory assistance postoperatively. In the majority of cardiac patients, the anesthetic technique determines postoperative ventilatory needs. Very poor preoperative physical status and unusually long procedures, however, will probably preclude early extubation or spontaneous ventilation and dictate the need for mechanical ventilation regardless of the anesthetic technique.

Hyponatremia in acute spinal cord injury

ObjectiveTo define the occurrence rate, time course, and potential etiologic factors of hyponatremia in patients with acute spinal cord injury. DesignAnalysis of data obtained from a retrospective review of medical records and from a systematized, prospective database pertaining to patients with spinal cord injury. SettingA university hospital with a federally funded regional spinal cord injury center and a dedicated spinal cord injury intensive care unit. PatientsTwo hundred eighty-two patients admitted between January 1, 1988 and December 31, 1989 with acute (<24-hr duration) spinal cord or vertebral column injury. InterventionsNone. Measurements and Main ResultsThe mean age of patients was 36.7 ± 17.6 (SD) yrs; 225 (80%) of the patients were male and 57 (20%) were female. Hyponatremia, when it occurred, developed at a mean time of 6.4 ± 6.7 days postadmission, reached its nadir at 8.7 ± 8.8 days, and occurred in 28% of those patients with cervical injuries, 34% with thoracic injuries, and 27% with lumbar injuries (p = NS). Logistic regression analysis demonstrated that the type of spinal cord injury (Frankel class: range is A = complete neurologic lesion to E = no neurologic lesion) was the strongest predictor of hyponatremia. The occurence rate of hyponatremia was as follows: Frankel class-A 62%; Frankel class-B 48%; Frankel class-C 41%; Frankel class-D 23%; Frankel class-E 16% (p < .0001). ConclusionsThe prevalence of hyponatremia in acute spinal cord injury is much higher than in the general medical or surgical patient population. This abnormality usually occurs within the first week postinjury. The most significant predictor of hyponatremia is the type rather than the level of spinal cord injury. The potential etiological factors are many and these factors are probably interrelated. The pathophysiologic mechanisms that result in hyponatremia must be explored so that this occurrence and its consequences can be prevented. (Crit Care Med 1994; 22:252–258)

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)

Pulmonary alveolar proteinosis in two siblings with decreased immunoglobulin A

A brother and sister with classic, biopsy proved pulmonary alveolar proteinosis are described. Both had low serum and low normal secretory immunoglobulin A (IgA) levels. A tendency for familial occurrence is possible and it is recommended that patients with pulmonary alveolar proteinosis, and their families, be evaluated for immunologic deficiencies.

Perioperative hypoxia: Perioperative hypoxia the clinical spectrum and current oxygen monitoring methodology

When searching for the source of hypoxia, the anesthesiologist and intensivist one served best by treating the patient in an organized approach--beginning with the environmental and pulmonary sources, searching for anemic and circulatory sources, and finally ruling out the less common histocytic causes. When treating hypoxia, the first maneuver should be to administer oxygen, ensure airway, ventilation, and circulation (the ABCs of basic life support). Further monitoring is addressed at global assessments and specific organ systems (especially in high-risk patients or during high-risk procedures). The ability to directly measure the oxygenation, blood flow, and function in each individual organ of the body is not yet available. Efforts are advancing in the ability to measure the function of important tissue beds, such as the brain and splanchnic circulation. In this regard, Table 5 provides a summary of the spectrum of monitoring technology available for various organs.

Reassessment of the assumed A-V oxygen content difference in the shunt calculation.

A study was undertaken in 15 patients to compare measured and assumed arteriovenous oxygen (A-V O2) content differences and their effects on resultant shunt calculations. All patients were on volume ventilators and demonstrated a stable cardiovascular state. Simultaneous measurements of the O2 content of a pulmonary artery (PA) and of a superior rena cava (SVC) sample were compared. A mean A-V O2 content difference of 3.5 ± 0.8 volumes percent was obtained from the PA and 2.6 ± 1.1 volumes percent from the SVC. The resultant shunt calculations derived from measured A-V O2 content differences were compared with the calculation based on an assumed A-V O2 content difference of 5 volumes percent. A method for extrapolating a “true” A-V O2 content difference from an SVC blood sample was obtained. The extrapolated value resulted in a more representative “true shunt” calculation in 13 of the 15 patients.