Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: John D. Pickard x
  • Refine by Access: all x
  • By Author: Piechnik, Stefan x
Clear All Modify Search
Restricted access

Marek Czosnyka, Piotr Smielewski, Stefan Piechnik, Luzius A. Steiner, and John D. Pickard

Object. The goal of this study was to examine the relationship between cerebral autoregulation, intracranial pressure (ICP), arterial blood pressure (ABP), and cerebral perfusion pressure (CPP) after head injury by using transcranial Doppler (TCD) ultrasonography.

Methods. Using ICP monitoring and TCD ultrasonography, the authors previously investigated whether the response of flow velocity (FV) in the middle cerebral artery to spontaneous variations in ABP or CPP provides reliable information about cerebral autoregulatory reserve. In the present study, this method was validated in 187 head-injured patients who were sedated and receiving mechanical ventilation. Waveforms of ICP, ABP, and FV were recorded over intervals lasting 20 to 120 minutes. Time-averaged mean FV and CPP were determined. The correlation coefficient index between FV and CPP (the mean index of autoregulation [Mx]) was calculated over 4-minute epochs and averaged for each investigation.

The distribution of averaged mean FV values converged with the shape of the autoregulatory curve, indicating lower (CPP < 55 mm Hg) and upper (CPP > 105 mm Hg) thresholds of autoregulation. The relationship between the Mx and either the CPP or ABP was depicted as a U-shaped curve. Autoregulation was disturbed in the presence of intracranial hypertension (ICP ≥ 25 mm Hg) and when mean ABP was too low (ABP < 75 mm Hg) or too high (ABP > 125 mm Hg). Disturbed autoregulation (p < 0.005) and higher ICP (p < 0.005) occurred more often in patients with unfavorable outcomes than in those with favorable outcomes.

Conclusions. Autoregulation not only is impaired when associated with a high ICP or low ABP, but it can also be disturbed by too high a CPP. The Mx can be used to guide intensive care therapy when CPP-oriented protocols are used.

Restricted access

Marek Czosnyka, Hugh K. Richards, Zofia Czosnyka, Stefan Piechnik, and John D. Pickard

Object. The aim of the study was to assess how cerebrospinal fluid (CSF) pressure—volume compensation depends on cerebrovascular tone.

Methods. In 26 New Zealand White rabbits, intracranial pressure (ICP), arterial blood pressure, and basilar artery blood flow velocity were measured continuously. Saline was infused into the cranial subarachnoid space to assess CSF compensatory parameters: the resistance to CSF outflow, the elastance coefficient, and the amplitude of the ICP pulsatile waveform. Infusions were repeated on two different levels of CO2 concentration in the arterial blood (PaCO2), at normotension and hypotension, and after the death of the animal.

An increase in PaCO2 from a mean of 27 to 48 mm Hg was accompanied by an 18% increase in the resistance to CSF outflow (p < 0.005) and a 64% increase (p < 0.05) in the elastance coefficient. A decrease in arterial blood pressure from a mean of 100 to 51 mm Hg caused a 25% decrease in CSF outflow resistance (p < 0.01) but did not affect the elastance coefficient. Postmortem, a 23% decrease in the CSF outflow resistance was associated with a 102% decrease in the elastance coefficient.

Conclusions. Cerebrovascular parameters have a limited but significant impact on CSF infusion studies. The vascular component of ICP may be identified as a significant factor contributing to this phenomenon. During infusion studies, physiological parameters influencing vascular conditions should be maintained as stable as possible.

Restricted access

Marek Czosnyka, Piotr Smielewski, Stefan Piechnik, Eric A. Schmidt, Pippa G. Al-Rawi, Peter J. Kirkpatrick, and John D. Pickard

Object. Plateau waves of intracranial pressure (ICP) are often recorded during intensive care monitoring of severely head injured patients. They are traditionally interpreted as meaningful secondary brain insults because of the dramatic decrease in cerebral perfusion pressure (CPP). The aim of this study was to investigate both the hemodynamic profile and the clinical consequences of plateau waves.

Methods. One hundred sixty head-injured patients were studied using continuous monitoring of ICP; almost 20% of these patients exhibited plateau waves. In 96 patients arterial pressure, ICP, and transcranial Doppler (TCD) blood flow velocity were studied daily for 20 minutes to 3 hours. Sixteen episodes of plateau waves in eight patients were recorded and analyzed.

The dramatic increase in ICP was followed by a profound fall in CPP (by 45%). In contrast, flow velocity fell by only 20%. Autoregulation was documented to be intact both before and after plateau but was disturbed during the wave (p < 0.05). Pressure-volume compensatory reserve was always depleted before the wave. Cerebrovascular resistance decreased during the wave by 60% (p <0.05) and TCD pulsatility increased (p <0.05). Plateau waves did not increase the probability of an unfavorable outcome following injury.

Conclusions. The authors have confirmed that the plateau waves are a hemodynamic phenomenon associated with cerebrovascular vasodilation. They are observed in patients with preserved cerebral autoregulation but reduced pressure-volume compensatory reserve.