Permissive hypercapnia
Permissive hypercapnia has been studied in 3 papers since 2023: 2 trials in people; 1 in the past year. The newest paper, Jul 21, 2026: “Effects of permissive hypercapnia on intraoperative cerebral oxygenation and early postoperative cognitive function in older patients with fragile brain function during the non-acute phase undergoing laparoscopic colorectal surgery: A randomized controlled trial”.
3 papers study it6 findingsUpdated
“PHC significantly increased rSO2 relative to conventional ventilation (left: adjusted mean difference [aMD] 10.64, 95% CI 8.96-12.33; right: aMD 10.16, 95% CI 8.22-12.11; both P < 0.001)”
1 of its findings points the other way.
- 2 independent labs in 1 country
- 1 finding against
- Funder: Department of Science & Technology of Liaoning Province
- Human trial2
Studies in people
2 studies gave permissive hypercapnia to people and measured what changed.
up: Increases regional cerebral oxygen saturationleft: aMD 10.64, 95% CI 8.96-12.33; right: aMD 10.16, 95% CI 8.22-12.11; both P < 0.001
no change: Has no effect on cognitive function
Randomized trial76 peopleolder
Older adults; non-acute fragile brain function undergoing elective laparoscopic colorectal surgery
Experimental gerontology, Jul 21, 2026
up: Improves regional cerebral oxygen saturation(64.04 ± 4.11)% vs. (56.43 ± 6.54)%
up: Improves cognitive functionadjusted mean difference at day 7 ++2.2 points, 95% CI +1.4 to +3.0
Treated cohort450 people55.24% vs. 53.33% maleaged 65 years or older30 days
Elderly patients who underwent laparoscopic surgery
Frontiers in medicine, Oct 9, 2025
What did studies of Permissive hypercapnia find?
2Studies of Permissive hypercapnia measured 2 outcomes; the most studied are cognitive function (2 studies) and regional cerebral oxygen saturation (2).
Cognitive function
no changein humans1upin humans1
2 studies
Cognitive function
no changein humans1upin humans1
Permissive hypercapnia has no effect on cognitive function in humans.
“However, early postoperative cognitive outcomes and serum biomarkers did not differ between groups.”
Human trialnon-acute fragile brain function undergoing elective laparoscopic colorectal surgeryn = 76
Experimental gerontology
Permissive hypercapnia improves cognitive function in humans (adjusted mean difference at day 7 ++2.2 points, 95% CI +1.4 to +3.0).
“Adjusted analyses yielded similar findings: PH was associated with smaller early declines in MMSE (adjusted mean difference at day 7 ++2.2 points, 95% CI +1.4 to +3.0; p < 0.001).”
Humans30 daysn = 450
Frontiers in medicine
Permissive hypercapnia improves cognitive function in humans (23.05 ± 0.23 vs. 20.67 ± 1.63; P < 0.001).
“MMSE scores demonstrated less pronounced decline at postoperative day 1 in the PH group (23.05 ± 0.23) versus controls (20.67 ± 1.63; P < 0.001)”
Humanslaparoscopic surgerypostoperative day 1n = 450
Frontiers in medicine
Regional cerebral oxygen saturation
upin humans2
2 studies
Regional cerebral oxygen saturation
upin humans2
Permissive hypercapnia increases regional cerebral oxygen saturation in humans (left: aMD 10.64, 95% CI 8.96-12.33; right: aMD 10.16, 95% CI 8.22-12.11; both P < 0.001).
“PHC significantly increased rSO2 relative to conventional ventilation (left: adjusted mean difference [aMD] 10.64, 95% CI 8.96-12.33; right: aMD 10.16, 95% CI 8.22-12.11; both P < 0.001)”
Human trialnon-acute fragile brain function undergoing elective laparoscopic colorectal surgeryn = 76
Experimental gerontology
Permissive hypercapnia improves regional cerebral oxygen saturation in humans ((64.04 ± 4.11)% vs. (56.43 ± 6.54)%).
“The intraoperative rSO2 of the PH group was considerably higher, especially 10 min after the establishment of pneumoperitoneum (t = 12.328, P < 0.05) and late during the operation [(64.04 ± 4.11)% vs. (56.43 ± 6.54)%, t = 14.778, P < 0.05].”
Humanscerebral tissue30 daysn = 450
Frontiers in medicine
Permissive hypercapnia improves regional cerebral oxygen saturation in humans (mean difference 4.62%, 95% CI 3.81-5.43; P < 0.001).
“Permissive hypercapnia was associated with significantly improved intraoperative cerebral oxygenation (rSO2) compared to conventional ventilation (mean difference 4.62%, 95% CI 3.81-5.43; P < 0.001)”
Humanslaparoscopic surgeryn = 450
Frontiers in medicine