Anesth Analg 2001;93:667-668
© 2001 International Anesthesia Research Society
TECHNOLOGY, COMPUTING, AND SIMULATION
A Simple and Inexpensive Nasal Cannula to Prevent Rebreathing for Spontaneously Breathing Patients Under Surgical Drapes
Ibrahim Kurt, MD,
Nil M. Kurt, MD,
Varlik K. Erel, MD,
Feray Gursoy, MD, and
Ayse Gurel, MD
Department of Anesthesiology & Reanimation, Adnan Menderes University, Faculty of Medicine, Aydin, Turkey
Address correspondence to Ibrahim Kurt, MD, Department of Anesthesiology, Adnan Menderes University, Aydin, 09100, Turkey. Address e-mail to ibrahimkurt_2000{at}yahoo.com
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Abstract
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IMPLICATIONS: A new nasal cannula that provides oxygenation and suctioning simultaneously prevents rebreathing during surgery in spontaneously breathing patients under surgical drapes. When air is not suctioned, inspired CO2 levels increase significantly, whereas suctioning prevents this increase. Expiratory CO2, respiratory rate, heart rate, and arterial blood pressure remain stable regardless of suctioning.
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Introduction
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Hypoxia and carbon dioxide rebreathing are potential problems during ophthalmic surgery performed under local anesthesia (1–3). Surgical drapes applied over the faces of spontaneously breathing patients give rise to hypercapnia and tachypnea (1–3). In this study, we investigated the effects of a newly designed nasal cannula on the prevention of carbon dioxide (CO2) rebreathing.
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Methods
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The apparatus was designed using a standard nasal cannula, a 14-gauge suction catheter, and a stopcock. The tubing between the two nasal prongs was occluded with a cotton ball soaked with Vaseline and inserted through one of the nasal prongs. The oxygen inlet tubing was cut immediately after the Y-junction. The proximal end was folded over itself and taped. A stopcock attached to a CO2 sampling line was adapted to the other cut end. This side of the nasal prong apparatus provided continuous CO2 sampling. The other intact tubing delivered oxygen to the patient (4). A suction catheter was taped alongside the oxygen inlet tubing to provide means for continuous suction of exhaled CO2 to prevent rebreathing (Fig. 1).
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Figure 1. Preparation of the cannula system. A, nasal oxygen cannula and suction catheter; B, after modification.
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The new cannula system was tried prospectively in 20 healthy volunteers in a single-blinded, cross-over study. The Ethics Committee of Adnan Menderes University approved the study protocol. After receiving written informed consent, 20 volunteers (ASA physical status I) without preexisting pulmonary disease or psychological or neurological disorders were entered into the study.
After the nasal cannula modification was fitted to the volunteers’ noses, their faces and heads were covered using double layers of cotton drapes in a fashion similar to the draping in ophthalmic operations. The experiment was completed in two stages. In Phase I, no suction was applied but oxygen was given at a constant flow of 3 L/min. In Phase II, air under the drapes was suctioned while oxygen was insufflated through the inlet side at a constant flow of 3 L/min.
The two phases were performed with an interval of at least 24 h. Whether Phase I preceded Phase II or vice versa was decided by tossing a coin. Each phase was completed in 30 min. The volunteers were not aware of the different stages because of the continuous hissing sound of oxygen through the inlet tube.
Electrocardiogram, pulse oximetry, noninvasive systolic and diastolic blood pressure, and respiratory rate were measured during the procedure by using the Cardiocap II Anesthesia monitor. Inspired CO2 (FICO2) and ETCO2 concentrations were measured with the same anesthesia monitor. Baseline values were obtained before the volunteers were draped. Additional measurements were taken at 5, 10, 15, 20, 25, and 30 min. Subjective complaints of anxiety and agitation were recorded for each volunteer.
Data are expressed as mean ± SD. Statistical analysis was performed using SPSS 9.0 (SPSS, Inc, Chicago, IL). In the case of significant differences, further comparisons between the groups and baseline measurements were made with the paired Student’s t-test. A P value of <0.05 was considered statistically significant.
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Results
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Demographic data are shown in Table 1. During the study no significant differences were found in heart rate, systolic and diastolic blood pressure, respiratory rate, SpO2, or ETCO2 between the two phases. The only differences between the two groups were in FICO2 levels. When ambient air was not suctioned, FICO2 levels increased as soon as the patient’s head was covered (P < 0.01) (Fig. 2).
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Figure 2. FICO2 and ETCO2 levels during two phases. *P < 0.01 compared with baseline and suction phase.
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During the nonsuction phase, 19 of 20 volunteers complained of shortness of breath. Two volunteers felt severe respiratory distress toward the end of this phase. However, the respiratory rate was not changed. Only one volunteer complained of the continuous sound in the suction phase. All volunteers except one preferred the suction phase.
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Discussion
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In this study a simple and inexpensive cannula that can be assembled rapidly in the operating room was tested on 20 volunteers. Suctioning ambient air under the drapes prevented rebreathing of CO2 whereas oxygen insufflation prevented hypoxemia.
Surprisingly, CO2 rebreathing, as evidenced by the increase in the measured FICO2 levels in the nonsuction phase, did not increase the respiratory rate or ETCO2 levels. Because the arterial CO2 levels were not monitored simultaneously, the results cannot be interpreted freely. It may be argued that ETCO2 may have escaped before being captured by the CO2 sampling line, but this would also prevent the increase in the FICO2 levels observed in this study. The nasal cannula is a more sensitive monitor to detect CO2 changes than the face mask method (5). Further studies should be designed where arterial CO2 levels are concomitantly monitored and compared with the unpredictably low ETCO2 levels in the nonsuction phase.
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References
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Schlager A, Luger TJ. Oxygen application by a nasal probe prevents hypoxia but not rebreathing of carbon dioxide in patients undergoing eye surgery under local anaesthesia. Br J Ophthalmol 2000; 84: 399–402.[Abstract/Free Full Text]
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Schlager A, Staud H. New equipment to prevent carbon dioxide rebreathing during eye surgery under retrobulbar anaesthesia. Br J Ophthalmol 1999; 83: 1131–4.[Abstract/Free Full Text]
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Schlager A, Lorenz IH, Luger TJ. Transcutaneous CO2/O2 and CO2/air suction in patients undergoing cataract surgery with retrobulbar anaesthesia. Anaesthesia 1998; 53: 1212–8.[Medline]
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Marino PL. Oximetry and capnography. In: The ICU book. 2nd ed. Baltimore: Williams & Wilkins, 1998:355–70.
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Loughnan TE, Monagle J, Copland JM, et al. A comparison of carbon dioxide monitoring and oxygenation between facemask and divided nasal cannula. Anaesth Intensive Care 2000; 28: 151–4.[Web of Science][Medline]
Accepted for publication May 1, 2001.
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Abstract
Introduction
