The causes of systemic secondary insult to injured brain include all of the following except -
Patients with primary brain injury whether due to any trauma or stroke are at significant risk for some secondary ischemic brain injury?

Causes of secondary brain injury are - Hypotension

Hypotension should be strictly avoided as significant hypotensive events as short as 10 minutes in duration have been shown to adversely influence the outcome after traumatic brain injury.
Even in patients with stroke or head trauma, who do not require I.C.P. monitoring, close attention to adequate cerebral perfusion is required.

Hypoxia

Hypoxia (percutaneous oxygen saturation < 90%) alone, or in combination with hypotension, also leads to secondary brain injury.

Fever

Fever can adversely affect the outcome of the patient.
So aggressive control of fever with a goal of normothermia is warranted and can usually be achieved with antipyretic medication and cooling blankets.

Hyperglycemia

This is also associated with worsened clinical outcome after stroke and trauma.
Intravenous insulin is encouraged for control of hyperglycemia as this allows better regulation of serum glucose level than subcutaneous insulin.
A reasonable goal is to maintain serum glucose level at < 160 mg/dl.

Also know,

Effect of hypothermia on secondary brain injury.

The drop in temperature inhibits the release of the excitatory neurotransmitter glutamate and attenuates the release of dopamine, in brain ischemia animal models, suggesting a protective effect of hypothermia in brain injury.

Secondary brain injury can be a major determinant in the outcome of the patient so strategies for minimizing secondary brain insults are an integral part of critical care of all patients.
Episodes of secondary brain insults are usually not associated with apparent neurological worsening, rather they lead to cumulative injury, which manifest as higher mortality or worsened long term functional outcome.
Thus clinical strategies to prevent secondary brain insults involve close monitoring of vital signs and risk factors to prevent secondary ischemia.
Hypercapnia
Hypoxemia
Hypotension
Hypothermia