Ronald A. Harrison

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.

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.

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.

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.