{"id":28404,"date":"2025-09-10T04:50:00","date_gmt":"2025-09-09T20:50:00","guid":{"rendered":"https:\/\/csccm.org.cn\/?p=28404"},"modified":"2025-09-10T06:00:22","modified_gmt":"2025-09-09T22:00:22","slug":"icu-management-practice-%e6%80%a5%e6%80%a7%e9%a2%85%e8%84%91%e6%8d%9f%e4%bc%a4%e6%82%a3%e8%80%85co2%e7%9a%84%e7%97%85%e7%90%86%e7%94%9f%e7%90%86%e4%bd%9c%e7%94%a8%e5%8f%8a%e7%ae%a1%e7%90%86","status":"publish","type":"post","link":"https:\/\/csccm.org.cn\/?p=28404","title":{"rendered":"[ICU Management &#038; Practice]: \u6025\u6027\u9885\u8111\u635f\u4f24\u60a3\u8005CO2\u7684\u75c5\u7406\u751f\u7406\u4f5c\u7528\u53ca\u7ba1\u7406"},"content":{"rendered":"\n<h1 class=\"wp-block-heading\">Pathophysiological Role and Management of Carbon Dioxide in Acute Brain Injury<\/h1>\n\n\n\n<ul>\n<li>In&nbsp;<a href=\"https:\/\/healthmanagement.org\/c\/icu\">ICU<\/a><\/li>\n\n\n\n<li>Mon, 12 May 2025<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/res.cloudinary.com\/healthmanagement-org\/image\/upload\/c_thumb,f_auto,fl_lossy,q_90\/v1747058697\/cw\/00130043_cw_image_wi_c04142533e5b21feca653570a15dea2f.webp\" alt=\"\"\/><\/figure>\n\n\n\n<p>Maintaining proper cerebral oxygen delivery is crucial for preventing secondary ischaemic injury in patients with acute brain injuries (ABI). Arterial carbon dioxide tension (PaCO\u2082) significantly influences cerebral blood flow (CBF). When intracranial pressure (ICP) is not elevated, adjusting PaCO\u2082 to an optimal level can support sufficient cerebral oxygenation and reduce ischaemic damage.&nbsp;<\/p>\n\n\n\n<p><br \/>A recent article discusses the relationship between PaCO\u2082 and CBF and highlights evidence-based strategies for managing PaCO\u2082 in common&nbsp;<a href=\"https:\/\/healthmanagement.org\/c\/icu\/News\/withdraw-or-withhold-life-sustaining-therapies-in-patients-with-and-without-acute-brain-injury\" target=\"_blank\" rel=\"noreferrer noopener\">ABI<\/a>&nbsp;conditions.<\/p>\n\n\n\n<p>The relationship between PaCO\u2082 and CBF is nearly linear within the range of 20\u201380 mmHg, with each 1 mmHg increase in PaCO\u2082 causing a 3\u20136% rise in CBF, and each 1 mmHg decrease leading to a 1\u20133% reduction in CBF. CO\u2082 reactivity, or the degree to which PaCO\u2082 influences CBF, can be reduced in older individuals or in severe ABI. The effects of PaCO\u2082 on CBF are regionally varied, with grey matter showing two- to three-fold greater CO\u2082 reactivity than white matter.<\/p>\n\n\n\n<p>The CBF response to CO\u2082 is driven by changes in cerebrospinal fluid (CSF) pH. CO\u2082 has a stronger and faster effect on CBF than systemic arterial pH because it easily crosses the blood-brain barrier and directly impacts perivascular pH. Hypercapnia causes CSF acidification, leading to vasodilation of pial resistance arterioles, increased CBF, and blood volume, which can raise intracranial pressure (ICP) in patients with limited compensatory reserve. In contrast, hypocapnia causes CSF alkalosis, vasoconstriction of pial arterioles, and reduced CBF, lowering blood volume and ICP, which is why hyperventilation is used clinically to control elevated ICP.<\/p>\n\n\n\n<p>Sustained, profound hyperventilation can lead to cerebral ischaemia by reducing CBF. PaCO\u2082 levels of 25 mmHg within the first 24\u201336 hours after ABI significantly increase metabolic stress markers in the cerebrospinal fluid. Imaging studies show a substantial reduction in CBF when PaCO\u2082 is lowered from 36 to 29 mmHg. Profound hyperventilation is only recommended briefly for refractory intracranial hypertension or imminent herniation. While robust data is lacking, mild hypocapnia (PaCO\u2082 32\u201335 mmHg) appears to pose less risk, supporting cautious, short-term hyperventilation when elevated ICP is a concern.<\/p>\n\n\n\n<p>Clinical guidelines recommend maintaining PaCO\u2082 between 35\u201345 mmHg in patients with ABI who do not have elevated ICP, with allowable reductions in cases of elevated ICP. A sub-analysis of the ENIO observational study (1476 patients) found a U-shaped relationship between PaCO\u2082 and outcomes, with significantly higher in-hospital mortality at PaCO\u2082 levels below 32 mmHg and above 45 mmHg compared to normal levels (35\u201345 mmHg). The highest mortality was observed with PaCO\u2082 levels below 26 mmHg.<\/p>\n\n\n\n<p>The Seattle International Brain Injury Consensus Consortium recommends a tiered approach to targeting PaCO\u2082 in patients with severe traumatic brain injury (TBI) to manage ICP: tier 1 (low-normal PaCO\u2082: 35\u201338 mmHg) and tier 2 (mild hypocapnia: 32\u201335 mmHg). The Brain Trauma Foundation advises against routinely lowering PaCO\u2082 below 30 mmHg, based on a 30-year-old randomised trial showing worse long-term outcomes with prolonged prophylactic hyperventilation compared to normocapnia. However, mean PaCO\u2082 levels vary across hospitals. Brain oxygen monitoring, such as jugular venous oximetry or brain tissue probes, is recommended to guide therapeutic hyperventilation and prevent CBF attenuation and hypoxia. In the ongoing BONANZA and BOOST-III trials, mild hypercapnia (45\u201350 mmHg) is being tested to improve brain tissue oxygen by increasing CBF when ICP is normal, though this strategy remains investigational and cannot be recommended without invasive intracranial monitoring.<\/p>\n\n\n\n<p>Contemporary guidelines do not specifically address PaCO\u2082 targets for patients with ischaemic or haemorrhagic stroke, and recommendations are often drawn from TBI literature. Mechanical ventilation guidelines for ABI suggest PaCO\u2082 targets of 35\u201345 mmHg, including for stroke patients. However, several disease-specific factors should be considered when managing PaCO\u2082 in these cases.<\/p>\n\n\n\n<p>In patients with subarachnoid haemorrhage, spontaneous hyperventilation and hypocapnia are common. While hypocapnia can reduce CBF, especially in those with vasospasm or delayed cerebral ischaemia, normalising PaCO\u2082 may not always be advisable due to risks like sedation, paralysis, and loss of neurological assessment. An individualised approach is often needed. Conversely, controlled hypercapnia (up to 60 mmHg) has been shown to improve CBF and brain oxygenation without raising ICP in a study of six patients with high-grade subarachnoid haemorrhage. A subgroup analysis of the ENIO sub-study found mild hypocapnia was linked to higher in-hospital mortality following subarachnoid haemorrhage, while hypercapnia was not. Controlled hypercapnia may offer a therapeutic option for managing delayed cerebral ischaemia in certain patients, though further research is needed.<\/p>\n\n\n\n<p><br \/>In patients with intracranial haemorrhage, PaCO\u2082 management follows general guidelines. Avoiding hypercapnia is especially important for those with large hematomas causing mass effect, as even small increases in CBF and blood volume can raise ICP in cases of reduced intracranial compliance.<\/p>\n\n\n\n<p>Current guidelines for patients with post-cardiac arrest brain injury recommend adjusting ventilation targets to maintain PaCO\u2082 between 35\u201345 mmHg. The TAME trial, which included 1700 patients with out-of-hospital cardiac arrest, found that targeting a PaCO\u2082 of 50\u201355 mmHg did not improve neurological function or reduce mortality at 6 months compared to normocapnia (35\u201345 mmHg). This neutral outcome may be due to impaired CO\u2082 reactivity in many patients following cardiac arrest.<\/p>\n\n\n\n<p>After the return of spontaneous circulation, CBF typically experiences a brief hyperemic phase (10\u201330 minutes), followed by a prolonged low-flow phase. The risk of hypocapnia-induced ischaemia is particularly high during the low-flow phase, emphasising the importance of avoiding PaCO\u2082 levels below 35 mmHg once circulation is restored.<\/p>\n\n\n\n<p><br \/>Normocapnia is recommended for most patients with ABI, especially in the early phase, as PaCO\u2082-induced changes in CBF can significantly affect ICP and the risk of secondary brain injury. Mild hypocapnia achieved through hyperventilation can be useful for managing elevated ICP and acute ICP crises but should be used cautiously to avoid ischaemic complications. Controlled hypercapnia is still under research, and future studies should focus on personalised PaCO\u2082 management strategies.<\/p>\n\n\n\n<p>Source:&nbsp;<a href=\"https:\/\/link.springer.com\/article\/10.1007\/s00134-025-07913-1\" target=\"_blank\" rel=\"noreferrer noopener\">Intensive Care Medicine<\/a><\/p>\n\n\n\n<p>Image Credit: iStock<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">References:<\/h4>\n\n\n\n<p>Taran S, Sekhon M, Robba C (2025)&nbsp;<a href=\"https:\/\/link.springer.com\/article\/10.1007\/s00134-025-07913-1\" target=\"_blank\" rel=\"noreferrer noopener\">Carbon dioxide pathophysiology and targets following acute brain injury.<\/a>&nbsp;Intensive Care Med.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Pathophysiological Role and Management of Carbon Dioxid [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[24,23],"tags":[],"_links":{"self":[{"href":"https:\/\/csccm.org.cn\/index.php?rest_route=\/wp\/v2\/posts\/28404"}],"collection":[{"href":"https:\/\/csccm.org.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/csccm.org.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/csccm.org.cn\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/csccm.org.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=28404"}],"version-history":[{"count":1,"href":"https:\/\/csccm.org.cn\/index.php?rest_route=\/wp\/v2\/posts\/28404\/revisions"}],"predecessor-version":[{"id":28405,"href":"https:\/\/csccm.org.cn\/index.php?rest_route=\/wp\/v2\/posts\/28404\/revisions\/28405"}],"wp:attachment":[{"href":"https:\/\/csccm.org.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=28404"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/csccm.org.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=28404"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/csccm.org.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=28404"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}