Oxygen accumulation and associated dangers in rescue helicopters.

BACKGROUND: At the time of the COVID-19 pandemic, devastating incidents increased due to frequent oxygen administration to patients. The dangers associated with the use of oxygen, especially through local enrichments and formation of "oxygen clouds", have been well understood for years. Nevertheless, dramatic incidents continue to occur, since fire hazard increases exponentially with oxygen concentrations above 23%. Rescue helicopters are at a particular high risk, because of technical reasons such as oxygen use in a very small space, surrounded by kerosene lines, electronic relays and extremely hot surfaces. METHODS: In this study three different sized rescue helicopter models (Airbus H135, H145 and MD902) were examined. Oxygen enrichment in the cabin was measured with an oxymeter during a delivery rate of 15 l/min constant flow for 60 min. Furthermore, the clearance of the enriched atmosphere was tested in different situations and with different ventilation methods. To make the airflow visible, a fog machine was used to fill the helicopter cabin. RESULTS: Oxygen accumulation above 21% was detected in every helicopter. After 10-15 min, the critical 23% threshold was exceeded in all three aircrafts. The highest concentration was detected in the smallest machine (MD902) after 60 min with 27.4%. Moreover, oxygen clouds persisted in the rear and the bottom of the aircrafts, even when the front doors were opened. This was most pronounced in the largest aircraft, the H145 from Airbus Helicopters. Complete and rapid removal of elevated oxygen concentrations was achieved only by cross-ventilation within 1 min. CONCLUSIONS: Oxygen should be handled with particular care in rescue helicopters. Adapted checklists and precautions can help to prevent oxygen accumulation, and thus, fatal incidents. To our knowledge, this is the first study, which analyzed oxygen concentrations in different settings in rescue helicopters.

Outcome after interposition of vein grafts for arterial repair of extremity injuries in civilians.

OBJECTIVE: The objective of this study was to report on immediate and long-term outcomes after vein graft interposition in patients with upper- and lower-limb arterial injuries. METHODS: In the retrospective data analysis, all patients who underwent vein graft repair of limb arterial injuries in our civilian institution since 1990 were included, analyzed, and followed. Study end points were crude early and long-term patency, vascular reintervention, limb salvage, and perioperative death. RESULTS: A total 152 consecutive patients (127 men; median age, 31.7 years; range, 5.3-77.2) who presented with 158 lesions of limb arteries (lower limb: n = 90; upper limb: n = 68) underwent repair with the use of vein graft interposition. The vast majority of lesions were caused by blunt trauma (n = 144; 91%). In early results, the 30-day mortality rate was 3.3%. In-hospital limb loss rate was significantly lower in the upper limb (n = 2; 2.9%) than in the lower limb (n = 12; 13.3%; P < .05). Primary early patency was 93% (upper limb) and 89% (lower limb): early graft occlusions occurred both in the upper limb (n = 5; 7%) and the lower limb (n = 10; 11%; P = .59). Occlusions were followed by amputation in six cases (upper limb: one of five; lower limb: five of 10) despite successful revision of the occluded grafts. Long-term results after a median follow-up period of 6.0 years (range, 0.3-23.4) showed upper limb (62% of patients were followed): no late limb loss, no vascular reintervention; patency: 97.6%; lower limb (66% of patients were followed): one late limb loss, one redo bypass for vein graft dilation, patency: 98.3%. CONCLUSIONS: Emergency repair of civilian artery injuries with the use of vein grafts is associated with considerable risk of early occlusion and limb loss. When compared with the upper limb, limb loss rate is significantly higher in the lower extremity. Early graft occlusion is frequently followed by limb loss, especially in the lower limb. During long-term follow-up, occlusions of interposed vein grafts, vascular reinterventions, and late amputations are uncommon.