Table 3. Effect of HBOT on COVID-19 patient outcomes; *results that were reported as significant at P < 0.05; #60 controls and 20 patients treated with HBOT; bpm – breaths per minute; HCO3- − bicarbonate; HBOT – hyperbaric oxygen treatment; NR − not reported; P/F ratio − PaO₂/FiO₂, where PaO₂ is the arterial oxygen partial pressure and FiO₂ is the fraction of inhaled oxygen); SaO₂ – arterial oxygen saturation; SpO₂ – peripheral oxygen saturation .

Study	n	Timing of outcome measurement	Clinical outcomes Data are mean (SD)	Biological outcomes Data are mean (SD)	Imaging outcomes	Safety outcomes
Chen[25]	5	Assessed before and after course of HBOT (average of five sessions per patient)	SpO2 improved: 73 (6) to 94 (2)%*	PaO2 and SaO2 increased* Lymphocyte count increased: 0.61(0.35) to 1.09 (0.24) x109·L-1* C-reactive protein levels decreased: data NR D-dimer decreased: data NR* Fibrinogen decreased: data NR*	CT improved (qualitatively)	NR
Gorenstein[30]	80#	Assessed at end of study (patients received up to five daily treatments as long as supplemental oxygen still required)	Inpatient mortality: HBOT: two (10%) died, none remained hospitalised at end study. Controls: 13 (22%) died, three (5%) remained hospitalised at end study. Mechanical ventilation: HBOT: 2 (10%) Controls: 18 (30%) Adjusted hazard ratios: Inpatient mortality = 0.37 (P = 0.14); Mechanical ventilation = 0.26*	N/A	N/A	Claustrophobia, ear pain (n = NR) Hypoxic arrest in unclear circumstances after transferring to the floor (n = 1)
Guo[29]	2	Assessed over 7-day course of HBOT	Dyspnoea eliminated immediately after the first HBOT session. Respiratory rate decreased daily; no need for mechanical ventilation SpO2 > 93% after the first session and continued to improve	D-dimers reduced. Lymphocyte counts improved. PaO2, P/F ratio, HCO3-, lactate improved Liver function (cholinesterase) improved. Data NR for any outcomes	CT pulmonary inflammation gradually improved	No adverse effects
Thibodeaux[27]	5	Assessed before and after course of HBOT (average of 5 treatments per patient [range: 1−6])	SpO2 improved: 96 (3) to 96 (1)%. All patients recovered without need for mechanical ventilation. Respiratory rate decreased: 35.4 (8.5) to 28 (7.6) bpm	Inflammatory markers decreased (reported for 1 patient, not reported for 4 patients)	N/A	No adverse effects
Qian[26]	4	Assessed before and one day after 7-day course of HBOT	SpO2 improved: 86 (5) to 92 (4)%*. Six-minute walk distance improved: 272 (62) to 346 (43) m*. Dyspnoea improved	Blood gas analysis indexes improved	CT resolution of inflammation to different degrees	NR
Zhong [28]	1	Assessed before and after course of HBOT (4 sessions)	Oxygenation improved. Patient was eventually extubated	CO2 reduced. Coagulation normalised. Kidney function improved	N/A	NR