Narendra S. Trivedi

Effects of motion, ambient light, and hypoperfusion on pulse oximeter function

Abstract Study Objective: To compare the performance of five pulse oximeters during hypoperfusion, probe motion, and exposure to ambient light interference. Design: Prospective study. Setting: Laboratory facility at a university medical center. Patients: 8 unanesthetized, ASA physical status I volunteers. Interventions: We evaluated five common pulse oximeters with respect to three scenarios: (1) an operating room light was shone on oximeter probes, (2) a motion generator was used to generate 2 Hz and 4 Hz hand motion, and (3) a pneumatic compression device overlying the brachial artery was used to simulate hypoperfusion. Electrocardiographic (ECG) and arterial blood gas values were considered gold standards for heart rate (HR) and oxygen saturation (SpO 2 ) respectively. SpO 2 nondisplay and values greater than 4% from simultaneous arterial SaO 2 -oximeter values were defined as errors. Nondisplay of HR, or HR greater than 5% from ECG values, were also considered errors. Measurements and Main Results: The Ohmeda and Nellcor N200 with finger probe had the highest total failure rates with respect to both SpO 2 and HR due to ambient light interference ( p 2 during 2 Hz and 4 hz. motion ( p 2 ( p Conclusion: There are significant differences in the accuracy of commercially available pulse oximeters during nonideal circumstances, with failure rates varying from approximately 5% to 50% depending on the oximeter and source of interference. Furthermore, no single oximeter performed the best under all conditions.

Anesthesia for thoracoscopic laser ablation of bullous emphysema

BackgroundWe describe the anesthetic management for a new surgical procedure: laser ablation of emphysematous bullae via thoracoscope. Although thoracoscopy is not new, this is the first description of a series of patients with bilateral, chronic lung disease who underwent long periods of one-lung ventilation (OLV) during thoracoscopic therapy. MethodsTwenty-six laser ablation procedures were performed in 22 patients. The patients were elderly (mean age 63 yr) with a large incidence of coexisting cardiovascular disease. Most required chronic home oxygen therapy. Patients were monitored invasively, and hemodynamic data were recorded every 5 min. Arterial blood gas analyses were performed every 15 min. Comparisons were made between three Intraoperative periods: two-lung ventilation (TLV) before thoracoscopy, OLV during thoracoscopy, and TLV after thoracoscopy. ResultsAll patients survived the operation despite a mean OLV duration of 170 min, but several experienced serious intraoperative problems, such as hypoxemia or hypotension. Hypoxemia was treated with nondependent lung continuous positive airway pressure and dependent lung positive end-expiratory pressure. In all patients the lungs were adequately ventilated, but bronchopleural fistulae occurred upon return to TLV in every case. The resulting air leaks, often 50% of inspired tidal volume, required the use of a pressure-cycled ventilator to maintain oxygenation. Postoperative air leaks greater than 50% of inspired tidal volume usually required subsequent surgical correction, while smaller leaks resolved spontaneously. Mechanical ventilation was required for an average of 5 days. Eighty-four percent have survived at least 6 months, and nearly all survivors report symptomatic improvement. ConclusionsAblation of bullae appears to provide symptomatic improvement, and thoracoscopy might be better tolerated than thoracotomy, especially in patients with severe bullous emphysema.

Pulse oximeter performance during desaturation and resaturation: A comparison of seven models

STUDY OBJECTIVE To compare pulse oximeter performance during induced hypoxemia. DESIGN Prospective investigation in human volunteers. SETTING Laboratory facility at a university medical center. PATIENTS 8 unanesthetized, healthy ASA physical status I volunteers. INTERVENTIONS We evaluated the accuracy and response times of seven popular pulse oximeters during induced hypoxemia. Arterial blood fractional oxygen saturation (SaO2) measurements were performed simultaneously and considered a gold standard. MEASUREMENTS AND MAIN RESULTS All oximeters were accurate (+/-2%) while subjects were breathing room air. During maximal hypoxemia (induced by breathing a FIO2 = 10% in nitrogen), large differences were noted between oxygen saturation as measured by pulse oximetry (SpO2) and SaO2 values, with pulse oximeters consistently underreporting SpO2 when actual SaO2 values were 75% or less. The Ohmeda 3740 (Ohmeda, Boulder, CO) using an ear probe was the first to detect desaturation (change in SpO2 > 3%) in 4 of 8 subjects (p < 0.05), and the Nellcor N200 reflectance oximeter (Nellcor, Inc., Pleasanton, CA) was first in 3 of 8 subjects (p < 0.05). During resaturation (after administering 100% oxygen), the Novametrix Oxypleth (Novametrix, Wallingford, CT) was significantly faster than other oximeters (p < 0.05) to return to baseline (SpO2 = 98%). CONCLUSION Most models of oximeters tested performed well when hemoglobin oxygen saturation was high, but all were inaccurate when SaO2 was approximately 75%. During induced hypoxemia, there were significant differences in the response times of oximeters tested, with no model demonstrably superior to others in all measures of performance.

Effects of Motion, Ambient Light, and Hypoperfusion on Pulse Oximeter Function

STUDY OBJECTIVE To compare the performance of five pulse oximeters during hypoperfusion, probe motion, and exposure to ambient light interference. DESIGN Prospective study. SETTING Laboratory facility at a university medical center. PATIENTS 8 unanesthetized, ASA physical status I volunteers. INTERVENTIONS We evaluated five common pulse oximeters with respect to three scenarios: (1) an operating room light was shone on oximeter probes, (2) a motion generator was used to generate 2 Hz and 4 Hz hand motion, and (3) a pneumatic compression device overlying the brachial artery was used to simulate hypoperfusion. Electrocardiographic (ECG) and arterial blood gas values were considered gold standards for heart rate (HR) and oxygen saturation (SpO2) respectively. SpO2 nondisplay and values greater than 4% from simultaneous arterial SaO2-oximeter values were defined as errors. Nondisplay of HR, or HR greater than 5% from ECG values, were also considered errors. MEASUREMENTS AND MAIN RESULTS The Ohmeda and Nellcor N200 with finger probe had the highest total failure rates with respect to both SpO2 and HR due to ambient light interference (p < 0.05). The Nellcor N200 with finger probe and N200 with C lock were the most accurate with regard to SpO2 during 2 Hz and 4 Hz motion (p < 0.05). However, all oximeters failed dramatically during 4 Hz motion when measuring HR. In the hypoperfusion model, the Nellcor N200 with finger probe and the Nellcor C Lock oximeters performed significantly better than all others in terms of both HR and SpO2 (P < 0.05), while the Criticare oximeter failed 100% of the time. CONCLUSION There are significant differences in the accuracy of commercially available pulse oximeters during nonideal circumstances, with failure rates varying from approximately 5% to 50% depending on the oximeter and source of interference. Furthermore, no single oximeter performed the best under all conditions.