Yugan Mudaliar

Cerebral vasomotor reactivity testing in head injury: the link between pressure and flow

Background: It has been suggested that a moving correlation index between mean arterial blood pressure and intracranial pressure, called PRx, can be used to monitor and quantify cerebral vasomotor reactivity in patients with head injury. Objectives: To validate this index and study its relation with cerebral blood flow velocity and cerebral autoregulation; and to identify variables associated with impairment or preservation of cerebral vasomotor reactivity. Methods: The PRx was validated in a prospective study of 40 head injured patients. A PRx value of less than 0.3 indicates intact cerebral vasomotor reactivity, and a value of more than 0.3, impaired reactivity. Arterial blood pressure, intracranial pressure, mean cerebral perfusion pressure, and cerebral blood flow velocity, measured bilaterally with transcranial Doppler ultrasound, were recorded. Dynamic cerebrovascular autoregulation was measured using a moving correlation coefficient between arterial blood pressure and cerebral blood flow velocity, the Mx, for each cerebral hemisphere. All variables were compared in patients with intact and impaired cerebral vasomotor reactivity. Results: No correlation between arterial blood pressure or cerebral perfusion pressure and cerebral blood flow velocity was seen in 19 patients with intact cerebral vasomotor reactivity. In contrast, the correlation between these variables was significant in 21 patients with impaired cerebral vasomotor reactivity, whose cerebral autoregulation was reduced. There was no correlation with intracranial pressure, arterial blood pressure, cerebral perfusion pressure, or interhemispheric cerebral autoregulation differences, but the values for these indices were largely within normal limits. Conclusions: The PRx is valid for monitoring and quantifying cerebral vasomotor reactivity in patients with head injury. This intracranial pressure based index reflects changes in cerebral blood flow and cerebral autoregulatory capacity, suggesting a close link between blood flow and intracranial pressure in head injured patients. This explains why increases in arterial blood pressure and cerebral perfusion pressure may be useful for reducing intracranial pressure in selected head injured patients (those with intact cerebral vasomotor reactivity).

The incidence of dysautonomia and its relationship with autonomic arousal following traumatic brain injury

Primary objective: To determine the incidence of autonomic arousal vs. Dysautonomia following traumatic brain injury (TBI) in an Intensive Care Unit (ICU) setting and to prospectively evaluate these groups against injury severity and outcome variables. Research design: Prospective observational group comparison (cohort) study of consecutive ICU admissions to a major trauma hospital over a 2-year period. Main outcomes and results: Eighty-nine of 113 subjects met inclusion and exclusion criteria, with consent gained for 79 subjects (61 male, 18 female: 89% of potential subjects). During the first 7 days post-injury, elevated autonomic parameters were almost universal in the sample (92%), predominantly hypertension and tachycardia. Nineteen of 79 subjects (24%) were autonomically aroused on day 7 (that is, had elevated heart rate, respiratory rate, blood pressure and temperature). Dysautonomia was diagnosed on day 14 post-injury in six of 79 subjects (8%) using previously published criteria. Autonomically aroused subjects had significantly more severe injuries, poorer outcomes and greater estimated costs than non-aroused subjects. Furthermore, Dysautonomic subjects within the autonomically aroused group had significantly worse outcome and, excluding early deaths, a greater period of hospitalization and higher estimated costs. Conclusions: The 8% incidence of Dysautonomia during ICU admission was in broad agreement with previous research. While day 7 autonomic arousal indicated a greater degree of injury, the diagnosis of Dysautonomia provided additional prognostic information. A coordinated multi-centre research effort into this condition appears appropriate.

Cerebral autoregulation and ageing.

Little is known about the effects of ageing on cerebral autoregulation (CA). To examine the relationship between age and CA in adults, we conducted a prospective study using a non-invasive protocol without external stimuli. We studied 32 subjects, aged 23-68 years. They were assigned to a young group (28+/-5 years) and an old group (54+/-8 years). The groups were sex-matched. Transcranial Doppler ultrasonography (TCD) was used to record bilateral middle cerebral artery flow velocities (CBFV, cm/sec). Noninvasive beat-to-beat tonometric arterial blood pressure (ABP) measurement of the radial artery was used to record spontaneous blood pressure fluctuations. The Mx, an index of dynamic cerebral autoregulation (dCA), was calculated from a moving correlation between ABP and CBFV. We did not find a correlation between age and Mx. No statistically significant difference in the Mx between the groups (0.27+/-0.23, young, vs. 0.37+/-0.24, old) was demonstrated. Age does not affect dynamic cerebral autoregulation assessed by the Mx index in healthy adult subjects. This study supports findings from previous papers wherein CA was measured with protocols which require external stimuli. Further studies are needed to determine CA in subjects above 70 years of age.

Do men and women differ in their course following traumatic brain injury? A preliminary prospective investigation of early outcome

Primary objective: To examine the effect of a patients sex on measures of outcome in a matched sample of patients admitted for acute traumatic brain injury (TBI). Research design: A prospective multi-centred group comparison study based in metropolitan Sydney, Australia. Methods and procedures: Data was collected on 25 women admitted for treatment following non-penetrating TBI. Forty-five men were then matched with regards to age and injury severity. All subjects met the study criteria of having a moderate-to-severe TBI and aged 50 years old or younger. Exclusion criteria included history of previous head injury, psychiatric disturbance and significant alcohol and/or substance abuse. Data included injury details and physiological and psychometric measures of outcome. Main outcomes and results: Women demonstrated better outcomes as indicated by their Glasgow Outcome Scale scores (adjusted for initial injury severity and age at injury odds ratio [OR] 4.2, 95% CI 1.4–12.7) and having shorter Length of Stay (adjusted OR 9.03, 95% CI 3.13–26.08). Conclusions: Understanding the presence of sex differences in outcome following TBI is an emerging area of research. This study indicated that, after matching for initial injury severity and age at injury, women with severe TBI demonstrate a better early outcome than men.

Cardiorespiratory effects of manually compressing the rib cage during tidal expiration in mechanically ventilated patients recovering from acute severe asthma

OBJECTIVES To determine the cardiorespiratory effects of manual expiratory rib cage compression in mechanically ventilated patients recovering from acute severe asthma; and to extrapolate these findings to emergency asthma management where ventilation cannot be achieved by positive-pressure ventilation. DESIGN A prospective, clinical study. SETTING Intensive care unit. PATIENTS Four intubated, mechanically ventilated (volume-controlled), adult patients recovering from acute severe asthma. INTERVENTIONS Patients were studied before, during, and after a 2- to 3-min period of manual compressions applied bilaterally over the lower rib cage (ribs 8 to 10) during consecutive tidal expirations. MEASUREMENTS AND MAIN RESULTS Air flow (pneumotachograph), airway pressure, radial or brachial arterial pressure, and the hand pressure applied to the patients rib cage were monitored and recorded on magnetic tape. Playback of the recorded data enabled measurement of changes in lung volume (air flow integration). Changes during rib cage compression consisted chiefly of small decreases in lung volume and peak inspiratory airway pressure that were only observed in the least obstructed patient and were fully reversed after the cessation of compressions. Air flow-time and air flow-volume plots demonstrated expiratory air flow limitation during essentially the entire tidal expiration in each patient, except the least obstructed patient. CONCLUSION The results suggest that manual compression of the rib cage during consecutive tidal expirations would be ineffective in reducing pulmonary hyperinflation during the emergency management of asthma when air flow obstruction is so severe that ventilation cannot be achieved by positive-pressure ventilation.

Rapid response systems: A prospective study of response times

PURPOSE The purpose of the study was to evaluate the time taken for delivery of each component of care following patient deterioration and to assess the effect on response times of strategies implemented to improve the system. METHODS A model identifying the sequence of organizational responses following a patients unexpected clinical deterioration was developed. The time to key events and interventions from initial deterioration was measured for 3 months in 2005 and again in 2006 at a tertiary care hospital with a rapid response team (RRT) in place. Strategies to improve compliance with the RRT system were introduced between the 2 periods. RESULTS The number of acute deterioration episodes identified increased (61 episodes in 2005; 154 episodes in 2006), but there was no improvement in response times. The 2 components contributing most frequently to delays were the time for nursing staff to call for assistance and, where needed, for physicians to call for higher-level care. Overall, 26% of episodes in 2006 and 30% in 2005 did not receive medical attention within 30 minutes of acute deterioration. CONCLUSIONS Significant delays in responding to acute deterioration persist despite strategies to facilitate the functioning of the RRT system. Simple strategies such as policy directives are not sufficient to effect change in complex health care systems.

Improving the quality of information on pathology request forms

Background: We have investigated the causes of incomplete pathology request forms received at our clinical chemistry laboratory. Based on a request form audit we found that the data most frequently missing from a pathology request form was the doctors name, unique identification provider number, or signature. Methods: We examined the effect of issuing the requesting doctors with self-inking stamps personalized with their name and a unique provider number. Results: The intervention led to an immediate and sustained improvement in compliance, with the proportion of incomplete forms falling from 43% to 2%. In contrast, distribution of a memorandum alone made no significant change to the number of pathology request forms with incomplete data arriving at the laboratory. Conclusion: This study describes a simple and low-cost solution to one of the causes of incomplete pathology request forms. It also demonstrates the effectiveness of systems improvement in health care.

Cerebrovascular autoregulation as a neuroimaging tool

Functional transcranial Doppler (fTCD) sonography provides a high temporal resolution measure of blood flow and has over the years proved to be a valuable tool in the clinical evaluation of patients with cerebrovascular disorders. More recently, due to advances in physics and computing, it has become possible to derive indices of cerebrovascular autoregulation (CA) as well as cerebrovascular pressure reactivity (CR), using non-invasive techniques. These indices provide a dynamic representation of the brains regulatory blood flow mechanisms not only in pathological states but also in health. However, whilst the temporal resolution of these regulatory indices is very good, spatially, the localization of brain regions remains very poor, thus limiting its brain mapping capacity. Functional MRI, on the contrary, is a brain-imaging technique that operates on similar blood flow principles; however, unlike fTCD, it provides high spatial resolution. Because both fTCD and fMRI determine blood flow-dependant imaging parameters, the coupling of fTCD with fMRI may provide greater insight into brain function by virtue of the combined enhanced temporal and spatial resolution that each technique affords. This review summarizes the fTCD technique with particular emphasis on the CA and CR indices and their relationship in traumatic brain injury as well as in health.

Establishment and First Audit of a New Perioperative Echocardiography Service

Intraoperative echocardiography has become an integral service for cardiothoracic surgery. Establishing a service requires new ultrasound technologies and a dedicated team prepared to be trained in this new discipline. The establishment of a new perioperative service at Westmead Hospital, Australia is outlined. Early experience, current practice, teaching and research programs are presented and the first audit is reported.