Intracranial pressure responses to alterations in arterial carbon dioxide pressure in patients with head injuries

Risk Factors for Intravenous Propacetamol-Induced Blood Pressure Drop in the Neurointensive Care Unit: A Retrospective Observational Study

BACKGROUND

Intravenous propacetamol is commonly used to control fever and pain in neurocritically ill patients in whom oral administration is often difficult. However, several studies reported that intravenous propacetamol may cause blood pressure drop. Thus, we aimed to investigate the occurrence and risk factors for intravenous propacetamol-induced blood pressure drop in neurocritically ill patients.

METHODS

This retrospective study included consecutive patients who were administered intravenous propacetamol in a neurointensive care unit at a single tertiary academic hospital between April 2013 and June 2020. The exact timing of intravenous propacetamol administration was collected from a database of the electronic barcode medication administration system. Blood pressure drop was defined as a systolic blood pressure below 90 mm Hg or a decrease by 30 mm Hg or more. Blood pressure, pulse rate, and body temperature were collected at baseline and within 2 h after intravenous propacetamol administration. The incidence of blood pressure drop was evaluated, and multivariable logistic regression analysis was performed to identify risk factors for blood pressure drop events.

RESULTS

A total of 16,586 instances of intravenous propacetamol administration in 4916 patients were eligible for this study. Intravenous propacetamol resulted in a significant decrease in systolic blood pressure (baseline 131.1 ± 17.8 mm Hg; within 1 h 124.6 ± 17.3 mm Hg; between 1 and 2 h 123.4 ± 17.4 mm Hg; P < 0.01). The incidence of blood pressure drop events was 13.5% within 2 h after intravenous propacetamol. Older age, lower or higher baseline systolic blood pressure, fever, higher Acute Physiology and Chronic Health Evaluation II score, and concomitant administration of vasopressors/inotropes or analgesics/sedatives were significant factors associated with the occurrence of blood pressure drop events after intravenous propacetamol administration.

CONCLUSIONS

Intravenous propacetamol can induce hemodynamic changes and blood pressure drop events in neurocritically ill patients. This study identified the risk factors for blood pressure drop events. On the basis of our results, judicious use of intravenous propacetamol is warranted for neurocritically ill patients with risk factors that make them more susceptible to hemodynamic changes.

Hyperventilation in Adult TBI Patients: How to Approach It?

Hyperventilation is a commonly used therapy to treat intracranial hypertension (ICTH) in traumatic brain injury patients (TBI). Hyperventilation promotes hypocapnia, which causes vasoconstriction in the cerebral arterioles and thus reduces cerebral blood flow and, to a lesser extent, cerebral blood volume effectively, decreasing temporarily intracranial pressure. However, hyperventilation can have serious systemic and cerebral deleterious effects, such as ventilator-induced lung injury or cerebral ischemia. The routine use of this therapy is therefore not recommended. Conversely, in specific conditions, such as refractory ICHT and imminent brain herniation, it can be an effective life-saving rescue therapy. The aim of this review is to describe the impact of hyperventilation on extra-cerebral organs and cerebral hemodynamics or metabolism, as well as to discuss the side effects and how to implement it to manage TBI patients.

Quantitative MRI volumetry, diffusivity, cerebrovascular flow, and cranial hydrodynamics during head-down tilt and hypercapnia: the SPACECOT study

To improve the pathophysiological understanding of visual changes observed in astronauts, we aimed to use quantitative MRI to measure anatomic and physiological responses during a ground-based spaceflight analog (head-down tilt, HDT) combined with increased ambient carbon dioxide (CO2). Six healthy, male subjects participated in the double-blinded, randomized crossover design study with two conditions: 26.5 h of −12° HDT with ambient air and with 0.5% CO2, both followed by 2.5-h exposure to 3% CO2. Volume and mean diffusivity quantification of the lateral ventricle and phase-contrast flow sequences of the internal carotid arteries and cerebral aqueduct were acquired at 3 T. Compared with supine baseline, HDT (ambient air) resulted in an increase in lateral ventricular volume ( P = 0.03). Cerebral blood flow, however, decreased with HDT in the presence of either ambient air or 0.5% CO2( P = 0.002 and P = 0.01, respectively); this was partially reversed by acute 3% CO2exposure. Following HDT (ambient air), exposure to 3% CO2increased aqueductal cerebral spinal fluid velocity amplitude ( P = 0.01) and lateral ventricle cerebrospinal fluid (CSF) mean diffusivity ( P = 0.001). We concluded that HDT causes alterations in cranial anatomy and physiology that are associated with decreased craniospinal compliance. Brief exposure to 3% CO2augments CSF pulsatility within the cerebral aqueduct and lateral ventricles.

NEW & NOTEWORTHY Head-down tilt causes increased lateral ventricular volume and decreased cerebrovascular flow after 26.5 h. Additional short exposure to 3% ambient carbon dioxide levels causes increased cerebrovascular flow associated with increased cerebrospinal fluid pulsatility at the cerebral aqueduct. Head-down tilt with chronically elevated 0.5% ambient carbon dioxide and acutely elevated 3% ambient carbon dioxide causes increased mean diffusivity of cerebral spinal fluid within the lateral ventricles.

Prehospital Hyperventilation After Brain Injury: A Prospective Analysis of Prehospital and Early Hospital Hyperventilation of the Brain-Injured Patient

Background:

The Brain Trauma Foundation's Guidelines for the Management of Severe Head Injury state that the use of prophylactic hyperventilation after traumatic brain injury (TBI) should be avoided because it can compromise cerebral perfusion. The objective of this study was to assess the prevalence of unintentional hyperventilation.

Methods:

A prospective evaluation of all intubated trauma patients with a diagnosis of TBI was performed. Patients with signs of impending hernia-tion were excluded.

Results:

Forty patients were included in the study. The average Glasgow Coma Scale (GCS) was 6.3. Of these, 28 patients (70%) were unintentionally hyperventilated. Eleven (39%) of the hyperventilated patients died or were discharged in a persistent vegetative state. Of the remaining 12 patients who experienced normal ventilation, three patients (25%) died or were discharged in a vegetative state (p = ns) (Table 1).

Conclusion:

Hyperventilation was common after TBI. However, patients ventilated to a normal PaCO2 were significantly more acidotic. Prehospital personnel should undergo educational training after development of strict ventilation protocols for patients suffering TBI.

Hyperventilation in head injury: a review

The aim of this review was to consider the effects of induced hypocapnia both on systemic physiology and on the physiology of the intracranial system. Hyperventilation lowers intracranial pressure (ICP) by the induction of cerebral vasoconstriction with a subsequent decrease in cerebral blood volume. The downside of hyperventilation, however, is that cerebral vasoconstriction may decrease cerebral blood flow to ischemic levels. Considering the risk-benefit relation, it would appear to be clear that hyperventilation should only be considered in patients with raised ICP, in a tailored way and under specific monitoring. Controversy exists, for instance, on specific indications, timing, depth of hypocapnia, and duration. This review has specific reference to traumatic brain injury, and is based on an extensive evaluation of the literature and on expert opinion.

Cerebral blood flow and vasoresponsivity within and around cerebral contusions

There is increasing evidence that regional ischemia plays a major role in secondary brain injury. Although the cortex underlying subdural hematomas seems particularly vulnerable to ischemia, little is known about the adequacy of cerebral blood flow (CBF) or the vasoresponsivity within the vascular bed of contusions. The authors used the xenon-enhanced computerized tomography (CT) CBF technique to define the CBF and vasoresponsivity of contusions, pericontusional parenchyma, and the remainder of the brain 24 to 48 hours after severe closed head injury in 10 patients: six patients with one contusion and four with two contusions, defined as mixed or high-density lesions on CT scanning. The CBF within the contusions (29.3 +/- 16.4 ml/100 g/minute, mean +/- standard deviation) was significantly lower than both that found in the adjacent 1-cm perimeter of normal-appearing tissue (42.5 +/- 15.8 ml/100 g/minute) and the mean global CBF (52.5 +/- 17.5 ml/100 g/minute) (p < 0.004, repeated-measures analysis of variance). A subset of seven patients (10 contusions) also underwent a second Xe-CT CBF study during mild hyperventilation (a PaCO2 of 24-32 mm Hg). In only two of these 10 contusions was vasoresponsivity less than 1% (range 0%-7.6%); in the rim of normal-appearing pericontusional tissue, it was 0.4% to 9.1%. The authors conclude that CBF within intracerebral contusions is highly variable and is often above 18 ml/100 g/minute, the reported threshold for irreversible ischemia. Intracontusional CBF is significantly reduced relative to surrounding brain parenchyma, and CO2 vasoresponsivity is usually present. In the contusion and the surrounding parenchyma, vasoresponsivity may be nearly three times normal, suggesting hypersensitivity to hyperventilation therapy. Given this possible hypersensitivity and relative hypoperfusion within and around cerebral contusions, these lesions are particularly vulnerable to secondary injury such as that which may be caused by hypotension or aggressive hyperventilation.

Cerebrovascular carbon dioxide reactivity assessed by intracranial pressure dynamics in severely head injured patients

Appropriate management of intracranial pressure (ICP) in severely head injured patients depends in part on the cerebral vessel reactivity to PCO2; loss of CO2 reactivity has been associated with poor outcome. This study describes a new method for evaluating vascular reactivity in head-injured patients by determining the sensitivity of ICP change to alterations in PCO2. This method was combined with measurements of the pressure volume index (PVI), which allowed calculation of blood volume change necessary to alter ICP. The objective of this study was to investigate the ICP response and the blood volume change corresponding to alterations in PCO2 and to examine the correlation of responsivity and outcome as measured on the Glasgow Outcome Scale. The PVI and ICP at different end-tidal PCO2 levels produced by mild hypo- and hyperventilation were obtained in 49 patients with Glasgow Coma Scale scores of less than 8 and over a wide range of PCO2 (25 to 40 mm Hg) in eight patients. Given the assumption that the PVI remained constant during alteration of PaCO2, the estimated blood volume change per torr change of PCO2 was calculated by the following equation: BVR = PVI x delta log(ICP)/delta PCO2, where BVR = blood volume reactivity. The data in this study showed that PVI remained stable with changes in PCO2, thus validating the assumption used in the blood volume estimates. Moreover, the response of ICP to PCO2 alterations followed an exponential curve that could be described in terms of the responsivity indices to capnic stimuli. It was found that responsivity to hypocapnia was reduced by 50% compared to responsivity to hypercapnia measured within 24 hours of injury (p < 0.01). The sensitivity of ICP to estimated blood volume changes in patients with a PVI of less than 15 ml was extremely high with only 4 ml of blood required to raise ICP by 10 mm Hg. The authors conclude from these data that, following traumatic injury, the resistance vessels are in a state of persistent vasoconstriction, possibly due to vasospasm or compression. Furthermore, BVR correlates with outcome on the Glasgow Coma Scale, indicating that assessment of cerebrovascular response within the first 24 hours of injury may be of prognostic value.

Safe use of PEEP in patients with severe head injury

Thirty-three patients with severe head trauma were studied to determine whether the use of positive end-expiratory pressure (PEEP) would cause an increase in intracranial pressure (ICP). Changes in ICP induced by PEEP were then correlated with a panel of physiological variables to try to explain these changes. Mean ICP increased from 13.2 +/- 7.7 mm Hg (+/- standard deviation) to 14.5 +/- 7.5 mm Hg (p less than 0.005) due to 10 cm H2O PEEP, but the eight patients with elevated baseline ICP experienced no significant increase. Cardiac output and venous admixture (Qs/Qt) declined significantly, while central venous pressure, peak inspiratory pressure, functional residual capacity, and arterial pCO2 increased significantly due to PEEP. Blood pressure and cerebral perfusion pressure were unchanged. The change in ICP due to PEEP correlated significantly with a combination of cardiac output, peak inspiratory pressure, Qs/Qt, and changes in blood pressure and arterial pCO2 due to PEEP, indicating that the effect of PEEP on ICP could be largely explained by its effect on hemodynamic and respiratory variables. No patient deteriorated clinically due to PEEP. It is concluded that 10 cm H2O PEEP increases ICP slightly via its effect on other physiological variables, but that this small increase in ICP is clinically inconsequential.

Ventilatory status early after head injury

The ventilatory status of patients within the first few hours following head injury has not been well established. We prospectively studied 63 patients who presented to an urban trauma center with varying severity of head injury to determine whether any trend toward hypo- or hyperventilation existed within the first two hours following injury. Arterial blood gas analysis done on emergency presentation showed that 14 patients with severe head injury (Glasgow coma scale less than or equal to 4) had mean pH values of 7.29 and mean PaCO2 of 41.86 torr. Twenty patients categorized as moderate head injury (GCS = 5-11) had mean pH values of 7.38 with a mean PaCO2 of 34.1 torr. Twenty-nine patients with GCS greater than or equal to 12 had mean pH and PaCO2 values of 7.4 and 31.8 torr, respectively. These differences in pH and PaCO2 were statistically significant between the GCS groups with mild and severe head injury (P less than or equal to .01 pH), (P = .05 PCO2), and could not be explained on the basis of hypoxemia, blood alcohol level, hypotension, or associated chest injury. It is concluded that patients with severe craniocerebral trauma show an early trend toward hypercapnea and acidosis. Immediate control of airway and assisted ventilation is necessary in order to reduce PaCO2 to optimal levels in patients with severe head injury.

Nonvolumetric methods of detecting impaired intracranial compliance or reactivity: pulse width and wave form analysis

The authors have attempted to find a clinically reliable method of measuring intracranial pressure (ICP) compliance or reactivity that does not require volumetric manipulation. An analysis was undertaken of ICP, pulse widths and of the presence or absence of B waves, both experimentally in dogs and clinically in postoperative human patients. In both dogs and humans, ICP pulse width generally increased with increasing ICP and with increasing intracranial mass, and definitely increased with systolic arterial blood pressure. Nonetheless, ICP pulse width commonly failed to increase with increasing cerebral reactivity, and low ICP pulse width measurements were at times recorded in distinctly pathological situations. From the clinical study it was found that B waves were encountered more commonly in patients with increased ICP or increased ICP pulse width. However, the correlation between B waves alone or in combination with increased ICP or ICP pulse width and quantitative measurements of ICP reactivity was not significant. Mean reactivity and the range of reactivity measurements were almost identical in patient groups with and without B waves. For the time being the "ICP reserve test" remains the most accurate, the safest, and the most clinically useful method of quantitating ICP reserve.

Increase in cerebral perfusion pressure by arterial hypertension in brain swelling. A mathematical model of the volume-pressure relationship

Brain swelling was produced in monkeys and cats by the inflation af an epidural balloon against the parietal lobe. Resulting changes in intracranial pressure (ICP) were correlated to variation in systemic arterial pressure (SAP). Intracranial perfusion pressure (ICPP) defined as the difference between SAP and ICP, was found to vary with the degree of arterial hyper-and hypotension. The relationship between SAP and ICP can be explained by an existing equilibrium between extramural pressure and vessel wall circumferential tension. A positive perfusion pressure can exist in brain swelling as long as vessel wall tension is preserved and the degree of expanding brain tissue volume is held below certain limits.

Evaluation of hyperventilation in treatment of head injuries

Reduction of the partial pressure of carbon dioxide in the arterial blood by mechanical hyperventilation (Pco(2) 25-30 mm Hg; Po(2) 100-150 mm Hg) may be beneficial in cases of severe head injury. To evaluate its efficacy and establish prognostic guidelines intracranial pressure, radiocirculograms, and cerebrospinal fluid (C.S.F.) lactate levels were studied in 31 patients. In survivors intracranial pressure fell and cerebral blood flow improved with treatment. A C.S.F. lactate greater than 55 mg/100 ml was associated with a poor prognosis. Selection of patients was based on clinical judgement, and adults with signs of extensive brain damage were excluded. The importance of an adequate airway and resuscitation is stressed before a final decision is made. The object of treatment is to improve the quality of survival and the criteria measured may aid in the distinction between patients with a potential for good recovery and those capable only of a vegetative existence. Many associated factors as well as hypocapnia reduce intracranial pressure, and these are discussed. We believe that hyperventilation may improve some head injuries, and further study is indicated.