Altitude and gas expansion in repaired rhegmatogenous retinal detachment

With 40.3 million flights per year and over 4 thousand million passengers flying in the pre-COVID time [1], there is a great chance that patients encounter problems relating to gas expansion. In addition, a significant proportion of patients in higher altitude countries such as Switzerland, Nepal or Peru may experience problems with gas expansion when returning to their home after surgery.

According to the Boyle’s law [2] pressure is inversely proportional to the volume. In other words, if there is a decrease in the pressure on a gas, the total volume of this gas will increase. Based on this law, the interaction between altitude and gas is an important point to consider at the moment of instilling the gas endotamponade during vitreoretinal surgery.

Certainly, the clinical scenarios that we need to face will influence the strategies that we put in place to address this issue. In the case that patients need to fly urgently, scleral buckling (SB) is generally the best option and in our opinion, the gold standard to allow the patients to fly. In the end, SB was for many years the gold standard for the management of rhegmatogenous retinal detachment (RRD), with a high overall primary success rate reported [3]. However, the number of SB surgeries performed in the last two decades has decreased gradually and, as a consequence, newly trained vitreoretinal surgeons are less familiar with SB surgery [3]. For this reason, SB is not always performed as a first line treatment option in cases with altitude-related problems.

Another alternative is the use of a silicone oil (SO) endotamponade. This option should be considered if SB is not feasible, such as in cases with concurrent vitreous haemorrhage or severe PVR. The volume of SO is unaffected by atmospheric pressure, nevertheless we need to verify that there is no remaining bubble of air in the vitreous cavity or in the SO before authorising the patient to fly. In addition, SO use requires extensive discussion and counselling about the possible risk of toxicity and unexplained visual loss after removal of the oil, especially in macula-on RRD [4, 5].

The third scenario is patients living in high-altitude areas. This is a common scenario for the authors, considering that the catchment area of the University Hospital Bern includes cities over 1000 metres above sea-level. For this reason, decisions on the surgical management take into account the patient´s general history including current residency and mode of transport to return home. Second, our gas of choice is sulphur hexafluoride (SF₆) 20%, because the half-life in phakic human eyes is comparatively short with 2.8 days [6]. Third, patients living more than 1000 metres above sea level are instructed to take 500 mg PO acetazolamide before leaving the hospital. They are advised to go home by car and make a stop every 500 metres of altitude increase, take again 500 mg PO acetazolamide and wait for 2 h. They are advised to return to lower levels if there are signs of IOP increase such as pain or even loss of vision. Following this strategy, we have minimised the gas-expansion related problem in our patients.

Finally, it has been largely reported that the reabsorption of intraocular gases (SF₆ and C₃F₈) is subjected to a first-order kinetics, leading to the possible persistence of small gas volumes and the risk of intraocular pressure (IOP) increase after several weeks from RRD surgery [6]. Some reports have stated that patients with a small residual gas bubble (around 0.6 ml, 10% of the whole eye volume) may compensate the decrease in cabin pressure and, in some cases, even larger volumes of gas may be tolerated when a decompression smaller than 8000 ft is present in the airplane;[7, 8] however, these are experimental and anecdotical cases and we recommend patients not to fly after RRD surgery with gas tamponade, because there are many variables which need to be taken into account including altitude, which can be modified in relation to the airplane route or in case of flight emergencies. Another factor is cabin pressure. Values cannot be predicted because different aircraft designs allow different degrees of pressurisation, which can markedly affect the cabin altitude to which passengers are exposed [8]. Another non-negligible variable is the presence of meteorological factors, which have been reported to be associated with changes in the barometric pressure and the subsequently variation of the gas bubble size, representing, therefore, another unpredictable factor to consider after gas tamponade vitreoretinal surgery [9].

For the above-mentioned reasons, we advise patients against flight if there is still gas within the eye. The risk and consequences of altitude-related IOP modifications in those patients should not be underestimated.

Author contributions

RA, LFD and MZ conceived and designed the article, analysed and interpreted the literature, drafted the manuscript and made critical revision of the manuscript.

Competing interests

The authors declare no competing interests.