Hypercapnia

• In most cases, the increase CO2 per se is not a problem (exception e.g. neurosurgery)
• In most cases, the cause is simply hypoventilation (i.e. V < ~100mls/min/kg)
• In most other cases (where the minute volume would otherwise be adequate), the treatment, if any is required, is still simply to increase the minute volume

Situations requiring specific Rx (other than simply increasing ventilation)

• Malignant hyperpyrexia
• thyroid storm
• circuit problems (* = increased FiCO2)
exhausted soda lime *
expiratory valve failure *
inadequate fresh gas flow in partial rebreathing circuits *
excessive circuit dead space (i.e. on patient side of Y-piece)

MH ­ Is it?…Isn’t it?…

• Unfortunately, signs with higher +ve predictive values are not available immediately (e.g. increased CK, myoglobinuria, worsening metabolic acidosis)
• Immediately available clinical signs are non-specific (e.g. increased HR)
• Beware masseter spasm, rigidity of other muscle groups, mottled skin, increased T°C (late sign)
• Keep MH in mind if CO2 continues to rise despite adequate minute ventilation

Management

• Ensure adequate oxygenation
• Ensure adequate ventilation
• Check FiO2
• Blood gases to confirm capnography
• Consider secondary causes, especially those requiring specific Rx (MH, thyroid storm etc.)
• Treat complications of hypercapnia

Ensure adequate ventilation

• Check airway (e.g. is LMA seated well)
• Check circuit (e.g. ventilate manually ­ any obstruction?)
• Check minute ventilation (e.g. ventilator settings or spirometry on ADU if available)

If FiCO2 raised:

• Check valves (e.g. expiratory valve stuck open)
• Check if soda lime exhausted
• Check if fresh gas flow inadequate

Complications of hypercapnia

• Hypertension, tachycardia
• Pulmonary hypertension
• Arrhythmias

Causes of hypercapnia

• Increased CO2 production
• Decreased CO2 excretion
• Increased CO2 delivery to lungs

Increased CO2 production

• Increased temperature (including MH, sepsis)
• Hyperthyroidism (including thyroid storm)
• Exogenous (e.g. CO2 pneumoperitoneum)
• NaHCO3 administration
• Tourniquet release
• Shivering
• Convulsions
• Parenteral nutrition
• Compensation for metabolic alkalosis

Decreased CO2 excretion

• IPPV: inadequate ventilator settings
• Spontaneous ventilation: respiratory depressant drugs
• Partial airway obstruction
• Altered respiratory mechanics (e.g. decreased compliance due to pneumoperitoneum, obesity, Trendelenburg)

Increased CO2 delivery to the lungs

• Increased cardiac output
• R to L shunt