Table 20.
—[Section 6.1] Summary of Findings: Should Compression Stockings Compared With No Compression Stockings Be Used by People Taking Long Flights?142
| Outcome | No. of Patients (Studies) | Quality of the Evidence (GRADE) | Relative Effect (95% CI) | Anticipated Absolute Effects |
|
| Baseline Risk Without Stocking | Risk Difference With Stocking (95% CI) | ||||
| Symptomatic DVT | 2,637 (9) | Moderate due to imprecisiona | Not estimable | 0 per 1,000 | −1.5% to 1.5% |
| Pulmonary embolism | 2,637 (9) | Not estimable | Not estimable | 0 per 1,000 | − 1.5% to 1.5% |
| Symptomatic DVT (inferred from surrogate, symptomless DVT) | 2,637 (9) | Moderate due to indirectnessb | RR, 0.10 (0.04-0.25) | Low-risk populationc | |
| 5 per 10,000 | 0.5 per 10,000 (0 to 1.25) | ||||
| High-risk populationc | |||||
| 18 per 10,000 | 1.8 per 10,000 (1 fewer to 8 fewer) | ||||
| Symptomatic pulmonary embolism (inferred from surrogate, symptomless DVT) | 2,637 (9) | Moderate due to indirectnessb | RR, 0.10 (0.04-0.25) | Low-risk populationc | |
| 27 per million | 3 per million (1 fewer to 7 fewer) | ||||
| High-risk populationc | |||||
| 97 per million | 10 per million (4 fewer to 95 fewer) | ||||
| Superficial vein thrombosis | 1,804 (8) | Moderate due to imprecision | RR, 0.45 (0.18-1.13) | 13 per 1,000 | 6 per 1,000 (2 fewer to 15 more) |
| Edema postflight values measured on a scale from 0, no edema, to 10, maximum edema. | 1,246 (6) | Lowb due to risk of bias (unblinded, unvalidated measure) | Not estimable | The mean edema score ranged across control groups from 6.4 to 8.9 | The mean edema score in the intervention groups was on average 4.72 lower (95% CI, 4.91-4.52). |
| Death | 2,637 (9) | Not estimabled | Not estimable | Estimates not available, but risk extremely low | |
| Adverse effects | 1,182 (4) | Not estimabled | Not estimable | Not estimable | Not estimable |
All the stockings in the nine trials included in this review were below-knee compression stockings. In four trials the compression strength was 20-30 mm Hg at the ankle. It was 10-20 mm Hg in the other four trials. Stockings come in different sizes. If a stocking is too tight around the knee it can prevent essential venous return, causing the blood to pool around the knee. Compression stockings should be fitted properly. A stocking that is too tight could cut into the skin on a long flight and potentially cause ulceration and increased risk of DVT. Some stockings can be slightly thicker than normal leg covering and can be potentially restrictive with tight footwear. It is a good idea to wear stockings around the house prior to travel to ensure a good, comfortable fitting. Stockings were put on 2 to 3 h before the flight in most of the trials. The availability and cost of stockings can vary. See Table 4 legend for expansion of abbreviations.
The imprecision refers to absolute measures, not the relative. For the relative, it is not possible to make an estimate. This is also true for pulmonary embolism.
There are two reasons for indirectness: estimates of relative risk reduction come from the surrogate, and there is uncertainty regarding the baseline risk.
Estimates for control event rates for venous thrombosis and for pulmonary embolism come from Philbrick et al.131 Definition of high risk includes previous episodes of DVT, coagulation disorders, severe obesity, limited mobility due to bone or joint problems, neoplastic disease within the previous 2 years, or large varicose veins.
None of the other trials reported adverse effects, apart from four cases of superficial vein thrombosis in varicose veins in the knee region that were compressed by the upper edge of the stocking in one trial.131