There is an inverse relationship between alveolar CO2 tension (PaCO2) and alveolar minute ventilation assuming CO2 production is constant. (Fig 1)

Adverse effects of hypercarbia

Causes and management

Fig 1 PaCO2 plotted against alveolar minute ventilation

There is an inverse relationship between alveolar CO2 tension (PaCO2) and alveolar minute ventilation assuming CO2 production is constant. (Fig 1)

Adverse effects of hypercarbia
The main adverse effects of acute hypercarbia relevant to anaesthesia are:

  • Increased sympathetic activity
  • Direct myocardial depression
  • Acidosis
  • Increased ICP and intraocular pressure
  • Narcosis

Causes and management

Fig 1 PaCO2 plotted against alveolar minute ventilation

There is an inverse relationship between alveolar CO2 tension (PaCO2) and alveolar minute ventilation assuming CO2 production is constant. (Fig 1)

Adverse effects of hypercarbia

Causes and management

Causes

Management

Reduced alveolar minute volume:

   • Inadequate ventilation

Increase minute ventilation.

Rebreathing:

   • Excessive dead space

   • Inadequate fresh gas      flow

   • Exhausted soda lime in      circle system

Eliminate rebreathing.

Severe lung disease.

Optimize ventilator settings, treat underlying disease.

Increased CO2 load:

   • Carbo peritoneum       (laparoscopy)

   • Following tissue      revascularization (e.g.      following aortic cross      clamp release)

   • Malignant hyperthermia

     (MH)

Increase minute ventilation if feasible. It may be necessary to monitor and tolerate a degree of hypercarbia whilst assessing any resulting patient compromise.
Treatment of MH if indicated.

Table 1 Causes and management of hypercarbia