Background and Goal of Study: Patients undergoing vitrectomy or scleral buckle receive deep iv sedation and O2 via nasal cannula (NC) during retrobulbar block. O2 desaturation (Desat) may occur while the needle is in place. A plastic sheet has been shown to convert a NC to a face tent at no cost1–2. It improves oxygenation in deeply sedated patients during upper endoscopy2. It has been used in “Eye Room”. We wish to confirm its effectiveness in improving oxygenation while ascertaining FiO2.
Materials and Methods: This retrospective review of patients undergoing vitrectomy or scleral buckle identified 2 groups. NC (n=66) patients received NC O2 and FT (n=63) received NC O2 and a plastic sheet covering the nose and mouth1. It was removed after the block. After pre-oxygenation (3–5 l/min), patients received iv propofol to achieve deep sedation for the block. Data collected included age, weight, height, O2 saturation (Sat), the amount of propofol and O2/CO2 levels. Student t-test and Chi Square test were used for analysis. A p value <0.05 was considered as significant. (Mean±S.D.)
Results and Discussion: There were no differences in age (NC: 66±15; FT: 69±14 yrs), BMI (NC: 27.1±5.3; FT: 27.4±4.8), ASA Status (NC: 2.1±0.7; FT: 2.2±0.7), room air O2 Sat, ETCO2 and need for assisted ventilation. There were differences in O2 Sat 5 min after O2, highest O2 flow, lowest O2 Sat and severe Desat. Despite receiving higher amount of propofol and lower O2 flow than NC group, sedation had less depressive effects on oxygenation in FT patients. FT (n=38) had higher FiO2 (NC: 23±1; FT: 50±14%) and FeO2 (NC: 45±17; FT: 74±16%) with a lower O2 flow than NC (n=7) and rebreathed a small amount of CO2.(NC: 0±0 mmHg; FT: 7±5)
Conclusion(s): Data show that a plastic sheet converts a NC to a face tent that increases O2 delivery without increasing flow or cost. It improves oxygenation and prevents severe desaturation during retrobulbar block.