From the Guidelines

Permissive hypertension can be an effective approach in certain clinical scenarios, particularly in the context of acute ischemic stroke.

The concept of permissive hypertension is based on the idea of maintaining or slightly increasing blood pressure to improve cerebral blood flow to the ischemic penumbra, an area of brain tissue that is at risk of infarction but may still be salvageable 1.
Studies have shown that induced hypertension, using agents such as phenylephrine, can improve neurological outcomes in patients with acute ischemic stroke, particularly those who are not eligible for thrombolytic therapy 1.
The optimal management of blood pressure in patients with acute ischemic stroke remains controversial, but permissive hypertension is recommended as a potential strategy to improve outcomes 1.

Patients with acute ischemic stroke may benefit from permissive hypertension, but this approach should be individualized and carefully monitored to avoid potential complications, such as conversion to a hemorrhagic lesion 1.
The use of permissive hypertension should be guided by serial neurological examinations and imaging studies, such as diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI), to assess the response to therapy and adjust the treatment plan as needed 1.
The target blood pressure goals for permissive hypertension in acute ischemic stroke are not well-defined, but a common approach is to aim for a systolic blood pressure or mean arterial pressure that is 20% to 30% above baseline 1.

From the Research

Permissive hypertension is a approach used in the management of acute ischemic stroke, where antihypertensive treatment is withheld unless the systolic blood pressure is greater than 220 mm Hg or the diastolic blood pressure is greater than 120 mm Hg 2, 3.
This approach is based on the concern that decreasing blood pressure may reduce penumbral blood flow and exacerbate vasogenic edema, leading to worsened outcomes 2.
The use of predictable and titratable medications to judiciously reduce the initial presenting mean arterial pressure by approximately 10% to 15% is recommended in situations where antihypertensive treatment is warranted 2.

The optimal blood pressure target in patients undergoing mechanical thrombectomy is less clear, but guidelines recommend a blood pressure < 185/110 mmHg in patients treated with intravenous t-PA and "permissive hypertension" up to 220/120 mmHg in those not treated with intravenous t-PA 4.
During and after thrombectomy, the guidelines recommend a blood pressure < 180/105 mmHg, but several studies have suggested that the primary goal should be to prevent significant low blood pressure or high blood pressure 4.

The effectiveness of permissive hypertension in improving outcomes in acute ischemic stroke patients is not clearly established, and large, randomized-control studies are needed to define optimal blood pressure goals and to address factors such as baseline blood pressure, timing and degree of revascularization, and estimated risk of reperfusion injury 2, 4, 3.
Current research focuses on both hemodynamic augmentation of low blood pressures and the effects of further lowering the blood pressure after acute ischemic stroke, and a cautious approach to the treatment of arterial hypertension is generally recommended until more definitive data are available 3.